155 research outputs found
Anderson Localization in high temperature QCD: background configuration properties and Dirac eigenmodes
We investigate the properties of the background gauge field configurations
that act as disorder for the Anderson localization mechanism in the Dirac
spectrum of QCD at high temperatures. We compute the eigenmodes of the M\"obius
domain-wall fermion operator on configurations generated for the gauge
theory with two flavors of fermions, in the temperature range .
We identify the source of localization of the eigenmodes with gauge
configurations that are self-dual and support negative fluctuations of the
Polyakov loop , in the high temperature sea of . The dependence
of these observations on the boundary conditions of the valence operator is
studied. We also investigate the spatial overlap of the left-handed and
right-handed projected eigenmodes in correlation with the localization and the
corresponding eigenvalue. We discuss an interpretation of the results in terms
of monopole-instanton structures.Comment: 27 pages, 16 figures, 2 tables, minor corrections and typo
Finite size phase transitions in QCD with adjoint fermions
We perform a lattice investigation of QCD with three colors and 2 flavors of
Dirac (staggered) fermions in the adjoint representation, defined on a 4d space
with one spatial dimension compactified, and study the phase structure of the
theory as a function of the size Lc of the compactified dimension. We show that
four different phases take place, corresponding to different realizations of
center symmetry: two center symmetric phases, for large or small values of Lc,
separated by two phases in which center symmetry is broken in two different
ways; the dependence of these results on the quark mass is discussed. We study
also chiral properties and how they are affected by the different realizations
of center symmetry; chiral symmetry, in particular, stays spontaneously broken
at the phase transitions and may be restored at much lower values of the
compactification radius. Our results could be relevant to a recently proposed
conjecture of volume indepedence of QCD with adjoint fermions in the large Nc
limit.Comment: 9 pages, 12 figures; extended discussion about the chiral limit and
the chiral properties; 2 figures and references adde
Partial restoration of chiral symmetry in the color flux tube
Using the quark eigenmodes computed on the lattice with the overlap-Dirac
operator, we investigate the spatial distribution of the chiral condensate
around static color sources corresponding to quark-antiquark and three-quark
systems. A flux structure of chromo fields appears in the presence of such
color charges. The magnitude of the chiral condensate is reduced inside the
color flux, which implies partial restoration of chiral symmetry inside
hadrons. Taking a static baryon source in a periodic box as a toy model of
nuclear matter, we estimate the magnitude of the chiral symmetry restoration as
a function of baryon matter density.Comment: 21 pages, 14 figures, published version in Phys. Rev.
QCD simulations with staggered fermions on GPUs
We report on our implementation of the RHMC algorithm for the simulation of
lattice QCD with two staggered flavors on Graphics Processing Units, using the
NVIDIA CUDA programming language. The main feature of our code is that the GPU
is not used just as an accelerator, but instead the whole Molecular Dynamics
trajectory is performed on it. After pointing out the main bottlenecks and how
to circumvent them, we discuss the obtained performances. We present some
preliminary results regarding OpenCL and multiGPU extensions of our code and
discuss future perspectives.Comment: 22 pages, 14 eps figures, final version to be published in Computer
Physics Communication
The Roberge-Weiss endpoint in N_f = 2 QCD
We present the results of extensive simulations regarding the critical
behavior at the endpoint of the Roberge-Weiss transition for N_f = 2 QCD. We
confirm early evidence, presented in arXiv:0909.0254, according to which the
Roberge-Weiss endpoint is first order in the limit of large or small quark
masses, and second order for intermediate masses. A systematic study of the
transition strength as a function of the quark mass in the first order regions,
permits us to estimate the tricritical values of the quark mass separating the
second order region from the first order ones.Comment: 10 pages, 20 figures. References and figures updated. Matches the
published versio
Staggered fermions simulations on GPUs
We present our implementation of the RHMC algorithm for staggered fermions on
Graphics Processing Units using the NVIDIA CUDA programming language. While
previous studies exclusively deal with the Dirac matrix inversion problem, our
code performs the complete MD trajectory on the GPU. After pointing out the
main bottlenecks and how to circumvent them, we discuss the performance of our
code.Comment: Poster presented at the XXVIII International Symposium on Lattice
Field Theory, June 14-19, 2010, Villasimius, Sardinia Ital
Topological susceptibility in 2+1-flavor QCD with chiral fermions
We compute the topological susceptibility of 2+1-flavor lattice QCD
with dynamical M\"obius domain-wall fermions, whose residual mass is kept at 1
MeV or smaller. In our analysis, we focus on the fluctuation of the topological
charge density in a "slab" sub-volume of the simulated lattice, as proposed by
Bietenholz et al. The quark mass dependence of our results agrees well with the
prediction of the chiral perturbation theory, from which the chiral condensate
is extracted. Combining the results for the pion mass and decay
constant , we obtain = 0.227(02)(11) at the
physical point, where the first error is statistical and the second is
systematic.Comment: 8 pages, 3 figures, talk given at the 35th International Symposium on
Lattice Field Theory, 18-24 June 2017, Granada, Spai
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