Alberto Romagnoni

We study the decay of a standard model-like Higgs boson into a gravitino and a neutralino, which subsequently decays promptly into another gravitino and a photon. Such a decay can be important in scenarios where the supersymmetry breaking scale is of the order of a few TeV, and in the region of low transverse momenta of the photon, it may provide the dominant contribution to the final state with a photon and two gravitinos. We estimate the relevant standard model backgrounds and the prospects for discovering this Higgs decay through a photon and missing transverse energy signal at the LHC in terms of a simplified model. We also give an explicit model with manifest, but spontaneously broken, supersymmetry in which the usual MSSM soft terms are promoted to supersymmetric operators involving a dynamical goldstino supermultiplet. This model can give rise to a SM-like CP-even neutral Higgs particle with a mass of 125 GeV, without requiring substantial radiative corrections, and with couplings sufficiently large for a signal discovery through the above mentioned Higgs decay channel with the upcoming data from the LHC.

Extensions of the Standard Model with an extra U′(1) abelian group generically generate terms coming from loops of heavy fermions, leading to three gauge boson couplings, in particularZ′Zγ. We show that WMAP data constrains the gauge coupling of the groupg_Dto values comparable with the electro-weak ones, rather independently of the mass ofZ′. Moreover, the model predicts a monochromatic γ-ray line which can fit a 130 GeV signal at the FERMI telescope for natural values of the Chern-Simons terms and a dark matter mass around 144.5 GeV.

We consider a supersymmetric realization of the MSSM Higgs sector, where the soft terms are promoted to supersymmetric operators and a minimal weakly coupled hidden sector is included. The model exhibits long-lived meta-stable vacua in which supersymmetry and electroweak symmetry are spontaneously broken. The spectrum contains, in addition to the usual MSSM particles and the goldstino fermion, a CP-even and a CP-odd scalar in the neutral Higgs sector corresponding to the complex sgoldstino scalar. By treating all the components of the goldstino supermultiplet dynamically and taking into account their interactions with the Higgs fields, additional couplings beyond those of the MSSM are induced. When the supersymmetry breaking scale is low, these couplings can raise the masses of all the Higgs particles above the LEP bound, already at tree level and for any value of tan(beta). The model includes a scenario where, for any choice of the supersymmetry breaking scale, the set of parameters is reduced to the standard set (mu, Bmu, tan(beta)) of the MSSM Higgs sector but where novel decays of doublet-like states into sgoldstino-like states are kinematically allowed.