Showing papers in "Physical Review D in 1986"

Unified dynamics for microscopic and macroscopic systems

Abstract: An explicit model allowing a unified description of microscopic and macroscopic systems is exhibited. First, a modified quantum dynamics for the description of macroscopic objects is constructed and it is shown that it forbids the occurrence of linear superpositions of states localized in far-away spatial regions and induces an evolution agreeing with classical mechanics. This dynamics also allows a description of the evolution in terms of trajectories. To set up a unified description of all physical phenomena, a modification of the dynamics, with respect to the standard Hamiltonian one, is then postulated also for microscopic systems. It is shown that one can consistently deduce from it the previously considered dynamics for the center of mass of macroscopic systems. Choosing in an appropriate way the parameters of the so-obtained model one can show that both the standard quantum theory for microscopic objects and the classical behavior for macroscopic objects can all be derived in a consistent way. In the case of a macroscopic system one can obtain, by means of appropriate approximations, a description of the evolution in terms of a phase-space density distribution obeying a Fokker-Planck diffusion equation. The model also provides the basis for a conceptually appealing description of quantum measurement.

Baryons in a relativized quark model with chromodynamics

Abstract: We have studied the three quark system in a relativized version of the quark potential model with chromodynamics. With parameters consistent with those of an analogous study of meson spectroscopy we obtain a successful description of the spectrum of baryons. The model naturally explains the apparent absence of spin‐orbit interactions in baryons.

Quantum source of entropy for black holes.

Abstract: We associate to any quantum field propagating in the background metric of a black hole an effective density matrix whose statistical entropy can be interpreted as a contribution to the total entropy of the black hole. By evaluating this contribution in a simplified case, we show that in general it can be expected to be finite and proportional to the area of the black hole. As a by-product of our calculation we obtain a general expression for the entropy of any real Gaussian density matrix.

Neutrino mass and baryon-number nonconservation in superstring models

Abstract: We propose new mechanisms for understanding neutrino masses in superstring models that contain ${\mathrm{E}}_{6}$-singlet zero-mass fields after compactification. We show that the low-energy gauge group of these models can be phenomenologically acceptable. We then comment on \ensuremath{\Delta}B=1 and \ensuremath{\Delta}B=2 baryon-number-violating processes in these models.

Detecting cold dark-matter candidates.

Abstract: The growing synergy between astrophysics, particle physics, and low background experiments strengthens the possibility of detecting astrophysical non-baryonic matter. The idea of direct detection is that an incident, massive weakly interacting particle could collide with a nucleus and transfer an energy that could be measured. The present low levels of background achieved by the PNL/USC Ge detector represent a new technology which yields interesting bounds on galactic cold dark matter and on light bosons emitted from the Sun. Further improvements require the development of cryogenic detectors, e.g. superheated superconducting colloid (SSCD) and crystal bolometers. We report two tests designed to study the practicality of a superheated superconducting colloid detector using a SQUID readout system. Furthermore, we show that in case of particles with spin interactions, one should consider detectors based on compounds of boron, lithium and fluorine.

Black-hole thermodynamics and the Euclidean Einstein action

Abstract: Using the approach to black-hole thermodynamics initiated by Gibbons and Hawking, in terms of the Euclidean Einstein action, I show that the canonical ensemble with elements of radius r and temperature T(r) for hot gravity with black holes is well defined. This follows from the double valuedness of solutions of the Euclidean Einstein equation with canonical boundary conditions. One of the solutions is a locally stable hole. Its partition function is well defined and implies the entropy S=4\ensuremath{\pi}${M}^{2}$ as well as a generalized version of black-hole thermodynamics that reduces to the usual form if ${\mathrm{rM}}^{\mathrm{\ensuremath{-}}1}$\ensuremath{\rightarrow}\ensuremath{\infty}. The density of states of the locally stable hole is real and nonpathological. The free energy of this hole can be negative, while that of the other (unstable) solution is always positive. Consequently, the direct nucleation of black holes from hot flat space, as proposed by Gross, Perry, and Yaffe, can be given a thermodynamically consistent description. The scaling laws for hot gravity are obtained and applied to phase transitions between hot flat space and locally stable holes. The free energy of the unstable solution forms the effective potential barrier between these phases. The ground state of the canonical ensemble is always locally stable in the semiclassical approximation. If N is the effective number of massless fields of helicity zero in hot flat space, then when either r\ensuremath{\lesssim}${N}^{1/2}$ or T\ensuremath{\gtrsim}${N}^{\mathrm{\ensuremath{-}}1/2}$, hot flat space is the most probable ground state. Independently of N, if rT${l(27)}^{1/2}$(8\ensuremath{\pi}${)}^{\mathrm{\ensuremath{-}}1}$ there can be no real black hole in the canonical ensemble.

Effective field equations for expectation values.

Abstract: We discuss functional methods which allow calculation of expectation values, rather than the usual in-out amplitudes, from a path integral. The technique, based on Schwinger's idea of summing over paths which go from the past to the future and then back to the past, provides effective field equations satisfied by the expectation value of the field. These equations are shown to be real and causal for a general theory up to two-loop order, and unitarity is checked to this order. These methods are applied to a simple quantum-mechanical example to illustrate the differences between the new formalism and the standard theory. When applied to the gravitational field, the new effective field equations should be useful for studies of quantum cosmology.

Cosmic and Local Mass Density of Invisible Axions

Abstract: If the Universe is axion dominated it may be possible to detect the axions which comprise the bulk of the mass density of the Universe. The feasibility of the proposed experiments depends crucially upon knowing the axion mass (or equivalently, the Peccei-Quinn symmetry-breaking scale) and the local mass density of axions. In an axion-dominated universe our galactic halo should be comprised primarily of axions. We calculate the local halo density to be at least 5\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}25}$ g ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$, and at most a factor of 2 larger. Unfortunately, it is not possible to pin down the axion mass, even to within an order of magnitude. In an axion-dominated universe we place an upper limit to the axion mass of about ${10}^{\mathrm{\ensuremath{-}}4}$ eV. We give precise formulas for the axion mass in an axion-dominated universe, and clearly point out all the uncertainties involved in determining the precise value of the mass.

Boundary conditions in quantum cosmology

Abstract: The problem of boundary conditions for the cosmological wave function \ensuremath{\psi} is analyzed using a simple model as an example. The model has two degrees of freedom: the scale factor and a homogeneous scalar field. A tunneling wave function is found for this model which describes an ensemble of universes tunneling from ``nothing'' to a de Sitter space, then evolving along the lines of an inflationary scenario and eventually collapsing to a singularity. A boundary condition in superspace is proposed which selects the tunneling solution for \ensuremath{\psi}. This boundary condition can be thought of as a quantum version of the Penrose condition in classical general relativity. The probability current, the concept of time, and the possibility of an experimental test of quantum cosmology are also discussed.

New contributions to neutrinoless double-beta decay in supersymmetric theories

Abstract: In supersymmetric theories with R-parity violation, there are new contributions to neutrinoless double-beta [(\ensuremath{\beta}\ensuremath{\beta}${)}_{0\ensuremath{ u}}$] decay that do not involve the exchange of Majorana neutrinos. Experimental information on (\ensuremath{\beta}\ensuremath{\beta}${)}_{0\ensuremath{ u}}$ decay can therefore be used to constrain parameters of supersymmetric theories. We also discuss neutrino mass in these theories. We then discuss how R-parity-violating interactions can be induced in the low-energy sector of a theory that respects R-parity conservation prior to symmetry breaking.

Membrane viewpoint on black holes: Properties and evolution of the stretched horizon

Abstract: This paper derives the ‘‘membrane formalism’’ for black holes. The membrane formalism rewrites the standard mathematical theory of black holes in a language and notation which (we hope) will facilitate research in black-hole astrophysics: The horizon of a black hole is replaced by a surrogate ‘‘stretched horizon,’’ which is viewed as a 2-dimensional membrane that resides in 3-dimensional space and evolves in response to driving forces from the external universe. This membrane, following ideas of Damour and Znajek, is regarded as made from a 2-dimensional viscous fluid that is electrically charged and electrically conducting and has finite entropy and temperature, but cannot conduct heat. The interaction of the stretched horizon with the external universe is described in terms of familiar laws for the horizon’s fluid, e.g., the Navier-Stokes equation, Ohm’s law, a tidal-force equation, and the first and second laws of thermodynamics. Because these laws have familiar forms, they are likely to help astrophysicists understand intuitively and compute quantitatively the behaviors of black holes in complex external environments. Previous papers have developed and elucidated electromagnetic aspects of the membrane formalism for time-independent rotating holes. This paper derives the full formalism for dynamical, evolving holes, with one exception: In its present form the formalism is not equipped to handle horizon caustics, where new generators attach themselves to the horizon.

Spontaneous Chiral Symmetry Breaking in Three-Dimensional QED

Abstract: A detailed analysis is given of chiral-symmetry breaking in the large-flavor (N) limit of quantum electrodynamics in (2+1) dimensions. Analytical and numerical solutions of the homogeneous Dyson-Schwinger equation for the fermion self-energy combined with a computation of the effective potential for the fermion bilinear show that it is energetically preferable for the theory to dynamically generate a mass for fermions. The magnitude of the mass is roughly exponentially suppressed in N from the fundamental dimensionful scale \ensuremath{\alpha}\ensuremath{\equiv}N ${e}^{2}$ of the gauge coupling constant, but the scale at which the self-mass begins to damp rapidly appears to be of order \ensuremath{\alpha}, so that there is no spontaneous breaking of an approximate scale invariance that the underlying theory possesses at momentum small compared to \ensuremath{\alpha}. Higher-order 1/N corrections are analyzed and it is shown that the 1/N expansion can be used consistently to demonstrate chiral-symmetry breaking. Open issues and possible improvements of the analysis are given and some avenues for future investigation suggested.

Unsharp reality and joint measurements for spin observables.

Abstract: On generalise le critere de realite EPR pour ajuster avec la notion d'observables a valeur d'operateur positif apparaissant en optique quantique, mecanique quantique stochastique

Spectral decomposition of the perturbation response of the Schwarzschild geometry

Abstract: The radiative Green's function for the one-dimensional wave equation with the Regge-Wheeler and Zerilli potentials is formally constructed from recently developed analytic representations for generalized spheroidal wave functions, and decomposed into a convergent sum over quasinormal modes, an integral around a branch cut in the frequency domain, and a high-frequency remnant of the free-space propagator. This paper discusses the contribution to the time response made by the quasinormal modes and, at very late times, by the branch-cut integral. The initial-value problem is considered for source fields with both compact and extended radial dependences, and the problem of the formal divergence of the integrals of extended sources over quasinormal-mode wave functions is solved. The branch-cut integral produces a weak late-time radiative power-law decay tail that will characterize the astrophysically observed radiation spectrum for times subsequent to the exponential decay of the quasinormal ringing, when (ct-${r}_{\mathrm{*}}$)\ensuremath{\gg}2MG/${c}^{2}$ and (ct-${r}_{\mathrm{*}}$)/${r}_{\mathrm{*}}$\ensuremath{\ll}1. This radiative decay tail is shown to diminish to Price's nonradiative tail in the final limit ct/${r}_{\mathrm{*}}$\ensuremath{\gg}1. The method is applied to a characteristic-value problem used to model the gravitational collapse of massive stars, and to the small-body radial in-fall problem. The analysis presented is generalizable, through the Newman-Penrose formalism and Teukolsky's equations, to obtain the radiative Green's function for perturbations to the Kerr geometry.

The R 2 cosmology: Inflation without a phase transition

Abstract: A pure gravity inflationary model for the Universe is examined which is based on adding an \ensuremath{\epsilon}${R}^{2}$ term to the usual gravitational Lagrangian. The classical evolution is worked out, including eventual particle production and the subsequent join to radiation-dominated Friedmann behavior. We show that this model gives significant inflation essentially independent of initial conditions. The model has only one free parameter which is bounded from above by observational constraints on scalar and tensorial perturbations and from below by both the need for standard baryogenesis and the need for galaxy formation. This requires ${10}^{11}$${\ensuremath{\epsilon}}^{\mathrm{\ensuremath{-}}1/2}$${10}^{13}$ GeV.

On the Relic, Cosmic Abundance of Stable Weakly Interacting Massive Particles

Abstract: In the context of the expanding Universe, we solve the Boltzmann equation to obtain the relic abundance of a stable, weakly interacting massive particle species with arbitrary mass and interaction strength We provide approximate analytic formulas for the evolution of the abundance and the final abundance Our formulas are typically accurate to better than 5%

Pion interferometry of quark-gluon plasma.

Abstract: Pion interferometry is discussed as a tool for viewing ultrarelativistic heavy-ion collisions. Several dynamical scenarios are considered for the phase transition into quark-gluon plasma. Experimental signatures for a first-order phase transition are predicted for collisions where the produced matter has no initial collective motion. Recommendations for future experiments are made.

Astrophysical axion bounds diminished by screening effects.

Abstract: ''Invisible axions'' could be produced in stellar interiors through Compton- and Primakoff-type photoproduction and through bremsstrahlung processes. We point out that in a plasma screening effects lead to important reductions of these emission rates. Limits on the axion mass and interaction strength are thereby relaxed to values less restrictive than limits previously thought to be firm. For the case of the Sun the Primakoff rate is reduced by two orders of magnitude. This process is the dominant emission mechanism for Kim-Shifman-Vainshtein-Zakharov- (KSVZ) type axions which do not couple directly to electrons. The mass limit is then relaxed by an order of magnitude to m/sub a/<20 eV. Dine-Fischler-Srednicki (DFS) axions couple directly to electrons and the dominant solar emission process becomes bremsstrahlung from electron-nucleus and electron-electron collisions while the previously thought dominant Primakoff rate is now suppressed. The mass limit accidentally remains at m/sub a/<3 eV. Model-dependent bounds based on axion emission from red giants are m/sub a/<1 eV (KSVZ) and m/sub a/<0.06 eV (DFS). The mass limits for the DFS axions are understood for the special case where the free parameter 2 cosSUS of the model equals unity. Our results can be easily translated to other hypothetical pseudoscalar particles ifmore » they are light compared with typical stellar temperatures.« less

Neutrino Oscillation Experiments at the Gosgen Nuclear Power Reactor

Abstract: A search for neutrino oscillations has been conducted at the 2800-MW (thermal) nuclear power reactor in Gosgen (Switzerland), providing 5×10^20 electron antineutrinos per second. The energy spectrum of the antineutrinos was measured at three distances, 37.9, 45.9, and 64.7 m, from the reactor core. The detection of the neutrinos is based on the reaction ν¯e+p→e++n. Roughly 10^4 antineutrinos were registered at each of the three measuring positions. The measured spectra are analyzed in terms of a two-neutrino oscillation model and the results are represented as exclusion plots for the oscillation parameters Δm^2 and sin^2(2theta). Two analyses are performed: Analysis A relies exclusively on the data measured at the three different distances; analysis B combines the measured data with additional information, in particular with the reactor antineutrino spectrum as derived from independent β-spectroscopic measurements. Both analyses show that the data are consistent with the absence of neutrino oscillations, and rule out large regions of parameters (Δm2,theta). The resulting limits on the oscillation parameters are Δm^2 5 eV^2.

Solar System Constraints and Signatures for Dark Matter Candidates

Abstract: We show that if our galactic halo were to consist of scalar or Dirac neutrinos with mass greater than \ensuremath{\sim}12 GeV, capture by the Earth and subsequent annihilation would yield a large flux of neutrinos at the surface which could be seen in proton-decay detectors. The luminosity of Uranus provides comparable constraints. Capture in the Sun can yield supplementary information, with detectable signals possible for masses as low as 6 GeV for both Dirac and Majorana neutrinos, scalar neutrinos, and photinos. We discuss in detail the question of evaporation, on which our results and others depend sensitively. We suggest one method of approximating evaporation rates from the Earth and Sun and discuss potential problems with earlier estimates. Finally, we describe how particles which avoid these constraints may still be detectable by bolometric neutrino detectors and isolate a new method to remove backgrounds to this signal in such detectors.

Gauge invariance and unitarity in higher-derivative quantum gravity

Abstract: The question of unitarity is examined in the renormalizable, ``higher-derivative'' theory of quantum gravity. It is pointed out that the presence of a massive spin-2 ghost in the bare propagator is inconclusive, since this excitation is unstable. In the presence of unstable particles, expansions using bare propagators are impossible---modified expansions with dressed propagators that exhibit the complex nature of the unstable pole must be employed. It is found, however, that the position of the complex poles in the dressed propagator is explicitly gauge dependent. It turns out that this is a specifically gravitational effect; it does not occur in gauge theories with an internal-symmetry gauge group. On the other hand, a physical S matrix between in and out states containing only transverse, massless gravitons and physical massless matter fields is shown to be gauge independent. It then follows by a standard, albeit formal, argument that the contribution of all gauge-variant poles to its intermediate states must cancel. The physical S matrix should therefore, be unitary. In this development, the standard rules of quantum field theory are followed throughout; no ad hoc modifications, such as the Lee-Wick prescription, are ever invoked.

Limits on cold-dark-matter candidates from deep underground detectors

Abstract: Weakly interacting massive particles which are candidates for the dark mass in the halo of the Galaxy would be captured by the Sun, accumulate in the solar core, and annihilate. We present a systematic evaluation of the neutrino signal produced by such annihilations. Since most annihilations occur in the dense solar interior, only prompt neutrinos escape with sufficiently high energy to be readily observable in deep underground detectors. We find that existing underground experiments are capable of finding: or excluding: several possible cold-dark-matter candidates.

Extra Gauge Bosons in E(6)

Abstract: Recent developments in superstring theories have renewed interest in E/sub 6/ as the group for grand unification. E/sub 6/ has rank 6, two more than the standard model, so that an E/sub 6/ grand unified theory can have extra gauge bosons. For example, it can have extra low-energy Z-italic's. If there is just one extra Z-italic at low energy, it can be a mixture of the two extra U(1)'s present in E/sub 6/. We parametrize this mixing by an angle t-italich-italice-italict-italica-italic. We consider the effects of Z-italic(t-italich-italice-italict-italica-italic) in neutral currents, putting limits on its mass. In addition, we consider the branching ratios, Drell-Yan production, and forward-backward asymmetries for Z-italic(t-italich-italice-italict-italica-italic). Another possibility is that, in addition to one extra Z-italic, there is an extra SU(2) present in the low-energy theory. It is SU(2)/sub I-italic/, the SU(2) which commutes with the electromagnetic charge. We consider the effects of the W-italic/sub I-italic/, which are electromagnetically neutral, in production of exotic particles and other rare processes, particularly flavor-changing neutral currents.

Supersymmetrization of N=1 ten-dimensional supergravity with Lorentz Chern-Simons term.

Abstract: The N-italic = 1 ten-dimensional supergravity with a Lorentz Chern-Simons term is supersymmetrized to the first order of the Noether expansion parameter ..gamma.. without a three-form field strength H-italic.

Dilepton emission and the QCD phase transition in ultrarelativistic nuclear collisions.

Abstract: The emission of dileptons from a matter distribution undergoing longitudinal hydrodynamic expansion as might be produced in ultrarelativistic nuclear collisions is computed. Contributions come from quark-gluon plasma, from pion gas, and from a mixed phase while the matter undergoes a first-order confinement phase transition. This yield is compared with that expected from other sources. It is found that the signals from quark-gluon plasma and pion gas probably exceed such background for sufficiently high initial temperature. The ratio of dilepton rapidity density to the square of the pion rapidity density may provide a measurement of the phase transition temperature. The dilepton mass distribution for various values of transverse energy may provide a measure of vector-meson masses as a function of temperature, and a mass shift due to the restoration of chiral symmetry might be seen.

Force on a Charge in the Space-Time of a Cosmic String

Abstract: We determine the electrostatic self-force acting on a point test charge in the space-time describing a static, cylindrically symmetric cosmic string. We find a repulsive interaction.

Cosmic strings and black holes

Abstract: The metric for a Schwarzschild black hole with a cosmic string passing through it is discussed. The thermodynamics of such an object is considered, and it is shown that S=(1/4)A, where S is the entropy and A is the horizon area. It is noted that the Schwarzschild mass parameter M, which is the gravitational mass of the system, is no longer identical to its energy. A solution representing a pair of black holes held apart by strings is discussed. It is nearly identical to a static, axially symmetric solution given long ago by Bach and Weyl. It is shown how these solutions, which were formerly a mathematical curiosity, may be given a more physical interpretation in terms of cosmic strings.

Candidates for the inflaton field in superstring models.

Abstract: We consider the flat directions of the potential that play a crucial role in the four-dimensional supersymmetric models that are believed to emerge from the compactification of superstring theories and study the possibility that they give rise to an inflationary scenario. None of the scalar fields present in these models---in particular the dilaton field connected with supersymmetry breaking and the SU(5)-singlet scalars in the matter sector---seem, however, to be good candidates for the inflaton, the scalar field whose cosmological evolution leads to an inflationary expansion of the Universe.

Spin-two fields and general covariance

Abstract: It is widely believed that all ``consistent'' theories of a spin-two field coupled to matter or nonlinearly self-coupled must be generally covariant. The extent to which this statement is true is investigated here. We consider at the classical level nonlinear equations of motion for a field ${\ensuremath{\gamma}}_{\mathrm{ab}}$ in a flat background spacetime which are derived from a Lagrangian and which reduce, in linear order, to the equations of a spin-two field. In a perturbation expansion about ${\ensuremath{\gamma}}_{\mathrm{ab}}$=0, we argue that in order for all the linearized solutions to give rise to a one-parameter family of exact solutions, the exact equations of motion must satisfy a certain type of divergence identity. (This is our ``consistency'' condition.) When the equations of motion arise from an action principle as we assume, this divergence identity implies an infinitesimal gauge invariance of the action. However, our main result is the demonstration that only a very restricted class of candidate infinitesimal gauge symmetries can actually arise from an exact (i.e., finite) gauge symmetry, as is necessary to realize the theory. Under some assumptions concerning the number of derivatives which occur in terms appearing in the divergence identity, we prove that only two types of gauge invariance are possible: (i) normal spin-two gauge invariance and (ii) general covariance. Explicit examples of nonlinear field theories of type (i) are constructed. When coupling to matter is considered, the requirement that in linear order ${\ensuremath{\gamma}}_{\mathrm{ab}}$ couple directly to the stress-energy tensor of matter may eliminate possibility (i), but I have shown this only in special cases. A similar analysis of nonlinear generalizations of the equations for a collection of spin-one fields is given, and it is shown that under analogous assumptions, the only possible type of gauge invariance for the nonlinear theory is Yang-Mills gauge invariance with respect to an arbitrary Lie algebra.