arXiv subjects

Sergey Kovalenko

Publications and source records attributed to Sergey Kovalenko.

At least 73 records · Page 4Linked to original sources

arXiv2013

Search for the Cosmic Neutrino Background and KATRIN

The spectrum of the Cosmic Microwave Background follows Planck's black body radiation formula and shows a remarkable constant temperature of T = 2.7. About 380 000 years after the Big Bang at a temperature of T = 3000 Kelvin in the matter dominated era the electrons combine with the protons and 4He and the photons move freely in the neutral universe. So the temperature and distribution of the photons give us information of the universe 380 000 years after the Big Bang. Information about earlier times can, in principle, be derived from the Cosmic Neutrino Background (relic neutrinos). The neutrinos decouple already about 1 second after the Big Bang at a temperature of around 1 MeV or 10^{10} Kelvin. Today their temperature is about 1.95 Kelvin. Registration of these neutrinos is an extremely challenging experimental problem, which can hardly be solved with the present technologies. On the other hand it represents a tempting opportunity to check one of key elements of the Big Bang Cosmology and to probe the early stages of the universe evolution. The search for the Cosmic Neutrino Background with the induced beta decay: relic neutrino + 3H --> 3He + e-, is the topic of this contribution. The signal would show up as a peak in the electron spectrum by an energy with the neutrino mass above the Q value. We discuss the prospects of this approach and argue that it is able to set limits on the Cosmic Neutrino density in our vicinity. We also discuss critically ways to increase with modifications of the present KATRIN spectrometer the Tritium source intensity by a factor 100, which would yield about 170 counts of relic neutrino captures per year. Presently such an increase of the Tritium source intensity seems not to be possible. But one should be able to find an upper limit for the local density of the relic neutrinos in our galaxy.

nucl-th↗

arXiv2013

Heavy neutrino searches at the LHC with displaced vertices

Sterile neutrinos with masses in the range (1-100) GeV, have been searched for in a variety of experiments. Here, we discuss the prospects to search for sterile neutrinos at the LHC using displaced vertices. Two different cases are discussed: (i) the standard model extended with sterile neutrinos and (ii) right-handed neutrinos in a left-right symmetric extension of the standard model. A dedicated displaced vertex search will allow to probe parts of the parameter space not accessible to other searches, but will require large luminosity in both cases.

hep-ph↗

arXiv2013

Sterile neutrinos in lepton number and lepton flavor violating decays

We study the contribution of massive dominantly sterile neutrinos, $N$, to the Lepton Number and Lepton Flavor Violating semileptonic decays of $τ$ and $B, D, K$-mesons. We focus on special domains of sterile neutrino masses $m_{N}$ where it is close to its mass-shell. This leads to an enormous resonant enhancement of the decay rates of these processes. This allows us to derive stringent limits on the sterile neutrino mass $m_{N}$ and its mixing $U_{αN}$ with active flavors. We apply a joint analysis of the existing experimental bounds on the decay rates of the studied processes. In contrast to other approaches in the literature our limits are free from ad hoc assumptions on the relative size of the sterile neutrino mixing parameters. We analyze the impact of this sort of assumptions on the extraction of the limits on $m_{N}$ and $U_{αN}$, and discuss the effect of finite detector size. Special attention was paid to the limits on meson decays with $e^{\pm}e^{\pm}$ in final state, derived from non-observation of $0νββ$-decay. We point out that observation of these decays may, in particular, shed light on the Majorana phases of the neutrino mixing matrix.

hep-ph↗

arXiv2013

Limits on Lepton Flavor Violation from μ-e-conversion

We revisit the status of Lepton Flavor Violating (LFV) μe qq contact interactions from the view point of μ- e -conversion in nuclei. We consider their contribution to this LFV process via the two mechanisms on the hadronic level: direct nucleon and meson exchange ones. In the former case the quarks are embedded directly into the nucleons while in the latter in mesons which then interact with nucleons in a nucleus. We revise and in some cases reevaluate the hadronic parameters relevant for both mechanisms and calculate the contribution of the above mentioned contact interactions in coherent μ- e -conversion in various nuclei. Then we update the existing upper bounds and also derive new ones for the scales of the μe qq contact interactions from the experimental limits on the capture rates of μ- e -conversion. We compare these limits with the ones derived in the literature from other LFV processes and comment on the prospects of LHC searches related to the contact μe qq interactions.

hep-ph↗

arXiv2011

Heavy Sterile Neutrinos in Tau Decays and the MiniBooNE Anomaly

Current results of the MiniBooNE experiment show excess events that indicate neutrino oscillations, but only if one goes beyond the standard 3 family scenario. Recently a different explanation of the events has been given, not in terms of oscillations but by the production and decay of a massive sterile neutrino with large transition magnetic moment. We study the effect of such a sterile neutrino in the rare decays $τ^- \rightarrow μ^- μ^+ π^- ν$ and $τ^{-}\rightarrow μ^{-} μ^{+} e^{-} νν$. We find that searches for these decays featuring displaced vertices between the $μ^-$ and the other charged particles, constitute good tests for the existence of the sterile neutrino proposed to explain the MiniBooNE anomaly. These searches could be done with already existing experimental data.

hep-ph↗

arXiv2011

New bounds on lepton flavor violating decays of vector mesons and the Z0 boson

We give an estimate for the upper bounds on rates of lepton flavor violating (LFV) decays M to mu(pm) + e(mp) of vector mesons M = rho0, omega, phi, J/psi, Upsilon and the Z0 boson in a model independent way, analyzing the corresponding lowest dimension effective operators. These operators also contribute to nuclear mu-e-conversion. Based on this observation and using the existing experimental limits on this LFV nuclear process, we show that the studied two-body LFV decays of vector bosons are strongly suppressed independent on the explicit realization of new physics. The upper limits on the rates of some of these decays are significantly more stringent than similar limits known in the literature. In view of these results experimental observation of the two-body LFV decays of vector bosons looks presently unrealistic.

hep-ph↗

arXiv2011

On Sterile neutrino explanation of LSND and MiniBooNE anomalies

We examine the compatibility between existing experimental data and a recently proposed explanation of the LSND and MiniBooNE anomalies, given in terms of a sterile neutrino $N$ whose decay is dominated by a radiative mode. We find that current experimental data on $τ\rightarrow μννγ$ decays are compatible with the sterile neutrino parameters required for the explanation of the anomalies, but $K\rightarrow μνγ$ shows a marginal tension with those parameters. We also propose experimental cuts on radiative $K$ decays that could test the sterile neutrino hypothesis better. Finally, we study the contribution of this sterile neutrino to $K\toμνe e$, and find that measurements of this process would provide powerful tests for the sterile neutrino explanation of the LSND and MiniBooNE anomalies, if the experimental cut on the invariant mass of the $e^{+}e^{-}$ pair could be reduced from its current value of 145 MeV to a value below 40 MeV.

hep-ph↗

arXiv2011

On sterile neutrino mixing with ν_τ

Matrix element $U_{τN}$ of sterile neutrino N mixing with $ν_τ$ is the least constrained in the literature among the three $U_{αN}$ ($α=e,μ,τ$) mixing parameters characterizing the sterile neutrino phenomenology. We study the contribution of massive dominantly sterile neutrinos to purely leptonic $τ$-decays and semileptonic decays of $τ$ and K, D mesons. We consider some decays allowed in the Standard Model (SM) as well as Lepton Flavor and Lepton Number Violating (LFV, LNV) decays forbidden in the SM. From the existing experimental data on the branching ratios of these processes we derived new limits on $U_{τN}$ more stringent than the ones existing in the literature. These limits are extracted in a model independent way without any ad hoc assumptions on the relative size of the three different sterile neutrino mixing parameters.

hep-ph↗

arXiv2011

Beta Decaying Nuclei as a Probe of Cosmic Neutrino Background

We analyze the possibility of detection of cosmological relic neutrinos via neutrino capture on beta decaying nuclei. This reaction has no threshold in neutrino energy, which is crucial for searching for relic neutrinos possessing very low energies. We focus on tritium (3H) and rhenium (187Re) beta radioactive isotopes to be used in KATRIN and MARE experiments dedicated to measurement of the electron neutrino mass at sub-eV scale. We examine these experiments from the viewpoint of searching for the cosmological neutrinos via neutrino capture. We conclude that even with possible gravitational clustering of relic neutrinos the prospects for their detection in these and other similar experiments are not optimistic. Nevertheless KATRIN and MARE experiments could establish some usefull constraints on density of relic neutrinos.

hep-ph↗

arXiv2010

Lepton number violation in theories with a large number of Standard Model copies

We examine lepton number violation (LNV) in theories with a saturated black hole bound on a large number of species. Such theories have been advocated recently as a possible solution to the hierarchy problem and an explanation of the smallness of neutrino masses. The violation of lepton number can be a potential phenomenological problem of this N-copy extension of the Standard Model as due to the low quantum gravity scale black holes may induce TeV scale LNV operators generating unacceptably large rates of LNV processes. We show, however, that this does not happen in this scenario due to a specific compensation mechanism between contributions of different Majorana neutrino states to these processes. As a result rates of LNV processes are extremely small and far beyond experimental reach, at least for the left-handed neutrino states.

hep-ph↗

arXiv2010

Lepton number, black hole entropy and 10 to the 32 copies of the Standard Model

Lepton number violating processes are a typical problem in theories with a low quantum gravity scale. In this paper we examine lepton number violation (LNV) in theories with a saturated black hole bound on a large number of species. Such theories have been advocated recently as a possible solution to the hierarchy problem and an explanation of the smallness of neutrino masses. Naively one would expect black holes to introduce TeV scale LNV operators, thus generating unacceptably large rates of LNV processes. We show, however, that this does not happen in this scenario due to a complicated compensation mechanism between contributions of different Majorana neutrino states to these processes. As a result rates of LNV processes are extremely small and far beyond experimental reach, at least for the left-handed neutrino states.

hep-ph↗

arXiv2010

B_s(d) - bar B_s(d) mixing constraints on flavor changing decays of t and b quarks

We study those dimension 6 effective operators which generate flavor-changing quark-gluon transitions of the third generation quarks, with t -> g + u(c) and b -> g + d(s), and which could be of interest for LHC experiments. We analyze the contribution of these operators to B_s(d) - bar B_s(d) mixing and derive limits on the corresponding effective couplings from the existing experimental data. The Standard Model gauge invariance relates these couplings to the couplings controlling t -> g + u(c). On this basis we derive upper limits for the branching ratios of these processes. We further show that forthcoming LHC experiments might be able to probe the studied operators and the physics beyond the Standard Model related to them.

hep-ph↗

arXiv2010

Lepton flavor violating decays of vector mesons

We estimate the rates of lepton flavor violating decays of the vector mesons $ρ, ω, ϕ\to e μ$. The theoretical tools are based on an effective Lagrangian approach without referring to any specific realization of the physics beyond the standard model responsible for lepton flavor violation (\Lfv). The effective lepton-vector meson couplings are extracted from the existing experimental bounds on the nuclear $μ^--e^-$ conversion. In particular, we derive an upper limit for the \Lfv branching ratio ${\rm Br}(ϕ\to e μ) \leq1.3 \times 10^{-21}$ which is much more stringent than the recent experimental result ${\rm Br}(ϕ\to e μ) < 2 \times 10^{-6}$ presented by the SND Collaboration. Very tiny limits on \Lfv decays of vector mesons derived in this letter make direct experimental observation of these processes unrealistic.

hep-ph↗

arXiv2009

Lepton Number Violating Processes Mediated by Majorana Neutrinos at Hadron Colliders

We study the Lepton number violating like-sign dilepton processes $h_1 h_2 \to l^\pm l^{\prime \pm} jj X$ and $h_1 h_2 \to l^\pm l^{\prime \pm} W^\pm X$, mediated by heavy GeV scale Majorana neutrinos. We focus on the resonantly enhanced contributions with a nearly on-mass-shell Majorana neutrino in the s-channel. We study the constraints on like-sign dilepton production at the Tevatron and the LHC on the basis of the existing experimental limits on the masses of heavy neutrinos and their mixings $U_{αN}$ with $α= ν_{e}, ν_μ, ν_τ$. Special attention is paid to the constraints from neutrinoless double beta decay. We note that searches for like-sign $e^{\pm} e^{\pm}$ events at Tevatron and LHC may shed light on CP-violation in neutrino sector. We also discuss the conditions under which it is possible to extract individual constraints on the mixing matrix elements in a model independent way.

hep-ph↗

arXiv2009

X(3872) as a hadronic molecule and its decays to charmonium states and pions

The X(3872) with quantum numbers J(PC) = 1(++) is considered as a composite hadronic state comprised of the dominant molecular D(0) D*(0) component and other hadronic pairs - D(+-) D*(-+), Jpsi omega and Jpsi rho. Applying the compositeness condition we constrain the couplings of the X(3872) to its constituents. We calculate two- and three-body hadronic decays of the X(3872) to charmonium states chi(cJ) and pions using a phenomenological Lagrangian approach. Next using the estimated X-Jpsi-omega and and X-Jpsi-rho couplings we calculate the widths of X(3872) to Jpsi + h, where h = pi(+) pi(-), pi(+) pi(-) pi(0), pi(0) gamma and gamma. The obtained results for the decay pattern of the X(3872) in a molecular interpretation could be useful for running and planned experiments.

hep-ph↗

arXiv2008

Pion dominance in RPV SUSY induced neutrinoless double beta decay

At the quark level there are basically two types of contributions of R-parity violating SUSY (RPV SUSY) to neutrinoless double beta decay: the short-range contribution involving only heavy virtual superpartners and the long-range one with the virtual squark and neutrino. Hadronization of the effective operators, corresponding to these two types of contributions, may in general involve virtual pions in addition to the close on-mass-shell nucleons. It is known that the short-range contribution is dominated by the pion exchange. In the present paper we show that this is also true for the long-range RPV SUSY contribution and, therefore, the RPV SUSY contributes to the neutrinoless double beta decay dominantly via charged pion exchange between the decaying nucleons.

hep-ph↗

arXiv2007

Ds0*(2317) and Ds1(2460) mesons in two-body B-meson decays

We analyze the branching ratios of B to D(*) + Ds0*(Ds1) decays using the factorization hypothesis. The B to D(*) transition form factors are taken from a model-independent analysis done by Caprini, Lellouch and Neubert based on heavy quark spin symmetry and dispersive constraints, including short-distance and power corrections. The leptonic decay constants fDs0* and fDs1 are calculated assuming a molecular structure for the Ds0* and Ds1 mesons. The calculated branching ratios of B-meson two-body decays are compared with experimental data and other theoretical results.

hep-ph↗

arXiv2007

Lepton Flavor Violating Photoleptonic Effect

We study lepton flavor violating analogs of the photoelectric effect, with a final $μ$ or $τ$ instead of an electron: $γe\to μ$ and $γe\to τ$. On the basis of the general parametrization of the matrix element of the electromagnetic current we estimate the upper limits for the cross sections and event rates of these processes, imposed by the current experimental bounds on $μ\to e γ$ and $τ\to e γ$ decays.

hep-ph↗