2,358 research outputs found
Chiral polarization scale of QCD vacuum and spontaneous chiral symmetry breaking
It has recently been found that dynamics of pure glue QCD supports the low
energy band of Dirac modes with local chiral properties qualitatively different
from that of a bulk: while bulk modes suppress chirality relative to
statistical independence between left and right, the band modes enhance it. The
width of such chirally polarized zone - chiral polarization scale Lambda_ch -
has been shown to be finite in the continuum limit at fixed physical volume.
Here we present evidence that Lambda_ch remains non-zero also in the infinite
volume, and is therefore a dynamical scale in the theory. Our experiments in
N_f=2+1 QCD support the proposition that the same holds in the massless limit,
connecting Lambda_ch to spontaneous chiral symmetry breaking. In addition, our
results suggest that thermal agitation in quenched QCD destroys both chiral
polarization and condensation of Dirac modes at the same temperature T_ch >
T_c.Comment: 5 pages, 4 figures. Proceedings of "Extreme QCD" workshop,
Washington, DC, Aug 21-23 201
Phases of SU(3) Gauge Theories with Fundamental Quarks via Dirac Spectral Density
We propose that, in SU(3) gauge theories with fundamental quarks, confinement
can be inferred from spectral density of the Dirac operator. This stems from
the proposition that its possible behaviors are exhausted by three distinct
types (Fig.1). The monotonic cases are standard and entail confinement with
valence chiral symmetry breaking (A) or the lack of both (C,C'). The bimodal
(anomalous) option (B) was frequently regarded as an artifact (lattice or
other) in previous studies, but we show for the first time that it persists in
the continuum limit, and conclude that it informs of a non-confining phase with
broken valence chiral symmetry. This generalization rests on the following.
We show that bimodality in =0 theory past deconfinement
temperature is stable with respect to removal of both infrared and
ultraviolet cutoffs, indicating that anomalous phase is not an artifact.
We demonstrate that transition to bimodality in =0 is
simultaneous with the loss of confinement: anomalous phase occurs for , where is the valence chiral restoration temperature.
Evidence is presented for thermal anomalous phase in =2+1 QCD
at physical quark masses, whose onset too coincides with the conventional
"crossover ''. We conclude that the anomalous regime is
very likely a feature of nature's strong interactions. Our past
studies of zero-temperature =12 theories revealed that bimodality also
arises via purely light-quark effects. As a result, we expect to encounter
anomalous phase on generic paths to valence chiral restoration. We predict its
existence also for massless flavors () in the range , where could be quite low. Conventional arguments would
associate with the onset of conformal window.Comment: 10 pages, 6 figures; v2: PRD version, few remarks/references added
and minor reformulations made, 11 pages, 6 figure
QCD at imaginary chemical potential with Wilson fermions
We investigate the phase diagram in the temperature, imaginary chemical
potential plane for QCD with three degenerate quark flavors using Wilson type
fermions. While more expensive than the staggered fermions used in past studies
in this area, Wilson fermions can be used safely to simulate systems with three
quark flavors. In this talk, we focus on the (pseudo)critical line that extends
from in the imaginary chemical potential plane, trace it to the
Roberge-Weiss line, and determine its location relative to the Roberge-Weiss
transition point. In order to smoothly follow the (pseudo)critical line in this
plane we perform a multi-histogram reweighting in both temperature and chemical
potential. To perform reweighting in the chemical potential we use the
compression formula to compute the determinants exactly. Our results are
compatible with the standard scenario.Comment: 7 pages, 5 figures. Proceedings of the 31st International Symposium
on Lattice Field Theory (Lattice 2013), 29 July - 3 August 2013, Mainz,
German
Chiral Symmetry Breaking and Chiral Polarization: Tests for Finite Temperature and Many Flavors
It was recently conjectured that, in SU(3) gauge theories with fundamental
quarks, valence spontaneous chiral symmetry breaking is equivalent to
condensation of local dynamical chirality and appearance of chiral polarization
scale . Here we consider more general association involving the
low-energy layer of chirally polarized modes which, in addition to its width
(), is also characterized by volume density of participating
modes () and the volume density of total chirality (). Few
possible forms of the correspondence are discussed, paying particular attention
to singular cases where emerges as the most versatile characteristic.
The notion of finite-volume "order parameter", capturing the nature of these
connections, is proposed. We study the effects of temperature (in N=0 QCD)
and light quarks (in N=12), both in the regime of possible symmetry
restoration, and find agreement with these ideas. In N=0 QCD, results from
several volumes indicate that, at the lattice cutoff studied, the deconfinement
temperature is strictly smaller than the overlap-valence chiral
transition temperature in real Polyakov line vacuum. Somewhat similar
intermediate phase (in quark mass) is also seen in N=12. It is suggested
that deconfinement in N=0 is related to indefinite convexity of absolute
X-distributions.Comment: 45 pages, 20 figures; v2: reduced the size of submission and fixed
references to appendices; v3: minor changes - published for
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