arXiv subjects

S. G. Kovalenko

Publications and source records attributed to S. G. Kovalenko.

At least 37 records · Page 2Linked to original sources

arXiv2007

Leptoquarks: Neutrino masses and accelerator phenomenology

Leptoquark-Higgs interactions induce mixing between leptoquark states with different chiralities once the electro-weak symmetry is broken. In such LQ models Majorana neutrino masses are generated at 1-loop order. Here we calculate the neutrino mass matrix and explore the constraints on the parameter space enforced by the assumption that LQ-loops explain current neutrino oscillation data. LQs will be produced at the LHC, if their masses are at or below the TeV scale. Since the fermionic decays of LQs are governed by the same Yukawa couplings, which are responsible for the non-trivial neutrino mass matrix, several decay branching ratios of LQ states can be predicted from measured neutrino data. Especially interesting is that large lepton flavour violating rates in muon and tau final states are expected. In addition, the model predicts that, if kinematically possible, heavier LQs decay into lighter ones plus either a standard model Higgs boson or a $Z^0/W^{\pm}$ gauge boson. Thus, experiments at the LHC might be able to exclude the LQ mechanism as explanation of neutrino data.

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arXiv2000

A superformula for neutrinoless double beta decay II: The short range part

A general Lorentz-invariant parameterization for the short-range part of the 0vBB decay rate is derived. Combined with the long range part already published this general parameterization in terms of effective B-L violating couplings allows one to extract the 0vBB limits on arbitrary lepton number violating theories.

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arXiv1999

Towards a superformula for neutrinoless double beta decay

A general Lorentz--invariant parameterization for the long-range part of the $0νββ$ decay rate is derived. Combined with the short range part this general parameterization in terms of effective $B-L$ violating couplings will allow it to extract the $0νββ$ limits on arbitrary lepton number violating theories. Several new nuclear matrix elements appear in the general formalism compared to the standard neutrino mass mechanism. Some of these new matrix elements have never been considered before and are calculated within pn-QRPA. Using these, limits on lepton number violating parameters are derived from experimental data on $^{76}$Ge.

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arXiv1998

On Prospects for Exploration of Supersymmetry in Double Beta Decay Experiments

We analyze constraints on the parameters of the R-parity violating supersymmetry which can be extracted from non-observation of the neutrinoless nuclear double beta decay ($0νββ$) at a given half-life lower bound. Our analysis covers a large class of phenomenologically viable R-parity violating SUSY models. We introduce special characteristics: the SUSY sensitivity of a $ββ$ decaying isotope and the SUSY reach of a $0νββ$ experiment. The former provides a physical criterion for a selection of the most promising isotopes for SUSY searches and the latter gives a measure of success for a $0νββ$ experiment in exploring the R-parity violating SUSY parameter space. On this basis we discuss prospects for exploration of supersymmetry in various $0νββ$ experiments.

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arXiv1997

A general parametrization for the long-range part of neutrinoless double beta decay

Double beta decay has been proven to be a powerful tool to constrain $B-L$ violating physics beyond the standard model. We present a representation for the long-range part of the general $0νββ$ decay rate allowed by Lorentz-invariance. Combined with the short range part this general parametrization in terms of effective $B-L$ violating couplings will provide the $0νββ$ limits on arbitrary lepton number violating theories.

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arXiv1997

R-parity Conserving Supersymmetry, Neutrino Mass and Neutrinoless Double Beta Decay

We consider contributions of R-parity conserving softly broken supersymmetry (SUSY) to neutrinoless double beta ($\znbb$) decay via the (B-L)-violating sneutrino mass term. The latter is a generic ingredient of any weak-scale SUSY model with a Majorana neutrino mass. The new R-parity conserving SUSY contributions to $\znbb$ are realized at the level of box diagrams. We derive the effective Lagrangian describing the SUSY-box mechanism of $\znbb$-decay and the corresponding nuclear matrix elements. The 1-loop sneutrino contribution to the Majorana neutrino mass is also derived. Given the data on the $\znbb$-decay half-life of $^{76}$Ge and the neutrino mass we obtain constraints on the (B-L)-violating sneutrino mass. These constraints leave room for accelerator searches for certain manifestations of the 2nd and 3rd generation (B-L)-violating sneutrino mass term, but are most probably too tight for first generation (B-L)-violating sneutrino masses to be searched for directly.

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arXiv1997

B-L-violation in Softly Broken Supersymmetry and Neutrinoless Double Beta Decay

We prove a low-energy theorem valid for any model of weak scale softly broken supersymmetry. It claims that the neutrino Majorana mass, the B-L violating mass of the sneutrino and the neutrinoless double beta decay amplitude are intimately related to each other such that if one of them is non-zero the other two are also non-zero and, vice versa, if one of them vanishes the other two vanish as well. The theorem is a consequence of the underlying supersymmetry and independent of the mechanisms of neutrinoless double beta decay and (s-)neutrino mass generation.

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arXiv1997

B-L-violating Masses in Softly Broken Supersymmetry

We prove a general low-energy theorem establishing a generic relation between the neutrino Majorana mass and the superpartner sneutrino B-L-violating "Majorana"-like mass term. The theorem states that, if one of these two quantities is non-zero the other one is also non-zero and, vice versa, if one of them vanishes the other vanishes, too. The theorem is a consequence of the underlying supersymmetry (SUSY) and valid for any realistic gauge model with weak scale softly broken SUSY.

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arXiv1996

Superlight neutralino as a dark matter particle candidate

We address the question of how light can be the lightest supersymmetric particle neutralino to be a reliable cold dark matter (CDM) particle candidate. To this end we have performed a combined analysis of the parameter space of the Minimal Supersymmetric Standard Model (MSSM) taking into account cosmological and accelerator constraints including those from the radiative $b\rightarrow sγ$ decay. Appropriate grand unification (GUT) scenarios were considered. We have found that the relaxation of gaugino mass unification is sufficient to obtain a phenomenologically and cosmologically viable solution of the MSSM with the neutralino as light as 3~GeV. We have found good prospects for direct detection of these superlight CDM neutralinos via elastic scattering off various nuclei in the forthcoming experiments with low-threshold DM detectors. In a certain sense, these experiments can probe the gaugino mass unification giving constraints on the possible GUT scenarios within the MSSM.

hep-ph↗

arXiv1996

Is SUSY accessible by direct dark matter detection?

We performed a combined analysis of the parameter space of the Minimal Supersymmetric Standard Model (MSSM) taking into account cosmological and accelerator constraints including those from the radiative $b\rightarrow sγ$ decay measured by the CLEO collaboration. Special attention is paid to the event rate, $R$, of direct dark matter neutralino detection. We have found domains of the parameter space with $R\simeq 5-10$~events/kg/day. This would be within the reach of current dark matter experiments. The $b\rightarrow sγ$ data do not essentially reduce these large event rate domains of the MSSM parameter space.

hep-ph↗

arXiv1996

Combined Fit of Low Energy Constraints to Minimal Supersymmetry and Discovery Potential at LEP II

Within the Constrained Minimal Supersymmetric Standard Model it is possible to predict the low energy gauge couplings and masses of the 3. generation particles from a few parameters at the GUT scale. In addition the MSSM predicts elektroweak symmetry breaking due to large radiative corrections from Yukawa couplings, thus relating the Z^0 boson mass to the top quark mass. From a χ^2 analysis, in which these constraints can be considered simultaneously, one can calculate the probability for each point in the MSGUT parameter space. Our fits include full second order corrections for the gauge and Yukawa couplings, low energy treshold effects, contributions of all (s)particles to the Higgs potential and corrections to m_b from qluinos and higgsinos, which exclude (in our notation) positive values of the mixing parameter in the Higgs potential μfor the large tan βregion. Further constraints can be derived from the branching ratio for the radiative (penguin) decay of the b-quark into s γand the lower limit on the lifetime of the universe, which requires the dark matter density due to the Lightest Supersymmetric Particle (LSP) not to overclose the universe. For particles, which are most likely to have masses in the LEP II energy range, the cross sections are given for the various energy scenarios at LEP II. For low tan βthe production of the lightest Higgs boson, which is expected to have a mass below 103 GeV, is the most promising channel, while for large tan βthe production of charginos and/or neutralinos covers the preferred parameter space.

hep-ph↗

arXiv1996

New Leptoquark Mechanism of Neutrinoless Double Beta Decay

A new mechanism for neutrinoless double beta ($\znbb$) decay based on leptoquark exchange is discussed. Due to the specific helicity structure of the effective four-fermion interaction this contribution is strongly enhanced compared to the well-known mass mechanism of $\znbb$ decay. As a result the corresponding leptoquark parameters are severely constrained from non-observation of $\znbb$-decay. These constraints are more stringent than those derived from other experiments.

hep-ph↗

arXiv1996

New Low-energy Leptoquark Interactions

We discuss an extension of the standard model (SM) with vector and scalar leptoquarks. The renormalizable leptoquark Lagrangian consistent with the SM gauge symmetry is presented including the leptoquark-Higgs interactions previously not considered in the literature. We discuss the importance of these new interactions for leptoquark phenomenology. After the electro-weak symmetry breaking they generate non-trivial leptoquark mass matrices. These lead to mixing between different $SU(2)_L$-multiplets of the leptoquarks and induce at low energies new effective 4-fermion lepton-quark vertices. The latter affect the standard leptoquark phenomenology. We discuss constraints on these interactions from the helicity-suppressed $π\rightarrow ν+ e$ decay.

hep-ph↗

arXiv1995

On the SUSY Accompanied Neutrino Exchange Mechanism of Neutrinoless Double Beta Decay

The neutrinoless double beta decay ($\znbb$) induced by light Majorana neutrino exchange between decaying nucleons, accompanied by the squark exchange inside one nucleon, recently discussed by Babu and Mohapatra, is carefully analyzed both from the particle and nuclear physics sides. New nuclear matrix elements relevant to this mechanism are calculated. We extend the analysis to include mixing of light neutrinos with heavy and "sterile" neutrinos. It introduces another supersymmetric (SUSY) contribution to $\znbb$. We discuss constraints on the \rp MSSM parameters imposed by the current experimental limit on $\znbb$ decay half-life of $^{76}$Ge.

hep-ph↗

arXiv1995

On the observability of Majoron emitting double beta decays

Because of the fine--tuning problem in classical Majoron models in recent years several new models were invented. It is pointed out that double beta decays with Majoron emission depend on new matrix elements, which have not been considered in the literature. A calculation of these matrix elements and phase space integrals is presented. We find that for new Majoron models extremely small decay rates are expected.

hep-ph↗

arXiv1995

Expectations for Supersymmetric Dark Matter Searches Underground

We consider the neutralino as a dominant Dark Matter particle in the galactic halo and investigate some general issues of direct Dark Matter searches via elastic neutralino-nucleus scattering. On the basis of conventional assumptions about the nuclear and nucleon structure we analyse constraints on SUSY model parameter space accessible by the direct Dark Matter searches. This analysis shows that Dark Matter detectors fall into the THREE different categories with respect to their sensitivity to different groups of the SUSY model parameters. We calculate the event rate for various experimentally interesting isotopes within the Minimal Supersymmetric Standard Model (MSSM) taking into account the known accelerator and cosmological constraints on the MSSM parameter space. We investigate the role of nuclear spin in elastic neutralino - nucleus scattering. It is found that the contribution of the spin-dependent interaction to this process is subdominant for nuclei with atomic weights A > 50.

hep-ph↗

arXiv1995

Combined Fit of Low Energy Constraints to Minimal Supersymmetry and Discovery Potential at LEP II

Within the Constrained Minimal Supersymmetric Standard Model (CMSSM) it is possible to predict the low energy gauge couplings and masses of the 3.generation particles from a few parameters at the GUT scale, and electroweak symmetry breaking. Further constraints can be derived from the branching ratio for the radiative (penguin) decay of the b-quark into s gamma and the lower limit on the lifetime of the universe, which requires the dark matter density due to the Lightest Supersymmetric Particle (LSP) not to overclose the universe. From a chi^2 analysis, in which these constraints can be considered simultaneously, one can calculate the probability for each point in the MSGUT parameter space. The recently measured top quark mass prefers two solutions for the mixing angle in the Higgs sector: tan beta in the range between 1 and 3 or alternatively tan beta approx 25-50. For both cases we find a unique chi^2 minimum in the parameter space. For the low tan beta solution these additional constraints can be fulfilled simultaneously for quite a large region of the parameter space. In contrast, for the high tan beta solution the correct value for the b --> s gamma rate is obtained only for small values of the gaugino scale. For particles, which are most likely to have masses in the LEP II energy range, the cross sections are given for the various energy scenarios at LEP II. The highest LEP II energies (205 GeV) are just high enough to cover a large region of the preferred parameter space, both for the low and high tan beta solutions. For low tan beta the production of the lightest Higgs boson, which is expected to have a mass below 115 GeV, is the most promising channel, while for large tan beta the production of charginos and/or neutralinos covers the preferred parameter space.

hep-ph↗

arXiv1995

Supersymmetry and Neutrinoless Double Beta Decay

Neutrinoless double beta decay ($\znbb$) induced by superparticle exchange is investigated. Such a supersymmetric (SUSY) mechanism of $\znbb$ decay arises within SUSY theories with R-parity non-conservation (\rp). We consider the minimal supersymmetric standard model (MSSM) with explicit \rp terms in the superpotential (\rp MSSM). The decay rate for the SUSY mechanism of $\znbb$ decay is calculated. Numerical values for nuclear matrix elements for the experimentally most interesting isotopes are calculated within pn-QRPA. Constraints on the \rp MSSM parameter space are extracted from current experimental half-life limits. The most stringent limits are derived from data on $^{76}$Ge. It is shown that these constraints are more stringent than those from other low-energy processes and are competitive to or even more stringent than constraints expected from accelerator searches.

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