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In a physics paper I found a very complicated Gaussian matrix model:

$$ Z = \int \frac{d\mu}{(2\pi)^n} \frac{d\nu}{(2\pi)^n} \frac{ \prod_{i < j}\left[2 \sinh \frac{\mu_i - \mu_j}{2} \right]^2 \prod_{i < j}\left[2 \sinh \frac{\nu_i - \nu_j}{2} \right]^2 }{\prod_{i,j}\left[ 2 \cosh \frac{\mu_i - \nu_j}{2} \right]^2} e^{\frac{ik}{4\pi}\sum (\mu_i^2 - \nu_i^2)} $$

Such a formula looks vaguely like the formula for Haar measure on the grou of Unitary matrices - whose exact formula I forget. Let's derive several simplified versions of this measure:

$$ Z = \int \frac{d\mu}{(2\pi)^n} \frac{d\nu}{(2\pi)^n} e^{\frac{ik}{4\pi}\sum (\mu_i^2 - \nu_i^2)} $$ One question is how to meaningfully ascribe a value to a Gaussian integral where the variance is a complex number. And actually $\mu^2 - \nu^2$ could be negative... so this could be like integrating over the maximual torus of a super-matrix model.

$$ Z = \int \frac{d\mu}{(2\pi)^n} \frac{d\nu}{(2\pi)^n} \frac{ \prod_{i < j}\left[\mu_i - \mu_j \right]^2 \prod_{i < j}\left[\nu_i - \nu_j \right]^2 }{\prod_{i,j}\left[\mu_i - \nu_j \right]^2} e^{\frac{ik}{4\pi}\sum (\mu_i^2 - \nu_i^2)} $$ This could be like Haar measure on the unitary group $SU(N|N)$ except for the Gaussian. One more variant is if we use $\sin$ instaed of $\sinh$:

$$ Z = \int \frac{d\mu}{(2\pi)^n} \frac{d\nu}{(2\pi)^n} \frac{ \prod_{i < j}\left[2 \sin \frac{\mu_i - \mu_j}{2} \right]^2 \prod_{i < j}\left[2 \sin \frac{\nu_i - \nu_j}{2} \right]^2 }{\prod_{i,j}\left[ 2 \cos \frac{\mu_i - \nu_j}{2} \right]^2} $$ This could be an integral over some matrix-like objects or over a Lie super algebra. Also there is something like the Cauchy-Binet formula.

What are the appropriate Lie Groups for these setups? In physics these go under various names like Lens Space model or Chern-Simons theory

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  • $\begingroup$ Could you link the paper in question? $\endgroup$
    – AHusain
    Commented Aug 9, 2016 at 19:20
  • $\begingroup$ ABJM Theory as a Fermi Gas arxiv.org/abs/1110.4066 $\endgroup$ Commented Aug 9, 2016 at 19:48
  • $\begingroup$ This looks like an integral over $\left(\mathrm{SL}_n(\mathbb{R})\right)^2$ in $KAK$ coordinates. I don't see why it should converge. $\endgroup$ Commented Aug 9, 2016 at 20:41
  • $\begingroup$ @LiorSilberman that may very well be integral doesn't converge. that is the integral being discussed in the physics paper. Often $k \in \mathbb{Z}$, so that $ik$ is purely imaginary. $\endgroup$ Commented Aug 9, 2016 at 22:05

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