arXiv subjects

A. Gynther

Publications and source records attributed to A. Gynther.

12 recordsLinked to original sources

arXiv2012

Thermodynamics and phase diagram of anisotropic Chern-Simons deformed gauge theories

We consider 3+1-dimensional gauge theories at finite temperature and a finite density of charges which couple to a 2+1-dimensional Chern-Simons operator, giving rise to a theta-term with constant spatial gradient of theta. The strong-coupling limit of thermal N=4 super-Yang-Mills theory with this kind of anisotropic deformation has been used in the context of the AdS/CFT correspondence as a model for strongly coupled anisotropic quark-gluon plasma. In this paper we work out the thermodynamics and the (nontrivial) phase diagram in the limit of vanishing gauge coupling and compare with the corresponding strong-coupling results.

hep-th↗

arXiv2011

Holographic Anomalous Conductivities and the Chiral Magnetic Effect

We calculate anomaly induced conductivities from a holographic gauge theory model using Kubo formulas, making a clear conceptual distinction between thermodynamic state variables such as chemical potentials and external background fields. This allows us to pinpoint ambiguities in previous holographic calculations of the chiral magnetic conductivity. We also calculate the corresponding anomalous current three-point functions in special kinematic regimes. We compare the holographic results to weak coupling calculations using both dimensional regularization and cutoff regularization. In order to reproduce the weak coupling results it is necessary to allow for singular holographic gauge field configurations when a chiral chemical potential is introduced for a chiral charge defined through a gauge invariant but non-conserved chiral density. We argue that this is appropriate for actually addressing charge separation due to the chiral magnetic effect.

hep-th↗

arXiv2009

The N_f^3 g^6 term in the pressure of hot QCD

We determine the first independent part of the g^6 coefficient in the weak coupling expansion of the QCD pressure at high temperatures, the one proportional to the maximal power of the number of quark flavors N_f. In addition to introducing and developing computational methods that can be used in evaluating other parts of the expansion, our calculation provides a result that becomes dominant in the limit of large N_f and a fixed effective coupling g_{eff}^2 = g^2 N_f/2.

hep-ph↗

arXiv2009

On the dispersion of fundamental particles in QCD and N=4 Super Yang-Mills theory

We study thermal corrections to the dispersion relations of massive fundamental particles immersed in weakly coupled non-Abelian plasmas. The cases covered include quarks in the QCD (quark-gluon) plasma, as well as N=2 quarks and scalars in an N=4 Super Yang-Mills plasma. We perform the calculations to leading order in a weak coupling expansion, and consider all mass scales of the fundamental fields, ranging from massless particles all the way to bare masses parametrically larger than the temperature.

hep-ph↗

arXiv2008

The fermion mass at next-to-leading order in the HTL effective theory

The calculation of the real part of a quasi-particle dispersion relation at next-to-leading order in the hard thermal loop effective theory is a very difficult problem. Even though the hard thermal loop effective theory is almost 20 years old, there is only one next-to-leading order calculation of the real part of a quasi-particle dispersion relation in the literature. In this paper, we calculate the fermion mass in QED and QCD at next-to-leading order. For QED the result is M=eT/sqrt{8} * [1-(1.427 \pm 0.02)e/4pi] and for QCD with N_f=2 and N_c=3 we obtain M=gT/sqrt{6} * [1+(1.867 \pm 0.02)g/4pi].

hep-ph↗

arXiv2007

Energetic di-leptons from the Quark Gluon Plasma

In this paper we study the production of energetic di-leptons. We calculate the rate for 2 $\to$ 2 processes. The log term is obtained analytically and the constant term is calculated numerically. When the photon mass is of the order of the thermal quark mass, the result is insensitive to the photon mass and the soft logarithmic divergence is regulated by the thermal quark mass, exactly as in the case of real photons. We also consider the production of thermal Drell-Yan dileptons (thermal quark and antiquark pairs produced by virtual photons) and calculate the rate systematically in the context of the hard thermal loop effective theory. We obtain analytic and numerical results. We compare our results with those of previous calculations.

hep-ph↗

arXiv2007

Four-loop pressure of massless O(N) scalar field theory

Inspired by the corresponding problem in QCD, we determine the pressure of massless O(N) scalar field theory up to order g^6 in the weak-coupling expansion, where g^2 denotes the quartic coupling constant. This necessitates the computation of all 4-loop vacuum graphs at a finite temperature: by making use of methods developed by Arnold and Zhai at 3-loop level, we demonstrate that this task is manageable at least if one restricts to computing the logarithmic terms analytically, while handling the ``constant'' 4-loop contributions numerically. We also inspect the numerical convergence of the weak-coupling expansion after the inclusion of the new terms. Finally, we point out that while the present computation introduces strategies that should be helpful for the full 4-loop computation on the QCD-side, it also highlights the need to develop novel computational techniques, in order to be able to complete this formidable task in a systematic fashion.

hep-ph↗

arXiv2006

Pressure of the standard model

We review the computation of the thermodynamic pressure of the entire minimal standard model to three loop order, performed in hep-ph/0510375 and hep-ph/0512177.

hep-ph↗

arXiv2006

Thermodynamics of electroweak matter

This paper is a slightly modified version of the introductory part of a PhD thesis, also containing the articles hep-ph/0303019, hep-ph/0510375 and hep-ph/0512177. We provide a short history of the research of electroweak thermodynamics and a brief introduction to the theory as well as to the necessary theoretical tools needed to work at finite temperatures. We then review computations regarding the pressure of electroweak matter at high temperatures (the full expression of the perturbative expansion of the pressure is given in the appendix) and the electroweak phase diagram at finite chemical potentials. Finally, we compare electroweak and QCD thermodynamics.

hep-ph↗

arXiv2006

Pressure of the Standard Model Near the Electroweak Phase Transition

We extend our previous determination of the thermodynamic pressure of the Standard Model so that the result can be applied down to temperatures corresponding to the electroweak crossover. This requires a further resummation which can be cleanly organised within the effective theory framework. The result allows for a precise determination of the expansion rate of the Universe for temperatures around the electroweak crossover.

hep-ph↗

arXiv2005

Pressure of the Standard Model at High Temperatures

We compute the pressure of the standard model at high temperatures in the symmetric phase to three loops, or to O(g^5) in all coupling constants. We find that the terms of the perturbative expansion in the SU(2) + Higgs sector decrease monotonically with increasing order, but the large values of the strong coupling constant g_s and the Yukawa coupling of the top quark g_Y make the expansion in the full theory converge more slowly. The final result is observed to be about 10% smaller than the ideal gas pressure commonly used in cosmological calculations.

hep-ph↗

arXiv2003

Electroweak phase diagram at finite lepton number density

We study the thermodynamics of the electroweak theory at a finite lepton number density. The phase diagram of the theory is calculated by relating the full 4-dimensional theory to a 3-dimensional effective theory which has been previously solved using nonperturbative methods. It is seen that the critical temperature increases and the value of the Higgs boson mass at which the first order phase transition line ends decreases with increasing leptonic chemical potential.

hep-ph↗