Exact BPS double-kinks in generalized $\phi^4$, $\phi^6$ and sine-Gordon models

Abstract

We consider a $(1+1)$-dimensional theory with a single real scalar field $\phi$ whose kinematics is modified by a generalizing function $f(\phi)$. After briefly reviewing its Bogomol'nyi-Prasad-Sommerfield (BPS) structure, we focus on a particular $f(\phi)$ to obtain analytic BPS double-kink solutions in three different models governed by the $\phi^4$, $\phi^6$, and sine-Gordon superpotentials. In all cases, the resulting double-kinks approach the boundaries by following an exponential decay, with the generalizing function controlling its dependence on $x$ and mass. We also calculate the BPS bound explicitly and study how the double kinks behave near the origin. The energy distribution of the novel BPS states engenders symmetric two-lump profiles for the $\phi^4$ and sine-Gordon superpotentials. Whereas, for the $\phi^6$ superpotential, the BPS energy profiles form asymmetric two-lumps.