Neutron Stars with Bose-Einstein Condensation of Antikaons as MIT Bags

We investigate the properties of an antikaon in medium, regarding itas a MIT bag. We first construct the MIT bag model for a kaon with$\sigma^*$ and $\phi$ in order to describe the interaction of$s$-quarks in hyperonic matter in the framework of the modifiedquark-meson coupling model. The coupling constant $g'^{B_K}_\sigma$in the density-dependent bag constant $B(\sigma)$ is treated as afree parameter to reproduce the optical potential of a kaon in asymmetric matter and all other couplings are determined by usingSU(6) symmetry and the quark counting rule. With various values ofthe kaon potential, we calculate the effective mass of a kaon inmedium to compare it with that of a point-like kaon. We thencalculate the population of octet baryons, leptons and $K^-$ and theequation of state for neutron star matter. The results show thatkaon condensation in hyperonic matter is sensitive to the $s$-quarkinteraction and also to the way of treating the kaon. The mass andthe radius of a neutron star are obtained by solving theTolmann-Oppenheimer-Volkoff equation.Comment: 14 figure

Nonmonotonic behavior of resistance in a superconductor-Luttinger liquid junction

Transport through a superconductor-Luttinger liquid junction is considered. When the interaction in the Luttinger liquid is repulsive, the resistance of the junction with a sufficiently clean interface shows nonmonotonic temperature- or voltage-dependence due to the competition between the superconductivity and the repulsive interaction. The result is discussed in connection with recent experiments on single-wall carbon nanotubes in contact with superconducting leads.Comment: Revtex4, 2 eps figure files, slightly revised from an earlier version submitted to PRL on 2001.12.

Parity-violating asymmetry in γd→n⃗p\gamma d \to \vec{n}p with a pionless effective theory

Nuclear parity violation is studied with polarized neutrons in the photodisintegration of the deuteron at low energies. A pionless effective field theory with di-baryon fields is used for the investigation. Hadronic weak interactions are treated by parity-violating di-baryon-nucleon-nucleon vertices, which have undetermined coupling contants. A parity-violating asymmetry in the process is calculated for the incident photon energy up to 30 MeV. If experimental data for the parity-violating asymmetry become available in the future, we will be able to determine the unknown coupling contants in the parity-violating vertices.Comment: 4 pages. A contribution to APFB2011, August 22-26, 2011, Seoul, Kore

Production of Neutral Fermion in Linear Magnetic Field through Pauli Interaction

We calculate the production rate of neutral fermions in linear magnetic fields through the Pauli interaction. It is found that the production rate is exponentially decreasing function with respect to the inverse of the magnetic field gradient, which shows the non-perturbative characteristics analogous to the Schwinger process. It turns out that the production rate density depends on both the gradient and the strength of magnetic fields in 3+1 dimension. It is quite different from the result in 2+1 dimension, where the production rate depends only on the gradient of the magnetic fields, not on the strength of the magnetic fields. It is also found that the production of neutral fermions through the Pauli interaction is a magnetic effect whereas the production of charged particles through minimal coupling is an electric effect.Comment: 11 pages, 2 figure

ESR Study of (C_5H_{12}N)_2CuBr_4

ESR studies at 9.27, 95.4, and 289.7 GHz have been performed on (C$_5$H$_{12}$N)$_2$CuBr$_4$ down to 3.7 K. The 9.27 GHz data were acquired with a single crystal and do not indicate the presence of any structural transitions. The high frequency data were collected with a polycrystalline sample and resolved two absorbances, consistent with two crystallographic orientations of the magnetic sites and with earlier ESR studies performed at 300 K. Below $B_{C1}=6.6$ T, our data confirm the presence of a spin singlet ground state.Comment: 2 pages, 4 figs., submitted 23rd International Conference on Low Temperature Physics (LT-23), Aug. 200

Observable form of pulses emitted from relativistic collapsing objects

In this work, we discuss observable characteristics of the radiation emitted from a surface of a collapsing object. We study a simplified model in which a radiation of massless particles has a sharp in time profile and it happens at the surface at the same moment of comoving time. Since the radiating surface has finite size the observed radiation will occur during some finite time. Its redshift and bending angle are affected by the strong gravitational field. We obtain a simple expression for the observed flux of the radiation as a function of time. To find an explicit expression for the flux we develop an analytical approximation for the bending angle and time delay for null rays emitted by a collapsing surface. In the case of the bending angle this approximation is an improved version of the earlier proposed Beloborodov-Leahy-approximation. For rays emitted at $R > 2R_g$ the accuracy of the proposed improved approximations for the bending angle and time delay is of order (or less) than 2-3%. By using this approximation we obtain an approximate analytical expression for the observed flux and study its properties.Comment: 13 pages, 10 figures;Typos in equations and refrences are corrected. No change in the results and discussion

Radiative neutron capture on a proton at BBN energies

The total cross section for radiative neutron capture on a proton, $np \to d \gamma$, is evaluated at big bang nucleosynthesis (BBN) energies. The electromagnetic transition amplitudes are calculated up to next-to leading order within the framework of pionless effective field theory with dibaryon fields. We also calculate the $d\gamma\to np$ cross section and the photon analyzing power for the $d\vec{\gamma}\to np$ process from the amplitudes. The values of low energy constants that appear in the amplitudes are estimated by a Markov Chain Monte Carlo analysis using the relevant low energy experimental data. Our result agrees well with those of other theoretical calculations except for the $np\to d\gamma$ cross section at some energies estimated by an R-matrix analysis. We also study the uncertainties in our estimation of the $np\to d\gamma$ cross section at relevant BBN energies and find that the estimated cross section is reliable to within $\sim$1% error.Comment: 21 pages and 12 eps figures; 6 eps figures and 2 references added, and accepted for publication in Phys. Rev.