Collider signals of a composite Higgs in the Standard Model with four generations

TL;DR

This paper explores how a composite Higgs, arising from a fourth generation of heavy quarks in the Standard Model, can produce distinctive signals at the LHC, especially through enhanced decay channels.

Contribution

It proposes new Higgs decay modes involving fourth generation quarks and analyzes their potential observability at the LHC within a composite Higgs framework.

Findings

Higgs can decay to single heavy 4th generation quarks via 3-body decays.

Enhanced Higgs decay rates to heavy quarks at the LHC due to large width effects.

Flavor-changing Higgs decays to 4th generation quarks can have sizable branching ratios.

Abstract

Recent fits of electroweak precision data to the Standard Model (SM) with a 4th sequential family (SM4) point to a possible "three-prong composite solution": (1) the Higgs mass is at the TeV-scale, (2) the masses of the 4th family quarks t',b' are of O(500) GeV and (3) the mixing angle between the 4th and 3rd generation quarks is of the order of the Cabibbo angle, \theta_{34} ~ O(0.1). Such a manifestation of the SM4 is of particular interest as it may suggest that the Higgs is a composite state, predominantly of the 4th generation heavy quarks. Motivated by the above, we show that the three-prong composite solution to the SM4 can have interesting new implications for Higgs phenomenology. For example, the Higgs can decay to a single heavy 4th generation quark via the 3-body decays (through an off-shell t' or b') H -> t'(bar) t'* -> t'(bar) b W+ and H -> b'(bar) b'* -> b'(bar) t W-. These flavor diagonal decays can be dramatically enhanced at the LHC (by several orders of magnitudes) due to the large width effects of the resonating heavy Higgs in the processes gg -> H -> t'(bar) t'* -> t'(bar) b W+ and gg -> H -> b'(bar) b'* -> b'(bar) t W-, thus yielding a viable signal above the corresponding continuum QCD production rates. In addition, the Higgs can decay to a single t' and b' in the loop-generated flavor changing (FC) channels H -> b' b(bar), t' t(bar). These FC decays are essentially "GIM-free" and can, therefore, have branching ratios as large as 10^{-4} - 10^{-3}.