Positively Identifying HEFT or SMEFT

TL;DR

This paper derives bounds on Higgs effective field theory coefficients using fundamental principles, revealing regions compatible with HEFT but forbidden by SMEFT positivity, with implications for collider searches.

Contribution

It establishes unitarity and analyticity bounds on Wilson coefficients, identifying a region where HEFT allows phenomena forbidden by SMEFT positivity constraints.

Findings

Identifies a subspace allowed by HEFT but forbidden by SMEFT positivity.

Pinpoints a unique pair of operators within SMEFT relevant for collider tests.

Proposes that some EFT regions could mislead interpretations of UV physics.

Abstract

We establish the bounds on Wilson coefficients of the Higgs effective field theory (HEFT) mandated by unitarity and analyticity. These positivity constraints can be projected into the space of the standard model effective field theory (SMEFT) as HEFT$\,\supset\,$SMEFT. Doing so reveals a subspace allowed by the HEFT but forbidden by SMEFT positivity, thereby identifying a region that could herald the use of the wrong EFT rather than a pathological UV. Restricting to custodial symmetric dimension-eight Higgs operators, there is a unique pair within the SMEFT where this concept can be sharply realized and is already being probed at colliders.