We develop the Ginzburg-Landau approach to comparing different possible crystal structures for the crystalline color superconducting phase of QCD, the QCD incarnation of the Larkin-Ovchinnikov-Fulde-Ferrell phase. In this phase, quarks of different flavor with differing Fermi momenta form Cooper pairs with nonzero total momentum, yielding a condensate that varies in space like a sum of plane waves. We work at zero temperature, as is relevant for compact star physics. The Ginzburg-Landau approach predicts a strong first-order phase transition (as a function of the chemical potential difference between quarks) and for this reason is not under quantitative control. Nevertheless, by organizing the comparison between different possible arrangements of plane waves (i.e., different crystal structures) it provides considerable qualitative insight into what makes a crystal structure favorable. Together, the qualitative insights and the quantitative, but not controlled, calculations make a compelling case that the favored pairing pattern yields a condensate which is a sum of eight plane waves forming a face-centered cubic structure. They also predict that the phase is quite robust, with gaps comparable in magnitude to the BCS gap that would form if the Fermi momenta were degenerate. These predictions may be tested in ultracold gases made of fermionic atoms. In a QCD context, our results lay the foundation for a calculation of vortex pinning in a crystalline color superconductor, and thus for the analysis of pulsar glitches that may originate within the core of a compact star.

It has been argued that the observed core density profile of galaxies is inconsistent with having a dark matter particle that is collisionless and that alternative dark matter candidates which are self-interacting may explain observations better. One new class of self-interacting dark matter that has been proposed in the context of mirror universe models of particle physics is the mirror hydrogen atom, whose stability is guaranteed by the conservation of mirror baryon number. We show that the effective transport cross section for mirror hydrogen atoms has the right order of magnitude for solving the “cuspy” halo problem. Furthermore, the suppression of dissipation effects for mirror atoms due to a higher mirror mass scale prevents the mirror halo matter from collapsing into a disk, strengthening the argument for mirror matter as galactic dark matter.

We argue that bouncing branes occur naturally when there is more than one extra dimension. We consider three-branes embedded in space-times with a horizon and an isometry group $\mathrm{SO}\left(6\right).$ As soon as the brane angular momentum is large enough, a repulsive barrier prevents the branes from reaching the horizon. We illustrate this phenomenon with the case of D3-branes in an ${\mathrm{AdS}}_5-\mathrm{Schwarzschild}\times {\mathrm{S}}_5$ background and asymptotically flat space-time.

We present a complete analysis of the chiral extrapolation of lattice moments of all twist-2 isovector quark distributions, including corrections from $N\pi$ and $\Delta \pi$ loops. Even though the $\Delta$ resonance formally gives rise to higher order non-analytic structure, the coefficients of the higher order terms for the helicity and transversity moments are large and cancel much of the curvature generated by the wave function renormalization. The net effect is that, whereas the unpolarized moments exhibit considerable curvature, the polarized moments show little deviation from linearity as the chiral limit is approached.

A simplified but very instructive analysis of the seesaw mechanism is here performed. Assuming a nearly diagonal Dirac neutrino mass matrix, we study the forms of the Majorana mass matrix of right-handed neutrinos, which reproduce the effective mass matrix of left-handed neutrinos. As a further step, the important effect of a nondiagonal Dirac neutrino mass matrix is explored. The corresponding implications for baryogenesis via leptogenesis and for the neutrinoless double beta decay are reviewed. We propose two distinct models where the baryon asymmetry is enhanced.

We explore the anomalous right-handed $\overline{t}\mathrm{sW}$ and $\overline{t}\mathrm{bW}$ couplings using $\overrightarrow{B}{X}_s\gamma$ and $\overrightarrow{B}{X}_s{l}^{+}{l}^{-}$ decays induced by the flavor-changing penguin diagrams. The anomalous $\overline{t}\mathrm{sW}$ coupling can yield 10% enhancement of the $\overrightarrow{B}{X}_s{l}^{+}{l}^{-}$ decay rate under the constraint from the present $\overrightarrow{B}{X}_s\gamma$ data, while it does not affect the forward-backward asymmetry of the charged lepton. The allowed region for the anomalous $\overline{t}\mathrm{bW}$ coupling by the $\overrightarrow{B}{X}_s\gamma$ constraint is twofold: the small value region and the large value region. Although the effect of the small anomalous coupling on the $\overrightarrow{B}{X}_s{l}^{+}{l}^{-}$ branching ratio is very small, it can yield a substantial change for the forward-backward asymmetry.

A detailed, quantitative reexamination of the effect of hadron dynamics on baryon decay, modeled in terms of Skyrme-field tunneling, indicates that any hadronic suppression should be quite mild. This appears to be another illustration of the “Cheshire-cat” phenomenon, that variation of the apportionment between description of the nucleon as a bag of quarks and description as a Skyrme field configuration has little influence on many nucleon properties. Perhaps the largest remaining uncertainty in evaluating the decay rate has to do with the overlap between a specified quark-antiquark configuration and a final meson state.

It is shown that the dynamics of domain walls in left-right symmetric models, separating respective regions of unbroken ${\mathrm{SU}\left(2\right)\mathrm{}}_L$ and ${\mathrm{SU}\left(2\right)\mathrm{}}_R$ in the early universe, can give rise to baryogenesis via leptogenesis. Neutrinos have a spatially varying complex mass matrix due to CP-violating scalar condensates in the domain wall. The motion of the wall through the plasma generates a flux of lepton number across the wall which is converted to a lepton asymmetry by helicity-flipping scatterings. Subsequent processing of the lepton excess by sphalerons results in the observed baryon asymmetry, for a range of parameters in left-right symmetric models.

We consider new cosmological solutions with a collapsing, an intermediate and an expanding phase. The boundary between the expanding (collapsing) phase and the intermediate phase is seen by comoving observers as a cosmological past (future) horizon. The solutions are naturally embedded in string and M theory. In the particular case of a two-dimensional cosmology, space-time is flat with an identification under boost and translation transformations. We consider the corresponding string theory orbifold and calculate the modular invariant one-loop partition function. In this case there is a strong parallel with the BTZ black hole. The higher dimensional cosmologies have a timelike curvature singularity in the intermediate region. In some cases the string coupling can be made small throughout all of space-time but string corrections become important at the singularity. This happens where string winding modes become light which could resolve the singularity. The new proposed space-time causal structure could have implications for cosmology, independently of string theory.

We discuss an equivalence between the Baumgarte-Shapiro-Shibata-Nakamura (BSSN) formulation of the Einstein evolution equations, a subfamily of the Kidder-Scheel-Teukolsky formulation, and other strongly or symmetric hyperbolic first order systems with fixed shift and densitized lapse. This allows us to show under which conditions the BSSN system is, in a sense to be discussed, hyperbolic. This desirable property may account in part for the empirically observed better behavior of the BSSN formulation in numerical evolutions involving black holes.

Recently, the holographic aspects of asymptotically de Sitter spacetimes have generated substantial literary interest. The plot continues in this paper, as we investigate a certain class of dilatonically deformed “topological” de Sitter solutions [which were introduced by R. Cai, Y. Myung, and Y. Zhang, Phys. Rev. D 65, 084019 (2002)]. Although such solutions possess a detrimental cosmological singularity, their interpretation from a holographic perspective remains somewhat unclear. The current focus is on the associated generalized C functions, which are shown to maintain their usual monotonicity properties in spite of this exotic framework. These findings suggest that such topological solutions may still play a role in our understanding of quantum gravity with a positive cosmological constant.

It has been suggested that the overdense region as a result of inhomogeneities in the early Universe would have undergone a collapse into primordial black holes (PBHs). In this work, we discuss a possible constraint on PBH formation in the radiation dominated epoch by imposing the generalized second law of thermodynamics in the context of a spherically collapsing scenario. It is found that both the critical temperature $T_c$ over which the formation of PBH is not possible and the lower bound on the mass of PBH depend on the number of degrees of freedom at the time of PBH formation. In the standard model, one can show that the lower bound on the mass of the PBH known in the literature, of the order of the Planck mass, is consistent with the thermodynamic constraint constructed in this work. We also point out the possibility that the critical temperature (lower bound on PBH mass) can be lowered (increased) provided the number of relativistic degrees of freedom of the Universe is increased substantially beyond the standard model.

The simple independent quark models have difficulties explaining simultaneously the totality of the known hyperon magnetic moments and hyperon semileptonic decay rates. We show that both the Goldstone boson loop contributions and two-quark effective exchange currents are essential in explaining these observables.

We show how quark-hadron duality can emerge for valence spin-averaged structure functions, and for the non-forward distributions of deeply virtual Compton scattering. Novel factorizations of the non-forward amplitudes are proposed. Some implications for large angle scattering and deviations from the quark counting rules are illustrated.

We compute the probability of photon-axion oscillations in the presence of both intergalactic magnetic fields and an electron plasma and investigate the effect on type Ia supernovae observations. The conversion probability is calculated using a density matrix formalism by following light paths through simulated universes in a Monte Carlo fashion. We find that, even though the effect is highly frequency dependent, one needs to analyze relatively narrow spectral features of high redshift objects in order to discriminate between the dimming effect from oscillations and a cosmological constant, in contrast with earlier claims that broadband photometry is sufficient. However, it should be possible to put severe constraints on the effect by studying, e.g., quasar-, gamma-ray burst-, and galaxy-spectra.

We discuss some controversial aspects of the evaluation of the thermal energy of a scalar field in a one-dimensional compact space. The calculations are carried out using a generalized zeta function approach.

We perform some numerical studies of the secular triaxial instability of rigidly rotating homogeneous fluid bodies in general relativity. In the Newtonian limit, this instability arises at the bifurcation point between the Maclaurin and Jacobi sequences. It can be driven in astrophysical systems by viscous dissipation. We locate the onset of instability along several constant baryon mass sequences of uniformly rotating axisymmetric bodies for compaction parameter $M/R=0\mathrm{}–\mathrm{0.275.}$ We find that general relativity weakens the Jacobi-like bar mode instability, but the stabilizing effect is not very strong. According to our analysis the critical value of the ratio of the kinetic energy to the absolute value of the gravitational potential energy $(T/|W|{)}_{\mathrm{crit}}$ for a compaction parameter as high as $0.275$ is only $30\%$ higher than the Newtonian value. The critical value of the eccentricity depends very weakly on the degree of relativity and for $M/R=0.275\mathrm{}$ is only $2\%$ larger than the Newtonian value at the onset for the secular bar mode instability. We compare our numerical results with recent analytical investigations based on the post-Newtonian expansion.

We consider the effect of inhomogeneous neutrino degeneracy on big bang nucleosynthesis for the case where the distribution of neutrino chemical potentials is given by a Gaussian. The chemical potential fluctuations are taken to be isocurvature, so that only inhomogeneities in the electron chemical potential are relevant. Then the final element abundances are a function only of the baryon-photon ratio $\eta ,$ the effective number of additional neutrinos $\Delta N_{\nu },$ the mean electron neutrino degeneracy parameter $\overline{\xi },$ and the rms fluctuation of the degeneracy parameter, ${\sigma }_{\xi }.$ We find that for fixed $\eta ,$ $\Delta N_{\nu },$ and $\overline{\xi },$ the abundances of ${}^4\mathrm{He},$ D, and ${}^7\mathrm{Li}$ are, in general, increasing functions of ${\sigma }_{\xi }.$ Hence, the effect of adding a Gaussian distribution for the electron neutrino degeneracy parameter is to decrease the allowed range for $\eta .$ We show that this result can be generalized to a wide variety of distributions for $\xi .$

We consider issues related to tachyonic inflation with an exponential potential. We find an exact solution of the evolution equations in the slow roll limit in FRW cosmology. We also carry out a similar analysis in the case of brane assisted tachyonic inflation. We investigate the phase space behavior of the system and show that the dustlike solution is a late time attractor. The difficulties associated with reheating in the tachyonic model are also indicated.

We develop a theory in which relic gravitational waves and primordial density perturbations are generated by strong variable gravitational field of the early Universe. The generating mechanism is the superadiabatic (parametric) amplification of the zero-point quantum oscillations. The generated fields have specific statistical properties of squeezed vacuum quantum states. Macroscopically, squeezing manifests itself in a nonstationary character of variances and correlation functions of the fields, the periodic structures of the metric power spectra, and, as a consequence, in the oscillatory behavior of the higher order multipoles $C_l$ of the cosmic microwave background anisotropy. We start with the gravitational wave background and then apply the theory to primordial density perturbations. We derive an analytical formula for the positions of peaks and dips in the angular power spectrum ${l(l+1\mathrm{})C}_l$ as a function of l. This formula shows that the values of l at the peak positions are ordered in the proportion $1:3:5:\dots ,$ whereas at the dips they are ordered as $1:2:3:\dots .$ We compare the derived positions with the actually observed features, and find them to be in reasonably good agreement. It appears that the observed structure is better described by our analytical formula based on the (squeezed) metric perturbations associated with the primordial density perturbations, rather than by the acoustic peaks reflecting the existence of plasma sound waves at the last scattering surface. We formulate a forecast for other features in the angular power spectrum that may be detected by the advanced observational missions, such as the Microwave Anisotropy Probe and Planck. We tentatively conclude that the observed structure is a macroscopic manifestation of squeezing in the primordial metric perturbations.