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

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

Possible experimental signatures at the LHC of strongly interacting electro-weak symmetry breaking

If electro-weak symmetry is broken by a new strongly interacting sector, new physics will probably manifest itself in gauge boson scattering at the LHC. The relevant dynamics is well described in terms of an effective lagrangian. We discuss the probable size of the coefficients of the relevant operators under a combination of model-independent constraints and reasonable assumptions based on two models of the strongly interacting sector. We compare these values with LHC sensitivity and argue that they will be too small to be seen. Therefore, the presence of vector and scalar resonances required by unitarity will be the only characteristic signature. We analyze the most likely masses and widths of these resonances.Comment: 14 pages, pdftex, 5 figures, improved discussion of bounds, 1 footnote remove

Graviton scattering in matrix theory and supergravity

I briefly review recent work on the comparison between two and three graviton scattering in supergravity and matrix theoryComment: Talk given at the TMR meeting, Kerkyria, September 1998, to appear in the proceeding