The question of how perturbations evolve through a bounce in the Cyclic and Ekpyrotic models of the Universe remains a topical one. Issues concerning singularities at the background level and at the level of perturbation theory continue to be a matter of debate. In this report we hope to demonstrate a nonsingular collision between the boundary branes at the background level, and circumstances under which all perturbation variables remain bounded through the collision. As expected, we find most collisions to be singular even in the full 5D formalism, where first order perturbation theory breaks down for at least one perturbation variable. Only in the case that the boundary branes approach each other with constant velocity shortly before the bounce, can a consistent, nonsingular solution be found. It is then possible to follow the perturbations explicitly until the actual collision. In this case, we find that if a scale-invariant spectrum developed on the hidden brane, it will get transferred to the visible brane during the bounce.

Vacuum expectation value of the surface energy-momentum tensor is evaluated for a massive scalar field with general curvature coupling parameter subject to Robin boundary conditions on two parallel branes located on $(D+1)$-dimensional anti-de Sitter bulk. The general case of different Robin coefficients on separate branes is considered. As a regularization procedure the generalized zeta function technique is used, in combination with contour integral representations. The surface energies on the branes are presented in the form of the sums of single brane and second brane-induced parts. For the geometry of a single brane both regions, on the left (L-region) and on the right (R-region), of the brane are considered. The surface densities for separate L- and R-regions contain pole and finite contributions. For an infinitely thin brane taking these regions together, in odd spatial dimensions the pole parts cancel and the total surface energy is finite. The parts in the surface densities generated by the presence of the second brane are finite for all nonzero values of the interbrane separation. It is shown that for large distances between the branes the induced surface densities give rise to an exponentially suppressed cosmological constant on the brane. In the Randall-Sundrum braneworld model, for the interbrane distances solving the hierarchy problem between the gravitational and electroweak mass scales, the cosmological constant generated on the visible brane is of the right order of magnitude with the value suggested by the cosmological observations.

We present a comprehensive study of the massless scalar field perturbation in the Reissner-Nordström anti-de Sitter (RNAdS) space-time and compute its quasinormal modes (QNM). For the lowest lying mode, we confirm and extend the dependence of the QNM frequencies on the black hole charge obtained in previous works. In near extreme limit, under the scalar perturbation we find that the imaginary part of the frequency tends to zero, which is consistent with the previous conjecture based on electromagnetic and axial gravitational perturbations. For the extreme value of the charge, the asymptotic field decay is dominated by a power-law tail, which shows that the extreme black hole can still be stable to scalar perturbations. We also study the higher overtones for the RNAdS black hole and find large variations of QNM frequencies with the overtone number and black hole charge. The nontrivial dependence of frequencies on the angular index $\ell$ is also discussed.

We have studied scalar perturbations as well as fermion perturbations in pure de Sitter spacetimes. For scalar perturbations we have shown that well-defined quasinormal modes in $d$-dimensions can exist provided that the mass of scalar field $m>\frac{d-1}{2l}$. The quasinormal modes of fermion perturbations in three and four dimensional cases have also been investigated. We found that different from other dimensional cases, in the three dimensional pure de Sitter spacetime there is no quasinormal mode for the s-wave. This interesting difference caused by the spacial dimensions is true for both scalar and fermion perturbations.

In this paper I show that one can have asymptotically de Sitter, anti-de Sitter (AdS), and flat solutions in Gauss-Bonnet gravity without a cosmological constant term in field equations. First, I introduce static solutions whose three surfaces at fixed $r$ and $t$ have constant positive ($k=1$), negative ($k=-1$), or zero ($k=0$) curvature. I show that for $k=\pm 1$ one can have asymptotically de Sitter, AdS, and flat spacetimes, while for the case of $k=0$, one has only asymptotically AdS solutions. Some of these solutions present naked singularities, while some others are black hole or topological black hole solutions. I also find that the geometrical mass of these five-dimensional spacetimes is $m+2\alpha |k|$, which is different from the geometrical mass $m$ of the solutions of Einstein gravity. This feature occurs only for the five-dimensional solutions, and is not repeated for the solutions of Gauss-Bonnet gravity in higher dimensions. Second, I add angular momentum to the static solutions with $k=0$, and introduce the asymptotically AdS charged rotating solutions of Gauss-Bonnet gravity. Finally, I introduce a class of solutions which yields an asymptotically AdS spacetime with a longitudinal magnetic field, which presents a naked singularity, and generalize it to the case of magnetic rotating solutions with two rotation parameters.

We study the effective potential of a scalar field based on the 5D gauged supergravity for the Randall-Sundrum type one brane model in terms of the brane running method. The scalar couples to the brane such that the Bogomolnyi-Prasad-Sommerfield conditions are satisfied for the bulk configuration. The resulting effective potential implies that the interbrane distance is undetermined in this case, and we need a small Bogomolnyi-Prasad-Sommerfield breaking term on the brane to stabilize the interbrane distance at a finite length. We also discuss the relationship to the Goldberger-Wise model.

We consider the conditions which must be satisfied for a Majorana RH sneutrino, a massive right-handed (RH) sneutrino associated with the seesaw mechanism of Majorana neutrino masses, to play the role of the curvaton. Planck-scale suppressed nonrenormalizable terms in the RH neutrino superpotential must be eliminated to a high-order if the RH sneutrino curvaton is to dominate the energy density before it decays, which can be achieved via an R-symmetry which is broken to R-parity by the Giudice-Maseiro mechanism. In order to evade thermalization of the curvaton condensate, one RH neutrino mass eigenstate must have small Yukawa couplings, corresponding to a lightest neutrino mass $m_{{\nu }_1}\lesssim {10}^{-3}\mathrm{e}\mathrm{V}$. A time-dependent lepton asymmetry will be induced in the RH sneutrino condensate by the Affleck-Dine mechanism driven by SUSY breaking B-terms associated with the RH neutrino masses. Requiring that the resulting baryon asymmetry and isocurvature perturbations are acceptably small imposes an upper bound on the RH neutrino mass. We show that a scenario consistent with all constraints is obtained for a RH neutrino mass in the range ${10}^2-{10}^4\mathrm{G}\mathrm{e}\mathrm{V}$ when the RH sneutrino decay temperature is greater than $100\mathrm{G}\mathrm{e}\mathrm{V}$ and lightest neutrino mass $m_{{\nu }_1}\approx {10}^{-3}\mathrm{e}\mathrm{V}$. Larger RH neutrino masses are possible for smaller $m_{{\nu }_1}$. The resulting scenario is generally consistent with a solution of the cosmic string problem of D-term inflation.

Scalar-tensor theories of gravity provide a consistent framework to accommodate an ultralight quintessence scalar field. While the equivalence principle is respected by construction, deviations from general relativity and standard cosmology may show up at nucleosynthesis, cosmic microwave background, and solar system tests of gravity. After imposing all the bounds coming from these observations, we consider the expansion rate of the Universe at weakly interacting massive particle decoupling, showing that it can lead to an enhancement of the dark matter relic density up to few orders of magnitude with respect to the standard case. This effect can have an impact on supersymmetric candidates for dark matter.

Inflation of a universe filled by an elastic continuous medium is considered. Elastic inflation, while capable of describing current observations, is qualitatively different from standard inflationary models. The scalar and tensor modes keep evolving after crossing the horizon. Because of this superhorizon evolution, the amplitude of the tensor mode (inflationary gravitational wave) is not simply proportional to the energy density of the universe at the time of horizon crossing. The spectral index of tensor modes can be positive.

We study the cosmic microwave background (CMB) anisotropies constraints on two Dark Energy models described by scalar fields with different Lagrangians, namely, a Klein-Gordon and a Born-Infeld field. The speed of sound of field fluctuations are different in these two theories, and therefore the predictions for CMB and structure formation are different. Employing the Wilkinson Microwave Anisotropy Probe data on CMB, we make a likelihood analysis on a grid of theoretical models. We constrain the parameters of the models and compute the probability distribution functions for the equation of state. We show that the effect of the different sound speeds affects the low multipoles of CMB anisotropies, but is at most marginal for the class of models studied here.

We show that the process of spontaneous symmetry breaking can trap a field theoretic system in a highly nontrivial state containing a lattice of domain walls. In one large compact space dimension, a lattice is inevitably formed. In two dimensions, the probability of lattice formation depends on the ratio of sizes $L_x$, $L_y$ of the spatial dimensions. We find that a lattice can form even if $R\equiv L_y/L_x$ is of order unity. We numerically determine the number of walls in the lattice as a function of $L_x$ and $L_y$.

We study the effect of Faraday rotation due to a uniform magnetic field on the polarization of the cosmic microwave background. Scalar fluctuations give rise only to parity-even $E$-type polarization of the cosmic microwave background. However in the presence of a magnetic field, a nonvanishing parity-odd $B$-type polarization component is produced through Faraday rotation. We derive the exact solution for the $E$ and $B$ modes generated by scalar perturbations including the Faraday rotation effect of a uniform magnetic field, and evaluate their cross correlations with temperature anisotropies. We compute the angular autocorrelation function of the $B$-modes in the limit that the Faraday rotation is small. We find that uniform primordial magnetic fields of present strength around $B_0={10}^{-9}\mathrm{G}$ rotate $E$-modes into $B$-modes with amplitude comparable to those due to the weak gravitational lensing effect at frequencies around $\nu =30\mathrm{G}\mathrm{H}z$. The strength of $B$-modes produced by Faraday rotation scales as $B_0/{\nu }^2$. We evaluate also the depolarizing effect of Faraday rotation upon the cross correlation between temperature anisotropy and $E$-type polarization.

We use multifrequency information in first year Wilkinson microwave anisotropy probe (WMAP) data to search for the Sunyaev-Zeldovich (SZ) effect. WMAP has sufficiently broad frequency coverage to constrain the SZ effect without the addition of higher frequency data: the SZ power spectrum amplitude is expected to increase 50% from W to Q frequency band. This, in combination with the low noise in WMAP, allows us to strongly constrain the SZ contribution. We derive an optimal frequency combination of WMAP cross-spectra to extract the SZ effect in the presence of noise, cosmic microwave background (CMB), and radio point sources, which are marginalized over. We find that the SZ contribution is less than 2% (95% C.L.) at the first acoustic peak in W band. Under the assumption that the removed radio point sources are not correlated with the SZ effect this limit implies ${\sigma }_8<1.07$ at 95% C.L. We investigate the effect on the cosmological parameters of allowing an SZ component. We run Monte Carlo Markov chains with and without an SZ component and find that the addition of the SZ effect does not affect any of the cosmological conclusions. We conclude that the SZ effect does not contaminate the WMAP CMB or change cosmological parameters, refuting the recent claims that they may be corrupted.

The sensitivity of the $B\to \pi K$ mode to electroweak penguin diagrams and the recent experimental data for the $B\to \pi \pi ,\pi K$ modes has given rise to what is known as the “$B\to \pi K$ puzzle.” Recently it has been observed that this puzzle can be resolved by considering the new physics which can enter via $Z^0$ penguin diagrams. In this note we analyze the effect of these enhanced $Z^0$ penguin diagrams on the lepton polarization asymmetries of $b\to s{\ell }^{+}{\ell }^{-}$.

We present calculations of the magnetic moment contribution to neutrino electron scattering in large extra dimension brane-bulk models (LED) with three bulk neutrinos. We discuss the cases with two and three large extra dimensions of sizes $R$. The calculations are done using reactor flux from Uranium, ${}^{235}\mathrm{U}$ as the neutrino source. We find that if the electron neutrino mass is chosen to be in the range of 1 eV, the differential cross section for $\overline{\nu }-e$ scattering for low electron recoil energy can be of the same order as the presently explored values in reactor experiments. Furthermore the spectral shape for the LED models is different from the four dimensional case. Future higher precision reactor experiments can therefore be used to provide new constraints on a class of large extra dimension theories.

We examine the process of Compton scattering, in the presence of a Lorentz- and $CPT$-violating modification to the structure of the electron. We calculate the complete tree-level contribution to the cross section; our result is valid to all orders in the Lorentz-violating parameter. We find a cross section that differs qualitatively from the Klein-Nishina result at small frequencies, and we also encounter a previously undescribed complication that will arise in the calculation of many Lorentz-violation cross sections: The Lorentz violation breaks the spin degeneracy of the external states, so we cannot use a closure relation to calculate the unpolarized cross section.

We obtain relations between partial-wave amplitudes for $\pi N\to \pi N$ and $\pi N\to \pi \Delta$ directly from large $N_c$ QCD. While linear relations among certain amplitudes holding at leading order (LO) in $1/N_c$ were derived in the context of chiral soliton models two decades ago, the present work employs a fully model-independent framework based on consistency with the large $N_c$ expansion. At LO in $1/N_c$ we reproduce the soliton model results; however, this method allows for systematic corrections. At next-to-leading order (NLO), most relations require additional unknown functions beyond those appearing at LO and thus have little additional predictive power. However, three NLO relations for the $\pi N\to \pi \Delta$ reaction are independent of unknown functions and make predictions accurate at this order. The amplitudes relevant to two of these relations were previously extracted from experiment. These relations describe experiment dramatically better than their LO counterparts.

We propose a mechanism to generate hierarchy between masses of the top and bottom quarks without fine-tuning of the Yukawa coupling constants in the context of the two Higgs doublet model (THDM). In the THDM with a discrete symmetry, there exists the vacuum where only the top quark receives the mass of the order of the electroweak symmetry breaking scale $v(\simeq 246\mathrm{G}\mathrm{e}\mathrm{V})$, while the bottom quark remains massless. By introducing a small soft-breaking parameter $m_3^2$ of the discrete symmetry, the bottom quark perturbatively acquires a nonzero mass. We show a model in which the small $m_3^2[\sim v^2/(4\pi {)}^2]$ is generated by the dynamics above the cutoff scale of the THDM. The ratio $\tan \beta$ of the two vacuum expectation values is necessarily very large, i.e., $\tan \beta \sim m_t/m_b$. We also find a salient relation, $1/\tan \beta \simeq m_3^2/m_H^2$, where $m_H$ is the mass of the extra $CP$-even Higgs boson. Our scenario yields some specific features that can be tested in future collider experiments.

We present an effective flavor model for the radiative generation of fermion masses and mixings based on a $\mathrm{S}\mathrm{U}(5{)}_V\times \mathrm{U}(2{)}_H$ symmetry. We assume that the original source of flavor breaking resides in the supersymmetry-breaking sector. Flavor violation is transmitted radiatively to the fermion Yukawa couplings at low energy through finite supersymmetric threshold corrections. This model can fit the fermion mass ratios and Cabibbo-Kobayashi-Maskawa matrix elements, explain the nonobservation of proton decay, and overcome the present constraints on flavor changing processes through an approximate radiative alignment between the Yukawa and the soft trilinear sector. The model predicts relations between dimensionless fermion mass ratios in the three fermion sectors, and the quark mixing angles, $|V_{us}|\approx [m_d/m_s{]}^{1/2}\approx [m_u/m_c{]}^{1/4}\approx 3[m_e/m_{\mu }{]}^{1/2}$ and $\frac{1}{2}|V_{cb}/V_{us}|\approx [m_s^3/m_b^2{m}_d{]}^{1/2}\approx [m_c^3/m_t^2{m}_u{]}^{1/2}\approx \frac{1}{9}[m_{\mu }^3/m_{\tau }^2{m}_e{]}^{1/2}$, which are confirmed by the experimental measurements.

Although at asymptotically high temperatures the quark-gluon plasma (QGP) is a gas of weakly interacting quasiparticles (modulo long-range magnetism), and it has quite different properties at temperatures of the order of a few times the critical temperature $T=(1–3)T_c$. As experiments and lattice simulations are now showing, in this region the QGP displays strong interactions between the constituents. In this paper we try to develop a theory of one of its consequences, namely, the properties of a large number of binary bound states, both hadronlike (colorless) and exotic (colored) bound pairs $gq$, $qq$, and $gg$. We evaluate their binding energies and zero-binding lines on the phase diagram and estimate their contribution to bulk thermodynamics (pressure). Their role in the transport properties (viscosity), emphasized in our previous paper, will be addressed elsewhere.