Chiral symmetry breaking and confinement effects on dilepton and photon production around TcT_c

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 $T_c$. We find that the production rates of dileptons with large momenta and of photons originating from the QGP around $T_c$ 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, $\omega\rightarrow 0$ (frequency) and $k\rightarrow 0$ (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