Showing papers in "Physical Review D in 1996"

Supersymmetry and attractors.

Abstract: We find a general principle which allows one to compute the area of the horizon of $N=2$ extremal black holes as an extremum of the central charge. One considers the ADM mass equal to the central charge as a function of electric and magnetic charges and moduli and extremizes this function in the moduli space (a minimum corresponds to a fixed point of attraction). The extremal value of the square of the central charge provides the area of the horizon, which depends only on electric and magnetic charges. The doubling of unbroken supersymmetry at the fixed point of attraction for $N=2$ black holes near the horizon is derived via conformal flatness of the Bertotti-Robinson-type geometry. These results provide an explicit model-independent expression for the macroscopic Bekenstein-Hawking entropy of $N=2$ black holes which is manifestly duality invariant. The presence of hypermultiplets in the solution does not affect the area formula. Various examples of the general formula are displayed. We outline the attractor mechanism in $N=4, 8$ super-symmetries and the relation to the $N=2$ case. The entropy-area formula in five dimensions, recently discussed in the literature, is also seen to be obtained by extremizing the $5d$ central charge.

New tools for low energy dynamical supersymmetry breaking.

Abstract: We report the construction of large new classes of models which break supersymmetry dynamically. We then turn to model building. Two of the principal obstacles to constructing simple models of dynamical supersymmetry breaking are the appearance of Fayet-Iliopoulos {ital D} terms and difficulties in generating a {mu} term for the Higgs fields. Among the new models are examples in which symmetries prevent the appearance of Fayet-Iliopoulos terms. A gauge singlet field, which may play a role in explaining the hierarchy in quark and lepton parameters, can generate a suitable {mu} term. The result is a comparatively simple model, with a low energy structure similar to that of the MSSM, but with far fewer arbitrary parameters. We begin the study of the phenomenology of these models. {copyright} {ital 1996 The American Physical Society.}

Consistency conditions for orientifolds and d manifolds

Abstract: We study superstrings with orientifold projections and with generalized open string boundary conditions (D branes). We find two types of consistency condition, one related to the algebra of Chan-Paton factors and the other to cancellation of divergences. One consequence is that the Dirichlet five branes of the type I theory carry a symplectic gauge group, as required by string duality. As another application we study the type I theory on a $K3$ ${Z}_{2}$ orbifold, finding a family of consistent theories with various unitary and symplectic subgroups of U(16)\ifmmode\times\else\texttimes\fi{}U(16). We argue that the $K3$ orbifold with spin connection embedded in gauge connection corresponds to an interacting conformal field theory in the type I theory.

Density perturbations and black hole formation in hybrid inflation.

Abstract: We investigate the recently proposed hybrid inflation models with two stages of inflation. We show that quantum fluctuations at the time corresponding to the phase transition between the two inflationary stages can trigger the formation of a large number of inflating topological defects. In order to study density perturbations in these models we further develop a method to calculate density perturbations in a system of two scalar fields. We show that density perturbations in hybrid inflation models of the new type can be very large on the scale corresponding to the phase transition. The resulting density inhomogeneties lead to a copious production of black holes. This could be an argument against hybrid inflation models with two stages of inflation. However, we find a class of models where this problem can be easily avoided. The number of black holes produced in these models can be made extremely small, but in general it could be sufficiently large to have important cosmological and astrophysical implications. In particular, for certain values of parameters these black holes may constitute the dark matter in the Universe. It is also possible to have hybrid models with two stages of inflation where the black hole production is not suppressed, but where the typical masses of the black holes are very small. Such models lead to a completely different thermal history of the Universe, where postinflationary reheating occurs via black hole evaporation.

Entropy and temperature of black 3-branes.

Abstract: We consider slightly non-extremal black 3-branes of type IIB supergravity and show that their Bekenstein-Hawking entropy agrees, up to a mysterious factor, with an entropy derived by counting non-BPS excitations of the Dirichlet 3-brane. These excitations are described in terms of the statistical mechanics of a 3+1 dimensional gas of massless open string states. This is essentially the classic problem of blackbody radiation. The blackbody temperature is related to the temperature of the Hawking radiation. We also construct a solution of type IIB supergravity describing a 3-brane with a finite density of longitudinal momentum. For extremal momentum-carrying 3-branes the horizon area vanishes. This is in agreement with the fact that the BPS entropy of the momentum-carrying Dirichlet 3-branes is not an extensive quantity.

Barbero's Hamiltonian derived from a generalized Hilbert-Palatini action

Abstract: Barbero recently suggested a modification of Ashtekar's choice of canonical variables for general relativity. Although leading to a more complicated Hamiltonian constraint this modified version, in which the configuration variable still is a connection, has the advantage of being real. In this article we derive Barbero's Hamiltonian formulation from an action, which can be considered as a generalization of the ordinary Hilbert-Palatini action.

Universality of supersymmetric attractors

Abstract: The macroscopic entropy-area formula for supersymmetric black holes in {ital N}=2,4,8 theories is found to be universal: in {ital d}=4 it is always given by the square of the largest of the central charges extremized in moduli space. The proof of universality is based on the fact that the doubling of unbroken supersymmetry near the black hole horizon requires that all central charges other than {ital Z}={ital M} vanish at the attractor point for {ital N}=4,8. The ADM mass at the extremum can be computed in terms of duality symmetric quartic invariants which are moduli independent. The extension of these results for {ital d}=5, {ital N}=1,2,4 is also reported. A duality symmetric expression for the energy of the ground state with spontaneous breaking of supersymmetry is provided by the power 1/2 (2/3) of the black hole area of the horizon in {ital d}=4 ({ital d}=5). It is suggested that the universal duality symmetric formula for the energy of the ground state in supersymmetric gravity is given by the modulus of the maximal central charge at the attractor point in any supersymmetric theory in any dimension. {copyright} {ital 1996 The American Physical Society.}

Lepton-flavor violation via right-handed neutrino Yukawa couplings in the supersymmetric standard model.

Abstract: Various lepton-flavor-violating (LFV) processes in the supersymmetric standard model with right-handed neutrino supermultiplets are investigated in detail. It is shown that large LFV rates are obtained when $tan\ensuremath{\beta}$ is large. In the case where the mixing matrix in the lepton sector has a similar structure as the Kobayashi-Maskawa matrix and the third-generation Yukawa coupling is as large as that of the top quark, the branching ratios can be as large as $B(\ensuremath{\mu}\ensuremath{\rightarrow}e\ensuremath{\gamma})\ensuremath{\simeq}{10}^{\ensuremath{-}11}$ and $B(\ensuremath{\tau}\ensuremath{\rightarrow}\ensuremath{\mu}\ensuremath{\gamma})\ensuremath{\simeq}{10}^{\ensuremath{-}7}$, which are within the reach of future experiments. If we assume a large mixing angle solution to the atmospheric neutrino problem, the rate for the process $\ensuremath{\tau}\ensuremath{\rightarrow}\ensuremath{\mu}\ensuremath{\gamma}$ becomes larger. We also discuss the difference between our case and the case of the minimal SU(5) grand unified theory.

Muon anomalous magnetic dipole moment in the minimal supersymmetric standard model.

Abstract: The muon anomalous magnetic dipole moment (MDM) is calculated in the framework of the minimal supersymmetric standard model (MSSM). In this paper, we discuss how the muon MDM depends on the parameters in the MSSM in detail. We show that the contribution of the superparticle loop becomes significant especially when $tan\ensuremath{\beta}$ is large. Numerically, it becomes of order ${10}^{\ensuremath{-}8}$-${10}^{\ensuremath{-}9}$ in a wide parameter space, which is within the reach of the new Brookhaven E821 experiment.

Connection between Feynman integrals having different values of the space-time dimension.

Abstract: A systematic algorithm for obtaining recurrence relations for dimensionally regularized Feynman integrals with respect to the space-time dimension {ital d} is proposed. The relation between {ital d}- and ({ital d}{minus}2)-dimensional integrals is given in terms of a differential operator for which an explicit formula can be obtained for each Feynman diagram. We show how the method works for one-, two-, and three-loop integrals. The new recurrence relations with respect to {ital d} are complementary to the recurrence relations which derive from the method of integration by parts. We find that the problem of the irreducible numerators in Feynman integrals can be naturally solved in the framework of the proposed generalized recurrence relations. {copyright} {ital 1996 The American Physical Society.}

Dilatonic black holes in higher curvature string gravity

Abstract: We give analytical arguments and demonstrate numerically the existence of black hole solutions of the 4D effective superstring action in the presence of Gauss-Bonnet quadratic curvature terms. The solutions possess nontrivial dilaton hair. The hair, however, is of "secondary type," in the sense that the dilaton charge is expressed in terms of the black hole mass. Our solutions are not covered by the assumptions of existing proofs of the "no-hair" theorem. We also find some alternative solutions with singular metric behavior, but finite energy. The absence of naked singularities in this system is pointed out.

Can Quantum-Mechanical Description of Physical Reality be Considered Complete?

Abstract: Phys. Rev. 48 (1935) 696–702 (Received July 13, 1935) It is shown that a certain “criterion of physical reality” formulated in a recent article with the above title by A. Einstein, B. Podolsky and N. Rosen contains an essential ambiguity when it is applied to quantum phenomena. In this connection a viewpoint termed “complementarity” is explained from which quantum-mechanical description of physical phenomena would seem to fulfill, within its scope, all rational demands of completeness.

Tensor-scalar gravity and binary-pulsar experiments

Abstract: Some recently discovered nonperturbative strong-field effects in tensor-scalar theories of gravitation are interpreted as a scalar analogue of ferromagnetism: "spontaneous scalarization." This phenomenon leads to very significant deviations from general relativity in conditions involving strong gravitational fields, notably binary-pulsar experiments. Contrary to solar-system experiments, these deviations do not necessarily vanish when the weak-field scalar coupling tends to zero. We compute the scalar "form factors" measuring these deviations, and notably a parameter entering the pulsar timing observable $\ensuremath{\gamma}$ through scalar-field-induced variations of the inertia moment of the pulsar. An exploratory investigation of the confrontation between tensor-scalar theories and binary-pulsar experiments shows that nonperturbative scalar field effects are already very tightly constrained by published data on three binary-pulsar systems. We contrast the probing power of pulsar experiments with that of solar-system ones by plotting the regions they exclude in a generic two-dimensional plane of tensor-scalar theories.

Gravitational energy in spherical symmetry.

Abstract: Various properties of the Misner-Sharp spherically symmetric gravitational energy E are established or reviewed. In the Newtonian limit of a perfect fluid, E yields the Newtonian mass to leading order and the Newtonian kinetic and potential energy to the next order. For test particles, the corresponding H\'aj\'{\i}\ifmmode \check{c}\else \v{c}\fi{}ek energy is conserved and has the behavior appropriate to energy in the Newtonian and special-relativistic limits. In the small-sphere limit, the leading term in E is the product of volume and the energy density of the matter. In vacuo, E reduces to the Schwarzschild energy. At null and spatial infinity, E reduces to the Bondi-Sachs and Arnowitt-Deser-Misner energies, respectively. The conserved Kodama current has charge E. A sphere is trapped if Eg1/2r, marginal if E=1/2r, and untrapped if E1/2r, where r is the areal radius. A central singularity is spatial and trapped if Eg0, and temporal and untrapped if E0. On an untrapped sphere, E is nondecreasing in any outgoing spatial or null direction, assuming the dominant energy condition. It follows that E\ensuremath{\ge}0 on an untrapped spatial hypersurface with a regular center, and E\ensuremath{\ge}1/2${\mathit{r}}_{0}$ on an untrapped spatial hypersurface bounded at the inward end by a marginal sphere of radius ${\mathit{r}}_{0}$. All these inequalities extend to the asymptotic energies, recovering the Bondi-Sachs energy loss and the positivity of the asymptotic energies, as well as proving the conjectured Penrose inequality for black or white holes. Implications for the cosmic censorship hypothesis and for general definitions of gravitational energy are discussed. \textcopyright{} 1996 The American Physical Society.

Thermal inflation and the moduli problem.

Abstract: In supersymmetric theories a field can develop a vacuum expectation value M\ensuremath{\gg}${10}^{3}$ GeV, even though its mass m is of order ${10}^{2}$ to ${10}^{3}$ GeV. The finite temperature in the early Universe can hold such a field at zero, corresponding to a false vacuum with an energy density ${\mathit{V}}_{0}$\ensuremath{\sim}${\mathit{m}}^{2}$${\mathit{M}}^{2}$. When the temperature falls below ${\mathit{V}}_{0}^{1/4}$, the thermal energy density becomes negligible and an era of thermal inflation begins. It ends when the field rolls away from zero at a temperature of order m, corresponding to of order 10 e-folds of inflation which does not affect the density perturbation generated during ordinary inflation. Thermal inflation can solve the Polonyi or moduli problem if M is within one or two orders of magnitude of ${10}^{12}$ GeV. Parametric resonance may lead to rapid partial reheating giving a high enough temperature for a variety of methods of baryogenesis. One can also have double thermal inflation which can solve the Polonyi or moduli problem even more efficiently. \textcopyright{} 1996 The American Physical Society.

Weak scale superstrings.

Abstract: Recent developments in string duality suggest that the string scale may not be irrevocably tied to the Planck scale Two explicit but unrealistic examples are described where the ratio of the string scale to the Planck scale is arbitrarily small Solutions that are more realistic may exist in the intermediate coupling or {open_quote}{open_quote}truly strong coupling{close_quote}{close_quote} region of the heterotic string Weak scale superstrings have dramatic experimental consequences for both collider physics and cosmology {copyright} {ital 1996 The American Physical Society}

Cosmological-parameter determination with microwave background maps.

Abstract: The angular power spectrum of the cosmic microwave background (CMB) contains information on virtually all cosmological parameters of interest, including the geometry of the Universe (Ω), the baryon density, the Hubble constant (h), the cosmological constant (Λ), the number of light neutrinos, the ionization history, and the amplitudes and spectral indices of the primordial scalar and tensor perturbation spectra. We review the imprint of each parameter on the CMB. Assuming only that the primordial perturbations were adiabatic, we use a covariance-matrix approach to estimate the precision with which these parameters can be determined by a CMB temperature map as a function of the fraction of sky mapped, the level of pixel noise, and the angular resolution. For example, with no prior information about any of the cosmological parameters, a full-sky CMB map with 0.5° angular resolution and a noise level of 15 μK per pixel can determine Ω, h, and Λ with standard errors of ±0.1 or better, and provide determinations of other parameters which are inaccessible with traditional observations. Smaller beam sizes or prior information on some of the other parameters from other observations improves the sensitivity. The dependence on the underlying cosmological model is discussed.

Search templates for gravitational waves from inspiraling binaries: Choice of template spacing.

Abstract: Gravitational waves from inspiraling, compact binaries will be searched for in the output of the LIGO-VIRGO interferometric network by the method of ``matched filtering''---i.e., by correlating the noisy output of each interferometer with a set of theoretical wave form templates. These search templates will be a discrete subset of a continuous, multiparameter family, each of which approximates a possible signal. The search might be performed hierarchically, with a first pass through the data using a low threshold and a coarsely spaced, few-parameter template set, followed by a second pass on threshold-exceeding data segments, with a higher threshold and a more finely spaced template set that might have a larger number of parameters. Alternatively, the search might involve a single pass through the data using the larger threshold and finer template set. This paper extends and generalizes the Sathyaprakash-Dhurandhar (SD) formalism for choosing the discrete, finely spaced template set used in the final (or sole) pass through the data, based on the analysis of a single interferometer. The SD formalism is rephrased in geometric language by introducing a metric on the continuous template space from which the discrete template set is drawn. This template metric is used to compute the loss of signal-to-noise ratio and reduction of event rate which result from the coarseness of the template grid. Correspondingly, the template spacing and total number N of templates are expressed, via the metric, as functions of the reduction in event rate. The theory is developed for a template family of arbitrary dimensionality (whereas the original SD formalism was restricted to a single nontrivial dimension). The theory is then applied to a simple ${\mathrm{post}}^{1}$-Newtonian template family with two nontrivial dimensions. For this family, the number of templates N in the finely spaced grid is related to the spacing-induced fractional loss L of event rate and to the minimum mass ${\mathit{M}}_{\mathrm{min}}$ of the least massive star in the binaries for which one searches by N\ensuremath{\sim}2\ifmmode\times\else\texttimes\fi{}${10}^{5}$(0.1/L)(0.2${\mathit{M}}_{\mathrm{\ensuremath{\bigodot}}}$/${\mathit{M}}_{\mathrm{min}}$${)}^{2.7}$ for the first LIGO interferometers and by N\ensuremath{\sim}8\ifmmode\times\else\texttimes\fi{}${10}^{6}$(0.1/L)(0.2${\mathit{M}}_{\mathrm{\ensuremath{\bigodot}}}$/${\mathit{M}}_{\mathrm{min}}$${)}^{2.7}$ for advanced LIGO interferometers. This is several orders of magnitude greater than one might have expected based on Sathyaprakash's discovery of a near degeneracy in the parameter space, the discrepancy being due to that paper's high choice of ${\mathit{M}}_{\mathrm{min}}$ and less stringent choice of L. The computational power P required to process the steady stream of incoming data from a single interferometer through the closely spaced set of templates is given in floating-point operations per second by P\ensuremath{\sim}3\ifmmode\times\else\texttimes\fi{}${10}^{10}$(0.1/L)(0.2${\mathit{M}}_{\mathrm{\ensuremath{\bigodot}}}$/${\mathit{M}}_{\mathrm{min}}$${)}^{2.7}$ for the first LIGO interferometers and by P\ensuremath{\sim}4\ifmmode\times\else\texttimes\fi{}${10}^{11}$(0.1/L)(0.2${\mathit{M}}_{\mathrm{\ensuremath{\bigodot}}}$/${\mathit{M}}_{\mathrm{min}}$${)}^{2.7}$ for advanced LIGO interferometers. This will be within the capabilities of LIGO-era computers, but a hierarchical search may still be desirable to reduce the required computing power. \textcopyright{} 1996 The American Physical Society.

Solitonic strings and BPS saturated dyonic black holes.

Abstract: We consider a six-dimensional solitonic string solution described by a conformal chiral null model with nontrivial $N=4$ superconformal transverse part. It can be interpreted as a five-dimensional dyonic solitonic string wound around a compact fifth dimension. The conformal model is regular with the short-distance ("throat") region equivalent to a Wess-Zumino-Witten (WZW) theory. At distances larger than the compactification scale the solitonic string reduces to a dyonic static spherically symmetric black hole of toroidally compactified heterotic string. The new four-dimensional solution is parametrized by five charges, saturates the Bogomol'nyi bound, and has a nontrivial dilaton-axion field and moduli fields of a two-torus. When acted on by combined $T$- and $S$-duality transformations it serves as a generating solution for all the static spherically symmetric Bogomol'nyi-Prasad-Sommerfield saturated configurations of the low-energy heterotic string theory compactified on a six-torus. Solutions with regular horizons have the global space-time structure of extreme Reissner-Nordstr\"om black holes with the non-zero thermodynamic entropy which depends only on conserved (quantized) charge vectors. The independence of the thermodynamic entropy on moduli and axion-dilaton couplings strongly suggests that it should have a microscopic interpretation as counting degeneracy of underlying string configurations. This interpretation is supported by arguments based on the corresponding six-dimensional conformal field theory. The expression for the level of the WZW theory describing the throat region implies a renormalization of the string tension by a product of magnetic charges, thus relating the entropy and the number of oscillations of the solitonic string in compact directions.

Free energy of QCD at high temperature.

Abstract: Effective-field-theory methods are used to separate the free energy for a non-Abelian gauge theory at high temperature $T$ into the contributions from the momentum scales $T$, $\mathrm{gT}$, and ${g}^{2}T$, where $g$ is the coupling constant at the scale $2\ensuremath{\pi}T$. The effects of the scale $T$ enter through the coefficients in the effective Lagrangian for the three-dimensional effective theory obtained by dimensional reduction. These coefficients can be calculated as power series in ${g}^{2}$. The contribution to the free energy from the scale $\mathrm{gT}$ can be calculated using perturbative methods in the effective theory. It can be expressed as an expansion in $g$ starting at order ${g}^{3}$. The contribution from the scale ${g}^{2}T$ must be calculated using nonperturbative methods, but nevertheless it can be expanded in powers of $g$ beginning at order ${g}^{6}$. We calculate the free energy explicitly to order ${g}^{5}$. We also outline the calculations necessary to obtain the free energy to order ${g}^{6}$.

Non-Abelian Weizsäcker-Williams field and a two-dimensional effective color charge density for a very large nucleus.

Abstract: We consider a very large ultrarelativistic nucleus. Assuming a simple model of the nucleus and weak coupling we find a classical solution for the gluon field of the nucleus and construct the two-dimensional color charge density for McLerran-Venugopalan model out of it. We prove that the density of states distribution, as a function of color charge density, is Gaussian, confirming the assumption made by McLerran and Venugopalan.

Color-octet quarkonia production

Abstract: Gluon fragmentation represents the dominant source of high energy prompt quarkonia at hadron colliders. Fragmentation approximations break down, however, when a quarkonium’s tranvserse momentum becomes comparable to its mass. In this paper we identify a large class of color-octet diagrams that mediate quarkonia production at all energies and reduce to the dominant set of gluon fragmentation graphs in the high p⊥ limit. They contribute to quarkonia differential cross sections at the same order as color-singlet diagrams and bring theoretical predictions for Υ and Ψ production at the Fermilab Tevatron into agreement with experimental measurements. Using recent CDF data we extract numerical values for bottomonia and charmonia color-octet matrix elements which are consistent with NRQCD scaling rules. We also find that quarkonia generated via the color-octet mechanism are strongly polarized at low as well as high energies. Spin alignment measurements can thus test the color-octet quarkonia production picture.

Black plane solutions in four-dimensional spacetimes.

Abstract: The static, plane symmetric solutions and cylindrically symmetric solutions of Einstein-Maxwell equations with a negative cosmological constant are investigated. These black configurations are asymptotically anti-de Sitter-type not only in the transverse directions, but also in the membrane or string directions. Their causal structure is similar to that of Reissner-Nordstr\"om black holes, but their Hawking temperature goes with ${M}^{\frac{1}{3}}$, where $M$ is the ADM mass density. We also discuss the static plane solutions in Einstein-Maxwell-dilaton gravity with a Liouville-type dilaton potential. The presence of the dilaton field changes drastically the structure of solutions. They are asymptotically "anti-de Sitter-" or "de Sitter-type" depending on the parameters in the theory.

Relativity Parameters Determined from Lunar Laser Ranging

Abstract: Analysis of 24 years of lunar laser ranging data is used to test the principle of equivalence, geodetic precession, the PPN parameters beta and gamma, and G/G. Recent data can be fitted with a rms scatter of 3 cm. (a) Using the Nordtvedt effect to test the principle of equivalence, it is found that the Moon and Earth accelerate alike in the Sun's field. The relative accelerations match to within 5 x 10(exp -13) . This limit, combined with an independent determination of y from planetary time delay, gives beta. Including the uncertainty due to compositional differences, the parameter beta differs from unity by no more than 0.0014; and, if the weak equivalence principle is satisfied, the difference is no more than 0.0006. (b) Geodetic precession matches its expected 19.2 marc sec/yr rate within 0.7%. This corresponds to a 1% test of gamma. (c) Apart from the Nordtvedt effect, beta and gamma can be tested from their influence on the lunar orbit. It is argued theoretically that the linear combination 0.8(beta) + 1.4(gamma) can be tested at the 1% level of accuracy. For solutions using numerically derived partial derivatives, higher sensitivity is found. Both 6 and y match the values of general relativity to within 0.005, and the linear combination beta+ gamma matches to within 0,003, but caution is advised due to the lack of theoretical understanding of these sensitivities. (d) No evidence for a changing gravitational constant is found, with absolute value of G/G less than or equal to 8 x lO(exp -12)/yr. There is significant sensitivity to G/G through solar perturbations on the lunar orbit.

Hawking spectrum and high frequency dispersion.

Abstract: We study the spectrum of created particles in two-dimensional black hole geometries for a linear, Hermitian scalar field satisfying a Lorentz noninvariant field equation with higher spatial derivative terms that are suppressed by powers of a fundamental momentum scale ${k}_{0}$. The preferred frame is the "free-fall frame" of the black hole. This model is a variation of Unruh's sonic black hole analogy. We find that there are two qualitatively different types of particle production in this model: a thermal Hawking flux generated by "mode conversion" at the black hole horizon, and a nonthermal spectrum generated via scattering off the background into negative free-fall frequency modes. This second process has nothing to do with black holes and does not occur for the ordinary wave equation because such modes do not propagate outside the horizon with positive Killing frequency. The horizon component of the radiation is astonishingly close to a perfect thermal spectrum: for the smoothest metric studied, with Hawking temperature ${T}_{H}\ensuremath{\simeq}0.0008{k}_{0}$, agreement is of order ${(\frac{{T}_{H}}{{k}_{0}})}^{3}$ at frequency $\ensuremath{\omega}={T}_{H}$, and agreement to order $\frac{{T}_{H}}{{k}_{0}}$ persists out to $\frac{\ensuremath{\omega}}{{T}_{H}}\ensuremath{\simeq}45$ where the thermal number flux is \ensuremath{\sim}${10}^{\ensuremath{-}20}$. The flux from scattering dominates at large $\ensuremath{\omega}$ and becomes many orders of magnitude larger than the horizon component for metrics with a "kink," i.e., a region of high curvature localized on a static world line outside the horizon. This nonthermal flux amounts to roughly 10% of the total luminosity for the kinkier metrics considered. The flux exhibits oscillations as a function of frequency which can be explained by interference between the various contributions to the flux.

Dyonic BPS saturated black holes of heterotic string on a six-torus.

Abstract: Within effective heterotic superstring theory compactified on a six-torus we derive minimum energy (supersymmetric), static, spherically symmetric solutions, which are manifestly invariant under the target space O(6,22) and the strong-weak coupling SL(2) duality symmetries with 28 electric and 28 magnetic charges subject to one constraint. The class of solutions with a constant axion corresponds to dyonic configurations subject to two charge constraints, with purely electric (or purely magnetic) and dyonic configurations preserving 1/2 and 1/4 of {ital N}=4 supersymmetry, respectively. General dyonic configurations in this class have a space-time of extreme Reissner-Nordstr{umlt o}m black holes while configurations with more constrained charges have a null or a naked singularity. {copyright} {ital 1996 The American Physical Society.}

Hadronic photon-photon interactions at high energies.

Abstract: Photon-photon collisions are investigated in the framework of the two-component dual parton model. The model contains contributions from direct, resolved soft, and resolved hard interactions. All free parameters of the model are determined in fits to hadron-hadron and photon-hadron cross section data. The model is shown to agree well with hadron production data from hadron-hadron and photon-hadron collisions. The multiparticle production in hadron-hadron, photon-hadron, and photon-photon collisions as predicted by the model is compared. Strong differences are only found as a function of the transverse momentum variable. The hadron production in photon-photon collisions at present and future electron-positron colliders is studied using photon spectra according to bremsstrahlung, beamstrahlung, and backscattered laser radiation.

Entropy of nonextreme charged rotating black holes in string theory.

Abstract: We give the explicit expression for four-dimensional rotating charged black hole solutions of $N=4$ (or $N=8$) superstring vacua, parametrized by the ADM mass, four charges [two electric and two magnetic charges, each arising from a different U(1) gauge factor], and the angular momentum (as well as the asymptotic values of four toroidal moduli of a two-torus and the dilaton-axion field). The explicit form of the thermodynamic entropy is parametrized in a suggestive way as a sum of the product of the "left-moving" and the "right-moving" terms, which may have an interpretation in terms of the microscopic degrees of freedom of the corresponding $D$-brane configuration. We also give an analogous parametrization of the thermodynamic entropy for the recently obtained five-dimensional rotating charged black holes parametrized by the ADM mass, three U(1) charges, and two rotational parameters (as well as the asymptotic values of one toroidal modulus and the dilaton).

Does back reaction enforce the averaged null energy condition in semiclassical gravity

Abstract: The expectation value $〈{T}_{\mathrm{ab}}〉$ of the renormalized stress-energy tensor of quantum fields generically violates the classical, local positive energy conditions of general relativity. Nevertheless, it is possible that $〈{T}_{\mathrm{ab}}〉$ may still satisfy some nonlocal positive energy conditions. Most prominent among these nonlocal conditions is the averaged null energy condition (ANEC), which states that $\ensuremath{\int}〈{T}_{\mathrm{ab}}〉{k}^{a}{k}^{b}d\ensuremath{\lambda}g~0$ along any complete null geodesic, where ${k}^{a}$ denotes the geodesic tangent, with affine parameter $\ensuremath{\lambda}$. If the ANEC holds, then traversable wormholes cannot occur. However, although the ANEC holds in Minkowski spacetime, it is known that the ANEC can be violated in curved spacetimes if one is allowed to choose the spacetime and quantum state arbitrarily, without imposition of the semiclassical Einstein equation, ${G}_{\mathrm{ab}}=8\ensuremath{\pi}〈{T}_{\mathrm{ab}}〉$. In this paper, we investigate whether the ANEC holds for self-consistent solutions of the semiclassical Einstein equation. We study a free, linear, massless scalar field with arbitrary curvature coupling in the context of perturbation theory about the flat spacetime/vacuum solution, and we modify the perturbed semiclassical equations by the "reduction of order" procedure to eliminate spurious solutions. We also restrict attention to the limit in which the length scales determined by the state and metric are much larger than the Planck length. At first order in the metric and state perturbations, and for pure states of the scalar field, we find that the ANEC integral vanishes, as it must for any positivity result to hold. For mixed states, the ANEC integral can be negative. However, we prove that if we average the ANEC integral transverse to the geodesic, using a suitable Planck scale smearing function, a strictly positive result is obtained in all cases except for the trivial flat spacetime/vacuum solution. Similar results hold for pure states at second order in perturbation theory, when we additionally specialize to the situation where incoming classical gravitational radiation does not dominate the first-order metric perturbation. These results suggest---in agreement with conclusions drawn by Ford and Roman from entirely independent arguments---that if traversable wormholes do exist as self-consistent solutions of the semiclassical equations, they cannot be macroscopic but must be "Planck scale." In the course of our analysis, we investigate a number of more general issues relevant to doing perturbative expansions of the semiclassical equations off of flat spacetime, including an analysis of the nature of the semiclassical Einstein equation and of prescriptions for extracting physically relevant solutions. A large portion of our paper is devoted to the treatment of these more general issues.