2,529 research outputs found
Temperature-dependence of the QCD topological susceptibility
We recently obtained an estimate of the axion mass based on the hypothesis
that axions make up most of the dark matter in the universe. A key ingredient
for this calculation was the temperature-dependence of the topological
susceptibility of full QCD. Here we summarize the calculation of the
susceptibility in a range of temperatures from well below the finite
temperature cross-over to around 2 GeV. The two main difficulties of the
calculation are the unexpectedly slow convergence of the susceptibility to its
continuum limit and the poor sampling of nonzero topological sectors at high
temperature. We discuss how these problems can be solved by two new techniques,
the first one with reweighting using the quark zero modes and the second one
with the integration method.Comment: 9 pages, 6 figures, to be published in Proceedings of the 35th
International Symposium on Lattice Field Theory (Lattice2017)}: Granada,
Spain}, to appear in EPJ Web Con
The localization transition in SU(3) gauge theory
We study the Anderson-like localization transition in the spectrum of the
Dirac operator of quenched QCD. Above the deconfining transition we determine
the temperature dependence of the mobility edge separating localized and
delocalized eigenmodes in the spectrum. We show that the temperature where the
mobility edge vanishes and localized modes disappear from the spectrum,
coincides with the critical temperature of the deconfining transition. We also
identify topological charge related close to zero modes in the Dirac spectrum
and show that they account for only a small fraction of localized modes, a
fraction that is rapidly falling as the temperature increases.Comment: 7 pages, 5 figures, v3: additional data on finer lattice; final,
published versio
Instanton Effects in Hadron Spectroscopy in SU(2) (Lattice) Gauge Theory
We describe quenched spectroscopy in SU(2) gauge theory using smoothed gauge
field configurations. We investigate the properties of quarks moving in
instanton background field configurations, where the sizes and locations of the
instantons are taken from simulations of the full gauge theory. By themselves,
these multi-instanton configurations do not confine quarks, but they induce
chiral symmetry breaking.Comment: 13 pages, LaTeX, 8 eps figure
Stochastic perturbations in open chaotic systems: random versus noisy maps
We investigate the effects of random perturbations on fully chaotic open
systems. Perturbations can be applied to each trajectory independently (white
noise) or simultaneously to all trajectories (random map). We compare these two
scenarios by generalizing the theory of open chaotic systems and introducing a
time-dependent conditionally-map-invariant measure. For the same perturbation
strength we show that the escape rate of the random map is always larger than
that of the noisy map. In random maps we show that the escape rate and
dimensions of the relevant fractal sets often depend nonmonotonically on
the intensity of the random perturbation. We discuss the accuracy (bias) and
precision (variance) of finite-size estimators of and , and show
that the improvement of the precision of the estimations with the number of
trajectories is extremely slow (). We also argue that the
finite-size estimators are typically biased. General theoretical results
are combined with analytical calculations and numerical simulations in
area-preserving baker maps.Comment: 12 pages, 3 figures, 1 table, manuscript submitted to Physical Review
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