# Scattering in pseudo-Hermitian quantum field theory and causality violation

## TL;DR

This paper investigates how nonlocality in pseudo-Hermitian quantum field theories affects observable quantities, revealing causality violations in scattering amplitudes despite real mass corrections.

## Contribution

It demonstrates the relation between non-Hermitian and Hermitian S-matrices and computes correlation functions showing causality violation in a specific model.

## Key findings

- Perturbative S-matrix of Hermitian model derived from non-Hermitian model.
- 1-loop mass correction is real, indicating no decay.
- 2-to-2 scattering amplitude exhibits causality violation.

## Abstract

The non-Hermitian but $\mathcal{PT}$-symmetric quantum field theories are known to have a pseudo-Hermitian interpretation. However the corresponding intertwining operator happens to be nonlocal that raises the question to what extent this nonlocality affects observable quantities. We consider the case when the intrinsic parity of the interaction terms is determined by degree of coupling constant. We show that the perturbative S-matrix of the equivalent Hermitian description can be easily obtained from the perturbative S-matrix of the non-Hermitian model. Namely, the first order vanishes whereas the second order is given by the real part of the second order T-matrix of the non-Hermitian model. We compute directly the 2-point and 4-point correlation functions in the equivalent Hermitian model for the $i\phi^3$ model and find the results consistent with this relation. The 1-loop correction to the mass happens to be real reflecting the disappearance of 2-body decays. However the 2 to 2 scattering amplitude obtained using LSZ formula has poles taken in principal value which implies the violation of the causality.