It has been suggested recently that the observed dimming of distant type Ia supernovae may be a consequence of mixing of the photons with very light axions. We point out that the effect of the plasma, in which the photons are propagating, must be taken into account. This effect changes the oscillation probability and renders the dimming frequency dependent, contrary to observations. One may hope to accommodate the data by averaging the oscillations over many different coherence domains. We estimate the effect of coherence loss, either due to the inhomogeneities of the magnetic field or of the intergalactic plasma. These estimates indicate that the achromaticity problem can be resolved only with very specific, and probably unrealistic, properties of the intergalactic medium.

We propose a scenario which can explain large lepton asymmetry and small baryon asymmetry simultaneously. Large lepton asymmetry is generated through the Affleck-Dine (AD) mechanism and almost all the produced lepton numbers are absorbed into Q-balls $(L$-balls). If the lifetime of the L-balls is longer than the onset of electroweak phase transition but shorter than the epoch of big bang nucleosynthesis (BBN), the large lepton asymmetry in the L-balls is protected from sphaleron effects. On the other hand, small (negative) lepton numbers are evaporated from the L-balls due to thermal effects, which are converted into the observed small baryon asymmetry by virtue of sphaleron effects. Large and positive lepton asymmetry of electron type is often requested from BBN. In our scenario by choosing an appropriate flat direction in the minimal supersymmetric standard model, we can produce positive lepton asymmetry of the electron type but totally negative lepton asymmetry.

We study inhomogeneous cosmological variations in the fine structure ‘’constant” $\alpha$ in Friedmann universes. Inhomogeneous motions of the scalar field driving changes in $\alpha$ display spatial oscillations that decrease in amplitude with increasing time. The inhomogeneous evolution quickly approaches that found for exact Friedmann universes. We prove a theorem to show that oscillations of α in time (or redshift) cannot occur in Friedmann universes in the Bekenstein-Sandvik-Barrow-Magueijo theories considered here.

The searches at LEP II for the processes $e^{+}{e}^{-}\to h^{0}Z$ and $e^{+}{e}^{-}\to h^0{A}^0$ in the minimal supersymmetric standard model fail to exclude regions of the $m_h{,m}_A$ plane where $\tan \beta <1,$ thus allowing a very light $A^0$ ${(m}_A<20\mathrm{}\hspace{0.5em}\mathrm{GeV}).\mathrm{}$ Such a parameter choice would predict a light $H^{\pm }$ with $m_{H^{\pm }}<m_W.$ Although the potentially large branching ratio for $H^{\pm }\to A^0{W}^{*}$ would ensure that $H^{\pm }$ also escaped detection in direct searches at LEP II and the Tevatron Run I, we show that this elusive parameter space is overwhelmingly disfavored by electroweak precision measurements through its large contribution to the $\mathrm{Zb}\overline{b}$ vertex.

The meron cluster algorithm solves the sign problem in a class of interacting fermion lattice models with a chiral phase transition. Within this framework, we study the geometrical features of the clusters built by the algorithm that suggest the occurrence of a generalized percolating phase transition at the chiral critical temperature in close analogy with Fortuin-Kasteleyn percolation in spin models.

The one-loop corrections to the bottomonium mass spectrum due to the finite charm mass are evaluated in the framework of the relativistic quark model. The obtained corrections are compared with the results of perturbative QCD.

We argue that the $〈A_{\mathrm{OPE}}^2〉$ condensate found in the Landau gauge on lattices, when an operator product expansion of Green’s functions is performed, might be explained by instantons. We use cooling to estimate the instanton contribution and extrapolate back the result to the thermalized configuration. The resulting $〈A_{\mathrm{inst}}^2〉$ is similar to $〈A_{\mathrm{OPE}}^2〉.$

A detailed study is made of four-dimensional SU(2) lattice gauge theory with static adjoint “quarks” in the context of string breaking. A tadpole-improved action is used to do simulations on lattices with coarse spatial spacings $a_s,$ allowing the static potential to be probed at large separations at a dramatically reduced computational cost. Highly anisotropic lattices are used, with fine temporal spacings $a_t,$ in order to assess the behavior of the time-dependent effective potentials. The lattice spacings $a_s$ and renormalized anisotropies are determined from the static potential for quarks in the fundamental representation. Simulations of the Wilson loop in the adjoint representation are done, and the energies of magnetic and electric “gluelumps” (adjoint-quark–gluon bound states), which set the energy scale for string breaking, are calculated. In addition, correlators of gauge-fixed static quark propagators, without a connecting string of spatial links, are analyzed. We also consider a matrix of correlation functions in a basis that includes a state with valence gluons; analogous correlators have recently been proposed for observing string breaking in full QCD and in other models. A thorough discussion of the relevance of Wilson loops over other operators for studies of string breaking is presented, using the simulation results presented here to support a number of new arguments.

It is shown how to obtain recently proposed two-zero Majorana mass textures in models with three Higgs triplets with small vacuum expectation values and a sufficiently massive triplet Majoron by using Abelian discrete symmetries. The relationship in SU(5) grand unification where the triplets occur in 15’s of the neutrino textures to up- and down-quark mass textures is briefly discussed.

We perform a detailed study of the Earth matter effects on supernova neutrinos with neutrino oscillation parameter LMA and small ${\theta }_{13}.$ The Earth effects show significant dependences on the neutrino path length inside the Earth and the value of $\Delta m_{12}^2.$ We investigate rather optimistically the possibility that we can probe the value of $\Delta m_{12}^2$ by the Earth effects. We assume that ${\theta }_{12}$ and the direction of the supernova are known with enough accuracy and that the resonance that occurs at higher density in supernova envelope is completely nonadiabatic. Further the neutrino spectra before neutrinos go through the Earth are assumed to be known. Then we show that, making use of these dependences, we can obtain an implication for the value of $\Delta m_{12}^2$ by comparing the observed energy spectrum to the predicted one. When SK detects neutrinos from supernova at 10 kpc which traveled through Earth (nadir angle $<80\mathrm{}°),\hspace{0.5em}\hspace{0.5em}\Delta m_{12}^2$ can be determined with an accuracy of $\sim 10\%.$ In much of the neutrino-detection-time-$\Delta m_{12}^2$ plane, $\Delta m_{12}^2$ might be determined with an accuracy equal to or better than $\pm 0.5\times {10}^{-5}{\mathrm{eV}}^2.$

We show that the high temperature limit of the noncommutative thermal Yang-Mills theory can be directly obtained from the Boltzmann transport equation of classical particles. As an illustration of the simplicity of the Boltzmann method, we evaluate the two- and the three-point gluon functions in the noncommutative $U\left(N\right)\mathrm{}$ theory at high temperatures T. These amplitudes are gauge invariant and satisfy simple Ward identities. Using the constraint satisfied at order $T^2$ by the covariantly conserved current, we construct the hard thermal loop effective action of the noncommutative theory.

Nonsupersymmetric multiwall configurations are generically unstable. It is proposed that stabilization in compact space can be achieved by introducing a winding number into the model. A Bogomol’nyi-Prasad-Sommerfield- (BPS)-like bound is studied for the energy of a configuration with nonvanishing winding number. The winding number is implemented in an $\mathcal{N}=1\mathrm{}$ supersymmetric nonlinear sigma model with two chiral scalar fields, and bound states of BPS and anti-BPS walls are found to exist in noncompact spaces. Even in the compactified space $S^1,$ this nontrivial bound state persists above a critical radius of the compact dimension.

The appearance of the triangle graph infrared axial anomaly in reduced quark loops contributing to QCD triple-Regge interactions is studied. In a dispersion relation formalism, the anomaly can only be present in the contributions of unphysical triple discontinuities. In this paper an asymptotic discontinuity analysis is applied to high-order Feynman diagrams to show that the anomaly does indeed occur in sufficiently high-order Reggeized gluon interactions. The Reggeon states involved must contain Reggeized gluon combinations with the quantum numbers of the anomaly (winding-number) current. A direct connection with the well-known U(1) problem is thus established. Closely related diagrams that contribute to the pion or Pomeron and triple Pomeron couplings in color superconducting QCD are also discussed.

We use the anti–de Sitter (AdS) conformal field theory correspondence to calculate the conserved charges and the Euclidean actions of the charged rotating black string in four dimensions both in the canonical and the grand-canonical ensemble. The four-dimensional solution of the Einstein-Maxwell equations with a positive cosmological constant is introduced, and its conserved quantities and actions for fixed charge and fixed electric potential are calculated. We also study the thermodynamics of the asymptotically AdS black strings and perform a stability analysis both in the canonical and the grand-canonical ensembles. We find that the asymptotically AdS black string in the canonical ensemble is locally stable, while in the grand-canonical ensemble it is stable only for a part of the phase space.

We study numerically the stability of the first Morris-Thorne traversible wormhole, shown previously by Ellis to be a solution for a massless ghost Klein-Gordon field. Our code uses a dual-null formulation for spherically symmetric space-time integration, and the numerical range covers both universes connected by the wormhole. We observe that the wormhole is unstable against Gaussian pulses in either exotic or normal massless Klein-Gordon fields. The wormhole throat suffers a bifurcation of horizons and either explodes to form an inflationary universe or collapses to a black hole if the total input energy, is, respectively, negative or positive. As the perturbations become small in total energy, there is evidence for critical solutions with a certain black-hole mass or Hubble constant. The collapse time is related to the initial energy with an apparently universal critical exponent. For normal matter, such as a traveller traversing the wormhole, collapse to a black hole always results. However, carefully balanced additional ghost radiation can maintain the wormhole for a limited time. The black-hole formation from a traversible wormhole confirms the recently proposed duality between them. The inflationary case provides a mechanism for inflating, to macroscopic size, a Planck-sized wormhole formed in space-time foam.

We study the possibility of generalizing the Einstein-Straus model to anisotropic settings by considering the matching of locally cylindrically symmetric static regions to the set of $G_4$ on $S_3$ locally rotationally symmetric (LRS) spacetimes. We show that such matchings preserving the symmetry are only possible for a restricted subset of the LRS models in which there is no evolution in one spacelike direction. These results are applied to spatially homogeneous (Bianchi) exteriors where the static part represents a finite bounded interior region without holes. We find that it is impossible to embed finite static strings or other locally cylindrically symmetric static objects (such as bottle or coin-shaped objects) in reasonable Bianchi cosmological models, irrespective of the matter content. Furthermore, we find that if the exterior spacetime is assumed to have a perfect fluid source satisfying the dominant energy condition, then only a very particular family of LRS stiff fluid solutions are compatible with this model. Finally, given the interior-exterior duality in the matching procedure, our results have the interesting consequence that the Oppenheimer-Snyder model of collapse cannot be generalized to such anisotropic cases.

Scalar and tensor perturbations arising in an inflationary braneworld scenario driven by a single scalar field are considered, where the bulk on either side of the brane corresponds to anti–de Sitter spaces with different cosmological constants. A consistency relation between the two spectra is derived and found to have an identical form to that arising in standard single-field inflation based on conventional Einstein gravity. The de Sitter/conformal field theory correspondence may provide further insight into the origin of this degeneracy. Possible ways of lifting such a degeneracy are discussed.

We consider the population evolution and evaporation of primordial black holes in the simplest braneworld cosmology: Randall-Sundrum type II. We demonstrate that black holes forming during the high-energy phase of this theory (where the expansion rate is proportional to the density) have a modified evaporation law, resulting in a longer lifetime and lower temperature at evaporation, while those forming in the standard regime behave essentially as in the standard cosmology. For sufficiently large values of the AdS radius, the high-energy regime can be the one relevant for primordial black holes evaporating at key epochs such as nucleosynthesis and the present. We examine the formation epochs of such black holes, and delimit the parameter regimes where the standard scenario is significantly modified.