Speaker
Description
We extend the covariant variational approach for Yang-Mills theory
in Landau gauge to non-zero temperatures. The renormalization of the system
is revisited and it is shown how the zero-temperature counter terms can be
used to render the system finite at any temperature. Numerical solutions
for the thermal propagators are presented and compared to high-precision
lattice data. To study the deconfinement phase transition, we adapt the
formalism to background gauge and compute the effective action of the
Polyakov loop for the colour groups SU(2) and SU(3). Using the zero-temperature
propagators as input, all parameters are fixed at T=0 and we find a clear signal
for a deconfinement phase transition at finite temperatures, which is second
order for SU(2) and first order for SU(3). The critical temperatures obtained
are in reasonable agreement with lattice data. Continuing this investigation,
we study thermodynamics and, in particular, the pressure of the Yang-Mills
system, and compare to both lattice data and the results of the non-convariant
Hamiltonian approach. Finally, we briefly discuss the inclusion of fermions and
possible ways to extended our method beyond the Gaussian ansatz.
