# Standard Model EFT and Extended Scalar Sectors

## TL;DR

This paper explores how adding scalar multiplets to the Standard Model affects low-energy physics, focusing on heavy scalars, effective field theory matching, and experimental constraints on extended scalar sectors.

## Contribution

It provides a detailed analysis of scalar extensions in the Standard Model, including EFT matching and constraints from unitarity and electroweak precision tests.

## Key findings

- Effective field theory accurately reproduces kinematic distributions for Higgs pair production.
- Heavy scalar models are highly constrained by unitarity and electroweak measurements.
- Viable parameter space for triplet and quartet models is significantly restricted.

## Abstract

One of the simplest extensions of the Standard Model is the inclusion of an additional scalar multiplet, and we consider scalars in the $SU(2)_L$ singlet, triplet, and quartet representations. We examine models with heavy neutral scalars, $m_H\sim 1-2$ TeV, and the matching of the UV complete theories to the low energy effective field theory. We demonstrate the agreement of the kinematic distributions obtained in the singlet models for the gluon fusion of a Higgs pair with the predictions of the effective field theory. The restrictions on the extended scalar sectors due to unitarity and precision electroweak measurements are summarized and lead to highly restricted regions of viable parameter space for the triplet and quartet models.