Study of the O(N) linear σ model at finite temperature using the 2PPI expansion
University of Gent, Department of Mathematical Physics and Astronomy, Krijgslaan 281-S9, 9000 Gent, Belgium
Revised: 3 September 2001
Published online: 14 December 2001
We show that a new expansion, which sums seagull and bubble graphs to all orders, can be applied to the O(N) linear σ-model at finite temperature. We prove that this expansion can be renormalized with the usual counterterms in a mass independent scheme and that Goldstone's theorem is satisfied at each order. At the one loop order of this expansion, the Hartree result for the effective potential (daisy and superdaisy graphs) is recovered. We show that at one loop 2PPI order, the self-energy of the σ-meson can be calculated exactly and that diagrams are summed beyond the Hartree approximation.
© Società italiana di Fisica, Springer-Verlag, 2001