7,571 research outputs found
Weak matrix elements for CP violation
We present preliminary results of matrix elements of four-fermion operators
relevant to the determination of e and e'/e using staggered fermions.Comment: 3 pages, 4 figures, Lattice 2001 (Hadronic Matrix Elements
Threshold Pion Electroproduction in Chiral Perturbation Theory
Electroproduction of pions on the nucleon near the threshold is analyzed
within the framework of baryon chiral perturbation theory. We give a thorough
discussion of the low--energy theorems related to charged and neutral
electropionproduction. It is shown how the axial radius of the nucleon can be
related to the S--wave multipoles and . The chiral
perturbation theory calculations of the reaction
are found to be in good agreement with the recent near threshold data. We also
discuss the influence of some isospin--breaking effects in this channel. For
future experimental tests of the underlying chiral dynamics, extensive
predictions of differential cross sections and multipole amplitudes are
presented.Comment: 44pp, TeX, 15 figures available upon request, BUTP-93/23 and CRN
93-4
Relations Among Correlation Functions in the High Temperature Phase of QCD with Broken SU(3)
Group-theoretic arguments are used to determine the dependence of two-point
correlators of quark bilinears on the current quark masses. The leading
difference between and correlators is found to be of order
times a U(1)-violating correlator. These general
arguments are consistent with Schaefer's observation that if
U(1) violation persists to high enough temperatures
then the strange can be lighter than the non-strange one.Comment: 8 page
Perturbative matching of staggered four-fermion operators with hypercubic fat links
We calculate the one-loop matching coefficients between continuum and lattice
four-fermion operators for lattice operators constructed using staggered
fermions and improved by the use of fattened links. In particular, we consider
hypercubic fat links and SU(3) projected Fat-7 links, and their mean-field
improved versions. We calculate only current-current diagrams, so that our
results apply for operators whose flavor structure does not allow
``eye-diagrams''. We present general formulae, based on two independent
approaches, and give numerical results for the cases in which the operators
have the taste (staggered flavor) of the pseudo-Goldstone pion. We find that
the one-loop corrections are reduced down to the 10-20% level, resolving the
problem of large perturbative corrections for staggered fermion calculations of
matrix elements.Comment: 37 pages, no figure, 20 table
One loop matching coefficients for a variant overlap action--and some of its simpler relatives
I present one-loop perturbative calculations of matching coefficients between
matrix elements in continuum regulated QCD and lattice QCD with overlap
fermions, with emphasis a recently-proposed variant discretization of the
overlap. These fermions have extended (``fat link'') gauge connections. The
scale for evaluation of the running coupling constant (in the context of the
Lepage-Mackenzie fixing scheme) is also given.
A variety of results (for additive mass renormalization, local currents, and
some non-penguin four-fermion operators) for naive, Wilson, clover, and overlap
actions are shown.Comment: 17 pages, Revtex, 11 postscript figures. COLO-HEP-48
Thermodynamics of a weakly interacting Bose-Einstein gas
The one-loop effective potential for non-relativistic bosons with a delta
function repulsive potential is calculated for a given chemical potential using
functional methods. After renormalization and at zero temperature it reproduces
the standard ground state energy and pressureas function of the particle
density. At finite temperatures it is found necessary to include ring
corrections to the one-loop result in order to satisfy the Goldstone theorem.
It is natural to introduce an effective chemical potential directly related to
the order parameter and which uniformly decreases with increasing temperatures.
This is in contrast to the the ordinary chemical potential which peaks at the
critical temperature. The resulting thermodynamics in the condensed phase at
very low temperatures is found to be the same as in the Bogoliubov
approximation where the degrees of freedom are given by the Goldstone bosons.
At higher temperatures the ring corrections dominate and result in a critical
temperature unaffected by the interaction.Comment: 39 pages, 9 figures, picTex, submitted to Annals of Physics.
Discussions on renormalization and off-diagonal self energies are made
clearer in this version. A short derivation of the non-relativistic limit is
adde
Light Hadron Spectroscopy
Recent developments in calculations of the light hadron spectrum are
reviewed. Particular emphasis is placed on discussion of to what extent the
quenched spectrum agrees with experiment. Recent progress, both for quenched
and full QCD, in reducing scaling violation with the use of improved actions is
presented.Comment: Plenary talk presented at Lattice 97, 13 pages, LaTeX (espcrc2,epsf),
14 ps figure
Perturbative Matching of the staggered four-fermion operators for e'/e
Using staggered fermions, we calculate the perturbative corrections to the
bilinear and four-fermion operators that are used in the numerical study of
weak matrix elements for . We present results for one-loop
matching coefficients between continuum operators, calculated in the Naive
Dimensional Regularization (NDR) scheme, and gauge invariant staggered fermion
operators. These results, combined with existing results for penguin diagrams,
provide the complete one-loop renormalization of the staggered four-fermion
operators.Comment: 36 pages. will appear in physical review
Kaon B Parameter in Quenched QCD
I calculate the kaon B-parameter with a lattice simulation in quenched
approximation. The lattice simulation uses an action possessing exact lattice
chiral symmetry, an overlap action. Computations are performed at two lattice
spacings, about 0.13 and 0.09 fm (parameterized by Wilson gauge action
couplings beta=5.9 and 6.1) with nearly the same physical volumes and quark
masses. I describe particular potential difficulties which arise due to the use
of such a lattice action in finite volume. My results are consistent with other
recent lattice determinations using domain-wall fermions.Comment: 23 pages, Revtex, 16 postscript figure
Functional MRI To Evaluate âSense of Selfâ following Perforator Flap Breast Reconstruction
Background: Breast reconstruction is associated with high levels of patient satisfaction. Previous patient satisfaction studies have been subjective. This study utilizes functional magnetic resonance imaging (fMRI) to objectively evaluate âsense of selfâ following deep inferior epigastric perforator (DIEP) flap breast reconstruction in an attempt to better understand patient perception.
Methods: Prospective fMRI analysis was performed on four patients before and after delayed unilateral DIEP flap breast reconstruction, and on four patients after immediate unilateral DIEP flap breast reconstruction. Patients were randomly cued to palpate their natural breast, mastectomy site or breast reconstruction, and external silicone models. Three regions of interest (ROIs) associated with self-recognition were examined using a general linear model, and compared using a fixed effects and random effects ANOVA, respectively.
Results: In the delayed reconstruction group, activation of the ROIs was significantly lower at the mastectomy site compared to the natural breast (p<0.01). Ten months following reconstruction, activation of the ROIs in the reconstructed breast was not significantly different from that observed with natural breast palpation. In the immediate reconstruction group, palpation of the reconstructed breast was also similar to the natural breast. This activity was greater than that observed during palpation of external artificial models (p<0.01).
Conclusions: Similar activation patterns were observed during palpation of the reconstructed and natural breasts as compared to the non-reconstructed mastectomy site and artificial models. The cognitive process represented by this pattern may be a mechanism by which breast reconstruction improves self-perception, and thus patient satisfaction following mastectomy
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