abstract

The presence of Coulomb diffraction interference has been investigated for single-proton breakup from \(^{23}\)Al nucleus reaction. The study is performed for light, medium, and heavy targets i.e. , \(^{12}\)C, \(^{58}\)Ni, and \(^{208}\)Pb cases at 40 and 80 MeV/nucleon beam energies. The Coulomb interaction between core–target and proton–target are treated to all orders, including the full-multipole expansion of the Coulomb potential, while nuclear diffraction dissociation is treated with eikonal approximation. The effects of Coulomb diffraction interference on single-proton breakup cross-section and Full Width Half Maxima (FWHM) width of core longitudinal momentum distribution (LMD) have been investigated. Interferences between the core–target (recoil interaction) and proton–target (direct interaction) Coulomb interactions are also being examined. The nature of interferences is constructive as well as destructive depending on the target atomic number and incident energy. Consequently, enhancement and reduction in breakup cross sections and the LMD widths have been observed in a significant magnitude. The interference effects for \(^{58}\)Ni target case are found almost three to four times of that of \(^{12}\)C and \(^{208}\)Pb target cases. We believe that our investigation would help in planning future experiments involving proton halo breakup reactions as well as for better understanding and interpretation of experimental data of \(^{23}\)Al breakup reaction.

abstract

A rapidly converging 4-dimensional Fourier shape parametrization is used to model the fission process of heavy nuclei. Potential energy landscapes are computed within the macroscopic–microscopic approach, on top of which the multi-dimensional Langevin equation is solved to describe the fission dynamics. Charge equilibration at scission and de-excitation by neutron evaporation of the primary fragments after scission is investigated. The model describes various observables, including fission-fragment mass, charge, and kinetic energy yields, as well as post-scission neutron multiplicities and, most importantly, their correlations, which are crucial to unravel the complexity of the fission process. The parameters of the dynamical model were tuned to reproduce experimental data obtained from thermal neutron-induced fission of \(^{235}\)U, which allows us to discuss the transition from asymmetric to symmetric fission along the Fm isotopic chain.

abstract

The variation of excitation energies of yrast \(2^{+}\) states and ratios \(E_{4^{+}}/E_{2^{+}}\) with \(N_{p}N_{n}\) in the mass range of \(A=6\)–136 having valence nucleons in the same shell is studied. The mass range \(A=6\)–136 was considered due to the availability of data when valence protons and neutrons fill in the same major shell. It has been noticed that the depression in \(E_{2^{+}}\) and ascension in \(R\) appear in isobars that differ from the predictions of the \(N_{p}N_{n}\) scheme in which isotones are expected. A new correlation scheme, the product of valence nucleon \(N_\mathrm {T}\), and holes \(\bar {N}_\mathrm {T}\), i.e. , \(N_\mathrm {T}\bar {N}_\mathrm {T}\) is proposed to explain the experimental observations.

abstract

Tachyon condensation in quantum field theory (QFT) plays a central role in models of fundamental interactions and cosmology. Inspired by tower truncation in string field theory, ultraviolet completions were proposed with infinite-derivative form factors that preclude the appearance of pathological ghosts in the particle spectrum, contrary to other local higher-derivative QFTs. However, if the infinite-derivative QFT exhibits other vacua, each of them has its own spectrum, which is generally not ghost-free: an infinite tower of ghost-like resonances pops up above the nonlocal scale at tree-level, whose consistency is unclear. In this article, a new weakly nonlocal deformation of a generic local QFT is introduced via a Lorentz and gauge covariant star-product of fields, which is commutative but nonassociative in general. This framework realizes tachyon condensation without ghosts at the perturbative level, with applications for spontaneous symmetry breaking.