# Maxi-sizing the trilinear Higgs self-coupling: how large could it be?

## TL;DR

This paper investigates the maximum possible deviation of the Higgs trilinear self-coupling from its Standard Model value, considering theoretical and experimental constraints, and finds current data limits such deviations to within a few times the Standard Model prediction.

## Contribution

It provides a comprehensive analysis of the potential size of Higgs self-coupling deviations using effective operators and UV models, incorporating various theoretical and experimental constraints.

## Key findings

- Perturbativity constraints limit large deviations.
- Current measurements exclude deviations above a factor of a few.
- Vacuum stability considerations are also analyzed.

## Abstract

In order to answer the question on how much the trilinear Higgs self-coupling could deviate from its Standard Model value in weakly coupled models, we study both theoretical and phenomenological constraints. As a first step, we discuss this question by modifying the Standard Model using effective operators. Considering constraints from vacuum stability and perturbativity, we show that only the latter can be reliably assessed in a model-independent way. We then focus on UV models which receive constraints from Higgs coupling measurements, electroweak precision tests, vacuum stability and perturbativity. We find that the interplay of current measurements with perturbativity already exclude self-coupling modifications above a factor of few with respect to the Standard Model value.