Vacuum structure and effective potential at finite temperature: a variational approach

We compute the effective potential for φ4 theory with a squeezed coherent state type of construct for the ground state. The method essentially consists in optimising the basis at zero and finite temperatures. The gap equation becomes identical to resumming the infinite series of daisy and super daisy graphs while the effective potential includes multiloop effects and agrees with that obtained through composite operator formalism at finite temperature. Typeset using REVTEX Present Address: Institut fur Theoretische Physik, Universitat Frankfurt, Robert Mayer Str.10, D-60054, Frankfurt am Main, Germany, e-mail: [email protected] Present Address: Fakultat fur Physik, Universitat Bielefeld, Universitat Strasse 25, D-33615, Bielefeld, Germany, e-mail: [email protected] 1