Search

We consider neutrino Minimal extension of the Standard Model ($\nu$MSM), which by introducing only three sterile neutrinos in sub electroweak region can explain active neutrino oscillations (via seesaw type I mechanism), baryon asymmetry of the Universe (leptogenesis via oscillations) and dark matter phenomena (with keV-scale sterile neutrino forming dark matter). We estimate sterile neutrino virtual contributions to various lepton flavor and lepton number violating processes. The contributions are too small, giving no chance for indirect searches to compete with direct measurements in exploring $\nu$MSM., Comment: 13 pages, 4 figures; replaced with the journal version

The Starobinsky model of modified gravity suggested to explain dark energy may be also considered in the astrophysical context. Recently it has been pointed out that in contracting regions curvature oscillations around the GR value may lead to the production of high energy particles which contribute to the cosmic ray flux. We revisit these calculations in the Einstein frame and show that the continuous approximation for the matter density used in the original calculations is not valid. We show that this problem is generic in $F(R)$-gravity models introduced to describe the dark energy. We go beyond the approximation and find the rate of particle production to be negligible., Comment: 9 pages; v2: replaced with revised version; v3: extended discussion, new appendix with 3 figures added, journal version

We study the creation of high energy SM particles in the Starobinsky model of dark energy (a variant of F(R)-gravity) inside the regions contracting due to the Jeans instability. In this modification of gravity the additional degree of freedom -- scalaron -- behaves as a particle with mass depending on matter density. So when the mass changes light scalarons could be created at a non-adiabatic stage. Later scalaron mass grows and could reach large values, even the value of 10^{13} GeV, favored by early-time inflation. Heavy scalarons decay contributing to the cosmic ray flux. We analytically calculated the number density of created particles for the case of exponential (Jeans) contraction and found it negligibly small provided the phenomenologically viable and cosmologically interesting range of model parameters. We expect similar results for a generic model of F(R)-gravity mimicking cosmological constant., Comment: 11 pages; prepared for a special issue of JETP dedicated to the 60th birthday of Valery Rubakov

For the Warm Dark Matter (WDM) candidates the momentum distribution of particles becomes important, since it can be probed with observations of Lyman-$\alpha$ forest structures and confronted with coarse grained phase space density in galaxy clusters. We recall the calculation bt Kaplinghat (2005) of the spectrum in case of dark matter non-thermal production in decays of heavy particles emphasizing on the inherent applicability conditions, which are rather restrictive and sometimes ignored in literature. Cold part of the spectrum requires special care when WDM is considered., Comment: 6 pages, 3 figures. Detailed discussion of the main points added to the paper

Renewed interest in GeV-scale sterile neutrinos capable of explaining active neutrino oscillations via see-saw type I mechanism has been expressed in several proposals of direct searches. Given this activity we estimate the minimal values of sterile-active mixing angles provided one, two, or three sterile neutrinos are lighter than D-meson., Comment: 7 pages, 2 figures

Recent cosmological data favour R^2-inflation and some amount of non-standard dark radiation in the Universe. We show that a framework of high energy scale invariance can explain these data. The spontaneous breaking of this symmetry provides gravity with the Planck mass and particle physics with the electroweak scale. We found that the corresponding massless Nambu--Goldstone bosons -- dilatons -- are produced at reheating by the inflaton decay right at the amount needed to explain primordial abundances of light chemical elements and anisotropy of the cosmic microwave background. Then we extended the discussion on the interplay with Higgs-inflation and on general class of inflationary models where dilatons are allowed and may form the dark radiation. As a result we put a lower limit on the reheating temperature in a general scale invariant model of inflation., Comment: 15 pages, 4 figures; v2: replaced with revised version recently published

We introduce conformal coupling of the Standard Model Higgs field to gravity and discuss the subsequent modification of $R^2$-inflation. The main observation is a lower temperature of reheating which happens mostly through scalaron decays into gluons due to the conformal (trace) anomaly. This modifies all predictions of the original $R^2$-inflation. To the next-to-leading order in slow roll parameters we calculate amplitudes and indices of scalar and tensor perturbations produced at inflation. The results are compared to the next-to-leading order predictions of $R^2$-inflation with minimally coupled Higgs field and of Higgs-inflation. We discuss additional features in gravity wave signal that may help to distinguish the proposed variant of $R^2$-inflation. Remarkably, the features are expected in the region available for study at future experiments like BBO and DECIGO. Finally, we check that (meta)stability of electroweak vacuum in the cosmological model is consistent with recent results of searches for the Higgs boson at LHC., Comment: 15 pages, 1 figure; replaced with journal version: tunnelling after inflation is studied

We show that the cusp in the dark matter (DM) distribution required to explain the recently found excess in the gamma-ray spectrum at energies ~130 GeV in terms of the DM annihilations cannot survive the tidal forces if it is offset by ~1.5^\circ from the Galactic centre as suggested by observations., Comment: 3 pages, replaced with journal version

We present three features which can be used to distinguish the R^2-inflation Higgs-inflation from with ongoing, upcoming and planned experiments, assuming no new physics (apart form sterile neutrinos) up to inflationary scale. (i) Slightly different tilt of the scalar perturbation spectrum n_s and ratio r of scalar-to-tensor perturbation amplitudes. (ii) Gravity waves produced within R^2-model by collapsing, merging and evaporating scalaron clumps formed in the post-inflationary Universe. (iii) Different ranges of the possible Standard Model Higgs boson masses, where the electroweak vacuum remains stable while the Universe evolves after inflation. Specifically, in the R^2-model Higgs boson can be as light as 116 GeV. These effects mainly rely on the lower reheating temperature in the R^2-inflation., Comment: 10 pages, updated to match the journal version (various clarifications added compared to v1)

We argue that the data published by the Pierre Auger Collaboration (arXiv:0711.2256) disfavor at 99% confidence level their hypothesis that most of the highest-energy cosmic rays are protons from nearby astrophysical sources, either Active Galactic Nuclei or other objects with a similar spatial distribution., Comment: 1000 words, 2 figures, scicite.sty

An extension of the Standard Model by three singlet fermions with masses smaller than the electroweak scale allows to explain simultaneously neutrino oscillations, dark matter and baryon asymmetry of the Universe. We discuss the properties of neutral leptons in this model and the ways they can be searched for in particle physics experiments. We establish, in particular, a lower and an upper bound on the strength of interaction of neutral leptons coming from cosmological considerations and from the data on neutrino oscillations. We analyse the production of neutral leptons in the decays of different mesons and in $pp$ collisions. We study in detail decays of neutral leptons and establish a lower bound on their mass coming from existing experimental data and Big Bang Nucleosynthesis. We argue that the search for a specific missing energy signal in kaon decays would allow to strengthen considerably the bounds on neutral fermion couplings and to find or definitely exclude them below the kaon threshold. To enter into cosmologically interesting parameter range for masses above kaon mass the dedicated searches similar to CERN PS191 experiment would be needed with the use of intensive proton beams. We argue that the use of CNGS, NuMI, T2K or NuTeV beams could allow to search for singlet leptons below charm in a large portion of the parameter space of the nuMSM. The search of singlet fermions in the mass interval 2-5 GeV would require a considerable increase of the intensity of proton accelerators or the detailed analysis of kinematics of more than 10^{10} B-meson decays., Comment: 45 pages, 17 figures; v2: references added, journal version

It is shown by an explicit calculation that the excitations about the self-accelerating cosmological solution of the Dvali--Gabadaze--Porrati model contain a ghost mode. This raises serious doubts about viability of this solution. Our analysis reveals the similarity between the quadratic theory for the perturbations around the self-accelerating Universe and an Abelian gauge model with two Stueckelberg fields., Comment: Revtex, 9 pages, no figures

We present a complete description of a new physical model with goldstino supermultiplet for CompHEP software package. The model contains MSSM content supplemented by three new fields: {\it goldstino} -- two component spinor, scalar {\it sgoldstino} and pseudoscalar {\it sgoldstino}. To the leading order in 1/F, where F is the parameter of supersymmetry breaking, and to zero order in MSSM gauge and Yukawa coupling constants, the interactions between the component fields of goldstino supermultiplet and MSSM fields are derived. They correspond to the most attractive for collider studies processes where only one of these {\it new} particles appears in a final state. In this case light gravitino behaves exactly as goldstino. For sgoldstinos, as they are R-even, we include in the package only sgoldstino couplings to goldstino and sgoldstino couplings to SM fields as the most interesting phenomenologically. All new coupling constants between the components of goldstino supermultiplet and MSSM fields are completely determined by the ratios of soft supersymmetry breaking parameters and F. Thus, in addition to the MSSM coupling constants there are three new parameters in the package: the scale of supersymmetry breaking, $\sqrt{F}$, and masses of scalar and pseudoscalar sgoldstinos. The CompHEP notations for the new fields and parameters are presented. The package was successfully tested and all relevant results known in literature have been reproduced with good accuracy. It may be used in order to calculate any tree-level process with one gravitino or sgoldstino on mass shell. Universality of the Lagrangian allows to apply the package in study of phenomenology of any supersymmetric extension of the Standard Model., Comment: 10 pages; the software package is available at http://theory.sinp.msu.ru/~semenov/mssm.html