37 research outputs found
Chiral symmetry breaking and confinement effects on dilepton and photon production around
Production rates of dileptons and photons from the quark-gluon (QGP) phase
are calculated taking into account effects of confinement and spontaneous
chiral symmetry breaking (\chi SB) not far from the transition temperature
. We find that the production rates of dileptons with large momenta and of
photons originating from the QGP around are suppressed by the \chi SB
effect. We also discuss to what extent information about details of the chiral
transition, such as its characteristic temperature range and the steepness of
the crossover, are reflected in these quantities.Comment: 15 pages, 11 figures; v2: figures 11 and 12 are added, discussion on
comparison with other results is added in summary; v3: Typos in reference 36
are correcte
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-i\zeta, where \zeta is 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.Comment: 3 pages, 1 figure, presented by D. Satow at the 19th Particles and
Nuclei International Conference, PANIC 2011, MIT, Cambridge, MA (July 24-29,
2011
Chiral Magnetic Effect at Weak Coupling with Relaxation Dynamics
We provide a resolution of an old issue in weak coupling computation of the
Chiral Magnetic Effect (CME) current, where a free chiral fermion theory gives
two different results depending on the order of the two limits,
(frequency) and (spatial momentum). We
first argue based on hydrodynamics that in any reasonable interacting theory of
chiral fermions the non-commutativity between the two limits should be absent,
and we demonstrate this at weak coupling regime in two different frameworks:
kinetic theory in the relaxation time approximation, and diagrammatic
computation with resummation of damping rate. In the latter computation, we
also show that the "pinch" singularity, which would make the summation of
ladder diagrams necessary as in the P-even correlation function, is absent in
the relevant P-odd correlation function. The correct value of CME current is
reproduced even in the presence of relaxation dynamics in both computations.Comment: 26 pages, 3 figure
Diagrammatic and Kinetic Equation Analysis of Ultrasoft Fermionic Sector in Quark-Gluon Plasma
At so high temperature (T) that the coupling constant (g) is small and the
masses of the particles are negligible, different scheme has to be applied in
each energy scale in the analysis of the quark-gluon plasma (QGP). In the soft
energy region (p gT), the simple perturbative expansion called the hard thermal
loop (HTL) approximation can be applied, and that approximation expects the
existence of the bosonic and fermionic collective excitations called plasmon
and plasmino. On the other hand, in the ultrasoft energy region (p g^2T), the
HTL approximation is inapplicable due to infrared singularity, so the question
whether there are any excitation modes in that energy region has not been
studied well. In this thesis, we analyze the quark spectrum whose energy is
ultrasoft in QGP, using the resummed perturbation theory which enables us to
successfully regularize the infrared singularity. Since the Yukawa model and
QED are simpler than QCD but have some similarity to QCD, we also work in these
models. As a result, we establish the existence of a novel fermionic mode in
the ultrasoft energy region, and obtain the expressions of the pole position
and the strength of that mode. We also show that the Ward-Takahashi identity is
satisfied in the resummed perturbation theory in QED/QCD. Furthermore, we
derive the linearized and generalized Boltzmann equation for the ultrasoft
fermion excitations in the Kadanoff-Baym formalism, and show that the resultant
equation is equivalent to the self-consistent equation in the resummed
perturbation theory. We also derive the equation which determines the n-point
functions with external lines for a pair of fermions and (n-2) bosons with
ultrasoft momenta, by considering the non-linear response regime using the
gauge symmetry. We also derive the Ward-Takahashi identity from the
conservation law of the electromagnetic current in the Kadanoff-Baym formalism.Comment: 77pages, 18 figures; revised version of Ph. D. thesis, which was
accepted by Kyoto university in January 201