Hisao Nakkagawa, Hiroshi Yokota, Koji Yoshida
In this paper we carried out a nonperturbative analysis of a thermal quasifermion in the chiral symmetric thermal QCD/QED medium by studying its self-energy function through the Dyson-Schwinger equation (DSE) with the HTL resummed improved ladder kernel. Our analysis reveals several interesting results, some of which may force us to change the image of thermal quasifermions; (1) The thermal mass of a quasifermion begins to decrease as the strength of the coupling gets stronger and finally disappears in the strong coupling region, thus showing a property of a massless particle, and (2) its imaginary part (i.e., the decay width) persists to have $O(g^2T \log(1/g))$ behavior. These results suggest that in the recently produced sQGP, the thermal mass of a quasiquark should vanish. Taking into account the largeness of the imaginary part, it seems very hard for a quark to exist as a qausiparticle in the sQGP phase. Other important findings are as follows; (3) The collective plasmino mode disappears also in the strongly coupled system, and (4) there exisits an ultrasoft third peak in the quasifermion spectral density at least in the weakly coupled QED/QCD plasma, indicating the existence of the ultrasoft fermionic mode.
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http://arxiv.org/abs/1208.6386
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