Optimized perturbation theory for charged scalar fields at finite temperature and in an external magnetic field

Abstract

Symmetry restoration in a theory of a self-interacting charged scalar field at finite temperature and in the presence of an external magnetic field is examined. The effective potential is evaluated nonperturbatively in the context of the optimized perturbation theory method. It is explicitly shown that in all ranges of the magnetic field, from weak to large fields, the phase transition is second order and that the critical temperature increases with the magnetic field. In addition, we present an efficient way to deal with the sum over the Landau levels, which is of interest especially in the case of working with weak magnetic fields.

Chiral and deconfinement transitions in a magnetic background using the functional renormalization group with the Polyakov loop

“…The qualitative behavior of the transition temperature for physical quark masses is in disagreement with model calculations using either the (Polyakov-loop extended) Nambu-Jona-Lasinio ((P)NJL) model or the (Polyakov-loop extended) quarkmeson model ((P)QM); in these models, the critical temperature is an increasing function of the magnetic field, see e.g. [10][11][12][13][14][15][16][17][18][19][20]. Possible resolutions to the disagreement have been suggested [21][22][23][24][25][26][27][28] and we will discuss these at the end of the paper.…”

“…These may be several orders of magnitude larger than the magnetic fields in ordinary neutron stars. On the surface, the magnetic field may be as strong as 10 14 -10 15 Gauss and it could be as strong as 10 16 -10 19 Gauss in the interior of the star. This has spurred the interest in strongly interacting matter at finite temperature, density and magnetic field, see for example ref.…”

On the symmetry improved CJT formalism in the O(4) linear sigma model

“…Unlike the CJT effective action, the usual One-particle-irreducible (1PI) action does not suffer from above pathology and respects all global and local symmetries order by order in perturbation theory. Hence, in the 1PI formalism, the Goldstone theorem will retain in any truncation of the 1PI effective action, even such a truncation is loopwise or includes partial resummation of graphs [20][21] [38]. This result is guaranteed by the Ward Identities associated with global symmetries of the theory in the 1PI formalism.…”

Effect of the magnetized medium on the decay of neutral scalar bosons

“…In particular, the study of how external conditions might affect decay widths are of particular importance to understand the dynamics that might be in play in cosmology [51]. It is also known that the presence of an external magnetic field can influence the order of phase transitions [47,52]. By also influencing the decay processes happening in these phase transitions, this can be potentially important in the problem of baryogenesis in the early Universe.…”