International Journal of Modern Physics E

We review the particle physics aspects of neutrino-less double beta decay. This process can be mediated by light massive Majorana neutrinos (standard interpretation) or by something else (non-standard interpretations). The physics potential of both interpretations is summarized and the consequences of future measurements or improved limits on the half-life of neutrino-less double beta decay are discussed. We try to cover all proposed alternative realizations of the decay, including light sterile neutrinos, supersymmetric or left-right symmetric theories, Majorons, and other exotic possibilities. Ways to distinguish the mechanisms from one another are discussed. Experimental and nuclear physics aspects are also briefly touched, alternative processes to double beta decay are discussed, and an extensive list of references is provided.

Using the α-like cluster and uncluster nucleonic structure of ²⁴Mg and ²⁸Si nuclei, α-nucleus single-folding cluster optical potentials have been generated based upon effective α–α and α-nucleon (N) interactions. Angular distributions of the differential cross-section of α elastic scattering by ²⁴Mg, and ²⁸ Si nuclei have been analyzed over a wide range of incident energies, E_α = 21.9-175.5 MeV, where anomaly in large angle scattering and rainbow scattering features have been investigated. We successfully reproduce the elastic scattering differential cross-section for energy range E_α = 22.2-172.5 MeV for ²⁴Mg target and 21.9-166 MeV for ²⁸Si target without renormalization except a few cases at low energies. The energy dependence of the extracted real and imaginary volume integrals and total reaction cross-section has been investigated.

Expressions of temperature-dependent perpendicular (ℑ_⊥) and parallel (ℑ_‖) moments of inertia, including isovector pairing effects, have been established using the cranking method. They are derived from recently proposed temperature-dependent gap equations. The obtained expressions generalize the conventional finite-temperature BCS (FTBCS) ones. Numerical calculations have been carried out within the framework of the schematic Richardson model as well as for nuclei such as N = Z, using the single-particle energies and eigenstates of a deformed Woods–Saxon mean-field. ℑ_⊥ and ℑ_‖ have been studied as a function of the temperature. It has been shown that the isovector pairing effect on both the perpendicular and parallel moments of inertia is non-negligible at finite temperature. These correlations must thus be taking into account in studies of warm rotating nuclei in the N ≃ Z region.

The paper discusses the parity of the neutral pion. It is shown that the recent determination of the parity of the neutral pion using the double Dalitz decay π⁰→e⁺e^-e⁺e^- is compatible with the mixed-parity nature of the neutral pion predicted by a recent composite model.

Properties of the ¹S₀ superfluid phase are studied for symmetric nuclear matter at finite temperature. It is described within a covariant hadronic field model, of the σ–ω type, with addition of density dependent correlations simulating effects due to finite extension of nucleons. The model is solved in a self-consistent Hartree–Bogoliubov approach, assuming instantaneous interactions in the superfluid phase. A comparison with the results obtained from several hadronic field models is made. Main characteristics of our description of the superfluid gap are in qualitative agreement with some studies using microscopic potentials, although further refinements could improve its performance.

The effects of auxiliary contribution in forms of electromagnetic tensors and relativistic electromagnetic exchange in local density approximation as well as δ meson and isovector density-dependent nonlinear terms in standard relativistic mean field model constrained by nuclear matter stability criteria in some selected finite nuclei and nuclear matter properties are studied. It is found that in the case of finite nuclei, the electromagnetic tensors play the most dominant part compared to other auxiliary terms. Due to the presence of electromagnetic tensors, the binding energies prediction of the model can be improved quite significantly. However, these terms do not yield demanded effects for rms radii prediction. In the case of nuclear matter properties, the isovector density-dependent nonlinear term plays the most crucial role in providing predictions which are quite compatible with experimental constraints. We have also shown these auxiliary contributions are indeed unable to improve the single particle spectrum results of the model.

We develop an isospin-like formulation with particles and their antiparticle counterparts. This leads to a new shortlived interaction between them, valid at very high energies and mediated by massive particles. We point out that evidence for this is already suggested by the very recent observations by the CDF collaboration at Fermilab.

In the present work, we report a microscopic optical potential analysis of the extensive neutron elastic scattering data from ¹²C, ⁴⁰Ca and ²⁰⁸Pb in the 65–225 MeV energy region. Brueckner–Hartree–Fock method has been used to calculate the optical potential, where one requires internucleon potential to calculate reaction matrices which are then folded over the nucleon densities in the target nuclei. We report the predictions of the calculated potential using Argonne v-18 and Urbana v-14 local nucleon–nucleon potentials. The modern potential v-18 has been used for the first time to calculate the nucleon–nucleus optical potential. We also compare our predictions with the empirical potentials. The results indicate that the predictions of our microscopic potential are in better agreement with the experimental data as compared with the empirical global optical potentials.

This study reveals the analysis of ring-like and jet-like events in terms of factorial correlations of ¹⁶O–Ag/Br interactions at 60A GeV. The investigation revealed that the correlated moments are found to increase with decreasing bin–bin separation D and follows a power-law which suggests the presence of an intermittent nature of self-similar dynamical fluctuations pattern for ring-like and jet-like events. From the analysis we find that for jet-like events the strength of non-statistical fluctuation is greater than the ring-like and total event set. Jet-like events follow the bin size independence according to α model of intermittency as like total events, whereas ring-like events are not consistent with the prediction of α model of intermittency.

The breakup cross-sections in the reaction ⁶He + ¹²C are calculated at about 40 MeV/nucleon using the high-energy approximation (HEA) and with the help of microscopic optical potentials (OP) of interaction with the target nucleus ¹²C of the projectile nucleus fragments ⁴He and 2n. Considering the di-neutron h = 2n as a single particle the relative motion hα wave function is estimated so that to explain both the separation energy of h in ⁶He and the rms radius of the latter. The stripping and absorbtion total cross-sections are calculated and their sum is compared with the total reaction cross-section obtained within a double-folding microscopic OP for the ⁶He + ¹²C scattering. It is concluded that the breakup cross-sections contribute to about 50% of the total reaction cross-section.

Our model (Refs. 1–7) with a complex action in a functional integral formulation with path integrals extending over all times, both past and future, is reviewed. Several numerical relations between coupling constants are presented as supporting evidence. The new evidence is that several more hitherto unexplained coincidences are explained by our model:

(1) The "scale problem" is solved because the Higgs field expectation value is predicted to be very small compared to say some fundamental scale, that might be the Planck scale.

(2) The Higgs VEV need not be just zero, but rather is predicted to be so that the running top-quark Yukawa coupling just is about to be unity at this scale; in this way the (weak) scale easily becomes "exponentially small." Instead of the top-Yukawa we should rather say the highest flavor Yukawa coupling here.

These predictions are only achieved by allowing the principle of minimization of the imaginary part of the action S_I(history) to a certain extent adjust some coupling constants in addition to the initial conditions.

If supersymmetric partners are not found at LHC it would strengthen the need for a "solution" to the hierarchy problem in our direction of an explanation via a fine-tuning scheme inside the Standard Model, from say minimizing "the imaginary part of the action" in our complex action model.