Finite temperature one-point functions in non-diagonal integrable field theories: the sine-Gordon model

Understand

We study the finite-temperature expectation values of exponential fields in the sine-Gordon model.

• Using finite-volume regularization, we give a low-temperature expansion of such quantities in terms of the connected diagonal matrix elements, for which we provide explicit formulas.
• For special values of the exponent, computations by other methods are available and used to validate our findings.
• Our results can also be interpreted as a further support for a previous conjecture about the connection between finite- and infinite-volume form factors valid up to terms exponentially decaying in the volume.