Chiral Symmetry Restoration Temperature Research Articles

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 μ5, 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 f0(500) and ρ(770) resonances. Within the saturation approach, the thermal f0(500) pole allows to determine Tc(μ5), the transition temperature for chiral symmetry restoration. Our results confirm the growing behavior of Tc(μ5) found in previous works and, through a fit to lattice results, we improve the uncertainty range of the low-energy constants associated to μ5 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. Published by the American Physical Society 2024

Fluctuations of conserved charges, chiral-spin symmetry, and deconfinement in an SU(2)color subgroup of SU(3)color above Tc

Above a pseudocritical temperature of chiral symmetry restoration T_c the energy and the pressure are very far from the quark-gluon-plasma limit (i.e. ideal gas of free quarks and gluons). At the same time very soon above T_c fluctuations of conserved charges behave as if quarks were free particles. Within the T_c - 3T_c interval a chiral spin symmetry emerges in QCD which is not consistent with free quarks and suggests that degrees of freedom are chirally symmetric quarks bound into the color-singlet objects by the chromoelectric field. Here we analyse temporal and spatial correlators in this interval and demonstrate that they indicate simultaneously the chiral spin symmetry as well as absence of the interquark interactions in channels constrained by a current conservation. The latter channels are responsible for both fluctuations of conserved charges and for dileptons. Assuming that a SU(2)_color subgroup of SU(3)_color is deconfined soon above T_c but confinement persits in SU(3)_color/SU(2)_color in the interval T_c - 3T_c we are able to reconcile all empirical facts listed above.

Thermodynamic Geometry of Yang–Mills Vacua

We study vacuum fluctuation properties of an ensemble of S U ( N ) gauge theory configurations, in the limit of many colors, viz. N c → ∞ , and explore the statistical nature of the topological susceptibility by analyzing its critical behavior at a non-zero-vacuum parameter θ and temperature T. We find that the system undergoes a vacuum phase transition at the chiral symmetry restoration temperature as well as at an absolute value of θ . On the other hand, the long-range correlation length solely depends on θ for the theories with critical exponent e = 2 or T = T d + 1 , where T d is the decoherence temperature. Furthermore, it is worth noticing that the unit-critical exponent vacuum configuration corresponds to a non-interacting statistical basis pertaining to a constant mass of η ′ .

Influence of chiral chemical potential, parallel electric, and magnetic fields on the critical temperature of QCD

We study the influence of external electric, $E$, and magnetic, $B$, fields parallel to each other, and of a chiral chemical potential, $\mu_5$, on the chiral phase transition of Quantum Chromodynamics. Our theoretical framework is a Nambu-Jona-Lasinio model with a contact interaction. Within this model we compute the critical temperature of chiral symmetry restoration, $T_c$, as a function of the chiral chemical potential and field strengths. We find that the fields inhibit and $\mu_5$ enhances chiral symmetry breaking, in agreement with previous studies.

Critical temperature of chiral symmetry restoration for quark matter with a chiral chemical potential

In this article we study the restoration of chiral symmetry at a finite temperature for quark matter with a chiral chemical potential, , by means of a nonlocal Nambu–Jona–Lasinio model. This model allows the introduction of, in the simplest way possible, a Euclidean momentum, pE, dependent quark mass function which decays (neglecting logarithms) as for large pE, in agreement with the asymptotic behaviour expected in quantum chromodynamics in the presence of a nonperturbative quark condensate. We focus on the critical temperature for chiral symmetry restoration in the chiral limit, Tc, versus , as well as on the order of the phase transition. We find that Tc increases with , and that the transition remains of the second order for the whole range of considered.

Induced magnetic moment in the magnetic catalysis of chiral symmetry breaking

The chiral symmetry breaking in a Nambu-Jona-Lasinio effective model of quarks in the presence of a magnetic field is investigated. We show that new interaction tensor channels open up via Fierz identities due to the explicit breaking of the rotational symmetry by the magnetic field. We demonstrate that the magnetic catalysis of chiral symmetry breaking leads to the generation of two independent condensates, the conventional chiral condensate and a spin-one condensate. While the chiral condensate generates, as usual, a dynamical fermion mass, the new condensate enters as a dynamical anomalous magnetic moment in the dispersion of the quasiparticles. Since the pair, formed by a quark and an antiquark with opposite spins, possesses a resultant magnetic moment, an external magnetic field can align it giving rise to a net magnetic moment for the ground state. The two condensates contribute to the effective mass of the LLL quasiparticles in such a way that the critical temperature for chiral symmetry restoration becomes enhanced.

N f = 1 QCD in external magnetic fields: staggered fermions

We investigate N$_f$ = 1 QCD in external magnetic fields on the lattice. The background field is introduced by means of the so-called Schrodinger functional. We adopt standard staggered fermions with constant bare mass $am = 0.025$ and magnetic fields with constant magnetic flux up to $a^2 e H \simeq 2.3562$. We find that the the deconfinement and chiral symmetry restoration temperatures do not depend on the strength of the applied magnetic field. Our method allow us to easily study the effects of the external magnetic fields on the QCD thermodynamics. We determine the influences of applied magnetic fields to the free energy, pressure, and equation of state of strongly interacting matter.

Weak magnetic field effects on chiral critical temperature in a nonlocal Nambu–Jona-Lasinio model

In this paper we study the nonlocal Nambu–Jona-Lasinio model with a Gaussian regulator in the chiral limit. Finite temperature effects and the presence of a homogeneous magnetic field are considered. The magnetic evolution of the critical temperature for chiral symmetry restoration is then obtained. Here, we restrict ourselves to the case of low magnetic field values, being this a complementary discussion to the existing analysis in nonlocal models in the strong magnetic field regime.

The role of asymptotic freedom for the pseudocritical temperature in magnetized quark matter

Motivated by discrepancies observed between lattice QCD simulations and quark models regarding the behavior of the pseudo critical temperature for chiral symmetry restoration as a function of the magnetic field B, we investigate the effects of a running the quark coupling constant G with temperature T and the magnetic field B in the context of the Nambu-Jona- Lasinio model(NJL). Our point that when asymptotic freedom, an essential feature of QCD and absent in the model, is included through a running of G with T and B results from the NJL model can be brought in qualitative agreement with lattice QCD simulations.

Quark and Gluon Condensates at Finite Temperatures by the Linear Sigma Model Approach

Based on a linear sigma model, we discuss the mixing between a quark condensate and a gluon condensate. It is shown that the linear sigma model will not be self-consistent if we switch off the mixing coupling between glueball and chiral fields. By introducing a proper mixing coupling, we realize the second-order phase transitions of chiral symmetry restoration and deconfinement. We further show that the critical temperature of chiral symmetry restoration could not be larger than the temperature of deconfinement phase transition in all possible parameter spaces of our model.

New look at the QCD ground state in a magnetic field

We explore chiral symmetry breaking in a magnetic field within a Nambu-Jona-Lasinio model of interacting massless quarks including tensor channels. We show that the new interaction channels open up via Fierz identities due to the explicit breaking of the rotational symmetry by the magnetic field. We demonstrate that the magnetic catalysis of chiral symmetry breaking leads to the generation of two independent condensates, the conventional chiral condensate and a spin-one condensate. While the chiral condensate generates a dynamical fermion mass, the new condensate gives rise to a dynamical anomalous magnetic moment for the fermions. As a consequence, the spectrum of the excitations in all Landau levels, except the lowest one, exhibits Zeeman splitting. Since the pair, formed by a quark and an antiquark with opposite spins, possesses a resultant magnetic moment, an external magnetic field can align it giving rise to a net magnetic moment for the ground state. This is the physical interpretation of the spin-one condensate. Our results show that the magnetically catalyzed ground state in QCD is actually richer than previously thought. The two condensates contribute to the effective mass of the LLL quasiparticles in such a way that the critical temperature for chiral symmetry restoration becomes enhanced.

Physical mechanism of the (tri)critical point generation

We discuss some ideas resulting from a phenomenological relation recently declared between the tension of string connecting the static quark-antiquark pair and surface tension of corresponding cylindrical bag. This relation analysis leads to the temperature of vanishing surface tension coefficient of the QGP bags at zero baryonic charge density as T_\sigma = 152.9 +- 4.5 MeV. We develop the view point that this temperature value is not a fortuitous coincidence with the temperature of (partial) chiral symmetry restoration as seen in the lattice QCD simulations. Besides, we argue that T_\sigma defines the QCD (tri)critical endpoint temperature and claim that a negative value of surface tension coefficient recently discovered is not a sole result, but should also exist in ordinary liquids at the supercritical temperatures.

Phase Diagram and Critical End Point for Strongly Interacting Quarks

We introduce a method based on chiral susceptibility, which enables one to draw a phase diagram in the chemical-potential-temperature plane for strongly interacting quarks whose interactions are described by any reasonable gap equation, even if the diagrammatic content of the quark-gluon vertex is unknown. We locate a critical end point at (μ(E),T(E))∼(1.0,0.9)T(c), where T(c) is the critical temperature for chiral-symmetry restoration at μ=0, and find that a domain of phase coexistence opens at the critical end point whose area increases as a confinement length scale grows.

HOLOGRAPHIC STUDY OF MAGNETICALLY INDUCED QCD EFFECTS

We study the effect of a constant external magnetic field on the rho meson mass m(rho) on the one hand, and on the chiral symmetry restoration temperature T-chi on the other hand, using the Sakai-Sugimoto model with two quenched flavours and non-zero constituent quark masses, which is a holographic dual of a QCD-like theory in the quenched approximation and chiral limit. We find that the explicit chiral symmetry breaking caused by the presence of the magnetic field eB manifests itself in a stronger chiral magnetic catalysis effect for the up than for the down quarks, resulting in two separate chiral symmetry restoration temperatures T-chi(u) and T-chi(d) with T-chi(u)(eB) > T-chi(d)(eB) > T-c (the deconfinement temperature) for each value of eB. The Landau levels described in the rho meson mass equation indicate an instability of the QCD vacuum towards condensation of rho mesons at eB similar to 1.1 mp(rho)(2) approximate to 0.67 GeV2, confirming a recent prediction of Chernodub.

QCD phase transition in a strong magnetic background

We investigate the properties of the deconfining/chiral restoring transition for two flavor QCD in presence of a uniform background magnetic field. We adopt a standard staggered discretization of the fermion action and a lattice spacing of the order of 0.3 fm. We explore different values of the bare quark mass, corresponding to pion masses in the range 200 - 480 MeV, and magnetic fields up to |e|B ~ 0.75 GeV^2. The deconfinement and chiral symmetry restoration temperatures remain compatible with each other and rise very slightly (< 2 % for our largest magnetic field) as a function of the magnetic field. On the other hand, the transition seems to become sharper as the magnetic field increases.

Adjoint quarks and fermionic boundary conditions

We study quenched SU(2) lattice gauge theory with adjoint fermions in a wide range of temperatures. We focus on spectral quantities of the Dirac operator and use the temporal fermionic boundary conditions as a tool to probe the system. We determine the deconfinement temperature through the Polyakov loop, and the chiral symmetry restoration temperature for adjoint fermions through the gap in the Dirac spectrum. This chiral transition temperature is about four times larger than the deconfinement temperature. In between the two transitions we find that the system is characterized by a non-vanishing chiral condensate which differs for periodic and anti-periodic fermion boundary conditions. Only for the latter (physical) boundary conditions, the condensate vanishes at the chiral transition. The behavior between the two transitions suggests that deconfinement manifests itself as the onset of a dependence of spectral quantities of the Dirac operator on boundary conditions. This picture is supported further by our results for the dual chiral condensate.

Thermal properties of heavy-light quark pseudoscalar and vector mesons

The thermal behaviour of the mass, leptonic decay constant, and width of heavy-light quark peseudoscalar and vector mesons is analized in the framework of thermal Hilbert moment QCD sum rules. In all the cases, the meson leptonic decay constants decrease with increasing T , and vanish at a critical temperature Tc, while the mesons develop a width which increases dramatically, diverging when T ! Tc, where Tc is the temperature for chiral-symmetry restoration. The spectral function becomes a smooth function of the energy. This is interpreted as a signal for deconfinement at T = Tc. In contrast, the thermal masses are stable, except when T ! Tc, where the pseudoscalar meson mass increases slightly by 10-20 %, and the vector meson mass decreases by some 20-30 %.

Response of holographic QCD to electric and magnetic fields

We study the response of the Sakai-Sugimoto holographic model of large N_c QCD at nonzero temperature to external electric and magnetic fields. In the electric case we find a first-order insulator-conductor transition in both the confining and deconfining phases of the model. In the deconfining phase the conductor is described by the parallel 8-brane-anti-8-brane embedding with a current of quarks and anti-quarks. We compute the conductivity and show that it agrees precisely with a computation using the Kubo formula. In the confining phase we propose a new kind of 8-brane embedding, corresponding to a baryonic conductor. In the magnetic field case we show that the critical temperature for chiral-symmetry restoration in the deconfined phase increases with the field and approaches a finite value in the limit of an infinite magnetic field. We also illustrate the nonlinear behavior of the electric and magnetic susceptibilities in the different phases.

Rho meson condensation at finite isospin chemical potential in a holographic model for QCD

We analyze the effect of an isospin chemical potential μI in the Sakai-Sugimoto model, which is the string dual of a confining gauge theory related to large Nc QCD, at temperatures below the chiral symmetry restoration temperature. For small chemical potentials we show that the results agree with expectations from the low-energy chiral Lagrangian, and the charged pion condenses. When the chemical potential reaches a critical value μI = μcrit ≃ 1.7mρ, the lowest vector meson (the ``rho meson'') becomes massless, and it condenses (in addition to the pion condensate) for μI > μcrit. This spontaneously breaks the rotational symmetry, as well as a residual U(1) flavor symmetry. We numerically construct the resulting new ground state for μI > μcrit.

Holographic melting and related properties of mesons in a quark-gluon plasma

We analyze mesons at finite temperature in a chiral, confining string dual. The temperature dependence of low-spin as well as high-spin meson masses is shown to exhibit a pattern familiar from the lattice. Furthermore, we find the dissociation temperature of mesons as a function of their spin, showing that at a fixed quark mass, mesons with larger spins dissociate at lower temperatures. The Goldstone bosons associated with chiral symmetry breaking are shown to disappear above the chiral symmetry restoration temperature. Finally, we show that holographic considerations imply that large-spin mesons do not experience drag effects when moving through the quark-gluon plasma. They do, however, have a maximum velocity for fixed spin, beyond which they dissociate.