We give matrix and supergravity descriptions of type IIA F strings polarizing into cylindrical D2 branes. When a RR four-form field strength $F_4$ is turned on in a supersymmetric fashion (with 4 supercharges), a complete analysis of the solutions reveals the existence of a moduli space of $F\overrightarrow{1}\mathrm{D}2$ polarizations for some fractional strengths of the perturbation, and of no polarization whatsoever for all other strengths of the perturbation. This is a very intriguing phenomenon, whose physical implications we can only speculate about. In the matrix description of the polarization we use the non-Abelian Born-Infeld action in an extreme regime, where the commutators of the fields are much larger than 1. The validity of the results we obtain provides a direct confirmation of this action, although it does not confirm or disprove the symmetrized trace prescription.

The superdiffeomorphisms invariant description of N-extended spinning particle is constructed in the framework of the nonlinear realization approach. The action is universal for all values of N and describes the time evolution of $D+2\mathrm{}$ different group elements of the superdiffeomorphisms group of the $\mathrm{}(1,N)\mathrm{}$ superspace. The form of this action coincides with the one-dimensional version of the gravity action, analogous to Trautman’s.

We generalize the Weisskopf-Wigner theory for the line shape and transition rates of decaying states to the case of the energy-driven stochastic Schrödinger equation that has been used as a phenomenology for state vector reduction. Within the standard approximations used in the Weisskopf-Wigner analysis, and assuming that the perturbing potential inducing the decay has vanishing matrix elements within the degenerate manifold containing the decaying state, the stochastic Schrödinger equation linearizes. Solving the linearized equations, we find no change from the standard analysis in the line shape or the transition rate per unit time. The only effect of the stochastic terms is to alter the early time transient behavior of the decay, in a way that eliminates the quantum Zeno effect. We apply our results to estimate experimental bounds on the parameter governing the stochastic effects. In addition, elegant stochastic-theoretic methods suggested by Diósi are used to rederive the principal results, without the assumptions needed to linearize the stochastic equation, and to give analogous results for the Rabi oscillations of a two-level system.

We present a coordinate-independent method for extracting the mass ${(M}_{\Delta })$ and angular momentum ${(J}_{\Delta })$ of a black hole in numerical simulations. This method, based on the isolated horizon framework, is applicable both at late times when the black hole has reached equilibrium, and at early times when the black holes are widely separated. Assuming that the spatial hypersurfaces used in a given numerical simulation are such that apparent horizons exist and have been located on these hypersurfaces, we show how $J_{\Delta }$ and $M_{\Delta }$ can be determined in terms of only those quantities which are intrinsic to the apparent horizon. We also present a numerical method for finding the rotational symmetry vector field (required to calculate $J_{\Delta })$ on the horizon.

We investigate here the occurrence and nature of a naked singularity for the inhomogeneous gravitational collapse of higher dimensional Tolman-Bondi dust clouds. The final state of collapse, a black hole or naked singularity, turns out to depend on the order of the first nonvanishing derivative of the density at the center. The study of the collapse along radial null geodesics seems to suggest that higher dimensions $(D>~6)$ respect the CCH, if one chooses a smooth analytic density profile as initial data.

We investigate the problem of detecting gravitational waves from binaries of nonspinning black holes with masses $m=5\mathrm{}–{20M}_{\odot },$ moving on quasicircular orbits, which are arguably the most promising sources for first-generation ground-based detectors. We analyze and compare all the currently available post-Newtonian approximations for the relativistic two-body dynamics; for these binaries, different approximations predict different waveforms. We then construct examples of detection template families that embed all the approximate models and that could be used to detect the true gravitational-wave signal (but not to characterize accurately its physical parameters). We estimate that the fitting factor for our detection families is $\gtrsim 0.95$ (corresponding to an event rate loss $\lesssim 15\%)$ and we estimate that the discretization of the template family, for $\sim {10}^4$ templates, increases the loss to $\lesssim 20\%.$

We present a model with minimal assumptions for nonthermal leptogenesis with almost degenerate superheavy right-handed neutrinos in a supersymmetric setup. In this scenario the gauge singlet inflaton is directly coupled to the right-handed (s)neutrinos with a mass heavier than the inflaton mass. This helps to avoid potential problems which can naturally arise otherwise. The inflaton decays into standard model leptons and Higgs bosons via off-shell right-handed (s)neutrinos and reheats the Universe. The same channel is also responsible for generating the lepton asymmetry, thus requiring no stage of preheating in order to excite superheavy (s)neutrinos. The suppressed decay rate of the inflaton naturally leads to a sufficiently low reheat temperature, which in addition, prevents any wash out of the yielded asymmetry. We will particularly elaborate on important differences from leptogenesis with on-shell (s)neutrinos. It is shown that for nearly degenerate neutrinos a successful leptogenesis can be accommodated for a variety of inflationary models with a rather wide ranging inflationary scale.

We study the production of a heavy CP-odd $A^0$ boson in association with a photon $e^{+}{e}^{-}\to A^0\gamma$ and a Z boson $e^{+}{e}^{-}\to A^{0}Z$ as well as the single production of $A^0$ via $e^{+}{e}^{-}\to {\nu }_e{\overline{\nu }}_e{A}^0$ in the minimal supersymmetric standard model (MSSM) with CP violating phases. In the case of $e^{+}{e}^{-}\to A^0\gamma {/A}^{0}Z,$ we show that the squark contribution, which vanishes in the MSSM with real parameters, turns out to be sizable in the presence of CP violating phases in the soft supersymmetric parameters. For $e^{+}{e}^{-}\to {\nu }_e{\overline{\nu }}_e{A}^0$ in both the two Higgs doublet model and the MSSM with real parameters, the cross section does not reach observable rates at a Next Linear Collider. It is found that, with a large CP violating phase for $A_t,$ cross sections of the order of 0.08 fb are attainable for all the processes $e^{+}{e}^{-}\to A^0\gamma ,$ $e^{+}{e}^{-}\to A^{0}Z,$ and $e^{+}{e}^{-}\to {\nu }_e{\overline{\nu }}_e{A}^0.$

We compute several coefficients needed for $O\left(a\right)\mathrm{}$ improvement of currents in perturbation theory, using the Brodsky-Lepage-Mackenzie prescription for choosing an optimal scale $q^{*}.$ We then compare the results to non-perturbative calculations. Normalization factors of the vector and axial vector currents show good agreement, especially when allowing for small two-loop effects. On the other hand, there are large discrepancies in the coefficients of $O\left(a\right)\mathrm{}$ improvement terms. We suspect that they arise primarily from power corrections inherent in the nonperturbative methods.

We present a lattice QCD calculation of the scattering phase shift for the $I=2\mathrm{}S$-wave two-pion system using the finite size method proposed by Lüscher. We work in the quenched approximation employing the standard plaquette action at $\beta =5.9\mathrm{}$ for gluons and the Wilson fermion action for quarks. The phase shift is extracted from the energy eigenvalues of the two-pion system, which are obtained by a diagonalization of the pion four-point function evaluated for a set of relative spatial momenta. In order to change the momentum of the two-pion system, calculations are carried out on ${24}^3\times 60,$ ${32}^3\times 60,$ and ${48}^3\times 60$ lattices. The phase shift is successfully calculated over the momentum range $0<\mathrm{}{p}^2<0.3\mathrm{}{\mathrm{GeV}}^2.$

We show with two numerical examples that the conventional expansion in powers of the field for the critical potential of 3-dimensional $O\left(N\right)\mathrm{}$ models in the large-$N$ limit does not converge for values of ${\phi }^2$ larger than some critical value. This can be explained by the existence of conjugated branch points in the complex ${\phi }^2$ plane. Padé approximants $[L+3/L]$ for the critical potential apparently converge at large ${\phi }^2.$ This allows high-precision calculation of the fixed point in a more suitable set of coordinates. We argue that the singularities are generic and not an artifact of the large-$N$ limit. We show that ignoring these singularities may lead to inaccurate approximations.

“Dimension bubbles” of the type previously studied by Blau and Guendelman [S.K. Blau and E.I. Guendelman, Phys. Rev. D $40,$ 1909 (1989)], which effectively enclose a region of 5D spacetime and are surrounded by a region of 4D spacetime, can arise in a 5D theory with a compact extra dimension that is dimensionally reduced to give an effective 4D theory. These bubbles with thin domain walls can be stabilized against total collapse in a rather natural way by a scalar field which, as in the case with “ordinary” nontopological solitons, traps light scalar particles inside the bubble.

We present a supersymmetric version of the two-brane Randall-Sundrum scenario, with arbitrary brane tensions $T_1$ and $T_2,$ subject to the bound $|T_{1,2}|<~\sqrt{-6{\Lambda }_5},$ where ${\Lambda }_5<0\mathrm{}$ is the bulk cosmological constant. Dimensional reduction gives $N=1,$ $D=4\mathrm{}$ supergravity, with the cosmological constant ${\Lambda }_4$ in the range $\frac{1}{2}{\Lambda }_5<~{\Lambda }_4<~0.$ The case with ${\Lambda }_4=0\mathrm{}$ requires $T_1=-T_2=\sqrt{-6{\Lambda }_5}.$ This work unifies and generalizes previous approaches to the supersymmetric Randall-Sundrum scenario. It also shows that the Randall-Sundrum fine-tuning is not a consequence of supersymmetry.

We extend and improve earlier estimates of the ability of the proposed LISA (Laser Interferometer Space Antenna) gravitational wave detector to place upper bounds on the graviton mass $m_g$ by comparing the arrival times of gravitational and electromagnetic signals from binary star systems. We show that the best possible limit on $m_g$ obtainable this way is $\sim 50$ times better than the current limit set by solar system measurements. Among currently known, well-understood binaries, 4U1820-30 is the best for this purpose; LISA observations of 4U1820-30 should yield a limit $\approx 3-4$ times better than the present solar system bound. AM CVn-type binaries offer the prospect of improving the limit by a factor of $10,$ if such systems can be better understood by the time of the LISA mission. We briefly discuss the likelihood that radio and optical searches during the next decade will yield binaries that more closely approach the best possible case.

In a previous paper we set up the Wheeler-DeWitt equation which describes the quantum general relativistic collapse of a spherical dust cloud. In the present paper we specialize this equation to the case of matter perturbations around a black hole, and show that, in the WKB approximation, the wave functional describes an eternal black hole in equilibrium with a thermal bath at Hawking temperature.

We construct open cosmic string solutions in Schwarzschild black hole and nondilatonic black p-brane backgrounds. These strings can be thought to stretch between two D-branes or between a D-brane and the horizon in curved space-time. We study small fluctuations around these solutions and discuss their basic properties.

We present new solutions to Einstein-Maxwell-dilaton-axion (EMDA) gravity in four dimensions describing black holes which asymptote to the linear dilaton background. In the nonrotating case they can be obtained as the limiting geometry of dilaton black holes. The rotating solutions (possibly endowed with a NUT parameter) are constructed using a generating technique based on the $\mathrm{Sp}(4,R)\mathrm{}$ duality of the EMDA system. In a certain limit (with no event horizon present) our rotating solutions coincide with supersymmetric Israel-Wilson-Perjès type dilaton-axion solutions. In the presence of an event horizon supersymmetry is broken. The temperature of the static black holes is constant, and their mass does not depend on it, so the heat capacity is zero. We investigate geodesics and wave propagation in these spacetimes and find superradiance in the rotating case. Because of the nonasymptotically flat nature of the geometry, certain modes are reflected from infinity; in particular, all superradiant modes are confined. This leads to a classical instability of the rotating solutions. The nonrotating linear dilaton black holes are shown to be stable against spherical perturbations.

Time-dependent solutions of supergravity and string theory are studied. The examples are obtained from de Sitter deformation of gauge-gravity dualities, analytical continuation of static solutions, and “exactly solvable” worldsheet models. Among other things, it is shown that turning on a Hubble parameter in the background of a confining gauge theory in four dimensions can restore chiral symmetry. Some of the solutions obtained from analytical continuation have the interpretation of a universe with a bounce separating a big bang from a big crunch singularity. In the worldsheet context, it is argued why string propagation close to a Milne-type cosmological singularity might be physically nonsingular.

A cosmological model in which primordial black holes (PBHs) are present in the cosmic fluid at some instant ${t=t}_0$ is investigated. The time $t_0$ is naturally identified with the end of the inflationary period. The PBHs are assumed to be nonrelativistic in the comoving fluid, to have the same mass, and may be subject to evaporation for $t>\mathrm{}{t}_0.$ Our present work is related to an earlier paper of Zimdahl and Pavón [Phys. Rev. D 58, 103506 (1998)], but in contradistinction to these authors we assume that the (negative) production rate of the PBHs is zero. This assumption appears to us to be more simple and more physical. The consequences of the formalism are worked out. In particular, the four-divergence of the entropy four-vector in combination with the second law of thermodynamics show in a clear way how the case of PBH evaporation corresponds to a production of entropy. Accretion of radiation onto the black holes is neglected. We consider both a model where two different subfluids interact, and a model involving one single fluid only. In the latter case an effective bulk viscosity naturally appears in the formalism.

Tentative observations and theoretical considerations have recently led to renewed interest in models of fundamental physics in which certain “constants” vary in time. Assuming fixed black hole mass and the standard form of the Bekenstein-Hawking entropy, Davies, Davis and Lineweaver have argued that the laws of black hole thermodynamics disfavor models in which the fundamental electric charge e changes. I show that with these assumptions, similar considerations severely constrain “varying speed of light” models, unless we are prepared to abandon cherished assumptions about quantum gravity. Relaxation of these assumptions permits sensible theories of quantum gravity with “varying constants,” but also eliminates the thermodynamic constraints, though the black hole mass spectrum may still provide some restrictions on the range of allowable models.