Erratum to: J Low Temp Phys DOI 10.1007/s10909-012-0853-7

Due to some typos in the preparation of the revised version of this manuscript, some equations are incorrect. We show the correct equations as follows. All the discussions and conclusions remain intact. Equation (115) should be

Equation (116) should be

Equation (117) should be

Please ignore the statement “which is the same as its EM counterpart except there is a minus sign.” below Eq. (117). Equation (118) should be

Moreover, the equation number for the Ward identity (or WI) above Eqs. (113) and (118) was labeled as (74), but it should be labeled as (118).