Global limit theorem for parabolic equations with a potential

We obtain the asymptotics, as $t+\mathrm{\mid }x\mathrm{\mid }\to \mathrm{\infty }$, of the fundamental solution to the heat equation with a compactly supported potential. It is assumed that the corresponding stationary operator has at least one positive eigenvalue. Two regions with different types of behavior are distinguished: inside a certain conical surface in the $(t,x)$ space, the asymptotics is determined by the principal eigenvalue and the corresponding eigenfunction; outside of the conical surface, the main term of the asymptotics is a product of a bounded function and the fundamental solution of the unperturbed operator, with the contribution from the potential becoming negligible if $\mathrm{\mid }x\mathrm{\mid }\mathrm{/}t\to \mathrm{\infty }$. A formula for the global asymptotics, as $t+\mathrm{\mid }x\mathrm{\mid }\to \mathrm{\infty }$, of the solution in the entire half-space $t > 0$ is provided. In probabilistic terms, the result describes the asymptotics of the density of particles in a branching diffusion with compactly supported branching and killing potentials.