Masses and Couplings of the Lightest Higgs Bosons in the (M+1)SSM

TL;DR

Ellwanger and Hugonie analyze the masses and couplings of the lightest Higgs bosons in the (M+1)SSM, incorporating dominant two-loop corrections to the effective potential. They derive an analytic upper bound on the lightest Higgs mass and show how singlet–doublet mixing can shift the identity of the lightest versus second-lightest state, making the search for reduced-coupling Higgs states essential. Two complementary parameter scans (constrained and general) map $m_{1,2}$ and the $ZZ$ couplings $R_i$, highlighting the role of the tree-level $\lambda$ term and maximal stop mixing in raising the masses. The results provide practical bounds and strategies for LEP, Tevatron, and LHC searches, and stress that full coverage of the (M+1)SSM requires probing Higgs bosons with reduced couplings, potentially up to $m_1\sim 135$ GeV and various $m_2$ depending on $R_2$.

Abstract

We study the upper limits on the mass of the lightest and second lightest CP even Higgs bosons in the (M+1)SSM, the MSSM extended by a gauge singlet. The dominant two loop contributions to the effective potential are included, which reduce the Higgs masses by 10 GeV. Since the coupling R of the lightest Higgs scalar to gauge bosons can be small, we study in detail the relations between the masses and couplings of both lightest scalars. We present upper bounds on the mass of a 'strongly' coupled Higgs (R > 1/2) as a function of lower experimental limits on the mass of a 'weakly' coupled Higgs (R < 1/2). With the help of these results, the whole parameter space of the model can be covered by Higgs boson searches.