arXiv subjects

S. C. Lee

Publications and source records attributed to S. C. Lee.

134 records · Page 8Linked to original sources

arXiv2004

The On-Orbit Performance of the Galaxy Evolution Explorer

We report the first year on-orbit performance results for the Galaxy Evolution Explorer (GALEX), a NASA Small Explorer that is performing a survey of the sky in two ultraviolet bands. The instrument comprises a 50 cm diameter modified Ritchey-Chretien telescope with a 1.25 degree field of view, selectable imaging and objective grism spectroscopic modes, and an innovative optical system with a thin-film multilayer dichroic beam splitter that enables simultaneous imaging by a pair of photon counting, microchannel plate, delay line readout detectors. Initial measurements demonstrate that GALEX is performing well, meeting its requirements for resolution, efficiency, astrometry, bandpass definition and survey sensitivity.

astro-ph↗

arXiv2001

Quantum transport calculations for quantum cascade laser structures

We apply a quantum transport theory based on nonequilibrium Green's functions to quantum cascade laser (QCL) structures, treating simultaneously the transmission through the injector regions and the relaxation due to scattering in the active region. The quantum kinetic equations are solved self-consistently using self-energies for interface roughness and phonon scattering processes within the self-consistent Born approximation. In this way, we obtain the current density J, and the average electronic distribution f(E) at a given energy E, as a function of applied bias. As a test case, we apply the theory to a GaAs/Al_xGa_{1-x}As QCL structure reported in the literature. The theoretical results reproduce well reported voltage-current (V-I) measurements, and also demonstrate a population inversion at a bias that agrees well with the range of currents and fields at which lasing is observed.

cond-mat.mes-hall↗

arXiv2001

Prospect of a very long baseline neutrino oscillation experiment: HIPA to Beijing

We discuss the prospects of a very long baseline neutrino oscillation experiment from HIPA to Beijing. The current understanding of neutrino oscillations, both theoretically and experimentally, are summarized. The figure of merits for interested physics measurements are defined and compared at different distances: 300 km, 700 km, 2100 km and 3000 km. We conclude that a baseline more than 2100 km is optimal. A large water cerenkov calorimeter was proposed and its performance is satisfactory from a Monte Carlo simulation study. Such a large detector can do many other measurements on cosmic-rays physics and astrophysics.

hep-ph↗

arXiv1997

The Okubo relation for the baryon magnetic moments and chiral perturbation theory

We analyze the Okubo SU(3) relation among the hyperon magnetic moments in the usual scheme of chiral perturbation theory (ChPT). We classify the one-loop diagrams, including those with intermediate decuplet baryons, in a simple way according to whether or not they satisfy the Okubo relation. Contrary to the conventional wisdom, we find that one-loop contributions to the hyperon magnetic moments in general violate the Okubo relation if the physical masses are employed for the meson propagators in the loops.

hep-ph↗

arXiv1997

SU(3) breaking and baryon magnetic moments

We show that the magnetic moments of the octet baryons can be fitted to an accuracy of 1.5 percent by a phenomenological Lagrangian in which SU(3) breaking corrections appear only linearly. This is in contrast to conventional chiral perturbation theory in which corrections non-analytic in SU(3) breaking dominate and tend to spoil the agreement with the data. Motivated by this observation, we propose a modified scheme for chiral perturbation theory that gives rise to a similar linear breaking of SU(3) symmetry. (Pacs 13.40.Em, 14.20.-c, 11.30.Rd)

hep-ph↗

arXiv1996

Heavy-baryon chiral perturbation theory and reparametrization invariance

We examine the constraints imposed by reparametrization invariance on heavy-baryon chiral perturbation theory (HBChPT). We study the case of 3 flavors and consider both the strong and weak ($|ΔS| =1$) interaction sector. Some of the parameters in the HBChPT Lagrangian are fixed as a consequence of reparametrization invariance. We discuss the consequences for the calculation of hyperon weak radiative decays in HBChPT.

hep-ph↗

arXiv1996

Hyperon weak radiative decays in chiral perturbation theory

We investigate the leading-order amplitudes for weak radiative decays of hyperons in chiral perturbation theory. We consistently include contributions from the next-to-leading order weak-interaction Lagrangian. It is shown that due to these terms Hara's theorem is violated. The data for the decays of charged hyperons can be easily accounted for. However, at this order in the chiral expansion, the four amplitudes for the decays of neutral hyperons satisfy relations which are in disagreement with the data. The asymmetry parameters for all the decays can not be accounted for without higher-order terms. We shortly comment on the effect of the 27-plet part of the weak interaction.

hep-ph↗

arXiv1994

Baryon Chiral Perturbation Theory up to Next-to-Leading Order

We examine the general lagrangian for baryon chiral perturbation theory with SU(3) flavor symmetry, up to the next-to-leading order. We consider both the strong and the weak interaction. The inverse of the baryon mass is treated as an additional small expansion parameter, and heavy fermion effective field theory techniques are employed to provide a consistent expansion scheme. A detailed account is given on the restrictions imposed on the lagrangian by the various symmetries. Corrections due to the finite baryon mass are also discussed.

hep-ph↗