We discuss radiative corrections to how quark mass thresholds are crossed, as a function of the temperature, in basic thermodynamic observables such as the pressure, the energy and entropy densities, and the heat capacity of high temperature QCD. The indication from leading order that the charm quark plays a visible role at surprisingly low temperatures, is confirmed. We also sketch a way to obtain phenomenological estimates relevant for generic expansion rate computations at temperatures between the QCD and electroweak scales, pointing out where improvements over the current knowledge are particularly welcome.

Quark mass thresholds in QCD thermodynamics

We all know that doctors make the worst patients because they always laughingly tell us so. But how do we rate at taking our own medicine?

view from the chair: I go to a friend

We determine the 2-loop effective gauge coupling of QCD at high temperatures, defined as a matching coefficient appearing in the dimensionally reduced effective field theory. The result allows to improve on one of the classic non-perturbative probes for the convergence of the weak-coupling expansion at high temperatures, the comparison of full and effective theory determinations of an observable called the spatial string tension. We find surprisingly good agreement almost down to the critical temperature of the deconfinement phase transition. We also determine one new contribution of order (g6T4) to the pressure of hot QCD.

http://iopscience.iop.org/article/10.1088/1126-6708/2005/03/067/pdf

Two-loop QCD gauge coupling at high temperatures

We consider spatial correlation lengths xi for various QCD light quark bilinears, at temperatures above a few hundred MeV. Some of the correlation lengths (such as that related to baryon density) coincide with what has been measured earlier on from glueball-like states; others do not couple to glueballs, and have a well-known perturbative leading-order expression as well as a computable next-to-leading-order correction. We determine the latter following analogies with the NRQCD effective theory, used for the study of heavy quarkonia at zero temperature: we find (for the quenched case) xi(-1) = 2piT + 0.1408g(2)T, and compare with lattice results. One manifestation of U-A(1) symmetry non-restoration is also pointed out.

Mesonic correlation lengths in high-temperature QCD

. Althoughcosmologyisusuallyconsideredanobservationalscience,wherethereislittleornospaceforexperimentation,otherapproachescan(andhave been) alsoconsid-ered.Inparticular,wecanchange ratherdrasticallytheabove,morepassive,observationalperspective and ask the following question: could it be possible, and how, to create a uni-verse in a laboratory? As a matter of fact, this seems to be possible, according to at leasttwo different paradigms; both of them help to evade the consequences of singularity the-orems. In this contribution we will review some of these models and we will also discusspossible extensions and generalizations, by paying a critical attention to the still open is-sues as, for instance, the detectability of child universes and the properties of quantumtunnelling processes. 1.1 The studies so far ... The world Cosmology stems from the Greek word cosmos , which meant beauty , harmony , and is the name of that branch of science which studies the origin andevolution of the universe. Thus, considering its name and the object of its study,it is, perhaps, natural to take a “passive” point of view when dealing with cos-mological problems,whereweuse theword

/pdf/what-comes-beyond-the-standard-models-2hug97e3p6.pdf

What comes beyond the standard models

High temperature 3D QCD: dimensional reduction at work

QCD with adjoint scalars in 2D: properties in the colourless scalar sector

We discuss the screening masses and residue factorisation of the SU(3) (2 + 1)D theory in the dimensional reduction formalism. The phase structure of the reduced model is also investigated.

Screening masses in dimensionally reduced (2+1)D gauge theory

Z(3) symmetric dimensional reduction of (2+1)D QCD

We construct the strong-coupling series in 4d simplicial quantum gravity up to volume 38. It is used to calculate estimates for the string susceptibility exponent γ for various modifications of the theory. It provides a very efficient way to get a first view of the phase structure of the models.

K. Petrov

Papers

High temperature 3D QCD: dimensional reduction at work

QCD with adjoint scalars in 2D: properties in the colourless scalar sector

Screening masses in dimensionally reduced (2+1)D gauge theory

Z(3) symmetric dimensional reduction of (2+1)D QCD

The strong-coupling expansion in simplicial quantum gravity