In the framework of an effective minimal supersymmetric extension of the standard model without gaugino-mass unification at a grand unification scale, we set a lower bound on the neutralino mass based on the new WMAP data on ${\Omega }_{\mathrm{CDM}}$ $(R$-parity conservation is assumed). Our lower bound $m_{\chi }\gtrsim 6\mathrm{GeV}$ leaves much room for relic neutralinos significantly lighter than those commonly considered ${(m}_{\chi }\gtrsim 50\mathrm{GeV}).\mathrm{}$ We prove that these light neutralinos may produce measurable effects in weakly interacting massive particle direct detection experiments of low energy threshold and large exposure.

We consider the possibility that a right-handed sneutrino can serve as the source of energy density perturbations leading to structure formation in cosmology. The cosmological evolution of a coherently oscillating condensate of right-handed sneutrinos is studied for the case where reheating after inflation is due to perturbative inflaton decays. For the case of Dirac neutrinos, it is shown that some suppression of Planck scale-suppressed corrections to the right-handed neutrino superpotential is necessary in order to have sufficiently late decay of the right-handed sneutrinos. ${\mathrm{cH}}^2$ corrections to the sneutrino mass squared term must also be suppressed during inflation $(|c|\lesssim 0.1),$ in which case, depending on the magnitude of $|c|$ during inflation, a significantly blue (if $c>\mathrm{}0)$ or red (if $c<\mathrm{}0)$ perturbation spectrum is possible. R parity must also be broken in order to ensure that the Universe is not overclosed by the lightest supersymmetric particles from the late decay (at temperatures $1-10\mathrm{MeV})$ of the right-handed sneutrino condensate. The resulting expansion rate during inflation can be significantly smaller than in conventional supersymmetric inflation models (as low as ${10}^6\mathrm{GeV}$ is possible). For the case of Majorana neutrinos, a more severe suppression of Planck-suppressed superpotential corrections is required. In addition, the Majorana sneutrino condensate is likely to be thermalized before it can dominate the energy density, which would exclude the Majorana right-handed sneutrino as a curvaton.

We consider the nonleptonic and semileptonic decays of $D_s$ mesons into $\phi$ and $f_0\mathrm{}\left(980\right)\mathrm{}$ mesons. QCD sum rules are used to calculate the form factors associated with these decays and the corresponding decay rates. On the basis of data on $D_s^{+}\to {\pi }^{+}{\pi }^{+}{\pi }^{-},$ which goes dominantly via the transition $D_s^{+}\to {\pi }^{+}{f}_0\mathrm{}\left(980\right),$ we conclude that there is space for a sizeable light quark component on $f_0\mathrm{}\left(980\right).$

Recently, it was pointed out that soft masses of the supersymmetric gauge theories with extra dimensions tend to a flavor conserving point, which is a desirable scenario in gravity mediation models. We point out that in 6D we must consider the anomaly-free condition in addition to the condition on asymptotic freedom. From this, we find that $E_6,E_7,$ and $E_8$ are natural candidates in 6D. There is no $\mathrm{SU}\left(N\right)\mathrm{}$ model, but there exist two $\mathrm{SO}\left(10\right)\mathrm{}$ models and $\mathrm{SO}\left(2n\right)\mathrm{}$ models (one each for each $n>~6)$ satisfying these conditions. In five dimensions, there is no such condition on anomaly freedom, but the softening may not be enough.

The signals of the neutral top-pion ${\pi }_t^0$ at the first muon collider (FMC) are discussed by calculating its contributions to the processes ${\mu }^{+}{\mu }^{-}\to b\overline{b}$ and ${\mu }^{+}{\mu }^{-}\to \overline{t}c.\mathrm{}$ We find that the contributions to the process ${\mu }^{+}{\mu }^{-}\to b\overline{b}$ are very small and the ratio of the signal over the square root of the background $(S/\sqrt{B})$ is smaller than 0.2. However, in most of the parameter space, the ${\pi }_t^0$ can generate 36 and up to 649 observable $\overline{t}c$ events at the FMC. The signals of the neutral top-pion ${\pi }_t^0$ may be detected via the process ${\mu }^{+}{\mu }^{-}\to \overline{t}c$ at the FMC.

We report on our study of two-flavor full QCD on anisotropic lattices using $O\left(a\right)\mathrm{}$-improved Wilson quarks coupled with a renormalization-group-improved glue. The bare gauge and quark anisotropies corresponding to the renormalized anisotropy $\xi {=a}_s{/a}_t=2\mathrm{}$ are determined as functions of $\beta$ and $\kappa ,$ which cover the region of spatial lattice spacings $a_s\approx 0.28–0.16\mathrm{fm}$ and $m_{\mathrm{PS}}{/m}_V\approx 0.6–\mathrm{0.9.}$ The calibrations of the bare anisotropies are performed with the Wilson loop and the meson dispersion relation at four lattice cutoffs and 5–6 quark masses. Using the calibration results we calculate the meson mass spectrum and the Sommer scale $r_0.$ We confirm that the values of $r_0$ calculated for the calibration using pseudoscalar and vector meson energy momentum dispersion relations coincide in the continuum limit within errors. This work serves to lay the groundwork for studies of heavy quark systems and the thermodynamics of QCD including the extraction of the equation of state in the continuum limit using Wilson-type quark actions.

We perform a quark model calculation of the $b\overline{b}$ and $c\overline{c}$ spectra from a screened funnel potential form suggested by unquenched lattice calculations. A connection between the lattice screening parameter and an effective gluon mass directly derived from QCD is established. Spin-spin energy splittings, leptonic widths, and radiative decays are also examined providing a test for the description of the states.

In the study of $\mathrm{CP}$ violation signals in $\overrightarrow{\Omega }\pi \Xi$ nonleptonic decays, the strong $J=3/2\mathrm{}$ P, and D phase shifts for the $\pi \Xi$ final-state interactions are needed. These phases are calculated using an effective Lagrangian model that considers $\Xi ,$ ${\Xi }^{*}\mathrm{}\left(1530\right),$ $\rho ,$ and the $\sigma$ term, in the intermediate states. The $\sigma$ term is calculated in terms of the scalar form factor of the baryon.

Detailed differential cross sections for high energy bremsstrahlung and pair production are derived with specific attention to the differences between the two processes, which are considerable. For the integrated cross sections, which are the only cross sections specifically known until now, the final state integration theorem guarantees that the exact cross section formulas can be exchanged between bremsstrahlung and pair production by the same substitution rules as for the Born-approximation Bethe-Heitler cross sections, for any amount of atomic screening. In fact the theorem states that the Coulomb corrections to the integrated bremsstrahlung and pair production cross sections are identical for any amount of screening. The analysis of the basic differential cross sections leads to fundamental physical differences between bremsstrahlung and pair production. Coulomb corrections occur for pair production in the strong electric field of the atom for “large” momentum transfer of the order of mc. For bremsstrahlung, on the other hand, the Coulomb corrections take place at a “large” distance from the atom of the order of $(ħ/mc)\epsilon ,$ with a “small” momentum transfer $mc/\epsilon ,$ where $\epsilon$ is the initial electron energy in units of ${\mathrm{mc}}^2.$ And the Coulomb corrections can be large, of the order of larger than ${\mathrm{}(Z/137\mathrm{})\mathrm{}}^2,$ which is considerably larger than the integrated cross section corrections.

Neutrino oscillation experiments (excluding the Liquid Scintillator Neutrino Detector experiment) suggest a tribimaximal form for the lepton mixing matrix. This form indicates that the mixing matrix is probably independent of the lepton masses, and suggests the action of an underlying discrete family symmetry. Using these hints, we conjecture that the contrasting forms of the quark and lepton mixing matrices may both be generated by such a discrete family symmetry. This idea is that the diagonalization matrices out of which the physical mixing matrices are composed have large mixing angles, which cancel out due to a symmetry when the CKM matrix is computed, but do not do so in the MNS case. However, in the cases where the Higgs bosons are singlets under the symmetry, and the family symmetry commutes with ${\mathrm{SU}\left(2\right)\mathrm{}}_L,$ we prove a no-go theorem: no discrete unbroken family symmetry can produce the required mixing patterns. We then suggest avenues for future research.

We reanalyze the issue of the PQCD factorization scale in the exclusive ρ production in diffractive deep inelastic scattering from the $k_t$-factorization point of view. We find that this scale differs significantly from the widely used value ${(Q}^2{+m}_{\rho }^2)/4,$ and it is a much flatter function of $Q^2.$ With these results in mind, we discuss the $Q^2$ shape of the ρ meson production cross section and comment on the recent ZEUS observation of energy-independent ratio $\sigma \left({\gamma }^{*}\overrightarrow{p}\rho p\right)/{\sigma }_{\mathrm{tot}}\left({\gamma }^{*}p\right).\mathrm{}$

We study the production of $J/\psi +c\overline{c}$ in $e^{+}{e}^{-}$ annihilation through two virtual photons. The cross section is estimated to be 23 fb at $\sqrt{s}=10.6\mathrm{}\mathrm{GeV},$ which is smaller by a factor of 6 than the calculated cross section for the same process but through one virtual photon. As a result, while the annihilation into two photons may be important for certain exclusive production processes, the big difference between the inclusive production cross section $\sigma {(e}^{+}{e}^{-}\to J/\psi +c\overline{c})\simeq 0.9\mathrm{pb}$ observed by Belle and the current nonrelativistic QCD prediction of $\simeq 0.15\mathrm{pb}$ still remains very puzzling. We find, however, that as the center-of-mass energy increases $(\sqrt{s}>20\mathrm{}\mathrm{GeV})$ the production through two virtual photons $e^{+}{e}^{-}\to 2{\gamma }^{*}\to J/\psi +c\overline{c}$ will prevail over that through one virtual photon, because in the former process the photon fragmentation into $J/\psi$ and into the charmed quark pair becomes more important at higher energies.

We outline the construction of metastable de Sitter vacua of type IIB string theory. Our starting point is highly warped IIB compactifications with nontrivial NS and RR three-form fluxes. By incorporating known corrections to the superpotential from Euclidean D-brane instantons or gaugino condensation, one can make models with all moduli fixed, yielding a supersymmetric AdS vacuum. Inclusion of a small number of $\overline{\mathrm{D}3}$-branes in the resulting warped geometry allows one to uplift the AdS minimum and make it a metastable de Sitter ground state. The lifetime of our metastable de Sitter vacua is much greater than the cosmological time scale of ${10}^{10}\mathrm{yr}.$ We also prove, under certain conditions, that the lifetime of dS space in string theory will always be shorter than the recurrence time.

We point out that the worldvolume coordinate functions $x^{\mu }\left(\xi \right)$ of a p-brane, treated as an independent object interacting with dynamical gravity, are Goldstone fields for spacetime diffeomorphisms gauge symmetry. The presence of this gauge invariance is exhibited by its associated Noether identity, which expresses that the source equations follow from the gravitational equations. We discuss the spacetime counterpart of the Higgs effect and show that a p-brane does not carry any local degrees of freedom, extending early known general relativity features. Our considerations are also relevant for brane world scenarios.

We investigate prospects for indirect detection of Kaluza-Klein dark matter, focusing on the annihilation radiation of the first Kaluza-Klein excitation of the hypercharge gauge boson $B^{\mathrm{}\left(1\right)\mathrm{}}$ in the galactic halo; in particular we estimate neutrino, gamma-ray and synchrotron fluxes. Comparing the predicted fluxes with observational data we are able to constrain the $B^{\mathrm{}\left(1\right)\mathrm{}}$ mass (and therefore the compactification scale). The constraints depend on the specific model adopted for the dark matter density profile. For a Navarro, Frenk, and White profile the analysis of synchrotron radiation puts a lower bound on the $B^{\mathrm{}\left(1\right)\mathrm{}}$ mass of the order of $\simeq 300\mathrm{GeV}.$

We present the results from a numerical study of critical gravitational collapse of axisymmetric distributions of massless scalar field energy. We find threshold behavior that can be described by the spherically symmetric critical solution with axisymmetric perturbations. However, we see indications of a growing, nonspherical mode about the spherically symmetric critical solution. The effect of this instability is that the small asymmetry present in what would otherwise be a spherically symmetric self-similar solution grows. This growth continues until a bifurcation occurs and two distinct regions form on the axis, each resembling the spherically symmetric self-similar solution. The existence of a nonspherical unstable mode is in conflict with previous perturbative results, and we therefore discuss whether such a mode exists in the continuum limit, or whether we are instead seeing a marginally stable mode that is rendered unstable by numerical approximation.

We present a simple approach to determine the self-force acting on an accelerating charged particle. In this approach one considers an extended charged object of finite size $\epsilon ,$ and calculates the overall contribution of the mutual electromagnetic forces at the limit $\overrightarrow{\epsilon }0.$ Previous implementations of this approach often yielded a divergent term $\propto 1/\epsilon$ that could not be cured by mass renormalization. Here we explain the origin of this problem and provide a simple method for fixing it, thereby generalizing and simplifying previous analyses. We obtain a consistent, universal, expression for the extended-object self-force, which conforms with Dirac’s well known formula.

We formulate Dirac fermions on a (1+1)-dimensional lattice based on a Hamiltonian formalism. The species doubling problem of the lattice fermion is resolved by introducing hopping interactions that mix left- and right-handed fermions around the momentum boundary. Approximate chiral symmetry is realized on the lattice. The deviation of the fermion propagator from the continuum one is small.

A model for deeply virtual Compton scattering, based on analytical light-cone hadron wave functions, is presented and studied at energies currently accessible at Jefferson Laboratory, DESY, and beyond. It is shown that perpendicular vector components play an important role at $Q^2<10\mathrm{}{\mathrm{GeV}}^2$ and that the meson-exchange diagrams are important at all energies. This could significantly impact the physical interpretation of the underlying hadronic amplitudes.

We apply the method of QCD light-cone sum rules to calculate nonfactorizable contributions to the $\overrightarrow{B}J/\psi K$ decay and estimate soft nonfactorizable corrections to the $a_2$ parameter. The corrections appear to be positive, favoring the positive sign of $a_2,$ in agreement with recent theoretical considerations and experimental data. Our result also confirms expectations that in the color-suppressed decay nonfactorizable corrections are sizable.