In models with an extended Higgs sector there exists an alignment limit, in which the lightest CP-even Higgs boson mimics the Standard Model Higgs. The alignment limit is commonly associated with the decoupling limit, where all non-standard scalars a
re significantly heavier than the $Z$ boson. However, alignment can occur irrespective of the mass scale of the rest of the Higgs sector. In this work we discuss the general conditions that lead to alignment without decoupling, therefore allowing for the existence of additional non-standard Higgs bosons at the weak scale. The values of $tanbeta$ for which this happens are derived in terms of the effective Higgs quartic couplings in general two-Higgs-doublet models as well as in supersymmetric theories, including the MSSM and the NMSSM. Moreover, we study the information encoded in the variations of the SM Higgs-fermion couplings to explore regions in the $m_A - tanbeta$ parameter space.
In spite of rapid experimental progress, windows for light superparticles remain. One possibility is a ~100 GeV tau slepton whose t-channel exchange can give the correct thermal relic abundance for a relatively light neutralino. We pedagogically revi
ew how this region arises and identify two distinct scenarios that will be tested soon on multiple fronts. In the first, the neutralino has a significant down-type higgsino fraction and relatively large rates at direct detection experiments are expected. In the second, there is large mixing between two relatively light staus, which could lead to a significant excess in the Higgs boson branching ratio to photons. In addition, electroweak superpartners are sufficiently light that direct searches should be effective.
The ATLAS and CMS experiments have recently announced the discovery of a Higgs-like resonance with mass close to 125 GeV. Overall, the data is consistent with a Standard Model (SM)-like Higgs boson. Such a particle may arise in the minimal supersymme
tric extension of the SM with average stop masses of the order of the TeV scale and a sizable stop mixing parameter. In this article we discuss properties of the SM-like Higgs production and decay rates induced by the possible presence of light staus and light stops. Light staus can affect the decay rate of the Higgs into di-photons and, in the case of sizable left-right mixing, induce an enhancement in this production channel up to $sim$ 50% of the Standard Model rate. Light stops may induce sizable modifications of the Higgs gluon fusion production rate and correlated modifications to the Higgs diphoton decay. Departures from SM values of the bottom-quark and tau-lepton couplings to the Higgs can be obtained due to Higgs mixing effects triggered by light third generation scalar superpartners. We describe the phenomenological implications of light staus on searches for light stops and non-standard Higgs bosons. Finally, we discuss the current status of the search for light staus produced in association with sneutrinos, in final states containing a $W$ gauge boson and a pair of $tau$s.
We analyze the stability of the vacuum and the electroweak phase transition in the NMSSM close to the Peccei-Quinn symmetry limit. This limit contains light Dark Matter (DM) particles with a mass significantly smaller than the weak scale and also lig
ht CP-even and CP-odd Higgs bosons. Such light particles lead to a consistent relic density and facilitate a large spin-independent direct DM detection cross section, that may accommodate the recently reported signatures at the DAMA and CoGeNT experiments. Studying the one-loop effective potential at finite temperature, we show that when the lightest CP-even Higgs mass is of the order of a few GeV, the electroweak phase transition tends to become first order and strong. The inverse relationship between the direct-detection cross-section and the lightest CP-even Higgs mass implies that a cross-section of the order of 10$^{-41}$ cm$^2$ is correlated with a strong first order phase transition.
