We study curved and flat Bogomol’nyi-Prasad-Sommerfield (BPS)-domain walls in 5D, $\mathcal{N}=4$ gauged supergravity and show that their effective dynamics along the flow is described by a generalized form of “fake supergravity.” This generalizes previous work in $\mathcal{N}=2$ supergravity and might hint towards a universal behavior of gauged supergravity theories in supersymmetric domain wall backgrounds. We show that BPS-domain walls in 5D, $\mathcal{N}=4$ supergravity can never be curved if they are supported by the supergravity scalar only. Furthermore, a purely Abelian gauge group or a purely semisimple gauge group can never lead to a curved domain wall, and the flat walls for these gaugings always exhibit a runaway behavior.

We consider the problem of gravitational forces between point particles on the branes in a Randall-Sundrum (R-S) two brane model with $S^1/Z_2$ symmetry. Matter is assumed to produce a perturbation to the R-S vacuum metric and all the 5D Einstein equations are solved to linearized order (for arbitrary matter on both branes). We show that while the gauge condition $h_{i5}=0,i=0,1,2,3$ can always be achieved without brane bending, the condition $h_{55}=0$ leads to large brane bending. The static potential arising from the zero modes and the corrections due to the Kaluza-Klein modes are calculated. Gravitational forces on the Planck ($y_1=0$) brane recover Newtonian physics with small Kaluza-Klein corrections (in accord with other work). However, forces on the TeV ($y_2$) brane due to particles on that brane are strongly distorted by large R-S exponentials.

We propose a phenomenological matrix model to study string theory in ${\mathrm{AdS}}_5\times S_5$ in the canonical ensemble. The model reproduces all the known qualitative features of the theory. In particular, it gives a simple effective potential description of Euclidean black hole nucleation and the tunneling between thermal anti-de Sitter (AdS) and the big black hole. It also has some interesting predictions. We find that there exists a critical temperature at which the Euclidean small black hole undergoes a Gross-Witten phase transition. We identify the phase transition with the Horowitz-Polchinski point where the black hole horizon size becomes comparable to the string scale. The appearance of the Hagedorn divergence of thermal AdS is due to the merger of saddle points corresponding to the Euclidean small black hole and thermal AdS. The merger can be described in terms of a cusp ($A_3$) catastrophe and divergences at the perturbative string level are smoothed out at finite string coupling using standard techniques of catastrophe theory.

It has recently been shown that traversable wormholes may be supported by phantom energy. In this work phantom wormhole geometries are modeled by matching an interior traversable wormhole solution, governed by the equation of state $p=\omega \rho$ with $\omega <-1$, to an exterior vacuum spacetime at a finite junction interface. The stability analysis of these phantom wormholes to linearized spherically symmetric perturbations about static equilibrium solutions is carried out. A master equation dictating the stability regions is deduced, and by separating the cases of a positive and a negative surface energy density, it is found that the respective stable equilibrium configurations may be increased by strategically varying the wormhole throat radius. The first model considered, in the absence of a thin shell, is that of an asymptotically flat phantom wormhole spacetime. The second model constructed is that of an isotropic pressure phantom wormhole, which is of particular interest, as the notion of phantom energy is that of a spatially homogeneous cosmic fluid, although it may be extended to inhomogeneous spherically symmetric spacetimes.

The Newtonian theory of gravitation and electrostatics admits equilibrium configurations of charged fluids where the charge density can be equal to the mass density, in appropriate units. The general relativistic analog for charged dust stars was discovered by Majumdar and by Papapetrou. In the present work we consider Einstein-Maxwell solutions in $d$-dimensional spacetimes and show that there are Majumdar-Papapetrou type solutions for all $d\ge 4$. It is verified that the equilibrium is independent of the shape of the distribution of the charged matter. It is also showed that for perfect fluid solutions satisfying the Majumdar-Papapetrou condition with a boundary where the pressure is zero, the pressure vanishes everywhere, and that the $(d-1)$-dimensional spatial section of the spacetime is conformal to a Ricci-flat space. The Weyl $d$-dimensional axisymmetric solutions are generalized to include electric field and charged matter.

We study the absorption of massive spin-half particles by a small Schwarzschild black hole by numerically solving the single-particle Dirac equation in Painlevé-Gullstrand coordinates. We calculate the absorption cross section $\sigma$ over a range of gravitational couplings $Mm/m_P{}^2$ and incident particle energies $E$. At high couplings, where the Schwarzschild radius $R_S$ is much greater than the particle wavelength $\lambda$, we find that $\sigma (E)$ approaches the classical result for a point particle. At intermediate couplings, where $R_S\sim \lambda$, we find oscillations around the classical limit whose precise form depends on the particle mass. At low couplings, where $R_S\ll \lambda$, we demonstrate that the minimum-possible cross section approaches $\pi R_S{}^2/2$. For high incident particle energies, the cross section converges on the geometric-optics value of $27\pi R_S{}^2/4$. At low particle energies we find agreement with an approximation derived by Unruh.

Three exact solutions say ${\varphi }_0$ of massless scalar theories on Euclidean space, i.e. $D=6{\varphi }^3$, $D=4{\varphi }^4$ and $D=3{\varphi }^6$ models are obtained which share similar properties. The information geometry of their moduli spaces coincide with the Euclidean ${\mathrm{AdS}}_7$, ${\mathrm{AdS}}_5$ and ${\mathrm{AdS}}_4$ respectively on which ${\varphi }_0$ can be described as a stable tachyon. In $D=4$ we recognize that the SU(2) instanton density is proportional to ${\varphi }_0^4$. The original action $S[\varphi ]$ written in terms of new scalars $\tilde{\varphi }=\varphi -{\varphi }_0$ is shown to be equivalent to an interacting scalar theory on $D$-dimensional de Sitter background.

The observed cosmic $\gamma$-ray background at $\sim \mathrm{MeV}$ has often been attributed to Type Ia supernovae (SNIa). Since SNIa is close to a standard candle, one can calculate the $\gamma$-ray intensity of SNIa integrated over redshifts fairly accurately, once the evolution of the SNIa rate is known. The latest SNIa rate measured at $z\lesssim 1.6$ [Dahlen et al., Astrophys. J. 613, 189 (2004)] indicates that the previous calculations of the $\gamma$-ray background consistently overestimated the SNIa rate. With the new rate, we find that the SNIa contribution is an order of magnitude smaller than observed, and thus new population(s) of sources should be invoked.

We try to understand the polarization puzzle in $B\to \varphi K^{*}$ decays with a simple Higgs model associated with flavor changing neutral current at tree level. The new interactions can effectively reduce the longitudinal polarization $|A_0{|}^2$. In particular, we find that if the couplings of $b$-quark in different chiralities to Higgs are the same, the transverse polarization $|A_{\perp }{|}^2$ can receive the largest contribution and its value can be as large as $30\%$. On the other hand, with opposite sign in the couplings, the other transverse polarization $|A_{\parallel }{|}^2$ is enhanced.

We study the effect of new physics on the $Z$ decay into $b\overline{b}$ pairs in the framework of 331 models. The decay $Z\to b\overline{b}$ is computed at one loop level and, using previous results, we evaluate this branching fraction in the framework of 331 models. A wide range of the space parameter of the model is considered and possible deviations from the standard model predictions are explored. From precision measurements at the $Z$ pole we find the allowed region for the mass of exotic quarks $M_{J_3}$ and bileptons $M_X$ at 95% CL.

We report on a study of jet shapes in inclusive jet production in $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$ using the upgraded collider detector at Fermilab in Run II (CDF II) and based on an integrated luminosity of $170\mathrm{p}{\mathrm{b}}^{-1}$. Measurements are carried out on jets with rapidity $0.1<|Y^{\mathrm{jet}}|<0.7$ and transverse momentum $37\mathrm{GeV}/c<P_T^{\mathrm{jet}}<380\mathrm{GeV}/c$. The jets have been corrected to the hadron level. The measured jet shapes are compared to leading-order QCD parton-shower Monte Carlo predictions as implemented in the PYTHIA and HERWIG programs. PYTHIA, tuned to describe the underlying event as measured in CDF Run I, provides a better description of the measured jet shapes than does PYTHIA or HERWIG with their default parameters.

Supersymmetric $U(N_{\mathrm{C}})$ gauge theory with $N_{\mathrm{F}}$ massive hypermultiplets in the fundamental representation is given by the brane configuration made of $N_{\mathrm{C}}$ fractional $\mathrm{D}p$-branes stuck at the ${\mathbf{Z}}_2$ orbifold singularity on $N_{\mathrm{F}}$ separated $\mathrm{D}(p+4)$-branes. We show that non-Abelian walls in this theory are realized as kinky fractional $\mathrm{D}p$-branes interpolating between $\mathrm{D}(p+4)$-branes. Wall solutions and their duality between $N_{\mathrm{C}}$ and $N_{\mathrm{F}}-N_{\mathrm{C}}$ imply extensions of the s-rule and the Hanany-Witten effect in brane dynamics. We also find that the reconnection of fractional D-branes occurs in this system. Diverse phenomena in non-Abelian walls found in field theory can be understood very easily by this brane configuration.

We employ the Schwinger-Keldysh formalism to study the nonequilibrium dynamics of the mirror with perfect reflection moving in a quantum field. In the case where the mirror undergoes the small displacement, the coarse-grained effective action is obtained by integrating out the quantum field with the method of influence functional. The semiclassical Langevin equation is derived, and is found to involve two levels of backreaction effects on the dynamics of mirrors: radiation reaction induced by the motion of the mirror and backreaction dissipation arising from fluctuations in quantum field via a fluctuation-dissipation relation. Although the corresponding theorem of fluctuation and dissipation for the case with the small mirror’s displacement is of model independence, the study from the first principles derivation shows that the theorem is also independent of the regulators introduced to deal with short-distance divergences from the quantum field. Thus, when the method of regularization is introduced to compute the dissipation and fluctuation effects, this theorem must be fulfilled as the results are obtained by taking the short-distance limit in the end of calculations. The backreaction effects from vacuum fluctuations on moving mirrors are found to be hardly detected while those effects from thermal fluctuations may be detectable.

To capture important physical properties of a spacetime we construct a new diagram, the card diagram, which accurately draws generalized Weyl spacetimes in arbitrary dimensions by encoding their global spacetime structure, singularities, horizons, and some aspects of causal structure including null infinity. Card diagrams draw only nontrivial directions providing a clearer picture of the geometric features of spacetimes as compared to Penrose diagrams, and can change continuously as a function of the geometric parameters. One of our main results is to describe how Weyl rods are traversable horizons and the entirety of the spacetime can be mapped out. We review Weyl techniques and as examples we systematically discuss properties of a variety of solutions including Kerr-Newman black holes, black rings, expanding bubbles, and recent spacelike-brane solutions. Families of solutions will share qualitatively similar cards. In addition we show how card diagrams not only capture information about a geometry but also its analytic continuations by providing a geometric picture of analytic continuation. Weyl techniques are generalized to higher dimensional charged solutions and applied to generate perturbations of bubble and S-brane solutions by Israel-Khan rods.

We present two examples of velocity distributions for light dark matter particles that reconcile the annual modulation signal observed by DAMA with all other negative results from dark matter searches. They are: (1) a conventional Maxwellian distribution for particle masses around 5 to 9 GeV; (2) a dark matter stream coming from the general direction of galactic rotation (not the Sagittarius stream). Our idea is based on attributing the DAMA signal to scattering off Na, instead of I, and can be tested in the immediate future by detectors using light nuclei, such as CDMS-II (using Si) and CRESST-II (using O).

We discuss the phenomena of symmetry nonrestoration and inverse symmetry breaking in the context of multi-scalar field theories at finite temperatures and present its consequences for the relativistic Higgs-Kibble multi-field sector as well as for a nonrelativistic model of hard core spheres. For relativistic scalar field models, it has been shown previously that temperature effects on the couplings do not alter, qualitatively, the phase transition pattern. Here, we show that for the nonrelativistic analogue of these models inverse symmetry breaking, as well as symmetry nonrestoration, cannot take place, at high temperatures, when the temperature dependence of the two-body couplings is considered. However, the temperature behavior in the nonrelativistic models allows for the appearance of reentrant phases.

We calculate the angular scale of the acoustic oscillation from the BOOMERANG and WMAP data on the cosmic microwave background (CMB) to constrain the holographic dark energy model recently proposed by Li. We find that only the phantomlike holographic dark energy survives the cosmological tests. This is, however, inconsistent with the positive energy condition implicitly assumed in constructing Li’s model. Therefore the model is marginally ruled out by the present CMB data. As a supplementary check, we also calculate the suppression of the matter density fluctuation due to the late time integrated Sach-Wolfe effect by the holographic dark energy, the result is within the tolerance of the cosmic variance. Some aspect about the saturation of the cosmic holographic bound is also discussed.

The mechanism of gravitational baryogenesis, based on the $CPT$-violating gravitational interaction between the derivative of the Ricci scalar curvature and the baryon-number current, is investigated in the context of the Gauss-Bonnet braneworld cosmology. We study the constraints on the fundamental five-dimensional gravity scale, the effective scale of $B$-violation and the decoupling temperature, for the above mechanism to generate an acceptable baryon asymmetry during the radiation-dominated era. The scenario of gravitational leptogenesis, where the lepton-number violating interactions are associated with the neutrino mass seesaw operator, is also considered.