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Simultaneous enhancement in gamma.gamma, b.b-bar and tau+.tau- rates in the NMSSM with nearly degenerate scalar and pseudoscalar Higgs bosons

We propose an experimental test of a scenario in the Next-to-Minimal Supersymmetric Standard Model in which both the lightest scalar and the lightest pseudoscalar Higgs bosons have masses around 125 GeV. The pseudoscalar can contribute significantly to the gamma.gamma rate at the LHC due to light Higgsino-like charginos in its effective one-loop coupling to two photons. Such charginos are obtained for small values of the mu_eff parameter which also results in enhanced b.b-bar and tau+.tau- rates compared to those expected for a Standard Model Higgs boson. This scenario should result in a clear discrepancy between the observed rates in these three decay channels and those in the WW and ZZ channels, since the pseudoscalar does not couple to the W and Z bosons. However, in the dominant gluon fusion production mode the pseudoscalar will stay hidden behind the SM-like scalar Higgs boson and in order for it to be observable the associated b.b-bar.h production mode has to be considered, the cross section for which is tiny in the Standard Model but tan.beta-enhanced in supersymmetry. We analyze the constrained NMSSM with non-universal Higgs sector parameters and identify regions of its parameter space where the lightest pseudoscalar with mass around 125 GeV and strongly enhanced gamma.gamma (up to 60%), b.b-bar and tau+.tau- rates in the b.b-bar.h mode can be obtained.