Vector-like top/bottom quark partners and Higgs physics at the LHC

TL;DR

This paper investigates vector-like quark partners of top and bottom quarks as solutions to anomalies in LEP and LHC Higgs data, proposing models that predict new particles within reach of future collider experiments.

Contribution

It introduces three models of vector-like quarks that can simultaneously explain LEP and LHC anomalies while remaining consistent with existing constraints.

Findings

VLQ states predicted in 1-2 TeV range accessible at LHC

Potential to probe VLQs up to 5 TeV with precision Higgs measurements

Exotic VLQs could be detected at 10 TeV at high-luminosity LHC

Abstract

Vector-like quarks (VLQs) that are partners of the heavy top and bottom quarks are predicted in many extensions of the Standard Model (SM). We explore the possibility that these states could explain not only the longstanding anomaly in the forward-backward asymmetry in $b$-quark production at LEP, $A_{\rm FB}^b $, but also the more recent $\sim 2\sigma$ deviation of the cross section for the associated Higgs production with top quark pairs at the LHC, $\sigma(pp\to t\bar t H)$. Introducing three illustrative models for VLQs with different representations under the SM gauge group, we show that the two anomalies can be resolved while satisfying all other theoretical and experimental constraints. In this case, the three different models predict VLQ states in the $1-2$ TeV mass range that can be soon probed at the LHC. In a second step, we discuss the sensitivity on the VLQ masses and couplings that could be obtained by means of a percent level accuracy in the measurement of ratios of partial Higgs decay widths, in particular $\Gamma(H \! \to\! \gamma\gamma)/\Gamma(H \! \to\! ZZ^*)$ and $\Gamma(H \! \to \! b\bar b)/\Gamma(H \! \to \! WW^*)$. We show that top and bottom VL partners with masses up to $\sim 5$ TeV and exotic VLQs with masses in the $10$ TeV range can be probed at the high-luminosity LHC.