False vacuum decay beyond the quadratic approximation: Summation of nonlocal self-energies

Using the 2PI effective action formalism, we study false vacuum decay beyond the quadratic approximation of the path integral. We derive a coupled system of equations for the bounce and the propagator, and we compute a semianalytic expression for the self-energy of a real scalar field with cubic and quartic interactions from the 2PI effective action truncated at two loops and without further approximations. Deriving numerical results, we can show that the Hartree approximation, where nonlocal contributions to the self-energy are neglected, is generally not justified. The procedure we develop is a key step towards the explicit computation of the quantum corrected bounce, the determinant of fluctuations about it, and the decay rate in the presence of classical zero modes that are lifted by quantum effects, e.g., classically scale-invariant models relevant for assessing the Higgs stability.