Pion condensation in electrically neutral cold matter with finite baryon density

The possibility of the pion condensation phenomenon in cold and electrically neutral dense baryonic matter is investigated in $\beta$-equilibrium. For simplicity, the consideration is performed in the framework of a NJL model with two quark flavors at zero current quark mass and for rather small values of the baryon chemical potential, where the diquark condensation might be ignored. Two sets of model parameters are used. For the first one, the pion condensed phase with finite baryon density is realized. In this phase both electrons and the pion condensate take part in the neutralization of the quark electric charge. For the second set of model parameters, the pion condensation is impossible if the neutrality condition is imposed. The behaviour of meson masses vs quark chemical potential has been studied in electrically neutral matter.Comment: 7 pages; 3 figures; one reference added; to be published in Eur.Phys.J.

Structural influence on atomic hopping and electronic states of Pd-based bulk metallic glasses

Atomic motion and electronic structures of Pd–Ni–Cu–P bulk metallic glasses were investigated using 31P nuclear magnetic resonance. The hopping rate of P atoms was determined by the stimulated echo technique. Significant hopping was observed in all alloys well below the glass transition temperature. Increasing the Cu content to above 25 at. % increases P hopping significantly, consistent with the previous finding that the openness of the structure increases with Cu content. In contrast, P hopping is not influenced by changes of local electronic states at P sites, induced by the substitution of Ni by Cu

Explicit Formulas for Neumann Coefficients in the Plane-Wave Geometry

We obtain explicit formulas for the Neumann coefficients and associated quantities that appear in the three-string vertex for type IIB string theory in a plane-wave background, for any value of the mass parameter mu. The derivation involves constructing the inverse of a certain infinite-dimensional matrix, in terms of which the Neumann coefficients previously had been written only implicitly. We derive asymptotic expansions for large mu and find unexpectedly simple results, which are valid to all orders in 1/mu. Using BMN duality, these give predictions for certain gauge theory quantities to all orders in the modified 't Hooft coupling lambda'. A specific example is presented.Comment: 28 pages, 2 figures, v2: reference added, new comments and appendix, typos fixed in eqs. (86) and (89

Meson Mixing in Pion Superfluid

We investigate meson mixing and meson coupling constants in pion superfluid in the framework of two flavor NJL model at finite isospin density. The mixing strength develops fast with increasing isospin chemical potential, and the coupling constants in normal phase and in the pion superfluid phase behave very differently.Comment: 6 pages, 4 figures. Updates from version 2: 1, Correct Some language mistakes and Some errors in the cited references. 2, Rewrite the last sentence in the summary to indicate a possible way to measure the isospin-asymmetry related meson propertie

Metallic "Ferroelectricity" in the Pyrochlore Cd2Re2O7

A class of materials known as ``ferroelectric metals'' was discussed theoretically by Anderson and Blount in 1965 [Phys. Rev. Lett. 14, 217 (1965)], but to date no examples of this class have been reported. Here we present measurements of the elastic moduli of Cd2Re2O7 through the 200 K cubic-to-tetragonal phase transition. A Landau analysis of the moduli reveals that the transition is consistent with Cd2Re2O7 being classified as a ``ferroelectric metal'' in the weaker sense described by Anderson and Blount (loss of a center of symmetry). First-principles calculations of the lattice instabilities indicate that the dominant lattice instability corresponds to a two-fold degenerate mode with Eu symmetry, and that motions of the O ions forming the O octahedra dominate the energetics of the transition.Comment: 4 pages, 2 figure

Phase Structure of Nambu-Jona-Lasinio Model at Finite Isospin Density

In the frame of flavor SU(2) Nambu--Jona-Lasinio model with $U_A(1)$ breaking term we found that, the structure of two chiral phase transition lines does not exist at low isospin density in real world, and the critical isospin chemical potential for pion superfluidity is exactly the pion mass in the vacuum.Comment: 8 pages, submitted to Phys.Lett.

Spectropolarimetry of Supernovae

Overwhelming evidence has accumulated in recent years that supernova explosions are intrinsically 3-dimensional phenomena with significant departures from spherical symmetry. We review the evidence derived from spectropolarimetry that has established several key results: virtually all supernovae are significantly aspherical near maximum light; core-collapse supernovae behave differently than thermonuclear (Type Ia) supernovae; the asphericity of core-collapse supernovae is stronger in the inner layers showing that the explosion process itself is strongly aspherical; core-collapse supernovae tend to establish a preferred direction of asymmetry; the asphericity is stronger in the outer layers of thermonuclear supernovae providing constraints on the burning process. We emphasize the utility of the Q/U plane as a diagnostic tool and revisit SN 1987A and SN 1993J in a contemporary context. An axially-symmetric geometry can explain many basic features of core-collapse supernovae, but significant departures from axial symmetry are needed to explain most events. We introduce a spectropolarimetry type to classify the range of behavior observed in polarized supernovae. Understanding asymmetries in supernovae is important for phenomena as diverse as the origins of gamma-ray bursts and the cosmological applications of Type Ia supernovae in studies of the dark energy content of the universe.Comment: Draft of Annual Review article prior to final copy editing; 85 pages, 13 figures, 1 tabl

Generalized Variance-Ratio Tests in the Presence of Statistical Dependence

This article extends and generalizes the variance-ratio (VR) statistic by employing an estimator of the asymptotic covariance matrix of the sample autocorrelations. The estimator is consistent under the null for general classes of innovations exhibiting statistical dependence including exponential generalized autoregressive conditional heteroskedasticity and non-martingale difference sequence processes. Monte Carlo experiments show that our generalized test statistics have good finite sample size and superior power properties to other recently developed VR versions. In an application to two major US stock indices, our new generalized VR tests provide stronger rejections of the null than do competing VR tests

On the Ground State of Two Flavor Color Superconductor

The diquark condensate susceptibility in neutral color superconductor at moderate baryon density is calculated in the frame of two flavor Nambu-Jona-Lasinio model. When color chemical potential is introduced to keep charge neutrality, the diquark condensate susceptibility is negative in the directions without diquark condensate in color space, which may be regarded as a signal of the instability of the conventional ground state with only diquark condensate in the color 3 direction.Comment: 4 pages, 2 figure

Decay Modes of Unstable Strings in Plane-Wave String Field Theory

The cubic interaction vertex of light-cone string field theory in the plane-wave background has a simple effective form when considering states with only bosonic excitations. This simple effective interaction vertex is used in this paper to calculate the three string interaction matrix elements for states of arbitrary bosonic excitation and these results are used to examine certain decay modes on the mass-shell. It is shown that the matrix elements of one string to two string decays involving only bosonic excitations will vanish to all orders in 1/mu on the mass-shell when the number of excitations on the initial string is less than or equal to two, but in general will not vanish when the number of excitations is greater than two. Also, a truncated calculation of the mass-shell matrix elements for one string to three string decays of two excitation states is performed and suggests that these matrix elements do not vanish on the mass-shell. There is, however, a quantitative discrepancy between this last result and its (also non-vanishing) gauge theory prediction from the BMN correspondence.Comment: 11 pages; v2: references added; v3: normalization of interaction vertex and corresponding amplitudes changed by a factor of mu to reflect SFT normalization (must now divide by mu to compare with BMN dual gauge theory), and minor errors correcte