...theorem

Wick's theorem states that the Gaussian average of a product can be evaluated from the average of all possible pairings:

20#20

where <...> indicates a Gaussian average.

.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.

...invariant

In nematic elastomers there is an elastic-nematic coupling involving the antisymmetric component of 58#58 and we cannot make this simplification.

.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.