85 research outputs found
Anomaly at finite density and chiral fermions on lattice
Using both perturbation theory in the Euclidean formalism as well as the
non-perturbative Fujikawa's method, we verify that the chiral anomaly equation
remains unaffected in continuum QCD in the presence of nonzero chemical
potential, \mu. We extend our considerations to lattice fermions with exact
chiral symmetry and discuss the consequences for the recent Bloch-Wettig
proposal for the Dirac operator at finite chemical potential. We propose a new
simpler method of incorporating \mu.Comment: Talk presented at the XXVII International Symposium on Lattice Field
Theory, July 26-31, 2009, Peking University, Beijing, China; 7 pages, 3
figure
Thermodynamics of free Domain Wall fermions
Studying various thermodynamic quantities for the free domain wall fermions
for both finite and infinite fifth dimensional extent N_5, we find that the
lattice corrections are minimum for for both energy density and
susceptibility, for its irrelevant parameter M in the range 1.45-1.50. The
correction terms are, however, quite large for small lattice sizes of
. We propose modifications of the domain wall operator, as well as
the overlap operator, to reduce the finite cut-off effects to within 10% of the
continuum results of the thermodynamic quantities for the currently used
N_T=6-8 lattices. Incorporating chemical potential, we show that \mu^2
divergences are absent for a large class of such domain wall fermion actions
although the chiral symmetry is broken for .Comment: 11 pages, 15 figures include
A faster method of computation of lattice quark number susceptibilities
We compute the quark number susceptibilities in two flavor QCD for staggered
fermions by adding the chemical potential as a Lagrange multiplier for the
point-split number density term. Since lesser number of quark propagators are
required at any order, this method leads to faster computations. We propose a
subtraction procedure to remove the inherent undesired lattice terms and check
that it works well by comparing our results with the existing ones where the
elimination of these terms is analytically guaranteed. We also show that the
ratios of susceptibilities are robust, opening a door for better estimates of
location of the QCD critical point through the computation of the tenth and
twelfth order baryon number susceptibilities without significant additional
computational overload.Comment: 10 pages, 12 figure
Exact Chiral Fermions and Finite Density on Lattice
Any mu^2-divergence is shown analytically to be absent for a class of actions
for Overlap and Domain Wall Fermions with nonzero chemical potential. All such
actions are, however, shown to violate the chiral invariance. While the
parameter M of these actions can be shown to be irrelevant in the continuum
limit, as expected, it is shown numerically that the continuum limit can be
reached with relatively coarser lattices for M in the range of 1.5-1.6.Comment: 8 pages, 3 figures, talk presented at The XXVI International
Symposium on Lattice Field Theory, July 14 - 19, 2008, Williamsburg,
Virginia, US
The topological susceptibility in finite temperature QCD and axion cosmology
We study the topological susceptibility in 2+1 flavor QCD above the chiral
crossover transition temperature using Highly Improved Staggered Quark action
and several lattice spacings, corresponding to temporal extent of the lattice,
and . We observe very distinct temperature dependences of
the topological susceptibility in the ranges above and below MeV. While
for temperatures above MeV, the dependence is found to be consistent with
dilute instanton gas approximation, at lower temperatures the fall-off of
topological susceptibility is milder. We discuss the consequence of our results
for cosmology wherein we estimate the bounds on the axion decay constant and
the oscillation temperature if indeed the QCD axion is a possible dark matter
candidate.Comment: 19 pages and 7 figures; v2: A new figure, a few references and minor
comments added; published versio
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