Showing papers in "Physical Review D in 1985"

Detectability of certain dark-matter candidates.

Abstract: We consider the possibility that the neutral-current neutrino detector recently proposed by Drukier and Stodolsky could be used to detect some possible candidates for the dark matter in galactic halos. This may be feasible if the galactic halos are made of particles with coherent weak interactions and masses 1--${10}^{6}$ GeV; particles with spin-dependent interactions of typical weak strength and masses 1--${10}^{2}$ GeV; or strongly interacting particles of masses 1--${10}^{13}$ GeV.

Power-law inflation

Abstract: The outstanding cosmological problems (horizon, flatness, . . .) which may be solved by the usual inflationary models may also find a solution in the frame of a ``generalized'' inflationary cosmology which is characterized by a suitable phase of accelerated expansion. The usual exponential growth of the scale factor S is just a particular case of such a general idea. Following this line of thought, we study in some detail a simple inflationary model characterized by a scale factor which grows like S\ensuremath{\sim}${t}^{p}$, with p a constant greater than one, which we call power-law inflation (PLI). Some properties of PLI have been analyzed, in different contexts, also by other authors. We consider the constraints on this model coming from the requirement of solving the horizon, flatness, ``good'' reheating, and ``convenient'' perturbation-spectrum problems. In order to obtain the perturbation spectrum when re-entering the horizon during the Friedmann phase, we extend to PLI the gauge-invariant approach developed by Bardeen et al. for the usual inflationary models. We find that the above constraints can be suitably satisfied. Finally, we outline possible connections between PLI and particular inflationary models which have recently been proposed.

Vacuum states in de Sitter space.

Abstract: We examine possible vacuum states for scalar fields in de Sitter space, concentrating on those states (1) invariant under the de Sitter group O(1,4) or (2) invariant under one of its maximal subgroups E(3). For massive fields there is a one-complex-parameter family of de Sitter-invariant states, which includes the ``Euclidean'' vacuum state as a special case. We show these states are generated from the Euclidean vacuum by a frequency-independent Bogoliubov transformation, and obtain formulas for the symmetric, antisymmetric, and Feynman functions. In the massless minimally coupled case we prove that there exists no de Sitter-invariant Fock vacuum state. However one can find Fock states which are E(3) invariant. These states include the Bunch-Davies and Ottewill-Najmi vacua as special cases.

Mass spectrum of chiral ten-dimensional N=2 supergravity on S5.

Abstract: We discuss the spontaneous compactification of chiral N = 2 ten-dimensional supergravity from ten to five dimensions on S/sup 5/. Harmonic analysis on S/sup 5/ is used to compute the complete mass spectrum. Our results indicate that scalars and spinors in different SO(6) multiplets have different masses, even within the ''massless'' supermultiplet. We show that the conformal diffeomorphisms, which remain after imposing certain covariant gauge conditions for the general coordinate invariance, can be used to gauge away twice as many modes as there are gauge parameters. A doubleton multiplet of pure gauge modes is identified, and all modes in the massless supermultiplet lie at the beginning of infinite towers of modes.

Origin of structure in the Universe.

Abstract: It is assumed that the Universe is in the quantum state defined by a path integral over compact four-metrics. This can be regarded as a boundary condition for the wave function of the Universe on superspace, the space of all three-metrics and matter field configurations on a three-surface. We extend previous work on finite-dimensional approximations to superspace to the full infinite-dimensional space. We treat the two homogeneous and isotropic degrees of freedom exactly and the others to second order. We justify this approximation by showing that the inhomogeneous or anisotropic modes start off in their ground state. We derive time-dependent Schr\"odinger equations for each mode. The modes remain in their ground state until their wavelength exceeds the horizon size in the period of exponential expansion. The ground-state fluctuations are then amplified by the subsequent expansion and the modes reenter the horizon in the matter- or radiation-dominated era in a highly excited state. We obtain a scale-free spectrum of density perturbations which could account for the origin of galaxies and all other structure in the Universe. The fluctuations would be compatible with observations of the microwave background if the mass of the scalar field that drives the inflation is ${10}^{14}$ GeV or less.

Particle Creation in de Sitter Space

Abstract: In this, the first of a series of papers on quantum field theory in de Sitter spacetime, the invariant vacuum state appropriate for inflationary models of the early universe is identified and shown to decay due to the Hawking effect. The created pairs have an energy-momentum which leads to a first-order decrease of the effective cosmological constant, independently of any matter phase transition. A mechanism for dynamically relaxing ..lambda../sub eff/..-->..0 is thereby suggested.

Generic instabilities in first-order dissipative relativistic fluid theories.

Abstract: We consider the stability of a general class of first-order dissipative relativistic fluid theories which includes the theories of Eckart and of Landau and Lifshitz as special cases. We show that all of these theories are unstable in the sense that small spatially bounded departures from equilibrium at one instant of time will diverge exponentially with time. The time scales for these instabilities are very short; for example, water at room temperature and pressure has an instability with a growth time scale of about ${10}^{\mathrm{\ensuremath{-}}34}$ seconds in these theories. These results provide overwhelming motivation (we believe) for abandoning these theories in favor of the second-order (Israel) theories which are free of these difficulties.

Flux-tube model for hadrons in QCD.

Abstract: We extract from the strong-coupling Hamiltonian lattice formulation of QCD a model for hadrons based on the use of quark and flux-tube degrees of freedom. The ordinary quark model of mesons and baryons is recovered as an appropriate limit, but the properties of hybrids, pure glue, and multiquark hadrons are also predicted by the model. The basic tenets of the model can be tested by lattice Monte Carlo simulations.

Bargmann structures and Newton-Cartan theory

Abstract: It is shown that Newton-Cartan theory of gravitation can best be formulated on a five-dimensional extended space-time carrying a Lorentz metric together with a null parallel vector field. The corresponding geometry associated with the Bargmann group (nontrivially extended Galilei group) viewed as a subgroup of the affine de Sitter group AO(4,1) is thoroughly investigated. This new global formalism allows one to recast classical particle dynamics and the Schroedinger equation into a purely covariant form. The Newton-Cartan field equations are readily derived from Einstein's Lagrangian on the space-time extension.

Classical and Quantum Cosmology of the Starobinsky Inflationary Model

Abstract: Starobinsky has suggested an inflationary cosmological scenario in which the inflation is driven by quantum corrections to the vacuum Einstein's equations. Here a detailed review of the Starobinsky scenario is given and an observational constraint on the parameters of the model is derived. The quantum mechanics of the model is studied first using the instanton method, and then by solving the corresponding Wheeler-DeWitt equation. A cosmological wave function is obtained describing a universe tunneling from ``nothing'' to the Starobinsky inflationary phase. The curvature fluctuations in the tunneling universe are calculated. This quantum analysis determines the initial conditions for the classical evolution of the model.

Gravitational radiation from cosmic strings

Abstract: Gravitational radiation from oscillating loops of string is studied both analytically and numerically. The total radiated power is found to be P=\ensuremath{\gamma}G${\ensuremath{\mu}}^{2}$, where \ensuremath{\mu} is the mass density of the string and \ensuremath{\gamma} is a numerical coefficient \ensuremath{\sim}100. The intensity and the spectrum of the stochastic gravitational-wave background produced by the loops are calculated. Gravitational radiation from asymmetric loops carries not only energy, but also momentum; the loop recoils and accelerates like a rocket. The momentum radiation rate from loops is calculated and it is shown that cosmological loops formed with sufficiently small initial velocities are slowed down by dynamical friction and do not rocket away.

Quantum mechanics of the scalar field in the new inflationary universe.

Abstract: An attempt is made to clarify the quantum theory of the ``slow-rollover'' phase transition which characterizes the new inflationary universe model. We discuss the theory of the upside-down harmonic oscillator as a toy model, with particular emphasis on the fact that the system can be described at late times by a classical probability distribution. An approximate but exactly soluble model for the scalar field is then constructed, based on three principal assumptions: (1) exact de Sit- ter expansion for all time; (2) a quadratic potential function which changes from stable to unstable as a function of time; and (3) an initial state which is thermal in the asymptotic past. It is proposed that this model would be the proper starting point for a perturbative calculation in more realistic models. The scalar field can also be described at late times by a classical probability distribution, and numerical calculations are carried out to illustrate how this distribution depends on the parameters of the model. For a suitable choice of these parameters, a sufficient period of inflation can be easily obtained. Density fluctuations can be calculated exactly in this model, and the results agree very well with those previously obtained using approximate methods.

Exact Gravitational Field of a String

Abstract: The exact spacetime metric representing the exterior of a static cylindrically symmetric string is found. The geometry is conical, with a deficit angle of 8\ensuremath{\pi}G\ensuremath{\mu}, where \ensuremath{\mu} is the linear energy density of the string. The results of Vilenkin, obtained using linearized gravity, are thus shown to be correct to all orders in G\ensuremath{\mu}. Strings with G\ensuremath{\mu}\ensuremath{\ge}(1/4) are found to collapse the exterior spacetime, resulting in dimensional reduction.

Dissipative Phenomena in Quark Gluon Plasmas

Abstract: Transport coefficients of small-chemical-potential quark-gluon plasmas are estimated and dissipative corrections to the scaling hydrodynamic equations for ultrarelativistic nuclear collisions are studied. The absence of heat-conduction phenomena is clarified. Lower and upper bounds on the shear-viscosity coefficient are derived. QCD phenomenology is used to estimate effects of color-electric and -magnetic shielding, and nonperturbative antiscreening. Bulk viscosity associated with the plasma-to-hadron transition is estimated within the relaxation-time approximation. Finally, effects of dissipative phenomena on the relation between initial energy density and final rapidity density are estimated.

Large-scale energy-density perturbations and inflation

Abstract: A first-order differential equation is given for large-scale energy-density perturbations in a Friedmann universe, which expresses the fact that each region of spacetime evolves like a separate Friedmann universe with small spatial curvature (the average curvature is taken to vanish). Using it perturbations generated in an inflationary era are evolved to the present (for sufficiently large scales) with essentially no assumption about intervening eras. The field fluctuations are shown to be essentially quantum mechanical until a few Hubble times after the scale leaves the horizon during the de Sitter era, but probably classical at later times. Full comparison with earlier work is made.

Detection rates for ‘‘invisible’’-axion searches

Abstract: Experiments are described to search for axions floating about in the halo of our galaxy and for axions emitted by the sun. Expressions are given for the signal strengths in these experiments.

Photon and dilepton emission from the quark-gluon plasma: Some general considerations.

Abstract: The emission rates for photons and di-leptons from a quark-gluon plasma is related to the thermal expectation value of an electromagnetic current-current correlation function. This correlation function possesses an invariant tensor decomposition with structure functions entirely analogous to W/sub 1/ and W/sub 2/ of deep inelastic scattering of leptons from hadronic targets. The thermal scaling properties of the appropriate structure functions for thermal emission are derived. The thermal structure functions may be computed in a weak coupling expansion at high plasma temperature. The rates for thermal emission are estimated, and for di-leptons, the thermal emissions rate is argued to dominate over the Drell-Yan process for di-lepton masses 600 MeV < M < 1 to 2 GeV using conservative estimates of the plasma temperature. We argue that higher temperatures are entirely possible within the context of the inside-outside cascade model of matter formation, perhaps temperatures as high as 500 to 800 MeV. If these high temperatures are achieved, the maximum di-lepton masses arising from thermal emission are argued to be 5 GeV. Signals for thermal emission are presented as the relative magnitude of invariant thermal structure functions, thermal scaling relations, and transverse momenta of thermal di-lepton pairs increasing with and proportionalmore » to the di-lepton pair mass. The transverse mass spectra is given for a high temperature plasma. The dependence of the spectra of thermal emission upon the existence of a first phase transition is studied. We argue that if there is a first order phase transition, as beam energy or nuclear baryon number is raised through the threshold for production of a plasma, the rate for photon or di-lepton emission might dramatically increase.« less

Langevin simulations of lattice field theories

Abstract: We present a new analysis of Langevin simulation techniques for lattice field theories, including a general discussion of errors and algorithm speed. We introduce Fourier techniques that greatly accelerate simulations on large lattices. We also introduce a new technique for including quark vacuum-polarization corrections that admits any number of flavors, odd or even, without the need for nested Monte Carlo calculations. Our analysis is supported by a variety of numerical experiments.

Laws of motion and precession for black holes and other bodies

Abstract: Laws of motion and precession are derived for a Kerr black hole or any other body which is far from all other sources of gravity ("isolated body") and has multipole moments that change slowly with time. Previous work by D’Eath and others has shown that to high accuracy the body moves along a geodesic of the surrounding spacetime geometry, and Fermi-Walker transports its angular-momentum vector. This paper derives the largest corrections to the geodesic law of motion and Fermi-Walker law of transport. These corrections are due to coupling of the body’s angular momentum and quadrupole moment to the Riemann curvature of the surrounding spacetime. The resulting laws of motion and precession are identical to those that have been derived previously, by many researchers, for test bodies with negligible self-gravity. However, the derivation given here is valid for any isolated body, regardless of the strength of its self-gravity. These laws of motion and precession can be converted into equations of motion and precession by combining them with an approximate solution to the Einstein field equations for the surrounding spacetime. As an example, the conversion is carried out for two gravitationally bound systems of bodies with sizes much less than their separations. The resulting equations of motion and precession are derived accurately through post1.5-Newtonian order. For the special case of two Kerr black holes orbiting each other, these equations of motion and precession (which include couplings of the holes’ spins and quadrupole moments to spacetime curvature) reduce to equations previously derived by D’Eath. The precession due to coupling of a black hole’s quadrupole moment to surrounding curvature may be large enough, if the hole lives at the center of a very dense star cluster, for observational detection by its effects on extragalactic radio jets. Unless the hole rotates very slowly, this quadrupole-induced precession is far larger than the spin-down of the hole by tidal distortion ("horizon viscosity"). When the hole is in orbit around a massive companion, the quadrupole-induced precession is far smaller than geodetic precession.

Search for Supersymmetric Particles in Hadron - Hadron Collisions

Abstract: Elementary cross sections for the production of supersymmetric partners of the known constituents and gauge bosons in collisions of quarks and gluons are calculated in tree approximation. Standard renormalization-group-improved parton-model methods are then used to estimate differential and integrated production cross sections in proton-proton and proton-antiproton collisions. For completeness, some analogous results are presented for electron-positron collisions. Decay modes, experimental signatures, and bounds on masses of supersymmetric partners are surveyed, and prospects for future searches are discussed.

Solving field theory in one space and one time dimension.

Abstract: By quantizing a realistic field theory in one space and one time dimension at equal light-cone time \ensuremath{\tau}=t+x/c rather than at equal time t, one can find exact solutions to the bound-state problem. The method is nonperturbative and amounts to the diagonalization of finite matrices in Fock space. It applies also for non-Abelian gauge theory in 1+1 dimensions, but is demonstrated here for the simple case of fermions interacting with scalar fields. The success of the light-cone quantization method rests on the existence of a new dynamical quantum number, the harmonic resolution K, which can be understood as the ratio of a characteristic length, the box size L, and the Compton wavelength of a massive particle. We emphasize the appearance of self-induced instantaneous inertias.

Quantum mechanics as a classical theory.

Abstract: The generator aspect of observables in classical mechanics leads naturally to a generalized classical mechanics, of which quantum mechanics is shown to be a particular case. Basic features of quantum mechanics follow, such as the identification of observables with self-adjoint operators, and canonical quantization rules. This point of view also gives a new insight on the geometry of quantum theory: Planck's constant is related for instance to the curvature of the quantum-mechanical space of states, and the uniqueness of quantum mechanics can be proved. Finally, the origin of the probabilistic interpretation is discussed.

Experimental tests of the gravitational inverse-square law for mass separations from 2 to 105 cm.

Abstract: We report two experiments which test the inverse-square distance dependence of the Newtonian gravitational force law. One experiment uses a torsion balance consisting of a 60-cm-long copper bar suspended at its midpoint by a tungsten wire, to compare the torque produced by copper masses 105 cm from the balance axis with the torque produced by a copper mass 5 cm from the side of the balance bar, near its end. Defining ${R}_{\mathrm{expt}}$ to be the measured ratio of the torques due to the masses at 105 cm and 5 cm, and ${R}_{\mathrm{Newton}}$ to be the corresponding ratio computed assuming an inverse-square force law, we find \ensuremath{\delta}\ensuremath{\equiv}(${R}_{\mathrm{expt}}$/${R}_{\mathrm{Newton}}$-1)=(1.2 \ifmmode\pm\else\textpm\fi{}7)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}4}$. Assuming a force deviating from an inverse-square distance dependence by a factor [1+\ensuremath{\epsilon} lnr(cm)], this result implies \ensuremath{\epsilon}=(0.5 \ifmmode\pm\else\textpm\fi{}2.7)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}4}$. An earlier experiment, which has been reported previously, is described here in detail. This experiment tested the inverse-square law over a distance range of approximately 2 to 5 cm, by probing the gravitational field inside a steel mass tube using a copper test mass suspended from the end of a torsion balance bar. This experiment yielded a value for the parameter \ensuremath{\epsilon} defined above: \ensuremath{\epsilon}=(1\ifmmode\pm\else\textpm\fi{}7)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}5}$. The results of both of these experiments are in good agreement with the Newton- ian prediction. Limits on the strength and range of a Yukawa potential term superimposed on the Newtonian gravitational potential are discussed.

Decaying particles do not "heat up" the Universe.

Abstract: It is usually assumed that a massive relic species, which comes to dominate the mass density of the Universe and later decays, ``heats up'' the Universe when the age of the Universe \ensuremath{\simeq} its lifetime. We show that if its decay follows the usual exponential decay law, then the Universe is never reheated, rather it just cools more slowly. We calculate the evolution of the temperature and entropy, and find that to within numerical factors of order unity, the usual estimates for the entropy increase are correct. Our results have implications for primordial nucleosynthesis in scenarios where a massive relic with lifetime \ensuremath{\simeq} ${10}^{\mathrm{\ensuremath{-}}2}$--${10}^{3}$ sec is present, and for baryogenesis in the new inflationary Universe scenario.

General Relativistic Strings

Abstract: The properties of infinite-length cosmic strings are investigated using the full coupled equations for the metric and the scalar and gauge fields which make up the string. It is argued that there exists a class of static cylindrically symmetric solutions of these equations representing an isolated string. All of these solutions approach Minkowski spacetime minus a wedge. An exact formula is given for the angle of light bending by the string. These results are substantially in agreement with earlier treatments of cosmic strings, which used approximations for the stress energy of the string.

Heterotic string in an arbitrary background field

Abstract: An expression for the light-cone gauge action for the first-quantized heterotic string in the presence of arbitrary background gauge, gravitational, and antisymmetric tensor fields is derived. The result is a two-dimensional local field theory with N=1/2 supersymmetry. The constraints imposed on the background fields in order to make this theory one-loop finite are derived. These constraints are identical to the equations of motion for the massless fields at the linearized level. Finally, it is shown that if there is no background antisymmetric tensor field, and if the gauge connection is set equal to the spin connection, the effective action is that of an N=1 supersymmetric nonlinear and N=2 supersymmetric Georgi-Glashow models the occurrence of the fermion fractionization is the necessity; the ignorance of it results in the inconsistency in the perturbative calculation of the mass splittings among the members of the supermultiplets. The notable feature of our result is that the degeneracy due to the Jackiw-Rebbi zero mode is not independent of the one required by the supersymmetry, suggesting a nontrivial structure in embedding the topology of Higgs fields into supersymmetric gauge theories.

Factorization of the Drell-Yan Cross-Section in Perturbation Theory

Abstract: We develop, through detailed one- and two-loop examples, a procedure for expressing the leading-twist Drell-Yan cross section in terms of the factored form proposed by Collins, Soper, and Sterman. We then show that this factorization program can be implemented to all orders in perturbation theory. The factored cross section takes the form of an on-shell qq\ifmmode\bar\else\textasciimacron\fi{} annihilation cross section (less certain collinear subtractions) convolved with structure functions for the incoming hadrons. The structure functions contain all the collinear singularities and spectator interactions. They are shown to be simply related to those that occur in deep-inelastic lepton scattering. We also demonstrate that the qq\ifmmode\bar\else\textasciimacron\fi{} cross section minus the collinear subtractions is free of infrared singularities if one integrates over the transverse momentum of the lepton pair.

Discretized light-cone quantization: Solution to a field theory in one space and one time dimension

Abstract: In the preceding paper, the field-theoretic bound-state problem in 1+1 dimensions was mapped to the problem of diagonalizing a strictly finite-dimensional Hamiltonian matrix by quantizing at equal light-cone time. In this paper, we calculate the invariant mass spectrum for the Yukawa theory \ensuremath{\psi}\ifmmode\bar\else\textasciimacron\fi{}\ensuremath{\varphi}\ensuremath{\psi}. The spectrum is shown to be independent of the momentum cutoff in the limit \ensuremath{\Lambda}\ensuremath{\rightarrow}\ensuremath{\infty} and more complex with increasing harmonic resolution K. The results are compared with the recent work of Brooks and Frautschi, who apply conventional space-time quantization. Because of incompatible cutoffs, we reproduce their results only qualitatively, for a rather small value of \ensuremath{\Lambda}. We propose an explanation for their nonunique mass renormalization. We also discuss the straightforward application of the discretized light-cone quantization to non-Abelian field theories in 1+1 dimensions, and the generalization to 3+1 dimensions.

Gaussian effective potential. II. lambda phi4 field theory.

Abstract: The Gaussian-effective-potential approach is used to explore the physics of lambdaphi/sup 4/ field theory in 1, 2, 3, and 4 spacetime dimensions. A simple and systematic approach to the renormalization, without explicit regularization, is employed. In four dimensions we find a viable, nontrivial theory arising from a bare coupling constant of a particular negative, infinitesimal form. The theory is ''precarious'': it is stable in the absence of an ultraviolet cutoff, but unstable when regularized. Perturbation theory is related to this form of the theory, though not straightforwardly. We also discuss particle masses, and the absence of two-particle bound states in phi/sup 4/ theory.

Quantum instability of de Sitter spacetime.

Abstract: Various interacting field theories in de Sitter spacetime which contain a massless, minimally coupled scalar field are investigated. It is shown that the vacuum expectation value of the energy-momentum tensor can contain a term which is proportional to the metric tensor but with a coefficient which, to first order in the coupling constant, is a linear function of time. This term can act in such a way as to tend to cancel the cosmological constant and to cause the curvature of de Sitter space to decrease. The possibility that pure quantum gravity without matter fields may lead to an instability of de Sitter space is also discussed.