$\Delta F=1$ constraints on composite Higgs models with LR parity

TL;DR

This paper investigates flavor-based constraints on composite Higgs models with custodial symmetry and LR parity, deriving bounds on top and bottom partner masses from $b o s\,\gamma$ processes, with implications for model viability.

Contribution

It provides a novel analysis of flavor constraints in composite Higgs models incorporating custodial symmetry and LR parity, focusing on bounds independent of flavor sector details.

Findings

Bounds on $(t_L, b_L)$ partner masses around 1 TeV from $b \to s\gamma$.

Custodial symmetry can mitigate constraints by protecting effective couplings.

Constraints from heavy fermion loops and $\,\epsilon'/\epsilon_K$ are also evaluated.

Abstract

We analyze the bounds on the spectrum of composite Higgs models (CHM) that come from flavor observables, by means of simple two-site effective Lagrangians, which incorporate a custodial symmetry and a Left-Right parity and which could also be adopted in further phenomenological studies on CHM. We derive, in particular, an important constraint on the masses of the $(t_L, b_L)$ partners, which does not depend on the flavor structure of the sector beyond the SM. This bound is obtained from the "infrared" contribution to $b \to s\gamma$ induced by the flavor-conserving effective vertex $Wt_Rb_R$. We find that the presence of a custodial symmetry can play a role in protecting this effective coupling and, as a consequence, in attenuating the constraint, which, however, remains of the order of 1 TeV. In addition to this bound, we calculate the constraints from the "ultraviolet" contribution to $b \to s \gamma$, induced by loops of heavy fermions, and to $\epsilon^{'}/\epsilon_K$.