  We study a quantum quench of the mass and 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 behaviour 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 we consider, it
assumes a squeezed state form that has been shown to evolve so as to exhibit
the equilibrium behaviour predicted by the Generalized Gibbs Ensemble.
