Dirichlet oscillator fluctuation determinant (source code)

= Dirichlet oscillator fluctuation determinant
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The quadratic fluctuation eigenvalues are $(n\pi/\mathcal T)^2+\omega^2$. Dividing by the free-particle determinant gives $\prod_{n\ge1}[1+(\omega\mathcal T/n\pi)^2]^{-1/2}=\sqrt{\omega\mathcal T/\sinh(\omega\mathcal T)}$. The short-time free kernel fixes the absolute normalization.