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Enrico Meggiolaro

Publications and source records attributed to Enrico Meggiolaro.

At least 19 recordsLinked to original sources
arXiv2026

Study of the scalar and pseudoscalar meson mass spectrum above the QCD chiral phase transition, using an effective Lagrangian approach

In this work, expanding on previous analyses, we employ an effective Lagrangian approach to investigate the mass spectrum of scalar and pseudoscalar mesons at finite temperature, above the (pseudo-)critical temperature $T_c$, in a "realistic" $N_f = 2 + 1$ flavor scenario with degenerate $up$ and $down$ quarks and a heavier $strange$ quark: $0 < m_u = m_d \ll m_s$. The model's predictions are then critically compared with available lattice QCD results (where meson screening masses are extracted from chiral susceptibilities, which correspond to two-point correlation functions of suitable interpolating operators), looking, in particular, for signatures of the breaking of the $U(1)$ axial symmetry above $T_c$.

hep-ph↗
arXiv2025

A new study of the interactions of the axion with mesons and photons using a chiral effective Lagrangian model

In this paper, we extend the results obtained in a previous work and investigate the most interesting decay processes involving axions, photons and the lightest pseudoscalar mesons in the more general case in which the quarks (and, therefore, the mesons) may be charged under the $U(1)$ Peccei-Quinn symmetry, making use of a chiral effective Lagrangian model with $N_f=3$ light quark flavors, which also includes the flavor-singlet pseudoscalar meson and implements the $U(1)$ axial anomaly of the fundamental theory. In particular, we compute the axion mass, the electromagnetic coupling of the axion to photons, and the amplitudes and widths of the decay processes $η/η'\rightarrow ππa$.

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arXiv2024

Study (using a chiral effective Lagrangian model) of the scalar and pseudoscalar meson mass spectrum of QCD at finite temperature, above $T_c$

In this work, we analyze (using a chiral effective Lagrangian model) the scalar and pseudoscalar meson mass spectrum of QCD at finite temperature, above the chiral transition at $T_c$, in the realistic case with $N_f = 2 + 1$ light quark flavors (that is, with $m_{u,d} \to 0$ and $m_s \neq 0$), looking, in particular, for signatures of the breaking of the $U(1)$ axial symmetry above $T_c$. A critical comparison with the corresponding results obtained (in a previous study) in the two limit cases $N_f = 2$ and $N_f = 3$ and with the available lattice results is performed, together with a discussion on the limits of validity of a description in terms of a chiral effective Lagrangian model.

hep-ph↗
arXiv2022

Study of some local and global $U(1)$ axial condensates in QCD at finite temperature

The aim of this work is to study some possible local and global $U(1)$ axial condensates in the high-temperature chirally restored phase of QCD, by means of two nonperturbative analytical techniques: (i) by expressing the functional averages in terms of the spectral density of the Euclidean Dirac operator and (ii) by evaluating the functional integrals in the instanton-background approximation. In this way, besides proving that these condensates are indeed different from zero in the high-temperature regime, we shall also derive their asymptotic temperature dependence and compare it with that of the topological susceptibility.

hep-ph↗
arXiv2020

QCD axion and topological susceptibility in chiral effective Lagrangian models at finite temperature

In this work we compute the axion mass and, from this (exploiting a well-known relation), we also derive an expression for the QCD topological susceptibility in the finite-temperature case, both below and above the chiral phase transition at $T_c$, making use of a chiral effective Lagrangian model which includes the axion, the scalar and pseudoscalar mesons and implements the $U(1)$ axial anomaly of the fundamental theory. We also provide a numerical estimate of the topological susceptibility at $T=0$ (in the physical case of three light quark flavors) and discuss the question of the temperature and quark-mass dependence of the topological susceptibility in the high-temperature regime.

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arXiv2020

Study of the interactions of the axion with mesons and photons using a chiral effective Lagrangian model

We investigate the most interesting decay processes involving axions, photons and the lightest pseudoscalar mesons, making use of a chiral effective Lagrangian model with $L=3$ light quark flavors, which also includes the flavor-singlet pseudoscalar meson and implements the $U(1)$ axial anomaly of the fundamental theory. In particular, we compute the electromagnetic coupling of the axion to photons and we compare our result with the prediction of the Chiral Effective Lagrangian with $L=2$ light quark flavors. Moreover, we study the decay channels $η/η'\rightarrow ππa$ and we estimate the corresponding decay widths, using the existing bounds on the $U(1)_{PQ}$ breaking scale.

hep-ph↗
arXiv2019

Theta dependence of the vacuum energy density in chiral effective Lagrangian models at finite temperature, above $T_c$

In this work, extending a previous study at zero temperature ($T=0$), we perform a systematic study of the modifications to the QCD vacuum energy density $ε_{vac}$ in the finite-temperature case, above the chiral transition at $T_c$, caused by a nonzero value of the parameter $θ$, using two different effective Lagrangian models which implement the $U(1)$ axial anomaly of the fundamental theory and which are both well defined also above $T_c$. In particular, we derive (and critically compare) the expressions for the topological susceptibility $χ$ and for the second cumulant $c_4$ starting from the $θ$ dependence of $ε_{vac}(θ)$ in the two models.

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arXiv2018

Study of the theta dependence of the vacuum energy density in chiral effective Lagrangian models at zero temperature

We perform a systematic study of the modifications to the QCD vacuum energy density $ε_{vac}$ in the zero-temperature case ($T=0$) caused by a small, but non-zero, value of the parameter $θ$, using different effective Lagrangian models which include the flavour-singlet meson field and implement the $U(1)$ axial anomaly of the fundamental theory. In particular, we derive the expressions for the topological susceptibility $χ$ and for the second cumulant $c_4$ starting from the $θ$ dependence of $ε_{vac}(θ)$ in the various models that we have considered. Moreover, we evaluate numerically our results, so as to compare them with each other, with the predictions of the Chiral Effective Lagrangian, and, finally, also with the available lattice data.

hep-ph↗
arXiv2016

Field-strength correlators for QCD in a magnetic background

We present the results of an exploratory study (by means of Monte Carlo simulations on the lattice) of the properties of the gauge-invariant two-point correlation functions of the gauge-field strengths for $N_f=2$ QCD at zero temperature and in the presence of a magnetic background field: the analysis provides evidence for the emergence of anisotropies in the nonperturbative part of the correlators and for an increase of the gluon condensate as a function of the external magnetic field.

hep-lat↗
arXiv2016

Gauge-invariant field-strength correlators for QCD in a magnetic background

We consider the properties of the gauge-invariant two-point correlation functions of the gauge-field strengths for QCD in the presence of a magnetic background field. We discuss the general structure of the correlators in this case and provide the results of an exploratory lattice study for $N_f = 2$ QCD discretized with unimproved staggered fermions. Our analysis provides evidence for the emergence of anisotropies in the non-perturbative part of the correlators and for an increase of the gluon condensate as a function of the external magnetic field.

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arXiv2015

Remarks on the static dipole-dipole potential at large distances

We determine the large-distance behaviour of the static dipole-dipole potential for a wide class of gauge theories on nonperturbative grounds, exploiting only general properties of the theory. In the case of QCD, we recover the known results in the regime of small dipole sizes, and discuss recent nonperturbative calculations. Moreover, we discuss the case of pure-gauge theories, and compare our prediction with the available lattice results.

hep-ph↗
arXiv2015

Comments on high-energy total cross sections in QCD

We discuss how hadronic total cross sections at high energy depend on the details of QCD, namely on the number of colours $N_c$ and the quark masses. We find that while a "Froissart"-type behaviour $σ_{\rm tot}\sim B\log^2s$ is rather general, relying only on the presence of higher-spin stable particles in the spectrum, the value of $B$ depends quite strongly on the quark masses. Moreover, we argue that $B$ is of order ${\cal O}(N_c^0)$ at large $N_c$, and we discuss a bound for $B$ which does not become singular in the $N_f=2$ chiral limit, unlike the Froissart-Łukaszuk-Martin bound.

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arXiv2014

Comments on the U(1) axial symmetry and the chiral transition in QCD

We analyze (using a chiral effective Lagrangian model) the scalar and pseudoscalar meson mass spectrum of QCD at finite temperature, above the chiral transition at $T_c$, looking, in particular, for signatures of a possible breaking of the $U(1)$ axial symmetry above $T_c$. A detailed comparison between the case with a number of light quark flavors $N_f\geq 3$ and the (remarkably different) case $N_f=2$ is performed.

hep-ph↗
arXiv2014

Hadronic total cross sections, Wilson loop correlators and the QCD spectrum

We show how to obtain rising hadronic total cross sections in QCD, in the framework of the nonperturbative approach to soft high-energy scattering based on Wilson-loop correlators. Total cross sections turn out to be of "Froissart"-type, i.e., the leading energy dependence is of the form $σ_{\rm tot} \sim B \log^2 s$, in agreement with experiments. The observed universality of the prefactor $B$ is obtained rather naturally in this framework. In this case, $B$ is entirely determined by the stable spectrum of QCD, and predicted to be $B_{th} = 0.22\, {\rm mb}$, in fair agreement with experiments.

hep-ph↗
arXiv2014

Hadronic total cross sections at high energy and the QCD spectrum

We show how to obtain the leading energy dependence of hadronic total cross sections, in the framework of the nonperturbative approach to soft high-energy scattering based on Wilson-loop correlation functions, if certain nontrivial analyticity assumptions are satisfied. The total cross sections turn out to be of "Froissart" type, $σ_{\rm tot}^{(hh)}(s) \mathop\sim B\log^2 s$ for ${s \to \infty}$. We also discuss under which conditions the coefficient $B$ is universal, i.e., independent of the hadrons involved in the scattering process. In the most natural scenarios for universality, $B$ can be related to the stable spectrum of QCD, and is predicted to be $B_{\rm th}\simeq 0.22~{\rm mb}$, in fair agreement with experimental results. If we consider, instead, the stable spectrum of the quenched (i.e., pure-gauge) theory, we obtain a quite larger value $B^{(Q)}_{\rm th} \ge 0.42~{\rm mb}$, suggesting (quite surprisingly) large unquenching effects due to the sea quarks.

hep-ph↗
arXiv2014

Effects of an extra U(1) axial condensate on the strong decays of pseudoscalar mesons

We consider a scenario (supported by some lattice results) in which a U(1)-breaking condensate survives across the chiral transition in QCD. This scenario has important consequences for the pseudoscalar-meson sector, which can be studied using an effective Lagrangian model. In particular, generalizing the results obtained in two previous papers, where the effects on the radiative decays eta,eta' --> gamma gamma were studied, in this paper we study the effects of the U(1) chiral condensate on the strong decays of the "light" pseudoscalar mesons, i.e., eta,eta' --> 3pi^0; eta,eta' --> pi^+ pi^- pi^0; eta' --> eta pi^0 pi^0; eta' --> eta pi^+ pi^-; and also on the strong decays of an exotic ("heavy") SU(3)-singlet pseudoscalar state eta_X, predicted by the model.

hep-ph↗
arXiv2012

Asymptotic Energy Dependence of Hadronic Total Cross Sections from Lattice QCD

The nonperturbative approach to soft high-energy hadron-hadron scattering, based on the analytic continuation of Wilson-loop correlation functions from Euclidean to Minkowskian theory, allows to investigate the asymptotic energy dependence of hadron-hadron total cross sections in lattice QCD. In this paper we will show, using best fits of the lattice data with proper functional forms satisfying unitarity and other physical constraints, how indications emerge in favor of a universal asymptotic high-energy behavior of the kind B log^2 s for hadronic total cross sections.

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