Date: November 12, from 14:30
Place: Main building, 213
Leturer:
Daisuke Satow (Kyoto University)
Title:
Ultrasoft Fermion Mode in Hot or Dense Boson-Fermion System
Abstract:
Investigation of fermion spectrum in a boson-fermion system
such as QED/QCD at high temperature (T) or chemical potential (μ) is
very important because it
gives us the information on the basic building block of the system.
In contrast to the case that the energy scale is of order gT or gμ (g:
coupling constant), in which the method for perturbative analysis
called "hard thermal/dense loop approximation" has been established,
perturbative analysis in p<< g^2T region is difficult because of the
infrared singularity.
In this seminar, we find a novel fermionic excitation and obtain the
expression of the dispersion relation, the decay width, and the
strength, using the resummed perturbation theory regularizing that
singularity in a hot QED/QCD plasma.
We also find that the excitation disappears in the high density case,
and discuss the reason of the disappearnce.
Finally we derive the new generalized Boltzmann equation which is
equivalent to the resummed perturbation from Kadanoff-Baym equation.
By using that equivalence, we discuss kinetic interpretation of the
resummed perturbation scheme, and show that the terms whose origin is
different from those in the Boltzmann equation, appear in that kinetic
equation.