# Validity of two Higgs doublet models with a scalar color octet up to a high energy scale

## TL;DR

This study examines the parameter space of two Higgs doublet models with a scalar color octet, ensuring their validity up to high energy scales like the GUT scale, and finds that constraints tighten with increasing scale, favoring the alignment limit.

## Contribution

It provides a detailed analysis of how high-scale validity constraints restrict the parameter space of 2HDM with a color octet, emphasizing the approach to the alignment limit.

## Key findings

- Parameter space shrinks with higher validity scale
- Masses of H^0, A, H^ become degenerate
- Color octet parameters are tightly constrained

## Abstract

We have recently studied theoretical constraints on the parameters of a 2HDM augmented with a color-octet scalar. In this paper we consider the consequences of requiring the model to remain valid up to very high energy scales, such as the GUT scale. The acceptable region of parameter space is reduced when one insists on vacuum stability, perturbative unitarity and the absence of Landau poles below a given scale. As the scale to which we require the model to be valid is increased, the acceptable region of parameter space for the 2HDM sector is reduced in such a way that it approaches the alignment limit, $\cos(\beta-\alpha)\to 0$, and the masses of $H^0$, $A$ and $H^\pm$ are pushed closer to each other. The parameters of the color octet sector are also restricted to an increasingly smaller region.