International Journal of Modern Physics E

In a previous paper, we reported the results of a partial-wave analysis (PWA) of the pion–nucleon (πN) differential cross-sections (DCSs) of the CHAOS Collaboration and came to the conclusion that the angular distribution of their π⁺p data sets is incompatible with the rest of the modern (meson factory) database. The present work, re-addressing this issue, has been instigated by a number of recent improvements in our analysis, namely regarding the inclusion of the theoretical uncertainties when investigating the reproduction of experimental data sets on the basis of a given "theoretical" solution, modifications in the parametrization of the form factors of the proton and of the pion entering the electromagnetic part of the πN amplitude, and the inclusion of the effects of the variation of the σ-meson mass when fitting the ETH model of the πN interaction to the experimental data. The new analysis of the CHAOS DCSs confirms our earlier conclusions and casts doubt on the value for the πN Σ term, which Stahov, Clement and Wagner have extracted from these data.

In this paper, magnetic field and equation of state (EoS) of neutron star matter are studied under relativistic mean field theory. A nonzero mass term of magnetic field in the Lagrangian is introduced, which depends on baryon density of charged particles. The magnetic field has not been treated as external as usual and the calculations of magnetic field strength at finite temperature reveal the existence of inflection points in certain densities.

A two-dimensional (2D) dynamical model based on Langevin equations was applied to study the fission dynamics of the compound nuclei ²²⁸U produced in ¹⁹F + ²⁰⁹Bi reactions at intermediate excitation energies. The distance between the centers of masses of the future fission fragments was used as the first dimension and the projection of the total spin of the compound nucleus onto the symmetry axis, K, was considered as the second dimension in Langevin dynamical calculations. The magnitude of post-saddle friction strength was inferred by fitting measured data on the average pre-scission neutron multiplicity for ²²⁸U. It was shown that the results of calculations are in good agreement with the experimental data by using values of the post-saddle friction equal to 6–8 × 10²¹s^-1.

We calculate the decay widths of the charmonium states, J/ψ, ψ(3686) and ψ(3770), to pairs, as well as the decay width of D* → Dπ, in isospin asymmetric strange hadronic matter, using a field theoretical model for composite hadrons with quark constituents. For this purpose, we use the quark–antiquark pair creation term of the free Dirac Hamiltonian written in terms of the constituent quark field operators, and use explicit charmonium, D, , D* and π states to evaluate the matrix elements for the charmonium as well as D* decay amplitudes. The medium modifications of the partial decay widths of charmonium to pair, arising from the mass modifications of the and the charmonium states calculated in a chiral effective model, are also included. The results of the present investigations are then compared with the decay widths computed earlier, in a model using light quark pair creation in ³P₀ state. As in ³P₀ model, the decay amplitude in the present model is multiplied with a strength parameter for the light quark pair creation, which is fitted from the observed vacuum decay width. The effects of the isospin asymmetry, the strangeness fraction of the hadronic matter on the masses of the charmonium states and mesons and hence on the decay widths, have also been studied. The isospin asymmetry effect is observed to be dominant for high densities, leading to appreciable difference in the decay channels of the charmonium to D⁺ D^- and pairs. The decay width of D* → Dπ in the hadronic matter has also been calculated within the composite quark model in the present work, accounting for the medium modifications of the D and D* masses. The density modifications of the charmonium states and D(D*) mesons, which are observed to be appreciable at high densities, will be of relevance in the compressed baryonic matter (CBM) experiments at the future facility of FAIR, GSI, where charmed hadrons will be produced by annihilation of antiprotons on nuclei. The interactions of the charmonium states and D(D*) with the nuclear medium could lead to the possibility of the formation of exotic bound states of the nuclei with the (excited) charmonium states as well as with D(D*) mesons.

A four parameter formula has been applied to all the yrast and excited superdeformed (SD) bands of even–even nuclei in the A~150 mass region to obtain band moment of inertia J₀. In even–even nuclei, totally three yrast SD bands and 16 excited SD bands have been fitted. The measured Q_t values and hence the axes ratios have been used to calculate the rigid body J₀ values and compared with the fitted values of J₀. It is interesting to look at the yrast SD band ¹⁵²Dy(1), the doubly magic SD nucleus and the first one to be discovered that the J₀ values are quite larger than that extracted from Q_t measurement. We found that all the excited SD bands in even–even nuclei are signature partner SD bands because the J₀ value of each signature partner SD band is almost identical. Among all these excited SD bands, ¹⁵⁰Gd(4) is found to be super-rigid in nature having J₀ value larger than that observed from the measured Q_t value.

Proton elastic scattering at various incident energies is one method to study nuclear density distributions and nuclear radii. Single folding potential describing the p-scattering on ⁴⁰Ca over a broad energy range 9–48.4 MeV is constructed. The resulting potential does not need any renormalization to fit the measured elastic scattering angular distributions and total reaction cross-sections. Furthermore, correlation between volume integral and proton incident energy is discussed. Theoretical calculations are in a good agreement with existing experimental data.

In this paper, we consider hadron production in high energy collisions as an Unruh radiation phenomenon. This mechanism describes the production pattern of newly formed hadrons and is directly applicable at vanishing baryon chemical potential, μ ≃ 0. It had already been found to correctly yield the hadronization temperature, in terms of the string tension σ. Here, we show that the Unruh mechanism also predicts hadronic freeze-out conditions, giving in terms of the entropy density s and for the average energy per hadron. These predictions provide a theoretical basis for previous phenomenological results and are also in accord with recent lattice studies.

Using HF + BCS method we study light nuclei with nuclear charge in the range 2 ≤ Z ≤ 8 and lying near the neutron drip line. The HF method uses effective Skyrme forces and allows for axial deformations. We find that the neutron drip line forms stability peninsulas at ¹⁸He and ⁴⁰C. These isotopes are found to be stable against one neutron emission and possess the highest known neutron to proton ratio in stable nuclei.

The thermal conductivity of pionic medium has been evaluated with the help of its standard expression from the relaxation time approximation, where inverse of pion relaxation time or pion thermal width has been obtained from the imaginary part of pion self-energy. In the real-time formalism of thermal field theory, the finite temperature calculations of pion self-energy for πσ and πρ loops have been done. The numerical value of our thermal conductivity increases with temperature very softly, though at particular temperature, our estimation has to consider a large band of phenomenological uncertainty.

In this paper, a general formula of the symmetry energy for many-body interaction is proposed and the commonly used two-body interaction symmetry energy is recovered. Within Landau's theory (Lt), we generalize two equations of state (EoS) CCSδ3 and CCSδ5 to asymmetric nuclear matter. We assume that the density and density difference between protons and neutrons divided by their sum are order parameters. We use different EoS to study neutron stars by solving the TOV equations. We demonstrate that different EoS give different mass and radius relation for neutron stars even when they have exactly the same ground state (gs) properties (E/A, ρ₀, K, S, L and K_sym). Furthermore, for one EoS we change K_sym and fix all the other gs parameters. We find that for some K_sym the EoS becomes unstable at high density even for neutron matter. This suggests that a neutron star (NS) can exist below and above the instability region but in different states: a quark gluon plasma (QGP) at high density and baryonic matter at low density. If the star's central density is in the instability region, then we associate these conditions to the occurrence of supernovae (SN).

The gauged Klein–Gordon equation, extended by a g_sσ_μνF^μν/4 interaction, the contraction of the electromagnetic field strength tensor, F^μν, with the generators, σ_μν/2, of the Lorentz group in (1/2, 0) ⊕ (0, 1/2), and g_s being the gyromagnetic factor, is examined with the aim to find out as to what extent it qualifies as a wave equation for general relativistic spin-1/2 particles transforming as (1/2, 0) ⊕ (0, 1/2) and possibly distinct from the Dirac fermions. This equation can be viewed as the generalization of the g_s = 2 case, known under the name of the Feynman–Gell-Mann equation, the only one which allows for a bilinearization into the gauged Dirac equation and its conjugate. At the same time, it is well-known a fact that a g_s = 2 value can also be obtained upon the bilinearization of the nonrelativistic Schrödinger into nonrelativistic Pauli equations. The inevitable conclusion is that it must not be necessarily relativity which fixes the gyromagnetic factor of the electron to g_(1/2) = 2, but rather the specific form of the primordial quadratic wave equation obeyed by it, that is amenable to a linearization. The fact is that space-time symmetries alone define solely the kinematic properties of the particles and neither fix the values of their interacting constants, nor do they necessarily prescribe linear Lagrangians. Information on such properties has to be obtained from additional physical inputs involving the dynamics. We here provide an example in support of the latter statement. Our case is that the spin-1/2^- fermion residing within the four-vector spinor triad, ψ_μ ~ (1/2⁺-1/2^--3/2^-), whose sectors at the free particle level are interconnected by spin-up and spin-down ladder operators, does not allow for a description within a linear framework at the interacting level. Upon gauging, despite transforming according to the irreducible (1/2, 1) ⊕ (1, 1/2) building block of ψ_μ, and being described by 16-dimensional four-vector spinors, though of only four independent components each, its Compton scattering cross sections, both differential and total, result equivalent to those for a spin-1/2 particle described by the generalized Feynman–Gell-Mann equation from above (for which we provide an independent algebraic motivation) and with g_(1/2^-) = -2/3. In effect, the spin-1/2^- particle residing within the four-vector spinor effectively behaves as a true relativistic "quadratic" fermion. The g_(1/2^-) = -2/3 value ensures in addition the desired unitarity in the ultraviolet. In contrast, the spin-1/2⁺ particle, in transforming irreducibly in the (1/2, 0) ⊕ (0, 1/2) sector of ψ_μ, is shown to behave as a truly linear Dirac fermion. Within the framework employed, the three spin sectors of ψ_μ are described on equal footing by representation- and spin-specific wave equations and associated Lagrangians which are of second-order in the momenta.