Classicalization and Unitarity

TL;DR

The paper argues that the classicalization scenario for UV completion is essentially a Wilsonian fixed point phenomenon, which conflicts with unitarity constraints, casting doubt on the viability of classicalizing unitary theories.

Contribution

It clarifies the nature of classicalization as a Wilsonian fixed point and discusses its tension with unitarity constraints in quantum field theories.

Findings

Classicalization corresponds to a Wilsonian fixed point with higher dimensional operators.

In classicalization, UV fluctuations are smaller than IR fluctuations.

There is a tension between classicalization and unitarity constraints.

Abstract

We point out that the scenario for UV completion by "classicalization", proposed recently is in fact Wilsonian in the classical Wilsonian sense. It corresponds to the situation when a field theory has a nontrivial UV fixed point governed by a higher dimensional operator. Provided the kinetic term is a relevant operator around this point the theory will flow in the IR to the free scalar theory. Physically, "classicalization", if it can be realized, would correspond to a situation when the fluctuations of the field operator in the UV are smaller than in the IR. As a result there exists a clear tension between the "classicalization" scenario and constraints imposed by unitarity on a quantum field theory, making the existence of classicalizing unitary theories questionable.