Ángel Gómez Nicola

Thermal rho and sigma mesons from chiral symmetry and unitarity

We study the temperature evolution of the rho and sigma mass and width, using a unitary chiral approach. The one-loop pipi scattering amplitude in chiral perturbation theory at Tnot equal0 is unitarized via the inverse amplitude method. Our results predict a clear increase with T of both the rho and sigma widths. The masses decrease slightly for high T, while the rhopipi coupling increases. The rho behavior seems to be favored by experimental results. In the sigma case, it signals chiral symmetry restoration.

Improved unitarized heavy baryon chiral perturbation theory for pi N scattering to fourth order

We extend our previous analysis of the unitarized pion-nucleon scattering amplitude including up to fourth order terms in heavy baryon chiral perturbation theory. We pay special attention to the stability of the generated Delta(1232) resonance, the convergence problems, and the power counting of the chiral parameters.

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. U(3) 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 f₀(500) thermal state are showed to play an essential role in the description of the transition through the scalar susceptibility.

Large-N pion scattering at finite temperature: The f_0(500) and chiral restoration

We consider the O(N + 1)/O(N) nonlinear sigma model for large N as an effective theory for low-energy QCD at finite temperature T, in the chiral limit. At T = 0 this formulation provides a good description of scattering data in the scalar channel and dynamically generates the f_0(500) pole, the pole position lying within experimental determinations. Previous T = 0 results with this model are updated using newer analysis of pion scattering data. We calculate the pion scattering amplitude at finite T and show that it exactly satisfies thermal unitarity, which had been assumed but not formally proven in previous works. We discuss the main differences with the T = 0 result, and we show that one can define a proper renormalization scheme with T = 0 counterterms such that the renormalized amplitude can be chosen to depend only on a few parameters. Next, we analyze the behavior of the f_0(500) pole at finite T, which is consistent with chiral symmetry restoration when the scalar susceptibility is saturated by the f_0(500) state, in a second-order transition scenario and in accordance with lattice and theoretical analysis.

Chiral symmetry restoration for the large-N pion gas

We analyze chiral restoration within the

Electromagnetic effects in the pion dispersion relation at finite temperature

O(N+1)/O(N)

Chiral Extrapolations of light resonances from dispersion relations and Chiral Perturbation Theory

Non-Linear Sigma Model for large

Free Energy of a Large-

N

N

as an effective theory for low-energy QCD at finite temperature

Pion Gas and Chiral Symmetry Restoration

T