LHC accessible second Higgs boson in the left-right model

Abstract

A second Higgs doublet arises naturally as a parity partner of the standard model (SM) Higgs, once the SM is extended to its left-right symmetric version (LRSM) to understand the origin of parity violation in weak interactions, as well as to accommodate small neutrino masses via the seesaw mechanism. The flavor-changing neutral Higgs (FCNH) effects in the minimal version of this model (LRSM), however, push the second Higgs mass to more than 15 TeV, making it inaccessible at the LHC. Furthermore, since the second Higgs mass is directly linked to the ${W}_{R}$ mass, discovery of a ``low'' mass ${W}_{R}$ (${M}_{{W}_{R}}\ensuremath{\le}5--6\text{ }\text{ }\mathrm{TeV}$) at the LHC would require values for some Higgs self-couplings larger than 1. In this paper we present an extension of LRSM by adding a vectorlike $SU(2{)}_{R}$ quark doublet which weakens the FCNH constraints, allowing the second Higgs mass to be near or below the TeV range and a third neutral Higgs below 3 TeV for a ${W}_{R}$ mass below 5 TeV. It is then possible to search for these heavier Higgs bosons at the LHC without conflicting with FCNH constraints. A right-handed ${W}_{R}$ mass in the few TeV range is quite natural in this class of models without having to resort to large scalar coupling parameters. The CKM mixings are intimately linked to the vectorlike quark mixings with the known quarks, which is the main reason why the constraints on the second Higgs mass are relaxed. We present a detailed theoretical and phenomenological analysis of this extended left-right model and point out some tests as well as its potential for discovery of a second Higgs at the LHC. Two additional features of the model are a $5/3$-charged quark and a fermionic top partner with masses in the TeV range.