We study a quantum quench of the interaction in the sinh-Gordon model starting from a large initial mass and zero initial coupling. Our focus is on the determination of the expansion of the initial state in terms of post-quench excitations. We argue that the large energy profile of the involved excitations can be relevant for the late time behavior of the system and common regularization schemes are unreliable. We therefore proceed in determining the initial state by first principles expanding it in a systematic and controllable fashion on the basis of the asymptotic states. Our results show that, for the special limit of pre-quench parameters that we consider, it assumes a so-called squeezed vacuum form that has been shown to evolve so as to exhibit the equilibrium behavior predicted by the Generalized Gibbs Ensemble.
