Strategies to link tiny neutrino masses with huge missing mass of the Universe

With the start of the LHC, interest in electroweak scale models for the neutrino mass has grown. In this letter, we review two specific models that simultaneously explain neutrino masses and provide a suitable DM candidate. We discuss the implications of these models for various observations and experiments including the LHC, Lepton Flavor Violating (LFV) rare decays, direct and indirect dark matter searches and Kaon decay.Comment: 17 pages, one diagram, talk given at International Conference on Flavor Physics in the LHC era in Singapor

On the Sources of CP-violation Contributing to the Electric Dipole Moments

In the framework of seesaw mechanism embedded in the constrained Minimal Supersymmetric Standard Model (cMSSM), phases of neutrino Yukawa coupling, $\mu$-term and $A$-terms can all contribute to the Electric Dipole Moment (EDM) of the electron. We discuss and classify the situations for which by combined analysis of the upcoming results on $d_e$, $d_{{\rm Hg}}$ and $d_D$ discriminating between these sources will be possible.Comment: 6 pages, 4 figures, talk presented at IPM-LHP06, Tehran, Ira

R-parity violation assisted thermal leptogenesis in the seesaw mechanism

Successful leptogenesis within the simplest type I supersymmetric seesaw mechanism requires the lightest of the three right-handed neutrino supermultiplets to be heavier than $\sim10^9$ GeV. Thermal production of such (s)neutrinos requires very high reheating temperatures which result in an overproduction of gravitinos with catastrophic consequences for the evolution of the universe. In this letter, we let R-parity be violated through a $\lambda_i \hat{N}_i \hat{H}_u \hat{H}_d$ term in the superpotential, where $\hat{N}_i$ are right-handed neutrino supermultiplets. We show that in the presence of this term, the produced lepton-antilepton asymmetry can be enhanced. As a result, even for $\hat{N}_1$ masses as low as $10^6$ GeV or less, we can obtain the observed baryon asymmetry of the universe without gravitino overproduction.Comment: 4 pages, 1 figure; v2: minor changes, references adde

SLIM at LHC: LHC search power for a model linking dark matter and neutrino mass

Recently a model has been proposed that links dark matter and neutrino masses. The dark matter candidate which is dubbed as SLIM has a mass of MeV scale and can show up at low energy experiments. The model also has a high energy sector which consists of a scalar doublet, $(\phi^-, \phi^0)$. We discuss the potential of the LHC for discovering the new scalars. We focus on the $\phi^+\phi^-$ and $\phi^{\pm} \phi^0$ production and the subsequent decay of the charged scalar to a charged lepton and the SLIM which appears as missing energy. Identifying the background, we estimate the signal significance and find that it can exceed $5 \sigma$ at 30 ${\rm fb}^{-1}$ for the 14 TeV run at the LHC. We comment on the possibility of extracting the flavor structure of the Yukawa couplings which also determine the neutrino mass matrix. Finally, we discuss the prospects of this search at the current 7 TeV run of the LHC.Comment: 26 pages, 21 figure

Are small neutrino masses unveiling the missing mass problem of the Universe?

We present a scenario in which a remarkably simple relation linking dark matter properties and neutrino masses naturally emerges. This framework points towards a low energy theory where the neutrino mass originates from the existence of a light scalar dark matter particle in the MeV mass range. A very surprising aspect of this scenario is that the required MeV dark matter is one of the favoured candidates to explain the mysterious emission of 511 keV photons in the centre of our galaxy. A possible interpretation of these findings is that dark matter is the stepping stone of a theory beyond the standard model instead of being an embarrassing relic whose energy density must be accounted for in any successful model building.Comment: 4pages, 2 figures. Two paragraphs have been added. One for the complex case; the other one for the UV completio

On the Effective Mass of the Electron Neutrino in Beta Decay

In the presence of mixing between massive neutrino states, the distortion of the electron spectrum in beta decay is, in general, a function of several masses and mixing angles. For $3\nu$-schemes which describe the solar and atmospheric neutrino data, this distortion can be described by a single effective mass, under certain conditions. In the literature, two different definitions for the effective mass have been suggested. We show that for quasi-degenerate mass schemes (with an overall mass scale $m$ and splitting $\Delta m^2$) the two definitions coincide up to $(\Delta m^2)^2/m^4$ corrections. We consider the impact of different effective masses on the integral energy spectrum. We show that the spectrum with a single mass can be used also to fit the data in the case of $4\nu$-schemes motivated, in particular, by the LSND results. In this case the accuracy of the mass determination turns out to be better than $(10 - 15)$.Comment: 15 pages, Version to appear in Phys. Lett.

Leptonic CP violation: zero, maximal or between the two extremes

Discovery of the CP-violation in the lepton sector is one of the challenges of the particle physics. We search for possible principles, symmetries and phenomenological relations that can lead to particular values of the CP-violating Dirac phase, $\delta$. In this connection we discuss two extreme cases: the zero phase, $\delta = 0$, and the maximal CP-violation, $\delta = \pm \pi/2$, and relate them to the peculiar pattern of the neutrino mixing. The maximal CP-violation can be related to the $\nu_\mu - \nu_\tau$ reflection symmetry. We study various aspects of this symmetry and introduce a generalized reflection symmetry that can lead to an arbitrary phase that depends on the parameter of the symmetry transformation. The generalized reflection symmetry predicts a simple relation between the Dirac and Majorana phases. We also consider the possibility of certain relations between the CP-violating phases in the quark and lepton sectors.Comment: 34 pages, no figures; v3: version appeared in JHE

Learning cover context-free grammars from structural data

We consider the problem of learning an unknown context-free grammar when the only knowledge available and of interest to the learner is about its structural descriptions with depth at most $\ell.$ The goal is to learn a cover context-free grammar (CCFG) with respect to $\ell$, that is, a CFG whose structural descriptions with depth at most $\ell$ agree with those of the unknown CFG. We propose an algorithm, called $LA^\ell$, that efficiently learns a CCFG using two types of queries: structural equivalence and structural membership. We show that $LA^\ell$ runs in time polynomial in the number of states of a minimal deterministic finite cover tree automaton (DCTA) with respect to $\ell$. This number is often much smaller than the number of states of a minimum deterministic finite tree automaton for the structural descriptions of the unknown grammar