Experimental results for the bremsstrahlung energy loss of 149, 207, and 287 GeV electrons in thin Ir, Ta, and Cu targets are presented. For each target and energy, a comparison between simulated values based on the Landau-Pomeranchuk-Migdal (LPM) suppression of incoherent bremsstrahlung is shown. For the electron energies investigated, the LPM effect enters the quantum regime where the recoil imposed on the electron by the emitted photon becomes important. Good agreement between simulations based on Migdal’s theory and data from the experiment is found, indicating that the LPM suppression is well understood also in the quantum regime. Results from a comparison between simulations with the “threshold” energy $E_{\mathrm{LPM}}$ as a free parameter and the data are shown. This analysis reproduces the expected trend as a function of nominal radiation length, but yields values that tend to be low compared to Migdal’s theory.

Numerical solutions of Einstein, scalar, and gauge field equations are found for static and inflating defects in a higher-dimensional spacetime. The defects have $\mathrm{}(3+1)\mathrm{}$-dimensional core and magnetic monopole configuration in $n=3\mathrm{}$ extra dimensions. For the symmetry-breaking scale $\eta$ below the critical value ${\eta }_c,$ the defects are characterized by a flat worldsheet geometry and asymptotically flat extra dimensions. The critical scale ${\eta }_c$ is comparable to the higher-dimensional Planck scale and has some dependence on the gauge and scalar couplings. For $\eta ={\eta }_c,$ the extra dimensions degenerate into a “cigar,” and for $\eta >{\eta }_c$ all static solutions are singular. The singularity can be removed if the requirement of staticity is relaxed and defect cores are allowed to inflate. The inflating solutions have de Sitter worldsheets and cigar geometry in the extra dimensions. Exact analytic solutions describing the asymptotic behavior of these inflating monopoles are found and the parameter space of these solutions is analyzed.

Gamma-ray bursts are believed to originate in the core collapse of massive stars. This produces an active MeV-nucleus containing a rapidly rotating Kerr black hole of mass $M_H$ and angular velocity ${\Omega }_H\simeq {1/2M}_H,$ surrounded by a uniformly magnetized torus of angular velocity ${\Omega }_T=\eta {\Omega }_H$ represented by two counteroriented current rings. We quantify black-hole–spin interactions with the torus and charged particles along open magnetic flux tubes subtended by the event horizon at a finite half-opening angle ${\theta }_H.$ A major output of $E_{\mathrm{gw}}\simeq 4\times {10}^{53}\left(\eta {/0.1\left)\right(M}_H{/7M}_{\odot }\right)\mathrm{erg}$ is radiated in gravitational waves of frequency $f_{\mathrm{gw}}\simeq 500\left(\eta {/0.1\left)\right(7M}_{\odot }{/M}_H\right)$ Hz by a quadrupole mass moment in the torus when its minor-to-major radius is less than 0.3260. The durations correspond to the lifetime $T_s$ of black hole spin, determined by a stability condition of poloidal magnetic field energy-to-kinetic energy $<1/15\mathrm{}$ in the torus. Consistent with observations of GRB-SNe, we find (i) $T_s\simeq 90\mathrm{s}$ (tens of s), (ii) aspherical SNe of kinetic energy $E_{\mathrm{SN}}\simeq 2\times {10}^{51}\mathrm{erg}$ $(2\mathrm{}\times {10}^{51}\mathrm{erg}$ in SN1998bw), and (iii) GRB-energies $E_{\gamma }\simeq 2\times {10}^{50}\mathrm{erg}(3\mathrm{}\times {10}^{50}\mathrm{erg}),$ upon associating ${\theta }_H$ with poloidal curvature of the magnetosphere. GRB-SNe occur perhaps about once a year within $D=100\mathrm{}\mathrm{Mpc}.$ Correlating LIGO-VIRGO detectors enables searches for nearby events and their spectral closure density $6\times {10}^{-9}$ around 250 Hz in the stochastic background radiation in gravitational waves. At current sensitivity, LIGO-Hanford may place an upper bound around ${150M}_{\odot }$ in GRB030329. Upcoming all-sky supernovae surveys may provide distances to GRB-SNe, conceivably coincident with weak wide-angle GRB emissions similar to the nearby event GRB980425/SN1998bw. Detection of $E_{\mathrm{gw}}$ thus provides a method for identifying Kerr black holes by calorimetry.

Various methods of searching for supersymmetric dark matter are sensitive to weakly interacting massive particles with different properties. One consequence of this is that the phenomenology of dark matter detection can vary dramatically in different supersymmetric breaking scenarios. In this paper, we consider the sensitivities to supersymmetric dark matter of different detection methods and techniques in a wide variety of supersymmetric breaking scenarios. We discuss the ability of various astrophysical experiments, such as direct experiments, gamma-ray satellites, neutrino telescopes, and positron and antiproton cosmic ray experiments, to test various supersymmetry breaking scenarios. We also discuss what information can be revealed about supersymmetry breaking by combining results from complementary experiments. We place emphasis on the differences between various experimental techniques.

The existing cosmological constraints on theories with large extra dimensions rely on the thermal production of the Kaluza-Klein (KK) modes of gravitons and radions in the early Universe. Successful inflation and reheating, as well as baryogenesis, typically requires the existence of a TeV-scale field in the bulk, most notably the inflaton. The nonthermal production of KK modes with masses of order 100 GeV accompanying the inflaton decay sets the lower bounds on the fundamental scale $M_{*}.$ For a 1-TeV inflaton, the late decay of these modes distorts the successful predictions of big bang nucleosynthesis unless $M_{*}>35,$ 13, 7, 5, and 3 TeV for two, three, four, five, and six extra dimensions, respectively. This improves the existing bounds from cosmology on $M_{*}$ for four, five, and six extra dimensions. Even more stringent bounds are derived for a heavier inflaton.

We estimate the probability of detecting gamma rays from the annihilation of neutralino dark matter in dense, central regions of Milky Way substructure. We characterize galactic substructure statistically based on Monte Carlo realizations of the formation of a Milky Way–like halo using a semianalytic method that has been calibrated against the results of high-resolution N-body simulations. We find that it may be possible for the upcoming experiments GLAST and VERITAS, working in concert, to detect gamma rays from dark matter substructure if the neutralino is relatively light ${(M}_{\chi }\lesssim 100\mathrm{GeV}),$ while for $M_{\chi }\gtrsim 500\mathrm{GeV}$ such a detection would be unlikely. We perform most of our calculations within the framework of the standard $\Lambda \mathrm{CDM}$ cosmological model; however, we also investigate the robustness of our results to various assumptions and find that the probability of detection is sensitive to poorly constrained input parameters, particularly those that characterize the primordial power spectrum. Specifically, the best-fitting power spectrum of the WMAP team, with a running spectral index, predicts roughly a factor of fifty fewer detectable subhalos compared to the standard $\Lambda \mathrm{CDM}$ cosmological model with scale-invariant power spectrum. We conclude that the lack of a detected gamma-ray signal gives very little information about the supersymmetric parameter space due to uncertainties associated with both the properties of substructure and cosmological parameters.

We study the dynamics of thermalization and the approach to equilibrium in the classical ${\phi }^4$ theory in $1+1$ spacetime dimensions. At thermal equilibrium we exploit the equivalence between the classical canonical averages and transfer matrix quantum traces of the anharmonic oscillator to obtain exact results for the temperature dependence of several observables, which provide a set of criteria for thermalization. In this context, comparing to the exact results we find that the Hartree approximation is remarkably accurate in equilibrium. The nonequilibrium dynamics is studied by numerically solving the equations of motion in light-cone coordinates for a broad range of initial conditions and energy densities. The long time evolution is described by several distinct stages, all characterized by a cascade of energy towards the ultraviolet. After an initial transient stage, the spatiotemporal gradient terms become larger than the nonlinear term, and there emerges a stage of universal cascade. This cascade starts at a time scale $t_0$ independent of the initial conditions (except for very low energy density). During this stage the power spectra feature universal scaling behavior and the front of the cascade $\overline{k}\mathrm{}\left(t\right)\mathrm{}$ moves to the ultraviolet as a power law $\overline{k}\mathrm{}\left(t\right)\mathrm{}\sim t^{\alpha }$ with $\alpha \lesssim 0.25$ an exponent weakly dependent on the energy density alone. The wake behind the cascade is described as a state of Local Thermodynamic Equilibrium (LTE) with all correlations being determined by the equilibrium functional form with an effective time dependent temperature $T_{\mathrm{eff}}\mathrm{}\left(t\right),$ which slowly decreases with time as $\sim t^{-\alpha }.$ Two well separated time scales emerge: while $T_{\mathrm{eff}}\mathrm{}\left(t\right)\mathrm{}$ varies slowly, the wave vectors in the wake with $k<\mathrm{}\overline{k}\mathrm{}\left(t\right)\mathrm{}$ attain LTE on much shorter time scales. This universal scaling stage ends when the front of the ultraviolet cascade reaches the cutoff at a time scale $t_1\sim a^{-1/\alpha }.$ Virialization starts to set much earlier than LTE. We find that strict thermalization is achieved only for an infinite time scale.

We prove by explicit construction that there exists a maximal slicing of the Schwarzschild spacetime such that the lapse has zero gradient at the puncture. This boundary condition has been observed to hold in numerical evolutions, but in the past it was not clear whether the numerically obtained maximal slices exist analytically. We show that our analytical result agrees with numerical simulation. Given the analytical form for the lapse, we can derive that at late times the value of the lapse at the event horizon approaches the value $\frac{3}{16}\sqrt{3}\approx 0.3248,$ justifying the numerical estimate of 0.3 that has been used for black hole excision in numerical simulations. We present our results for the nonextremal Reissner-Nordström metric, generalizing previous constructions of maximal slices.

Many quantum field theoretical models possess nontrivial solutions which are stable for topological reasons. We construct a self-consistent example for a self-interacting scalar field—the quantum (or dressed) kink—using a two particle irreducible effective action in the Hartree approximation. This new solution includes quantum fluctuations determined self-consistently and nonperturbatively at the 1-loop resummed level and allowed to back react on the classical mean-field profile. This dressed kink is static under the familiar Hartree equations for the time evolution of quantum fields. Because the quantum fluctuation spectrum is lower lying in the presence of the defect, the quantum kink has a lower rest energy than its classical counterpart. However its energy is higher than well-known strict 1-loop results, where back reaction and fluctuation self-interactions are omitted. We also show that the quantum kink exists at finite temperature and that its profile broadens as temperature is increased until it eventually disappears.

The nature of the fuel that drives today’s cosmic acceleration is an open and tantalizing mystery. We entertain the suggestion that the acceleration is not the manifestation of yet another new ingredient in the cosmic gas tank, but rather a signal of our first real lack of understanding of gravitational physics. By requiring that the underlying gravity theory respect Birkhoff’s law, we derive the modified gravitational force law necessary to generate any given cosmology, without reference to the fundamental theory, revealing modifications of gravity at scales typically much smaller than today’s horizon. We discuss how, through these modifications, the growth of density perturbations, the late-time integrated Sachs-Wolfe effect, and even solar-system measurements may be sensitive to whether today’s cosmic acceleration is generated by dark energy or modified gravitational dynamics, and are subject to imminent observational discrimination. We argue how these conclusions can be more generic, and probably not dependent on the validity of Birkhoff’s law.

We make a thorough investigation of the asymptotic quasinormal modes of the four- and five-dimensional Schwarzschild black holes for scalar, electromagnetic, and gravitational perturbations. Our numerical results give full support to all the analytical predictions by Motl and Neitzke for the leading term. We also compute the first-order corrections analytically, by extending to higher dimensions, previous work of Musiri and Siopsis and find excellent agreement with the numerical results. For a generic spacetime dimension number D the first-order corrections go as ${1/n}^{\left(D-3\right)/\left(D-2\right)}.$ This means that there is a more rapid convergence to the asymptotic value for the five-dimensional case than for the four-dimensional case, as we also show numerically.

We investigate four-dimensional effective theories which are obtained by dimensional reduction of multidimensional cosmological models with factorizable geometry and we consider the interaction between conformal excitations of the internal space (geometrical moduli excitations) and Abelian gauge fields. It is assumed that the internal space background can be stabilized by minima of an effective potential. The conformal excitations over such a background have the form of massive scalar fields (gravitational excitons) propagating in the external spacetime. We discuss cosmological and astrophysical implications of the interaction between gravexcitons and four-dimensional photons as well as constraints arising on multidimensional models of the type considered in our paper. In particular, we show that due to the experimental bounds on the variation of the fine-structure constant, gravexcitons should decay before nucleosynthesis starts. For a successful nucleosynthesis, the masses of the decaying gravexcitons should be $m\gtrsim {10}^4\mathrm{GeV}.$ Furthermore, we discuss the possible contribution of gravexcitons to ultrahigh-energy cosmic rays. It is shown that, at energies $E\sim {10}^{20}\mathrm{eV},$ the decay length of gravexcitons with masses $m\gtrsim {10}^4\mathrm{GeV}$ is very small, but that for $m\lesssim {10}^2\mathrm{GeV}$ it becomes much larger than the Greisen-Zatsepin-Kuzmin cutoff distance. Finally, we investigate the possibility for gravexciton-photon oscillations in strong magnetic fields of astrophysical objects. The corresponding estimates indicate that even the high-magnetic-field strengths B of magnetars (special types of pulsars with $B>\mathrm{}{B}_{\mathrm{critical}}\sim 4.4\times {10}^{13}\mathrm{G})$ are not sufficient for an efficient and copious production of gravexcitons.

We consider here whether it is possible to recover cosmic censorship when a transition is made to higher-dimensional spacetimes, by studying the spherically symmetric dust collapse in an arbitrary higher spacetime dimension. It is pointed out that if only black holes are to result as the end state of a continual gravitational collapse, several conditions must be imposed on the collapsing configuration, some of which may appear to be restrictive, and we need to study carefully if these can be suitably motivated physically in a realistic collapse scenario. It would appear, that, in a generic higher-dimensional dust collapse, both black holes and naked singularities would develop as end states as indicated by the results here. The mathematical approach developed here generalizes and unifies the earlier available results on higher-dimensional dust collapse as we point out. Further, the dependence of black hole or naked singularity end states as collapse outcomes on the nature of the initial data from which the collapse develops is brought out explicitly and in a transparent manner as we show here. Our method also allows us to consider here in some detail the genericity and stability aspects related to the occurrence of naked singularities in gravitational collapse.

It is shown that gravity in 2+1 dimensions coupled to point particles provides a nontrivial example of doubly special relativity (DSR). This result is obtained by interpretation of previous results in the field and by exhibiting an explicit transformation between the phase space algebra for one particle in 2+1 gravity found by Matschull and Welling and the corresponding DSR algebra. The identification of 2+1 gravity as a DSR system answers a number of questions concerning the latter, and resolves the ambiguity of the basis of the algebra of observables. Based on this observation a heuristic argument is made that the algebra of symmetries of ultra high energy particle kinematics in 3+1 dimensions is described by some DSR theory.

We present a formalism for Newtonian multifluid hydrodynamics derived from an unconstrained variational principle. This approach provides a natural way of obtaining the general equations of motion for a wide range of hydrodynamic systems containing an arbitrary number of interacting fluids and superfluids. In addition to spatial variations we use “time shifts” in the variational principle, which allows us to describe dissipative processes with entropy creation, such as chemical reactions, friction or the effects of external non-conservative forces. The resulting framework incorporates the generalization of the entrainment effect originally discussed in the case of the mixture of two superfluids by Andreev and Bashkin. In addition to the conservation of energy and momentum, we derive the generalized conservation laws of vorticity and helicity, and the special case of Ertel’s theorem for the single perfect fluid. We explicitly discuss the application of this framework to thermally conducting fluids, superfluids, and superfluid neutron star matter. The equations governing thermally conducting fluids are found to be more general than the standard description, as the effect of entrainment usually seems to be overlooked in this context. In the case of superfluid ${}^4\mathrm{He}$ we recover the Landau-Khalatnikov equations of the two-fluid model via a translation to the “orthodox” framework of superfluidity, which is based on a rather awkward choice of variables. Our two-fluid model for superfluid neutron star matter allows for dissipation via mutual friction and also “transfusion” via $\beta$ reactions between the neutron fluid and the proton-electron fluid.

A class of exact solutions of the Faddeev model, that is, the modified $\mathrm{SO}\left(3\right)\mathrm{}$ nonlinear $\sigma$ model with the Skyrme term, is obtained in four dimensional Minkowskian spacetime. The solutions are interpreted as the isothermal coordinates of a Riemannian surface. One special solution of the static vortex type is investigated numerically. It is also shown that the Faddeev model is equivalent to the mesonic sector of the $\mathrm{SU}\left(2\right)\mathrm{}$ Skyrme model where the baryon number current vanishes.

The decays of B mesons to a charmless vector $\mathrm{}\left(V\right)\mathrm{}$ and pseudoscalar $\mathrm{}\left(P\right)\mathrm{}$ meson are analyzed within a framework of flavor SU(3) in which symmetry breaking is taken into account through ratios of decay constants in tree $\mathrm{}\left(T\right)\mathrm{}$ amplitudes but exact SU(3) is assumed for color-suppressed and penguin amplitudes. The magnitudes and relative phases of tree and penguin amplitudes are extracted from data, the symmetry assumption is tested, and predictions are made for rates and $\mathrm{CP}$ asymmetries in as-yet-unseen decay modes. A key assumption for which we perform some tests and suggest others is a relation between penguin amplitudes in which the spectator quark is incorporated into either a pseudoscalar meson or a vector meson. Values of $\gamma$ slightly restricting the range currently allowed by fits to other data are favored, but outside this range there remain acceptable solutions which cannot be excluded solely on the basis of present $\overrightarrow{B}\mathrm{VP}$ experiments.

We reconsider the ${}^{187}\mathrm{Re}$ bound on the variation of the fine-structure constant. We combine the meteoritic measurement with several present-day lab measurements to firmly establish the quantitative upper limit to the time variation over the age of the solar system. We find that the relative change of the fine-structure constant between its present value and $\alpha$ of $\sim 4.6\mathrm{Gyr}$ ago is consistent with zero, $\Delta \alpha /\alpha =[-8\pm 8(1\mathrm{}\sigma \left)\right]\times {10}^{-7}.$ We also rederive this bound in models where all gauge and Yukawa couplings vary in an interdependent manner, as would be expected in unified theories.

We compute the gravitational radiation generated in the evolution of a family of close binary black hole configurations, using a combination of numerical and perturbative approximation methods. We evolve the binaries with spins s aligned or counteraligned with the orbital angular momentum from near the innermost stable circular orbit down to the final single rotating black hole. For the moderately spinning holes studied here the remnant Kerr black holes formed at the end of an inspiral process have rotation parameters $a/M\approx {0.72+0.32(s/m}_H),$ suggesting it is difficult (though not excluded) to end up with near maximally rotating holes from such scenarios.