[en] Neutrinoless double beta decay constitutes the main probe for lepton number violation at low energies, motivated by the expected Majorana nature of the light but massive neutrinos. On the other hand, the theoretical interpretation of the (non-)observation of this process is not straightforward as the Majorana neutrinos can destructively interfere in their contribution and many other New Physics mechanisms can additionally mediate the process. We here highlight the potential of combining neutrinoless double beta decay with searches for Tritium decay, cosmological observations and LHC physics to improve the quantitative insight into the neutrino properties and to unravel potential sources of lepton number violation

[en] We study the impact of minimal nonsupersymmetric models of resonant leptogenesis on charged-lepton flavor violation and the neutrino-mixing angle θ₁₃. Possible low-scale flavor realizations of resonant τ-, μ- and e-leptogenesis provide very distinct and predictive frameworks to explain the observed baryon asymmetry in the Universe by sphaleron conversion of an individual τ-, μ- and e-lepton-number asymmetry which gets resonantly enhanced via out-of-equilibrium decays of nearly degenerate heavy Majorana neutrinos. Based on approximate flavor symmetries, we construct viable scenarios of resonant τ-, μ- and e-leptogenesis compatible with universal right-handed neutrino masses at the grand unified theory scale, where the required heavy-neutrino mass splittings are generated radiatively. The heavy Majorana neutrinos in such scenarios can be as light as 100 GeV and their couplings to two of the charged leptons may be large. In particular, we explicitly demonstrate the compelling role that the three heavy Majorana neutrinos play, in order to obtain successful leptogenesis and experimentally testable rates for lepton-flavor violating processes, such as μ→eγ and μ→e conversion in nuclei.

[en] Neutrinoless double beta decay is the traditional tool to probe Majorana neutrino masses and lepton number violating physics in general. On the other hand, many models incorporating Majorana neutrino masses also predict new states and lepton number violating interactions at the TeV scale that can potentially be probed at the LHC. We provide a brief overview of the pertinent operators and a selection of physics models in order to highlight the interplay between neutrinoless double beta decay and LHC searches. (paper)

[en] We describe a hybrid model in which the light neutrino mass matrix receives both tree-level seesaw and loop-induced contributions. An additional U(1) gauge symmetry is used to stabilize the lightest right-handed neutrino as the Dark Matter candidate. After fitting the experimental neutrino data, we analyze and correlate the phenomenological consequences of the model, namely its impact on electroweak precision measurements, the Dark Matter relic abundance, lepton flavour violating rare decays and neutrinoless double beta decay. We find that natural realizations of the model characterized by large Yukawa couplings are compatible with and close to the current experimental limits.

[en] We compute the relic abundance of the right-handed sneutrinos in the supersymmetric F_D-term model of hybrid inflation. As well as providing a natural solution to the μ- and gravitino overabundance problems, the F_D-term model offers a new viable candidate to account for the cold dark matter in the Universe: the lightest right-handed sneutrino. In particular, the F_D-term model predicts a new quartic coupling of purely right-handed sneutrinos to the Higgs doublets that thermalizes the sneutrinos and makes them annihilate sufficiently fast to a level compatible with the current cosmic microwave background data. We analyze this scenario in detail and identify favourable regions of the parameter space within the framework of minimal supergravity, for which the lightest right-handed sneutrino becomes the thermal dark matter, in agreement with WMAP observations of cosmological inflation. Constraints derived from direct dark matter searches experiments are presented.

[en] We analyse the abundance of right-handed sneutrinos in the supersymmetric F_D-term model of hybrid inflation. As well as providing a natural solution to the μ- and gravitino overabundance problems, the model offers the lightest right-handed sneutrino as a candidate for thermal dark matter. The F_D-term model predicts a new quartic coupling of purely right-handed sneutrinos to the Higgs doublets that thermalises the sneutrinos and makes them annihilate sufficiently fast to a level compatible with the current cosmic microwave background data. We discuss this scenario and identify favourable regions of the parameter space within mSUGRA.

[en] A measurement of neutrinoless double beta decay in one isotope does not allow us to determine the underlying physics mechanism. We discuss the discrimination of mechanisms for neutrinoless double beta decay by comparing ratios of half-life measurements for different isotopes. Six prominent examples for specific new physics contributions to neutrinoless double beta decay are analyzed. We find that the change in corresponding ratios of half lives varies from 60% for supersymmetric models up to a factor of 5-20 for extra-dimensional and left-right-symmetric mechanisms

[en] We survey the lepton flavor violation decay rates Br(μ→eγ), Br(τ→μγ), and Br(τ→eγ), in mSUGRA at the level of the fundamental Lagrangian for a broad class of non-trivial lepton mass matrices that give nearly tribimaximal lepton mixing. SUSY SU(5) GUT models with non-Abelian discrete flavor symmetries as feasible origin will be presented. Moreover, we study the lepton flavor violation branching ratios for the most general CP-violating forms of the mass matrices. We show that the branching ratios are roughly enhanced by an order of magnitude as compared to the real case. The branching ratios exhibit, however, a strong dependence on the choice of the phases. In particular, for general CP-phases, the LFV-rates appear to be largely uncorrelated with the possible high- and low-energy lepton mixing parameters

[en] We review the collider phenomenology of neutrino physics and the synergetic aspects at energy, intensity and cosmic frontiers to test the new physics behind the neutrino mass mechanism. In particular, we focus on seesaw models within the minimal setup as well as with extended gauge and/or Higgs sectors, and on supersymmetric neutrino mass models with seesaw mechanism and with R-parity violation. In the simplest type-I seesaw scenario with sterile neutrinos, we summarize and update the current experimental constraints on the sterile neutrino mass and its mixing with the active neutrinos. We also discuss the future experimental prospects of testing the seesaw mechanism at colliders and in related low-energy searches for rare processes, such as lepton flavor violation and neutrinoless double beta decay. The implications of the discovery of lepton number violation at the Large Hadron Collider for leptogenesis are also studied

[en] We discuss the relation between the absolute neutrino mass scale, the effective mass measured in neutrinoless double beta decay, and the Majorana CP phases. Emphasis is placed on estimating the upper bound on the nuclear matrix element entering calculations of the double beta decay half-life. Combining the claimed evidence for neutrinoless double beta decay with the neutrino mass bound from cosmology, one of the Majorana CP phases can be constrained