Interpreting the 750 GeV digamma excess: a review

We summarise the main experimental, phenomenological and theoretical issues related to the 750 GeV digamma excessComment: To appear in the proceedings of the Moriond 2016 conference. Version 2: note added, it's dea

Sommerfeld corrections to type-II and III leptogenesis

We study thermal leptogenesis from decays of the electroweak triplets that mediate neutrino masses in type-II and type-III see-saw. We find that Sommerfeld corrections reduce the baryon asymmetry by ~30%, and that successful leptogenesis needs triplets heavier than 1.6 TeV, beyond the discovery reach of LHC.Comment: 12 pages, 4 figures, final version. The group theory of the non-abelian Sommerfeld effect presented in this paper can be relevant for scenarios of Dark Matter charged under new dark gauge groups, as suggested by recent dat

Distinguishing gauge-mediated from unified-supergravity spectra

We show that gauge-mediation and unified-supergravity give sufficiently firm and different predictions for the spectrum of supersymmetric particles to make it possible to discriminate the two scenarios even if the messenger mass is close to the unification scale.Comment: 6 page

Naturalness of supersymmetric models

After presenting a simple procedure for testing naturalness (similar to Bayesian inference and not more subjective than it) we show that LEP2 experiments pose a naturalness problem for `conventional' supersymmetric models. About 95% of the parameter space of minimal supergravity MSSM is excluded by LEP2 experiments. Moreover in this model electroweak baryogenesis, or detectable supersymmetric corrections to mixing of K and B mesons, are possible only in very small corners of the parameter space. The naturalness problem is stronger in gauge mediation models, expecially with light messengers. We recall some possible explanations (different from an improbable numerical accident) of why supersymmetry has not (yet?) been found.Comment: from a talk presented at Moriond 99. This paper is mainly a brief discussion of hep-ph/9811386, with only few original point

Implications of first LHC results

We discuss implications of first LHC results for models motivated by the hierarchy problem: large extra dimensions and supersymmetry. We present bounds, global fits and implications for naturalness.Comment: Talk at Moriond 2011. Updated to latest data (up to 165/pb

Radiatively induced light right-handed stop

A right-handed stop not much heavier or even lighter than the Z boson has today desirable phenomenological consequences. We study how it can result within the usual radiative scenario of electroweak symmetry breaking. A restriction on the gaugino mass parameters, M_2 < 0.3 m_10, arises if soft terms satisfy relations suggested by unification theories. Moreover, requiring to get a light stop without unnatural fine-tunings below the per-cent level, we obtain another more interesting upper bound on the chargino mass, M_chargino < M_Z, and we derive interesting conclusions about the masses of the gluino, M_3 \sim (150-300) GeV, of the heavy stop, M_stop \sim (250-500) GeV, and of the left/right mixing angle in the stop sector, |\theta_stop| < 0.3.Comment: 4 pages, figures included, one reference added. PS-file also available at http://www.ft.uam.es/~strumia/15Art/15Art2.p

The Region of Validity of Homogeneous Nucleation Theory

We examine the region of validity of Langer's picture of homogeneous nucleation. Our approach is based on a coarse-grained free energy that incorporates the effect of fluctuations with momenta above a scale k. The nucleation rate I = A_k exp(-S_k) is exponentially suppressed by the action S_k of the saddle-point configuration that dominates tunnelling. The factor A_k includes a fluctuation determinant around this saddle point. Both S_k and A_k depend on the choice of k, but, for 1/k close to the characteristic length scale of the saddle point, this dependence cancels in the expression for the nucleation rate. For very weak first-order phase transitions or in the vicinity of the spinodal decomposition line, the pre-exponential factor A_k compensates the exponential suppression exp(-S_k). In these regions the standard nucleation picture breaks down. We give an approximate expression for A_k in terms of the saddle-point profile, which can be used for quantitative estimates and practical tests of the validity of homogeneous nucleation theory.Comment: 8 pages, 4 figures. v2: Final version with extended discussio

Which solar neutrino experiment after KamLAND and Borexino?

We estimate how well we will know the parameters of solar neutrino oscillations after KamLAND and Borexino. The expected error on Delta m^2 is few per-mille in the VO and QVO regions, few per-cent in the LMA region, and around 10% in the LOW region. The expected error on sin^2 2theta is around 5%. KamLAND and Borexino will tell unambiguously which specific new measurement, dedicated to pp solar neutrinos, is able to contribute to the determination of theta and perhaps of Delta m^2. The present data suggest as more likely outcomes: no measurement, or the total pp rate, or its day/night variation.Comment: 12 pages, 4 figures. v2: comments and references added, final versio