arXiv subjects

Amand Faessler

Publications and source records attributed to Amand Faessler.

At least 55 records · Page 3Linked to original sources

arXiv2012

Extra Dimensions and Neutrinoless Double Beta Decay Experiments

The neutrinoless double beta decay is one of the few phenomena, belonging to the non-standard physics, which is extensively being sought for in experiments. In the present paper the link between the half-life of the neutrinoless double beta decay and theories with large extra dimensions is explored. The use of the sensitivities of currently planned $0\nu2β$ experiments: DAMA, CANDLES, COBRA, DCBA, CAMEO, GENIUS, GEM, MAJORANA, MOON, CUORE, EXO, and XMASS, gives the possibility for a non-direct `experimental' verification of various extra dimensional scenarios. We discuss also the results of the Heidelberg--Moscow Collaboration. The calculations are based on the Majorana neutrino mass generation mechanism in the Arkani-Hamed--Dimopoulos--Dvali model.

hep-ph↗

arXiv2011

Evaluation of the resonance enhancement effect in neutrinoless double-electron capture in 152Gd, 164Er and 180W atoms

We study the resonant neutrinoless double-electron capture (0nECEC) in 152Gd, 164Er and 180W atoms, associated with the ground-state to ground-state nuclear transitions. The corresponding matrix elements are calculated within the deformed QRPA using the realistic Bonn-CD nucleon-nucleon interaction. The half-lives are estimated with the use of the most recent precision data on the Q-values of these processes. Perspectives of experimental search for the 0nECEC with the isotopes 152Gd, 164Er and 180W are discussed.

hep-ph↗

arXiv2011

Hyperon forward spin polarizabilty gamma0

We present the results of a systematic leading order calculation of hyperon Compton scattering and extract the forward spin polarizability gamma0 of hyperons within the framework of SU(3) heavy baryon chiral perturbation theory (HBChPT). The results obtained for gamma0 in the case of nucleons agree with that of the known results of SU(2) HBChPT when kaon loops are not considered.

hep-ph↗

arXiv2011

Neutrinoless double-beta decay and seesaw mechanism

From the standard seesaw mechanism of neutrino mass generation, which is based on the assumption that the lepton number is violated at a large (~10exp(+15) GeV) scale, follows that the neutrinoless double-beta decay is ruled by the Majorana neutrino mass mechanism. Within this notion, for the inverted neutrino-mass hierarchy we derive allowed ranges of half-lives of the neutrinoless double-beta decay for nuclei of experimental interest with different sets of nuclear matrix elements. The present-day results of the calculation of the neutrinoless double-beta decay nuclear matrix elements are briefly discussed. We argue that if neutrinoless double-beta decay will be observed in future experiments sensitive to the effective Majorana mass in the inverted mass hierarchy region, a comparison of the derived ranges with measured half-lives will allow us to probe the standard seesaw mechanism assuming that future cosmological data will establish the sum of neutrino masses to be about 0.2 eV.

hep-ph↗

arXiv2011

Analytical description of the Coherent State Model for near vibrational and well deformed nuclei

Analytical formulas for the excitation energies as well as for the electric quadrupole reduced transition probabilities in the ground, beta and gamma bands were derived within the coherent state model for the near vibrational and well deformed nuclei. Numerical calculations were performed for 42 nuclei exhibiting various symmetries and therefore with specific properties. Comparison of the calculation results with the corresponding experimental data shows a good agreement. The parameters involved in the proposed model satisfy evident regularities being interpolated by smooth curves. Few of them, which fall out of the curves, are interpreted as signatures for a critical point in a specific phase transition. This is actually supported also by the figures showing the excitation energy dependence on the angular momentum. The formulas provided for energies and B(E2) values are very simple, being written in a compact form, and therefore easy to be handled to explain the new experimental data.

nucl-th↗

arXiv2011

New features of the triaxial nuclei described with a coherent state model

Supplementing the Liquid Drop Model (LDM) Hamiltonian, written in the intrinsic reference frame, with a sextic oscillator plus a centrifugal term in the variable $β$ and a potential in $γ$ with a minimum in $\fracπ{6}$, the Schödinger equation is separated for the two variables which results in having a new description for the triaxial nuclei, called Sextic and Mathieu Approach (SMA). SMA is applied for two non-axial nuclei, $^{180}$Hf and $^{182}$W and results are compared with those yielded by the Coherent State Model (CSM). As the main result of this paper we derive analytically the equations characterizing SMA from a semi-classical treatment of the CSM Hamiltonian. In this manner the potentials in $β$ and $γ$ variables respectively, show up in a quite natural way which contrasts their ad-hoc choice when SMA emerges from LDM.

nucl-th↗

arXiv2011

Dilepton production in pp and np collisions at 1.25 GeV

The inclusive reactions $pp \rightarrow e^+ e^- X$ and $np \rightarrow e^+ e^- X$ at the laboratory kinetic energy of 1.25 GeV are investigated in a model of dominance of nucleon and $Δ$ resonances. Experimental data for these reactions have recently been reported by the HADES Collaboration. In the original model, the dileptons are produced either from the decays of nucleon and $Δ$ resonances $R \rightarrow N e^+ e^-$ or from the Dalitz decays of $π^0$- and $η$-mesons created in the $R \to Nπ^0$ and $R \to Nη$ decays. We found that the distribution of dilepton invariant masses in the $pp \rightarrow e^+ e^- X$ reaction is well reproduced by the contributions of $R \rightarrow N e^+ e^-$ decays and $R \rightarrow N π^0$, $π^0 \to γe^+e^-$ decays. Among the resonances, the predominant contribution comes from the $Δ(1232)$, which determines both the direct decay channel $R \rightarrow N e^+ e^-$ and the pion decay channel. In the collisions $np \rightarrow e^+ e^- X$, additional significant contributions arise from the $η$-meson Dalitz decays, produced in the $np \rightarrow npη$ and $np \rightarrow dη$ reactions, the radiative capture $np \rightarrow d e^+ e^-$, and the $np \rightarrow np e^+ e^-$ bremsstrahlung. These mechanisms may partly explain the strong excess of dileptons in the cross section for collisions of $np$ versus $pp$, which ranges from 7 to 100 times for the dilepton invariant masses of 0.2 to 0.5 GeV.

nucl-th↗

arXiv2011

Origin of a sensitive dependence of calculated $ββ$-decay amplitudes on the particle-particle residual interaction

In the present work the sensitivity of the QRPA calculation results to a realistic residual interaction is analyzed in the framework of the approach of Refs. \cite{Rum98,Rodin05}. Both Gamow-Teller (GT) and Fermi (F) \bb-decay amplitudes $M^{2ν}$, along with the corresponding energy-weighted sum rules $S$, are calculated. General expressions relating $S$ to a realistic residual particle-particle interaction are derived, which show a pronounced sensitivity of $S$ to the singlet-channel interaction in the case of F transitions, and to the triplet-channel interaction in the case of GT transitions. Decompositions of $M^{2ν}$, as well as the monopole transition contributions to $M^{0ν}$, are obtained by the method of Refs. \cite{Rum98,Rodin05}. It is shown that in most of the cases almost the whole dependence of $M^{2ν}$ and $M^{0ν}$ on the particle-particle renormalization parameter $g_{pp}$ is accounted for by the $g_{pp}$-dependence of the corresponding sum rules $S$. Thus, the $g_{pp}$-sensitivity of calculated $M^{2ν}$ and $M^{0ν}$ is unavoidable since it is dictated by the generic structure of the $ββ$ amplitudes. Finally, a better isospin-consistent way of a renormalization of the realistic residual particle-particle interaction to use in QRPA calculations is suggested.

nucl-th↗

arXiv2011

Multi-isotope degeneracy of neutrinoless double beta decay mechanisms in the quasi-particle random phase approximation

We calculate nuclear matrix elements (NME) of neutrinoless double beta decay in four different candidate nuclei (Ge-76, Se-82, Mo-100, Te-130) within the quasiparticle random phase approximation (QRPA) and its uncertainties. We assume (up to) four coexisting mechanisms for neutrinoless double beta decay, mediated by light Majorana neutrino exchange, heavy Majorana neutrino exchange, R-parity breaking supersymmetry, and squark-neutrino, interfering either constructively or destructively with each other. We find that, unfortunately, current NME uncertainties appear to prevent a robust determination of the relative contribution of each mechanism to the decay amplitude, even assuming accurate measurements of decay lifetimes. The near-degeneracy of the decay mechanisms is analyzed with simple algebraic techniques, which do not involve assumptions about the statistical distribution of errors. We discuss implications of such degeneracy on prospective searches for absolute neutrino masses.

hep-ph↗

arXiv2011

Resonance enhancement of neutrinoless double electron capture

The process of neutrinoless double electron capture ($0ν$ECEC) is revisited for those cases where the two participating atoms are nearly degenerate in mass. The theoretical framework is the formalism of an oscillation of two atoms with different total lepton number (and parity), one of which can be in an excited state so that mass degeneracy is realized. In such a case and assuming light Majorana neutrinos, the two atoms will be in a mixed configuration with respect to the weak interaction. A resonant enhancement of transitions between such pairs of atoms will occur, which could be detected by the subsequent electromagnetic de-excitation of the excited state of the daughter atom and nucleus. Available data of atomic masses, as well as nuclear and atomic excitations are used to select the most likely candidates for such resonant $0ν$ECEC transitions. Assuming an effective mass for the Majorana neutrino of 1 eV, some half-lives are predicted to be as low as $10^{22}$ years in the unitary limit. It is argued that, in order to obtain more accurate predictions for the $0ν$ECEC half-lives, precision mass measurements of the atoms involved are necessary, which can readily be accomplished by today's high precision Penning traps. Further advancements also require a better understanding of high-lying excited states of the final nuclei (i.e. excitation energy, angular momentum and parity) and the calculation of the nuclear matrix elements.

hep-ph↗

arXiv2011

Hadronic and radiative three-body decays of J/psi involving the scalars f0(1370), f0(1500) and f0(1710)

We study the role of the scalar resonances f0(1370), f0(1500) and f0(1710) in the strong and radiative three-body decays of J/psi with J/psi to V + P P (gamma gamma) and J/psi to gamma + P P (V V), where P (V) denotes a pseudoscalar (vector) meson. We assume that the scalars result from a glueball-quarkonium mixing scheme while the dynamics of the transition process is described in an effective chiral Lagrangian approach. Present data on J/psi to V + P P are well reproduced, predictions for the radiative processes serve as further tests of this scenario.

hep-ph↗

arXiv2011

Double Beta Decay, Nuclear Structure and Physics beyond the Standard Model

Neutrinoless Double Beta Decay ($0νββ$) is presently the only known experiment to distinguisch between Dirac neutrinos, different from their antiparticles, and Majorana neutrinos, identical with their antiparticles. In addition $0νββ$ allows to determine the absolute scale of the neutrino masses. This is not possible with neutrino oscillations. To determine the neutrino masses one must assume, that the light Majorana neutrino exchange is the leading mechanism for $0νββ$ and that the matrix element of this transition can ba calculated reliably. The experimental $0νββ$ transition amplitude in this mechanism is a product of the light left handed effective Majorana neutrino mass and of this transition matrix element. The different methods, Quasi-particle Random Phase Approximation (QRPA), Shell Model (SM), Projected Hartree-Fock-Bogoliubov (PHFB) and Interacting Boson Model (IBM2) used in the literature and the reliability of the matrix elements in these approaches are reviewed. In the second part it is investigated how one can determine the leading mechanism or mechanisms from the data of the $0νββ$ decay in different nuclei. Explicite expressions are given for the transition matrix elements. is shown, that possible interference terms allow to test CP (Charge and Parity conjugation) violation.

nucl-th↗

arXiv2011

Electroproduction of the Roper resonance on the proton: the role of the three-quark core and the molecular N-sigma component

The Roper resonance is considered as a mixed state of a three-quark core configuration and a hadron molecular component N+sigma. Based on this ansatz we study electroproduction of the Roper resonance. The strong and electromagnetic couplings induced by the quark core are calculated in the 3P0 model. The contribution of the vector meson cloud to the electromagnetic transition is given in the framework of the VMD model. Results are compared with the recent JLab electroproduction data.

hep-ph↗

arXiv2011

The absolute mass of neutrino and the first unique forbidden beta-decay of 187Re

The planned rhenium beta-decay experiment MARE might probe the absolute mass scale of neutrinos with the same sensitivity as the tritium beta-decay experiment KATRIN, which will start data taking in 2011 and will proceed for five years. We present the energy distribution of emitted electrons for the first unique forbidden beta-decay of 187Re. It is found that the p-wave emission of electron dominates over the s-wave. By assuming mixing of three neutrinos the Kurie function for the rhenium beta-decay is derived. It is shown that the Kurie plot near the endpoint is within a good accuracy linear in the limit of massless neutrinos like the Kurie plot of the superallowed beta-decay of 3H.

hep-ph↗

arXiv2011

Uncovering Multiple CP-Nonconserving Mechanisms of $\betabeta$-Decay

We consider the possibility of several different mechanisms contributing to the $\betabeta$-decay amplitude in the general case of CP nonconservation: light Majorana neutrino exchange, heavy left-handed (LH) and heavy right-handed (RH) Majorana neutrino exchanges, lepton charge non-conserving couplings in SUSY theories with R-parity breaking. If the $\betabeta$-decay is induced by, e.g., two "non-interfering" mechanisms, one can determine $|η_i|^2$ and $|η_j|^2$, $η_i$ and $η_j$ being the two fundamental parameters characterising these mechanisms, from data on the half-lives of two nuclear isotopes. In the case when two "interfering" mechanisms are responsible for the $\betabeta$-decay, $|η_i|^2$ and $|η_j|^2$ and the interference term can be uniquely determined, in principle, from data on the half-lives of three nuclei. Given the half-life of one isotope, the "positivity conditions" $|η_i|^2\geq 0$ and $|η_j|^2\geq 0$ lead to stringent constraints on the half-lives of the other $\betabeta$-decaying isotopes. These conditions, as well as the conditions for constructive (destructive) interference are derived and their implications are analysed in two specific cases. The method considered by us can be generalised to the case of more than two $\betabeta$-decay mechanisms. It allows to treat the cases of CP conserving and CP nonconserving couplings generating the $\betabeta$-decay in a unique way.

hep-ph↗

arXiv2011

Strong three-body decays of Lambdac(2940)+

The Lambdac(2940)+ baryon with quantum numbers J(P) = 1/2(+) is considered as a hadronic molecule composed of a nucleon and D* meson. We give predictions for the width of the strong three-body decay processes Lambdac(2940)+ to Lambdac(2286)+ pi(+) pi(-) and Lambdac(2940)+ to Lambdac(2286)+ pi(0) pi(0) in this interpretation. Upcoming experimental facilities like a Super B factory at KEK or LHCb might be able to provide data on these decay modes.

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↗

arXiv2011

Neutrinoless double beta decay of deformed nuclei within QRPA with realistic interaction

In this paper a microscopic state-of-the-art approach to calculation of the nuclear matrix element $M^{0ν}$ for neutrinoless double beta decay with an account for nuclear deformation is presented in length and applied for $^{76}$Ge, $^{150}$Nd and $^{160}$Gd. The proton-neutron quasiparticle random phase approximation (QRPA) with a realistic residual interaction [the Brueckner $G$ matrix derived from the charge-depending Bonn (Bonn-CD) nucleon-nucleon potential] is used as the underlying nuclear structure model. The effects of the short range correlations and the quenching of the axial vector coupling constant $g_A$ are analyzed. The results show that neutrinoless double beta decay of $^{150}$Nd, to be measured soon by the SNO+ collaboration, provides one of the best probes of the Majorana neutrino mass. This confirms our preliminary conclusion in Ref. {Fang10}.

nucl-th↗