R. Kobes

Bremsstrahlung and photon production in thermal QCD

In this paper, we extend the study of bremsstrahlung photon production in a quark-gluon plasma to the cases of soft static photons

Energy and efficiency of adiabatic quantum search algorithms

(\mathit{q}=0)

Adiabatic quantum computation and Deutsch's algorithm

and hard real photons. The general framework of this study is the effective perturbative expansion based on the resummation of hard thermal loops. Despite the fact that bremsstrahlung only comes at two loops, we find that in both cases, it generates contributions of the same order of magnitude as those already calculated by several other groups at one loop. Furthermore, a new process contained in the two-loop diagrams dominates the emission of a very hard real photon. In all cases, the rate of real or virtual photon production in the plasma is appreciably increased compared to the one-loop predictions.

Enhanced photon production rate on the light cone.

We present the results of a detailed analysis o fag eneral, unstructured adiabatic quantum search of a database of N items. In particular, we examine the effects on the computation time of adding energy to the system. We find that by increasing the lowest eigenvalue of the time-dependent Hamiltonian temporarily to a maximum of ∝ √ N ,i t is possible to d ot hecalculation in constant time. This leads us to derive the general theorem which provides th ea diabatic analogue of the √ N bound of conventional quantum searches. The result suggests that the action associated with the oracle term in the timedependent Hamiltonian is a direct measure of the resources required by the adiabatic quantum search.

Shear viscosity in phi**4 theory from an extended ladder resummation

We show that by a suitable choice of a time-dependent Hamiltonian, Deutschs algorithm can be implemented by an adiabatic quantum computer. We extend our analysis to the Deutsch-Jozsa problem and estimate the required running time for both global and local adiabatic evolutions.

Mass and wave-function renormalization at finite temperature

Recent studies of the high temperature soft photon production rate on the light cone using Braaten-Pisarski resummation techniques have found the presence of collinear divergences. We show that there exists a class of terms outside the Braaten-Pisarski framework which, although also divergent, dominates over these previously considered terms. The divergences in these new terms may be alleviated by application of a recently developed resummation scheme for processes sensitive to the light cone. {copyright} {ital 1996 The American Physical Society.}

Effects of vaccination and population structure on influenza epidemic spread in the presence of two circulating strains

We study shear viscosity in weakly coupled hot

Two loop Compton and annihilation processes in thermal QCD

\phi^4

Cancellation of ladder graphs in an effective expansion

theory using the CTP formalism . We show that the viscosity can be obtained as the integral of a three-point function. Non-perturbative corrections to the bare one-loop result can be obtained by solving a decoupled Schwinger-Dyson type integral equation for this vertex. This integral equation represents the resummation of an infinite series of ladder diagrams which contribute to the leading order result. It can be shown that this integral equation has exactly the same form as the Boltzmann equation. We show that the integral equation for the viscosity can be reexpressed by writing the vertex as a combination of polarization tensors. An expression for this polarization tensor can be obtained by solving another Schwinger-Dyson type integral equation. This procedure results in an expression for the viscosity that represents a non-perturbative resummation of contributions to the viscosity which includes certain non-ladder graphs, as well as the usual ladders. We discuss the motivation for this resummation. We show that these resummations can also be obtained by writing the viscosity as an integral equation involving a single four-point function. Finally, we show that when the viscosity is expressed in terms of a four-point function, it is possible to further extend the set of graphs included in the resummation by treating vertex and propagator corrections self-consistently. We discuss the significance of such a self-consistent resummation and show that the integral equation contains cancellations between vertex and propagator corrections.

The General cancellation of ladder graphs at finite temperature

Using the real-time formulation of finite-temperature field theory by Niemi and Semenoff we present a rigorous analysis of how to include radiative QED self-energy corrections for thermal decay and scattering processes into suitable mass wave-function renormalization counterterms. Previous work is examined as a special case in our general framework. Our results have immediate applications in cosmology and astrophysics.