RAS Institute for Nuclear Research

Moscow, Russia

RAS Institute for Nuclear Research

Moscow, Russia

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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.


Gninenko S.N.,RAS Institute for Nuclear Research
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012

We report new limits on the π0→γX decay of the neutral pion into a photon and a new gauge boson X followed by the decay X→e +e -. If this process exists, one would expect a flux of high energy X's produced from π0's generated by the proton beam in a neutrino target. The X's would then penetrate the downstream shielding and be observed in a neutrino detector via their decays. Using bounds from the NOMAD and PS191 neutrino experiments at CERN that searched for an excess of e +e - pairs from heavy neutrino decays, stringent limits on the branching ratio as small as Br(π0→γX) 10 -15 are obtained. These limits are several orders of magnitude smaller than the previous experimental and cosmological bounds. The obtained results are used to constrain models, where the X interacts with quarks and leptons, or it is a new vector boson mixing with photons that transmits interaction between our world and hidden sectors consisting of SU(3) C×SU(2) L×U(1) Y singlet fields. © 2012 American Physical Society.


Matthies S.,RAS Institute for Nuclear Research
Journal of Applied Crystallography | Year: 2012

The recently developed GEO-MIX-SELF approximation (GMS) is applied to interpret the pressure dependence of the longitudinal ultrasonic wave velocities in a polycrystalline graphite sample that has already been investigated in a wide range of experimental contexts. Graphite single crystals have extremely anisotropic elastic properties, making this sample a challenging test to demonstrate the potential of the GMS method. GMS combines elements of well known self-consistent algorithms and of the geometric mean approximation. It is able to consider mixtures of different polycrystalline phases, each with its own nonspherical grain shape and preferred orientation (texture). Pores and cracks, typical for bulk graphite, are modeled as phases with empty grains. The pressure dependence (up to 150 MPa) of the experimental wave velocities can be well explained using the known texture of the sample by fitting the shape parameters and volume fractions of the graphite grains, cracks and spherical pores. The pressure dependence of these parameters describes a reasonable scenario for the closing of the cracks and pores with increasing pressure. © 2012 International Union of Crystallography Printed in Singapore-all rights reserved.


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.


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
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.


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.


Rubakov V.A.,RAS Institute for Nuclear Research
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

The null energy condition (NEC) can be violated in a consistent way in models with unconventional kinetic terms, notably, in Galileon theories and their generalizations. We make use of one of these, the scale-invariant kinetic braiding model, to discuss whether a universe can in principle be created by manmade processes. We find that, even though the simplest models of this sort can have both healthy Minkowski vacuum and a consistent NEC-violating phase, there is an obstruction for creating a universe in a straightforward fashion. To get around this obstruction, we design a more complicated model and present a scenario for the creation of a universe in the laboratory. © 2013 American Physical Society.


Gninenko S.N.,RAS Institute for Nuclear Research
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

Several models of dark matter suggest the existence of hidden sectors consisting of SU(3)C×SU(2)L×U(1)Y singlet fields. The interaction between the ordinary and hidden sectors could be transmitted by new Abelian U′(1) gauge bosons A ′ (dark or hidden photons) mixing with ordinary photons. If such A′'s have masses below the π0 meson mass, they would be produced through γ-A′ mixing in the π0→γ γ decays and be observed via decays A′→e +e-. Using bounds from the SINDRUM experiment at the Paul Scherrer Institute that searched for an excess of e+e- pairs in π-p interactions at rest, the area excluding the γ-A′ mixing Ïμâ‰10-3 for the A′ mass region 25â‰MA′ â‰120 MeV is derived. © 2013 American Physical Society.


Larin S.A.,RAS Institute for Nuclear Research
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2013

It is shown that the existing four-loop result for the Bjorken polarized sum rule for deep inelastic electron-nucleon scattering obtained within perturbative Quantum Chromodynamics should be supplemented by the calculation of the diagrams of the so-called singlet type. We also give an explanation of the interesting coincidence of two different classes of diagrams, one of the non-singlet and one of the singlet type, contributing the αs4-approximation to the total cross-section of electron-positron annihilation into hadrons. © 2013 Elsevier B.V.

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