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Register a new userTesting quasi-Dirac leptogenesis through neutrino oscillations
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The lightness of the Standard Model (SM) neutrinos could be understood if their masses were to be generated by new physics at a high scale, through the so-called seesaw mechanism involving heavy fermion singlets. If new physics violates baryon minus lepton number by only a small amount, the heavy fermion singlets as well as the SM neutrinos split into pairs of quasi-Dirac states. At the scale of the fermion singlets, this quasi-Diracness allows to enhance CP violation in their decays and the cosmic matter-antimatter asymmetry can be successfully generated through resonant leptogenesis. At lower scale, this quasi-Diracness results in small SM neutrino mass splitting which can be probed in oscillation experiments. Remarkably, the parameter space for viable leptogenesis spans over the regime relevant for solar and atmospheric neutrino oscillations.
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Right-handed neutrinos offer an elegant solution to two well established phenomena beyond the Standard Model (SM) - masses and oscillations of neutrinos, as well as the baryon asymmetry of the Universe. It is also a minimalistic solution since it requires only singlet Majorana fermions to be added to the SM particle content. If these fermions are nearly degenerate, the mass scale of right-handed neutrinos can be very low and accessible by the present and planned experiments. There are at least two well studied mechanisms of the low-scale leptogenesis: baryogenesis via oscillations and resonant leptogenesis. These two mechanisms were often considered separate, but they can in fact be understood as two different regimes of one and the same mechanism, described by a unique set of quantum kinetic equations. In this work we show, using a unified description based on quantum kinetic equations, that the parameter space of these two regimes of low-scale leptogenesis significantly overlap. We present a comprehensive study of the parameter space of the low-scale leptogenesis with the mass scale ranging from $0.1$ GeV to $sim 10^6$ GeV. The unified perspective of this work reveals the synergy between intensity and energy frontiers in the quest for heavy Majorana neutrinos.
We investigate potential quantum nonlinear corrections to Diracs equation through its sub-leading effect on neutrino oscillation probabilities. Working in the plane-wave approximation and in the $mu-tau$ sector, we explore various classes of nonlinearities, with or without an accompanying Lorentz violation. The parameters in our models are first delimited by current experimental data before they are used to estimate corrections to oscillation probabilities. We find that only a small subset of the considered nonlinearities have the potential to be relevant at higher energies and thus possibly detectable in future experiments. A falsifiable prediction of our models is an energy dependent effective mass-squared, generically involving fractional powers of the energy.
We present an analysis of the solar neutrino data in the context of a quasi-Dirac neutrino model in which the lepton mixing matrix is given at tree level by the tribimaximal matrix. When radiative corrections are taken into account, new effects in neutrino oscillations, as $ u_e to u_s$, appear. This oscillation is constrained by the solar neutrino data. In our analysis, we have found an allowed region for our two free parameters $epsilon$ and $m_1$. The radiative correction, $epsilon$, can vary approximately from $5times 10^{-9}$ to $10^{-6}$ and the calculated fourth mass eigenstate, $m_4$, 0.01 eV to 0.2 eV at 2$sigma$ level. These results are very similar to the ones presented in the literature.
We introduce simple analytic expressions for the neutrino survival probability in media valid in the quasi-adiabatic limit. These expressions provide a quick but accurate alternative to numerical solution of the neutrino propagation equations for the Mikheyev-Smirnov-Wolfenstein effect. They can also be used to extract information about the density scale height from the neutrino data. As an example, we present calculations for solar neutrinos.
We study a simple model of thermal dark matter annihilating to standard model neutrinos via the neutrino portal. A (pseudo-)Dirac sterile neutrino serves as a mediator between the visible and the dark sectors, while an approximate lepton number symmetry allows for a large neutrino Yukawa coupling and, in turn, efficient dark matter annihilation. The dark sector consists of two particles, a Dirac fermion and complex scalar, charged under a symmetry that ensures the stability of the dark matter. A generic prediction of the model is a sterile neutrino with a large active-sterile mixing angle that decays primarily invisibly. We derive existing constraints and future projections from direct detection experiments, colliders, rare meson and tau decays, electroweak precision tests, and small scale structure observations. Along with these phenomenological tests, we investigate the consequences of perturbativity and scalar mass fine tuning on the model parameter space. A simple, conservative scheme to confront the various tests with the thermal relic target is outlined, and we demonstrate that much of the cosmologically-motivated parameter space is already constrained. We also identify new probes of this scenario such as multi-body kaon decays and Drell-Yan production of $W$ bosons at the LHC.
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