We argue that smeared brane solutions, where a charged black $p$-brane is smeared uniformly over one of the transverse directions, can have a Gregory-Laflamme–type dynamical instability in the smeared direction even when the solution is locally thermodynamically stable. These thus seem to provide counterexamples to the Gubser-Mitra conjecture, which links local dynamical and thermodynamic stability. By exploiting an ansatz due to Harmark and Obers, which relates charged solutions to neutral ones, we demonstrate the existence of a threshold unstable mode. This provides strong evidence for the existence of a dynamical instability, although we do not demonstrate its existence directly.

We present a detailed study of a simple scalar field model that yields nonsingular cosmological solutions. We study both the qualitative dynamics of the homogeneous and isotropic background and the evolution of inhomogeneous linear perturbations. We calculate the spectrum of perturbations generated on super-Hubble scales during the collapse phase from initial vacuum fluctuations on small scales and then evolve these numerically through the bounce. We show there is a gauge in which perturbations remain well-defined and small throughout the bounce, even though perturbations in other commonly used gauges become large or ill-defined. We show that the comoving curvature perturbation calculated during the collapse phase provides a good estimate of the resulting large-scale adiabatic perturbation in the expanding phase while the Bardeen metric potential is dominated by what becomes a decaying mode after the bounce. We show that a power-law collapse phase with scale factor proportional to $(-t{)}^{2/3}$ can yield a scale-invariant spectrum of adiabatic scalar perturbations in the expanding phase, but the amplitude of tensor perturbations places important constraints on the allowed initial conditions.

Dark matter may be composed of superWIMPs, superweakly-interacting massive particles produced in the late decays of other particles. We focus on the case of gravitinos produced in the late decays of sleptons or sneutrinos and assume they are produced in sufficient numbers to constitute all of nonbaryonic dark matter. At leading order, these late decays are two-body and the accompanying energy is electromagnetic. For natural weak-scale parameters, these decays have been shown to satisfy bounds from Big Bang nucleosynthesis and the cosmic microwave background. However, sleptons and sneutrinos may also decay to three-body final states, producing hadronic energy, which is subject to even more stringent nucleosynthesis bounds. We determine the three-body branching fractions and the resulting hadronic energy release. We find that superWIMP gravitino dark matter is viable and determine the gravitino and slepton/sneutrino masses preferred by this solution to the dark matter problem. In passing, we note that hadronic constraints disfavor the possibility of superWIMPs produced by neutralino decays unless the neutralino is photinolike.

If the halo dark matter were composed of primordial black holes (PBHs) with mass between ${10}^{16}$ and ${10}^{20}\mathrm{g}$, their gravitational interaction with test masses of laser interferometer may lead to a detectable pulselike signal during the fly-by. If a proof-mass noise of $3\times {10}^{-15}\mathrm{m}/{\mathrm{s}}^{\mathrm{2}}/{\mathrm{H}\mathrm{z}}^{1/2}$ down to $\sim {10}^{-5}\mathrm{H}\mathrm{z}$ is achieved by the Laser Interferometer Space Antenna, the event rate, with signal-to-noise ratios greater than 5, could become $\sim 0.1$ per decade, involving black holes of mass $\sim {10}^{17}\mathrm{g}$. The detection rate could improve significantly for future space-based interferometers, though these events must be distinguished from those involving perturbations due to near-Earth asteroids. While the presence of primordial black holes below a mass of $\sim {10}^{16}\mathrm{g}$ is now constrained based on the radiation released during their evaporation, the gravitational-wave detectors could potentially extend the search for PBHs to several orders of magnitude higher masses.

We study the thermal leptogenesis in the scenario where the standard model is extended to include one $\mathrm{S}\mathrm{U}(2{)}_L$ triplet Higgs boson, in addition to three generations of the right-handed neutrinos. In the model, we introduce the coupling between the quintessence and the right-handed neutrinos, the triplet Higgs boson, so that the light neutrino masses vary during the evolution of the Universe. Assuming that the lepton number asymmetry is generated by the decays of the lightest right-handed neutrino $N_1$, we find the thermal leptogenesis can be characterized by four model independent parameters. In the case where the contribution of the triplet Higgs to the lepton asymmetry is dominant, we give the relation between the minimal $M_1$ and the absolute mass scale $\overline{m}$ of the light neutrinos, by solving the Boltzmann equations numerically. We will also show that, with the varying neutrino masses, the reheating temperature can be lowered in comparison to the traditional thermal leptogenesis.

We study how parameter error forecasts for tomographic cosmic shear observations are affected by sky coverage, density of source galaxies, inclusion of cosmic microwave background experiments, simultaneous fitting of nondark energy parameters, and the parametrization of the history of the dark energy equation-of-state parameter $w(z)$. We find tomographic shear-shear power spectra on large angular scales ($l<1000$) inferred from all-sky observations, in combination with Planck, can achieve $\sigma (w_0)=0.06$ and $\sigma (w_a)=0.09$ assuming the equation-of-state parameter is given by $w(z)=w_0+w_a[1-a(z)]$ and that nine other matter content and primordial power spectrum parameters are simultaneously fit. Taking parameters other than $w_0$, $w_a$, and ${\Omega }_m$ to be completely fixed by the cosmic microwave background (CMB), we find errors on $w_0$ and $w_a$ that are only 10% and 30% better, respectively, justifying this common simplifying assumption. We also study “dark energy tomography”   : reconstruction of $w(z)$ assumed to be constant within each of five independent $w$ bins. With smaller-scale information included by use of the Jain and Taylor ratio statistic, we find $\sigma (w_i)<0.1$ for all five $w$ bins and $\sigma (w_i)<0.02$ for both $w$ bins at $z<0.8$. Finally, addition of cosmic shear can also reduce errors on quantities already determined well by the CMB. We find the sum of neutrino masses can be determined to $\pm 0.013\mathrm{e}\mathrm{V}$ and that the primordial power spectrum power-law index, $n_S$, as well as $d{n}_s/d\ln k$, can be determined more than a factor of 2 better than by Planck alone. These improvements may be highly valuable since the lower bound on the sum of neutrino masses is 0.06 eV as inferred from atmospheric neutrino oscillations, and slow-roll models of inflation predict nonzero $d{n}_S/d\ln k$ at the forecasted error levels when $|n_S-1|>0.04$.

Laser interferometer gravitational wave detectors need vacuum tubes through which the laser beams pass. The light scattered from the arm cavity mirrors will make multiple reflections from the inside wall of the polished tube back onto the mirrors causing phase noise on the interferometer output beam. The TAMA300 has two 300 m length arms enclosed by vacuum tubes. By vibrating one of the tubes of the TAMA300, we directly observed the effect of the scattered light on the displacement sensitivity. It was found that a tube vibration amplitude of $5.6\mu \mathrm{m}$ at 776.5 Hz increased the mirror displacement noise by $1.2\times {10}^{-17}\mathrm{m}$. This noise level is consistent with the calculated noise due to the scattered light effect.

Time-delay interferometry (TDI) is the data processing technique needed for generating interferometric combinations of data measured by the multiple Doppler readouts available onboard the three Laser Interferometer Space Antenna (LISA) spacecraft. Within the space of all possible interferometric combinations TDI can generate, we have derived a specific combination that has zero response to the gravitational wave signal, and called it the zero-signal solution (ZSS). This is a two-parameter family of linear combinations of the generators of the TDI space, and its response to a gravitational wave becomes null when these two parameters coincide with the values of the angles of the source location in the sky. Remarkably, the ZSS does not rely on any assumptions about the gravitational waveform, and in fact it works for waveforms of any kind. Our approach is analogous to the data analysis method introduced by Gürsel and Tinto in the context of networks of Earth-based, wideband, interferometric gravitational wave detectors observing in coincidence a gravitational wave burst. The ZSS should be regarded as an application of the Gürsel and Tinto method to the LISA data.

Using a recent calculation of transition magnetic moments in the $1/N_c$ expansion and a calculation showing the suppression of $E2/M1$ by powers of $N_c$, we compute the widths for the radiative decays ${\Sigma }^{*}\to \Sigma \gamma$, ${\Sigma }^{*}\to \Lambda \gamma$, and ${\Xi }^{*}\to \Xi \gamma$.

In the linear moose framework, which naturally emerges in deconstruction models, we show that there is a unique solution for the vanishing of the $S$ parameter at the lowest order in the weak interactions. We consider an effective gauge theory based on $K$ SU(2) gauge groups, $K+1$ chiral fields, and electroweak groups $\mathrm{S}\mathrm{U}(2{)}_L$ and $\mathrm{U}(1{)}_Y$ at the ends of the chain of the moose. $S$ vanishes when a link in the moose chain is cut. As a consequence one has to introduce a dynamical nonlocal field connecting the two ends of the moose. Then the model acquires an additional custodial symmetry which protects this result. We examine also the possibility of a strong suppression of $S$ through an exponential behavior of the link couplings as suggested by the Randall Sundrum metric.

We show that in an $\mathrm{S}\mathrm{U}(2)\otimes \mathrm{U}(1)$ model with a Dine-Fischler-Srednicki–like invisible axion it is possible to obtain (i) the convergence of the three gauge coupling constants at an energy scale near the Peccei-Quinn scale; (ii) the correct value for ${sin}^2{\widehat{\theta }}_W(M_Z)$; (iii) the stabilization of the proton by the cyclic $Z_{13}\otimes Z_3$ symmetries which also stabilize the axion as a solution to the strong $CP$ problem. Concerning the convergence of the three coupling constants and the prediction of the weak mixing angle at the $Z$ peak, this model is as good as the minimal supersymmetric standard model with ${\mu }_{\mathrm{S}\mathrm{U}\mathrm{S}\mathrm{Y}}=M_Z$. We also consider the standard model with six and seven Higgs doublets. The main calculations were done in the 1-loop approximation but we briefly consider the 2-loop contributions.

In studies of the QCD deconfining phase transition or crossover by means of heavy ion experiments, one ought to be concerned about nonequilibrium effects due to heating and cooling of the system. In this paper we extend our previous study of Glauber dynamics of 2D Potts models to the 3D 3-state Potts model, which serves as an effective model for some QCD properties. We investigate the linear theory of spinodal decomposition in some detail. It describes the early time evolution of the 3D model under a quench from the disordered into the ordered phase well, but fails in 2D. Further, the quench leads to competing vacuum domains, which are difficult to equilibrate, even in the presence of a small external magnetic field. From our hysteresis study we find, as before, a dynamics dominated by spinodal decomposition. There is evidence that some effects survive in the case of a crossover. But the infinite volume extrapolation is difficult to control, even with lattices as large as ${120}^3$.

We calculate the cross section for ${\eta }_b$ production at the Tevatron at next-to-leading-order in the strong coupling and find that more than two millions of ${\eta }_b$’s are expected per inverse picobarn of integrated luminosity. We discuss the decay modes into charmed states and suggest that the decays into $D^{*}{D}^{(*)}$ mesons might be the most promising channels to observe the ${\eta }_b$ in Run II.

Based on the light-cone (LC) framework and the $k_T$ factorization formalism, the transverse momentum effects and the different helicity components' contributions to the pion form factor $F_{\pi }(Q^2)$ are recalculated. In particular, the contributions to the pion form factor from the higher-helicity components (${\lambda }_1+{\lambda }_2=\pm 1$), which come from the spin-space Wigner rotation, are analyzed in the soft and hard energy regions, respectively. Our numerical results show that the right power behavior of the hard contribution from the higher-helicity components can only be obtained by fully keeping the $k_T$ dependence in the hard amplitude, and that the $k_T$ dependence in LC wave function affects the hard and soft contributions substantially. As an example, we employ a model LC wave function to calculate the pion form factor and then compare the numerical predictions with the experimental data.

A neutral vector boson can possess static electromagnetic properties provided that the associated field is non-self-conjugate. This possibility is explored in the ${\mathrm{S}\mathrm{U}}_C(3)\times {\mathrm{S}\mathrm{U}}_L(3)\times {\mathrm{U}}_N(1)$ model with right-handed neutrinos, which predicts a complex neutral gauge boson $Y^0$ in a nontrivial representation of the electroweak group. In this model the only nonvanishing form factors are the CP-even ones, which arise from both the quark and gauge sectors, and contribute to the magnetic dipole and the electric quadrupole moments of this neutral particle.

Motivated by the E787 and E949 result for $K^{+}\to {\pi }^{+}\nu \overline{\nu }$ we examine the effects of a new nonuniversal right-handed $Z^{\prime }$ boson on flavor changing processes. We place bounds on the tree-level flavor-changing neutral current from $K-\overline{K}$ and $B-\overline{B}$ mixing as well as from the observed $CP$ violation in kaon decay. We discuss the implications for $K\to \pi \nu \overline{\nu }$, $B\to X\nu \overline{\nu }$ and $B\to {\tau }^{+}{\tau }^{-}$. We find that the existing bounds allow substantial enhancements in the $K^{+}\to {\pi }^{+}\nu \overline{\nu }$ rate, particularly through a new one-loop $Z^{\prime }$ penguin operator.

We report new results of a test of Lorentz invariance based on the comparison of a cryogenic sapphire microwave resonator and a hydrogen-maser. The experimental results are shown together with an extensive analysis of systematic effects. Previously, this experiment has set the most stringent constraint on Kennedy-Thorndike type violations of Lorentz invariance. In this work we present new data and interpret our results in the general Lorentz violating extension of the standard model of particle physics (SME). Within the photon sector of the SME, our experiment is sensitive to seven SME parameters. We marginally improve present limits on four of these, and by a factor seven to ten on the other three.

We investigate the implications of the nontrivial vacuum structure of little Higgs models. In particular, focusing on the littlest Higgs model, we demonstrate the existence of three types of topological defects. One is a global cosmic string that is truly topological. The second is more subtle; a semilocal cosmic string, which may be stable due to dynamical effects. The final defect is a $Z_2$ monopole solution with an unusual structure. We briefly discuss the possible cosmological consequences of such nonperturbative structures, although we note that these depend crucially on the fermionic content of the models.

The causal structure of the flat brane universe of RSII type is reinvestigated to clarify the boundary conditions for stochastic gravitational waves. In terms of the Gaussian normal coordinate of the brane, a singularity of the equation for gravitational waves appears in the bulk. We show that this singularity corresponds to the “seam singularity” which is a singular subspace on the brane universe. Based upon the causal structure, we discuss the boundary conditions for gravitational waves in the bulk. Introducing a null coordinate, we propose a numerical procedure to solve gravitational waves with appropriate boundary conditions and show some examples of our numerical results. This procedure could be also applied in scalar type perturbations. The problem in the choice of the initial condition for gravitational waves is briefly discussed.

The observational evidence for a population of quasars powered by supermassive black holes of mass $\gtrsim {10}^9{M}_{\odot }$ at redshifts $z\gtrsim 6$ poses a great challenge for any model describing the formation of galaxies. Assuming uninterrupted accretion at the Eddington limit, seed black holes of at least $1000M_{\odot }$ are needed at $z\approx 15$. Here I study whether seeds could be primordial black holes (PBHs) which have been produced in the very early universe by the collapse of primordial density fluctuations. In particular, I study the expected number densities of PBHs in the relevant mass range for several classes of spectra of primordial density fluctuations and confront the results with observational data. While it seems to be possible to produce the required PBHs with spectra showing large enhancements of fluctuations on a certain scale, our hypothesis can be clearly disproved for a scale free spectrum of primordial fluctuations described by a power-law slope consistent with recent observations.