Unitarity bounds and RG flows in time dependent quantum field theory

TL;DR

This paper extends unitarity bounds in conformal field theories to include spacetime-dependent couplings, showing how their evolution influences operator dimensions and unitarity constraints, especially in large-N double-trace flows and holographic models.

Contribution

It generalizes unitarity bounds to time-dependent couplings and analyzes their impact on operator dimensions in large-N theories, connecting to holographic cosmology.

Findings

Spacetime-dependent couplings can shift unitarity bounds and operator scaling.

Explicit analysis of large-N double-trace flows with time-dependent couplings.

Application to FRW holography explains flavor range constraints.

Abstract

We generalize unitarity bounds on operator dimensions in conformal field theory to field theories with spacetime dependent couplings. Below the energy scale of spacetime variation of the couplings, their evolution can strongly affect the physics, effectively shifting the infrared operator scaling and unitarity bounds determined from correlation functions in the theory. We analyze this explicitly for large-$N$ double-trace flows, and connect these to UV complete field theories. One motivating class of examples comes from our previous work on FRW holography, where this effect explains the range of flavors allowed in the dual, time dependent, field theory.