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

Effective mass theory of monolayer \delta-doping in the high-density limit

Monolayer \delta-doped structures in silicon have attracted renewed interest with their recent incorporation into atomic-scale device fabrication strategies as source and drain electrodes and in-plane gates. Modeling the physics of \delta-doping at this scale proves challenging, however, due to the large computational overhead associated with ab initio and atomistic methods. Here, we develop an analytical theory based on an effective mass approximation. We specifically consider the Si:P materials system, and the limit of high donor density, which has been the subject of recent experiments. In this case, metallic behavior including screening tends to smooth out the local disorder potential associated with random dopant placement. While smooth potentials may be difficult to incorporate into microscopic, single-electron analyses, the problem is easily treated in the effective mass theory by means of a jellium approximation for the ionic charge. We then go beyond the analytic model, incorporating exchange and correlation effects within a simple numerical model. We argue that such an approach is appropriate for describing realistic, high-density, highly disordered devices, providing results comparable to density functional theory, but with greater intuitive appeal, and lower computational effort. We investigate valley coupling in these structures, finding that valley splitting in the low-lying \Gamma band grows much more quickly than the \Gamma-\Delta band splitting at high densities. We also find that many-body exchange and correlation corrections affect the valley splitting more strongly than they affect the band splitting

Experimental demonstration of painting arbitrary and dynamic potentials for Bose-Einstein condensates

There is a pressing need for robust and straightforward methods to create potentials for trapping Bose-Einstein condensates which are simultaneously dynamic, fully arbitrary, and sufficiently stable to not heat the ultracold gas. We show here how to accomplish these goals, using a rapidly-moving laser beam that "paints" a time-averaged optical dipole potential in which we create BECs in a variety of geometries, including toroids, ring lattices, and square lattices. Matter wave interference patterns confirm that the trapped gas is a condensate. As a simple illustration of dynamics, we show that the technique can transform a toroidal condensate into a ring lattice and back into a toroid. The technique is general and should work with any sufficiently polarizable low-energy particles.Comment: Minor text changes and three references added. This is the final version published in New Journal of Physic

Electromagnetic and gravitational responses and anomalies in topological insulators and superconductors

One of the defining properties of the conventional three-dimensional ("$\mathbb{Z}_2$-", or "spin-orbit"-) topological insulator is its characteristic magnetoelectric effect, as described by axion electrodynamics. In this paper, we discuss an analogue of such a magnetoelectric effect in the thermal (or gravitational) and the magnetic dipole responses in all symmetry classes which admit topologically non-trivial insulators or superconductors to exist in three dimensions. In particular, for topological superconductors (or superfluids) with time-reversal symmetry which lack SU(2) spin rotation symmetry (e.g. due to spin-orbit interactions), such as the B phase of $^3$He, the thermal response is the only probe which can detect the non-trivial topological character through transport. We show that, for such topological superconductors, applying a temperature gradient produces a thermal- (or mass-) surface current perpendicular to the thermal gradient. Such charge, thermal, or magnetic dipole responses provide a definition of topological insulators and superconductors beyond the single-particle picture. Moreover we find, for a significant part of the 'ten-fold' list of topological insulators found in previous work in the absence of interactions, that in general dimensions the effective field theory describing the space-time responses is governed by a field theory anomaly. Since anomalies are known to be insensitive to whether the underlying fermions are interacting or not, this shows that the classification of these topological insulators is robust to adiabatic deformations by interparticle interactions in general dimensionality. In particular, this applies to symmetry classes DIII, CI, and AIII in three spatial dimensions, and to symmetry classes D and C in two spatial dimensions.Comment: 16 pages, 2 figure

SPEAR Far Ultraviolet Spectral Images of the Cygnus Loop

We present far-ultraviolet (FUV) spectral images, measured at C IV 1550, He II 1640, Si IV+O IV] 1400, and O III] 1664, of the entire Cygnus Loop, observed with the Spectroscopy of Plasma Evolution from Astrophysical Radiation (SPEAR) instrument, also known as FIMS. The spatial distribution of FUV emission generally corresponds with a limb-brightened shell, and is similar to optical, radio and X-ray images. The features found in the present work include a ``carrot'', diffuse interior, and breakout features, which have not been seen in previous FUV studies. Shock velocities of 140-160 km/s is found from a line ratio of O IV] to O III], which is insensitive not only to resonance scattering but also to elemental abundance. The estimated velocity indicates that the fast shocks are widespread across the remnant. By comparing various line ratios with steady-state shock models, it is also shown that the resonance scattering is widespread.Comment: 13 pages, 3 figures, 1 table, accepted for publication in ApJ

Synthetic Observations of Simulated Radio Galaxies I: Radio and X-ray Analysis

We present an extensive synthetic observational analysis of numerically- simulated radio galaxies designed to explore the effectiveness of conventional observational analyses at recovering physical source properties. These are the first numerical simulations with sufficient physical detail to allow such a study. The present paper focuses on extraction of magnetic field properties from nonthermal intensity information. Synchrotron and inverse-Compton intensities provided meaningful information about distributions and strengths of magnetic fields, although considerable care was called for. Correlations between radio and X-ray surface brightness correctly revealed useful dynamical relationships between particles and fields. Magnetic field strength estimates derived from the ratio of X-ray to radio intensity were mostly within about a factor of two of the RMS field strength along a given line of sight. When emissions along a given line of sight were dominated by regions close to the minimum energy/equipartition condition, the field strengths derived from the standard power-law-spectrum minimum energy calculation were also reasonably close to actual field strengths, except when spectral aging was evident. Otherwise, biases in the minimum- energy magnetic field estimation mirrored actual differences from equipartition. The ratio of the inverse-Compton magnetic field to the minimum-energy magnetic field provided a rough measure of the actual total energy in particles and fields in most instances, within an order of magnitude. This may provide a practical limit to the accuracy with which one may be able to establish the internal energy density or pressure of optically thin synchrotron sources.Comment: 43 pages, 14 figures; accepted for publication in ApJ, v601 n2 February 1, 200

Effective mass and decay of Θ+\Theta^+ in nuclear matter in quark-meson coupling model

The in-medium mass of a \thetaplus, \mtheta^*, in cold symmetric nuclear matter is calculated by using the quark-meson coupling model. The $\Theta^+$ is treated as an MIT bag with the quark content $uudd\bar s$. Bag parameters for a free \thetaplus are fixed to reproduce the observed mass of the \thetaplus. In doing so, we use three different values of the $s$-quark mass since the mass of the $s$-quark is not well known. As usual, the strengths of the $u$ and $d$ quark couplings to $\sigma$- and $\omega$-meson fields are determined to fit the nuclear saturation properties. However, the coupling constant $g_\sigma^s$ between the $s$-quark and the $\sigma$-meson cannot be fixed from the saturation properties, and thus we treat $g_\sigma^s$ as a free parameter and investigate how \mtheta^* depends on $g_\sigma^s$. %\mtheta^* is calculated up to 2.5 times the nuclear saturation density, %and we find that We find that \mtheta^* depends significantly on the value of $g_\sigma^s$ but not on the mass of the $s$-quark. Chemical potentials of the $\Theta^+$ and the $K+N$ system are calculated to discuss the decay of a $\Theta^+$ in nuclear matter. We calculate the effective mass of a kaon in nuclear matter in two ways; using the optical potential of $K^-$ in matter and using quark model. By comparing the effective masses calculated from these two methods, we find the magnitude of the real part of the optical potential that is consistent with the usual quark model is about 100 MeV.Comment: 16 pages, 4 figures, 3 table

Cosmological Shock Waves and Their Role in the Large Scale Structure of the Universe

We study the properties of cosmological shock waves identified in high-resolution, N-body/hydrodynamic simulations of a $\Lambda$CDM universe and their role on thermalization of gas and acceleration of nonthermal, cosmic ray (CR) particles. External shocks form around sheets, filaments and knots of mass distribution when the gas in void regions accretes onto them. Within those nonlinear structures, internal shocks are produced by infall of previously shocked gas to filaments and knots, and during subclump mergers, as well as by chaotic flow motions. Due to the low temperature of the accreting gas, the Mach number of external shocks is high, extending up to $M\sim 100$ or higher. In contrast, internal shocks have mostly low Mach numbers. For all shocks of $M\ge1.5$ the mean distance between shock surfaces over the entire computed volume is $\sim4 h^{-1}$ Mpc at present, or $\sim 1 h^{-1}$ Mpc for internal shocks within nonlinear structures. Identified external shocks are more extensive, with their surface area $\sim2$ times larger than that of identified internal shocks at present. However, especially because of higher preshock densities, but also due to higher shock speeds, internal shocks dissipate more energy. Hence, the internal shocks are mainly responsible for gas thermalization as well as CR acceleration. In fact, internal shocks with 2 \la M \la 4 contribute $\sim 1/2$ of the total dissipation. Using a nonlinear diffusive shock acceleration model for CR protons, we estimate the ratio of CR energy to gas thermal energy dissipated at cosmological shock waves to be $\sim1/2$ through the history of the universe. Our result supports scenarios in which the intracluster medium contains energetically significant populations of CRs.Comment: 25 pages, 8 figures including 1 in color. To appear in ApJ (v593 n2 August 20, 2003). Postscript file with full resolution ftp://canopus.chungnam.ac.kr/ryu/cosmoshock.p