Oblique corrections from vectorlike singlet and doublet quarks

Is the Decay of the Higgs Boson to a Photon and a Dark Photon Currently Observable at the LHC?

Many attempts have been made to observe the decay of the Higgs boson to a photon and an invisible massless dark photon. For this decay to be potentially observable at the LHC, new mediators that communicate between the standard model and the dark photon must exist. In this Letter, we study bounds on such mediators coming from the Higgs signal strengths, oblique parameters, electric dipole moment of the electron, and unitarity. We find that the branching ratio of the Higgs boson to a photon and a dark photon is constrained to be far smaller than the sensitivity of current collider searches, thus calling for a reconsideration of current experimental efforts.

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

Vector-like quarks (VLQ) 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 long-standing anomaly in the forward-backward asymmetry in b-quark production at LEP, [Formula: see text], but also the more recent [Formula: see text]2[Formula: see text] deviation of the cross section for the associated Higgs production with top-quark pairs at the LHC, [Formula: see text]. 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 [Formula: see text] and [Formula: see text]. We show that top and bottom VL partners with masses up to [Formula: see text]5 TeV and exotic VLQs with masses in the 10 TeV range can be probed at the high-luminosity LHC.