Mixing of active and sterile neutrinos

Self Cite

We explore the feasibility of detecting heavy neutrinos by the existing facilities of neutrino experiments. A heavy neutrino in the mass range 1 MeV M N 500 MeV is produced by pion or kaon decay, and decays to charged particles which leave signals in neutrino detectors. Taking the T2K experiment as a typical example, we estimate the heavy neutrino flux produced in the neutrino beam line. Due to massive nature of the heavy neutrino, the spectrum of the heavy neutrino is significantly different from that of the ordinary neutrinos. While the ordinary neutrinos are emitted to various directions in the laboratory frame due to their tiny masses, the heavy neutrinos tend to be emitted to the forward directions and frequently hit the detector. The sensitivity for the mixing parameters is studied by evaluating the number of signal events in the near detector ND280. For the electron-type mixing, the sensitivity of T2K at 10 21 POT is found to be better than that of the previous experiment PS191, which has placed the most stringent bounds on the mixing parameters of the heavy neutrinos for 140 MeV M N 500 MeV. IntroductionIn the last few decades, neutrino oscillation experiments have conclusively shown that neutrinos are massive [1]. The minimal version of the Standard Model is thus to be extended to accommodate the neutrino masses. In many possible extension of the Standard Model, neutral heavy leptons are often predicted. In the seesaw mechanism [2] for example, the right-handed neutrinos are introduced and they weakly mix with the ordinary neutrinos after the electroweak symmetry breaking.For the masses of the heavy neutrinos, a wide range of possibilities has been discussed in literature. In the canonical picture of the seesaw mechanism, heavy neutrino masses are supposed to be around the grand unification scale. These super-heavy neutrinos can account for the baryon asymmetry of the universe by the leptogenesis [3]. Another possibility to account for the baryon asymmetry has been suggested in [4,5] and further studied in [6]. In this scenario, two quasi-degenerate heavy neutrinos of O(100) MeV −O(10) GeV play a crucial role in the early universe. Heavy neutrinos in the mass range ∼ 0.2 GeV could enhance the energy transport from the core to the stalled shock and favor the supernova explosion [7]. Heavy neutrinos with a few keV mass have also attracted much interests as a viable dark matter candidate [8] and an agent of the pulsar velocities [9].Remarkably, the dark matter and the baryon asymmetry due to keV and GeV heavy neutrinos can originate in a simple framework so called νMSM [10,5], which is an extension of the Standard Model with just three generations of the right-handed neutrinos.Besides the super-heavy range much larger than TeV, such heavy neutrinos can be tested in existing and forthcoming experiments due to lower threshold energies of production (for example, see Ref. [11,12] and references therein).In this paper, we focus on the heavy neutrinos produced by kaon decays. The previous neutrino exper...

“…8). In addition, heavy neutrinos with masses smaller than O(100) MeV may give a significant effect on the neutrinoless double beta decays [39]. According to a rough estimation in Table 1 …”

Section: Discussionmentioning

confidence: 99%

Heavy neutrino search in accelerator-based experiments

Asaka

Eijima

Watanabe

2013

Self Cite

“…To avoid tension with the observed abundances of light elements in the intergalactic medium, they should be sufficiently short lived that their decay does not disturb the primordial nucleosynthesis [18]. Together with experimental constraints [19,20] this imposes a lower bound of roughly M i > 100 MeV on those N i that participate in neutrino mass generation. 1 The NA62 experiment [28] can probe precisely this mass range.…”

Section: Jhep07(2018)105mentioning

confidence: 99%

“…The smaller mass difference ("solar mass difference") is given by ∆m authors, see e.g. [16,19,20,31,37,38,[63][64][65]. The constraints depend on the number n of heavy neutrinos.…”

Section: Jhep07(2018)105mentioning

confidence: 99%

NA62 sensitivity to heavy neutral leptons in the low scale seesaw model

Drewes¹,

Hajer²,

Klarić³

et al. 2018

103

129

The sensitivity of beam dump experiments to heavy neutral leptons depends on the relative strength of their couplings to individual lepton flavours in the Standard Model. We study the impact of present neutrino oscillation data on these couplings in the minimal type I seesaw model and find that it significantly constrains the allowed heavy neutrino flavour mixing patterns. We estimate the effect that the DUNE experiment will have on these predictions. We then discuss implication that this has for the sensitivity of the NA62 experiment when operated in the beam dump mode and provide sensitivity estimates for different benchmark scenarios. We find that the sensitivity can vary by almost two orders of magnitude for general choices of the model parameters, but depends only weakly on the flavour mixing pattern within the parameter range that is preferred by neutrino oscillation data.

“…Other works have also considered a low-scale warped hidden sector [50][51][52] and for another use of bulk sterile neutrinos see [53]. Light sterile-neutrinos have been studied extensively within the context of the νMSM [54][55][56][57] and for a discussion of the low-scale (GeV) seesaw see [58]. Ref.…”

Section: Jhep07(2011)103mentioning

confidence: 99%

“…we do not assume any tuned cancellations of leading terms [57,58]). With the information from the previous sections one can calculate the the above factor and determine the size of the 0νββ-decay amplitude.…”

Section: Jhep07(2011)103mentioning

confidence: 99%

Neutrino mass and μ → e + γ from a mini-seesaw

Duerr

George

McDonald

2011

Abstract:The recently proposed "mini-seesaw mechanism" combines naturally suppressed Dirac and Majorana masses to achieve light Standard Model neutrinos via a lowscale seesaw. A key feature of this approach is the presence of multiple light (order GeV) sterile-neutrinos that mix with the Standard Model. In this work we study the bounds on these light sterile-neutrinos from processes like µ → e+ γ, invisible Z-decays, and neutrinoless double beta-decay. We show that viable parameter space exists and that, interestingly, key observables can lie just below current experimental sensitivities. In particular, a motivated region of parameter space predicts a µ → e + γ branching fraction within the range to be probed by MEG.