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Gninenko S.N.,RAS Institute for Nuclear Research
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2011

This work has attempted to reconcile puzzling neutrino oscillation results from the LSND, KARMEN, and MiniBooNE experiments. We show that the LSND evidence for ν̄μ→ν̄e oscillations, its long-standing disagreement with the results from KARMEN, and the anomalous event excess observed by MiniBooNE in νμ and ν ̄μ data could all be explained by the existence of a heavy sterile neutrino (νh). All these results are found to be consistent with each other, assuming that the νh is created in νμ neutral-current interactions and decays radiatively into a photon and a light neutrino. Assuming the νh is produced through mixing with νμ, the combined analysis of the LSND and MiniBooNe excess events suggests that the νh mass is in the range from 40 to 80 MeV, the mixing strength is |Uμh|210-3-10 -2, and the lifetime is τνh10-9s. Surprisingly, this LSND-MiniBooNE parameter window is found to be unconstrained by the results from the most sensitive experiments. We set new limits on |U μh|2 for the favorable mass region from the precision measurements of the Michel spectrum by the TWIST experiment. The results obtained provide a strong motivation for a sensitive search for the νh in a near future K decay or neutrino experiments, which fit well in the existing and planned experimental programs at CERN or FNAL. The question of whether the heavy neutrino is a Dirac or Majorana particle is briefly discussed.© 2011 American Physical Society.

Rubakov V.A.,RAS Institute for Nuclear Research
Physics-Uspekhi | Year: 2014

A brief review is given of scalar field theories with second-derivative Lagrangians yielding second-order field equations. Some of these theories permit solutions that violate the null energy condition but otherwise show no obvious inconsistencies. The use of these theories in constructing cosmological scenarios and in the context of a laboratory-created universe is illustrated with examples. ©2014 Uspekhi Fizicheskikh Nauk, Russian Academy of Sciences.

Gninenko S.N.,RAS Institute for Nuclear Research
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2012

Several models of dark matter motivate the concept of hidden sectors consisting of SU(3) C×SU(2) L×U(1) Y singlet fields. The interaction between our and hidden matter could be transmitted by new abelian U '(1) gauge bosons A ' mixing with ordinary photons. If such A ''s with the mass in the sub-GeV range exist, they would be produced through mixing with photons emitted in decays of η and η ' neutral mesons generated by the high energy proton beam in a neutrino target. The A ''s would then penetrate the downstream shielding and be observed in a neutrino detector via their A '→e +e - decays. Using bounds from the CHARM neutrino experiment at CERN that searched for an excess of e +e - pairs from heavy neutrino decays, the area excluding the γ-A ' mixing range 10 -7≲ε≲10 -4 for the A ' mass region 1≲MA'≲500 MeV is derived. The obtained results are also used to constrain models, where a new gauge boson X interacts with quarks and leptons. New upper limits on the branching ratio as small as Br(η→γX)v10 -14 and Br(η '→γX)≲10 -12 are obtained, which are several orders of magnitude more restrictive than the previous bounds from the Crystal Barrel experiment. © 2012 Elsevier B.V.

Gninenko S.N.,RAS Institute for Nuclear Research
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

In addition to gravity, there might be another very weak interaction between the ordinary and dark matter transmitted by U′(1) gauge bosons A′ (dark photons) mixing with our photons. If such A′'s exist, they could be searched for in a light-shining-through-a-wall experiment with a high-energy electron beam. The electron energy absorption in a calorimeter (CAL1) is accompanied by the emission of bremsstrahlung A′'s in the reaction eZ→eZA′ of electrons scattering on nuclei due to the γ-A′ mixing. A part of the primary beam energy is deposited in the CAL1, while the rest of the energy is transmitted by the A′ through the "CAL1 wall" and deposited in another downstream calorimeter CAL2 by the e+e- pair from the A′→e+e- decay in flight. Thus, the A′'s could be observed by looking for an excess of events with the two-shower signature generated by a single high-energy electron in the CAL1 and CAL2. A proposal to perform such an experiment to probe the still unexplored area of the mixing strength 10-5ε 10-3 and masses MA 100MeV by using 10-300 GeV electron beams from the CERN SPS is presented. The experiment can provide complementary coverage of the parameter space, which is intended to be probed by other searches. It has also a capability for a sensitive search for A′'s decaying invisibly to dark-sector particles, such as dark matter, which could cover a significant part of the still allowed parameter space. © 2014 American Physical Society.

Alikhanov I.,RAS Institute for Nuclear Research
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2015

Reactions νlγ→W+l- (l=e, μ, τ) near the threshold s=mW+ml are analyzed. Two independent calculations of the corresponding cross sections (straightforward calculations using the Standard Electroweak Lagrangian and calculations in the framework of the parton model) are compared. It is shown that the Standard Electroweak Theory strongly suggests that these reactions proceed via the Glashow resonances. Accordingly, a hypothesis that the on-shell W bosons in the reactions νlγ→W+l- are the Glashow resonances is put forward. A role of these reactions for testing T symmetry is discussed. A model with T-violating Glashow resonances for description of the distribution of the TeV-PeV neutrino events recently observed by the IceCube Collaboration is presented. © 2015 The Author.

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