Higgs decay into photons through a spin-2 loop

A new particle with proprieties similar to those of the Higgs boson in the Standard Model (SM) has been recently discovered. The biggest discrepancy is related to its diphoton decay, whose branching ratio seems to be around two times larger with respect to the correspondent SM value; this evidence, even if still affected by large uncertainties, suggests that clues of new physics related to the spontaneous breaking of the electroweak symmetry could be hidden under this loop-induced process. A new strongly-coupled sector responsible for this breaking, for instance, could produce in analogy with QCD a charged massive spin-2 state. In light of these arguments we calculate and discuss the role of such a resonance in the diphoton decay width of the Higgs.Comment: 12 pages + appendices, 5 figures. v2: minor changes, references adde

Natural minimal dark matter

We show how the Higgs boson mass is protected from the potentially large corrections due to the introduction of minimal dark matter if the new physics sector is made supersymmetric. The fermionic dark matter candidate (a 5-plet of $SU(2)_L$) is accompanied by a scalar state. The weak gauge sector is made supersymmetric and the Higgs boson is embedded in a supersymmetric multiplet. The remaining standard model states are non-supersymmetric. Non vanishing corrections to the Higgs boson mass only appear at three-loop level and the model is natural for dark matter masses up to 15 TeV--a value larger than the one required by the cosmological relic density. The construction presented stands as an example of a general approach to naturalness that solves the little hierarchy problem which arises when new physics is added beyond the standard model at an energy scale around 10 TeV.Comment: 6 pages, 4 figures. v2: Discussion on the mass splitting extended and improved. References adde

Fine Tuning in Quintessence Models with Exponential Potentials

We explore regions of parameter space in a simple exponential model of the form $V = V_0 e^{- \lambda \frac{Q}{M_p}}$ that are allowed by observational constraints. We find that the level of fine tuning in these models is not different from more sophisticated models of dark energy. We study a transient regime where the parameter $\lambda$ has to be less than $\sqrt{3}$ and the fixed point $\Omega_Q = 1$ has not been reached. All values of the parameter $\lambda$ that lead to this transient regime are permitted. We also point out that this model can accelerate the universe today even for $\lambda > \sqrt{2}$, leading to a halt of the present acceleration of the universe in the future thus avoiding the horizon problem. We conclude that this model can not be discarded by current observations.Comment: 15 pages, 8 figure

The breaking of the SU(2)L×U(1)YSU(2)_L\times U(1)_Y symmetry: The 750 GeV resonance at the LHC and perturbative unitarity

If the di-photon excess at 750 GeV hinted by the 2015 data at the LHC is explained in terms of a scalar resonance participating in the breaking of the electro-weak symmetry, this resonance must be accompanied by other scalar states for perturbative unitarity in vector boson scattering to be preserved. The simplest set-up consistent with perturbative unitarity and with the data of the di-photon excess is the Georgi-Machacek model.Comment: 9 pages, 5 figures. v2: Minor changes, bibliography updated. v3: Minor change