Calculate $\hbar \ln$ Gaussian Path Integral w/Einstein Summation

AI Thread Summary
The discussion focuses on calculating the expression involving the Gaussian path integral using the Einstein summation convention. The main equation being analyzed is related to the determinant of a matrix M_{ij} and its implications for the logarithmic properties in the context of path integrals. Participants express confusion over the treatment of the variables s and r, particularly questioning the need for a Fourier transform involving the delta function. Clarifications reveal that s and r are fundamentally different due to their respective roles in the mathematical formulation, with s being a scalar and r a vector. Ultimately, the conversation highlights the importance of correctly interpreting the equations from the referenced paper by R. Golestanian.
MadMax
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Einstein summation convention employed throughout

We want to calculate

\hbar \ln \int D x_i \exp[\frac{1}{32 \pi^3} \int ds \int d^3 r x_i(-is,r) M_{ij}(s,r) x_j(is,r)]

The answer is

\hbar \int \frac{ds}{2\pi} \ln \det[M_{ij}\delta^3(r-r')]

I know that

\int d^3 x_i e^{\frac{1}{2}x_i B_{ij} x_j} = \sqrt{\frac{(2\pi)^n}{\det B_{ij}}}

and that standard logarithmic properties will be used. Also the \delta^3(r-r') means that a Fourier transform involving that delta function will be employed at some point.

Beyond that I'm at a complete loss as to how to continue. One question is why we don't need to employ a Fourier transform involving a \delta(s-s')]. Any help would be much appreciated.
 
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I was hoping someone else would tackle this one, but here goes ...

The answer doesn't make sense to me. I don't see why s should be fundamentally different than r. I think you should have a \delta(s+s'), with + rather than - because the arguments have opposite sign, and that there should be no integral over s.

But perhaps there is something about the definition of x(is,r) that you haven't told us that would change this ...
 
Thanks.

What kind of things might make s different to r in that way?

Perhaps these? "is" is wick rotated frequency; and started out as the Fourier transform of time. r is real space. r is a vector and s is a scalar.
 
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MadMax said:
What kind of things might make s different to r in that way?
Perhaps these? "is" is wick rotated frequency; and started out as the Fourier transform of time. r is real space. r is a vector and s is a scalar.

No, none of that should matter.

Is this from a book? If so, which one?
 
He's just being sloppy. His eq.(1) is wrong, and should be what I said. Then he trades log det for Tr log, and the integral over zeta in eq.(3) is part of the trace, just like the integrals over r.
 
Ahh brilliant. Thanks again. :)
 
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