Related papers: Heavy neutral leptons and high-intensity observabl…
Physics beyond the Standard Model can manifest itself as both new light states and heavy degrees of freedom. In this paper, we assume that the former comprise only a sterile neutrino, $N$. Therefore, the most agnostic description of the new…
The quasi-degeneracy of heavier sterile neutrino masses in the Neutrino Minimal Standard Model ($\nu$MSM) facilitates the production of lepton asymmetry below the electroweak scale. The first order loop corrections to this mass-difference…
We discuss weak kaon decays in a scenario in which the Standard Model is extended by massive sterile fermions. After revisiting the analytical expressions for leptonic and semileptonic decays we derive the expressions for decay rates with…
Lepton mixing, which requires physics beyond the Standard Model, is surprisingly compatible with a minimal, symmetryless and unbiased approach, called anarchy. This contrasts with highly involved flavor symmetry models. On the other hand,…
We discuss the possibility of flavor symmetries to explain the pattern of charged lepton and neutrino masses and mixing angles. We emphasize what are the obstacles for the generation of an almost maximal atmospheric mixing and what are the…
The addition of gauge singlet fermions to the Standard Model Lagrangian renders the neutrinos massive and allows one to explain all that is experimentally known about neutrino masses and lepton mixing by varying the values of the Majorana…
Heavy neutral leptons (HNLs) are motivated by attempts to explain neutrino masses and dark matter. If their masses are in the MeV to several GeV range, HNLs are light enough to be copiously produced at collider and accelerator facilities,…
Sterile neutrinos with masses $\sim 0.1$ eV or higher would play an important role in astrophysics and cosmology. We explore possible signatures of such sterile neutrinos at long baseline experiments. We determine the neutrino conversion…
All pieces of concrete evidence for phenomena outside the standard model (SM) - neutrino masses and dark matter - are consistent with the existence of new degrees of freedom that interact very weakly, if at all, with those in the SM. We…
We discuss the current status and future prospects of heavy neutrino searches at the energy frontier, which might play an important role in vindicating the simplest seesaw paradigm as the new physics responsible for neutrino mass…
An explicit form of charged--lepton mass matrix, predicting $m_\tau = 1776.80$ MeV from the experimental values of $m_e$ and $m_\mu$ (in good agreement with the experimental figure $m_\tau = 1777.05^{+0.29}_{-0.26}$ MeV), is applied to…
Taken at face value, current experimental data indicate the existence of a new particle, the sterile neutrino, which must be a singlet under the Standard Model gauge group. Although they are not detectable through traditional means, such…
The discovery of non-zero neutrino masses points to the likely existence of multiple SM neutral fermions. When such states are heavy enough that they cannot be produced in oscillations, they are referred to as Heavy Neutral Leptons (HNLs).…
Long-lived light particles (LLLPs) appear in many extensions of the standard model. LLLPs are usually motivated by the observed small neutrino masses, by dark matter or both. Typical examples for fermionic LLLPs (a.k.a. heavy neutral…
In this work we propose a simple extension of standard-model (SM) by adding eleven new particles to it. Three heavy leptons ($f_{e},\ f_{\mu},\ f_{\tau}$) singlet under the $SU(3)_{c}\times SU(2)_{L}$ carrying respective Lepton-Numbers,…
Lepton flavour violation and neutrino masses are a signal for new Physics beyond the Standard Model and are deeply related. The minimal extension of the Standard Model to make it include neutrino masses is not satisfactory from a conceptual…
Experiments aiming to detect coherent neutrino-nucleus scattering present opportunities to probe new light weakly-coupled states, such as sub-GeV mass dark matter, in several extensions of the Standard Model. These states can be produced…
The existence of extra chiral generations with all fermions heavier than $M_Z$ is strongly disfavored by the precision electroweak data. The exclusion of one additional generation of heavy fermions in SUSY extension of Standard Model is…
We use the LHC Higgs data to derive updated constraints on electroweak-scale sterile neutrinos that naturally occur in many low-scale seesaw extensions of the Standard Model to explain the neutrino masses. We also analyze the signal…
The smallness of neutrino masses provides a tantalizing allusion to physics beyond the standard model. Heavy neutral leptons ($N$), such as hypothetical sterile neutrinos, accommodate a way to explain this observation, through the see-saw…