Vanishing thermal mass in the strongly coupled QCD/QED medium

Abstract

In this paper we perform a nonperturbative analysis of a thermal quasifermion in thermal QCD/QED by studying its self-energy function through the Dyson-Schwinger equation with the hard-thermal-loop resummed improved ladder kernel. Our analysis reveals several interesting results, some of which may force us to change the image of the thermal quasifermion: (1) The thermal mass of a quasifermion begins to decrease as the coupling gets stronger and finally disappears in the strong coupling region, (2) the imaginary part of the chiral invariant mass function (i.e., the decay width of the quasifermion) persists to have O(g 2 T log(1/g)) behavior. Present results suggest that in the recently produced strongly coupled quark-gluon-plasma, the thermal mass of a quasifermion should vanish. We also briefly comment on evidence of the existence of a massless, or an ultrasoft mode.

Emergence of soft quark excitations by the coupling with a soft mode of the QCD critical point

“…It was found that a novel peak is formed around the zero energy as well as the normal and the antiplasmino ones, which then makes a three-peak structure in the quark spectral function: The formation of the farlow-lying peak is owed to the mixing between a quark (antiquark) and an antiquark hole (quark hole) by a resonant scattering of the quasiquarks with the soft modes with small but nonzero masses [32][33][34]. Such a formation of the three-peak structure in the spectral function of a fermion coupled with a bosonic excitation at T ≠ 0 is now confirmed beyond one loop [35][36][37][38][39]. Furthermore, a similar third peak in the ultrasoft region has been shown to exist in gauge theories at high temperature beyond the HTL approximation on the basis of a novel resummation technique [40].…”

Thermal mass and dispersion relations of quarks in the deconfined phase of quenched QCD

“…In the weak coupling and high T limit it is realized not only for QCD, but also in a wide class of models where the fermion couples to a boson. Away from this limiting situation the fermion spectrum has been investigated in various theoretical settings [7][8][9][10][11][12][13][14][15][16]. An interesting observation made in these studies is that the fermion spectrum exhibits a variety of structures depending on parameters of the system.…”

Effect of the magnetic field on the photon radiation from quark–gluon plasma in heavy ion collisions

“…Our calculations show that due to multiple scattering the synchrotron contribution is small even for massless quarks. For this reason for the scenario of a strongly coupled QGP with a very small thermal quark mass [74] the effect of the magnetic field on the photon emission should remain small.…”

“…3 Note that just for this reason the parton energy loss is well defined in the massless limit [38][39][40]. It is worth noting that the fact that the synchrotron contribution in the presence of multiple scattering remains small even for massless quarks shows that it should be small also for the scenario of a strongly coupled QGP with a very small thermal quark mass [74].…”