arXiv subjects

Fedor Simkovic

Publications and source records attributed to Fedor Simkovic.

At least 55 records · Page 3Linked to original sources

arXiv2008

Anatomy of nuclear matrix elements for neutrinoless double-beta decay

We show that, within the Quasiparticle Random Phase Approximation (QRPA) and the renormalized QRPA (RQRPA) based on the Bonn CD nucleon-nucleon interaction, the competition between the pairing and the neutron-proton particle-particle and particle-hole interactions causes contributions to the neutrinoless double-beta decay matrix element to nearly vanish at internucleon distances of more than 2 or 3 fermis. As a result, the matrix element is more sensitive to short-range/high-momentum physics than one naively expects. We analyze various ways of treating that physics and quantify the uncertainty it produces in the matrix elements, with three different treatments of short-range correlations.

nucl-th↗

arXiv2007

Nuclear and particle physics aspects of the 2nbb-decay of 150Nd

A discussion is given on possible realization of the Single State Dominance (SSD) hypothesis in the case of the two-neutrino double beta decay(2nbb-decay) of 150Nd with 1^- ground state of the intermediate nucleus. We conclude that the SSD hypothesis is expected to be ruled out by precision measurement of differential characteristics of this process in running NEMO 3 or planed SuperNEMO experiments unlike some unknown low-lying 1^+ state of 150Pm does exist. This problem can be solved via (d,2He) charge-exchange experiment on 150Sm. Further, we address the question about possible violation of the Pauli exclusion principle for neutrinos and its consequences for the energy distributions of the 2nbb-decay of 150Nd. This phenomenon might be a subject of interest of NEMO 3 and SuperNEMO experiments as well.

hep-ph↗

arXiv2006

Transition magnetic moments of Majorana neutrinos in supersymmetry without R-parity in light of neutrino oscillations

The transition magnetic moments of Majorana neutrinos are calculated in grand unified theory (GUT) constrained Minimal Supersymmetric Standard Model (MSSM) with explicit R-parity violation. It is assumed that neutrinos acquire masses via one-loop (quark-squark and lepton-slepton) radiative corrections. The mixing of squarks, sleptons, and quarks is considered explicitly. The connection between neutrino magnetic moments and the entries of neutrino mass matrix is studied. The current upper limits on neutrino magnetic moments are deduced from the elements of phenomenological neutrino mass matrix, which is reconstructed using the neutrino oscillation data and the lower bound on the neutrinoless double beta decay half-life. Further, the results for transitional magnetic moments of Majorana neutrinos are presented for the cases of inverted and normal hierarchy of neutrino masses and different SUSY scenarios. The largest values are of the order of 10^{-17} in units of Bohr magneton.

hep-ph↗

arXiv2006

Uncertainties in the $0νββ$--decay nuclear matrix elements

The nuclear matrix elements $M^{0ν}$ of the neutrinoless double beta decay ($0νββ$) of most nuclei with known $2νββ$-decay rates are systematically evaluated using the Quasiparticle Random Phase Approximation (QRPA) and Renormalized QRPA (RQRPA). The experimental $2νββ$-decay rate is used to adjust the most relevant parameter, the strength of the particle-particle interaction. With such procedure the $M^{0ν}$ values become essentially independent on single-particle basis size, the axial vector quenching factor, etc. Theoretical arguments in favor of the adopted way of determining the interaction parameters are presented. It is suggested that most of the spread among the published $M^{0ν}$'s can be ascribed to the choices of implicit and explicit parameters, inherent to the QRPA method.

nucl-th↗

arXiv2004

Neutrino mass in GUT constrained supersymmetry with R-parity violation in light of neutrino oscillations

The neutrino masses are generated in grand unified theory (GUT) constrained supersymmetric model with R-parity violation. The neutrinos acquire masses via tree-level neutrino-neutralino mixing as well as via one-loop radiative corrections. The theoretical mass matrix is compared with the phenomenological one, which is reconstructed by using neutrino oscillation and neutrinoless double beta decay data. This procedure allows to obtain significantly stronger constraints on R-parity breaking parameters than those existing in the literature. The implication of normal and inverted neutrino mass hierarchy on the sneutrino expectation values, lepton-Higgs bilinear and trilinear R-parity breaking couplings is also discussed.

hep-ph↗

arXiv2004

Nuclear muon-positron conversion mediated by Majorana neutrinos

We study lepton number violating (LNV) process of muon-positron conversion in nuclei mediated by the exchange of light and heavy Majorana neutrinos. Nuclear structure calculations have been carried out for the case of experimentally interesting nucleus 48Ti in the framework of renormalized proton-neutron Quasiparticle Random Phase Approximation. We demonstrate that the imaginary part of the amplitude of light Majorana neutrino exchange mechanism gives an appreciable contribution to the muon-positron conversion rate. This specific feature is absent in the allied case of neutrinoless double beta decay. Using the present neutrino oscillations, tritium beta decay, accelerator and cosmological data we derived the limits on the effective masses of light _{μe} and heavy _{μe} neutrinos. The expected rates of muon-positron nuclear conversion, corresponding to these limits, were found to be so small that even within a distant future the muon-positron conversion experiments will hardly be able to detect the neutrino signal. Therefore, searches for this LNV process can only rely on the presence of certain physics beyond the trivial extension of the Standard Model by inclusion of massive Majorana neutrinos.

nucl-th↗

arXiv2003

Proton-neutron pairing in the deformed BCS approach

We examine isovector and isoscalar proton-neutron pairing correlations for the ground state of even-even Ge isotopes with mass number A=64-76 within the deformed BCS approach. For N=Z 64Ge the BCS solution with only T=0 proton-neutron pairs is found. For other nuclear systems (N>Z) a coexistence of a T=0 and T=1 pairs in the BCS wave function is observed. A problem of fixing of strengths of isoscalar and isovector pairing interactions is addressed. A dependence of number of like and unlike pairs in the BCS ground state on the difference between number of neutrons and protons is discussed. We found that for nuclei with N much bigger than Z the effect of proton-neutron pairing is small but not negligible.

nucl-th↗

arXiv2003

Two-neutrino double beta decay of 76Ge within deformed QRPA: A new suppression mechanism

The effect of deformation on the two-neutrino double decay (2nbb-decay) for ground state transition 76Ge -> 76Se is studied in the framework of the deformed QRPA with separable Gamow-Teller residual interaction. A new suppression mechanism of the 2nbb-decay matrix element based on the difference in deformations of the initial and final nuclei is included. An advantage of this suppression mechanism in comparison with that associated with ground state correlations is that it allows a simultaneous description of the single beta and the 2nbb-decay. By performing a detail calculation of the 2nbb-decay of 76Ge, it is found that the states of intermediate nucleus lying in the region of the Gamow-Teller resonance contribute significantly to the matrix element of this process.

nucl-th↗

arXiv2002

Neutrinoless Double Beta Decay of 134Xe

In view of recent great progress achieved in the experimental study of the neutrinoless double beta decay (0nbb-decay) of 134Xe we discuss theoretical aspects of this process. The light and heavy Majorana neutrino exchange as well as the trilinear R-parity breaking contributions to 0nbb-decay are considered. We show that the sensitivity of the studied process to the signal of lepton number violation is only by factor 2-3 weaker in comparison with the 0nbb-decay of 136Xe. The current limits on effective neutrino mass (light and heavy) and trilinear R-parity violating parameter lambda'_111 deduced from lower limits on the 0nbb-decay half-lifes of various nuclei are reviewed and perspectives of the experimental verification of recently announced evidence of the 0nbb-decay of 76Ge are discussed.

hep-ph↗

arXiv2001

Distinguishing the neutrinoless double beta decay mechanisms

Many new neutrinoless double beta decay (0nbb) experiments are planned or in preparation. If the 0nbb-decay will be detected, the key issue will be what is the dominant mechanism of this process. By measuring only transitions to the ground state one can not distinguish among many of the 0nbb-decay mechanisms (the light and heavy Majorana neutrino exchange mechanisms, the trilinear R-parity breaking mechanisms etc.). We show that if the ratio of the 0nbb-decay half-lifes for transitions to the 0^+ first excited and ground states is determined both theoretically and experimentally, it might be possible to determine, which 0nbb-decay mechanisms is dominant. For that purpose the corresponding nuclear matrix elements have to be evaluated with high reliability. The present work is giving strong motivations for experimental studies of the 0nbb-decay transitions to the first excited 0^+ states of the final nuclei.

hep-ph↗

arXiv2001

The (muon^-,muon^+) conversion in nuclei as a probe of new physics

A detailed study of the muonic analogue of neutrinoless double beta decay, (muon^-,muon^+) conversion, has been carried out for the A=44 nuclear system. We studied several lepton number violating (LNV) mechanisms potentially triggering this process: exchange by light and heavy Majorana neutrinos as well as exchange by supersymmetric particles participating in R-parity violating interactions. The nuclear structure has been taken into account within the renormalized Quasiparticle Random Phase Approximation method. To our knowledge, this is the first realistic treatment of nuclear structure aspects of the (muon^-,muon^+) conversion. We estimated the rate of this process utilizing the existing experimental constraints on the parameters of the underlying LNV interactions and conclude that the (muon^-,muon^+) conversion is hardly detectable in the near future experiments.

hep-ph↗

arXiv2001

The muon-positron conversion in nuclei mediated by light Majorana neutrinos

We study the lepton number violating muon-positron conversion in nuclei mediated by the exchange of virtual light Majorana neutrinos. We found that a previously overlooked imaginary part of this amplitude plays an important role. The numerical calculation has been made for the experimentally interesting muon-positron conversion in Ti48 using realistic renormalized proton-neutron QRPA wave functions. We also discuss the very similar case of the neutrinoless double beta decay of Ca48 The ratio of muon-positron conversion over the total muon absorption has been computed taking into account the current constraints from neutrino oscillation phenomenology. We compare our results with the experimental limits as well as with previous theoretical predictions. We have found that the Majorana neutrino mode of muon-positron conversion in Ti48 is too small to be measurable in the foreseeable future.

hep-ph↗

arXiv1999

Test of Physics beyond the Standard Model in Nuclei

The modern theories of Grand Unification (GUT) and supersymmetric (SUSY) extensions of standard model (SM) suppose that the conservation laws of the SM may be violated to some small degree. The nuclei are well-suited as a laboratory to test fundamental symmetries and fundamental interactions like lepton flavor (LF) and lepton number (LN) conservation. A prominent role between experiments looking for LF and total LN violation play yet not observed processes of neutrinoless double beta decay. The GUT's and SUSY models offer a variety of mechanisms which allow this process to occur. They are based on mixing of Majorana neutrinos and/or R-parity violation hypothesis. Although the neutrinoless double beta decay has not been seen it is possible to extract from the lower limits of the lifetime upper limits for the effective electron Majorana neutrino mass, effective right handed weak interaction parameters, the effective Majoron coupling constant, R-parity violating SUSY parameters etc. In this work the limits on the LN violating parameters extracted from current neutrinoless double beta decay experiments are listed. Studies in respect to future neutrinoless double beta decay experimental projects are also presented.

hep-ph↗

arXiv1999

Grand unified theory constrained supersymmetry and neutrinoless double beta decay

We analyze the contributions to the neutrinoless double $β$ decay ($0νββ$-decay) coming from the Grand Unified Theory (GUT) constrained Minimal Supersymmetric Standard Model (MSSM) with trilinear R-parity breaking. We discuss the importance of two-nucleon and pion-exchange realizations of the quark-level $0νββ$-decay transitions. In this context, the questions of reliability of the calculated relevant nuclear matrix elements within the Renormalized Quasiparticle Random Phase Approximation (pn-RQRPA) for several medium and heavy open-shell nuclei are addressed. The importance of gluino and neutralino contributions to $0νββ$-decay is also analyzed. We review the present experiments and deduce limits on the trilinear R-parity breaking parameter $λ_{111}'$ from the non-observability of $0νββ$-decay for different GUT constrained SUSY scenarios. In addition, a detailed study of limits on the MSSM parameter space coming from the $B \to X_s γ$ processes by using the recent CLEO and OPAL results is performed. Some studies in respect to the future $0νββ$-decay project GENIUS are also presented.

hep-ph↗

arXiv1999

Double Beta Decay

We review the recent developments in the field of nuclear double beta decay, which is presently an important topic in both nuclear and particle physics. The mechanism of lepton number violation within the neutrinoless double beta decay is discussed in context of the problem of neutrino mixing and the R-parity violating supersymmetric extensions of the Standard model. The problem of reliable determination of the nuclear matrix elements governing both two-neutrino and neutrinoless modes of the double beta decay is addressed. The validity of different approximation schemes in the considered nuclear structure studies is analyzed and the role of the Pauli exclusion principle for a correct treatment of nuclear matrix elements is emphasized. The constraints on different lepton number violating parameters like effective electron neutrino mass, effective right-handed weak interaction parameters, effective Majoron coupling constant and R-parity violating SUSY parameters are derived from the best presently available experimental limits on the half life of neutrinoless mode of this process.

hep-ph↗

arXiv1998

Pions in Nuclei and Manifestations of Supersymmetry in Neutrinoless Double Beta Decay

We examine the pion realization of the short ranged supersymmetric (SUSY) mechanism of neutrinoless double beta decay. It originates from the R-parity violating quark-lepton interactions of the SUSY extensions of the standard model of the electroweak interactions. We argue that pions are dominant SUSY mediators in neutrinoless double beta decay. The corresponding nuclear matrix elements for various isotopes are calculated within the proton-neutron renormalized quasiparticle random phase approximation. We define those isotopes which are most sensitive to the SUSY signal and outlook the present experimental situation with the double beta decay searches for the SUSY. Upper limits on the R-parity violating 1st generation Yukawa coupling are derived from various double beta decay experiments.

hep-ph↗

arXiv1997

Bilinear R-parity Violation in Neutrinoless Double Beta Decay

We discuss some phenomenological issues of the effective quark-lepton operators emerging from the bilinear lepton-Higgs couplings in the superpotential and in the soft supersymmetry (SUSY) breaking sector of the supersymmetric models without R-parity. The contribution of these operators to the neutrinoless double beta decay is derived. The corresponding nuclear matrix elements are calculated within the renormalized quasiparticle random phase approximation, which includes the Pauli effect of fermion pairs and does not collapse for the physical values of the nuclear force strength. On this basis we extract from the experimental data new stringent limits on the 1st generation mass parameter characterized the lepton-Higgs bilinear coupling and on the electron sneutrino vacuum expectation value.

hep-ph↗

arXiv1997

Pion Exchange Currents in Neutrinoless Double Beta Decay and Limits on Supersymmetry

We examine the pion exchange mode of neutrinoless double beta decay induced by the R-parity violating quark-lepton operators of the supersymmetric (SUSY) extensions of the standard model of the electroweak interactions. The corresponding nuclear matrix elements are evaluated within the renormalized quasiparticle random phase approximation with proton-neutron pairing, which includes the Pauli effect of fermion pairs and does not collapse for a physical value of the nuclear force strength. It is argued that the pion-exchange mode of neutrinoless double beta decay dominates over the conventional two-nucleon mode in the case of the SUSY mechanism. As a result sensitivity of neutrinoless double beta decay to the SUSY contribution turns out to be significantly better that previously expected from the two-nucleon mode calculations. An upper limit on the R-parity violating coupling $λ'_{111}$ is derived from non-observation of neutrinoless double beta decay. This limit is much stronger than that expected from the near future accelerator experiments.

hep-ph↗