Majorana Heavy Neutrinos Research Articles

One loop mechanism for neutrinoless double beta hyperon decay

Motivated by the large dataset to be accumulated of hyperon pairs produced in decays of $\mathcal{O}(10^{10})$ $J/\psi$ and $\psi^\prime$ charmonia states in the BES-III collaboration, we revisited the predictions of $\Delta L=2$ decays of hyperons $B^-_i\to B^+_f\ell^-\ell'^-$ in the one-loop model mechanism involving Majorana neutrinos previously presented in \cite{Barbero:2002wm}. Unlike the previous work, by modeling the momentum transfer dependence of the hyperon form factors in the computation we provide finite results for the loop integration. Furthermore, since we keep finite masses for the neutrinos throughout the calculations, we are able to consider the effects of heavy Majorana neutrinos. Thus, our results are applied to a simple model that involves two Majorana heavy neutrinos in the framework of a low-scale seesaw model. In order to provide and compare additional predictions, we study an alternative model where $\Delta L=2$ decays are induced by the short-range effects of a scalar boson coupled to di-leptons.

Exploring CP-violation, via heavy neutrino oscillations, in rare B meson decays at Belle II

In this article we study the rare B-meson decay via two on-shell almost-degenerate Majorana Heavy Neutrinos, into two charged leptons and two pseudoscalar mesons (B^{pm } rightarrow D^0 ell ^{pm }_1 ell ^{pm }_2 pi ^{mp }). We consider the scenario where the heavy neutrino masses are sim 2 GeV and the heavy-light mixing coefficients are |B_{ell N}|^2 sim 10^{-5}, and evaluate the possibility to measure the CP-asymmetry at Belle II. We present some realistic conditions under which the asymmetry could be detected.

Neutrinoless double beta decay versus other probes of heavy sterile neutrinos

We make a comparative study of the neutrinoless double beta decay constraints on heavy sterile neutrinos versus other direct and indirect constraints from both lepton number conserving and violating processes, as a sensitive probe of the extent of lepton number violation and possible interference effects in the sterile sector. We introduce a phenomenological parametrisation of the simplified one-generation seesaw model with one active and two sterile neutrino states in terms of experimentally measurable quantities, such as active-sterile neutrino mixing angles, CP phases, masses and mass splittings. This simple parametrisation enables us to analytically derive a spectrum of possible scenarios between the canonical seesaw with purely Majorana heavy neutrinos and inverse seesaw with pseudo-Dirac ones. We then go on to constrain the simplified parameters of this model from various experiments at the energy, intensity and cosmic frontiers. We emphasise that the constraints from lepton number violating processes strongly depend on the mass splitting between the two sterile states and the relative CP phase between them. This is particularly relevant for neutrinoless double beta decay, which is weakened for small mass splitting and opposite CP parities between the sterile states. On the other hand, neutrinoless double beta decay is especially sensitive for Majorana sterile neutrinos with masses around 0.1 − 10 GeV.

Production of heavy neutrino in next-to-leading order QCD at the LHC and beyond

Majorana and pseudo-Dirac heavy neutrinos are introduced into the type-I and inverse seesaw models, respectively, in explaining the naturally small neutrino mass. TeV scale heavy neutrinos can also be accommodated to have a sizable mixing with the Standard Model light neutrinos, through which they can be produced and detected at the high energy colliders. In this paper we consider the Next-to-Leading Order QCD corrections to the heavy neutrino production, and study the scale variation in cross-sections as well as the kinematic distributions with different final states at $14$ TeV LHC and also in the context of $100$ TeV hadron collider. The repertoire of the Majorana neutrino is realized through the characteristic signature of the same-sign dilepton pair, whereas, due to a small lepton number violation, the pseudo-Dirac heavy neutrino can manifest the trileptons associated with missing energy in the final state. Using the $\sqrt{s}=8$ TeV, $20.3$ fb$^{-1}$ and $19.7$ fb$^{-1}$ data at the ATLAS and CMS respectively, we obtain prospective scale dependent upper bounds of the light-heavy neutrino mixing angles for the Majorana heavy neutrinos at the $14$ TeV LHC and $100$ TeV collider. Further exploiting a recent study on the anomalous multilepton search by CMS at $\sqrt{s}=8$ TeV with $19.5$ fb$^{-1}$ data, we also obtain the prospective scale dependent upper bounds on the mixing angles for the pseudo-Dirac neutrinos. We thus project a scale dependent prospective reach using the NLO processes at the $14$ TeV LHC.

Multilepton collider signatures of heavy Dirac and Majorana neutrinos

We discuss the possibility of observing multi-lepton signals at the Large Hadron Collider (LHC) from the production and decay of heavy Standard Model (SM) singlet neutrinos added in extensions of SM to explain the observed light neutrino masses by seesaw mechanism. In particular, we analyze two `smoking gun' signals depending on the Dirac or Majorana nature of the heavy neutrino: (i) for Majorana case, the same-sign di-lepton signal which can be used as a probe of lepton-number violation, and (ii) for Dirac case, the tri-lepton signal which conserves lepton number but may violate lepton flavor. Within a minimal Left-Right symmetric framework in which these additional neutrino states arise naturally, we find that in both cases, the signals can be identified with virtually no background beyond a TeV, and the heavy gauge boson W_R can be discovered in this process. This analysis also provides a direct way to probe the nature of seesaw physics involving the SM singlets at TeV scale, and in particular, to distinguish type-I seesaw with purely Majorana heavy neutrinos from inverse seesaw with pseudo-Dirac counterparts.

Dirac and Majorana heavy neutrinos at LEP II

The possibility of detecting single heavy Dirac and/or Majorana neutrinos at LEP II is investigated for heavy neutrino masses in the range \(M_N=(s^{1/2}/2,s^{1/2})\). We study the process \(e^+e^- \longrightarrow \nu e^\pm q_i \bar q_j\) as a clear signature for heavy neutrinos. Numerical estimates for cross sections and distributions for the signal and the background are calculated and a Monte Carlo reconstruction of final state particles after hadronization is presented.

Supercollider signatures and correlations of heavy neutrinos.

Forthcoming proton supercolliders can discover a heavy neutrino lying hidden in the ${10}^{2}$-${10}^{3}$ GeV mass range, one that may harbinger a new set of heavy particles. For an unstable neutrino, the optimal search strategy will be to study a final state of charged dileptons and jets without missing ${p}_{T}$. Dilepton charge signs or angular correlations can discriminate between Dirac and Majorana heavy neutrinos.