Naive Gaussian approximation in a quark-meson model

A sequence of approximations is derived to go beyond the mean-field level in the case of a simple linear sigma model. A naive, local version of the Gaussian approximation is discussed for the $2+1$ flavor extended Polyakov quark-meson model at finite temperature and chemical potential. Although at small chemical potential the pion mass has an unphysical thermal behavior in the usual parameterizations, it is shown that the pseudocritical temperature decreases in the presence of the thermal pion fluctuations. Compared to the mean-field level, the location of the CEP is only slightly modified, while the critical scaling around the CEP is unaffected.