# EPS-HEP2021 conference

26-30 July 2021
Zoom
Europe/Berlin timezone

## An unambiguous test of positivity at lepton colliders

30 Jul 2021, 10:30
15m
Zoom

#### Zoom

Parallel session talk Searches for New Physics

Jiayin Gu

### Description

The diphoton channel at lepton colliders, $e^+e^- (\mu^+\mu^-) \to \gamma \gamma$, has a remarkable feature that the leading new physics contribution comes only from dimension-eight operators. This contribution is subject to a set of positivity bounds, derived from fundamental principles of Quantum Field Theory, such as unitarity, locality and analyticity. These positivity bounds are thus applicable to the most direct observable -- the diphoton cross sections. This unique feature provides a clear, robust, and unambiguous test of these principles. We estimate the capability of various future lepton colliders in probing the dimension-eight operators and testing the positivity bounds in this channel. We show that positivity bounds can lift certain degeneracies among the effective operators and significantly change the perspectives of a global analysis. We also perform a combined analysis of the $\gamma\gamma/Z\gamma/ZZ$ processes in the high energy limit and point out the important interplay among them.

based on 2011.03055

First author Jiayin Gu JGU Mainz jiagu@uni-mainz.de