Chiral dynamics of Σ\Sigma-hyperons in the nuclear medium

Using SU(3) chiral perturbation theory we calculate the density-dependent complex mean field $U_\Sigma(k_f)+ i W_\Sigma(k_f)$ of a $\Sigma$-hyperon in isospin-symmetric nuclear matter. The leading long-range $\Sigma N$-interaction arises from one-kaon exchange and from two-pion exchange with a $\Sigma$- or a $\Lambda$-hyperon in the intermediate state. We find from the $\Sigma N\to \Lambda N$ conversion process at nuclear matter saturation density $\rho_0 = 0.16$fm$^{-3}$ an imaginary single-particle potential of $W_\Sigma(k_{f0}) =-21.5$ MeV, in fair agreement with existing empirical determinations. The genuine long-range contributions from iterated (second order) one-pion exchange with an intermediate $\Sigma$- or $\Lambda$-hyperon sum up to a moderately repulsive real single-particle potential of $U_\Sigma(k_{f0})= 59$ MeV. Recently measured $(\pi^-,K^+$) inclusive spectra related to $\Sigma^-$-formation in heavy nuclei give evidence for a $\Sigma$-nucleus repulsion of similar size. Our results suggest that the net effect of the short-range $\Sigma N$-interaction on the $\Sigma$-nuclear mean field could be small.Comment: 7 pages, 2 figures, published in: Phys. Rev. C 71, 068201 (2005

Application of DWF to heavy-light mesons

We consider application of domain wall fermions to quarks with relatively heavy masses, aiming at precision calculations of charmed meson properties. Preliminary results for a few basic quantities are presented.Comment: Lattice2003(heavy), 3 pages, 3 figure

Evolution of non-thermal emission from shell associated with AGN jets

We explore the evolution of the emissions by accelerated electrons in shocked shells driven by jets in active galactic nuclei (AGNs). Focusing on powerful sources which host luminous quasars, we evaluated the broadband emission spectra by properly taking into account adiabatic and radiative cooling effects on the electron distribution. The synchrotron radiation and inverse Compton (IC) scattering of various photons that are mainly produced in the accretion disc and dusty torus are considered as radiation processes. We show that the resultant radiation is dominated by the IC emission for compact sources (< 10kpc), whereas the synchrotron radiation is more important for larger sources. We also compare the shell emissions with those expected from the lobe under the assumption that a fractions of the energy deposited in the shell and lobe carried by the non-thermal electrons are $\epsilon_e \sim 0.01$ and $\epsilon_{e, lobe} \sim 1$, respectively. Then, we find that the shell emissions are brighter than the lobe ones at infra-red and optical bands when the source size is > 10kpc, and the IC emissions from the shell at > 10 GeV can be observed with the absence of contamination from the lobe irrespective of the source size. In particular, it is predicted that, for most powerful nearby sources ($L_j \sim 10^{47} ergs s^{-1}$), TeV gamma-rays produced via the IC emissions can be detected by the modern Cherenkov telescopes such as MAGIC, HESS and VERITAS.Comment: 13 pages, 5 figures, accepted for publication in Ap

A correlation between light profile and [Mg/Fe] abundance ratio in early-type galaxies

We explore possible correlations between light profile shapes, as parameterized by the Sersic index or the concentration index C_re(1/3), and relevant stellar population parameters in early-type galaxies. Mean luminosity weighted ages, metallicities and abundance ratios were obtained from spectra of very high signal-to-noise and stellar population models that synthesize galaxy spectra at the resolution given by their velocity dispersions, in combination with an age indicator that is virtually free of the effects of metallicity. We do not find any significant correlation between the Sersic index (or C_re(1/3)) and mean age or metallicity, but a strong positive correlation of the shape parameters with [Mg/Fe] abundance ratio. This dependence is as strong as the [Mg/Fe] vs. velocity dispersion and C_re(1/3) vs. velocity dispersion relations. We speculate that early-type galaxies settle up their structure on time-scales in agreement with those imposed by their [Mg/Fe] ratios. This suggest that the global structure of larger galaxies, with larger [Mg/Fe] ratios and shorter time-scales, was already at place at high z, without experiencing a significant time evolution.Comment: 5 pages, 3 figures (to appear in The Astrophysical Journal Letters