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T. Altherr

Publications and source records attributed to T. Altherr.

7 recordsLinked to original sources
arXiv1994

Resummation of Perturbation Series in Non-Equilibrium Scalar Field Theory

The general behaviour of perturbation series in non-equilibrium scalar field theory is analysed in some detail, with a particular emphasis on the ``pathological terms'', generated by multiple products of $δ$-functions. Using an intuitive regularization method, it is shown that these terms give large contributions at all orders, even when considering small deviations from equilibrium. Fortunately, these terms can also be resummed and I give the general expressions for the resummed propagators in non-equilibrium scalar field theory, regardless of the size of deviations from equilibrium.

hep-ph↗
arXiv1993

The Electric Charge of Neutrinos and Plasmon Decay

By using both thermal field theory and a somewhat more intuitive method, we define the electric charge as well as the charge radius of neutrinos propagating inside a plasma. We show that electron neutrinos acquire a charge radius of order $\sim 6.5 \times 10^{-16}$ cm, regardless of the properties of the medium. Then, we compute the rate of plasmon decay which such an electric charge or a charge radius implies. Taking into account the relativistic effects of the degenerate electron gas, we compare our results to various approximations as well as to recent calculations and determine the regimes where the electric charge or the charge radius does mediate the decay of plasmons. Finally, we discuss the stellar limits on any anomalous charge radius of neutrinos.

hep-ph↗
arXiv1993

Axion Emission from Red Giants and White Dwarfs

Using thermal field theory methods, we recalculate axion emission from dense plasmas. We study in particular the Primakoff and the bremsstrahlung processes. The Primakoff rate is significantly suppressed at high densities, when the electrons become relativistic. However, the bound on the axion-photon coupling, $G<10^{-10}$ GeV, is unaffected, as it is constrained by the evolution of HB stars, which have low densities. In contradistinction, the same relativistic effects enhance the bremsstrahlung processes. From the red giants and white dwarfs evolution, we obtain a conservative bound on the axion-electron coupling, $g_{ae} < 2\times 10^{-13}$.

hep-ph↗
arXiv1993

Introduction to Thermal Field Theory

This is intended to be a very basic introduction and short (and of course incomplete) overview of thermal field theory. In the first part, I introduce the thermal propagator at a very simple level and give the Feynman rules using the time-path contour method. In the second part, I give examples of these rules in scalar theory and discuss the origin of the thermal mass and other important effects as infrared divergences and phase transitions. In the third part, I outline the resummation program of Braaten and Pisarski.

hep-ph↗
arXiv1992

Photon Propagation in Dense Media

Using thermal field theory, we derive simple analytic expressions for the spectral density of photons in degenerate QED plasmas, without assuming the usual non or ultra-relativistic limit. We recover the standard results in both cases. Although very similar in ultra-relativistic plasmas, transverse and longitudinal excitations behave very differently as the electron Fermi momentum decreases.

hep-ph↗
arXiv1992

Thermal Field Theory and Infinite Statistics

We construct a quantum thermal field theory for scalar particles in the case of infinite statistics. The extension is provided by working out the Fock space realization of a "quantum algebra", and by identifying the hamiltonian as the energy operator. We examine the perturbative behavior of this theory and in particular the possible extension of the KLN theorem, and argue that it appears as a stable structure in a quantum field theory context.

hep-th↗