Heavy Sterile Neutrinos Research Articles

Do We Need Stars to Reionize the Universe at High Redshifts? Early Reionization by Decaying Heavy Sterile Neutrinos

A remarkable result of the Wilkinson Microwave Anisotropy Probe (WMAP) observations is that the universe was significantly reionized at large redshifts. The standard explanation is that massive stars formed early and reionized the universe around redshift z=17. Here we explore an alternative possibility, in which the universe was reionized in two steps. An early boost of reionization is provided by a decaying sterile neutrino, whose decay products, relativistic electrons, result in partial ionization of the smooth gas. We demonstrate that a neutrino with a mass of m_nu ~ 200 MeV and a decay time of t ~ 4 * 10^{15} s can account for the electron scattering optical depth tau=0.16 measured by WMAP without violating existing astrophysical limits on the cosmic microwave and gamma ray backgrounds. Reionization is then completed by subsequent star formation at lower redshifts. This scenario alleviates constraints on structure formation models with reduced small-scale power, such as those with a running or tilted scalar index, or warm dark matter models.

Cosmological and astrophysical bounds on a 33.9 MeV sterile neutrino

Abstract In this talk we discuss astrophysical and cosmological bounds on heavy sterile neutrino with mass mvs = 33.9MeV, which was suggested some time ago as a possible interpretation of KARMEN anomaly. Combine experimental data constrain lifetime of this particle in the window ∼ 10−1sec < TS < 150 sec. We show that SN 1987A completely excludes this range of vs lifetime. Nucleosynthesis bound permit a narrow window for the TS around 0.1 sec. If vs possesses an anomalous interaction with nucleons, the SN bounds may not apply, while the nucleosynthesis ones would remain valid.

Sterile neutrinos in tau lepton decays

We study possible contributions of heavy sterile neutrinos νh to the decays τ−→e±(μ±)π∓π−. From the experimental upper bounds on their rates we derive new constraints on the νh–ντ mixing in the mass region 140.5 MeV⩽mνh⩽1637 MeV. We discuss cosmological and astrophysical status of νh in this mass region and compare our constraints with those recently derived by the NOMAD Collaboration.

Heavy sterile neutrinos - what they can be and what they can't

We review current astrophysical bounds on MeV sterile neutrinos, and then we discuss why a sterile keV neutrino is a natural warm dark matter candidate.

Tau-sterile neutrino mixing in NOMAD

For several years, the KARMEN experiment was reporting an anomalous signal which was interpreted as a possible existence of heavy sterile neutrinos. The NOMAD experiment has the capability to search for such an isosinglet neutrino. It is assumed that the (ν s ) couples to the ν τ produced in the SPS neutrino beam at CERN. Analysis of NOMAD data leads to a single candidate event, compatible with the background expectations. This allows a limit to be set for the first time on the mixing strength between sterile and tau neutrinos, in the mass range 10 to 190 MeV.

Heavy sterile neutrinos: bounds from big-bang nucleosynthesis and SN 1987A

Cosmological and astrophysical effects of heavy (10 - 200 MeV) sterile Dirac neutrinos, mixed with the active ones, are considered. The bounds on mass and mixing angle from both supernovae and big-bang nucleosynthesis are presented.

Cosmological and astrophysical bounds on a heavy sterile neutrino and the KARMEN anomaly

Constraints on the lifetime of the heavy sterile neutrino, that was proposed as a possible interpretation of the KARMEN anomaly, are derived from primordial nucleosynthesis and SN 1987A. Together with the recent experimental bounds on the nu_s lifetime, SN 1987A completely excludes this interpretation. Nucleosynthesis arguments permit a narrow window for the lifetime in the interval 0.1-0.2 sec. If nu_s possesses an anomalous interaction with nucleons, the SN bounds may not apply, while the nucleosynthesis ones would remain valid.

Three neutrinoΔm2scales and the singular seesaw mechanism

It is shown that the singular seesaw mechanism can simultaneously explain all the existing data supporting nonzero neutrino masses and mixing. The three mass-squared differences that are needed to accommodate the atmospheric neutrino data (through $\nu_\mu - \nu_s$ oscillation), the solar neutrino data via MSW mechanism (through $\nu_e - \nu_\tau$ oscillation), and the positive result of $\nu_\mu - \nu_e$ oscillation from LSND can be generated by this mechanism, whereas the vacuum oscillation solution to the solar neutrino problem is disfavored. We find that the electron and tau neutrino masses are of order $10^{-3}$ eV, and the muon neutrino and a sterile neutrino are almost maximally mixed to give a mass of order 1 eV. Two heavy sterile neutrinos have a mass of order 1 keV which can be obtained by the double seesaw mechanism with an intermediate mass scale $\sim 10^5$ GeV. A possible origin of such a scale is discussed.

Cosmological baryon number and kaon CP violation from a common source.

We extend an earlier model for radiatively generated fermion masses based on the Pati-Salam group to include CP violation. Spontaneous CP violation in the early universe gives rise to a complex mass matrix for heavy sterile neutrinos. The out-of-equilibrium decay of these neutrinos generates a B-L asymmetry. The sterile neutrinos also act as a mass seed in generating one-loop (complex) mass matrices for the quarks. Thus, the two low energy manifestations of CP violation, the CKM phase and the baryon number asymmetry, can both be traced in a calculable way to a common source. \textcopyright{} 1996 The American Physical Society.

Heavy sterile neutrinos and neutrinoless double beta decay

We investigate the possibility of producing neutrinoless double beta decay without having an electron neutrino with a mass in the vicinity of 1 eV. We do so by having a much lighter electron neutrino mix with a much heavier ( m ⪆ 1 GeV ) sterile neutrino. We study the constraints on the masses and mixings of such heavy sterile neutrinos from existing laboratory, astrophysical and cosmological information, and discuss the properties it would require in order to produce a detectable signal in current searches for neutrinoless double beta decay.