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Andrea Vioque-Rodríguez

Publications and source records attributed to Andrea Vioque-Rodríguez.

14 recordsLinked to original sources
arXiv2025

The QCD scalar susceptibility and thermal scalar resonances in chiral symmetry restoration

Building upon recent results on the role of thermal resonances in chiral symmetry restoration, we show that a description of the QCD scalar susceptibility at finite temperature $T$ saturated by the thermal properties of the lightest scalar resonance, the $f_0(500)$, is compatible both with lattice QCD data at nonzero $T$ and with the $T=0$ light resonance properties coming from experimental data. The thermal $f_0(500)$ is generated within the framework of Unitarized Chiral Perturbation Theory. This method allows us to achieve a good description of lattice QCD results with a reliable pion mass dependence. In particular, we perform direct fits to the chiral susceptibility measured in lattice data at different pion masses and temperatures, obtaining a remarkable agreement for the susceptibility and for mass differences of the light quark condensate. In addition, the fitted low-energy constants are compatible with $T=0$ phenomenology. Our results confirm the role of unitarized approaches and thermal resonances in the dynamics of the QCD transition.

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arXiv2023

Pion scattering, light resonances and chiral symmetry restoration at nonzero chiral imbalance and temperature

We calculate the pion scattering amplitude at nonzero temperature and nonzero $μ_5$, the chemical potential associated to chiral imbalance in a locally $P$-breaking scenario. The amplitude is calculated up to next to leading order in Chiral Perturbation Theory and is unitarized with the Inverse Amplitude Method to generate the poles of the $f_0(500)$ and $ρ(770)$ resonances. Within the saturation approach, the thermal $f_0(500)$ pole allows to determine $T_c(μ_5)$, the transition temperature for chiral symmetry restoration. Our results confirm the growing behaviour of $T_c(μ_5)$ found in previous works and, through a fit to lattice results, we improve the uncertainty range of the low-energy constants associated to $μ_5$ corrections in the chiral lagrangian. The results for the $ρ(770)$ pole are compatible with previous works regarding the dilepton yield in heavy-ion collisions.

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arXiv2023

The pion-kaon scattering amplitude and the $K^0(700)$ and $K^*(892)$ resonances at finite temperature

We perform a complete calculation of the pion-kaon scattering amplitude in Chiral Perturbation Theory at finite temperature, paying particular attention to the analytic structure of the amplitude and the main differences with respect to the zero temperature case. We also extend the Inverse Amplitude Method at finite temperature for unequal-mass scattering processes, which allows us to unitarize the amplitude and obtain the thermal evolution of the $K_0^*(700)$ and $K^*(892)$ pole parameters. As a direct application of our analysis, we show that the thermal evolution of the $K_0^*(700)$ resonance is crucial to explain the behavior of the scalar susceptibility for isospin $I=1/2$, which in turn, is directly connected with chiral and $U(1)_A$ restoration properties of the QCD phase diagram.

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arXiv2022

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 ${\cal O}(p^2)$, rendering in particular a shift of the critical value for Bose-Einstein condensation. To ${\cal O}(p^4)$ 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 ${\cal O}(p^4)$ corrections give rise to more significant deviations than those previously considered and remain compatible with lattice results.

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arXiv2022

Thermal hadron resonances in chiral and $U(1)_A$ restoration

We review recent work on thermal resonances and their connection with chiral symmetry and $U(1)_A$ restoration within the QCD phase diagram. In particular, the $f_0(500)$ and $K_0^* (700)$ states generated from $ππ$ and $πK$ scattering within Unitarized Chiral Perturbation Theory (ChPT) at finite temperature allow one to describe scalar susceptibilities, which combined with Ward Identities yield interesting conclusions regarding the interplay between chiral and $U(1)_A$ restoration, key to understand the nature of the transition

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arXiv2021

Studying chiral imbalance using Chiral Perturbation Theory

We analize the most general low-energy effective lagrangian including local parity violating terms parametrized by an axial chemical potential $μ_5$. This result is obtained following the external source method, up to $\mathcal{O}(p^4)$ order in the chiral expansion for two light flavours. We show that the $\mathcal{O}(p^4)$ lagrangian includes new terms proportional to $μ_5^2$ and new low-energy constants. Finally, the $μ_5$ and temperature dependences of several observables related to the vacuum energy density are studied.

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arXiv2021

The role of strangeness in chiral and $U(1)_A$ restoration

We use recently derived Ward identities and lattice data for the light- and strange-quark condensates to reconstruct the scalar and pseudoscalar susceptibilities ($χ_S^κ$, $χ_P^K$) in the isospin 1/2 channel. We show that $χ_S^κ$ develops a maximum above the QCD chiral transition, after which it degenerates with $χ_P^K$. We also obtain $χ_S^κ$ within Unitarized Chiral Perturbation Theory (UChPT) at finite temperature, when it is saturated with the $K_0^*(700)$ (or $κ$) meson, the dominant lowest-energy state in the isospin 1/2 scalar channel of $πK$ scattering. Such UChPT result reproduces the expected peak structure, revealing the importance of thermal interactions, and makes it possible to examine the $χ_S^κ$ dependence on the light- and strange-quark masses. A consistent picture emerges controlled by the $m_l/m_s$ ratio that allows one studying $K-κ$ degeneration in the chiral, two-flavor and $SU(3)$ limits. These results provide an alternative sign for $O(4)\times U(1)_A$ restoration that can be explored in lattice simulations and highlight the role of strangeness, which regulated by the strange-quark condensate helps to reconcile the current tension among lattice results regarding $U(1)_A$ restoration.

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arXiv2020

Chiral perturbation theory for nonzero chiral imbalance

We construct the most general low-energy effective lagrangian including local parity violating terms parametrized by an axial chemical potential or chiral imbalance $μ_5$, up to ${\cal O}(p^4)$ order in the chiral expansion for two light flavours. For that purpose, we work within the Chiral Perturbation Theory framework where only pseudo-NGB fields are included, following the external source method. The $\cal{O}(p^2)$ lagrangian is only modified by constant terms, while the $\cal{O}(p^4)$ one includes new terms proportional to $μ_5^2$ and new low-energy constants (LEC), which are renormalized and related to particular observables. In particular, we analyze the corrections to the pion dispersion relation and observables related to the vacuum energy density, namely the light quark condensate, the chiral and topological susceptibilities and the chiral charge density, providing numerical determinations of the new LEC when possible. In particular, we explore the dependence of the chiral restoration temperature $T_c$ with $μ_5$. An increasing $T_c(μ_5)$ is consistent with our fits to lattice data of the ChPT-based expressions. Although lattice uncertainties are still large and translate into the new LEC determination, a consistent physical description of those observables emerges from our present work, providing a theoretically robust model-independent framework for further study of physical systems where parity-breaking effects may be relevant, such as heavy-ion collisions.

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arXiv2020

Chiral symmetry restoration and the thermal $f_0(500)$ state

We analize the role played by the thermal $f_0(500)$ state or $σ$ in chiral symmetry restoration. The temperature corrections to the spectral properties of that state are included in order to provide a better description of the scalar susceptibility $χ_S$ around the transition region. We use the Linear Sigma Model to establish the relation between $χ_S$ and the $σ$ propagator, which is used as a benchmark to test the approach where $χ_S$ is saturated by the $f_0(500)$ inverse self-energy. Within such saturation approach, a peak for $χ_S$ around the chiral transition is obtained when considering the $f_0(500)$ generated as a $ππ$ scattering pole within Unitarized Chiral Perturbation Theory at finite temperature. That approach yields results complying with lattice data when the uncertainties of the low-energy constants are taken into account. Those uncertainties and the unitarization method are used to check the robustness of this approximation. Finally, we will discuss some recent results within the chiral lagrangian framework related to the topological susceptibility and its connection with chiral and $U_A(1)$ restoration.

hep-ph↗
arXiv2019

The QCD topological charge and its thermal dependence: the role of the $η'$

We analyze the contribution of the $η'(958)$ meson in the first two non-trivial moments of the QCD topological charge distribution, namely, the topological susceptibility and the fourth-order cumulant of the vacuum energy density. We perform our study within U(3) Chiral Perturbation Theory up to next-to-next-to-leading order in the combined chiral and large-$N_c$ expansion. We also describe the temperature dependence of these two quantities and compare them with previous analyses in the literature. In particular, we discuss the validity of the thermal scaling of the topological susceptibility with the quark condensate, which is intimately connected with a Ward Identity relating both quantities. We also consider isospin breaking corrections from the vacuum misalignment at leading order in the U(3) framework.

hep-ph↗
arXiv2019

Patterns and partners within the QCD phase diagram including strangeness

We review the current situation of the pattern of chiral symmetry restoration. In particular, we analyze partner degeneration for $O(4)$ and $U(1)_A$ symmetries within the context of Ward Identities and Effective Theories. The application of Ward Identities to the thermal scaling of screening masses is also discussed. We present relevant observables for which an Effective Theory description in terms of Chiral Perturbation Theory and its unitarized extension are compatible with lattice data even around the transition region. We pay special attention to the role of strangeness in this context.

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arXiv2017

Recent advances on chiral partners and patterns

We review recent results on chiral $SU(2)_L\times SU(2)_R\approx O(4)$ and $U(1)_A$ symmetry restoration in QCD. In particular, we discuss how Ward Identities allow one to derive general results on partner degeneration, which shed light on the distinction between the $O(4)$ and $O(4)\times U(1)_A$ patterns of the chiral transition. For that purpose, susceptibilities associated with the $O(4)$ and $U(1)_A$ symmetries are studied. From this analysis we conclude that in the ideal regime of exact $O(4)$ restoration (formally achieved in the limit of two massless flavours), $U(1)_A$ partners degenerate as well. We also discuss the role of the thermal $f_0(500)$ state to describe thermodynamic observables sensitive to chiral restoration, such as the scalar susceptibility. We pay special attention to the consistency of our results with recent lattice analysis.

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