1,493 research outputs found
Aspects on Effective Theories and the QCD transition
We review recent advances in the understanding of the Quantum Chromodynamics
(QCD) transition and its nature, paying special attention to the analysis of
chiral symmetry restoration within different approaches based on effective
theories. After presenting some of the main aspects of the current knowledge of
the phase diagram from the theoretical, experimental and lattice sides, we
discuss some recent problems where approaches relying on effective theories
have been particularly useful. In particular, the combination of ideas such as
Chiral Perturbation Theory, unitarity and Ward Identities allows us to describe
successfully several observables of interest. This is particularly relevant for
quantities expected to be dominated by the light meson components of the hadron
gas such as the scalar and topological susceptibilities. In addition, ward
identities and effective Lagrangians provide systematic results regarding
chiral and partner degeneration properties which are of great
importance for the interplay between those two transitions and the nature of
chiral symmetry restoration. Special attention is paid to the connection of
this theoretical framework with lattice simulations.Comment: Invited review paper submitted to Symmetry Journal, special issue
"Effective Field Theories - Chiral Perturbation Theory and Non-relativistic
QFT". 28 pages, 15 figures. Version accepted for publication. Various
comments and one reference adde
Light quarks at finite temperature: chiral restoration and the fate of the symmetry
We review recent results on the role of light quark states within the QCD
phase diagram. In particular, we will discuss how the combined use of
theoretical techniques such as Effective Theories, Unitarization and Ward
Identities helps to shed light on several important issues regarding chiral
symmetry restoration, building bridges with recent lattice analyses. Special
attention will be paid to the role of chiral and partners in the
interplay between those symmetries, which is crucial to properly understand the
transition pattern. Light scalar mesons at finite temperature will be shown to
be responsible for the description of susceptibilities encoding chiral and
restoration properties.Comment: Invited review paper submitted to European Physical Journal Special
Topics. 18 pages, 11 figures. Version accepted for publicatio
Chiral Symmetry restoration from the hadronic regime
We discuss recent advances on QCD chiral symmetry restoration at finite
temperature, within the theoretical framework of Effective Theories.
Ward Identities are derived between pseudoscalar susceptibilities and quark
condensates, allowing to explain the behaviour of lattice meson screening
masses. Unitarized interactions and the generated thermal state are
showed to play an essential role in the description of the transition through
the scalar susceptibilityComment: 10 pages, 9 figures. Proceedings of "XII Quark Confinement and the
Hadron Spectrum
On the effective lagrangian at nonzero isospin chemical potential
We revisit the most general effective lagrangian within Chiral Perturbation
Theory at nonzero isospin chemical potential. In addition to the contributions
already considered in the literature, we discuss the effects of new terms
allowed by the symmetries, derived within the external source method including
spurion fields, as well as of linear-field corrections. We study the influence
of those new contributions on the energy density at zero temperature and
observables derived from it, such as the pion and quark condensates and the
isospin density. Corrections are shown to be compatible with lattice results,
which favor a nonzero value for the only undetermined low-energy constant (LEC)
to leading order , rendering in particular a shift of the
critical value for Bose-Einstein condensation. To we study the
physical constraints on the new LEC, which renormalize the energy density and
whose numerical effect is estimated within natural values. The new corrections give rise to more significant deviations than those
previously considered and remain compatible with lattice results.Comment: 19 pages, 9 figure
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