arXiv subjects

Daisuke Satow

Publications and source records attributed to Daisuke Satow.

23 records · Page 2Linked to original sources

arXiv2012

Off-diagonal kinetic theory in ultrasoft momentum region at high temperature

We derive a linearized kinetic equation for fermionic excitations with an ultrasoft momentum, g^2T, from the Kadanoff-Baym equation in a Yukawa model and quantum electrodynamics (QED) at extremely high T, where g is the coupling constant. We show that this equation is equivalent to the self-consistent equation in the resummed perturbation theory used in the analysis of the fermion spectrum with the ultrasoft momentum. Furthermore, we derive the equation that determines the n-point function with external lines for a pair of fermions and (n-2) bosons with ultrasoft momenta in QED.

hep-ph↗

arXiv2011

Ultrasoft Fermionic Mode in Yukawa Theory at High Temperature

We explore whether an ultrasoft fermionic mode exists at extremely high temperature in Yukawa theory with massless fermion (coupling constant is g). We find that the fermion propagator has a pole at ω= \pm p/3-iζ, for ultrasoft momentum p, where ζ\sim g^4T ln 1/g, and the residue is Z \sim g^2. It is shown that one needs to take into account the asymptotic masses and the damping rate of hard particles to get a sensible result for such an ultrasoft fermionic mode; possible vertex correction turns out unnecessary for the scalar coupling in contrast to the gauge coupling.

hep-ph↗

arXiv2011

Ultrasoft Fermionic Modes at High Temperature

A possible collective fermionic excitation in the ultrasoft energy-momentum region is examined in Yukawa model with scalar coupling and quantum electrodynamics (QED) with g being coupling constant at extremely high temperature T where the fermion mass is negligible. We analytically sum up the ladder diagrams for the vertex correction in the leading order in QED, which is not necessary in the Yukawa model, and find that the fermion pole exists at ω= \pm p/3-iζwith ultrasoft momentum p both for the Yukawa model and QED; ζis the sum of the damping rates of fermion and boson with hard momenta. We also obtain the expression of the residue of the pole, which is as small as of order g^2. We show that the fermion propagator and the vertex function satisfy the Ward-Takahashi identity in QED. Thus we establish the existence of an ultrasoft fermionic mode at extremely high temperature, which was originally called phonino and was suggested in the context of supersymmetry and its breaking at finite T. We discuss the possible origin of such an ultrasoft fermionic mode without recourse to supersymmetry. The case of QCD is briefly mentioned.

hep-ph↗

arXiv2011

Fermion Spectrum at Ultrasoft Region in a Hot QED/QCD Plasma

An spectrum of an electron (quark) with ultrasoft momentum (p g^2T) is discussed at extremely high temperature in quantum electrodynamics (chromodynamics) with a resummed perturbation theory. We establish the existence of the pole suggested in the previous work of the electron (quark) propagator at ultrasoft region, and find that its pole position is p_0=\mp |p|/3-iζ, where ζis the damping rate which is of order g^2T ln 1/g, and the expression of its residue. We also discuss whether the resummation scheme preserves the gauge symmetry.

hep-ph↗

arXiv2010

Spectral Function of Fermion Coupled with Massive Vector Boson at Finite Temperature in Gauge Invariant Formalism

We investigate spectral properties of a fermion coupled with a massive gauge boson with a mass m at finite temperature (T) in the perturbation theory. The massive gauge boson is introduced as a U(1) gauge boson in the Stueckelberg formalism with a gauge parameter α. We find that the fermion spectral function has a three-peak structure for T \sim m irrespective of the choice of the gauge parameter, while it tends to have one faint peak at the origin and two peaks corresponding to the normal fermion and anti-plasmino excitations familiar in QED in the hard thermal loop approximation for T \gg m. We show that our formalism successfully describe the fermion spectral function in the whole T region with the correct high-T limit except for the faint peak at the origin, although some care is needed for choice of the gauge parameter for T \gg m. We clarify that for T \sim m, the fermion pole is almost independent of the gauge parameter in the one-loop order, while for T \gg m, the one-loop analysis is valid only for α\ll 1/g where g is the fermion-boson coupling constant, implying that the one-loop analysis can not be valid for large gauge parameters as in the unitary gauge.

hep-ph↗