Extra Neutral Scalars with Vector-like Fermions at the LHC

TL;DR

This paper calculates loop-induced couplings of new neutral scalars and vector-like fermions in BSM theories, constrains their properties using LHC data, and explores their production and decay at current and future colliders.

Contribution

It provides analytical expressions for effective couplings of CP-odd scalars to gauge bosons, and analyzes collider phenomenology in various models including 2HDM types.

Findings

Derived constraints on scalar couplings from LHC data

Computed gluon-fusion cross-sections at 8 and 14 TeV

Analyzed decay branching ratios into SM particles

Abstract

Many theories beyond the standard model (BSM) contain new CP-odd and CP-even neutral scalars $\phi = \{A,H\}$, and new vector-like fermions ($\psi_{VL}$). The couplings of the CP-odd scalar $A$ to two standard model (SM) gauge bosons cannot occur from renormalizable operators in a CP-conserving sector, but can be induced at the quantum loop level. We compute these effective couplings at the 1-loop level induced by the SM fermions and vector-like fermions, present analytical expressions for them, and plot them numerically. Using the 8~TeV Large Hadron Collider (LHC) $\gamma\gamma$, $\tau^{+} \tau^{-}$ and $t \bar t$ channel data, we derive constraints on the effective couplings of the $\phi$ to standard model gauge bosons and fermions. We present the gluon-fusion channel cross-sections of the $\phi$ at the 8~and~14~TeV LHC, and its branching-ratios into SM fermion and gauge-boson pairs. We present our results first model-independently, and then also for some simple models containing $\phi$ and $\psi_{VL}$ in the singlet and doublet representations of $SU(2)$. In the doublet case, we focus on the two-Higgs-doublet (2HDM) Type-II and Type-X models in the alignment limit.