1,771 research outputs found
Nonabelian Berry Phases in Baryons
We show how generic nonabelian gauge fields can be induced in baryons when a
hierarchy of fast degrees of freedom is integrated out. We identify them with
nonabelian Berry potentials and discuss their role in transmuting quantum
numbers in bag and soliton models of baryons. The resulting baryonic spectra
for both light and heavy quark systems are generic and resemble closely the
excitation spectrum of diatomic molecules. The symmetry restoration in the
system, i.e., the electronic rotational invariance in diatomic molecules, the
heavy-quark symmetry in heavy baryons etc. is interpreted in terms of the
vanishing of nonabelian Berry potentials that otherwise govern the hyperfine
splitting.Comment: Latex 35 pages (2 figures not added, will be faxed if requested),
NTG-92-2
Neutrino Interactions In Color-Flavor-Locked Dense Matter
At high density, diquarks could condense in the vacuum with the QCD color
spontaneously broken. Based on the observation that the symmetry breaking
pattern involved in this phenomenon is essentially the same as that of the
Pati-Salam model with broken electroweak--color SU(3) group, we determine the
relevant electroweak interactions in the color-flavor locked (CFL) phase in
high density QCD. We briefly comment on the possible implications on the
cooling of neutron stars.Comment: 13 pages. LaTeX. Talk given at the First KIAS Workshop on
Astrophysics, Seoul, May 2000; V2. references added. comments on cooling
change
The Gluon Spin in the Chiral Bag Model
We study the gluon polarization contribution at the quark model
renormalization scale to the proton spin, , in the chiral bag model. It
is evaluated by taking the expectation value of the forward matrix element of a
local gluon operator in the axial gauge . It is shown that the confining
boundary condition for the color electric field plays an important role. When a
solution satisfying the boundary condition for the color electric field, which
is not the conventionally used but which we favor, is used, the has a
positive value for {\it all} bag radii and its magnitude is comparable to the
quark spin polarization. This results in a significant reduction in the
relative fraction of the proton spin carried by the quark spin, which is
consistent with the small flavor singlet axial current measured in the EMC
experiments.Comment: Corrections to figure
Radiative neutron capture on a proton at BBN energies
The total cross section for radiative neutron capture on a proton, , 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 cross section and the photon
analyzing power for the 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 cross section at some energies estimated by an
R-matrix analysis. We also study the uncertainties in our estimation of the
cross section at relevant BBN energies and find that the
estimated cross section is reliable to within 1% error.Comment: 21 pages and 12 eps figures; 6 eps figures and 2 references added,
and accepted for publication in Phys. Rev.
Chandra Observations of SN 2004et and the X-ray Emission of Type IIp Supernovae
We report the X-ray detection of the Type II-plateau supernova SN 2004et in
the spiral galaxy NGC 6946, using the Chandra X-Ray Observatory. The position
of the X-ray source was found to agree with the optical position within ~0.4
arcsec. Chandra also surveyed the region before the 2004 event, finding no
X-ray emission at the location of the progenitor. For the post-explosion
observations, a total of 202, 151, and 158 photons were detected in three
pointings, each ~29 ks in length, on 2004 October 22, November 6, and December
3, respectively. The spectrum of the first observation is best fit by a thermal
model with a temperature of kT=1.3 keV and a line-of-sight absorption of
N_H=1.0 x 10^{22} cm^{-2}. The inferred unabsorbed luminosity (0.4-8 keV) is
~4x10^{38} erg/s, adopting a distance of 5.5 Mpc. A comparison between hard and
soft counts on the first and third epochs indicates a softening over this time,
although there is an insufficient number of photons to constrain the variation
of temperature and absorption by spectral fitting. We model the emission as
arising from the reverse shock region in the interaction between the supernova
ejecta and the progenitor wind. For a Type IIP supernova with an extended
progenitor, the cool shell formed at the time of shock wave breakout from the
star can affect the initial evolution of the interaction shell and the
absorption of radiation from the reverse shock. The observed spectral softening
might be due to decreasing shell absorption. We find a pre-supernova mass loss
rate of (2-2.5)x 10^{-6} M_{\odot} /yr for a wind velocity of 10 kms, which is
in line with expectations for a Type IIP supernova.Comment: total 19 pages including 7 figures. ApJ, in press. See
http://spider.ipac.caltech.edu/staff/rho/preprint/SN2004etms.ps for the paper
including full resolution image
Demonstration of nanoimprinted hyperlens array for high-throughput sub-diffraction imaging
11124Nsciescopu
Lattice dynamics and the electron-phonon interaction in CaRuO
We present a Raman scattering study of CaRuO, in which we investigate
the temperature-dependence of the lattice dynamics and the electron-phonon
interaction below the metal-insulator transition temperature ({\it T}). Raman spectra obtained in a backscattering geometry with light polarized
in the ab-plane reveal 9 B phonon modes (140, 215, 265, 269, 292, 388,
459, 534, and 683 cm) and 9 A phonon modes (126, 192, 204, 251, 304,
322, 356, 395, and 607 cm) for the orthorhombic crystal structure
(PbcaD). With increasing temperature toward {\it T},
the observed phonon modes shift to lower energies and exhibit reduced spectral
weights, reflecting structural changes associated with the elongation of the
RuO octahedra. Interestingly, the phonons exhibit significant increases in
linewidths and asymmetries for {\it T} {\it T}. These results
indicate that there is an increase in the effective number of electrons and the
electron-phonon interaction strengths as the temperature is raised through {\it
T}, suggesting the presence of orbital fluctuations in the
temperature regime {\it T} {\it T} {\it T}.Comment: 6 pages, 4 figure
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