Searching for sterile neutrinos fromπandKdecays

Abstract

The production of heavy sterile neutrinos from π − , K − decay at rest yields charged leptons with negative helicity (positive for π + , K + ). We obtain the branching ratio for this process and argue that a Stern-Gerlach filter with a magnetic field gradient leads to spatially separated domains of both helicity components with abundances determined by the branching ratio. Complemented with a search of the monochromatic peak, this setup can yield both the mass and mixing angles for sterile neutrinos with masses in the range 3 MeV m s 414 MeV in next generation high intensity experiments. We also study oscillations of light Dirac and Majorana sterile neutrinos with m s ≃ eV produced in meson decays including decoherence aspects arising from lifetime effects of the decaying mesons and the stopping distance of the charged lepton in short baseline experiments. We obtain the transition probability from production to detection via charged current interactions including these decoherence effects for 3 + 1 and 3 + 2 scenarios, also studying |∆L| = 2 transitions from ν ↔ ν oscillations for Majorana neutrinos and the impact of these effects on the determination of CP-violating amplitudes. We argue that decoherence effects are important in current short baseline accelerator experiments, leading to an underestimate of masses, mixing and CP-violating angles. At MiniBooNE/SciBooNE we estimate that these effects lead to an ∼ 15% underestimate for sterile neutrino masses m s 3 eV. We argue that reactor and current short baseline accelerator experiments are fundamentally different and suggest that in future high intensity experiments with neutrinos produced from π, K decay at rest, stopping the charged leptons on distances much smaller than the decay length of the parent meson suppresses considerably these decoherence effects.

Pre-slow-roll initial conditions: Large scale power suppression and infrared aspects during inflation

“…Recently in ref. [47] a detailed study of the impact of the fast-roll stage on non-Bunch Davies initial conditions for curvature perturbations and on the suppression of the low multipoles has been reported. The results of this reference are independent of the inflaton potential and suggest that a 5 − 10% suppression of the quadrupole is consistent with a fast roll stage with a ratio of kinetic to potential contributions 10 κ 100.…”

“…More recently a detailed analysis of modifications of power spectra for curvature and tensor perturbations from a kinetic dominated pre-slow roll stage has been reported [47].…”

“…[41][42][43][44][45][46] and more recently in ref. [47], ii) to assess how the modified initial conditions impact infrared phenomena in scalar fields. In particular we focus on the impact of non-Bunch-Davies initial conditions as a consequence of a pre-slow-roll stage on non-perturbative phenomena, such as dynamical mass generation, decay of quanta and superhorizon correlations arising from the quantum entanglement of the daughter particles.…”

Sterile neutrinos in leptonic and semileptonic decays

“…All experimental searches performed so far have led to negative results, allowing to set stringent limits for sterile neutrinos with masses in the MeV-GeV range and fuelling plans for future experiments [28].…”

Effect of steriles states on lepton magnetic moments and neutrinoless double beta decay

“…In addition to accommodating neutrino data [37][38][39][40][41], these extensions must comply with unitarity bounds [42,43], laboratory bounds [44], electroweak precision tests [23,45,46], LHC constraints (as those arising from Higgs decays) [24][25][26][27][28], bounds from rare decays [14,15,21,22] as well as cosmological constraints [10,47]. New sources of lepton number violation can trigger neutrinoless double beta decay (see, for example, [29]), and the sterile states can contribute to the decay rate: the additional mixings and possible new Majorana phases might enhance the effective mass, potentially rendering it within experimental reach, or even leading to the exclusion of certain regimes due to conflict with the current bounds (the most recent results on neutrinoless double beta decay have been obtained by the GERDA experiment [48]).…”