In Prof. Eduardo Fradkin's lecture, he computed the free energy (up to a divergent normalization constant) of the (d+1)-dim free massive scalar theory at finite temperature T as
F(T)=VT2∫ddp(2π)d∞∑n=−∞lnβ[ω2n+|p|2+m2], (see his Eq. (5.204))
where
ωn=2πn/β is the Matsubara frequency,
n∈Z,
V is the volume of the spatial part and
T is the finite temperature. This summation is formally divergent. He then mentioned that we can make use of the divergent normalization constant to regularize this summation. My understanding is that we add to
F(T) a constant that is also formally divergent:
Freg(T)=F(T)+A
where
A is some constant and
Freg(T) is the regularized free energy. And then
Freg(T) will no longer be divergent (up to the
VT infrared divergence). The result he gave us immediately turns out to be
Freg(T)=VT∫ddp(2π)dln[(β(|p|2+m2)1/2)∞∏n=1(1+|p|2+m2ω2n)]. (see his Eq. (5.205))
However, I am not quite sure how to systematically obtain this result. Certainly we can work backward and find
F(T)=VT2∫ddp(2π)d(lnβ(|p|2+m2)+2∞∑n=1lnβ(ω2n+|p|2+m2))=VT∫ddp(2π)dln[(β(|p|2+m2)1/2)∞∏n=1(1+|p|2+m2ω2n)]+VT∫ddp(2π)d(−12lnβ+∞∑n=1ln(βω2n))
And then we choose
A in
Freg(T)=F(T)+A to be
A=−VT∫ddp(2π)d(−12lnβ+∞∑n=1ln(βω2n))
such that we obtain
Freg(T)=VT∫ddp(2π)dln[(β(|p|2+m2)1/2)∞∏n=1(1+|p|2+m2ω2n)].
But this is not a systematic way that I am seeking for. Are there any suggestions or reference that carry out this sort of regularization in details? Thanks.