International Journal of Modern Physics E

Hypothetical neutrinoless double beta decay is possible only if the neutrino is a truly neutral particle and if it is massive. A truly neutral particle (e.g. a particle identical with its antiparticle) should have all its algebraic intrinsic properties equal to zero, in particular, its lepton number should be 0. Now, since the neutrino is a lepton, its lepton number should be 1. This contradiction would lead one to conclude that neutrinoless double beta decay cannot take place in nature. This conclusion is, up to now, in agreement with persistent failures to find evidence for this long sought key hypothetical decay despite huge efforts dedicated to this aim.

The radiative capture process np→dγ is considered within the framework of a recently developed six-quark dressed-bag model for the nucleon-nucleon interaction. The calculations presented here include both the nucleon current and the meson-exchange current contributions. The latter uses short-range hadronic form factors for the pion exchange currents consistent with the soft cut-off parameter Λ_πNN from the NN-potential. Contributions of the pion exchange current and Δ-isobar current to the total cross-section still cannot explain the discrepancy between the theoretical and experimental cross-sections. Possibilities for new types of meson exchange currents associated with chiral fields inside multi-quark dressed-bag states in nuclei are discussed.

We present the tangential velocity corrections to the second-order Coulomb-modified eikonal model at the distance of closest approach. It has been applied to elastic angular distributions of the ¹⁶O+¹⁶O system at E_lab=350 and 480 MeV. The calculated results with tangential velocity show better agreements with the experimental data compared to those with asymptotic velocity. The Fraunhöfer oscillations observed in the elastic angular distributions can be explained by the strong interference between the near- and the far-side amplitudes. Airy structures can be shown by reducing the effective imaginary potential strength. It is found that the Airy minimum is more visible as the effective imaginary potential strength is reduced. Deep real potentials associated with rather weak imaginary ones are found to be essential to describe the refractive ¹⁶O+¹⁶O elastic scatterings at E_lab=350 and 480 MeV.

The study presented here pertains to the model-based analyses for production of some important charged secondaries in lead-lead and gold-gold collisions at AGS, SPS and RHIC energies. We examine the role of a particular version of the Sequential Chain Model (SCM) in interpreting the data on the production of only the secondary mesons of the most abundant variety in relativistic nucleus-nucleus collisions. The initial results derived for basic pp collisions have been transformed into the corresponding cases for nucleus-nucleus collisions through the appropriate physical-mathematical formalisms. The agreement between the model of choice and the measured data for the most important varieties of mesons in the two above-stated nuclear collisions could so far be rated to be barely modest. This is presumably due to our neglect of the effects of rescattering and cascading, while we choose to obtain only the first-order results in the initial attempt.

The solutions of four-quark equations using the method of extracting leading singularities of the amplitudes are obtained. The calculations of cryptoexotic meson amplitudes provide the estimates of four-quark amplitude, glueball amplitude and hadronic molecule amplitudes. We find that the main contributions to the cryptoexotic meson amplitude are given by the four-quark state and the glueball.

The main parameters of the FEL–RHIC collider are estimated. The physics search potential of this machine is illustrated using excitations of the ²³²Th nucleus as an example. It is shown that, due to the tunability and monochromacity of the FEL beam and high statistics, the proposed collider will play an important role in the field of "traditional" nuclear physics. In addition, spin and parity of nucleus excitations can be easily identified at FEL-nucleus colliders.

The Debye screening masses of the σ, ω and neutral ρ mesons and the photon are calculated in the relativistic mean-field approximation. As the density of the nucleon increases, all the screening masses of mesons increase. A different result with Brown–Rho scaling is shown, which implies a reduction in the mass of all the mesons in the nuclear matter, except the pion. Replacing the masses of the mesons with their corresponding screening masses in the Walecka-1 model, five saturation properties of the nuclear matter are fixed reasonably, and then a density-dependent relativistic mean-field model is proposed without introducing the nonlinear self-coupling terms of mesons.

The solutions of the Klein–Gordon equation with a Coulomb potential in D dimensions are obtained exactly, and the energy levels E(n,l,D) are analytically presented. The dependence of the energy difference ΔE(n,l,D) for D and D-1 on the dimension D is demonstrated as three different kinds of rules. The dependence of the energy E(n,l,D) on the dimension D is also analyzed. It is shown that the energy E(n,l,D) (l≠0) is almost independent of the quantum number l, while E(n,0,D) first decreases and then increases as the dimension D increases. There is no bound state of the S-wave for D=2.