Multiparticle amplitudes in a scalar EFT

At sufficiently high energies the production of a very large number of particles is kinematically allowed. However, it is well-known that already in the simplest case of a weakly-coupled massive lambda phi(4) theory, n-particle amplitudes become non-perturbative in the limit where n scales with energy. In this case, the effective expansion parameter, lambda n, is no longer small and the perturbative approach breaks down. In general, the associated n-particle production rates were argued to be described by an exponential that, depending on the specifics of the underlying Quantum Field Theory model, could be either growing or decaying in the large-n regime. We investigate such processes in general settings of Effective Field Theory (EFT), involving arbitrary higher-dimensional operators of phi. We perform the resummation of all leading loop corrections arising from EFT vertices for amplitudes at the multiparticle threshold. We find that the net effect of higher-dimensional operators amounts to an exponentially growing factor. We show that if an exponential growth was already generated by the renormalizable interactions, it would then be further enhanced by the EFT contributions. On the other hand, if the multiparticle rates computed in the renormalizable part of the theory were suppressed, this suppression would not be lifted in the EFT.

Automated summary

At sufficiently high energies, the production of a large number of particles is allowed. However, in certain cases, the perturbative approach fails and an effective field theory is needed to describe the phenomena. By studying the effects of higher-dimensional operators in the effective field theory, we find that they contribute to an exponential growth factor.