Hiroaki Kohyama

Quantum field theories in nonextensive Tsallis statistics

Within the framework of Tsallis statistics with q ≃ 1, we construct a perturbation theory for treating relativistic quantum field systems. We find that there appear initial correlations, which do not exist in the Boltzmann-Gibbs statistics. Applying this framework to a quark-gluon plasma, we find that the so-called thermal masses of quarks and gluons are smaller than in the case of Boltzmann-Gibbs statistics.

Phase diagram of quark-antiquark and diquark condensates at finite temperature and density in the 3-dimensional Gross-Neveu model

We construct the phase diagrams of the quark-antiquark and diquark condensates at finite temperature and density in the 3-dimensional (3D) 2-flavor Gross-Neveu model. We found that, in contrast to the case of the 4D Nambu-Jona-Lasinio model, there is no region where the quark-antiquark and diquark condensates coexist. The phase diagrams obtained for some parameter region show similar structure with the 4D QCD phase diagram.

Cancellation of energy divergences and renormalizability in Coulomb gauge QCD within the Lagrangian formalism

In Coulomb gauge QCD in the Lagrangian formalism, energy divergences arise in individual diagrams. We give a proof on cancellation of these divergences to all orders of perturbation theory without obstructing the algebraic renormalizability of the theory.

Thermal operator representation of finite-temperature amplitudes in the presence of a chemical potential

In a recent paper [Phys. Rev. D 72, 085006 (2005)], Brandt et al. deduced the thermal operator representation for a thermal N-point amplitude, both in the imaginary-time and real-time formalisms. In the case when a chemical potential present, however, the representation is not as simple as in the case with vanishing chemical potential. We propose a much simpler and transparent representation for the case of nonzero chemical potential.