Instanton Corrections to the MSTB Kink Mass

The Montonen-Sarker-Trullinger-Bishop (MSTB) model enjoys two classically degenerate kink solutions in the same topological sector. We construct the instanton that interpolates between them and argue that the two lowest lying Hamiltonian eigenstates in the kink sector of the corresponding quantum theory correspond to symmetric and antisymmetric combinations of coherent states localized at these two solutions. We use the instanton gas approximation to provide a simple, analytic formula for the leading contribution to the mass splitting between these two states.