In gravitational theories with extra dimensions, it is argued that the existence of a positive vacuum energy generically implies catastrophic instability of our four-dimensional world. The most generic instability is a decompactification transition to growth of the extra dimensions, although other equally bad transitions may take place. This follows from simple considerations based on the form of the potential for the size modulus of the extra dimensions, and apparently offers a resolution of the conundrums presented by eternal de Sitter space. This argument is illustrated in the context of string theory with a general discussion of potentials generated by fluxes, wrapped branes, and stringy corrections. Moreover, it is unlikely that the present acceleration of the Universe represents an ongoing transition in a quintessence scenario rolling toward decompactification, unless the higher-dimensional theory has a cosmological constant.

We compare different methods used for nonperturbative calculations in strongly interacting fermionic systems. Mean field theory often shows a basic ambiguity related to the possibility to perform Fierz transformations. The results may then depend strongly on an unphysical parameter which reflects the choice of the mean field, thus limiting the reliability. This ambiguity is absent for Schwinger-Dyson equations or fermionic renormalization group equations. Also renormalization group equations in a partially bosonized setting can overcome the Fierz ambiguity if the truncation is chosen appropriately. This is reassuring since the partially bosonized renormalization group approach constitutes a very promising basis for the explicit treatment of condensates and spontaneous symmetry breaking even for situations where the bosonic correlation length is large.

We discuss the quantum scattering process in a moduli space consisting of two maximally charged dilaton black holes. The black hole moduli space geometry has different structures for arbitrary dimensions and various values of the dilaton coupling. We study the quantum effects of the different moduli space geometries with scattering process. Then, it is found that there is a resonance state on certain moduli spaces.

Development of large mass detectors for low-energy neutrinos and dark matter may allow supernova detection via neutrino-nucleus elastic scattering. An elastic-scattering detector could observe a few, or more, events per ton for a galactic supernova at 10 kpc $(3.1\mathrm{}\times {10}^{20}\mathrm{m}).\mathrm{}$ This large yield, a factor of at least 20 greater than that for existing light-water detectors, arises because of the very large coherent cross section and the sensitivity to all flavors of neutrinos and antineutrinos. An elastic scattering detector can provide important information on the flux and spectrum of ${\nu }_{\mu }$ and ${\nu }_{\tau }$ from supernovae. We consider many detectors and a range of target materials from ${}^4\mathrm{He}$ to ${}^{208}\mathrm{Pb}.$ Monte Carlo simulations of low-energy backgrounds are presented for the liquid-neon-based Cryogenic Low Energy Astrophysics with Noble gases detector. The simulated background is much smaller than the expected signal from a galactic supernova.

The cosmological dust has begun to settle. A likely picture is a universe comprised (predominantly) of three components: ordinary baryons $({\Omega }_B\approx 0.05),$ nonbaryonic dark matter $({\Omega }_{\mathrm{dark}}\approx 0.22)$ and dark energy $({\Omega }_{\Lambda }\approx 0.7).$ We suggest that the observed similarity of the abundances of ordinary baryons and nonbaryonic dark matter $({\Omega }_B/{\Omega }_{\mathrm{dark}}\approx 0.20)$ hints at an underlying similarity between the fundamental properties of ordinary and dark matter particles. This is necessarily the case if dark matter is identified with mirror matter. We examine a specific mirror matter scenario where ${\Omega }_B/{\Omega }_{\mathrm{dark}}\approx 0.20$ is naturally obtained.

The field dynamics in a rapidly expanding system is investigated by transforming from space-time to the rapidity–proper-time frame. The proper-time dependence of different contributions to the total energy is established. For systems characterized by a finite momentum cutoff, a freeze-out time can be defined after which the field propagation in rapidity space ends and the system decays into decoupled solitons, antisolitons, and local vacuum fluctuations. Numerical simulations of field evolutions on a lattice for the $\mathrm{}(1+1)\mathrm{}$-dimensional ${\Phi }^4$ model illustrate the general results and show that the freeze-out time and average multiplicities of kinks (plus antikinks) produced in this “phase transition” can be obtained from simple averages over the initial ensemble of field configurations. An extension to explicitly include additional dissipation is discussed. The validity of an adiabatic approximation for the case of an overdamped system is investigated. The $\mathrm{}(3+1)\mathrm{}$-dimensional generalization may serve as model for baryon-antibaryon production after heavy-ion collisions.

The branching ratio of the lightest Higgs boson decay into $b\overline{b},$ $\tau \overline{\tau }$ and $c\overline{c}$ is sensitive to supersymmetric effects. We include in this work the effects of $\mathrm{CP}$ phases on the Higgs boson decays. Specifically we compute the deviation of the $\mathrm{CP}$ phase dependent branching ratio from the standard model result. The analysis includes the full one loop corrections of fermion masses including $\mathrm{CP}$ phases involving the gluino, the chargino and the neutralino exchanges. The analysis shows that the supersymmetric effects with $\mathrm{CP}$ phases can change the branching ratios by as much as 100% for the lightest Higgs boson decay into $b\overline{b}$ and $\tau \overline{\tau }$ with similar results holding for the heavier Higgs boson decays. A detailed analysis is also given for the effects of $\mathrm{CP}$ phases on the Higgs boson decays into $c\overline{c}.$ The deviations of $R_{b/\tau }$ and $R_{b/c}$ from the standard model result are investigated as a possible signature of supersymmetry and $\mathrm{CP}$ effects. Thus a measurement of the decays of the Higgs boson into $b\overline{b},$ $\tau \overline{\tau }$ and $c\overline{c}$ may provide important clues regarding the existence of supersymmetry and $\mathrm{CP}$ phases.

We study the possibility of uniquely identifying the effects of graviton exchange from other new physics in high energy $e^{+}{e}^{-}$ annihilation into fermion pairs. For this purpose, we use as the basic observable a specific asymmetry among integrated differential distributions that seems particularly suitable for direct testing for such gravitational effects in the data analysis.

We study the implications of minimal nonuniversal boundary conditions in the sfermion soft supersymmetry breaking (SSB) masses of minimal supergravity. We impose asymptotic $b-\tau$ Yukawa coupling unification and we resort to a parametrization of the deviation from universality in the SSB motivated by the multiplet structure of the $\mathrm{SU}\left(5\right)\mathrm{}$ grand unified theory. A set of cosmophenomenological constraints, including the recent results from the Wilkinson Microwave Anisotropy Probe, determines the allowed parameter space of the models under consideration. We highlight a “new coannihilation corridor” where $\tilde{\chi }-b_1$ and $\tilde{\chi }-{\tilde{\tau }}_1-{\tilde{\nu }}_{\tau }$ coannihilations significantly contribute to the reduction of the neutralino relic density.

We present results of a simulation of QCD on a ${16}^3\times 4$ lattice with 2 continuum flavors of a $p4\mathrm{}$-improved staggered fermion with mass $m/T=\mathrm{0.4.}\mathrm{}$ Derivatives of the thermodynamic grand potential $\Omega$ with respect to the quark chemical potential ${\mu }_q$ up to fourth order are calculated, enabling estimates of the pressure, quark number density and associated susceptibilities as functions of ${\mu }_q$ via Taylor series expansion. Discretization effects associated with various staggered fermion formulations are discussed in some detail. In addition it is possible to estimate the radius of convergence of the expansion as a function of temperature. We also discuss the calculation of energy and entropy densities which are defined via mixed derivatives of $\Omega$ with respect to the bare couplings and quark masses.

Previous detailed studies of direct photon production from both fixed-target and collider experiments have witnessed a pattern of deviation between the measured inclusive cross sections and the corresponding theoretical expectations in the low transverse momentum ${(p}_T)$ regime. Most data sets display steeper $p_T$ dependence than the next-to-leading-order (NLO) perturbative QCD (PQCD) calculations with standard choices of scales and parton distribution functions in this region. A simple implementation of higher-order soft-gluon corrections to the NLO PQCD predictions significantly improves the agreement between data and theory. This interesting feature motivated us to investigate the DØ and CDF measurements of inclusive photon cross section at $\sqrt{s}=1.8\mathrm{}\mathrm{TeV}$ from the run $1b$ and also at $\sqrt{s}=630\mathrm{}\mathrm{GeV}.$ We use the latest updated parton distribution function CTEQ6M in the NLO QCD calculations for direct photon cross section to describe the data. The conventional theoretical uncertainties originating from scale dependence and gluon distributions have been illustrated. We estimate the impact of additional soft-gluon radiation on the direct photon production using PYTHIA (LO PQCD), which adds transverse momentum $k_T$ to initial-state partons through a Gaussian smearing. The impact of $k_T$ effects on the discrepancy in the low-$p_T$ region is explored using a phenomenological model, wherein we merge the NLO calculations with $k_T$ correction factors. We show that this approach provides a much more acceptable description of the Fermilab Tevatron data.

We have searched for the baryon-containing radiative penguin decays $B^{-}\to \Lambda \overline{p}\gamma$ and $B^{-}\to {\Sigma }^0\overline{p}\gamma ,$ using a sample of $9.7\times {10}^6$ $B\overline{B}$ events collected at the ${\rm Y}\mathrm{}\left(4S\right)\mathrm{}$ with the CLEO detector. We find no evidence for either, and set 90% confidence level upper limits of $\mathcal{B}{(B}^{-}\to \Lambda \overline{p}\gamma )+0.3\mathrm{}\mathcal{B}{(B}^{-}\to {\Sigma }^0\overline{p}\gamma ){]}_{E_{\gamma }>2.0\mathrm{}\hspace{0.5em}\mathrm{GeV}}<3.3\mathrm{}\times {10}^{-6},$ $[\mathcal{B}{(B}^{-}\to {\Sigma }^0\overline{p}\gamma )+0.4\mathrm{}\mathcal{B}{(B}^{-}\to \Lambda \overline{p}\gamma ){]}_{E_{\gamma }>2.0\mathrm{}\hspace{0.5em}\mathrm{GeV}}<6.4\mathrm{}\times {10}^{-6}.$ From the latter, we estimate $\mathcal{B}(\overrightarrow{B}{X}_s\gamma {,X}_s\hspace{0.5em}\mathrm{containing}\mathrm{}\mathrm{baryons}{)}_{E_{\gamma }>2.0\mathrm{}\hspace{0.5em}\mathrm{GeV}}<3.8\mathrm{}\times {10}^{-5}.$ This limit implies upper limits on corrections to CLEO’s recent measurement of branching fraction, mean photon energy, and variance in photon energy from $\overrightarrow{b}s\gamma$ that are less than half the combined statistical and systematic errors quoted on these quantities.

We investigate the decoherence of histories of local densities for linear oscillators models. It is shown that histories of local number, momentum and energy density are approximately decoherent, when coarse grained over sufficiently large volumes. Decoherence arises directly from the proximity of these variables to exactly conserved quantities (which are exactly decoherent), and not from environmentally induced decoherence. We discuss the approach to local equilibrium and the subsequent emergence of hydrodynamic equations for the local densities.

We use the general solution to the trace of the 4-dimensional Einstein equations for static, spherically symmetric configurations as a basis for finding a general class of black hole (BH) metrics, containing one arbitrary function $g_{\mathrm{tt}}=A\left(r\right)\mathrm{}$ which vanishes at some ${r=r}_h>0,$ the horizon radius. Under certain reasonable restrictions, BH metrics are found with or without matter and, depending on the boundary conditions, can be asymptotically flat or have any other prescribed asymptotic. It is shown that our procedure generically leads to families of globally regular BHs with a Kerr-like global structure as well as symmetric wormholes. Horizons in space-times with zero scalar curvature are shown to be either simple or double. The same is generically true for horizons inside a matter distribution, but in special cases there can be horizons of any order. A few simple examples are discussed. A natural application of the above results is the brane world concept, in which the trace of the 4D gravity equations is the only unambiguous equation for the 4D metric, and its solutions can be continued into the 5D bulk according to the embedding theorems.

It has recently been shown that the uniqueness theorem for stationary black holes cannot be extended to five dimensions. However, uniqueness is an important assumption of the string theory black hole entropy calculations. This paper justifies this assumption by proving a uniqueness theorem for supersymmetric black holes in five dimensions. Some remarks concerning general properties of nonsupersymmetric higher dimensional black holes are made. It is conjectured that there exist new families of stationary higher dimensional black hole solutions with fewer symmetries than any known solution.

In this paper, we develop a Newtonian approach to the collapse of galaxy fluctuations of scalar field dark matter under initial conditions inferred from simple assumptions. The full relativistic system, the so-called Einstein-Klein-Gordon system, is reduced to the Schrödinger-Newton one in the weak-field limit. The scaling symmetries of the SN equations are exploited to track the nonlinear collapse of single scalar matter fluctuations. The results can be applied to both real and complex scalar fields.

Phantom energy which violates the dominant-energy condition and is not excluded by current constraints on the equation of state may be dominating the evolution of the universe now. It has been pointed out that in such a case the fate of the universe may be a big rip where the expansion is so violent that all galaxies, planets and even atomic nuclei will be successively ripped apart in finite time. Here we show, however, that there are certain unified models for dark energy which are stable to perturbations in matter density where the presence of phantom energy does not lead to such a cosmic doomsday.

We present and discuss a class of exact solutions to the stationary axisymmetric Einstein equations which describe a regular black hole surrounded by a disk of infinite extension with finite inner radius. The spacetimes are asymptotically flat and equatorially symmetric. They form a subclass of Korotkin’s solutions to the Ernst equation on partially degenerate hyperelliptic Riemann surfaces of genus $g+2.\mathrm{}$ The metric is given explicitly in terms of theta functions on a surface of genus g. The case of genus zero when the solutions are given in terms of elementary functions is discussed in detail.

We calculate the one-loop QCD virtual corrections to all helicity amplitudes for parton level virtual Compton scattering processes. We include the amplitudes both on the quark target process ${\gamma }^{*}\overrightarrow{q}\gamma q$ and on the gluon target process ${\gamma }^{*}\overrightarrow{g}\gamma g.\mathrm{}$ The infrared pole structure of the amplitudes is in agreement with the prediction of Catani’s general formalism for the singularities of one-loop amplitudes, while expressions for the finite remainder are given in terms of logarithms and dilogarithms that are real in the physical region.

Using data collected on the ${\rm Y}\mathrm{}\left(4S\right)\mathrm{}$ resonance and the nearby continuum by the CLEO detector at the Cornell Electron Storage Ring, we have searched for the semileptonic decay of B mesons to $e\overline{p}$ inclusive final states. We obtain an upper limit for $\overrightarrow{b}c$ decays of $\mathcal{B}\left(\overrightarrow{B}\overline{p}{e}^{-}{\overline{\nu }}_{e}X\right)<\mathrm{}5.9\mathrm{}\times {10}^{-4}.$ For the $\overrightarrow{b}u$ decay, we find an upper limit of $\mathcal{B}{(B}^{-}\to p\overline{p}{e}^{-}{\overline{\nu }}_e)<\mathrm{}1.2\mathrm{}\times {10}^{-3}$ based on a $V-A$ model, while a phase space model gives an upper limit of $\mathcal{B}{(B}^{-}\to p\overline{p}{e}^{-}{\overline{\nu }}_e)<\mathrm{}5.2\mathrm{}\times {10}^{-3}.$ All upper limits are measured at the 90% confidence level.