Showing papers in "Physical Review D in 1995"

Rigorous QCD analysis of inclusive annihilation and production of heavy quarkonium

Abstract: A rigorous QCD analysis of the inclusive annihilation decay rates of heavy quarkonium states is presented. The effective-field-theory framework of nonrelativistic QCD is used to separate the short-distance scale of annihilation, which is set by the heavy quark mass M, from the longer-distance scales associated with quarkonium structure. The annihilation decay rates are expressed in terms of nonperturbative matrix elements of four-fermion operators in nonrelativistic QCD, with coefficients that can be computed using perturbation theory in the coupling constant ${\mathrm{\ensuremath{\alpha}}}_{\mathit{s}}$(M). The matrix elements are organized into a hierarchy according to their scaling with v, the typical velocity of the heavy quark. An analogous factorization formalism is developed for the production cross sections of heavy quarkonium in processes involving momentum transfers of order M or larger. The factorization formulas are applied to the annihilation decay rates and production cross sections of S-wave states at next-to-leading order in ${\mathit{v}}^{2}$ and P-wave states at leading order in ${\mathit{v}}^{2}$.

Hilbert space representation of the minimal length uncertainty relation.

Abstract: The existence of a minimal observable length has long been suggested in quantum gravity as well as in string theory. In this context a generalized uncertainty relation has been derived which quantum theoretically describes the minimal length as a minimal uncertainty in position measurements. Here we study in full detail the quantum mechanical structure which underlies this uncertainty relation. DAMTP/94-105, hep-th/9412167, and Phys.Rev.D52:1108 (1995)

N=2 extremal black holes.

Abstract: It is shown that extremal magnetic black hole solutions of N=2 supergravity coupled to vector multiplets ${\mathit{X}}^{\mathrm{\ensuremath{\Lambda}}}$ with a generic holomorphic prepotential F(${\mathit{X}}^{\mathrm{\ensuremath{\Lambda}}}$) can be described as supersymmetric solitons which interpolate between maximally symmetric limiting solutions at spatial infinity and the horizon. A simple exact solution is found for the special case that the ratios of the ${\mathit{X}}^{\mathrm{\ensuremath{\Lambda}}}$ are real, and it is seen that the logarithm of the conformal factor of the spatial metric equals the K\"ahler potential on the vector multiplet moduli space. Several examples are discussed in detail.

Evolution of three-dimensional gravitational waves: Harmonic slicing case

Abstract: We perform numerical simulations of a three-dimensional (3D) time evolution of pure gravitational waves. We use a conformally flat and K=0 initial condition for the evolution of the spacetime. We adopt several slicing conditions to check whether a long time integration is possible in those conditions. For the case in which the amplitude of the gravitational waves is low, a long time integration is possible by using the harmonic slice and the maximal slice, while in the geodesic slice (\ensuremath{\alpha}=1) it is not possible. As in the axisymmetric case and also in the 3D case, gravitational waves with a sufficiently high amplitude collapse by their self-gravity and their final fates seem to be as black holes. In this case, the singularity avoidance property of the harmonic slice seems weak, so that it may be inappropriate for the formation problems of the black hole. By means of the gauge-invariant wave extraction technique we compute the waveform of the gravitational waves at an outer region. We find that the nonlinearity of Einstein gravity induces the higher multipole modes even if only a quadrupole mode exists initially.

Low energy dynamical supersymmetry breaking simplified.

Abstract: We present a model in which supersymmetry is dynamically broken at comparatively low energies. Previous efforts to construct simple models of this sort have been hampered by the presence of axions. The present model, which exploits an observation of Bagger, Poppitz and Randall to avoid this problem, is far simpler than previous constructions. Models of this kind do not suffer from the naturalness difficulties of conventional supergravity models, and make quite definite predictions for physics over a range of scales from $100$'s of GeV to $1000$'s of TeV. Thus ``Renormalizable Visible Sector Models'' are a viable alternative to more conventional approaches. Our approach also yields a viable example of hidden sector dynamical supersymmetry breaking.

Real Ashtekar variables for Lorentzian signature space-times.

Abstract: I suggest in this letter a new strategy to attack the problem of the reality conditions in the Ashtekar approach to classical and quantum general relativity. By writing a modified Hamiltonian constraint in the usual $SO(3)$ Yang-Mills phase space I show that it is possible to describe space-times with Lorentzian signature without the introduction of complex variables. All the features of the Ashtekar formalism related to the geometrical nature of the new variables are retained; in particular, it is still possible, in principle, to use the loop variables approach in the passage to the quantum theory. The key issue in the new formulation is how to deal with the more complicated Hamiltonian constraint that must be used in order to avoid the introduction of complex fields.

Universe reheating after inflation

Abstract: We study the problem of scalar particle production after inflation by an inflaton field which is oscillating rapidly relative to the expansion of the universe. We use the framework of the chaotic inflation scenario with quartic and quadratic inflaton potentials. Particles produced are described by a quantum scalar field \ensuremath{\chi}, which is coupled to the inflaton via linear and quadratic couplings. The particle production effect is studied using the standard technique of Bogolyubov transformations. Particular attention is paid to parametric resonance phenomena which take place in the presence of the quickly oscillating inflaton field. We have found that in the region of applicability of perturbation theory the effects of parametric resonance are crucial, and estimates based on first-order Born approximation often underestimate the particle production. In the case of the quartic inflaton potential V(cphi)=\ensuremath{\lambda}${\mathit{cphi}}^{4}$, the particle production process is very efficient for either type of coupling between the inflaton field and the scalar field \ensuremath{\chi} even for small values of coupling constants. The energy density of the universe after the decay of the inflaton oscillations is in this case a factor [\ensuremath{\lambda} ln(1/\ensuremath{\lambda})${]}^{\mathrm{\ensuremath{-}}1}$ times larger than the corresponding estimates based on first-order Born approximation. In the case of the quadratic inflaton potential the reheating process depends crucially on the type of coupling between the inflaton and the scalar field \ensuremath{\chi} and on the magnitudes of the coupling constants. If the inflaton coupling to fermions and its linear (in inflaton field) coupling to scalar fields are suppressed, then, as previously discussed by Kofman, Linde, and Starobinsky, the inflaton field will eventually decouple from the rest of the matter, and the residual inflaton oscillations may provide the (cold) dark matter of the universe. In the case of the quadratic inflaton potential we obtain the lowest and the highest possible bounds on the effective energy density of the inflaton field when it freezes out.

Spin networks and quantum gravity.

Abstract: We introduce a new basis on the state space of non-perturbative quantum gravity. The states of this basis are linearly independent, are well defined in both the loop representation and the connection representation, and are labeled by a generalization of Penrose's spin netoworks. The new basis fully reduces the spinor identities (SU(2) Mandelstam identities) and simplifies calculations in non-perturbative quantum gravity. In particular, it allows a simple expression for the exact solutions of the Hamiltonian constraint (Wheeler-DeWitt equation) that have been discovered in the loop representation. Since the states in this basis diagnolize operators that represent the three geometry of space, such as the area and volumes of arbitrary surfaces and regions, these states provide a discrete picture of quantum geometry at the Planck scale.

Sonic analogue of black holes and the effects of high frequencies on black hole evaporation.

Abstract: The naive calculation of black hole evaporation makes the thermal emission depend on the arbitrary high frequency behavior of the theory where the theory is certainly wrong. Using the sonic analogue to black holes, ``dumb holes,'' I show numerically that a change in the dispersion relation at high frequencies does not seem to alter the evaporation process, lending weight to the reality of the black hole evaporation process. I also suggest a reason for the insensitivity of the process to the high frequency regime.

Gravity and global symmetries.

Abstract: There exists a widely held notion that gravitational effects can strongly violate global symmetries. If this is correct, it may lead to many important consequences. We argue, in particular, that nonperturbative gravitational effects in the axion theory lead to a strong violation of CP invariance unless they are suppressed by an extremely small factor g\ensuremath{\lesssim}${10}^{\mathrm{\ensuremath{-}}82}$. One could hope that this problem disappears if one represents the global symmetry of a pseudoscalar axion field as a gauge symmetry of the Ogievetsky-Polubarinov-Kalb-Ramond antisymmetric tensor field. We show, however, that this gauge symmetry does not protect the axion mass from quantum corrections. The amplitude of gravitational effects violating global symmetries could be strongly suppressed by ${\mathit{e}}^{\mathrm{\ensuremath{-}}\mathit{S}}$, where S is the action of a wormhole which may absorb the global charge. Unfortunately, in a wide variety of theories based on the Einstein theory of gravity the action appears to be fairly small, S\ensuremath{\sim}10. However, we find that the existence of wormholes and the value of their action are extremely sensitive to the structure of space on the nearly Planckian scale. We consider several examples (Kaluza-Klein theory, conformal anomaly, ${\mathit{R}}^{2}$ terms) which show that modifications of the Einstein theory on the length scale l\ensuremath{\lesssim}10${\mathit{M}}_{\mathit{P}}^{\mathrm{\ensuremath{-}}1}$ may strongly suppress violation of global symmetries. We find also that in string theory there exists an additional suppression of topology change by the factor ${\mathit{e}}^{\mathrm{\ensuremath{-}}8\mathrm{\ensuremath{\pi}}2}$/${\mathit{g}}^{2}$. This effect is strong enough to save the axion theory for the natural values of the stringy gauge coupling constant.

Coalescing binary systems of compact objects to (post)5/2-Newtonian order. V. Spin effects.

Abstract: We examine the effects of spin-orbit and spin-spin couplings on the inspiral of a coalescing binary system of spinning compact objects and on the gravitational radiation emitted therefrom. Using a formalism developed by Blanchet, Damour, and Iyer we calculate the contributions due to the spins of the bodies to the symmetric trace-free radiative multipole moments which are used to calculate the waveform, energy loss, and angular momentum loss from the inspiraling binary. Using equations of motion which include terms due to spin-orbit and spin-spin couplings we evolve the orbit of a coalescing binary and use the orbit to calculate the emitted gravitational waveform. We find the spins of the bodies affect the waveform in several ways: (1) the spin terms contribute to the orbital decay of the binary, and thus to the accumulated phase of the gravitational waveform; (2) the spins cause the orbital plane to precess, which changes the orientation of the orbital plane with respect to an observer, thus causing the shape of the waveform to be modulated; (3) the spins contribute directly to the amplitude of the waveform. We discuss the size and importance of spin effects for the case of two coalescing neutron stars, and for the case of a neutron star orbiting a rapidly rotating 10${\mathit{M}}_{\mathrm{\ensuremath{\bigodot}}}$ black hole.

Comparison of the Noether charge and Euclidean methods for computing the entropy of stationary black holes.

Abstract: The entropy of stationary black holes has recently been calculated by a number of different approaches. Here we compare the Noether charge approach (defined for any diffeomorphism invariant Lagrangian theory) with various Euclidean methods, specifically, (i) the microcanonical ensemble approach of Brown and York, (ii) the closely related approach of Ba\~nados, Teitelboim, and Zanelli which ultimately expresses black hole entropy in terms of the Hilbert action surface term, (iii) another formula of Ba\~nados, Tetelboim, and Zanelli (also used by Susskind and Uglum) which views black hole entropy as conjugate to a conical deficit angle, and (iv) the pair creation approach of Garfinkle, Giddings, and Strominger. All of these approaches have a more restrictive domain of applicability than the Noether charge approach. Specifically, approaches (i) and (ii) appear to be restricted to a class of theories satisfying certain properties litsed in Sec. II; approach (iii) appears to require the choice of a ``regularizing'' scheme to deal with curvature singularities (except in the case of Lovelock gravity theories), and approach (iv) requires the existence of suitable instanton solutions. However, we show that within their domains of applicability, all of these approaches yield results in agreement with the Noether charge approach. In the course of our analysis we generalize the definition of the Brown-York quasilocal energy to a much more general class of diffeomorphism invariant, Lagrangian theories of gravity. In an appendix we show that in an arbitrary diffeomorphism invariant theory of gravity the ``volume term'' in the ``off-shell'' Hamiltonian associated with a time evolution vector field ${\mathit{t}}^{\mathit{a}}$ always can be expressed as the spatial integral of ${\mathit{t}}^{\mathit{a}}$${\mathit{scrC}}_{\mathit{a}}$, where ${\mathit{scrC}}_{\mathit{a}}$=0 are the constraints associated with the diffeomorphism invariance.

Dust as a standard of space and time in canonical quantum gravity.

Abstract: The coupling of the metric to an incoherent dust introduces into spacetime a privileged dynamical reference frame and time foliation. The comoving coordinates of the dust particles and the proper time along the dust worldlines become canonical coordinates in the phase space of the system. The Hamiltonian constraint can be resolved with respect to the momentum that is canonically conjugate to the dust time. Formal imposition of the resolved constraint as an operator restriction on the quantum states yields a functional Schr\"odinger equation. The ensuing Hamiltonian density has an extraordinary feature: it depends only on the geometric variables, not on the dust coordinates or time. This has three important consequences. First, the functional Schr\"odinger equation can be solved by separating the dust time from the geometric variables. Second, disregarding the standard factor-ordering difficulties, the Hamiltonian densities strongly commute and therefore can be simultaneously defined by spectral analysis. Third, the standard constraint system of vacuum gravity is cast into a form in which it generates a true Lie algebra. The particles of dust introduce into space a privileged system of coordinates that allows the supermomentum constraint to be solved explicitly. The Schr\"odinger equation yields a formally conserved inner product that can be written in terms of either the instantaneous state functionals or the solutions of constraints. Gravitational observables admit a similar dual representation. Examples of observables are given, though neither the intrinsic metric nor the extrinsic curvature are observables. This comes as close as one can reasonably expect to a satisfactory phenomenological quantization scheme that is free of most of the problems of time.

Determination of inflationary observables by cosmic microwave background anisotropy experiments.

Abstract: Inflation produces nearly scale-invariant scalar and tensor perturbation spectra which lead to anisotropy in the cosmic microwave background (CMB). The amplitudes and shapes of these spectra can be parametrized by ${\mathit{Q}}_{\mathit{S}}^{2}$, r\ensuremath{\equiv}${\mathit{Q}}_{\mathit{T}}^{2}$/${\mathit{Q}}_{\mathit{S}}^{2}$, ${\mathit{n}}_{\mathit{S}}$, and ${\mathit{n}}_{\mathit{T}}$ where ${\mathit{Q}}_{\mathit{S}}^{2}$ and ${\mathit{Q}}_{\mathit{T}}^{2}$ are the scalar and tensor contributions to the square of the CMB quadrupole and ${\mathit{n}}_{\mathit{S}}$ and ${\mathit{n}}_{\mathit{T}}$ are the power-law spectral indices. Even if we restrict ourselves to information from angles greater than one-third of a degree, three of these observables can be measured with some precision. The combination ${105}_{\mathit{S}}^{1\mathrm{\ensuremath{-}}\mathit{n}}$${\mathit{Q}}_{\mathit{S}}^{2}$ can be known to better than \ifmmode\pm\else\textpm\fi{}0.3%. The scalar index ${\mathit{n}}_{\mathit{S}}$ can be determined to better than \ifmmode\pm\else\textpm\fi{}0.02. The ratio r can be known to about \ifmmode\pm\else\textpm\fi{}0.1 for ${\mathit{n}}_{\mathit{S}}$\ensuremath{\simeq}1 and slightly better for smaller ${\mathit{n}}_{\mathit{S}}$. The precision with which ${\mathit{n}}_{\mathit{T}}$ can be measured depends weakly on ${\mathit{n}}_{\mathit{S}}$ and strongly on r. For ${\mathit{n}}_{\mathit{S}}$\ensuremath{\simeq}1, ${\mathit{n}}_{\mathit{T}}$ can be determined with a precision of about \ifmmode\pm\else\textpm\fi{}0.056(1.5+r)/r. A full-sky experiment with a 20 arc min beam using technology available today, similar to those being planned by several groups, can achieve the above precision. Good angular resolution is more important than high signal-to-noise ratio; for a given detector sensitivity and observing time a smaller beam provides more information than a larger beam. The uncertainties in ${\mathit{n}}_{\mathit{S}}$ and r are roughly proportional to the beam size. We briefly discuss the effects of uncertainty in the Hubble constant, baryon density, cosmological constant, and ionization history.

Effective Hamiltonian for B → X s e + e − Beyond Leading Logarithms in the NDR and HV Schemes ∗

Abstract: We calculate the next-to-leading QCD corrections to the effective Hamiltonian for B\ensuremath{\rightarrow}${\mathit{X}}_{\mathit{s}}$${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{\ensuremath{-}}}$ in the NDR and tHV schemes. We give for the first time analytic expressions for the Wilson coefficient of the operator ${\mathit{Q}}_{9}$=(s\ifmmode\bar\else\textasciimacron\fi{}b${)}_{\mathit{V}\mathrm{\ensuremath{-}}\mathit{A}}$(e\ifmmode\bar\else\textasciimacron\fi{}e${)}_{\mathit{V}}$ in the NDR and HV schemes. Calculating the relevant matrix elements of local operators in the spectator model we demonstrate the scheme independence of the resulting short-distance contribution to the physical amplitude. Keeping consistently only leading and next-to-leading terms, we find an analytic formula for the differential dilepton invariant mass distribution in the spectator model. A numerical analysis of the ${\mathit{m}}_{\mathit{t}}$, ${\mathrm{\ensuremath{\Lambda}}}_{\mathrm{MS}\mathrm{\ifmmode\bar\else\textasciimacron\fi{}}}$, and \ensuremath{\mu}=O(${\mathit{m}}_{\mathit{b}}$) dependences of this formula is presented. We compare our results with those given in the literature.

CPT, strings, and meson factories.

Abstract: Spontaneous breaking of CPT is possible in string theory. We show that it can arise at a level within reach of experiments at meson factories currently being built or designed. For \ensuremath{\varphi}, B, and \ensuremath{\tau}-charm factories, we discuss the likely experimental string signatures and provide estimates of the bounds that might be attained in these machines.

Entropy, area, and black hole pairs.

Abstract: We clarify the relation between gravitational entropy and the area of horizons. We first show that the entropy of an extreme Reissner-Nordstr\"om black hole is zero, despite the fact that its horizon has nonzero area. Next, we consider the pair creation of extremal and nonextremal black holes. It is shown that the action which governs the rate of this pair creation is directly related to the area of the acceleration horizon and (in the nonextremal case) the area of the black hole event horizon. This provides a simple explanation of the result that the rate of pair creation of nonextreme black holes is enhanced by precisely the black hole entropy. Finally, we discuss black hole annihilation, and argue that Planck scale remnants are not sufficient to preserve unitarity in quantum gravity.

Electroweak baryogenesis and standard model CP violation.

Abstract: We analyze the mechanism of electroweak baryogenesis proposed by Farrar and Shaposhnikov in which the phase of the CKM mixing matrix is the only source of [ital CP] violation. This mechanism is based on a phase separation of baryons via the scattering of quasiparticles by the wall of an expanding bubble produced at the electroweak phase transition. In agreement with the recent work of Gavela, Hernandez, Orloff, and Pene, we conclude the QCD damping effects reduce the asymmetry produced to a negligible amount. We interpret the damping as quantum decoherence. We compute the asymmetry analytically. Our analysis reflects the observation that only a thin, outer layer of the bubble contributes to the coherent scattering of the quasiparticles. The generality of our arguments rules out any mechanism of electroweak baryogenesis that does not make use of a new source of [ital CP] violation.

Global QCD Analysis and the CTEQ Parton Distributions

Abstract: The CTEQ program for the determination of parton distributions through a global QCD analysis of data for various hard scattering processes is fully described. A new set of distributions, CTEQ3, incorporating several new types of data is reported and compared to the two previous sets of CTEQ distributions. A comparison with current data is discussed in some detail. The remaining uncertainties in the parton distributions and methods to further reduce them are assessed. Comparisons with the results of other global analyses are also presented.

Gravitational waves from inspiraling compact binaries: Parameter estimation using second-post-Newtonian waveforms.

Abstract: The parameters of inspiraling compact binaries can be estimated using matched filtering of gravitational-waveform templates against the output of laser-interferometric gravitational-wave detectors. The estimates are most sensitive to the accuracy with which the phases of the template and signal waveforms match over the many cycles received in the detector frequency bandwidth. Using a recently calculated formula, accurate to second post-Newtonian (2PN) order [order (v/c${)}^{4}$, where v is the orbital velocity], for the frequency sweep (dF/dt) induced by gravitational radiation damping, we study the statistical errors in the determination of such source parameters as the ``chirp mass'' scrM, reduced mass \ensuremath{\mu}, and spin parameters \ensuremath{\beta} and \ensuremath{\sigma} (related to spin-orbit and spin-spin effects, respectively). We find that previous results using template phasing accurate to 1.5PN order actually underestimated the errors in scrM, \ensuremath{\mu}, and \ensuremath{\beta}. Templates with 2PN phasing yield somewhat larger measurement errors because the 2PN corrections act to suppress slightly the importance of spin-orbit contributions to the phase, thereby increasing the measurement error on \ensuremath{\beta}. This, in turn, results in larger measurement errors on scrM and \ensuremath{\mu} because of the strong correlations among the parameters. For two inspiraling neutron stars, the measurement errors increase by less than 16%.

Novel ‘‘no-scalar-hair’’ theorem for black holes

Abstract: We formulate a new ``no-hair'' theorem for black holes in general relativity which rules out a multicomponent scalar field dressing of any asymptotically flat, static, spherically symmetric black hole. The field is assumed to be minimally coupled to gravity, and to bear a non-negative energy density as seen by any observer, but its field Lagrangian need not be quadratic in the field derivatives. The proof centers on energy-momentum conservation and the Einstein equations. One kind of field ruled out is the Higgs field with a double (or multiple) well potential. The theorem is also proved for scalar-tensor gravity.

Semileptonic meson decays in the quark model: An update.

Abstract: The authors present the predictions of ISGW2, an update of the ISGW quark model for semileptonic meson decays. The updated model incorporates a number of features which should make it more reliable, including the constraints imposed by Heavy Quark Symmetry, hyperfine distortions of wave-functions, and form factors with more realistic high recoil behaviors.

Gravitational waves from the inspiral of a compact object into a massive, axisymmetric body with arbitrary multipole moments

Abstract: The gravitational waves, emitted by a compact object orbiting a much more massive central body, depend on the central body’s spacetime geometry. This paper is a first attempt to explore that dependence. For simplicity, the central body is assumed to be stationary, axially symmetric (but rotating), and reflection symmetric through an equatorial plane, so its (vacuum) spacetime geometry is fully characterized by two families of scalar multipole moments Ml and Sl with l=0,1,2,3,..., and it is assumed not to absorb any orbital energy (e.g., via waves going down a horizon or via tidal heating). Also for simplicity, the orbit is assumed to lie in the body’s equatorial plane and to be circular, except for a gradual shrinkage due to radiative energy loss. For this idealized situation, it is shown that several features of the emitted waves carry, encoded within themselves, the values of all the body’s multipole moments Ml, Sl (and thus, also the details of its full spacetime geometry). In particular, the body’s moments are encoded in the time evolution of the waves’ phase Φ(t) (the quantity that can be measurd with extremely high accuracy by interferometric gravitational-wave detectors), and they are also encoded in the gravitational-wave spectrum ΔE(f) (energy emitted per unit logarithmic frequency interval). If the orbit is slightly elliptical, the moments are also encoded in the evolution of its periastron precession frequency as a function of wave frequency, Ωρ(f); if the orbit is slightly inclined to the body’s equatorial plane, then they are encoded in its inclinational precession frequency as a function of wave frequency, Ωz(f). Explicit algorithms are derived for deducing the moments from ΔE(f), Ωρ(f), and Ωz(f). However, to deduce the moments explicitly from the (more accurately measurable) phase evolution Φ(t) will require a very difficult, explicit analysis of the wave generation process—a task far beyond the scope of this paper.

D* D pi and B* B pi couplings in QCD

Abstract: We calculate the ${\mathit{D}}^{\mathrm{*}}$D\ensuremath{\pi} and ${\mathit{B}}^{\mathrm{*}}$B\ensuremath{\pi} couplings using QCD sum rules on the light cone. In this approach, the large-distance dynamics is incorporated in a set of pion wave functions. We take into account two-particle and three-particle wave functions of twist 2, 3, and 4. The resulting values of the coupling constants are ${\mathit{g}}_{\mathit{D}}^{\mathrm{*}}$D\ensuremath{\pi}=12.5\ifmmode\pm\else\textpm\fi{}1 and ${\mathit{g}}_{\mathit{B}}^{\mathrm{*}}$B\ensuremath{\pi}=29\ifmmode\pm\else\textpm\fi{}3. From this we predict the partial width \ensuremath{\Gamma}(${\mathit{D}}^{\mathrm{*}+}$\ensuremath{\rightarrow}${\mathit{D}}^{0}$${\mathrm{\ensuremath{\pi}}}^{+}$)=32\ifmmode\pm\else\textpm\fi{}5 keV. We also discuss the soft-pion limit of the sum rules which is equivalent to the external axial field approach employed in earlier calculations. Furthermore, using ${\mathit{g}}_{\mathit{B}}^{\mathrm{*}}$B\ensuremath{\pi} and ${\mathit{g}}_{\mathit{D}}^{\mathrm{*}}$D\ensuremath{\pi} the pole dominance model for the B\ensuremath{\rightarrow}\ensuremath{\pi} and D\ensuremath{\rightarrow}\ensuremath{\pi} semileptonic form factors is compared with the direct calculation of these form factors in the same framework of ligh-cone sum rules.

Thin-shell wormholes: Linearization stability.

Abstract: The class of spherically symmetric thin-shell wormholes provides a particularly elegant collection of exemplars for the study of traversable Lorentzian wormholes. In the present paper we consider linearized (spherically symmetric) perturbations around some assumed static solution of the Einstein field equations. This permits us to relate stability issues to the (linearized) equation of state of the exotic matter which is located at the wormhole throat. {copyright} 1995 The American Physical Society.

Gluon production from non-Abelian Weizsäcker-Williams fields in nucleus-nucleus collisions.

Abstract: We consider the collisions of large nuclei using the theory of McLerran and Venugopalan. The two nuclei are ultrarelativistic and sources of non-Abelian Weizs\ifmmode\ddot\else\textasciidieresis\fi{}acker-Williams fields. These sources are in the end averaged over all color orientations locally with a Gaussian weight. We show that there is a solution of the equations of motion for the two nucleus scattering problem where the fields are time and rapidity independent before the collision. After the collision the solution depends on proper time, but is independent of rapidity. We show how to extract the produced gluons from the classical evolution of the fields.

Primordial spectral indices from generalized Einstein theories

Abstract: Primordial spectral indices are calculated to second order in slow-roll parameters for three closely related models of inflation, all of which contain a scalar field nonminimally coupled to the Ricci curvature scalar. In most cases, ${\mathit{n}}_{\mathit{s}}$ may be written as a function of the nonminimal curvature coupling strength \ensuremath{\xi} alone, with ${\mathit{n}}_{\mathit{s}}$(\ensuremath{\xi})\ensuremath{\le}1, although the constraints on \ensuremath{\xi} differ greatly between ``new inflation'' and ``chaotic inflation'' initial conditions. Under ``new inflation'' initial conditions, there are discrepancies between the values of ${\mathit{n}}_{\mathit{s}}$ as calculated in the Einstein frame and the Jordan frame. The sources for these discrepancies are addressed, and shown to have negligible effects on the numerical predictions for ${\mathit{n}}_{\mathit{s}}$. No such discrepancies affect the calculations under ``chaotic inflation'' initial conditions.

Electrons and positrons in the galactic cosmic rays.

Abstract: The detection of primary cosmic ray electrons with energies above 1 TeV implies the existence of a nearby, r\ensuremath{\le}100 pc, and relatively young, t\ensuremath{\le}${10}^{5}$ yr, source(s) of accelerated electrons. Therefore a correct treatment of the formation of the spectra of electrons during their propagation in the interstellar medium requires a separate consideration of the contribution of one (or a few) nearby source(s) from the contribution of distant (R\ensuremath{\ge}1 kpc) sources. To implement this approach, the problem of energy-dependent diffusive propagation of relativistic particles from a single source is considered, and the analytical solution to the diffusion equation in the general case of arbitrary energy losses and injection spectrum of primary particles is found. We show that in the framework of the proposed two-component approach, i.e., separating the contribution of the local (discrete) source(s) from the contribution of distant sources, it is possible to explain all the locally observed features of the energy spectrum of cosmic ray electrons from sub-GeV to TeV energies. In addition, assuming that the local source produces electrons and positrons in equal amounts, the model allows us to explain also the reported increase of the positron content in the flux above 10 GeV.

Description of the Riemannian geometry in the presence of conical defects.

Abstract: A consistent approach to the description of integral coordinate invariant functionals of the metric on manifolds ${\cal M}_{\alpha}$ with conical defects (or singularities) of the topology $C_{\alpha}\times\Sigma$ is developed. According to the proposed prescription ${\cal M}_{\alpha}$ are considered as limits of the converging sequences of smooth spaces. This enables one to give a strict mathematical meaning to a number of invariant integral quantities on ${\cal M}_{\alpha}$ and make use of them in applications. In particular, an explicit representation for the Euler numbers and Hirtzebruch signature in the presence of conical singularities is found. Also, higher dimensional Lovelock gravity on ${\cal M}_{\alpha}$ is shown to be well-defined and the gravitational action in this theory is evaluated. Other series of applications is related to computation of black hole entropy in the higher derivative gravity and in quantum 2-dimensional models. This is based on its direct statistical-mechanical derivation in the Gibbons-Hawking approach, generalized to the singular manifolds ${\cal M}_{\alpha}$, and gives the same results as in the other methods.