Filling the Gap in the Vectorlike Quark Searches

Direct searches for the vectorlike quarks (VLQs) generally assume that they decay exclusively to a third-generation quark and a heavy vector-boson or a Higgs. The current mass limits on the VLQs lie between 1.2–1.6 TeV, for various weak representations and decays. These limits can relax drastically if the VLQs have additional decay(s). Here, we discuss a scenario where the VLQs decay substantially to a new singlet scalar (or pseudoscalar) that couples exclusively to the VLQs. Such a singlet state is well-motivated in many BSM models. We reinterpret the current bounds on the VLQs in this scenario and show that the allowed parameter space for such models is largely unrestricted. We also discuss the strategies to isolate VLQ signatures of weak-singlet top and bottom partners amidst the huge SM background and their prospects at the high luminosity LHC (HL-LHC).