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+[
+  {
+    "title": "Causality and dielectric functions for linear media with spatial   dispersion",
+    "authors": [
+      "Josep Llosa",
+      "Francesc Salvat"
+    ],
+    "abstract": "We extend Kramers-Kronig relations beyond the optical approximation to dielectric functions that depend not only on frequency but on the wave number as well. This implies extending the notion of causality commonly used in the theory of Kramers-Kronig relations to include the fact that signals cannot propagate faster than light in vacuo. The extension is applied to some microscopic models for the dielectric function and is compared with previous generalizations. The results derived here also apply to general theories of isotropic linear response in which the response function depends on both wave number and frequency.",
+    "arxiv_id": "1905.06069v6",
+    "categories": [
+      "physics.class-ph",
+      "math-ph",
+      "math.MP",
+      "30E15, 30E20, 78A99"
+    ],
+    "primary_category": "physics.class-ph",
+    "published_date": "2019-05-15T10:19:49Z",
+    "updated_date": "2024-09-23T13:39:41Z",
+    "pdf_url": "https://arxiv.org/pdf/1905.06069v6",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\1905.06069v6.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "Spectral decomposition of field operators and causal measurement in   quantum field theory",
+    "authors": [
+      "Robert Oeckl"
+    ],
+    "abstract": "We construct the spectral decomposition of field operators in bosonic quantum field theory as a limit of a strongly continuous family of POVM decompositions. The latter arise from integrals over families of bounded positive operators. Crucially, these operators have the same locality properties as the underlying field operators. We use the decompositions to construct families of quantum operations implementing measurements of the field observables. Again, the quantum operations have the same locality properties as the field operators. What is more, we show that these quantum operations do not lead to superluminal signaling and are possible measurements on quantum fields in the sense of Sorkin.",
+    "arxiv_id": "2409.08748v1",
+    "categories": [
+      "hep-th",
+      "math-ph",
+      "math.FA",
+      "math.MP",
+      "math.SP",
+      "quant-ph"
+    ],
+    "primary_category": "hep-th",
+    "published_date": "2024-09-13T11:59:28Z",
+    "updated_date": "2024-09-13T11:59:28Z",
+    "pdf_url": "https://arxiv.org/pdf/2409.08748v1",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\2409.08748v1.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "Characterizing Signalling: Connections between Causal Inference and   Space-time Geometry",
+    "authors": [
+      "Maarten Grothus",
+      "V. Vilasini"
+    ],
+    "abstract": "Causality is pivotal to our understanding of the world, presenting itself in different forms: information-theoretic and relativistic, the former linked to the flow of information, the latter to the structure of space-time. Leveraging a framework introduced in PRA, 106, 032204 (2022), which formally connects these two notions in general physical theories, we study their interplay. Here, information-theoretic causality is defined through a causal modelling approach. First, we improve the characterization of information-theoretic signalling as defined through so-called affects relations. Specifically, we provide conditions for identifying redundancies in different parts of such a relation, introducing techniques for causal inference in unfaithful causal models (where the observable data does not \"faithfully\" reflect the causal dependences). In particular, this demonstrates the possibility of causal inference using the absence of signalling between certain nodes. Second, we define an order-theoretic property called conicality, showing that it is satisfied for light cones in Minkowski space-times with $d>1$ spatial dimensions but violated for $d=1$. Finally, we study the embedding of information-theoretic causal models in space-time without violating relativistic principles such as no superluminal signalling (NSS). In general, we observe that constraints imposed by NSS in a space-time and those imposed by purely information-theoretic causal inference behave differently. We then prove a correspondence between conical space-times and faithful causal models: in both cases, there emerges a parallel between these two types of constraints. This indicates a connection between informational and geometric notions of causality, and offers new insights for studying the relations between the principles of NSS and no causal loops in different space-time geometries and theories of information processing.",
+    "arxiv_id": "2403.00916v2",
+    "categories": [
+      "gr-qc",
+      "math-ph",
+      "math.MP",
+      "math.ST",
+      "quant-ph",
+      "stat.TH"
+    ],
+    "primary_category": "gr-qc",
+    "published_date": "2024-03-01T19:00:45Z",
+    "updated_date": "2024-08-16T13:52:00Z",
+    "pdf_url": "https://arxiv.org/pdf/2403.00916v2",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\2403.00916v2.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "Matter in Discrete Space-Times",
+    "authors": [
+      "P. P. Divakaran"
+    ],
+    "abstract": "The unitary representations of the Poincare group of a discrete space-time are constructed, following the Wigner method in continuum relativity. They can be interpreted as elementary particles with one significant new feature: the momentum space being the 4-torus is identified as the Brillouin zone of space-time where all physical phenomena occur. Consequently 4-momentum is defined and conserved only modulo a reciprocal lattice vector of the order of the Planck mass, implying that there is no notion of an invariant mass except when it vanishes. In particular the propagation of massive particles have superluminal phases under very large (trans-Planckian) boosts. This behaviour leads to new features in early cosmology which are not in conflict with current knowledge.",
+    "arxiv_id": "2404.04548v1",
+    "categories": [
+      "gr-qc",
+      "hep-ph",
+      "hep-th",
+      "math-ph",
+      "math.MP",
+      "quant-ph"
+    ],
+    "primary_category": "gr-qc",
+    "published_date": "2024-04-06T08:12:15Z",
+    "updated_date": "2024-04-06T08:12:15Z",
+    "pdf_url": "https://arxiv.org/pdf/2404.04548v1",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\2404.04548v1.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "Extending the Known Region of Nonlocal Boxes that Collapse Communication   Complexity",
+    "authors": [
+      "Pierre Botteron",
+      "Anne Broadbent",
+      "Marc-Olivier Proulx"
+    ],
+    "abstract": "Non-signalling boxes (NS) are theoretical resources defined by the principle of no-faster-than-light communication. They generalize quantum correlations, and some of them are known to collapse communication complexity (CC). However, this collapse is strongly believed to be unachievable in Nature, so its study provides intuition on which theories are unrealistic. In the present letter, we find a better sufficient condition for a nonlocal box to collapse CC, thus extending the known collapsing region. In some slices of NS, we show this condition coincides with an area outside of an ellipse.",
+    "arxiv_id": "2302.00488v2",
+    "categories": [
+      "quant-ph",
+      "cs.IT",
+      "math-ph",
+      "math.IT",
+      "math.MP"
+    ],
+    "primary_category": "quant-ph",
+    "published_date": "2023-02-01T14:50:08Z",
+    "updated_date": "2024-02-16T16:32:32Z",
+    "pdf_url": "https://arxiv.org/pdf/2302.00488v2",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\2302.00488v2.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "Exact Analytical Solution of the One-Dimensional Time-Dependent   Radiative Transfer Equation with Linear Scattering",
+    "authors": [
+      "Vladimir Allaxwerdian",
+      "Dmitry V. Naumov"
+    ],
+    "abstract": "The radiative transfer equation (RTE) is a cornerstone for describing the propagation of electromagnetic radiation in a medium, with applications spanning atmospheric science, astrophysics, remote sensing, and biomedical optics. Despite its importance, an exact analytical solution to the RTE has remained elusive, necessitating the use of numerical approximations such as Monte Carlo, discrete ordinate, and spherical harmonics methods.   In this paper, we present an exact solution to the one-dimensional time-dependent RTE. We delve into the moments of the photon distribution, providing a clear view of the transition to the diffusion regime. This analysis offers a deeper understanding of light propagation in the medium.   Furthermore, we demonstrate that the one-dimensional RTE is equivalent to the Klein-Gordon equation with an imaginary mass term determined by the inverse reduced scattering length. Contrary to naive expectations of superluminal solutions, we find that our solution is strictly causal under appropriate boundary conditions, determined by the light transport problem.   We validate the found solution using Monte Carlo simulations and benchmark the performance of the latter. Our analysis reveals that even for highly forward scattering, dozens of random light scatterings are required for an accurate estimate, underscoring the complexity of the problem.   Moreover, we propose a method for faster convergence by adjusting the parameters of Monte Carlo sampling. We show that a Monte Carlo method sampling photon scatterings with input parameters $(\\mu_s,g)$, where $\\mu_s$ is the inverse scattering length and $g$ is the scattering anisotropy parameter, is equivalent to that with $(\\mu_s(1-g)/2,-1)$. This equivalence leads to a significantly faster convergence to the exact solution, offering a substantial improvement of the Monte Carlo method for the one-dimensional RTE.",
+    "arxiv_id": "2401.09511v1",
+    "categories": [
+      "physics.optics",
+      "hep-ex",
+      "math-ph",
+      "math.MP",
+      "physics.class-ph"
+    ],
+    "primary_category": "physics.optics",
+    "published_date": "2024-01-17T13:56:57Z",
+    "updated_date": "2024-01-17T13:56:57Z",
+    "pdf_url": "https://arxiv.org/pdf/2401.09511v1",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\2401.09511v1.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "Universal horizons and black hole spectroscopy in gravitational theories   with broken Lorentz symmetry",
+    "authors": [
+      "Chao Zhang",
+      "Anzhong Wang",
+      "Tao Zhu"
+    ],
+    "abstract": "The violation of Lorentz invariance (LI) in gravitational theories, which allows superluminal propagations, dramatically alters the causal structure of the spacetime and modifies the notion of black holes (BHs). Instead of metric horizons, now universal horizons (UHs) define the boundaries of BHs, within which a particle cannot escape to spatial infinities even with an infinitely large speed. Then, a natural question is how the quasi-normal modes (QNMs) of a BH are modified, if one considers the UH as its causal boundary. In this paper, we study in detail this problem in Einstein-aether theory, a vector-tensor theory that violates LI but yet is self-consistent and satisfies all observations to date. Technically, this poses several challenges, including singularities of the perturbation equations across metric horizons and proper identifications of ingoing modes at UHs. After overcoming these difficulties, we show that the QNMs of the Schwarzschild BH, also a solution of Einstein-aether theory, consist of two parts, the metric and aether parts. The QNMs of the metric perturbations are quite similar to those obtained in general relativity and are consistent with current observations of gravitational waves. But the ones from aether perturbations are different, and our numerical studies indicate that they are even not stable. The latter is consistent with our previous studies, which showed that the stealth Schwarzschild BH suffers a Laplacian instability along the angular direction. The method and techniques developed in this paper can be applied to the studies of QNMs in other theories of gravity with broken LI.",
+    "arxiv_id": "2209.04735v3",
+    "categories": [
+      "gr-qc",
+      "hep-ph",
+      "hep-th",
+      "math-ph",
+      "math.MP"
+    ],
+    "primary_category": "gr-qc",
+    "published_date": "2022-09-10T19:58:43Z",
+    "updated_date": "2023-09-24T07:39:39Z",
+    "pdf_url": "https://arxiv.org/pdf/2209.04735v3",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\2209.04735v3.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "The Maslov index and some applications to dispersion relations in curved   space times",
+    "authors": [
+      "Juliana Osorio Morales",
+      "Osvaldo Santill\u00e1n"
+    ],
+    "abstract": "The aim of the present work is to generalize the results given in |81] to a generic situation for causal geodesics. It is argued that these results may be of interest for causality issues. Recall that the presence of superluminal signals in a generic space time $(M, g_{\\mu\\nu})$ does not necessarily imply violations of the principle of causality [1]-[12]. In flat spaces, global Lorenz invariance leads to the conclusion that closed time like curves appear if these signals are present. In a curved space instead, there is only local Poincare invariance, and the presence of closed causal curves may be avoided even in presence of a superluminal mode, specially when terms violating the strong equivalence principle appear in the action. This implies that the standard analytic properties of the spectral components of these functions are therefore modified and, in particular, the refraction index $n(\\omega)$ is not analytic in the upper complex $\\omega$ plane. The emergence of this singularities may also take place for non superluminal signals, due to the breaking of global Lorenz invariance in a generic space time. In the present work, it is argued that the homotopy properties of the Maslov index \\cite{maslov} are useful for studying how the singularities of $n(\\omega)$ vary when moving along a geodesic congruence. In addition, several conclusions obtained in [1]-[12] are based on the Penrose limit along a null geodesic, and they are restricted to GR with matter satisfying strong energy conditions. The use of the Maslov index may allow a more intrinsic description of singularities, not relying on that limit, and a generalization of these results about non analiticity to generic gravity models with general matter content.",
+    "arxiv_id": "2210.03229v3",
+    "categories": [
+      "gr-qc",
+      "hep-th",
+      "math-ph",
+      "math.MP"
+    ],
+    "primary_category": "gr-qc",
+    "published_date": "2022-10-06T21:53:18Z",
+    "updated_date": "2022-10-17T12:11:56Z",
+    "pdf_url": "https://arxiv.org/pdf/2210.03229v3",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\2210.03229v3.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "About apparent superluminal drives in generic gravity theories",
+    "authors": [
+      "J. Osorio Morales",
+      "O. Santill\u00e1n"
+    ],
+    "abstract": "As is well known, there exists warp drives in GR, such as the Alcubierre bubbles, which achieve an apparent faster than light travel \\cite{alcubierre}. A result due to Gao and Wald \\cite{gaowald} suggests that such a travel is unlikely for GR with matter satisfying both the Null Energy and the Null Generic Conditions. There exists a generalization of this statement due to Galloway, that ensures that the Gao-Wald result is true regardless the underlying gravity model, unless there exists at least one inextendible null geodesic with achronal image in the space time (a null line). The proof of this proposition is based on techniques of causal theories, and has never been released. In the present work an independent proof of this result is presented by use of the Raychaudhuri equation, and avoiding several technical complications described along the text. Some consequences of these affirmations are discussed at last section, in particular their potential use in problems of causality.",
+    "arxiv_id": "2004.12523v4",
+    "categories": [
+      "gr-qc",
+      "hep-th",
+      "math-ph",
+      "math.MP"
+    ],
+    "primary_category": "gr-qc",
+    "published_date": "2020-04-27T00:55:03Z",
+    "updated_date": "2022-04-14T23:52:31Z",
+    "pdf_url": "https://arxiv.org/pdf/2004.12523v4",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\2004.12523v4.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "Another Proof of Born's Rule on Arbitrary Cauchy Surfaces",
+    "authors": [
+      "Sascha Lill",
+      "Roderich Tumulka"
+    ],
+    "abstract": "In 2017, Lienert and Tumulka proved Born's rule on arbitrary Cauchy surfaces in Minkowski space-time assuming Born's rule and a corresponding collapse rule on horizontal surfaces relative to a fixed Lorentz frame, as well as a given unitary time evolution between any two Cauchy surfaces, satisfying that there is no interaction faster than light and no propagation faster than light. Here, we prove Born's rule on arbitrary Cauchy surfaces from a different, but equally reasonable, set of assumptions. The conclusion is that if detectors are placed along any Cauchy surface $\\Sigma$, then the observed particle configuration on $\\Sigma$ is a random variable with distribution density $|\\Psi_\\Sigma|^2$, suitably understood. The main different assumption is that the Born and collapse rules hold on any spacelike hyperplane, i.e., at any time coordinate in any Lorentz frame. Heuristically, this follows if the dynamics of the detectors is Lorentz invariant.",
+    "arxiv_id": "2104.13861v2",
+    "categories": [
+      "math-ph",
+      "math.MP",
+      "quant-ph"
+    ],
+    "primary_category": "math-ph",
+    "published_date": "2021-04-28T16:11:50Z",
+    "updated_date": "2021-10-14T19:49:29Z",
+    "pdf_url": "https://arxiv.org/pdf/2104.13861v2",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\2104.13861v2.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "Relativistic limits on quantum operations",
+    "authors": [
+      "Tein van der Lugt"
+    ],
+    "abstract": "In this essay, we explore the limits imposed by the impossibility of superluminal signalling on the class of physically realisable quantum operations, focusing on the difference in approaches one can take towards this problem in Hilbert space quantum theory and algebraic quantum field theory (AQFT). We review a recent proposal by Fewster and Verch for a generally covariant measurement scheme in AQFT, which we call the FV scheme; along the way, we argue that the framework as set up in its original proposal can be greatly simplified without losing generality or physical motivation. We then discuss the problem, introduced by Sorkin, that naive generalisations of the notion of operation to the relativistic context can lead to signalling between spacelike observers by introducing a third observer. We consider approaches to tackle this problem in Hilbert space quantum theory and argue that these are sometimes ambiguous, since the physical (im)possibility of operations depends in part on the specific spacetime embodiment of the quantum system under consideration, which lies outside the Hilbert space formalism. In the AQFT context, we review and generalise a recent result showing that operations induced by the FV measurement scheme do not enable superluminal signalling. We connect this result to Hilbert space by introducing a concrete model of AQFT, which we call the `hybrid model' as it provides a way to explicitly embed Hilbert space quantum theory into spacetime using the formalism of AQFT. Finally, we show that in this model, under suitable necessary and sufficient conditions, the converse result also holds: every operation that does not enable superluminal signalling can be implemented in the FV framework.",
+    "arxiv_id": "2108.05904v1",
+    "categories": [
+      "math-ph",
+      "math.MP",
+      "physics.hist-ph",
+      "quant-ph"
+    ],
+    "primary_category": "math-ph",
+    "published_date": "2021-08-12T18:04:20Z",
+    "updated_date": "2021-08-12T18:04:20Z",
+    "pdf_url": "https://arxiv.org/pdf/2108.05904v1",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\2108.05904v1.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "Impossible measurements require impossible apparatus",
+    "authors": [
+      "Henning Bostelmann",
+      "Christopher J. Fewster",
+      "Maximilian H. Ruep"
+    ],
+    "abstract": "A well-recognised open conceptual problem in relativistic quantum field theory concerns the relation between measurement and causality. Naive generalisations of quantum measurement rules can allow for superluminal signalling ('impossible measurements'). This raises the problem of delineating physically allowed quantum measurements and operations. We analyse this issue in a recently proposed framework in which local measurements (in possibly curved spacetime) are described physically by coupling the system to a probe. We show that the state-update rule in this setting is consistent with causality provided that the coupling between the system and probe is local. Thus, by establishing a well-defined framework for successive measurements, we also provide a class of physically allowed operations. Conversely, impossible measurements can only be performed using impossible (non-local) apparatus.",
+    "arxiv_id": "2003.04660v4",
+    "categories": [
+      "quant-ph",
+      "gr-qc",
+      "hep-th",
+      "math-ph",
+      "math.MP"
+    ],
+    "primary_category": "quant-ph",
+    "published_date": "2020-03-10T12:25:10Z",
+    "updated_date": "2021-04-26T11:57:35Z",
+    "pdf_url": "https://arxiv.org/pdf/2003.04660v4",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\2003.04660v4.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "Rotating fermions inside a spherical boundary",
+    "authors": [
+      "Zheng Zhang",
+      "Chao Shi",
+      "Xiaofeng Luo",
+      "Hong-Shi Zong"
+    ],
+    "abstract": "We apply the cannonical quantization procedure to the Dirac field inside a spherical boundary with rotating coordinates. The rotating quantum states with two kinds of boundary conditions, namely, spectral and MIT boundary conditions, are defined. To avoid faster-than-light, we require the speed on the surface to be less than the speed of light. For this situation, the definition of vacuum is unique and identical with the Minkowski vacuum. Finally, we calculate the thermal expectation value of the fermion condensate in a thermal equilibrium rotating fermion field and find it depends on the boundary condition.",
+    "arxiv_id": "2006.00677v2",
+    "categories": [
+      "math-ph",
+      "hep-th",
+      "math.MP"
+    ],
+    "primary_category": "math-ph",
+    "published_date": "2020-06-01T02:47:05Z",
+    "updated_date": "2020-08-21T02:44:08Z",
+    "pdf_url": "https://arxiv.org/pdf/2006.00677v2",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\2006.00677v2.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "Good Fibrations: Packing Rules for Diabolic Domains",
+    "authors": [
+      "Randall D. Kamien",
+      "Thomas Machon"
+    ],
+    "abstract": "We describe a theory of packing hyperboloid 'diabolic' domains in bend-free textures of liquid crystals. The domains sew together continuously, providing a menagerie of bend-free textures akin to the packing of focal conic domains in smectic liquid crystals. We show how distinct domains may be related to each other by Lorentz transformations, and that this process may lower the elastic energy of the system. We discuss a number of phases that may be formed as a result, including splay-twist analogues of blue phases. We also discuss how these diabolic domains may be subject to \"superluminal boosts\", yielding defects analogous to shocks waves. We explore the geometry of these textures, demonstrating their relation to Milnor fibrations of the Hopf link. Finally, we show how the theory of these domains is unified in four-dimensional space.",
+    "arxiv_id": "2007.05850v1",
+    "categories": [
+      "cond-mat.soft",
+      "math.DG"
+    ],
+    "primary_category": "cond-mat.soft",
+    "published_date": "2020-07-11T20:53:34Z",
+    "updated_date": "2020-07-11T20:53:34Z",
+    "pdf_url": "https://arxiv.org/pdf/2007.05850v1",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\2007.05850v1.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "Operational causality in spacetime",
+    "authors": [
+      "Micha\u0142 Eckstein",
+      "Pawe\u0142 Horodecki",
+      "Ryszard Horodecki",
+      "Tomasz Miller"
+    ],
+    "abstract": "The no-signalling principle preventing superluminal communication is a limiting paradigm for physical theories. Within the information-theoretic framework it is commonly understood in terms of admissible correlations in composite systems. Here we unveil its complementary incarnation --- the 'dynamical no-signalling principle' ---, which forbids superluminal signalling via measurements on simple physical objects (e.g. particles) evolving in time. We show that it imposes strong constraints on admissible models of dynamics. The posited principle is universal --- it can be applied to any theory (classical, quantum or post-quantum) with well-defined rules of calculating detection statistics in spacetime. As an immediate application we show how one could exploit the Schr\\\"odinger equation to establish a fully operational superluminal protocol in the Minkowski spacetime. This example illustrates how the principle can be used to identify the limits of applicability of a given model of quantum or post-quantum dynamics.",
+    "arxiv_id": "1902.05002v2",
+    "categories": [
+      "quant-ph",
+      "gr-qc",
+      "math-ph",
+      "math.MP",
+      "81P16 (Primary), 81P15, 28E99, 60B05 (Secondary)"
+    ],
+    "primary_category": "quant-ph",
+    "published_date": "2019-02-13T16:44:36Z",
+    "updated_date": "2020-02-05T21:08:49Z",
+    "pdf_url": "https://arxiv.org/pdf/1902.05002v2",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\1902.05002v2.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "Bohmian mechanics of Klein-Gordon equation via quantum metric and mass",
+    "authors": [
+      "S. Jalalzadeh",
+      "A. J. S. Capistrano"
+    ],
+    "abstract": "The causal stochastic interpretation of relativistic quantum mechanics has the problems of superluminal velocities, motion backward in time and the incorrect non-relativistic limit. In this paper, according to the original ideas of de Broglie, Bohm and Takabayasi, we have introduced simultaneous quantum mass and quantum metric of curved spacetime to obtain a correct relativistic theory free of mentioned problems. \\keywords{Bohmian mechanics; Klein-Gordon equation; quantum conformal transformations.",
+    "arxiv_id": "2001.00551v1",
+    "categories": [
+      "gr-qc",
+      "math-ph",
+      "math.MP",
+      "quant-ph"
+    ],
+    "primary_category": "gr-qc",
+    "published_date": "2020-01-02T18:19:17Z",
+    "updated_date": "2020-01-02T18:19:17Z",
+    "pdf_url": "https://arxiv.org/pdf/2001.00551v1",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\2001.00551v1.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "Born's Rule for Arbitrary Cauchy Surfaces",
+    "authors": [
+      "Matthias Lienert",
+      "Roderich Tumulka"
+    ],
+    "abstract": "Suppose that particle detectors are placed along a Cauchy surface $\\Sigma$ in Minkowski space-time, and consider a quantum theory with fixed or variable number of particles (i.e., using Fock space or a subspace thereof). It is straightforward to guess what Born's rule should look like for this setting: The probability distribution of the detected configuration on $\\Sigma$ has density $|\\psi_\\Sigma|^2$, where $\\psi_\\Sigma$ is a suitable wave function on $\\Sigma$, and the operation $|\\cdot|^2$ is suitably interpreted. We call this statement the \"curved Born rule.\" Since in any one Lorentz frame, the appropriate measurement postulates referring to constant-$t$ hyperplanes should determine the probabilities of the outcomes of any conceivable experiment, they should also imply the curved Born rule. This is what we are concerned with here: deriving Born's rule for $\\Sigma$ from Born's rule in one Lorentz frame (along with a collapse rule). We describe two ways of defining an idealized detection process, and prove for one of them that the probability distribution coincides with $|\\psi_\\Sigma|^2$. For this result, we need two hypotheses on the time evolution: that there is no interaction faster than light, and that there is no propagation faster than light. The wave function $\\psi_\\Sigma$ can be obtained from the Tomonaga--Schwinger equation, or from a multi-time wave function by inserting configurations on $\\Sigma$. Thus, our result establishes in particular how multi-time wave functions are related to detection probabilities.",
+    "arxiv_id": "1706.07074v3",
+    "categories": [
+      "math-ph",
+      "math.MP",
+      "quant-ph"
+    ],
+    "primary_category": "math-ph",
+    "published_date": "2017-06-21T18:16:09Z",
+    "updated_date": "2019-09-17T15:49:04Z",
+    "pdf_url": "https://arxiv.org/pdf/1706.07074v3",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\1706.07074v3.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "Causal properties of nonlinear gravitational waves in modified gravity",
+    "authors": [
+      "Arthur George Suvorov",
+      "Andrew Melatos"
+    ],
+    "abstract": "Some exact, nonlinear, vacuum gravitational wave solutions are derived for certain polynomial $f(R)$ gravities. We show that the boundaries of the gravitational domain of dependence, associated with events in polynomial $f(R)$ gravity, are not null as they are in general relativity. The implication is that electromagnetic and gravitational causality separate into distinct notions in modified gravity, which may have observable astrophysical consequences. The linear theory predicts that tachyonic instabilities occur, when the quadratic coefficient $a_{2}$ of the Taylor expansion of $f(R)$ is negative, while the exact, nonlinear, cylindrical wave solutions presented here can be superluminal for all values of $a_{2}$. Anisotropic solutions are found, whose wave-fronts trace out time- or space-like hypersurfaces with complicated geometric properties. We show that the solutions exist in $f(R)$ theories that are consistent with Solar System and pulsar timing experiments.",
+    "arxiv_id": "1709.01628v1",
+    "categories": [
+      "gr-qc",
+      "astro-ph.HE",
+      "math-ph",
+      "math.MP",
+      "83Dxx, 83Cxx, 53Zxx, 53Axx"
+    ],
+    "primary_category": "gr-qc",
+    "published_date": "2017-09-05T23:43:49Z",
+    "updated_date": "2017-09-05T23:43:49Z",
+    "pdf_url": "https://arxiv.org/pdf/1709.01628v1",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\1709.01628v1.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "Causal evolution of wave packets",
+    "authors": [
+      "Micha\u0142 Eckstein",
+      "Tomasz Miller"
+    ],
+    "abstract": "Drawing from the optimal transport theory adapted to the relativistic setting we formulate the principle of a causal flow of probability and apply it in the wave packet formalism. We demonstrate that whereas the Dirac system is causal, the relativistic-Schr\\\"odinger Hamiltonian impels a superluminal evolution of probabilities. We quantify the causality breakdown in the latter system and argue that, in contrast to the popular viewpoint, it is not related to the localisation properties of the states.",
+    "arxiv_id": "1610.00764v1",
+    "categories": [
+      "quant-ph",
+      "gr-qc",
+      "math-ph",
+      "math.MP",
+      "81P16 (Primary), 53B30, 28E99, 60B05 (Secondary)"
+    ],
+    "primary_category": "quant-ph",
+    "published_date": "2016-10-03T21:45:48Z",
+    "updated_date": "2016-10-03T21:45:48Z",
+    "pdf_url": "https://arxiv.org/pdf/1610.00764v1",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\1610.00764v1.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "Dynamics and scattering of a massless particle",
+    "authors": [
+      "Avy Soffer"
+    ],
+    "abstract": "We estimate the probability of a photon to move faster than light, under the Einstein dynamics which, unlike the wave equation or Maxwell wave dynamics, has singular dispersion relation at zero momentum. We show that this probability goes to zero with time, using propagation estimates suitably multi-scaled to control the contribution of low frequencies. We then prove minimal velocity bounds",
+    "arxiv_id": "1606.03516v1",
+    "categories": [
+      "math-ph",
+      "math.MP",
+      "math.SP"
+    ],
+    "primary_category": "math-ph",
+    "published_date": "2016-06-11T01:04:13Z",
+    "updated_date": "2016-06-11T01:04:13Z",
+    "pdf_url": "https://arxiv.org/pdf/1606.03516v1",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\1606.03516v1.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "Probabilities and signalling in quantum field theory",
+    "authors": [
+      "Robert Dickinson",
+      "Jeff Forshaw",
+      "Peter Millington"
+    ],
+    "abstract": "We present an approach to computing probabilities in quantum field theory for a wide class of source-detector models. The approach works directly with probabilities and not with squared matrix elements, and the resulting probabilities can be written in terms of expectation values of nested commutators and anti-commutators. We present results that help in the evaluation of these, including an expression for the vacuum expectation values of general nestings of commutators and anti-commutators in scalar field theory. This approach allows one to see clearly how faster-than-light signalling is prevented, because it leads to a diagrammatic expansion in which the retarded propagator plays a prominent role. We illustrate the formalism using the simple case of the much-studied Fermi two-atom problem.",
+    "arxiv_id": "1601.07784v2",
+    "categories": [
+      "hep-th",
+      "hep-ph",
+      "math-ph",
+      "math.MP",
+      "quant-ph"
+    ],
+    "primary_category": "hep-th",
+    "published_date": "2016-01-28T14:54:07Z",
+    "updated_date": "2016-03-28T13:44:58Z",
+    "pdf_url": "https://arxiv.org/pdf/1601.07784v2",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\1601.07784v2.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "Classical and Quantum Gauged Massless Rarita-Schwinger Fields",
+    "authors": [
+      "Stephen L. Adler"
+    ],
+    "abstract": "We show that, in contrast to known results in the massive case, a minimally gauged massless Rarita-Schwinger field yields consistent classical and quantum theories, with a generalized fermionic gauge invariance. To simplify the algebra, we study a two-component left chiral reduction of the massless theory. We formulate the classical theory in both Lagrangian and Hamiltonian form for a general non-Abelian gauging, and analyze the constraints and the Rarita-Schwinger gauge invariance of the action. An explicit wave front calculation for Abelian gauge fields shows that wave-like modes do not propagate with superluminal velocities. The quantized case is studied in gauge covariant radiation gauge and $\\Psi_0=0$ gauge for the Rarita-Schwinger field, by both functional integral and Dirac bracket methods. In $\\Psi_0=0$ gauge, the constraints have the form needed to apply the Faddeev-Popov method for deriving a functional integral. The Dirac bracket approach in $\\Psi_0=0$ gauge yields consistent Hamilton equations of motion, and in covariant radiation gauge leads to anticommutation relations with the correct positivity properties. We discuss relativistic covariance of the anticommutation relations, and of Rarita-Schwinger scattering from an Abelian potential. We note that fermionic gauge transformations are a canonical transformation, but further details of the transformation between different fermionic gauges are left as an open problem.",
+    "arxiv_id": "1502.02652v5",
+    "categories": [
+      "hep-th",
+      "hep-ph",
+      "math-ph",
+      "math.MP"
+    ],
+    "primary_category": "hep-th",
+    "published_date": "2015-02-09T20:59:07Z",
+    "updated_date": "2015-08-17T14:22:04Z",
+    "pdf_url": "https://arxiv.org/pdf/1502.02652v5",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\1502.02652v5.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "Averaged null energy condition and quantum inequalities in curved   spacetime",
+    "authors": [
+      "Eleni-Alexandra Kontou"
+    ],
+    "abstract": "The Averaged Null Energy Condition (ANEC) states that the integral along a complete null geodesic of the projection of the stress-energy tensor onto the tangent vector to the geodesic cannot be negative. ANEC can be used to rule out spacetimes with exotic phenomena, such as closed timelike curves, superluminal travel and wormholes. We prove that ANEC is obeyed by a minimally-coupled, free quantum scalar field on any achronal null geodesic (not two points can be connected with a timelike curve) surrounded by a tubular neighborhood whose curvature is produced by a classical source. To prove ANEC we use a null-projected quantum inequality, which provides constraints on how negative the weighted average of the renormalized stress-energy tensor of a quantum field can be. Starting with a general result of Fewster and Smith, we first derive a timelike projected quantum inequality for a minimally-coupled scalar field on flat spacetime with a background potential. Using that result we proceed to find the bound of a quantum inequality on a geodesic in a spacetime with small curvature, working to first order in the Ricci tensor and its derivatives. The last step is to derive a bound for the null-projected quantum inequality on a general timelike path. Finally we use that result to prove achronal ANEC in spacetimes with small curvature.",
+    "arxiv_id": "1507.06299v1",
+    "categories": [
+      "gr-qc",
+      "math-ph",
+      "math.MP"
+    ],
+    "primary_category": "gr-qc",
+    "published_date": "2015-07-22T19:58:26Z",
+    "updated_date": "2015-07-22T19:58:26Z",
+    "pdf_url": "https://arxiv.org/pdf/1507.06299v1",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\1507.06299v1.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "Maximal Fermi charts and geometry of inflationary universes",
+    "authors": [
+      "David Klein"
+    ],
+    "abstract": "A proof is given that the maximal Fermi coordinate chart for any comoving observer in a broad class of Robertson-Walker spacetimes consists of all events within the cosmological event horizon, if there is one, or is otherwise global. Exact formulas for the metric coefficients in Fermi coordinates are derived. Sharp universal upper bounds for the proper radii of leaves of the foliation by Fermi spaceslices are found, i.e., for the proper radii of the spatial universe at fixed times of the comoving observer. It is proved that the radius at proper time $\\tau$ diverges to infinity for non inflationary cosmologies as $\\tau\\to\\infty$, but not necessarily for cosmologies with periods of inflation. It is shown that any spacelike geodesic orthogonal to the worldline of a comoving observer has finite proper length and terminates within the cosmological event horizon (if there is one) at the big bang. Geometric properties of inflationary versus non inflationary cosmologies are compared, and opposite inequalities for the inflationary and non inflationary cases, analogous to Hubble's law, are obtained for the Fermi relative velocities of comoving test particles. It is proved that the Fermi relative velocities of radially moving test particles are necessarily subluminal for inflationary cosmologies in contrast to non inflationary models, where superluminal relative Fermi velocities necessarily exist.",
+    "arxiv_id": "1210.7651v4",
+    "categories": [
+      "math-ph",
+      "gr-qc",
+      "math.DG",
+      "math.MP",
+      "83F05, 83C10"
+    ],
+    "primary_category": "math-ph",
+    "published_date": "2012-10-29T13:25:05Z",
+    "updated_date": "2015-07-09T14:52:17Z",
+    "pdf_url": "https://arxiv.org/pdf/1210.7651v4",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\1210.7651v4.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "Chiral fermions as classical massless spinning particles",
+    "authors": [
+      "C. Duval",
+      "P. A. Horvathy"
+    ],
+    "abstract": "Semiclassical chiral fermion models with Berry term are studied in a symplectic framework. In the free case, the system can be obtained from Souriau's model for a relativistic massless spinning particle by \"enslaving\" the spin. The Berry term is identified with the classical spin two-form of the latter model. The Souriau model carries a natural Poincar\\'e symmetry that we highlight, but spin enslavement breaks the boost symmetry. However the relation between the models allows us to derive a Poincare symmetry of unconventional form for chiral fermions. Then we couple our system to an external electromagnetic field. For gyromagnetic ratio $g=0$ we get curious superluminal Hall-type motions; for $g=2$ and in a pure constant magnetic field in particular, we find instead spiraling motions.",
+    "arxiv_id": "1406.0718v4",
+    "categories": [
+      "hep-th",
+      "cond-mat.str-el",
+      "hep-ph",
+      "math-ph",
+      "math.MP"
+    ],
+    "primary_category": "hep-th",
+    "published_date": "2014-06-03T14:08:57Z",
+    "updated_date": "2015-01-23T17:07:24Z",
+    "pdf_url": "https://arxiv.org/pdf/1406.0718v4",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\1406.0718v4.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "The Existence of Superluminal Particles is Consistent with Relativistic   Dynamics",
+    "authors": [
+      "Judit X. Madar\u00e1sz",
+      "Gergely Sz\u00e9kely"
+    ],
+    "abstract": "Within an axiomatic framework, we prove that the existence of faster than light particles is consistent with (does not contradict) the dynamics of Einstein's special relativity.",
+    "arxiv_id": "1303.0399v2",
+    "categories": [
+      "gr-qc",
+      "math-ph",
+      "math.LO",
+      "math.MP"
+    ],
+    "primary_category": "gr-qc",
+    "published_date": "2013-03-02T16:32:01Z",
+    "updated_date": "2014-07-24T18:10:49Z",
+    "pdf_url": "https://arxiv.org/pdf/1303.0399v2",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\1303.0399v2.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "Faster than light motion does not imply time travel",
+    "authors": [
+      "H. Andr\u00e9ka",
+      "J. X. Madar\u00e1sz",
+      "I. N\u00e9meti",
+      "M. Stannett",
+      "G. Sz\u00e9kely"
+    ],
+    "abstract": "Seeing the many examples in the literature of causality violations based on faster-than- light (FTL) signals one naturally thinks that FTL motion leads inevitably to the possibility of time travel. We show that this logical inference is invalid by demonstrating a model, based on (3+1)-dimensional Minkowski spacetime, in which FTL motion is permitted (in every direction without any limitation on speed) yet which does not admit time travel. Moreover, the Principle of Relativity is true in this model in the sense that all observers are equivalent. In short, FTL motion does not imply time travel after all.",
+    "arxiv_id": "1407.2528v1",
+    "categories": [
+      "gr-qc",
+      "math-ph",
+      "math.LO",
+      "math.MP"
+    ],
+    "primary_category": "gr-qc",
+    "published_date": "2014-07-09T15:41:47Z",
+    "updated_date": "2014-07-09T15:41:47Z",
+    "pdf_url": "https://arxiv.org/pdf/1407.2528v1",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\1407.2528v1.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "Relativistic $<\u03c3v_\\text{rel}>$ in the calculation of relics   abundances: a closer look",
+    "authors": [
+      "M. Cannoni"
+    ],
+    "abstract": "In this paper we clarify the relation between the invariant relativistic relative velocity $V_\\text{r}$, the M\\o{}ller velocity $\\bar{v}$, and the non-relativistic relative velocity $v_r$. Adopting $V_{\\text{r}}$ as the true physical relative velocity for pair-collisions in a non-degenerate relativistic gas, we show that in the frame co-moving with the gas (i) the thermally averaged cross section times relative velocity $<\\sigma v_\\text{rel}>$ that appears in the density evolution equation for thermal relics is reformulated only in terms of $V_\\text{r}$ and $\\mathcal{P}(V_{\\text{r}})$ in a manifestly Lorentz invariant form; (ii) the frame-dependent issues of the standard formulation in terms of the M\\o{}ller velocity, as well as \"superluminal\" relative velocities, are not present in this formulation. Furthermore, considering the annihilation of dark matter into a particle-antiparticle pair $f\\bar{f}$, in the cases $m_f=0$, $m_f=m$ and $m_f \\gg m$, we find that the coefficients of the low velocity expansion of $<\\sigma V_{\\text{r}}>$ admit an exact analytical representation in terms of the Meijer $G$ functions that can be reduced to combinations of modified Bessel functions of the second kind.",
+    "arxiv_id": "1311.4508v2",
+    "categories": [
+      "astro-ph.CO",
+      "hep-ph",
+      "math-ph",
+      "math.MP",
+      "nucl-th"
+    ],
+    "primary_category": "astro-ph.CO",
+    "published_date": "2013-11-18T19:33:42Z",
+    "updated_date": "2014-05-30T18:18:16Z",
+    "pdf_url": "https://arxiv.org/pdf/1311.4508v2",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\1311.4508v2.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "Why Do the Relativistic Masses and Momenta of Faster-than-Light   Particles Decrease as their Speeds Increase?",
+    "authors": [
+      "Judit X. Madar\u00e1sz",
+      "Mike Stannett",
+      "Gergely Sz\u00e9kely"
+    ],
+    "abstract": "It has recently been shown within a formal axiomatic framework using a definition of four-momentum based on the St\\\"uckelberg-Feynman-Sudarshan-Recami \"switching principle\" that Einstein's relativistic dynamics is logically consistent with the existence of interacting faster-than-light inertial particles. Our results here show, using only basic natural assumptions on dynamics, that this definition is the only possible way to get a consistent theory of such particles moving within the geometry of Minkowskian spacetime. We present a strictly formal proof from a streamlined axiom system that given any slow or fast inertial particle, all inertial observers agree on the value of $\\mathsf{m}\\cdot \\sqrt{|1-v^2|}$, where $\\mathsf{m}$ is the particle's relativistic mass and $v$ its speed. This confirms formally the widely held belief that the relativistic mass and momentum of a positive-mass faster-than-light particle must decrease as its speed increases.",
+    "arxiv_id": "1309.3713v2",
+    "categories": [
+      "gr-qc",
+      "math-ph",
+      "math.LO",
+      "math.MP",
+      "70A05, 03B30, 83A05"
+    ],
+    "primary_category": "gr-qc",
+    "published_date": "2013-09-15T00:39:05Z",
+    "updated_date": "2014-01-11T08:30:43Z",
+    "pdf_url": "https://arxiv.org/pdf/1309.3713v2",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\1309.3713v2.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "A logical treatment of special relativity, with and without   faster-than-light observers",
+    "authors": [
+      "Benjamin Hoffman"
+    ],
+    "abstract": "There are three goals of this thesis. First: to present a concise yet accessible description of basic mathematical logic and model theory. Second: to develop an axiomatization of special relativity using only two undefined predicates. Ideally, these axioms should be empirically verifiable and supported by a large body of evidence. Finally: to weaken this axiomatization so as to allow for the existence of faster-than-light observers, which are normally excluded from the theory of special relativity. The modifications to the axiom system should be as slight as possible, and should be motivated by the question: what features of the original axiom system preclude the existence of faster-than-light observers?",
+    "arxiv_id": "1306.6004v1",
+    "categories": [
+      "math.LO",
+      "math-ph",
+      "math.MP"
+    ],
+    "primary_category": "math.LO",
+    "published_date": "2013-06-25T15:37:59Z",
+    "updated_date": "2013-06-25T15:37:59Z",
+    "pdf_url": "https://arxiv.org/pdf/1306.6004v1",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\1306.6004v1.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "A note on \"Einstein's special relativity beyond the speed of light by   James M. Hill and Barry J. Cox\"",
+    "authors": [
+      "Hajnal Andr\u00e9ka",
+      "Judit X. Madar\u00e1sz",
+      "Istv\u00e1n N\u00e9meti",
+      "Gergely Sz\u00e9kely"
+    ],
+    "abstract": "We show that the transformations J. M. Hill and B. J. Cox introduce between inertial observers moving faster than light with respect to each other are consistent with Einstein's principle of relativity only if the spacetime is 2 dimensional.",
+    "arxiv_id": "1211.2246v2",
+    "categories": [
+      "gr-qc",
+      "math-ph",
+      "math.MP"
+    ],
+    "primary_category": "gr-qc",
+    "published_date": "2012-11-09T21:12:57Z",
+    "updated_date": "2013-02-17T09:03:25Z",
+    "pdf_url": "https://arxiv.org/pdf/1211.2246v2",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\1211.2246v2.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "Droplet-shaped waves: Causal finite-support analogs of X-shaped waves",
+    "authors": [
+      "Andrei B. Utkin"
+    ],
+    "abstract": "A model of steady-state X-shaped wave generation by a superluminal (supersonic) pointlike source infinitely moving along a straight line is extended to a more realistic causal scenario of a source pulse launched at time zero and propagating rectilinearly at constant superluminal speed. In the case of infinitely short (delta) pulse, the new model yields an analytical solution, corresponding to the propagation-invariant X-shaped wave clipped by a droplet-shaped support, which perpetually expands along the propagation and transversal directions, thus tending the droplet-shaped wave to the X-shaped one.",
+    "arxiv_id": "1110.3494v3",
+    "categories": [
+      "physics.optics",
+      "math-ph",
+      "math.MP",
+      "physics.class-ph"
+    ],
+    "primary_category": "physics.optics",
+    "published_date": "2011-10-16T15:55:54Z",
+    "updated_date": "2013-01-02T18:20:35Z",
+    "pdf_url": "https://arxiv.org/pdf/1110.3494v3",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\1110.3494v3.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "Relative velocities, geometry, and expansion of space",
+    "authors": [
+      "Vicente J. Bol\u00f3s",
+      "Sam Havens",
+      "David Klein"
+    ],
+    "abstract": "What does it mean to say that space expands? One approach to this question is the study of relative velocities. In this context, a non local test particle is \"superluminal\" if its relative velocity exceeds the local speed of light of the observer. The existence of superluminal relative velocities of receding test particles, in a particular cosmological model, suggests itself as a possible criterion for expansion of space in that model. In this point of view, superluminal velocities of distant receding galaxy clusters result from the expansion of space between the observer and the clusters. However, there is a fundamental ambiguity that must be resolved before this approach can be meaningful. The notion of relative velocity of a nonlocal object depends on the choice of coordinates, and this ambiguity suggests the need for coordinate independent definitions. In this work, we review four (inequivalent) geometrically defined and universal notions of relative velocity: Fermi, kinematic, astrometric, and spectroscopic relative velocities. We apply this formalism to test particles undergoing radial motion relative to comoving observers in expanding Robertson-Walker cosmologies, and include previously unpublished results on Fermi coordinates for a class of inflationary cosmologies. We compare relative velocities to each other, and show how pairs of them determine geometric properties of the spacetime, including the scale factor with sufficient data. Necessary and sufficient conditions are given for the existence of superluminal recessional Fermi speeds in general Robertson-Walker cosmologies. We conclude with a discussion of expansion of space.",
+    "arxiv_id": "1210.3161v1",
+    "categories": [
+      "gr-qc",
+      "astro-ph.CO",
+      "math-ph",
+      "math.MP",
+      "83F05, 83C99"
+    ],
+    "primary_category": "gr-qc",
+    "published_date": "2012-10-11T09:31:13Z",
+    "updated_date": "2012-10-11T09:31:13Z",
+    "pdf_url": "https://arxiv.org/pdf/1210.3161v1",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\1210.3161v1.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "Invariant solutions for equations of axion electrodynamics",
+    "authors": [
+      "Oksana Kuriksha",
+      "A. G. Nikitin"
+    ],
+    "abstract": "Using the three-dimensional subalgebras of the Lie algebra of Poincar\\'e group an extended class of exact solutions for the field equations of the axion electrodynamics is obtained. These solutions include arbitrary parameters and arbitrary functions as well. The most general solutions include six arbitrary functions. Among them there are bound and square integrable solutions which propagate faster than light. However, their energy velocities are smaller than the velocity of light.",
+    "arxiv_id": "1002.0064v6",
+    "categories": [
+      "math-ph",
+      "hep-th",
+      "math.MP",
+      "81V99"
+    ],
+    "primary_category": "math-ph",
+    "published_date": "2010-01-30T12:36:53Z",
+    "updated_date": "2012-08-16T09:59:50Z",
+    "pdf_url": "https://arxiv.org/pdf/1002.0064v6",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\1002.0064v6.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "Optical mesh lattices with PT-symmetry",
+    "authors": [
+      "Mohammad-Ali Miri",
+      "Alois Regensburger",
+      "Ulf Peschel",
+      "Demetrios N. Christodoulides"
+    ],
+    "abstract": "We investigate a new class of optical mesh periodic structures that are discretized in both the transverse and longitudinal directions. These networks are composed of waveguide arrays that are discretely coupled while phase elements are also inserted to discretely control their effective potentials and can be realized both in the temporal and the spatial domain. Their band structure and impulse response is studied in both the passive and parity-time (PT) symmetric regime. The possibility of band merging and the emergence of exceptional points along with the associated optical dynamics are considered in detail both above and below the PT-symmetry breaking point. Finally unidirectional invisibility in PT-synthetic mesh lattices is also examined along with possible superluminal light transport dynamics.",
+    "arxiv_id": "1208.1722v1",
+    "categories": [
+      "physics.optics",
+      "math-ph",
+      "math.MP",
+      "quant-ph"
+    ],
+    "primary_category": "physics.optics",
+    "published_date": "2012-08-08T17:49:55Z",
+    "updated_date": "2012-08-08T17:49:55Z",
+    "pdf_url": "https://arxiv.org/pdf/1208.1722v1",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\1208.1722v1.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "Testing the reliability of a velocity definition in dispersive medium",
+    "authors": [
+      "Mehmet Emre Tasgin"
+    ],
+    "abstract": "We introduce a method to test if a given velocity definition corresponds to an actual physical flow, when the pulse propagation in dispersive medium is considered. i) We calculate the mean arrival time between two positions in space, using the Fourier expansion in real-\\omega space. ii) We calculate the mean spatial displacement between two points in time, using the Fourier expansion in real-k space. We compare the velocities calculated in the two approaches. If the velocity definition truly corresponds to an actual flow, the two velocities must be the same. However, we show that the two velocities differ significantly (4%) in the region of superluminal propagation even for the successful definition introduced by Peatross et al. [Phys. Rev. Lett. 84, 2370 (2000)].",
+    "arxiv_id": "1204.5460v2",
+    "categories": [
+      "physics.optics",
+      "math-ph",
+      "math.MP"
+    ],
+    "primary_category": "physics.optics",
+    "published_date": "2012-04-24T19:02:19Z",
+    "updated_date": "2012-07-20T07:53:44Z",
+    "pdf_url": "https://arxiv.org/pdf/1204.5460v2",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\1204.5460v2.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "Symmetries and solutions of field equations of axion electrodynamics",
+    "authors": [
+      "A. G. Nikitin",
+      "Oksana Kuriksha"
+    ],
+    "abstract": "The group classification of models of axion electrodynamics with arbitrary self interaction of axionic field is carried out. It is shown that extensions of the basic Poincar\\'e invariance of these models appear only for constant and exponential interactions. The related conservation laws are discussed. Using the In\\\"on\\\"u-Wigner contraction the non-relativistic limit of equations of axion electrodynamics is found. An extended class of exact solutions for the electromagnetic and axion fields is obtained. Among them there are solutions including up to six arbitrary functions. In particular, solutions which describe propagation with velocities faster than the velocity of light are found. These solutions are smooth and bounded functions which correspond to positive definite and bounded energy density.",
+    "arxiv_id": "1201.4935v3",
+    "categories": [
+      "hep-th",
+      "math-ph",
+      "math.MP",
+      "81Qxx, 81Rxx"
+    ],
+    "primary_category": "hep-th",
+    "published_date": "2012-01-24T09:44:56Z",
+    "updated_date": "2012-07-04T09:57:49Z",
+    "pdf_url": "https://arxiv.org/pdf/1201.4935v3",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\1201.4935v3.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "Beyond the speed of light on Finsler spacetimes",
+    "authors": [
+      "Christian Pfeifer",
+      "Mattias N. R. Wohlfarth"
+    ],
+    "abstract": "As a prototypical massive field theory we study the scalar field on the recently introduced Finsler spacetimes. We show that particle excitations exist that propagate faster than the speed of light recognized as the boundary velocity of observers. This effect appears already in Finsler spacetime geometries with very small departures from Lorentzian metric geometry. It switches on for a sufficiently large ratio of the particle four-momentum and mass, and is the consequence of a modified version of the Coleman-Glashow velocity dispersion relation. The momentum dispersion relation on Finsler spacetimes is shown to be the same as on metric spacetimes, which differs from many quantum gravity models. If similar relations resulted for fermions on Finsler spacetimes, these generalized geometries could explain the potential observation of superluminal neutrinos claimed by the Opera Collaboration.",
+    "arxiv_id": "1109.6005v4",
+    "categories": [
+      "gr-qc",
+      "hep-th",
+      "math-ph",
+      "math.MP"
+    ],
+    "primary_category": "gr-qc",
+    "published_date": "2011-09-27T19:56:24Z",
+    "updated_date": "2012-05-22T09:41:34Z",
+    "pdf_url": "https://arxiv.org/pdf/1109.6005v4",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\1109.6005v4.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "Pseudo-Hermitian Quantum Dynamics of Tachyonic Spin-1/2 Particles",
+    "authors": [
+      "U. D. Jentschura",
+      "B. J. Wundt"
+    ],
+    "abstract": "We investigate the spinor solutions, the spectrum and the symmetry properties of a matrix-valued wave equation whose plane-wave solutions satisfy the superluminal (tachyonic) dispersion relation E^2 = p^2 - m^2, where E is the energy, p is the spatial momentum, and m is the mass of the particle. The equation reads (i gamma^mu partial_mu - gamma^5 m) psi = 0, where gamma^5 is the fifth current. The tachyonic equation is shown to be CP invariant, and T invariant. The tachyonic Hamiltonian H_5 = alpha.p + beta gamma^5 m breaks parity and is non-Hermitian but fulfills the pseudo-Hermitian property H_5(r) = P H^+_5(-r) P^{-1} = PP H^+_5(-r) PP^{-1} where P is the parity matrix and PP is the full parity transformation. The energy eigenvalues and eigenvectors describe a continuous spectrum of plane-wave solutions (which correspond to real eigenvalues for |p|>=m and evanescent waves, which constitute resonances and antiresonances with complex-conjugate pairs of resonance eigenvalues (for |p|<=m) . In view of additional algebraic properties of the Hamiltonian which supplement the pseudo-Hermiticity, the existence of a resonance energy eigenvalues E implies that E^*, -E, and -E^* also constitute resonance energies of H_5.",
+    "arxiv_id": "1110.4171v3",
+    "categories": [
+      "hep-ph",
+      "math-ph",
+      "math.MP",
+      "quant-ph"
+    ],
+    "primary_category": "hep-ph",
+    "published_date": "2011-10-19T03:33:02Z",
+    "updated_date": "2012-04-19T01:08:47Z",
+    "pdf_url": "https://arxiv.org/pdf/1110.4171v3",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\1110.4171v3.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "Relative velocities for radial motion in expanding Robertson-Walker   spacetimes",
+    "authors": [
+      "Vicente J. Bol\u00f3s",
+      "David Klein"
+    ],
+    "abstract": "The expansion of space, and other geometric properties of cosmological models, can be studied using geometrically defined notions of relative velocity. In this paper, we consider test particles undergoing radial motion relative to comoving (geodesic) observers in Robertson-Walker cosmologies, whose scale factors are increasing functions of cosmological time. Analytical and numerical comparisons of the Fermi, kinematic, astrometric, and the spectroscopic relative velocities of test particles are given under general circumstances. Examples include recessional comoving test particles in the de Sitter universe, the radiation-dominated universe, and the matter-dominated universe. Three distinct coordinate charts, each with different notions of simultaneity, are employed in the calculations. It is shown that the astrometric relative velocity of a radially receding test particle cannot be superluminal in any expanding Robertson-Walker spacetime. However, necessary and sufficient conditions are given for the existence of superluminal Fermi speeds, and it is shown how the four concepts of relative velocity determine geometric properties of the spacetime.",
+    "arxiv_id": "1106.3859v2",
+    "categories": [
+      "gr-qc",
+      "math-ph",
+      "math.MP",
+      "83F05, 83C99"
+    ],
+    "primary_category": "gr-qc",
+    "published_date": "2011-06-20T10:40:38Z",
+    "updated_date": "2012-02-03T10:19:02Z",
+    "pdf_url": "https://arxiv.org/pdf/1106.3859v2",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\1106.3859v2.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "Noncommutative Common Cause Principles in Algebraic Quantum Field Theory",
+    "authors": [
+      "G\u00e1bor Hofer-Szab\u00f3",
+      "P\u00e9ter Vecserny\u00e9s"
+    ],
+    "abstract": "States in algebraic quantum field theory \"typically\" establish correlation between spacelike separated events. Reichenbach's Common Cause Principle, generalized to the quantum field theoretical setting, offers an apt tool to causally account for these superluminal correlations. In the paper we motivate first why commutativity between the common cause and the correlating events should be abandoned in the definition of the common cause. Then we show that the Noncommutative Weak Common Cause Principle holds in algebraic quantum field theory with locally finite degrees of freedom. Namely, for any pair of projections A, B supported in spacelike separated regions V_A and V_B, respectively, there is a local projection C not necessarily commuting with A and B such that C is supported within the union of the backward light cones of V_A and V_B and the set {C, non-C} screens off the correlation between A and B.",
+    "arxiv_id": "1201.4813v1",
+    "categories": [
+      "math-ph",
+      "math.MP"
+    ],
+    "primary_category": "math-ph",
+    "published_date": "2012-01-23T19:05:33Z",
+    "updated_date": "2012-01-23T19:05:33Z",
+    "pdf_url": "https://arxiv.org/pdf/1201.4813v1",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\1201.4813v1.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "The 2d Gross-Neveu Model for Pseudovector Fermions and Tachyonic Mass   Generation",
+    "authors": [
+      "V. K. Oikonomou"
+    ],
+    "abstract": "Recent observations in the OPERA experiment suggest that the neutrino could propagate with speed that is superluminal. Based on early theoretical work on tachyonic fermions we shall study a modification of the Gross-Neveu model in two dimensions. We shall see that the theory results to the dynamical generation of real and imaginary masses. These imaginary masses indicate the possibility that tachyonic solutions (or instabilities) could exist in the theory. The implications of a tachyonic neutrino coming from astrophysical sources are critically discussed. Moreover, we present a toy model that consists of an U(2,2) invariant Dirac Lagrangian. This theory can have tachyonic masses as solutions. A natural mass splitting between the solutions is a natural outcome of the formalism.",
+    "arxiv_id": "1109.6170v3",
+    "categories": [
+      "hep-th",
+      "gr-qc",
+      "hep-ph",
+      "math-ph",
+      "math.MP",
+      "quant-ph"
+    ],
+    "primary_category": "hep-th",
+    "published_date": "2011-09-28T11:19:40Z",
+    "updated_date": "2011-11-20T10:21:42Z",
+    "pdf_url": "https://arxiv.org/pdf/1109.6170v3",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\1109.6170v3.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "The Mass Spectrum of Neutrinos",
+    "authors": [
+      "E. Capelas de Oliveira",
+      "W. A. Rodrigues Jr.",
+      "J. Vaz Jr"
+    ],
+    "abstract": "In a previous paper we showed that Weyl equation possess superluminal solutions and moreover we showed that those solutions that are eigenstates of the parity operator seem to describe a coupled pair of a monopole anti-monopole system. This result suggests to look for a solution of Maxwell equation \\partialF^{\\infty}=-gJ with a current J as source and such that the Lorentz force on the current is null. We first identify a solution where J={\\gamma}^{5}J_{m}is a spacelike field (even if F is not a superluminal solution of the homogeneous Maxwell equation). More surprisingly we find that there exists a solution F of the free Maxwell \\partialF=0 that is equivalent to the non homogeneous equation for F^{\\infty}. Once this result is proved it suggests by itself to look for more general subluminal and superluminal solutions F of the free Maxwell equation equivalent to a non homogeneous Maxwell equation for a field F_{0} with a current term as source which may be subluminal or superluminal. We exhibit one such subluminal solution, for which the Dirac-Hestenes spinor field {\\psi} associated the electromagnetic field F_{0} satisfies a Dirac equation for a bradyonic neutrino under the ansatz that the current is ce^{{\\lambda}{\\gamma}^{5}}g{\\psi}{\\gamma}^{0}{\\psi}, with g the quantum of magnetic charge and {\\lambda} a constant to be determined in such a way that the auto-force be null. Together with Dirac's quantization condition this gives a quantized mass spectrum (Eq.49) for the neutrinos, with the masses of the different flavor neutrinos being of the same order of magnitude (Eq.50) which is in accord with recent experimental findings. As a last surprise we show that the mass spectrum found in the previous case continues to hold if the current is taken spacelike, i.e., ce^{{\\lambda}{\\gamma}^{5}}g{\\psi}_{>}{\\gamma}^{3}{\\psi}_{>} with {\\psi}_{>}, in this case, satisfying a tachyonic Dirac-Hestenes equation.",
+    "arxiv_id": "1110.5040v2",
+    "categories": [
+      "math-ph",
+      "hep-ph",
+      "math.MP"
+    ],
+    "primary_category": "math-ph",
+    "published_date": "2011-10-23T13:12:49Z",
+    "updated_date": "2011-10-25T08:12:09Z",
+    "pdf_url": "https://arxiv.org/pdf/1110.5040v2",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\1110.5040v2.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "Superluminal Neutrinos from OPERA Experiment and Weyl Equation",
+    "authors": [
+      "E. Capelas de Oliveira",
+      "W. A. Rodrigues Jr.",
+      "J. Vaz Jr"
+    ],
+    "abstract": "By analyzing the structure of the Weyl spinor field in the Clifford bundle formalism we show that in each spinorial frame it is represented by F\\insec(\\doublebarwedge^0 T^\\starM + \\doublebarwedge^2 T^\\star M + \\doublebarwedge^{4} T^\\star M)\\hookrightarrowsecC\\ell(M,g) satisfying the equation \\partialF=0, where \\partial is the Dirac operator acting on sections of the Clifford bundle C\\ell(M,g). With this result we show that introducing a generalized potential A=(A + \\gamma_5 B)\\insec(\\doublebarwedge^{1}T^{\\star}M + \\doublebarwedge^3 T^\\star M)\\hookrightarrowsecC\\ell(M,g) for the Weyl field such that F=\\partialA it is possible to exhibit superluminal solutions (including one with a front moving at superluminal speed) for Weyl equation, which surprisingly describes the propagation of a massive tachyonic neutrino. We propose to interpret these extraordinary solutions in order that eventually they may serve as possible models for the emission process and propagation of the superluminal neutrinos observed at the OPERA experiment. Moreover, complementing this study we show that general local chiral invariance of Weyl equation implies that it describes for all solutions that are eigenstates of the parity operator a pair of `sub-particles' carrying opposite magnetic charges (thus possibly carrying a small magnetic moment) which thus interact with an external electromagnetic field. Even if at the Earth's electromagnetic field the effect may result negligible, eventually the idea may be a useful one to study neutrinos leaving the electromagnetic field of stars.",
+    "arxiv_id": "1110.2219v1",
+    "categories": [
+      "math-ph",
+      "hep-ph",
+      "math.MP"
+    ],
+    "primary_category": "math-ph",
+    "published_date": "2011-10-10T22:21:53Z",
+    "updated_date": "2011-10-10T22:21:53Z",
+    "pdf_url": "https://arxiv.org/pdf/1110.2219v1",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\1110.2219v1.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "Exact deflection of a Neutral-Tachyon in the Kerr's Gravitational field",
+    "authors": [
+      "G. V. Kraniotis"
+    ],
+    "abstract": "We solve in closed analytic form space-like geodesic equations in the Kerr gravitational field. Such geodesic equations describe the motion of neutral tachyons (faster than light particles) in the Kerr spacetime. More specifically we derive the closed form solution for the deflection angle of a neutral tachyon on an equatorial orbit in Kerr spacetime. The solution is expressed elegantly in terms of Lauricella's hypergeometric function F_{D}.We applied our results to three cases: first, for the calculation of the deflection angle of a neutral tachyon on an equatorial trajectory in the gravitational field of a Kerr black hole. Subsequently, we applied our exact solutions to compute the deflection angle of equatorial spacelike geodesics in the gravitational fields of Sun and Earth assuming the Kerr spacetime geometry.",
+    "arxiv_id": "1110.1223v1",
+    "categories": [
+      "gr-qc",
+      "math-ph",
+      "math.MP"
+    ],
+    "primary_category": "gr-qc",
+    "published_date": "2011-10-06T11:04:11Z",
+    "updated_date": "2011-10-06T11:04:11Z",
+    "pdf_url": "https://arxiv.org/pdf/1110.1223v1",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\1110.1223v1.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "Quantum points/patterns, Part 1. From geometrical points to quantum   points in a sheaf framework",
+    "authors": [
+      "Antonina N. Fedorova",
+      "Michael G. Zeitlin"
+    ],
+    "abstract": "We consider some generalization of the theory of quantum states, which is based on the analysis of long standing problems and unsatisfactory situation with the possible interpretations of quantum mechanics. We demonstrate that the consideration of quantum states as sheaves can provide, in principle, more deep understanding of some phenomena. The key ingredients of the proposed construction are the families of sections of sheaves with values in the category of the functional realizations of infinite-dimensional Hilbert spaces with special (multiscale) filtration. Three different symmetries, kinematical (on space-time), hidden/dynamical (on sections of sheaves), unified (on filtration of the full scale of spaces) are generic objects generating the full zoo of quantum phenomena (e.g., faster than light propagation).",
+    "arxiv_id": "1109.5035v1",
+    "categories": [
+      "quant-ph",
+      "math-ph",
+      "math.MP",
+      "nlin.PS"
+    ],
+    "primary_category": "quant-ph",
+    "published_date": "2011-09-23T11:28:24Z",
+    "updated_date": "2011-09-23T11:28:24Z",
+    "pdf_url": "https://arxiv.org/pdf/1109.5035v1",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\1109.5035v1.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "The sine-Gordon equation in the semiclassical limit: critical behavior   near a separatrix",
+    "authors": [
+      "Robert J. Buckingham",
+      "Peter D. Miller"
+    ],
+    "abstract": "We study the Cauchy problem for the sine-Gordon equation in the semiclassical limit with pure-impulse initial data of sufficient strength to generate both high-frequency rotational motion near the peak of the impulse profile and also high-frequency librational motion in the tails. Subject to suitable conditions of a general nature, we analyze the fluxon condensate solution approximating the given initial data for small time near points where the initial data crosses the separatrix of the phase portrait of the simple pendulum. We show that the solution is locally constructed as a universal curvilinear grid of superluminal kinks and grazing collisions thereof, with the grid curves being determined from rational solutions of the Painleve-II system.",
+    "arxiv_id": "1106.5716v1",
+    "categories": [
+      "math-ph",
+      "math.AP",
+      "math.MP"
+    ],
+    "primary_category": "math-ph",
+    "published_date": "2011-06-28T16:13:44Z",
+    "updated_date": "2011-06-28T16:13:44Z",
+    "pdf_url": "https://arxiv.org/pdf/1106.5716v1",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\1106.5716v1.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "Tachyons in General Relativity",
+    "authors": [
+      "Charles Schwartz"
+    ],
+    "abstract": "We consider the motion of tachyons (faster-than-light particles) in the framework of General Relativity. An important feature is the large contribution of low energy tachyons to the energy-momentum tensor. We also calculate the gravitational field produced by tachyons in particular geometric arrangements; and it appears that there could be self-cohering bundles of such matter. This leads us to suggest that such theoretical ideas might be relevant to major problems (dark matter and dark energy) in current cosmological models.",
+    "arxiv_id": "1011.4847v2",
+    "categories": [
+      "math-ph",
+      "gr-qc",
+      "math.MP"
+    ],
+    "primary_category": "math-ph",
+    "published_date": "2010-11-22T15:25:06Z",
+    "updated_date": "2011-03-29T19:18:09Z",
+    "pdf_url": "https://arxiv.org/pdf/1011.4847v2",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\1011.4847v2.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "The Maximal Velocity of a Photon",
+    "authors": [
+      "Avy Soffer"
+    ],
+    "abstract": "The probability of a photon to move faster than light, under the Einstein Quantum dynamics is shown to vanish for large times. The proof is based on using propagation estimates on multiscaled energy intervals, to control the singular symbol of the Hamiltonian, at zero.",
+    "arxiv_id": "1103.3031v1",
+    "categories": [
+      "math-ph",
+      "math.AP",
+      "math.MP"
+    ],
+    "primary_category": "math-ph",
+    "published_date": "2011-03-15T20:39:41Z",
+    "updated_date": "2011-03-15T20:39:41Z",
+    "pdf_url": "https://arxiv.org/pdf/1103.3031v1",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\1103.3031v1.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "Fermi coordinates, simultaneity, and expanding space in Robertson-Walker   cosmologies",
+    "authors": [
+      "David Klein",
+      "Evan Randles"
+    ],
+    "abstract": "Explicit Fermi coordinates are given for geodesic observers comoving with the Hubble flow in expanding Robertson-Walker spacetimes, along with exact expressions for the metric tensors in Fermi coordinates. For the case of non inflationary cosmologies, it is shown that Fermi coordinate charts are global, and space-time is foliated by space slices of constant Fermi (proper) time that have finite extent. A universal upper bound for the proper radius of any leaf of the foliation, i.e., for the proper radius of the spatial universe at any fixed time of the geodesic observer, is given. A general expression is derived for the geometrically defined Fermi relative velocity of a test particle (e.g. a galaxy) comoving with the Hubble flow away from the observer. Least upper bounds of superluminal recessional Fermi velocities are given for spacetimes whose scale factors follow power laws, including matter-dominated and radiation-dominated cosmologies. Exact expressions for the proper radius of any leaf of the foliation for this same class of spacetimes are given. It is shown that the radii increase linearly with proper time of the observer moving with the Hubble flow. These results are applied to particular cosmological models.",
+    "arxiv_id": "1010.0588v3",
+    "categories": [
+      "math-ph",
+      "astro-ph.CO",
+      "gr-qc",
+      "math.MP",
+      "83F05, 83C10"
+    ],
+    "primary_category": "math-ph",
+    "published_date": "2010-10-04T13:53:12Z",
+    "updated_date": "2011-03-05T22:29:17Z",
+    "pdf_url": "https://arxiv.org/pdf/1010.0588v3",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\1010.0588v3.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "Can We Make a Bohmian Electron Reach the Speed of Light, at Least for   One Instant?",
+    "authors": [
+      "Daniel V. Tausk",
+      "Roderich Tumulka"
+    ],
+    "abstract": "In Bohmian mechanics, a version of quantum mechanics that ascribes world lines to electrons, we can meaningfully ask about an electron's instantaneous speed relative to a given inertial frame. Interestingly, according to the relativistic version of Bohmian mechanics using the Dirac equation, a massive particle's speed is less than or equal to the speed of light, but not necessarily less. That is, there are situations in which the particle actually reaches the speed of light---a very non-classical behavior. That leads us to the question of whether such situations can be arranged experimentally. We prove a theorem, Theorem 5, implying that for generic initial wave functions the probability that the particle ever reaches the speed of light, even if at only one point in time, is zero. We conclude that the answer to the question is no. Since a trajectory reaches the speed of light whenever the quantum probability current psi-bar gamma^mu psi is a lightlike 4-vector, our analysis concerns the current vector field of a generic wave function and may thus be of interest also independently of Bohmian mechanics. The fact that the current is never spacelike has been used to argue against the possibility of faster-than-light tunnelling through a barrier, a somewhat similar question. Theorem 5, as well as a more general version provided by Theorem 6, are also interesting in their own right. They concern a certain property of a function psi: R^4 --> C^4 that is crucial to the question of reaching the speed of light, namely being transverse to a certain submanifold of C^4 along a given compact subset of space-time. While it follows from the known transversality theorem of differential topology that this property is generic among smooth functions psi: R^4 --> C^4, Theorem 5 asserts that it is also generic among smooth solutions of the Dirac equation.",
+    "arxiv_id": "0806.4476v4",
+    "categories": [
+      "quant-ph",
+      "math-ph",
+      "math.MP"
+    ],
+    "primary_category": "quant-ph",
+    "published_date": "2008-06-27T12:41:58Z",
+    "updated_date": "2011-01-07T19:03:35Z",
+    "pdf_url": "https://arxiv.org/pdf/0806.4476v4",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\0806.4476v4.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "Inadequacies in the conventional treatment of the radiation field of   moving sources",
+    "authors": [
+      "Houshang Ardavan",
+      "Arzhang Ardavan",
+      "John Singleton",
+      "Joseph Fasel",
+      "Andrea Schmidt"
+    ],
+    "abstract": "There is a fundamental difference between the classical expression for the retarded electromagnetic potential and the corresponding retarded solution of the wave equation that governs the electromagnetic field. While the boundary contribution to the retarded solution for the {\\em potential} can always be rendered equal to zero by means of a gauge transformation that preserves the Lorenz condition, the boundary contribution to the retarded solution of the wave equation governing the {\\em field} may be neglected only if it diminishes with distance faster than the contribution of the source density in the far zone. In the case of a source whose distribution pattern both rotates and travels faster than light {\\em in vacuo}, as realized in recent experiments, the boundary term in the retarded solution governing the field is by a factor of the order of $R^{1/2}$ {\\em larger} than the source term of this solution in the limit that the distance $R$ of the boundary from the source tends to infinity. This result is consistent with the prediction of the retarded potential that part of the radiation field generated by a rotating superluminal source decays as $R^{-1/2}$, instead of $R^{-1}$, a prediction that is confirmed experimentally. More importantly, it pinpoints the reason why an argument based on a solution of the wave equation governing the field in which the boundary term is neglected (such as appears in the published literature) misses the nonspherical decay of the field.",
+    "arxiv_id": "0908.1350v1",
+    "categories": [
+      "math-ph",
+      "math.MP"
+    ],
+    "primary_category": "math-ph",
+    "published_date": "2009-08-10T16:19:53Z",
+    "updated_date": "2009-08-10T16:19:53Z",
+    "pdf_url": "https://arxiv.org/pdf/0908.1350v1",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\0908.1350v1.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "Response to \"Comment on `Method of handling the divergences in the   radiation theory of sources that move faster than their own waves'\" [J. Math.   Phys. 40, 4331 (1999)]",
+    "authors": [
+      "Houshang Ardavan",
+      "Arzhang Ardavan",
+      "John Singleton",
+      "Joseph Fasel",
+      "Andrea Schmidt"
+    ],
+    "abstract": "There is a fundamental difference between the classical expression for the retarded electromagnetic potential and the corresponding retarded solution of the wave equation that governs the electromagnetic field. While the boundary contribution to the retarded solution for the potential can always be rendered equal to zero by means of a gauge transformation that preserves the Lorenz condition, the boundary contribution to the retarded solution of the wave equation governing the field may be neglected only if it diminishes with distance faster than the contribution of the source density in the far zone. In the case of a source whose distribution pattern rotates superluminally (i.e., faster than the speed of light in vacuo), the boundary term in the retarded solution governing the field is by a factor of the order of R^(1/2) larger than the source term of this solution in the limit where the distance R of the boundary from the source tends to infinity. This result is consistent with the prediction of the retarded potential that the radiation field generated by a rotating superluminal source decays as 1/R^(1/2), instead of 1/R. It also explains why an argument based on the solution of the wave equation governing the field in which the boundary term is neglected, such as Hannay presents in his Comment, misses the nonspherical decay of the field.",
+    "arxiv_id": "0805.0304v1",
+    "categories": [
+      "math-ph",
+      "math.MP"
+    ],
+    "primary_category": "math-ph",
+    "published_date": "2008-05-02T19:57:05Z",
+    "updated_date": "2008-05-02T19:57:05Z",
+    "pdf_url": "https://arxiv.org/pdf/0805.0304v1",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\0805.0304v1.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "The Theory of Kairons",
+    "authors": [
+      "Arkadiusz Jadczyk"
+    ],
+    "abstract": "In relativistic quantum mechanics wave functions of particles satisfy field equations that have initial data on a space--like hypersurface. We propose a dual field theory of ``wavicles'' that have their initial data on a time--like worldline. Propagation of such fields is superluminal, even though the Hilbert space of the solutions carries a unitary representation of the Poincare group of mass zero. We call the objects described by these field equations ``Kairons''. The paper builds the field equations in a general relativistic framework, allowing for a torsion. Kairon fields are section of a vector bundle over space-time. The bundle has infinite--dimensional fibres.",
+    "arxiv_id": "0711.4716v2",
+    "categories": [
+      "math-ph",
+      "gr-qc",
+      "math.MP",
+      "quant-ph"
+    ],
+    "primary_category": "math-ph",
+    "published_date": "2007-11-29T13:42:22Z",
+    "updated_date": "2008-03-03T12:31:20Z",
+    "pdf_url": "https://arxiv.org/pdf/0711.4716v2",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\0711.4716v2.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "A Local Concept of Wave Velocities",
+    "authors": [
+      "I. V. Drozdov",
+      "A. A. Stahlhofen"
+    ],
+    "abstract": "The classical characterization of \\wp, as a typical concept for far field phenomena, has been successfully applied to many \\w phenomena in past decades. The recent reports of superluminal tunnelling times and negative group velocities challenged this concept. A new local approach for the definition of \\wvs avoiding these difficulties while including the classical definitions as particular cases is proposed here. This generalisation of the conventional non-local approach can be applied to arbitrary \\w forms and propagation media. Some applications of the formalism are presented and basic properties of the concept are summarized.",
+    "arxiv_id": "0704.1485v1",
+    "categories": [
+      "math-ph",
+      "math.MP"
+    ],
+    "primary_category": "math-ph",
+    "published_date": "2007-04-11T20:29:32Z",
+    "updated_date": "2007-04-11T20:29:32Z",
+    "pdf_url": "https://arxiv.org/pdf/0704.1485v1",
+    "local_pdf_path": "data\\arxiv\\pdfs\\mathematics\\0704.1485v1.pdf",
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "Covariant path integral formalism of relativistic quantum mechanics   along proper time",
+    "authors": [
+      "H. Y. Geng"
+    ],
+    "abstract": "A space-time symmetric and explicitly Lorentz covariant path integral formalism of relativistic quantum mechanics is proposed, which produces partial locally correlations of quantum processes of massive particles with the velocity of light at low energy limits. A superluminal correlation is also possible if anti-particles that moving along reverse time direction are excited. This provides a new point of view to interpret EPR experiments, also leaks a light of hope for hidden variable theories.",
+    "arxiv_id": "0703201v1",
+    "categories": [
+      "quant-ph",
+      "math-ph",
+      "math.MP"
+    ],
+    "primary_category": "quant-ph",
+    "published_date": "2007-03-22T07:16:46Z",
+    "updated_date": "2007-03-22T07:16:46Z",
+    "pdf_url": "https://arxiv.org/pdf/0703201v1",
+    "local_pdf_path": null,
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "Relativistic diffusion processes and random walk models",
+    "authors": [
+      "J\u00f6rn Dunkel",
+      "Peter Talkner",
+      "Peter H\u00e4nggi"
+    ],
+    "abstract": "The nonrelativistic standard model for a continuous, one-parameter diffusion process in position space is the Wiener process. As well-known, the Gaussian transition probability density function (PDF) of this process is in conflict with special relativity, as it permits particles to propagate faster than the speed of light. A frequently considered alternative is provided by the telegraph equation, whose solutions avoid superluminal propagation speeds but suffer from singular (non-continuous) diffusion fronts on the light cone, which are unlikely to exist for massive particles. It is therefore advisable to explore other alternatives as well. In this paper, a generalized Wiener process is proposed that is continuous, avoids superluminal propagation, and reduces to the standard Wiener process in the non-relativistic limit. The corresponding relativistic diffusion propagator is obtained directly from the nonrelativistic Wiener propagator, by rewriting the latter in terms of an integral over actions. The resulting relativistic process is non-Markovian, in accordance with the known fact that nontrivial continuous, relativistic Markov processes in position space cannot exist. Hence, the proposed process defines a consistent relativistic diffusion model for massive particles and provides a viable alternative to the solutions of the telegraph equation.",
+    "arxiv_id": "0608023v3",
+    "categories": [
+      "cond-mat.stat-mech",
+      "astro-ph",
+      "hep-th",
+      "math-ph",
+      "math.MP"
+    ],
+    "primary_category": "cond-mat.stat-mech",
+    "published_date": "2006-08-01T14:03:51Z",
+    "updated_date": "2007-01-19T09:08:18Z",
+    "pdf_url": "https://arxiv.org/pdf/0608023v3",
+    "local_pdf_path": null,
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "Finite Energy Superluminal Solutions of Maxwell Equations",
+    "authors": [
+      "E. Capelas de Oliveira",
+      "W. A. Rodrigues Jr"
+    ],
+    "abstract": "We exhibit exact finite energy superluminal solutions of Maxwell equations in vacuum.",
+    "arxiv_id": "0105043v4",
+    "categories": [
+      "math-ph",
+      "math.MP",
+      "35L05, 35Q60,83Cxx"
+    ],
+    "primary_category": "math-ph",
+    "published_date": "2001-05-29T18:05:57Z",
+    "updated_date": "2001-11-05T12:42:06Z",
+    "pdf_url": "https://arxiv.org/pdf/0105043v4",
+    "local_pdf_path": null,
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "Mass and Spin Renormalization in Lorentz Electrodynamics",
+    "authors": [
+      "Walter Appel",
+      "Michael K. -H. Kiessling"
+    ],
+    "abstract": "A new, relativistically covariant, massive Lorentz Electrodynamics (LED) is presented in which the bare particle has a finite positive bare rest mass and moment of inertia. The particle's electromagnetic self-interaction renormalizes its mass and spin. Most crucially, the renormalized particle is a soliton: after any scattering process its rest mass and spin magnitude are dynamically restored to their pre-scattering values. This guarantees that ``an electron remains an electron,'' poetically speaking. A renormalization flow study of the limit of vanishing bare rest mass is conducted for this model. This limit yields a purely electromagnetic classical field theory with ultra-violet cutoff at about the electron's Compton wavelength! The renormalized limit model matches the empirical electron data as orderly as one can hope for at the level of Lorentz theory. In particular, no superluminal equatorial gyration speeds occur.",
+    "arxiv_id": "0009003v2",
+    "categories": [
+      "math-ph",
+      "gr-qc",
+      "math.MP"
+    ],
+    "primary_category": "math-ph",
+    "published_date": "2000-09-02T22:25:17Z",
+    "updated_date": "2000-10-08T21:19:03Z",
+    "pdf_url": "https://arxiv.org/pdf/0009003v2",
+    "local_pdf_path": null,
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  },
+  {
+    "title": "On an attempt to resolve the EPR-Bell paradox via Reichenbachian concept   of common cause",
+    "authors": [
+      "Laszlo E. Szabo"
+    ],
+    "abstract": "Reichenbach's Common Cause Principle claims that if there is correlation between two events and none of them is directly causally influenced by the other, then there must exist a third event that can, as a common cause, account for the correlation. The EPR-Bell paradox consists in the problem that we observe correlations between spatially separated events in the EPR-experiments, which do not admit common-cause-type explanation; and it must therefore be inevitably concluded, that, contrary to relativity theory, in the realm of quantum physics there exists action at a distance, or at least superluminal causal propagation is possible; that is, either relativity theory or Reichenbach's common cause principle fails. By means of closer analyses of the concept of common cause and a more precise reformulation of the EPR experimental scenario, I will sharpen the conclusion we can draw from the violation of Bell's inequalities. It will be explicitly shown that the correla-tions we encounter in the EPR experiment could have common causes; that is, Reichen-bach's Common Cause Principle does not fail in quantum mechanics. Moreover, these common causes satisfy the locality conditions usually required. In the Revised Version of the paper I added a Postscript from which it turns out that the solution such obtained is, contrary to the original title, incomplete. It turns out that a new problem arises: some combinations of the common cause events do statistically cor-relate with the measurement operations.",
+    "arxiv_id": "9806074v3",
+    "categories": [
+      "quant-ph",
+      "gr-qc",
+      "hep-th",
+      "math-ph",
+      "math.MP",
+      "physics.hist-ph",
+      "physics.pop-ph"
+    ],
+    "primary_category": "quant-ph",
+    "published_date": "1998-06-23T17:12:53Z",
+    "updated_date": "2000-03-06T01:02:37Z",
+    "pdf_url": "https://arxiv.org/pdf/9806074v3",
+    "local_pdf_path": null,
+    "comment": "",
+    "journal_ref": "",
+    "doi": ""
+  }
+]