Motivated by various theoretical arguments that the Planck energy ${(E}_{\mathrm{Planck}}\sim {10}^{19}\mathrm{GeV})$ should herald departures from Lorentz invariance, and the possibility of testing these expectations in the not too distant future, two so-called “doubly special relativity” theories have been suggested—the first by Amelino-Camelia (DSR1) and the second by Smolin and Magueijo (DSR2). These theories contain two fundamental scales—the speed of light and an energy usually taken to be $E_{\mathrm{Planck}}.$ The symmetry group is still the Lorentz group, but in both cases acting nonlinearly on the energy-momentum sector. Since energy and momentum are no longer additive quantities, finding their values for composite systems (and hence finding appropriate conservation laws) is a nontrivial matter. Ultimately it is these possible deviations from simple linearly realized relativistic kinematics that provide the most promising observational signal for empirically testing these models. Various investigations have narrowed the conservation laws down to two possibilities per DSR theory. We derive unique exact results for the energy momentum of composite systems in both DSR1 and DSR2, and indicate the general strategy for arbitrary nonlinear realizations of the Lorentz group.

We discuss a new model of quintessence in which the quintessence field is identified with the extra component of a gauge field in a compactified five-dimensional theory. We show that the extremely tiny energy scale $\sim (3\mathrm{}\times {10}^{-3}\mathrm{eV}{)}^4$ needed to account for the present acceleration of the Universe can be naturally explained in terms of high energy scales such as the scale of grand unification.

We present a realistic supergravity inflation model that is free from the overproduction of potentially dangerous relics in cosmology, namely, moduli and gravitinos, which can lead to inconsistencies with the predictions of baryon asymmetry and nucleosynthesis. The radiative correction turns out to play a crucial role in our analysis, raising the mass of the supersymmetry breaking field to an intermediate scale. We pay particular attention to the nonthermal production of gravitinos using the nonminimal Kähler potential we obtained from loop correction. This nonthermal gravitino production is diminished, however, because of the relatively small scale of the inflaton mass and the small amplitudes of the hidden sector fields.

We consider the two Higgs doublet model of type III which leads to flavor changing neutral currents at the tree level. In the framework of this model we can use an appropriate form of the Yukawa Lagrangian that makes the type II model limit of the general type III couplings apparent. This way is useful in order to compare with the experimental data which is model dependent. The analytical expressions of the partial width $\Gamma \left(\overrightarrow{t}{H}^{+}b\right)$ are derived and we compare with the data available at this energy range. We examine the limits on the new parameters ${\lambda }_{\mathrm{ij}}$ from the validness of perturbation theory.

By assuming certain analytic properties of the propagator, it is shown that universal features of the spectral function, including threshold enhancement, arise if a pole describing a particle at high temperature approaches in the complex energy plane the threshold position of its two-body decay with the variation of T. The case is considered when one can disregard any other decay processes. The quality of the proposed description is demonstrated by comparing it with the detailed large N solution of the linear $\sigma$ model around the pole-threshold coincidence.

We study the interaction of an n-dimensional topological defect $(n$-brane) described by the Nambu-Goto action with a higher-dimensional Schwarzschild black hole moving in the bulk spacetime. We derive the general form of the perturbation equations for an n-brane in the weak field approximation and solve them analytically in the most interesting cases. We especially analyze applications to brane world models. We calculate the induced geometry on the brane generated by a moving black hole. From the point of view of a brane observer, this geometry can be obtained by solving $\mathrm{}(n+1\mathrm{})\mathrm{}$-dimensional Einstein’s equations with a nonvanishing right-hand side. We calculate the effective stress-energy tensor corresponding to this “shadow matter.” We explicitly show that there exist regions on the brane where a brane observer sees an apparent violation of energy conditions. We also study the deflection of light propagating in the region of influence of this shadow matter.

Black strings, one class of higher dimensional analogues of black holes, were shown to be unstable to long wavelength perturbations by Gregory and Laflamme in 1992, via a linear analysis. We reexamine the problem through the numerical solution of the full equations of motion, and focus on trying to determine the end state of a perturbed, unstable black string. Our preliminary results show that such a spacetime tends towards a solution resembling a sequence of spherical black holes connected by thin black strings, at least at intermediate times. However, our code fails then, primarily due to large gradients that develop in metric functions, as the coordinate system we use is not well adapted to the nature of the unfolding solution. We are thus unable to determine how close the solution we see is to the final end state, though we do observe rich dynamical behavior of the system in the intermediate stages.

Recent analysis of the observation data indicates that the equation of state of the dark energy might be smaller than $-1,$ which leads to the introduction of phantom models featured by their negative kinetic energy to account for the regime of equation of state $w<\mathrm{}-1.$ In this paper, we generalize the idea to the Born-Infeld-type Lagrangian with a negative kinetic energy term and give the condition for the potential under which the late time attractor solution exists and also analyze a viable cosmological model in such a scheme.

It is well known that the neutrino mass matrix contains more parameters than experimentalists can hope to measure in the foreseeable future even if we impose CP invariance. Thus, various authors have proposed Ansätze to restrict the form of the neutrino mass matrix further. Here we propose that $m_{{\nu }_1}{+m}_{{\nu }_2}{+m}_{{\nu }_3}=0.\mathrm{}$ With this condition, the absolute neutrino mass can be obtained in terms of the mass-squared differences. When combined with the accumulated experimental data, this condition predicts two types of mass hierarchies, with one of them characterized by $m_{{\nu }_3}\approx -{2m}_{{\nu }_1}\approx -{2m}_{{\nu }_2}\approx 0.063\mathrm{eV},$ and the other by $m_{{\nu }_1}\approx -m_{{\nu }_2}\approx 0.054\mathrm{eV}$ and $m_{{\nu }_3}\approx 0.0064\mathrm{eV}.$ The range predicted for $|m_{{\nu }_1}|+|m_{{\nu }_2}|+|m_{{\nu }_3}|$ is below the cosmological upper bound of 0.69 eV from recent Wilkinson Microwave Anisotropy Probe data and can be probed in the near future. We also point out some implications for direct laboratory measurement of neutrino masses and the neutrino mass matrix.

We show that for a neutrino factory baseline of $L\sim 7300–7600\mathrm{km}$ a “clean” measurement of ${\sin }^{2}2{\theta }_{13}$ becomes possible, which is almost unaffected by parameter degeneracies. We call this baseline the “magic” baseline, because its length depends only on the matter density profile. For a complete analysis, we demonstrate that the combination of the magic baseline with a baseline of 3 000 km is the ideal solution to perform equally well for ${\sin }^{2}2{\theta }_{13},$ the sign of $\Delta m_{31}^2,$ and CP violation sensitivities. In particular, this combination can very successfully resolve parameter degeneracies even below ${\sin }^{2}2{\theta }_{13}<{10}^{-4}.$

No realistic black holes localized on a 3-brane in the Randall-Sundrum infinite braneworld have been found so far. The problem of finding a static black hole solution is reduced to a boundary value problem. We solve it by means of a numerical method, and show numerical examples of a localized black hole whose horizon radius is small compared to the bulk curvature scale. The sequence of small localized black holes exhibits a smooth transition from a five-dimensional Schwarzschild black hole, which is a solution in the limit of small horizon radius. The localized black hole tends to flatten as its horizon radius increases. However, it becomes difficult to find black hole solutions as its horizon radius increases.

We report an improved measurement of the partial-rate CP asymmetry in $B^{\pm }\to K^0{\pi }^{\pm }$ decays. The analysis is based on a data sample of $85\times {10}^6$ $B\overline{B}$ pairs collected at the ${\rm Y}\mathrm{}\left(4S\right)\mathrm{}$ resonance with the Belle detector at the KEKB $e^{+}{e}^{-}$ storage ring. We measure ${\mathcal{A}}_{\mathrm{CP}}(K^0{\pi }^{\pm }{)=0.07\mathrm{}}_{-0.08}^{+0.09\mathrm{}}{}_{-0.03}^{+0.01\mathrm{}},$ where the first and second errors are statistical and systematic, respectively; the corresponding 90% confidence-level interval is $-0.10<\mathrm{}{\mathcal{A}}_{\mathrm{CP}}\left(K^0{\pi }^{\pm }\right)<\mathrm{}\mathrm{0.22.}\mathrm{}$

Using $S\left(\mathrm{pacelike}\right)$-branes defined through rolling tachyon solutions, we show how the dynamical formation of D(irichlet)-branes and strings in tachyon condensation can be understood. Specifically, we present solutions of S-brane actions illustrating the classical confinement of electric and magnetic flux into fundamental strings and D-branes. The role of S-branes in string theory is further clarified and their Ramond-Ramond charges are discussed. In addition, by examining “boosted” S-branes, we find what appears to be a surprising dual S-brane description of strings and D-branes, which also indicates that the critical electric field can be considered as a self-dual point in string theory. We also introduce new tachyonic S-branes as Euclidean counterparts to non-Bogomol’nyi-Prasad-Sommerfield branes.

Continuing our previous work, we consider a class of higher dimensional brane models with the topology of ${\mathrm{AdS}}_{D_1+1\mathrm{}}\times \Sigma ,$ where $\Sigma$ is a one-parameter compact manifold and two branes of codimension one are located at the orbifold fixed points. We consider a setup where such a solution arises from Einstein-Yang-Mills theory and evaluate the one-loop effective potential induced by gauge fields and by a generic bulk scalar field. We show that this type of brane model resolves the gauge hierarchy between the Planck and electroweak scales through redshift effects due to the warp factor ${a=e}^{-\pi \mathrm{kr}}.$ The value of a is then fixed by minimizing the effective potential. We find that, as in the Randall-Sundrum case, the gauge field contribution to the effective potential stabilizes the hierarchy without fine-tuning as long as the Laplacian ${\Delta }_{\Sigma }$ on $\Sigma$ has a zero eigenvalue. Scalar fields can stabilize the hierarchy depending on the mass and the nonminimal coupling. We also address the quantum self-consistency of the solution, showing that the classical brane solution is not spoiled by quantum effects.

Using quasiparticle models and imposing thermodynamic consistency, lattice data for the equation of state of deconfined QCD can be mapped to finite chemical potential. We consider a refinement of existing simple massive quasiparticle models using the nonlocal hard-thermal-loop propagators, and certain next-to-leading-order corrections thereof, to obtain the thermodynamic potential as a function of temperature and chemical potential. At small chemical potential we find that the results for the slope of constant pressure from our main model for two massless quark flavors is in good agreement with recent lattice data for 2+1 flavors while it deviates somewhat from lattice data for two flavors from another group. For zero temperature, we obtain an estimate for the critical chemical potential which is close to that obtained from simpler quasiparticle models.

The problem of constructing gauge invariant currents in terms of light-front bound-state wave functions is solved by utilizing the gauging of equations method. In particular, we show how to construct perturbative expansions of the electromagnetic current in the light-front formalism such that current conservation is satisfied at each order of the perturbation theory.

We consider the end state of collapsing null radiation with a string fluid. It is shown that, if diffusive transport is assumed for the string, a naked singularity can form (at least locally). The model has the advantage of not being asymptotically flat. We also analyze the case of a radiation-string two-fluid and show that a locally naked singularity can result in the collapse of such matter. We contrast this model with that of strange quark matter.

We present the effective equations to describe the four-dimensional gravity of a brane world, assuming that a five-dimensional bulk spacetime satisfies the Einstein equations and gravity is confined on the $Z_2$ symmetric brane. Applying this formalism, we study the induced-gravity brane model first proposed by Dvali, Gabadadze, and Porrati. In a generalization of their model, we show that an effective cosmological constant on the brane can be extremely reduced in contrast with the case of the Randall-Sundrum model even if a bulk cosmological constant and a brane tension are not fine tuned.

We propose a new definition for the mass and angular momentum of neutral or electrically charged black holes in 2+1 gravity with two Killing vectors. These finite conserved quantities, associated with the $\mathrm{SL}(2,R)\mathrm{}$ invariance of the reduced mechanical system, are shown to be identical to the quasilocal conserved quantities for an improved gravitational action corresponding to mixed boundary conditions. They obey a general Smarr-like formula and, in all cases investigated, are consistent with the first law of black hole thermodynamics. Our framework is applied to the computation of the mass and angular momentum of black hole solutions to several field-theoretical models.

We consider the problem of finding the gravitational radiation output, or news, within the context of a numerical simulation of a spacetime by means of the null-cone, or characteristic, approach to numerical relativity. We develop a method for computing the news that uses an explicit coordinate transformation to a coordinate system that satisfies the Bondi conditions. The method has been implemented computationally. We present results of applying the method to certain test problems, demonstrating second order convergence of the news to the analytic value.