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+{
+    "9312/astro-ph9312014_arXiv.txt": {
+        "abstract": "Davidsen et al. (1991) have argued that the failure to detect $uv$ photons from the dark matter DM) in cluster A665 excludes the decaying neutrino  hypothesis.  Sciama et al. (1993) argued that  because  of high  central concentration  the  DM  in that cluster  must  be baryonic.  We  study the  DM profile  in clusters of galaxies simulated using the Harrison--Zel'dovich  spectrum of density fluctuations,   and an  amplitude  previously  derived  from numerical simulations (Melott 1984b; Anninos et  al. 1991) and in agreement with microwave background  fluctuations (Smoot et  al. 1992).  We find that with this  amplitude normalization  cluster neutrino DM densities  are comparable to observed cluster DM values.  We conclude that given this normalization, the cluster DM should  be at least largely composed  of neutrinos. The constraint of Davidsen et al. can be  somewhat weakened by the presence of baryonic DM; but it cannot  be eliminated given our assumptions. ",
+        "introduction": "Over a period spanning  roughly the last ten  years a number of papers have  examined the astrophysical  and  cosmological consequences of  a massive neutrino species possessing a specific radiative decay mode to photons with energies of roughly 15 eV and  at a rate of approximately $10^{-24}  {\\rm s^{-1}}$.    Melott  (1984a)  was  able  to provide an explanation for the  morphological segregation of  dwarf galaxies near large parent galaxies as seen by Einasto et al. (1974) by arguing that near  the  large  parent galaxy  the flux  of   {\\it  uv} photons from neutrino decay would be larger and therefore one would expect that the satellite  galaxies   found nearer  the  parent galaxy  should exhibit little  neutral gas  and  hence little   star formation.  While  those satellite galaxies further away  from  the  parent galaxy  would see a much smaller {\\it uv} flux and hence contain larger amounts of neutral gas.   In  addition Melott was  able to derive  the slope dividing the morphological  types fitting,   the observations of    Einasto et  al. (1974).   In  1988  Melott  et al.   extended   the model  to  provide explanations for another series of effects. Using a simple equilibrium argument they were able to show that with  a neutrino of mass $\\approx 30$  eV  and lifetime  $\\approx  10^{24}$ seconds, that   ionizing the universe to  those  levels  required   by the  Gunn-Peterson test   is completely reasonable  in  the  neutrino decay   scenario    (see also Rephaeli \\& Szalay 1981 and Sciama 1982). More  recently Sciama (1990) has provided several additional problems that the neutrino decay model can   provide  a  simple  explanation for if  $\\tau  \\sim (1-3) \\times 10^{23}$ sec.  Several attempts have been made for  an  unambiguous detection  of the {\\it uv} flux from the neutrino decay, ever since the earlier theories of Cowsik  (1977)  and de  Rujula  \\& Glashow  (1980) (see  Shipman \\& Cowsik 1981; Henry \\& Feldman  1981;  Holberg \\& Barber  1985; Fabian, Naylor  \\& Sciama 1991). In  1991 Davidsen et al.,   using the Hopkins Ultraviolet Telescope,  performed a series of  observations  hoping to provide  evidence for or   against  Sciama's (1990)  decaying neutrino model. The  Davidsen  et al. experiment   centered  around  the galaxy cluster A665.   This cluster is known  to be among  the  richest known clusters, therefore  one would expect  that it  might  possess a large dark matter (DM) halo.  The DM halo consisting primarily  of neutrinos would generate a {\\it uv} flux due to the decay of the neutrinos.  The Davidsen experiment was unable to find any convincing evidence for the predicted {\\it uv} flux at the level anticipated from  the decaying DM model, and they  concluded that $log  \\ \\tau  ({\\rm seconds}) >  24.5$ roughly. Furthermore they argued that the theory can only remain valid if one  of the following conditions  holds:(1) the cluster  is several times  less massive  than estimated in their work  (or  there exists a significant baryonic dark matter  component) and the  redshifted decay photon energy happens to lie near the Ly $\\beta$  airglow line, or (2) there is substantial absorption along the line of sight.  Sciama et  al.  (1993) argue that based  upon  several  new  pieces of evidence  that assuming that all  of  the DM  in the cluster is in the form  of  neutrinos may perhaps be  an overly restrictive requirement. The first new piece of  evidence concerns recent X-ray observations of A665. In 1992   Hughes \\&  Tanaka  found strong  evidence that the  DM distribution in A665 is more   centrally condensed  than  either   the galaxy distribution or the hot  X-ray emitting  plasma.  Sciama et al. (1993) argue for  a  baryonic form  of DM  in the  central core of the cluster because    the  neutrinos  being   nearly  collisionless would presumably  be incapable of  dissipating their  energy enough to  fall deeply into the potential of  the cluster.  Secondly, a calculation by Persic \\& Salucci (1992)  of   the contribution  of visual matter   to $\\Omega = \\rho/ \\rho_{\\rm{crit}}$  shows  that  $\\Omega_{\\rm{vis}} \\approx 0.003$. Comparing this   to     the   value   of    $\\Omega_{\\rm{B}}   \\approx 0.06\\,h_{50}^{-2}$  from  primordial nucleosynthesis  (e.g.,  Kolb  \\& Turner  1990;  Peebles  et al.   1991)  argues  for the  existence  of baryonic DM.  With these two observations Sciama et al. concluded that it  may be premature to  argue that the Davidsen  et al.   observation conclusively rules out the decaying neutrino model.  Our goal in the present  paper is to test the  conjecture of Sciama et al. (1993) against a set of reasonable assumptions.   We will do so by deriving detailed  density profiles  for   the neutrinos using  N-body experiments,   which  have   initial   density  fluctuation amplitudes consistent  with  the  recent COBE   measurement (Smoot et al.  1992). Within this   framework, this  will    enable   us to  make   definite conclusions as to whether the neutrino DM  is capable of providing the principal component to the DM distribution in the core of the cluster, and to assess the need for baryonic DM in the cluster core as required by Sciama et al. to evade the Davidsen et al. null result.  In this paper we use $H_0=50\\,h_{50}$ km s$^{-1}$ Mpc$^{-1}$. ",
+        "conclusions": ""
+    },
+    "9312/astro-ph9312021_arXiv.txt": {
+        "abstract": " ",
+        "introduction": "A particle with a discrete symmetry may have a different mass on either side of the domain wall, which may form in an early Universe phase transition with the spontaneous breaking of the discrete symmetry. When a particle has less energy than the rest mass it would have on the other side of the wall, it can become trapped inside a region with a closed domain wall as the boundary. Closed domain walls filled with such particles have been named ``cosmic balloons'' [\\ref{CB}]. Due to effects such as the emission of gravitational radiation, irregular shapes of balloons oscillate and eventually settle down to spheres. Here we are only concerned with a spherical cosmic balloon.  Cosmic balloons are stable objects. The pressure of the relativistic gas inside the balloon balances the surface tension of the wall. An incarnation of a cosmic balloon is a neutrino ball [\\ref{NB}], which is a spherical domain wall with light right-handed neutrinos trapped inside. Details of neutrino balls have been worked out which seem to indicate that they are plausible astrophysical objects [\\ref{NB}], possibly providing an alternative explaination for the mass of quasars and other astrophysical phenomena.  In this work, we follow Ref[\\ref{CB}] in the study of general properties of cosmic balloons, in particular, the mass of the balloon as a function of its radius. The analytical approximation in Ref[\\ref{CB}] has an extremely involved numerical form, and the mass versus radius curve found there is numerically incomplete. In another previous work with similar objectives, Ref[\\ref{Po}], an analytical approximation was applied beyond its valid range and led to incorrect numerical solutions of the mass and radius. In this work, we find simple and transparent analytical expressions which are useful in helping us understand the cosmic balloon solutions qualitatively, and we compute the complete set of mass and radius numerically with and without the application of the analytical approximation. ",
+        "conclusions": ""
+    },
+    "9312/astro-ph9312035_arXiv.txt": {
+        "abstract": "\\noindent  There exists a growing body of observational evidence supporting a non-vanishing cosmological constant at the present epoch. We examine the possibility that such a term may arise directly from the potential energy which drove an inflationary expansion of the very early universe. To avoid arbitrary alterations in the shape of this potential at various epochs it is necessary to introduce a time-dependent viscosity into the system. The evolution of the effective Planck mass in scalar-tensor theories is a natural candidate for such an effect. In these models there are observational constraints arising from anisotropies in the cosmic microwave background, large-scale galactic structure, observations of the primordial Helium abundance and solar system tests of general relativity. Decaying power law and exponential potentials are considered, but for these models it is very difficult to simultaneously satisfy all of the limits.  This may have implications for the joint evolution of the gravitational and cosmological constants.     \\vspace*{12pt}  PACS numbers: 98.80.-k, 98.80.Cq    \\small e mail: $^[email protected]; ~~~$^[email protected]  \\vspace{3cm}  To Appear {\\em International Journal of Modern Physics} {\\bf D} ",
+        "introduction": "\\def\\theequation{\\thesection.\\arabic{equation}} \\setcounter{equation}{0}  The solution to vacuum general relativity with a cosmological constant $\\Lambda$ is de Sitter space and this constant and solution have often been invoked to reconcile theory with observation. Originally Einstein believed the universe to be static and introduced a constant $\\Lambda$-term into his field equations to cancel the expansionary behaviour found when $\\Lambda =0$.$^1$ Some decades later the steady state scenario based on de Sitter space was developed because observations of Hubble's constant suggested the Earth was older than the universe itself.$^2$ More recently the inflationary scenario has been proposed to solve some of the problems of the hot, big bang model.$^3$ During inflation the potential energy of a quantum scalar field dominates the energy-momentum tensor and behaves as a cosmological constant for a finite time.  Realistic inflationary models predict that the current value of the density parameter, $\\Omega_0$, should be very close to unity.$^4$ There are a number of problems associated with the $({\\Lambda}=0,{\\Omega}=1)$ universe which can be resolved if $\\Lambda \\ne 0$.  Firstly, its age is $t_0 \\approx 6.52h^{-1}$ Gyr, where $h$ is the current expansion rate in units of $100$ km ${\\rm sec}^{-1}$ ${\\rm Mpc}^{-1}$.  This is very close to the age of the oldest globular clusters in the galaxy, $t_{\\rm GC} =(13-15)\\pm 3$ Gyr, if $h \\ge 0.6$ as suggested by some observations.$^5$ If ${\\Lambda} \\ne 0$, however, the expansion rate is increased and $t_0$ may exceed $t_{\\rm GC}$ if ${\\Omega}_{\\rm vacuum} \\approx 0.8$.$^6$ Moreover, most dynamical determinations of $\\Omega_0$ suggest $\\Omega_0 = 0.2 \\pm 0.1$ up to scales 30 Mpc and the apparent inconsistency with inflation is again resolved if $\\Omega_{\\rm vacuum} \\approx 0.8$.$^7$ Finally, the introduction of vacuum energy into the standard cold dark matter model of galaxy formation accounts for the extra large-scale clustering observed in galaxy surveys.$^8$  Hence, there are a number of reasons for supposing that a cosmological constant may be influential at the present epoch.$^9$ This work investigates whether the potential energy that drove the inflationary expansion could be such a term.  This has been investigated previously within the context of general relativity by Peebles and Ratra,$^{10}$ but their models required the form of the potential to change drastically at various epochs and therefore suffered from an element of ad-hoc fine-tuning. If the potential is relevant at the current epoch, it must either have a minimum at $V\\ne 0$ or contain a non-vanishing decaying tail. Although the first possibility is not ruled out, it requires severe fine\\---tuning, so we focus on the second. This implies that thermalization of the false vacuum will not proceed via rapid oscillations of the scalar field about some global minimum and the form of the potential must change at various epochs. In general relativity the potential must be sufficiently flat for the strong energy condition to be initially violated, but must then become steep enough for reheating to proceed. But the energy density of the field must redshift at a slower rate than the ordinary matter components at late times if the vacuum energy is to once more dominate the dynamics.$^{54}$  Instead of altering the shape of the potential we extend the gravitational sector of the theory beyond general relativity and investigate whether inflation was driven by potentials which are (a) too steep to lead to inflation in general relativity and (b) do not contain a global minimum. We shall refer to these as {\\em steep\\/} potentials. A number of unified field theories lead to scalar field potentials which exhibit both of these characteristics. The mechanism leading to inflation is very simple.  In pure Einstein gravity containing a single, minimally coupled scalar {\\em inflaton} field, $\\sigma$, the strong energy condition is violated if the condition ${\\dot{\\sigma}}^2<V$ holds, \\ie the potential energy dominates over the field's kinetic energy.  Clearly this condition must break down at some point as steeper potentials are considered. But a finite interval of inflation is possible with steep potentials if one introduces a viscosity into the inflaton field equation which decays as the universe expands.  This viscosity slows the field down and can lead to inflation. As the viscosity becomes weaker, however, the inflaton's kinetic energy increases significantly and a natural exit from inflation proceeds as the expansion becomes subluminal. We identify the dilaton field which arises in scalar-tensor theories as the natural source of this viscosity.  This paper is organised as follows.  We survey theories that lead to inflation with steep potentials in section 2.  In section 3 we derive expressions for the amplitudes of the primordial fluctuation spectra and discuss the most stringent observational constraints which any viable model of this type must satisfy. These limits arise from the observations of large\\---scale galactic structure,$^{11}$ anisotropies in the cosmic microwave background radiation (CMBR),$^{12}$ nucleosynthesis calculations$^{14,15}$ and time\\---delay experiments in the solar system.$^{16}$ Numerical results for both decaying power law and exponential potentials are presented in section 4 and we conclude that successful inflation based on this mechanism is unlikely for the examples considered. Some possible implications of this conclusion are discussed in section 5.  Unless otherwise stated, units are chosen such that $c=\\hbar=1$, and the present day value of the Planck mass is normalized to $\\m =1$. ",
+        "conclusions": ""
+    },
+    "9312/astro-ph9312032_arXiv.txt": {
+        "abstract": "We have conducted timing observations of the eclipsing millisecond binary pulsar PSR~B1957+20, extending the span of data on this pulsar to more than five years. During this time the orbital period of the system has varied by roughly $\\Delta P_b/P_b = 1.6 \\times 10^{-7}$,  changing quadratically with time and displaying an orbital period  second derivative $\\ddot P_b = (1.43 \\pm 0.08) \\times 10^{-18}\\,$s$^{-1}$. The previous measurement of a large negative orbital period derivative reflected only the short-term behavior of the system during the early observations; the orbital period derivative is now positive and increasing rapidly. If, as we suspect, the PSR~B1957+20 system is undergoing quasi-cyclic orbital period variations similar to those found in other close binaries such as Algol and RS CVn, then the $0.025\\,M{_\\odot}$ companion to PSR~B1957+20 is most likely non-degenerate, convective, and magnetically active.  \\bigskip \\noindent {\\em Subject headings:\\/} pulsars --- binaries: evolution --- stars: eclipsing binaries --- stars: individual (PSR~B1957+20) ",
+        "introduction": "The evolutionary links between solitary millisecond pulsars and their presumed binary progenitor systems may involve a number of exotic astrophysical phenomena. In their late stages of evolution, neutron stars in low-mass X-ray and pulsar binaries may evaporate their companions through the strength of their radiation, turning themselves into solitary ``recycled'' pulsars \\cite{acrs82,rst89a,bv91}.  In some cases, material from the companion  may even reform to create planets \\cite{bs92,tb92,srp92}.  The discovery of PSR~B1957+20 \\cite{fst88}, a 1.6 ms pulsar in orbit with a $\\sim0.025\\,M_{\\odot}$ companion, has provided the strongest evidence that this scenario actually occurs in nature, and that interacting binary systems are indeed responsible for the creation of the fastest pulsars.  In spite of the small size of its companion, the pulsar's radio signal is eclipsed over approximately ten percent of the 9.2 hour orbit. Excess delays of the pulses are observed for many minutes after eclipse egress but only briefly before ingress, revealing the existence of an ionized wind from the companion which is continuously infused with new matter (\\pcite{fbb+90}, hereafter F90) and is responsible for the radio eclipse.  Optical observations of the companion provide estimates of its temperature, radius and thermal timescale (\\pcite{fg92} and references therein), and show a strong modulation with orbital phase of its optical luminosity  consistent with irradiation from the pulsar. Radio observations show  the  electron column density in the evaporated wind  to be small (F90; \\pcite{rt91b}, hereafter RT91), a result supported by observed transparency of the wind to unpulsed emission at $\\lambda = 20$\\,cm \\cite{fg92}.  However, RT91 also reported a large (negative) orbital period derivative over the $\\sim$2.5 years spanned by their observations, seemingly implying an unexpectedly short timescale of 30$\\,$Myr for orbital decay. This conclusion was difficult to reconcile with the low rate of mass loss suggested by the density of the companion's wind.  We have conducted further timing observations of PSR~B1957+20 beginning in November 1992 and spanning 9 months. Together with the earlier timing measurements described in F90 and RT91, our data reveal orbital evolution previously unobserved in binary systems containing a pulsar: the orbital period derivative ($\\dot P_b$) of the PSR~B1957+20 system has changed sign and has been increasing steadily. ",
+        "conclusions": "Although our observations reveal that the orbital period derivative discovered by RT91 is not constant and thus provides little direct information on the ultimate fate of the companion of PSR B1957+20, we cannot entirely rule out the most popular explanation of that first measurement, that the orbital period changes are caused by substantial mass loss \\cite{bs92,eic92,bt93,mfkr94}. Nonetheless, we find this proposition unlikely for a number of reasons. In order to transport sufficient angular momentum to produce the observed orbital period variations, the wind density must be several orders of magnitude higher than indicated by the electron density along the line of sight. Therefore, the bulk of the escaping material must either be hidden by the orbit's inclination or be overwhelmingly neutral; the latter explanation seems particularly unlikely given the large systemic escape velocity and the intensity of the pulsar radiation. Furthermore, to match our present results the angular momentum carried by the ablated matter must have varied smoothly over the past five years while doubling in magnitude and changing sign.  We believe a more natural explanation is that PSR B1957+20 undergoes small quasi-periodic oscillations in orbital period. Orbital variations comparable in magnitude to those witnessed here are fairly common in short-period binaries containing a low-mass main-sequence star and have been well-studied in Algol and RS~CVn systems \\cite{sod80,hal89,war88}. In such binaries, rotation of the main-sequence star is likely to be tidally locked to the orbital period; as a result, the ratio of rotational timescale to convective timescale, the star's ``Rossby number,'' is less than one. These stars are generally magnetically active and display substantial chromospheric activity, radio and x-ray flares and stellar winds $10^2$--$10^4$ times stronger than slowly rotating stars of similar spectral class \\cite{pl93,sim90}. The rapid rotation appears to maintain a magnetic dynamo which not only creates an energetic stellar atmosphere, but also distorts the star sufficiently to alter its gravitational quadrupole moment and, in turn, the orbital period \\cite{app92}.  If the companion to PSR B1957+20 is bloated and at least partially non-degenerate, as optical observations appear to imply \\cite{arc92,fg92}, then the stellar atmosphere should be convective and have an overturn timescale far in excess of the 9.2 hour binary period.  The Rossby number of the companion would then be less than one and, like the binaries discussed above, the system might be expected to display orbital period variations and the companion a strong stellar wind, even in the absence of a pulsar primary. Although the companion's external magnetic field is already constrained by Faraday delay measurements (less than a few gauss parallel to the line of sight at the edges of the eclipse region), a much stronger, toroidal, subsurface field could remain undetected by these observations.  If this hypothesis is true, the truly peculiar aspect of the system is not the activity of the companion, but rather its non-degeneracy, for this star is far too light to be burning hydrogen. Either the present irradiation by the pulsar must be responsible for the swollen state of this object, perhaps through a mechanism similar to that proposed by \\scite{pod91} for low-mass X-ray binaries, or evaporation of most of the companion's mass must have been sufficiently recent that it has not yet had time to shrink to degeneracy.  We suspect that rotationally-induced magnetic activity not only explains much of the behavior of the PSR B1957+20 system, but may also be important in understanding observations of two other eclipsing pulsars in short-period binaries, PSRs B1744$-$24A \\cite{lmd+90} and B1718$-$19 \\cite{lbhb93}. The companions of these pulsars are most likely low-mass main-sequence dwarfs, and in the case of PSR B1744$-$24A, the companion should nearly fill its Roche lobe. Both of these objects display evidence of excess material surrounding the entire binary, PSR B1744$-$24A through prolonged ``anomalous'' eclipses and pulse arrival delays \\cite{lmd+90,nttf90} and PSR B1718$-$19 through an inverted radio spectrum below 600\\,MHz. In each case, however, the energy density of the pulsar radiation impinging on the companion is far less than that to which the companion of PSR B1957+20 is exposed. (The observed spin-down rate of PSR B1744$-$24 is certainly contaminated by the system's acceleration in the gravitational potential of its cluster, but the pulsar flux at the companion can be estimated by assuming an intrinsic period derivative similar to that of other millisecond pulsars, \\pcite{nt92}.) While pulsar irradiation would seem incapable of expelling the observed material from the companion surfaces, a rotationally powered wind, such as those found in RS~CVn systems, could be sufficiently strong to produce the eclipses (a point that has been made independently by \\pcite{wp93} for PSR B1718$-$19) and could explain the seemingly ``episodic'' nature of the anomalous eclipses in PSR B1744$-$24A \\cite{lmd+90,nt92}. One might expect to see orbital period variations in these other two eclipsing systems, but the low flux densities and long spin periods of these pulsars may make the required timing accuracy difficult to obtain.  \\medskip M. F. Ryba and D. R. Stinebring built observing hardware and obtained some of the data that made this project possible. We are in their debt.  We are also grateful to F. Camilo and A.  V\\'{a}zquez for observing assistance, and to D. J. Nice, B.  Paczy\\'{n}ski, and C. Thompson for helpful discussions.  The Arecibo Observatory is part of the National Astronomy and Ionosphere Center, operated by Cornell University under cooperative agreement with the National Science Foundation. ASF was supported by a Hubble Fellowship awarded by NASA through the Space Telescope Science Institute.  \\newpage \\begin{table} \\begin{center} \\caption{Astrometric, Spin, and Orbital Parameters of PSR~B1957+20.} \\begin{tabular}{ll} \\hline \\hline Right ascension, $\\alpha$ (J2000)$^a$ \\dotfill & $19^{\\rm h}\\,59^{\\rm m}\\, 36\\fs76988(5)$ \\\\ Declination, $\\delta$ (J2000) \\dotfill & $20^\\circ\\,48'\\,15\\farcs1222(6)$ \\\\ $\\mu_{\\alpha}\\,({\\rm mas}\\;{\\rm yr}^{-1})$ \\dotfill & $-16.0\\pm0.5$ \\\\ $\\mu_{\\delta}\\,({\\rm mas}\\;{\\rm yr}^{-1})$ \\dotfill & $-25.8\\pm0.6$ \\\\ Period, $P$ (ms) \\dotfill & 1.60740168480632(3) \\\\ Period derivative, $\\dot P$ ($10^{-20}$) \\dotfill & 1.68515(9) \\\\ $\\ddot P$ ($10^{-31}\\,{\\rm s}^{-1}$) \\dotfill & $1.4\\pm0.4$ \\\\ Epoch (MJD) \\dotfill & 48196.0 \\\\ Dispersion measure, DM (cm$^{-3}\\;$pc) \\dots & 29.1168(7) \\\\ Projected semi-major axis, $x$ (lt-s) \\dotfill & 0.0892253(6) \\\\ Eccentricity, $e$ \\dotfill & $< 4 \\times 10^{-5}$ \\\\ Epoch of ascending node, $T_0$ (MJD) \\dotfill & 48196.0635242(6) \\\\ Orbital period, $P_b$ (s) \\dotfill & 33001.91484(8) \\\\ $\\dot P_b$ (10$^{-11}$) \\dotfill & 1.47$\\pm$0.08 \\\\ $\\ddot P_b$ (10$^{-18}\\,{\\rm s}^{-1}$) \\dotfill & 1.43$\\pm$0.08 \\\\ $|\\tdot P_b|$ (10$^{-26}\\,{\\rm s}^{-2})$ \\dotfill & $< 3$ \\\\ $|\\dot x|$ (10$^{-14}$) \\dotfill & $< 3$ \\\\ \\hline \\hline \\end{tabular} \\end{center} \\noindent $^a$Coordinates are given in the J2000 reference frame of the DE200 solar system ephemeris. Figures in parentheses are uncertainties in the last digits quoted. \\end{table}  \\newpage"
+    },
+    "9312/hep-ph9312293_arXiv.txt": {
+        "abstract": "{\\if@twocolumn ",
+        "introduction": "\\label{1}   Cosmological phase transitions offer a rich variety of physical phenomena for investigation, and some of their effects may be observable in the present Universe. In this Thesis the mechanisms of cosmological phase transitions are studied, concentrating on transitions which are related to strong and electroweak interactions.  All the phase transitions to be discussed are---or are assumed to be---first order. In the first-order transitions a metastable phase may exist alongside a stable one for some temperature range. In the thermodynamical limit, {\\em i.e.}, in an infinitely large system in which the temperature is changed with an infinitely slow rate, the phase transition takes place at a certain critical temperature~$T_c$.  If the rate of the temperature decrease is finite, as is the case in the expanding Universe, the phase transition temperature differs from the equilibrium value~$T_c$. At the critical temperature of a phase transition nothing happens, the high-temperature phase just moves into a supercooled state. At a somewhat lower temperature bubbles of the new phase begin to nucleate. The bubbles grow and convert the space to the new phase. The new phase has a lower energy density than the old phase. This means that in the phase transition the Universe is heated up to a certain temperature not higher than~$T_c$. After the transition is completed, the Universe starts to cool again in the usual way.  The supercooling is crucial for the scenarios in which the baryon asymmetry of the Universe is generated at the electroweak scale. There is more matter than antimatter in the Universe, and more than a billion photons for every baryon. This fundamental cosmological fact, crucial for us human beings, should be explained in a satisfactory way.  A few years ago it was realized that at temperatures above the critical temperature of the electroweak theory, certain electroweak processes mediated by the so-called sphalerons destroy any pre-existing baryon plus lepton number asymmetry [\\cite{KuzminRubakovShaposhnikov85}]. It became thus necessary to understand how the baryon asymmetry of the Universe could have been created at the electroweak phase transition. In principle, this is possible since all the three necessary conditions for generation of baryon asymmetry [\\cite{Sakharov67}] could have been satisfied during the transition. Firstly, due to the anomaly in the electroweak theory [\\cite{tHooft76a}, 1976b], baryon-number violating reactions were taking place. Secondly, CP--symmetry was violated because of fundamental gauge and Higgs interactions of quarks. The third condition, a departure from thermal equilibrium, was well satisfied because of the supercooling, provided the phase transition is first order.  In order to obtain any quantitative estimates for the amount of baryon asymmetry created, one must have a detailed understanding of how the electroweak phase transition proceeded. Motivated by this, we have investigated in this Thesis mechanisms of the electroweak phase transition.  The other phase transitions considered in this work are related to quantum chromodynamics. The possible observable consequences of the cosmological quark--hadron phase transition are due to the density inhomogeneities produced during the transition. If the length scale of these inhomogeneities had been large enough, they could have later affected the nucleosynthesis. This effect could be observed in the abundance of light elements in the present-day Universe. However, it seems probable that the length scale was too small for that, as will be discussed later on. In the case of the Z(3) phase transition suggested in this Thesis, it might in principle be that the density inhomogeneities generated could have affected later processes like the electroweak phase transition.  In addition to those questions considered in this work there are several other interesting topics related to cosmological phase transitions. For example, we have not studied the possible phase transition of a grand unified theory, which may have been cosmologically important as a driving source of inflation. Likewise, the topological defects, like monopoles or cosmic strings, which could have been created in cosmological first-order phase transitions are not discussed.  This Thesis is organized as follows. We first give a brief summary of the contents of the original research papers, which are appended. In Section~\\ref{2} the main events in the evolution of the Universe are described. In Section~\\ref{3} cosmological first-order phase transitions are discussed on a general level, without specifying the physical model. In Section~\\ref{4} the general methods presented in the previous Section are applied to two physical cases, to the electroweak and the quark--hadron phase transition. Finally, in Section~\\ref{5} we present conclusions and point out directions for the future work.        \\bigskip   \\vsass \\subsection*{Summary of the Original Papers}   \\label{1.1} \\addcontentsline{toc}{subsection}{Summary of the Original Papers} \\addtocontents{toc}{\\protect\\addvspace{3mm}}  \\medskip  \\paragraph{Paper~I: Nucleation and Bubble Growth in a First-Order Cosmological Electroweak Phase Transition.} In this paper the thermodynamical properties of electroweak matter near the critical temperature are systematically investigated for the first time. Assuming a quartic form for the Higgs potential (to be discussed in Subsection~\\ref{4.1} of this introductory review part), we derive an equation of state that describes the electroweak phase transition, and compare the electroweak transition with the quark--hadron transition. The nucleation rate of bubbles of the broken-symmetry phase is computed by solving numerically the field equation. We present a useful expression for the volume fraction not touched by the bubbles, slightly different from those given previously by other authors. We perform numerical simulations of bubble nucleation and growth which confirm our analytical calculations. Finally, we also study what velocities of the phase front are allowed assuming only that the general conditions of energy-momentum conservation and entropy increase are valid. Based on these considerations, we claim that in the cosmological electroweak phase transition the bubbles most likely grew as weak deflagrations. \\medskip   \\paragraph{Paper~II: Cosmological QCD Z(3) Phase Transition in the 10 TeV Temperature Range?} Using as a starting point the earlier observation that in the QCD there are metastable vacua at high temperatures, we develop a cosmological scenario which leads to a phase transition, not known before, at a temperature two orders of magnitude above the electroweak scale. Qualitatively, this phase transition differs from the usual ones in that the pressure difference between the stable and metastable vacua is huge, and in that there were only relatively few bubbles nucleated inside the horizon. Our scenario is based on the hypothesis that at very early times domains of metastable vacua were created and underwent an inflationary expansion due to some processes which could be related for instance to the breaking of the grand unified symmetry. This hypothesis is the main uncertainty in our scenario. Later on it has been also claimed that the metastable vacua should only be interpreted as field configurations that contribute to the Euclidean path integral, not as physically accessible states [\\cite{Belyaevetal92}; \\cite{ChenDobroliubovSemenoff92}]. In a more recent investigation it has been, however, argued that the metastable vacua do represent physically realizable systems [\\cite{GockschPisarski93}]. \\medskip   \\paragraph{Paper~III: Bubble Free Energy in Cosmological Phase Transitions.} In this paper the free energy of spherical bubbles is studied in order parameter or Higgs field models having the same quartic potential as used in Paper~I\\@. A numerical function with a good accuracy is given for the nucleation action. Using this nucleation free energy of critical bubbles as an input, the general free energy is solved as a function of the bubble radius and the temperature. The calculation is based on the approximation that all the temperature dependence in the free energy comes from the volume term. This approximation should be valid if one is not too far from the limit of small relative supercooling. The bubble radius and curvature-dependent interface tension are discussed in detail. The results of this study are applicable for the case of the electroweak phase transition, and probably for the quark--hadron transition as well.                \\newpage    \\vsas ",
+        "conclusions": "\\label{5}    The goal of this Thesis has been to achieve an insight to the physical processes that occurred in the Universe during different first-order phase transitions.  We have pointed out that especially the onset of a cosmological phase transition shows a universal behavior allowing for a general approach. We have presented in this work some general methods which can be applied to an analysis of the sequence of events taking place in cosmological first-order phase transitions.  In the case of the cosmological electroweak or quark--hadron phase transition, the quantitative description has not yet reached a fully satisfactory level. The reason for this is the lacking knowledge of the correct input values of the physical parameters. The case with the phase transition suggested in Paper~II is different in the sense that there the main uncertainty comes from the basic assumptions of the scenario itself.  In the future one will hopefully learn the correct values of the physical quantities related to the electroweak and quark--hadron phase transitions. With their improving accuracy lattice simulations should provide this information for QCD with physical quark masses, as well as for the electroweak theory.  Combining lattice simulations with analytical calculations in effective three-dimensional theories, it seems to be possible to derive for the electroweak theory a potential incorporating even non-perturbative effects [\\cite{Shaposhnikov93}; \\cite{Farakosetal93}]. Such a potential could then be employed for studying the electroweak phase transition.  In order to understand in detail the dynamics of cosmological phase transitions one must have a good knowledge of the bubble growth at microscopic level. At present we are investigating the growth of bubbles using a model in which there is a friction-like coupling between the order parameter  field and a cosmic fluid field.  By employing this model one is able to numerically simulate for instance  the collisions between bubbles. Moreover, the velocity of a deflagration wall can be determined exactly as a function of the friction coefficient. So far, we have applied the model in 1+1 dimensions [Ignatius, Kajantie, Kurki-Suonio and Laine 1993]. In the future, the computations should be extended  to include spherically symmetric three-dimensional bubbles. Furthermore, one could try to obtain a good estimate for the value of  the friction coupling that determines the velocity of the bubble wall.  By combining all these developments, one is led to the conclusion that it is possible to achieve an accurate quantitative description of different cosmological phase transitions in the not too distant future. It would then also be possible to calculate the value of the baryon asymmetry of the Universe from the first principles.                 \\clearpage     \\setlength{\\baselineskip}{.6cm}"
+    },
+    "9312/astro-ph9312037_arXiv.txt": {
+        "abstract": " ",
+        "introduction": "\\setcounter{equation}{0}     The origin and evolution of large scale structure is one of the most important problems in cosmology today. It is widely accepted that the growth of small fluctuations by gravitational instability leads to structure formation. The inflationary paradigm, whilst providing possible solutions to a number of other problems associated with the hot big bang model, also produces a Gaussian, adiabatic fluctuation spectrum which is nearly, though not exactly, scale-invariant (Guth 1981; Albrecht \\& Steinhardt 1982; Linde 1982; Olive 1990; Liddle \\& Lyth 1993).  Based on this prediction, the standard Cold Dark Matter (CDM) model of galaxy formation employs the flat, Harrison-Zel'dovich spectrum as an input parameter (Efstathiou 1990). The CDM model successfully accounts for small ($\\le 10h^{-1}$ Mpc) and intermediate ($10h^{-1}$ Mpc - $100h^{-1}$ Mpc) scale observations, if one introduces a bias in the distribution of luminous to dark matter (Davies et al. 1985).{\\footnote{The current value of the expansion rate is $H_0 = 100h$ km ${\\rm s}^{-1}$ ${\\rm Mpc}^{-1}$, where $0.4\\le h \\le 1$.}}  However, standard CDM has come under severe pressure from a number of recent observations (for a detailed review see Liddle \\& Lyth 1993). In particular, the APM angular galaxy-galaxy correlation function (Maddox et al. 1991) and the {\\em IRAS} QDOT redshift survey (Efstathiou et al. 1991) indicate that there exists more large scale structure than that predicted by standard CDM. One possible resolution to this problem is to consider {\\em tilted} CDM models. Here the primordial power spectrum is assumed to be of the form $P(k) \\propto A_S^2(k)k \\propto k^n$, where $k$ is the comoving wavenumber of the Fourier expansion of the perturbation, $A_S$ is the amplitude of the quantum fluctuation when it crosses the Hubble radius during the matter- or radiation-dominated eras and $n$ is the power spectrum. Other possibilities involve the addition of a cosmological constant or a hot dark matter component (Liddle \\& Lyth 1993).  Inflation also produces a spectrum of gravitational wave (tensor) perturbations, whose amplitude may or may not be comparable to that of the scalar fluctuations.  In this paper we shall concentrate on models which lead to tilted power spectra with a negligible gravitational wave component.  There exists a wide range of observational constraints on the tilt arising from large angle ($\\theta \\ge 3^o$) microwave background anisotropies (Smoot et al. 1992), galaxy clustering (Maddox et al. 1990; Efstathiou et al. 1990), peculiar velocity flows (Bertschinger \\& Dekel 1989; Dekel, Bertschinger \\& Faber 1990; Bertschinger et al. 1990), high redshift quasars (Efstathiou \\& Rees 1988) and the red shift of structure formation (Adams et al. 1993). When combined together these observations strongly limit the allowed value of $n$. It has been shown that tilted CDM can not fit all of the current data simultaneously (Adams et al. 1993; Liddle \\& Lyth 1993). For inflationary models in which gravitational wave production is negligible, a lower limit of $n>0.7$ is partially consistent with the COBE 2-sigma upper limit and the bulk flow data, if the clustering and pairwise velocity data are ignored. In models where the gravitational wave contribution to the microwave background anisotropy is important, however, this limit is strengthened to $n>0.8 4$. This is clearly inconsistent with the APM galaxy correlation function, which indicates that $0.3<n<0.7$ provides a good fit to the excess clustering data.  On the other hand, there is growing observational evidence for a departure from a pure power law at a scale $\\lambda \\approx 150 \\pm 50 h^{-1}$ Mpc (Einasto et al. 1993). The power spectrum of clusters of galaxies has spectral index $-2 \\le n \\le -1$ on intermediate scales, whilst it is consistent with $n=1$ on large scales (Peacock 1991).   In short, the current status of the observations is far from conclusive and it is therefore important to consider all the theoretical options available. In this paper we investigate the general circumstances in which a tilted power law scalar spectrum and a negligible gravitational wave amplitude arise in inflationary models. In Section 2, we summarize the details of a powerful framework which allows the general form of the inflaton potential to be derived in a straightforward manner. The form of such a potential is shown to be a hyperbolic secant function in Section 3. In Section 4, it is further shown that such a potential arises when a bulk viscous stress is added to the energy-momentum tensor of a perfect baryotropic fluid. It is illustrated how a number of plausible particle physics models, such as the quantum creation of fundamental strings (Turok 1988) and $N=2$ supergravity (Salam \\& Sezgin 1984), lead to a potential of this form.   \\vspace{.7cm} ",
+        "conclusions": ""
+    },
+    "9312/astro-ph9312002_arXiv.txt": {
+        "abstract": " ",
+        "introduction": "\\label{sec-intro}  \\noindent I will review the present status of solar neutrino astronomy and solar neutrino physics, with special emphasis on the discrepancy between the predicted and the observed counting rates in the experiments designed to detect solar neutrinos.  Since this symposium is partially a historical retrospective, it is interesting to begin with an ironic aspect of the proposal in 1964~\\cite{Bahcall64,Davis64} that a practical solar neutrino experiment could be carried out using a chlorine detector.  If you look back at those two papers, you will see that the only motivation presented for doing the experiment was to use neutrinos ``...to see into the interior of a star and thus directly verify the hypothesis of nuclear energy generation in stars.'' The energy-generating process being tested is   \\begin{equation} 4 p \\longrightarrow ^4He ~+~ 2e^+  ~+~ 2\\nu_e ~+~ 25~MeV, \\label{eq:Heburning} \\end{equation} by which four protons are burned to form an alpha particle, two positrons, two neutrinos, and thermal energy.  The goal of demonstrating that Eq.~(\\ref{eq:Heburning}) is the origin of sunshine has been achieved.  Solar neutrinos have been observed in four experiments with, to usual astronomical accuracy (a factor of two or three), about the right numbers and about the right energies. Moreover, the fact that the neutrinos come from the sun was established directly by the Kamiokande~II experiment which showed that electrons scattered by neutrinos recoil in the forward direction from the sun. These experimental results represent, in my view, a great triumph for the physics, chemistry,  and astronomy communities since they bring to a successful conclusion the development (which spanned much of the 20th century) of a theory of how main sequence stars shine.  However, most of the current interest in solar neutrinos is focused on an application of solar neutrino research that was not discussed or even considered at the time of the original experimental and theoretical proposals. It has subsequently been realized that one can use solar neutrinos for studying experimentally aspects of the weak interactions that are not currently accessible in laboratory experiments. These studies of new physics are based upon the quantitative discrepancy between the predictions and the observations for solar neutrinos.  To evaluate the significance of these discrepancies, one must carry out more precise calculations and pay closer attention to the theoretical uncertainties than is conventional in most stellar interior studies.  I will therefore discuss at some length the uncertainties in the theoretical calculations.  Nearly everyone in this room is an astronomer. Therefore, you will immediately recognize how the possible discovery of new physics with solar neutrinos differs from the astronomical discoveries with which you are familiar.  Astronomical discoveries, like the finding of quasars, of pulsars, of x-ray binaries with neutron stars or black holes, of strong infrared sources, of x-ray bursters and $\\gamma-$ ray bursters, of very young stars and very old galaxies, all resulted from pointing telescopes with exceptional equipment and finding something unpredicted but recognizable by qualitative features. Unfortunately, discoveries made using solar neutrinos are different. No one has an intuitive feel for how many solar neutrino events ought (or ought not) to be seen per year in a large detector.  Precise quantitative predictions must be made in order to determine if we have learned something new. The estimated uncertainties in those predictions are crucial for deciding on whether discoveries have been made.  When we compare solar neutrino calculations with solar neutrino observations, we begin with a combined standard model, the standard model of electroweak theory plus the standard solar model. We need the standard solar model to tell us how many neutrinos of what energies are produced in the solar interior.  And, we need the standard electroweak model--or some modification of the standard electroweak model--to tell us what happens to the neutrinos after they are created. We need to know how neutrinos are affected when they pass through the enormous amount of matter in the sun and travel the great distance from the solar interior to detectors on earth.  Do neutrinos change their flavor from electron-type to some other type during their journey from the sun to the earth?  The simplest version of the standard electroweak model says: ''No.''  Neutrinos have zero masses in this model and lepton flavor is conserved.  Nothing happens to the neutrinos after they are created.  It turns out that one can learn an enormous amount about neutrinos by observing experimentally what happens to solar neutrinos after they are created.  This fact is largely responsible for the great current interest in solar neutrinos.  There are four operating solar neutrino experiments, three of which use radiochemical detection (one chlorine and two gallium detectors) and one detector which is electronic (the Kamiokande pure water detector).  The first, and for two decades the only, solar neutrino experiment uses a radiochemical chlorine detector to observe electron-type neutrinos via the reaction~\\cite{Davis64}:   \\begin{equation} \\nu_{\\rm e} + {\\rm~^{37}Cl} \\to {\\rm e^-} + {\\rm~^{37}Ar} . \\label{eq:Clreaction} \\end{equation} The $^{37}$Ar atoms produced by neutrino capture are extracted chemically from the 0.6 kilotons of fluid, $C_2Cl_4$, in which they are created and are then counted using their characteristic radioactivity in small, gaseous proportional counters. The threshold energy is 0.8 MeV. The chlorine solar neutrino experiment is described by Davis~\\cite{Davis93} and references quoted therein.  The second solar neutrino experiment to have been performed, Kamiokande II~\\cite{Hirata89,Hirata91,Suzuki93} is based upon the neutrino-electron scattering reaction,   \\begin{equation} \\nu + {\\rm e} \\to \\nu^\\prime + {\\rm e}^\\prime, \\label{eq:NuScattering} \\end{equation} which occurs inside the fiducial mass of 0.68 kilo-tons of ultra pure water. Only \\b8 solar neutrinos are detectable in the Kamiokande~II experiment, for which the lowest published value for the detection threshold is 7.5 MeV. In the Kamiokande~II experiment, the electrons are detected by the Cerenkov light that they produce while moving through the water. Neutrino scattering experiments provide information that is not available from radiochemical detectors, including the direction from which the neutrinos come, the precise arrival times for individual events, information about the energy spectrum of the neutrinos, and some sensitivity to muon and tau neutrinos.  The fact that the neutrinos are coming from the sun is established by the Kamiokande~II experiment since the electrons are scattered in the forward direction in reaction Eq.~(\\ref{eq:NuScattering}).  The observed directions of the scattered electrons trace out the position of the sun in the sky.  There are two gallium experiments in progress, GALLEX~\\cite{Anselmann92,Anselmann93} and SAGE\\ \\cite{Abazov91a,Abazov91b,Bowles93}, that provide the first observational information about the low energy neutrinos from the basic proton-proton reaction. The GALLEX and SAGE experiments make use of neutrino absorption by gallium,  \\begin{equation} \\nu_{\\rm e} + {\\rm~^{71}Ga} \\to {\\rm e^-} + {\\rm~^{71}Ge} , \\label{eq:Gareaction} \\end{equation} which has a threshold of only 0.23 MeV for the detection of electron-type neutrinos. This low threshold makes possible the detection of the low energy neutrinos from the proton-proton (or $pp$) reaction; the $pp$ reaction initiates the nuclear fusion chain in the sun by producing neutrinos with a maximum energy of only 0.42 MeV. Both the GALLEX and the SAGE experiments use radiochemical procedures to extract and count a small number of atoms from a large detector, similar to what is done in the chlorine experiment.  Figure~1 shows a comparison between the predictions of the standard model~\\cite{Bahcall92} and the four operating solar neutrino experiments~\\cite{Davis93,Hirata89,Hirata91,Suzuki93,Anselmann92,Anselmann93,Abazov91a,Abazov91b,Bowles93} .  The unit used for the three radiochemical experiments is a $SNU ~=~ 10^{-36}$ events per target atom per second. The result for the Kamiokande water experiment is expressed, following the experimentalists, in terms of a ratio to the predicted event rate. The errors shown are, in all cases, effective $1\\sigma$ uncertainties, where I have combined quadratically the quoted statistical and systematic errors. I will use throughout this review the standard solar model results of Bahcall and Pinsonneault~\\cite{Bahcall92} since this is the only standard solar model published so far to take account of helium diffusion.  However, accurate solar models without helium diffusion have been published by many other authors and are in good agreement with the Bahcall-Pinsonneault solar model without helium diffusion.  All four of the solar neutrino experiments yield values less than the predicted value for that detector and outside the combined errors.  I shall present later in this talk a detailed comparison between the the theoretical predictions and the measured rates.  However, one fact is apparent already from Figure~1.  The discrepancy between theory and observation is about a factor of 3.5 for the chlorine experiment, whereas the discrepancy is only a factor of 2.0 for the Kamiokande experiment. These two experiments are primarily sensitive to the same neutrino source, the rare, high-energy  \\b8 solar neutrinos (maximum neutrino energy of 15 MeV).  Thus the disagreement between theory and experiment seems to depend upon the threshold for neutrino detection, being larger for chlorine (0.8 MeV threshold) than for the Kamiokande (water) experiment (7.5 MeV threshold).  This may be the most significant fact about the solar neutrino problem. ",
+        "conclusions": "\\label{sec-conclusions}  \\noindent The field of solar neutrino research is flourishing.  The four operating experiments have confirmed that the sun shines via nuclear fusion reactions that produce MeV neutrinos (see Eq.~(\\ref{eq:Heburning}) ). There are differences between the predictions and the observations (see Figure~1), but these differences are within the usual range of astronomical uncertainties (generally a factor of two or three).  The agreement between theory and observation is, from the astronomical point of view, remarkably good because the calculated neutrino fluxes depend sensitively upon the interior conditions.  Nevertheless, all four experiments disagree with the corresponding theoretical predictions based upon the simplest version of the standard electroweak theory.  These disagreements are larger than the estimated uncertainties.  The luminosity boundary condition and the helioseismological measurements are especially important in guaranteeing the robustness of the theoretical predictions (see discussion in \\ref{sec-Comparison}).  Monte Carlo experiments that make use of 1000 implementations of the standard solar model indicate that the chlorine and the Kamiokande~II (water-Cerenkov) experiments cannot be reconciled without an energy-dependent change in the \\b8 solar neutrino spectrum relative to the laboratory spectrum (see Figure~2-Figure~4).  New physics is required to explain an energy-dependent change in the shape of the neutrino spectrum. The gallium experiments, GALLEX and SAGE, strengthen the conclusion that new physics is required.  New experiments, SNO, Superkamiokande, and ICARUS, will test the conclusion that new physics is required independent of uncertainties due to solar models.  These experiments can determine the shape of the \\b8 solar neutrino energy spectrum and whether or not electron-flavor neutrinos have oscillated into some other flavor neutrinos."
+    },
+    "9312/astro-ph9312047_arXiv.txt": {
+        "abstract": " ",
+        "introduction": "The recent detection by the EROS \\cite{eros} and MACHO \\cite{macho} collaborations of microlensing events in the Large Magellanic Cloud (LMC) seems to support the hypothesis that at least part of the dark matter in our galaxy is baryonic, appearing in the form of massive astrophysical objects. Indirect evidence for the presence of galactic dark matter existed from several observations like measurements of the rotation curves of spiral galaxies, including our own, or velocity dispersions measured in elliptical galaxies.  At present, all dynamical observations in our galaxy are well fitted by models with at least three galactic components. These are: {\\it (i)} the (relatively thin and flat) {\\it disk}, with a surface mass density decreasing exponentially with $r$, the distance from the galactic centre, {\\it (ii)} the (approximately spherical) {\\it halo}, with density asymptotically falling as $r^{-2}$, which gives the main contribution to the total mass of the Galaxy and ensures the flatness of the rotation curve at large distances, and {\\it (iii)} the (approximately spherical) {\\it spheroid}, which contributes sizeably to the central part of the galaxy but has a faster radial decrease than the halo. In some models, additional components are also introduced.  The total mass in spheroid stars with mass $m$ larger than the minimum mass for hydrogen burning was estimated, on the basis of star counts at high galactic latitudes and of high velocity stars by Bahcall, Schmidt and Soneira \\cite{bss}, to be $M_S(m>0.085M_\\odot ) =0.9-3.2 \\times 10^9 M_\\odot$. On the other hand, the galactic models based on dynamical measurements and on 2.2~$\\mu$m infrared (IR) surveys of the galactic centre predict a much larger total mass for the spheroid, $M_S =5$--$7\\times 10^{10}M_\\odot$, which is comparable to the mass of the disk \\cite{co,oc,rk}. As recognized by Caldwell and Ostriker \\cite{co} and by Bahcall, Schmidt and Soneira \\cite{bss}, these two results can be made compatible by assuming that most of the mass of the spheroid is non-luminous, in the form of faint low-mass stars, neutron stars, brown dwarfs or Jupiters. An alternative solution \\cite{bss} to this apparent discrepancy is to consider a light spheroid, as determined by star counts and high velocity stars, together with a new galactic component, a central {\\it core} with large mass density and a sharp cut-off at about 1 kpc, which accounts for the innermost galactic observations. One should note however that there is no reason for the stellar mass function to become negligible just below the hydrogen burning limit. In fact, recent measurements of spheroid field stars \\cite{fahlman} indicate a steeply increasing mass function towards low masses, with no indications of flattening or of a cutoff near 0.1 $M_\\odot$, and this provides support for the heavy spheroid models constituted mainly by brown dwarfs.  We consider here the implications of the scenario with a heavy, mostly dark, spheroid for the ongoing microlensing searches, showing that it can give rise to a significant rate of events both for stars in the LMC and in the galactic bulge. The paper is organized as follows. In Sec. 2 we compare different galactic models and give the corresponding density profiles for the spheroid and the halo which will be used in our study. In Sec. 3 we discuss the prediction for the microlensing event rate at the LMC and compare the results with the EROS/MACHO data. Sections 4 and 5 are devoted to microlensing in the galactic bulge and in M31, where further signatures for spheroid dark objects can be found. Our conclusions are drawn in Sec. 6. ",
+        "conclusions": "Galactic models obtained by fitting dynamical observations predict a spheroid component considerably heavier than is accounted for by estimates of the brighter visible stars, suggesting that a ``missing mass\" problem exists in the spheroid. If such a spheroid dark matter really exists, it will certainly be baryonic. In this paper we have assumed, following Caldwell and Ostriker, that the spheroid population consists mainly of low-mass faint stars or dark objects and we have computed the rate for microlensing events for stars in the LMC. This rate is lower than the corresponding one for microlensing events coming from a galactic halo of dark objects, but it is still significant for observations of EROS/MACHO. We also note that, if the LMC has a heavy spheroid component, this could give an additional considerable contribution to the total rate of events, since the line-of-sight can pass very close to the LMC galactic centre. The example of M31, presented in Sec. 5, is illustrative of such an effect. Unfortunately, poor knowledge of the properties of the LMC does not allow us a reliable estimate.  It is very interesting that the rates for spheroid and halo microlensing vary considerably depending on the source. Searches towards the galactic centre seem particularly promising for distinguishing between them, since the rate for spheroid microlensing is larger than for halo microlensing and has a characteristic dependence on the galactic longitude. The much more challenging search in M31 can also provide important information, since the rate for spheroid microlensing can be very large and can present a strong dependence on the impact parameter, if M31 has indeed a spheroid component similar to the one of the Milky Way, as suggested by observations.  Therefore microlensing searches can map the distributions of dark heavy objects contained in the different galactic components, especially if results from different sources are compared. Knowledge of the amount of dark matter in the spheroid is of great interest for understanding the structure of our galaxy and for building reliable galactic models. Finally, we want to mention that the dark spheroid contributions to the total mass of the Universe are not cosmologically very significant, since the mass of the spheroid is comparable to the mass of the galactic disk.  While Turner \\cite{tur} has suggested that the preliminary EROS/MACHO data already point towards some deficiency with respect to the halo expectation, EROS \\cite{eros} has claimed that their result is consistent with their expectation, and MACHO \\cite{macho} has made no statement about it. Only improved statistics and a complete study of the experimental efficiencies (which has not been presented by the EROS/MACHO groups in their papers describing the discovery events \\cite{eros,macho}) can resolve the question. However, if a deficiency is indeed found, this could be interpreted as microlensing entirely due to dark objects in a heavy spheroid rather than in the halo. In this scenario, therefore, the galactic halo can consist entirely of non-baryonic dark matter and the EROS/MACHO observations could be reconciled with the presently favoured model of structure formation in a critical Universe. This of course would also have important consequences for the currently running experiments searching for halo dark matter from nuclear recoil and from annihilation products. The different distributions of the two dark matter components, with the baryonic one more concentrated towards the galactic centre, could naturally be accounted for by the dissipative processes undergone by the baryons during the galaxy collapse. This is in contrast to the picture proposed by Turner and Gates \\cite{tur2}, in which the same galactic component, the halo, is formed by a mixture of baryonic and non-baryonic dark matter.  \\bigskip  Note added: After submitting this paper we received a preprint by Gould, Miralda-Escud\\'e and Bahcall \\cite{gmb} where they discuss the possibility that the microlensing events are caused by dark objects in a thick (or a thin) disk. \\bigskip  We are greatly indebted to Alvaro de R\\'ujula for discussions, criticism, and encouragement. We thank K. Griest and J. Rich for useful correspondence. One of us (G.F.G.) wishes to thank Giacomo G. for charming and edifying conversations. We dedicate this work to him and to Javier R.. The work of S.M. was supported by a grant of the European Communities (Human Capital and Mobility Programme). E.R. was partially supported by Worldlab."
+    },
+    "9312/hep-ph9312280_arXiv.txt": {
+        "abstract": "It is shown that in models including the standard electroweak theory and for some particular values of the underlying parameters, electric currents can be spontaneously generated in cosmic strings, without the need of any external field (e.g., electric or magnetic) as is required in most models. This mechanism is then shown to break spontaneously the Lorentz invariance along the initially Goto-Nambu string. The characteristic time needed for the current to build up is estimated and found to lowest order to depend only on the mass of the intermediate $W$ vector boson and the fine structure constant. ",
+        "introduction": "The electroweak theory~\\cite{gsw} is based on the spontaneous breaking of the $SU(2)_L\\times U(1)_Y$ symmetry by means of an $SU(2)$ doublet Higgs field $H$ down to the electromagnetic $U(1)$ symmetry. This means that the vacuum has the topology of the quotient group $SU(2)\\times U(1)/U(1)$, which is isomorphic to $SU(2)$, i.e., it has the topology of the 3--sphere and is therefore simply connected. As a result, topologically stable cosmic strings are not present in this model (and in fact, due to the experimental bound on the Higgs mass $M_H \\gtrsim 65$~GeV~\\cite{Zprime}, even string-like solutions in this model are dynamically unstable~\\cite{Zstring,gsw-vortex}). In order to investigate the structure of cosmic strings in a realistic model that would take the electroweak theory into account, it is thus necessary to modify this theory first. There are basically two different approaches that can be followed to extend this model. The first one consists in assuming the Higgs realisation of the symmetry breaking not to be fundamental, and to consider instead dynamical symmetry breaking such as in the chiral approach~\\cite{chiral} involving the $SU(2)_L\\times SU(2)_R$ symmetry.  This leads to the existence of semi-topological defects [because only one direction of $SU(2)_R$ is actually gauged], which may be shown~\\cite{Zchiral} to be dynamically stable and moreover superconducting. The second approach, the one we shall follow, is to regard the Higgs representation, and thus the Higgs field $H$ itself, as fundamental, and to extend the gauge group. It turns out that the most simple such extension one can think of, consisting in an extra $U(1)$, also generates topologically stable (and superconducting) cosmic strings~\\cite{low-mass}.  The string-forming model we shall now examine is the following (this section is essentially useful to fix the notation used throughout): initially, the symmetry $SU(2)_L\\times U(1)_Y\\times U(1)_F$ (with $F$ the extra hypercharge) is broken down to $SU(2)_L\\times U(1)_Y$ by means of a Higgs field $\\Phi$, and this is followed by the usual electroweak phase transition. The model is minimal in the sense that we assign a vanishing $F$ hypercharge for the $H$ field, and symmetrically assume $\\Phi$ to be an $SU(2)$ singlet. We shall altogether neglect the fermionic sector of the model, but it may be remarked that the hypercharge $F$, with the previous assignement made on the Higgs fields, coincides with $B-L$ (up to a normalisation factor absorbable in the fermionic fields) in this sector, and that even though $U(1)_F$ is broken, the baryonic and leptonic numbers $B$ and $L$ are conserved. Also the model will be anomaly-free provided one includes a right-handed neutrino.  We therefore start with the Lagrangian density (again, without the fermions) \\begin{equation} {\\cal L} = -{1\\over 4} \\vec F_{\\mu\\nu} \\cdot \\vec F^{\\mu\\nu} - {1\\over 4} G_{\\mu\\nu} G^{\\mu\\nu} - {1\\over 4} H_{\\mu\\nu} H^{\\mu\\nu} - (D_\\mu H)^\\dagger D^\\mu H - (D_\\mu \\Phi)^\\star D^\\mu \\Phi - V(H,\\Phi),\\label{lag} \\end{equation} where the (classical) potential between the Higgs fields is (we assume that both phase transitions are second order so we neglect the logarithmic corrections~\\cite{order,first} in this zero temperature effective theory, see, however, Ref.~\\cite{stand-first} on that point) \\begin{equation} V(H,\\Phi )= \\lambda _H (H^\\dagger H - {v^2_H \\over 2})^2 + \\lambda _\\phi (|\\Phi |^2 - {v^2_\\phi \\over 2})^2 + f (H^\\dagger H - {v^2_H \\over 2}) (|\\Phi |^2 - {v^2_\\phi \\over 2}),\\label{pot}\\end{equation} and we have set the covariant derivative \\begin{equation} D_\\mu \\equiv \\partial _\\mu - ig{\\vec T\\over 2} \\cdot \\vec A_\\mu - i g' {Y\\over 2} B_\\mu - i q {F\\over 2} C_\\mu ,\\end{equation} with $T^i$ the generators of $SU(2)_L$ in the representation of the particle upon which the derivative acts, $g$, $g'$ and $q$ the gauge coupling constants of $SU(2)_L$, $U(1)_Y$ and $U(1)_F$ respectively, and the kinetic terms of the gauge vectors are expressed through \\begin{equation} F^i_{\\mu\\nu} = \\partial_\\mu A^i_\\nu - \\partial_\\nu A^i_\\mu + g \\varepsilon^{ijk} A^j_\\mu A^k_\\nu,\\end{equation} \\begin{equation} G_{\\mu\\nu} = \\partial_\\mu B_\\nu - \\partial_\\nu B_\\mu \\ \\ \\ , \\ \\ \\ H_{\\mu\\nu} = \\partial_\\mu C_\\nu - \\partial_\\nu C_\\mu . \\end{equation} The Higgs doublet is understood as $H = (H^+,H^0)$, and its vacuum expectation value (VEV) is experimentally known to be $\\sqrt{\\langle |H|^2 \\rangle _0 } = v_H /\\sqrt{2}\\simeq174$~GeV.  We are now interested in a vortex solution of this model, of the kind proposed by Nielsen and Olesen~\\cite{NO}, for the $\\Phi$ field. Since we are concerned by classical solutions, it is necessary that we fix the gauges. For the string-forming fields, there is a particularly convenient gauge choice: if the vortex solution is taken to be aligned along the $z$ axis (which is always possible since the curvature effects can be locally neglected), we can choose a cylindrical coordinate system, and in this system, the phase of the $\\Phi$ field is identified with the angular coordinate $\\theta$. The Nielsen--Olesen vortex solution then takes the simple form \\begin{equation} \\Phi = \\varphi (r) \\exp{i n \\theta} ,\\label{no} \\end{equation} with $n$ the winding number~\\cite{kibble,order,vil-rep}.  Let us now turn to the electroweak fields. Because of the disjoint structure of the initial invariance, we have not lost any freedom in going to the vortex gauge. We can thus choose the most convenient gauge with regard to the subsequent interpretation, namely the unitary gauge, in which only the neutral component of $H$ is considered: $H = [0, h(r)/\\sqrt{2}]$. Before going any further in the resolution of the Euler--Lagrange equations for this system, we wish to examine in more details what occurs in the strings core.  The string solution is defined as the set of points in space where $\\Phi =0$. Moreover, the vacuum (or the false vacuum in the case of the strings core) should represent a minimum of the potential~(\\ref{pot}). Varying this potential for $h$ and $\\varphi$, we see that the extremization yields two differents possibilities, namely, far from the strings core, i.e., in the usual vacuum, \\begin{equation} h=v_h \\ \\ \\hbox{and} \\ \\ \\varphi = v_\\phi /\\sqrt{2},\\label{reg-vac}\\end{equation} whereas in the strings core with $\\varphi =0$, then $h$ should satisfy (not taking the kinetic terms into account for the moment) \\begin{equation} h^2 = v_H^2 + f{v_\\phi ^2\\over \\lambda _H},\\label{S-vac}\\end{equation} from which we can conclude that two cases may occur in principle. The first case, already studied elsewhere~\\cite{low-mass}, is for $f>f_{crit}$, with \\begin{equation} f_{crit} = -\\lambda _H \\left( {v_H \\over v_\\phi }\\right)^2 ,\\label{f:crit}\\end{equation}  \\noindent which corresponds to a shift in the $SU(2)$ doublet Higgs VEV at $r=0$. The second case, to which we now turn definitely, is for $f\\leq f_{crit}$. If the underlying parameters are such that this inequality is satisfied, then there is no real solution to Eq.~(\\ref{S-vac}). Thus, one finds that the real minimum of the potential is now at $h=0$ as long as $\\varphi \\leq \\varphi _{min}$, where $\\varphi ^2 _{min} = v^2 _\\phi /2 - \\lambda _H v^2_H /|f|$ [given by inserting a nonzero value for $\\sigma$ into Eq.~(\\ref{S-vac}) and solving for $h=0$].  Fig.~1 illustrates the internal string structure which is obtained when the kinetic terms are included. This figure represents a solution of the field equations derived from the Lagrangian~(\\ref{lag}) under the gauge assumptions and with the vortex solution~(\\ref{no}), with zero vector fields $A_{i\\mu}$ and $B_\\mu$.This solution was obtained by means of a successive over relaxation method~\\cite{adler}, and the distances are in units of the inverse $\\Phi$ mass $(\\lambda _\\phi v_\\phi )^{-1}$. More details concerning the numerical procedure itself and the stability of the solution can be found in Ref.~\\cite{low-mass}, but here, and in particular in the next section, we shall be mainly interested in what occurs close to the strings core, namely the symmetry restoration. For the time being, let us just remark that since the Higgs field $h$ is real, there is no associated current with it, so the fact that it be trapped in the string, its VEV varying from $r=0$ to $r\\to\\infty$, merely changes the actual value of the string's energy per unit length, but otherwise does not break the Lorentz boost invariance along the string. Therefore, setting the stress-energy tensor in the form \\begin{equation} T^{\\mu\\nu} = U u^\\mu u^\\nu - T v^\\mu v^\\nu ,\\label{Tmn}\\end{equation}  \\noindent with $u$ and $v$ two unit timelike and spacelike vector respectively, tangent to the strings worldsheet, $U$ being the energy per unit length and $T$ the tension, the Lorentz invariance requires, whether there is a Higgs condensate or not, that the equation of state be that of Goto--Nambu, i.e., $U=T=$Cte~\\cite{vil-rep,eos}. This is important because once the current-generation mechanism which we will investigate in the next section has been at work, this degeneracy in the stress-energy tensor eigenvalues is spontaneously raised, so the Lorentz invariance is spoiled. ",
+        "conclusions": ""
+    }
+}