Speaker
Apostolos Pilaftsis
(University of Manchester (GB))
Description
The formalism introduced by Cornwall, Jackiw and Tomboulis (CJT)
provides a systematic analytic approach to consistently describing
non-perturbative effects in Quantum Thermal Field Theory. One major
limitation of the CJT effective action is that its loopwise expansion
introduces residual violations of possible global symmetries, thus
giving rise to massive Goldstone bosons in the spontaneously broken
phase of the theory. In my talk I will present a novel
symmetry-improved CJT formalism which consistently encodes global
symmetries in a loopwise expansion. Unlike other methods, I will
illustrate how the symmetry-improved CJT effective action satisfies a
number of important field-theoretic properties, such as the
masslessness of the Goldstone boson and the fact that the phase
transition is of second order in O(N) theories, already in the
Hartree-Fock approximation. After taking the sunset diagrams into
account, I show how the symmetry-improved CJT approach properly
describes the threshold properties of the massless Goldstone boson and
the Higgs particle within quantum loops. Finally, I will briefly
outline the derivation of a symmetry-improved CJT effective potential,
in which new topologies of infinite class of graphs can be resummed
that go well beyond the standard Coleman--Weinberg effective
potential. [This presentation is based on my paper with Daniele
Teresi, Nucl. Phys. B874 (2013) 594.]
Author
Apostolos Pilaftsis
(University of Manchester (GB))
Co-author
Daniele Teresi
(University of Manchester)
