Basing our discussion on the Lagrangian description of hydrodynamics, we studied the evolution of density fluctuation for nonlinear cosmological dynamics. Adhesion approximation (AA) is known as a phenomenological model that describes the nonlinear evolution of density fluctuation rather well and that does not form a caustic. In addition to this model, we have benefited from discussion of the relation between artificial viscosity in AA and velocity dispersion. Moreover, we found it useful to regard whether the velocity dispersion is isotropic produces effective pressure or viscosity terms. In this paper, we analyze plane- and spherical-symmetric cases and compare AA with Lagrangian models where pressure is given by a polytropic equation of state. From our analyses, the pressure model undergoes evolution similar to that of AA until reaching a quasinonlinear regime. Compared with the results of a numerical calculation, the linear approximation of the pressure model seems rather good until a quasinonlinear regime develops. However, because of oscillation arising from the Jeans instability, we could not produce a stable nonlinear structure.

We show that in Gauss-Bonnet gravity with negative Gauss-Bonnet coefficient and without a cosmological constant, one can explain the acceleration of the expanding Universe. We first introduce a solution of the Gauss-Bonnet gravity with negative Gauss-Bonnet coefficient and no cosmological constant term in an empty $(n+1)$-dimensional bulk. This solution can generate a de Sitter spacetime with curvature $n(n+1)/\{(n-2)(n-3)|\alpha |\}$. We show that an $(n-1)$-dimensional brane embedded in this bulk can have an expanding feature with acceleration. We also considered a four-dimensional brane world in a five-dimensional empty space with zero cosmological constant and obtain the modified Friedmann equations. The solution of these modified equations in matter-dominated era presents an expanding Universe with negative deceleration and positive jerk which is consistent with the recent cosmological data. We also find that for this solution, the “$n$” th derivative of the scale factor with respect to time can be expressed only in terms of Hubble and deceleration parameters.

During the transition from a neutral to a fully reionized universe, scattering of cosmic microwave background (CMB) photons via free electrons leads to a new anisotropy contribution to the temperature distribution. If the reionization process is inhomogeneous and patchy, the era of reionization is also visible via brightness temperature fluctuations in the redshifted 21 cm line emission from neutral hydrogen. Since regions containing electrons and neutral hydrogen are expected to trace the same underlying density field, the two are (anti)correlated and this is expected to be reflected in the anisotropy maps via a correlation between arcminute-scale CMB temperature and the 21 cm background. In terms of the angular cross-power spectrum, unfortunately, this correlation is insignificant due to a geometric cancellation associated with second-order CMB anisotropies. The same cross correlation between ionized and neutral regions, however, can be studied using a bispectrum involving large-scale velocity field of ionized regions from the Doppler effect, arcminute-scale CMB anisotropies during reionization, and the 21 cm background. While the geometric cancellation is partly avoided, the signal-to-noise ratio related to this bispectrum is reduced due to the large cosmic variance related to velocity fluctuations traced by the Doppler effect. Unless the velocity field during reionization can be independently established, it is unlikely that the correlation information related to the relative distribution of ionized electrons and regions containing neutral hydrogen can be obtained with a combined study involving CMB and 21 cm fluctuations.

Soliton solutions are recovered as scale-invariant asymptotic states of vacuum inhomogeneous cosmologies using renormalization group method. The stability analysis of these states is also given.

This paper describes a natural one-parameter family of generalized Skyrme systems, which includes the usual SU(2) Skyrme model and the Skyrme-Faddeev system. Ordinary Skyrmions resemble polyhedral shells, whereas the Hopf-type solutions of the Skyrme-Faddeev model look like closed loops, possibly linked or knotted. By looking at the minimal-energy solutions in various topological classes, and for various values of the parameter, we see how the polyhedral Skyrmions deform into looplike Hopf Skyrmions.

A mechanism for double suppression of flavor-changing neutral currents (FCNCs) and CP violating phases in supersymmetric models is suggested. At $M_{\mathrm{S}\mathrm{U}\mathrm{S}\mathrm{Y}}$ they are suppressed due to a nonabelian discrete flavor symmetry, and the infrared attractive force of gauge interactions in extra dimensions are used to suppress them at the compactification scale. We present a concrete model, which is a simple extension of $S_3$ invariant minimal supersymmetric standard model, where only $\mathrm{S}\mathrm{U}(2{)}_L$ and $\mathrm{S}\mathrm{U}(3{)}_C$ gauge multiplets are assumed to propagate in the bulk. We find that a disorder of 2 orders of magnitude in soft supersymmetry breaking parameters above the compactification scale may be allowed to satisfy experimental constraints on FCNC processes and CP violating phenomena.

We present a new approach for determining spatially optimized operators that can be used for lattice spectroscopy of excited hadrons. Jacobi smeared quark sources with different widths are combined to construct hadron operators with different spatial wave functions. We use the variational method to determine those linear combinations of operators that have optimal overlap with ground and excited states. The details of the new approach are discussed and we demonstrate the power of the method using examples from quenched baryon and meson spectroscopy. In particular, we study the Roper state and $\rho (1450)$ and discuss some physical implications of our tests.

We study non-Fermi liquid effects due to the exchange of unscreened magnetic gluons in the normal phase of high density QCD by using an effective field theory. A one-loop calculation gives the well-known result that magnetic gluons lead to a logarithmic enhancement in the fermion self-energy near the Fermi surface. The self-energy is of the form $\Sigma (\omega )\sim \omega \gamma \log (\omega )$, where $\omega$ is the energy of the fermion, $\gamma =O(g^2)$, and $g$ is the coupling constant. Using an analysis of the Dyson-Schwinger equations we show that, in the weak coupling limit, this result is not modified by higher order corrections even in the regime where the logarithm is large, $\gamma \log (\omega )\sim 1$. We also show that this result is consistent with the renormalization group equation in the high density effective field theory.

We study three-body nonleptonic decays $B\to VVP$ by introducing two-meson distribution amplitudes for the vector-pseudoscalar pair, such that the analysis is simplified into the one for two-body decays. The twist-2 and twist-3 $\varphi K$ two-meson distribution amplitudes, associated with longitudinally and transversely polarized $\varphi$ mesons, are constrained by the experimental data of the $\tau \to \varphi K\nu$ and $B\to \varphi K\gamma$ branching ratios. We then predict the $B\to \varphi K\gamma$ and $B\to \varphi \varphi K$ decay spectra in the $\varphi K$ invariant mass. Since the resonant contribution in the $\varphi K$ channel is negligible, the above decay spectra provide a clean test for the application of two-meson distribution amplitudes to three-body $B$ meson decays.

We examine whether an appreciable value of the lepton flavor mixing angle ${\theta }_{13}$ at the electroweak scale ${\Lambda }_{\mathrm{E}\mathrm{W}}$ can be radiatively generated from ${\theta }_{13}=0°$ at the grand unified theory (GUT) scale ${\Lambda }_{\mathrm{G}\mathrm{U}\mathrm{T}}$. It is found that the renormalization-group running and seesaw threshold effects may lead to ${\theta }_{13}\sim 5°$ at low energies for two simple large-maximal mixing patterns of the Maki-Nakagawa-Sakata matrix in the minimal supersymmetric standard model. If ${\theta }_{12}$ is sufficiently large at ${\Lambda }_{\mathrm{G}\mathrm{U}\mathrm{T}}$, it will be possible to radiatively produce ${\theta }_{13}\sim 5°$ at ${\Lambda }_{\mathrm{E}\mathrm{W}}$ both in the standard model and in its supersymmetric extensions. The mass spectrum of three heavy right-handed Majorana neutrinos and the cosmological baryon number asymmetry via leptogenesis are also calculated.

Cross sections for $e^{+}p$ neutral current deep inelastic scattering have been measured at a center-of-mass energy of $\sqrt{s}=318\mathrm{G}\mathrm{e}\mathrm{V}$ with the ZEUS detector at HERA using an integrated luminosity of $63.2{\mathrm{p}\mathrm{b}}^{-1}$. The double-differential cross section, $d^2\sigma /dxd{Q}^2$, is presented for $200{\mathrm{G}\mathrm{e}\mathrm{V}}^2<Q^2<30000{\mathrm{G}\mathrm{e}\mathrm{V}}^2$ and for $0.005<x<0.65$. The single-differential cross sections $d\sigma /d{Q}^2$, $d\sigma /dx$ and $d\sigma /dy$ are presented for $Q^2>200{\mathrm{G}\mathrm{e}\mathrm{V}}^2$. The effect of $Z$-boson-exchange is seen in $d\sigma /dx$ measured for $Q^2>10000{\mathrm{G}\mathrm{e}\mathrm{V}}^2$. The data presented here were combined with ZEUS $e^{+}p$ neutral current data taken at $\sqrt{s}=300\mathrm{G}\mathrm{e}\mathrm{V}$ and the structure function $F_2^{\mathrm{e}\mathrm{m}}$ was extracted. All results agree well with the predictions of the Standard Model.

We study D-branes of $N=2$ supersymmetric sigma models. Supersymmetric nonlinear sigma models with 2-dimensional target space have $p$-dimensional branes ($p=0,1,2$), which are realized as $A$- or $B$-type supersymmetric boundary conditions on the world sheet. When we embed the models in the string theory, the Kähler potential is restricted and leads to a 2-dimensional black hole metric with a dilaton background. The D-branes in this model are supersymmetric cycles and our analysis is consistent with that of conjugacy classes. The generalized metrics with $\mathrm{U}(n)$ isometry are proposed and dynamics on them are realized by linear sigma models. We investigate D-branes of the linear sigma models and compare the results with those in the nonlinear sigma models.

We show that the Dirac-Born-Infeld (DBI) action for the singlet sector of the tachyon in two-dimensional string theory has a $\mathrm{S}\mathrm{L}(2,R)$ symmetry, a real-time counterpart of the ground ring. The action can be rewritten as that of point particles moving in a de Sitter space, whose coordinates are given by the value of the eigenvalue and time. The symmetry then manifests as the isometry group of de Sitter space in two dimensions. We use this fact to write the collective field theory for a large number of branes, which has a natural interpretation as a fermion field in this de Sitter space. After spending some time building geometrical insight on facts about the condensation process, the state corresponding to a sD-brane is identified and standard results in quantum field theory in curved spacetime are used to compute the backreaction of the thermal background.

We place several new limits on Lorentz violating effects, which can modify particles' dispersion relations, by considering the highest energy cosmic rays observed. Since these are hadrons, this involves considering the partonic content of such cosmic rays. We get a number of bounds on differences in maximum propagation speeds, which are typically bounded at the ${10}^{-21}$ level, and on momentum dependent dispersion corrections of the form $v=1\pm p^2/{\Lambda }^2$, which typically bound $\Lambda >{10}^{21}\mathrm{G}\mathrm{e}\mathrm{V}$, well above the Planck scale. For ($CPT$ violating) dispersion correction of the form $v=1+p/\Lambda$, the bounds are up to 15 orders of magnitude beyond the Planck scale.

In relation to the Baumgarte-Shapiro-Shibata-Nakamura (BSSN) formulation of the Einstein equations, we write down the boundary conditions that result from the vanishing of the projection of the Einstein tensor normally to a timelike hypersurface. Furthermore, by setting up a well-posed system of propagation equations for the constraints, we show explicitly that there are three constraints that are incoming at the boundary surface and that the boundary equations are linearly related to them. This indicates that such boundary conditions play a role in enforcing the propagation of the constraints in the region interior to the boundary. Additionally, we examine the related problem for a strongly-hyperbolic first-order reduction of the BSSN equations and determine the characteristic fields that are prescribed by the three boundary conditions, as well as those that are left arbitrary.

We investigate the following question: Consider a small mass, with $ϵ$ (the ratio of the Schwarzschild radius and the bulk curvature length) much smaller than 1, that is confined to the TeV brane in the Randall-Sundrum I scenario. Does it form a black hole with a regular horizon, or a naked singularity? The metric is expanded in $ϵ$ and the asymptotic form of the metric is given by the weak field approximation (linear in the mass). In first order of $ϵ$ we show that the iteration of the weak field solution, which includes only integer powers of the mass, leads to a solution that has a singular horizon. We find a solution with a regular horizon but its asymptotic expansion in the mass also contains half integer powers.

A numerical solution of Einstein field equations for a spherical symmetric and stationary system of identical and autogravitating particles in phase transition is presented. The fluid possesses a perfect fluid energy-momentum tensor, and the internal interactions of the system are represented by a van der Walls-like equation of state, able to describe a first order phase transition of the type gas-liquid. We find that the space-time curvature, the radial component of the metric, and the pressure and density show discontinuities in their radial derivatives in the phase coexistence region. This region is found to be a spherical surface concentric with the star, and the system can be thought of as a foliation of acronal, concentric and isobaric surfaces in which the coexistence of phases occurs in only one of these surfaces. This kind of system can be used to represent a star with a high energy density core and low energy density mantle in hydrodynamic equilibrium.

A graviton of a nonzero mass and decay width propagates five physical polarizations. The question of interactions of these polarizations is crucial for viability of models of massive/metastable gravity. This question is addressed in the context of the DGP model of a metastable graviton. First, we argue that the well-known breakdown of a naive perturbative expansion at a low scale is an artifact of the weak-field expansion itself. Then, we propose a different expansion—the constrained perturbation theory—in which the breakdown does not occur and the theory is perturbatively tractable all the way up to its natural ultraviolet cutoff. In this approach the couplings of the extra polarizations to matter and their self-couplings appear to be suppressed and should be neglected in measurements at subhorizon scales. The model reproduces results of General Relativity at observable distances with high accuracy, while predicting deviations from them at the present day horizon scale.

The concept of acoustic torsion is introduced by making use of the scalar wave equation in Riemann-Cartan spacetime. Acoustic torsion extends the acoustic metric previously given by Unruh (PRL-1981). The wave equation describes irrotational perturbations in rotational nonrelativistic fluids. This physical motivation allows us to show that the acoustic line element can be conformally mapped to the line element of a stationary torsion loop in non-Riemannian gravity. Two examples of such sonic analogues are given. The first is the stationary torsion loop in teleparallel gravity. In the far from the vortex approximation, the Cartan torsion vector is shown to be proportional to the quantum vortex number of the superfluid. The torsion vector is also shown to be proportional to the superfluid vorticity in the presence of vortices. The formation of superfluid vortices is shown not to be favored by torsion loops in Riemann-Cartan spacetime, as long as this model is concerned. It is suggested that the teleparallel model may help to find a model for superfluid neutron stars vortices based on non-Riemannian gravity.

Recently, the SPI spectrometer on the INTEGRAL satellite observed strong 511 keV line emission from the galactic bulge. Although the angular distribution (spherically symmetric with width of $\sim 9°$) of this emission is difficult to account for with traditional astrophysical scenarios, light dark matter particles could account for the observation. In this paper, we consider the possibility that decaying axinos in an Repartee violating model of supersymmetry may be the source of this emission. We find that $\sim 1-300\mathrm{M}\mathrm{e}\mathrm{V}$ axinos with R-parity violating couplings can naturally produce the observed emission.