613 research outputs found
The Quantum Effective Action, Wave Functions and Yang-Mills (2+1)
We explore the relationship between the quantum effective action and the
ground state (and excited state) wave functions of a field theory. Applied to
the Yang-Mills theory in 2+1 dimensions, we find the leading terms of the
effective action from the ground state wave function previously obtained in the
Hamiltonian formalism by solving the Schrodinger equation.Comment: 16 pages, expanded discussion section, added references, version
accepted for Phys. Rev.
Strange mass dependence of the tricritical point in the U(3)_L x U(3)_R chiral sigma model
We study the strange quark mass dependence of the tricritical point of the
U(3)_L x U(3)_R linear sigma model in the chiral limit. Assuming that the
tricritical point is at a large strange mass value, the strange sector as well
as the \eta-a_0 sector decouples from the light degrees of freedom which
determines the thermodynamics. By tracing this decoupling we arrive from the
original U(3)_L x U(3)_R symmetric model, going through the U(2)_L x U(2)_R
symmetric one, at the SU(2)_L x SU(2)_R linear sigma model. One-loop level beta
functions for the running of the parameters in each of these models and
tree-level matching of the coupling of these models performed at intermediate
scales are used to determine the influence of the heavy sector on the
parameters of the SU(2)_L x SU(2)_R linear sigma model. By investigating the
thermodynamics of this latter model we identified the tricritical surface of
the U(3)_L x U(3)_R linear sigma model in the chiral limit. To apply the
results for QCD we used different scenarios for the m_s and \mu_q dependence of
the effective model parameters, then the \mu_q^TCP(m_s) function can be
determined. Depending on the details, a curve bending upwards or downwards near
\mu_q=0 can be obtained, while with explicit chemical potential dependence of
the parameters the direction of the curve can change with m_s, too.Comment: 17 pages, 6 figures, uses revtex4-
The three-flavor chiral phase structure in hot and dense QCD matter
Chiral symmetry restoration at nonzero temperature and quark densities are
investigated in the framework of a linear sigma model with N_f=3 light quark
flavors. After the derivation of the grand potential in mean-field
approximation, the nonstrange and strange condensates, the in-medium masses of
the scalar and pseudoscalar nonets are analyzed in hot and dense medium. The
influence of the axial anomaly on the nonet masses and the isoscalar mixings on
the pseudoscalar \eta-\eta' and scalar \sigma(600)-f_0(1370) complex are
examined. The sensitivity of the chiral phase transition as well as the
existence and location of a critical end point in the phase diagram on the
value of the sigma mass is explored. The chiral critical surface with and
without the influence of the axial U(1)_A anomaly is elaborated as a function
of the pion and kaon masses for several values of the sigma mass.Comment: 19 pages, 12 figures, 2 tables, RevTex4; revised version, accepted
for publication in PR
Has the QCD Critical Point been Signaled by Observations at RHIC ?
The shear viscosity to entropy ratio () is estimated for the hot and
dense QCD matter created in Au+Au collisions at RHIC ( GeV).
A very low value is found , which is close to the conjectured
lower bound (). It is argued that such a low value is indicative of
thermodynamic trajectories for the decaying matter which lie close to the QCD
critical end point.Comment: 4 pages, 3 figures. Revised version, accepted for publication in PR
Resummation scheme for 3d Yang-Mills and the two-loop magnetic mass for hot gauge theories
Perturbation theory for non-Abelian gauge theories at finite temperature is
plagued by infrared divergences caused by magnetic soft modes ,
which correspond to the fields of a 3d Yang-Mills theory. We revisit a gauge
invariant resummation scheme to solve this problem by self-consistent mass
generation using an auxiliary scalar field, improving over previous attempts in
two respects. First, we generalise earlier SU(2) treatments to SU(N). Second,
we obtain a gauge independent two-loop gap equation, correcting an error in the
literature. The resulting two-loop approximation to the magnetic mass
represents a correction to the leading one-loop value, indicating a
reasonable convergence of the resummation.Comment: 16 pages, 3 figure
The deconfinement transition of finite density QCD with heavy quarks from strong coupling series
Starting from Wilson's action, we calculate strong coupling series for the
Polyakov loop susceptibility in lattice gauge theories for various small N_\tau
in the thermodynamic limit. Analysing the series with Pad\'e approximants, we
estimate critical couplings and exponents for the deconfinement phase
transition. For SU(2) pure gauge theory our results agree with those from
Monte-Carlo simulations within errors, which for the coarser N_\tau=1,2
lattices are at the percent level. For QCD we include dynamical fermions via a
hopping parameter expansion. On a N_\tau=1 lattice with N_f=1,2,3, we locate
the second order critical point where the deconfinement transition turns into a
crossover. We furthermore determine the behaviour of the critical parameters
with finite chemical potential and find the first order region to shrink with
growing \mu. Our series moreover correctly reflects the known Z(N) transition
at imaginary chemical potential.Comment: 18 pages, 7 figures, typos corrected, version published in JHE
Heavy Quark Free Energies and Screening in SU(2) Gauge Theory
We investigate the singlet, triplet and colour average heavy quark free
energies in SU(2) pure gauge theory at various temperatures T. We focus on the
long distance behaviour of the free energies, studying in particular the
temperature dependence of the string tension and the screening masses. The
results are qualitatively similar to the SU(3) scenario, except near the
critical temperature Tc of the deconfining transition. Finally we test a
recently proposed method to renormalize the Polyakov loop.Comment: 5 pages, 4 figures, contribution to the Proceedings of SEWM 2002
(Heidelberg
Non-perturbative Debye mass in finite T QCD
Employing a non-perturbative gauge invariant definition of the Debye
screening mass m_D in the effective field theory approach to finite T QCD, we
use 3d lattice simulations to determine the leading O(g^2) and to estimate the
next-to-leading O(g^3) corrections to m_D in the high temperature region. The
O(g^2) correction is large and modifies qualitatively the standard
power-counting hierarchy picture of correlation lengths in high temperature
QCD.Comment: 4 pages, Late
Does quantitative heterogeneity of human fetal hemoglobin (Hb F) reveal friends or foes of KLF1 in globin gene switching?
The chemical heterogeneity of fetal hemoglobin (Hb F) due to variable
ratios of the Gγ and Aγ globin subunits reflects genetic complexity
because of common dimorphisms such as Hb F Sardegna (or Aγ75(E19)
Ile>Thr; also known as AγT) in Caucasians, and common variants such the
Gγ globin variant, Hb F Malta I (or Gγ117(G19) His>Arg) that is in tight
linkage disequilibrium with the β globin variant Hb Valletta (or β87(F3)
Thr>Pro) and is found in 1.8% of neonates from Malta.peer-reviewe
Assessing the Performance of Recent Density Functionals for Bulk Solids
We assess the performance of recent density functionals for the
exchange-correlation energy of a nonmolecular solid, by applying accurate
calculations with the GAUSSIAN, BAND, and VASP codes to a test set of 24 solid
metals and non-metals. The functionals tested are the modified
Perdew-Burke-Ernzerhof generalized gradient approximation (PBEsol GGA), the
second-order GGA (SOGGA), and the Armiento-Mattsson 2005 (AM05) GGA. For
completeness, we also test more-standard functionals: the local density
approximation, the original PBE GGA, and the Tao-Perdew-Staroverov-Scuseria
(TPSS) meta-GGA. We find that the recent density functionals for solids reach a
high accuracy for bulk properties (lattice constant and bulk modulus). For the
cohesive energy, PBE is better than PBEsol overall, as expected, but PBEsol is
actually better for the alkali metals and alkali halides. For fair comparison
of calculated and experimental results, we consider the zero-point phonon and
finite-temperature effects ignored by many workers. We show how Gaussian basis
sets and inaccurate experimental reference data may affect the rating of the
quality of the functionals. The results show that PBEsol and AM05 perform
somewhat differently from each other for alkali metal, alkaline earth metal and
alkali halide crystals (where the maximum value of the reduced density gradient
is about 2), but perform very similarly for most of the other solids (where it
is often about 1). Our explanation for this is consistent with the importance
of exchange-correlation nonlocality in regions of core-valence overlap.Comment: 32 pages, single pdf fil
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