Lepton parameters in the see-saw model extended by one extra Higgs doublet

We investigate the radiative generation of lepton masses and mixing angles in the Standard Model extended by one right-handed neutrino and one extra Higgs doublet. We assume approximate rank-1 Yukawa couplings at a high energy scale and we calculate the one loop corrected charged lepton and neutrino mass matrices at the low energy scale. We find that quantum effects generate, for typical high energy parameters, a hierarchy between the muon and the tau mass, a hierarchy between the solar and the atmospheric mass splittings, and a pattern of leptonic mixing angles in qualitative agreement with experiments

Sharp spectral features from light dark matter decay via gravity portals

We investigate the phenomenology of dark matter decay assuming that it is induced by non-minimal coupling to gravity, when the dark matter mass is in the sub-GeV range, i.e. below the QCD confinement scale. We show that the decay of the singlet scalar dark matter candidate produces sharp features in the photon spectrum, in the form of lines, boxes, and also in the form of a novel spectral feature, characterized by the decay into $e^+e^- \gamma$ through a contact interaction, with decay branching fractions depending only on a single parameter, namely the dark matter mass. We also derive upper limits on the strength of the gravity portal from the non-observation of sharp features in the isotropic diffuse gamma-ray spectra measured by COMPTEL, EGRET and Fermi-LAT, and the X-ray spectrum measured by INTEGRAL. Finally, we briefly comment on the impact of dark matter decay via non-minimal coupling to gravity on the reionization history of the Universe.Comment: 14 pages, 3 figure

Determining See-Saw Parameters from Weak Scale Measurements?

The see-saw mechanism is a very attractive explanation for small neutrino masses, parametrized at the GUT scale by the right-handed Majorana mass matrix, ${\cal M}$, and the neutrino Yukawa matrix, ${\bf Y_\nu}$. We show that in a SUSY model with universal soft terms, ${\cal M}$ and ${\bf Y_\nu}$ can be calculated from the light neutrino masses, the MNS matrix, and ${\bf Y^{\dagger}_\nu} {\bf Y_\nu}$, which enters into the left-handed slepton radiative corrections. This suggests that in principle the GUT-scale inputs of the seesaw could be reconstructed from the neutrino and sneutrino mass matrices. We briefly discuss why this is impractical, but advocate the neutrino and sneutrino mass matrices as an alternative bottom-up parametrization of the seesaw.Comment: Version to be published. References added, modified abstract, minor stylistic changes. Content unchange

Potential for probing three-body decays of Long-Lived Particles with MATHUSLA

Several extensions of the Standard Model predict the existence of Long-Lived Neutral Particles (LLNPs) with masses in the multi-GeV range and decay lengths of O(100 m) or longer. These particles could be copiously produced at the LHC, but the decay products cannot be detected with the ATLAS or CMS detectors. MATHUSLA is a proposed large-volume surface detector installed near ATLAS or CMS aimed to probe scenarios with LLNPs which offers good prospects for disentangling the physics underlying two-body decays into visible particles. In this work we focus on LLNP decays into three particles with one of them being invisible, which are relevant for scenarios with low scale supersymmetry breaking, feebly interacting dark matter or sterile neutrinos, among others. We analyze the MATHUSLA prospects to discriminate between two- and three-body LLNP decays, as well as the prospects for reconstructing the underlying model parameters.Comment: 11 pages, 4 figures, matches journal versio

Signatures of Majorana dark matter with t-channel mediators

Three main strategies are being pursued to search for non-gravitational dark matter signals: direct detection, indirect detection and collider searches. Interestingly, experiments have reached sensitivities in these three search strategies which may allow detection in the near future. In order to take full benefit of the wealth of experimental data, and in order to confirm a possible dark matter signal, it is necessary to specify the nature of the dark matter particle and of the mediator to the Standard Model. In this paper, we focus on a simplified model where the dark matter particle is a Majorana fermion that couples to a light Standard Model fermion via a Yukawa coupling with a scalar mediator. We review the observational signatures of this model and we discuss the complementarity among the various search strategies, with emphasis in the well motivated scenario where the dark matter particles are produced in the early Universe via thermal freeze-out.Comment: 40+11 pages, 19 figures, review article, v2: matches published versio