594 research outputs found
Resummed one-loop gluonic contributions to the color superconducting color charge density vanish
It is shown that gluonic corrections to the tadpole diagrams vanish in the
2SC and CFL phases at the order where one might have expected NLO corrections.
This implies that the gluonic part of the color charge density is negligible at
the order of our computation. This statement remains true after inclusion of
the gluon vertex correction and contributions from Nambu-Goldstone bosons.Comment: 9 pages, 3 figures, REVTeX4; title modified, comments about gauge
independence added, accepted for publication in Phys. Rev.
Fermionic dispersion relations in ultradegenerate relativistic plasmas beyond leading logarithmic order
We determine the dispersion relations of fermionic quasiparticles in
ultradegenerate plasmas by a complete evaluation of the on-shell
hard-dense-loop-resummed one-loop fermion self energy for momenta of the order
of the Fermi momentum and above. In the case of zero temperature, we calculate
the nonanalytic terms in the vicinity of the Fermi surface beyond the known
logarithmic approximation, which turn out to involve fractional higher powers
in the energy variable. For nonzero temperature (but much smaller than the
chemical potential), we obtain the analogous expansion in closed form, which is
then analytic but involves polylogarithms. These expansions are compared with a
full numerical evaluation of the resulting group velocities and damping
coefficients.Comment: 9 pages, 2 figures, REVTeX4, v2: minor improvement
Chiral Lattice Gauge Theories and The Strong Coupling Dynamics of a Yukawa-Higgs Model with Ginsparg-Wilson Fermions
The Yukawa-Higgs/Ginsparg-Wilson-fermion construction of chiral lattice gauge
theories described in hep-lat/0605003 uses exact lattice chirality to decouple
the massless chiral fermions from a mirror sector, whose strong dynamics is
conjectured to give cutoff-scale mass to the mirror fermions without breaking
the chiral gauge symmetry. In this paper, we study the mirror sector dynamics
of a two-dimensional chiral gauge theory in the limitof strong Yukawa and
vanishing gauge couplings, in which case it reduces to an XY model coupled to
Ginsparg-Wilson fermions. For the mirror fermions to acquire cutoff-scale mass
it is believed to be important that the XY model remain in its "high
temperature" phase, where there is no algebraic ordering--a conjecture
supported by the results of our work. We use analytic and Monte-Carlo methods
with dynamical fermions to study the scalar and fermion susceptibilities, and
the mirror fermion spectrum. Our results provide convincing evidence that the
strong dynamics does not "break" the chiral symmetry (more precisely, that the
mirror fermions do not induce algebraic ordering in two-dimensions), and that
the mirror fermions decouple from the infrared physics.Comment: 44 pages, 18 figures; v2: clarification of fermion operators,
discussion of recent related work
Lattice chirality and the decoupling of mirror fermions
We show, using exact lattice chirality, that partition functions of lattice
gauge theories with vectorlike fermion representations can be split into
"light" and "mirror" parts, such that the "light" and "mirror" representations
are chiral. The splitting of the full partition function into "light" and
"mirror" is well defined only if the two sectors are separately anomaly free.
We show that only then is the generating functional, and hence the spectrum, of
the mirror theory a smooth function of the gauge field background. This
explains how ideas to use additional non-gauge, high-scale mirror-sector
dynamics to decouple the mirror fermions without breaking the gauge
symmetry--for example, in symmetric phases at strong mirror Yukawa
coupling--are forced to respect the anomaly-free condition when combined with
the exact lattice chiral symmetry. Our results also explain a paradox posed by
a recent numerical study of the mirror-fermion spectrum in a toy
would-be-anomalous two-dimensional theory. In passing, we prove some general
properties of the partition functions of arbitrary chiral theories on the
lattice that should be of interest for further studies in this field.Comment: 29 pages, 2 figures; published version, new addendu
Extreme self-organization in networks constructed from gene expression data
We study networks constructed from gene expression data obtained from many
types of cancers. The networks are constructed by connecting vertices that
belong to each others' list of K-nearest-neighbors, with K being an a priori
selected non-negative integer. We introduce an order parameter for
characterizing the homogeneity of the networks. On minimizing the order
parameter with respect to K, degree distribution of the networks shows
power-law behavior in the tails with an exponent of unity. Analysis of the
eigenvalue spectrum of the networks confirms the presence of the power-law and
small-world behavior. We discuss the significance of these findings in the
context of evolutionary biological processes.Comment: 4 pages including 3 eps figures, revtex. Revisions as in published
versio
Topology and confinement at T \neq 0 : calorons with non-trivial holonomy
In this talk, relying on experience with various lattice filter techniques,
we argue that the semiclassical structure of finite temperature gauge fields
for T < T_c is dominated by calorons with non-trivial holonomy. By simulating a
dilute gas of calorons with identical holonomy, superposed in the algebraic
gauge, we are able to reproduce the confining properties below T_c up to
distances r = O(4 fm} >> \rho (the caloron size). We compute Polyakov loop
correlators as well as space-like Wilson loops for the fundamental and adjoint
representation. The model parameters, including the holonomy, can be inferred
from lattice results as functions of the temperature.Comment: Talk by M. M\"uller-Preussker at "Quark Confinement and Hadron
Structure VII", Ponta Delgada, Azores, Portugal, September 2 - 7, 2006, 4
pages, 2 figures, to appear in the Proceeding
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