Nuclear Theory

We use a dispersion representation based on unitarity and analyticity to study the low energy γ ??N?�πN process in the S 11 channel. Final state interactions among the ?N system are critical to this analysis. The left-hand part of the partial wave amplitude is imported from O( p 2 ) chiral perturbation theory result. On the right-hand part, the final state interaction is calculated through Omnès formula in S wave. It is found that a good numerical fit can be achieved with only one subtraction parameter, and the eletroproduction experimental data of multipole amplitudes E 0+ , S 0+ in the energy region below ?(1232) are well described when the photon virtuality Q 2 ??.1 GeV 2 .

Using classical description of spin degrees of freedom, we extend recent formulation of the perfect-fluid hydrodynamics for spin-polarized fluids to the case including dissipation. Our work is based on the analysis of classical kinetic equations for massive particles with spin-1/2, with the collision terms treated in the relaxation time approximation. The kinetic-theory framework determines the structure of viscous and diffusive terms and allows to explicitly calculate a complete set of new kinetic coefficients that characterize dissipative spin dynamics.

We study dynamical screening effects of nuclear charge on big bang nucleosynthesis (BBN). A moving ion in plasma creates a distorted electric potential leading to a screening effect which is different from the standard static Salpeter formula. We consider the electric potential for a moving test charge, taking into account dielectric permittivity in the unmagnetized Maxwellian plasma during the BBN epoch. Based on the permittivity in a BBN plasma condition, we present the Coulomb potential for a moving nucleus, and show that enhancement factor for the screening of the potential increases the thermonuclear reaction rates by a factor order of 10^(-7). In the Gamow energy region for nuclear collisions, we find that the contribution of the dynamical screening is less than that of the static screening case, consequently which primordial abundances hardly change. Based on the effects of dynamical screening under various possible astrophysical conditions, we discuss related plasma properties required for possible changes of the thermal nuclear reactions.

Understanding properties of Quark-Gluon Plasma requires an unbiased comparison of experimental data with theoretical predictions. To that end, we developed the dynamical energy loss formalism which, in distinction to most other methods, takes into account a realistic medium composed of dynamical scattering centers. The formalism also allows making numerical predictions for a wide number of observables with the same parameter set fixed to standard literature values. In this proceedings, we overview our recently developed DREENA-C and DREENA-B frameworks, where DREENA is a computational implementation of the dynamical energy loss formalism, and where C stands for constant temperature QCD medium, while B stands for the medium modeled by 1+1D Bjorken expansion. At constant temperature our predictions overestimate v 2 , in contrast to other models, but consistent with simple analytical estimates. With Bjorken expansion, we have a good agreement of the predictions with both R AA and v 2 measurements. We find that introducing medium evolution has a larger effect on v 2 predictions, but for precision predictions it has to be taken into account in R AA predictions as well. Based on numerical calculations and simple analytical derivations, we also propose a new observable, which we call path length sensitive suppression ratio, for which we argue that the path length dependence can be assessed in a straightforward manner. We also argue that Pb+Pb vs. Xe+Xe measurements make a good system to assess the path length dependence. As an outlook, we expect that introduction of more complex medium evolution (beyond Bjorken expansion) in the dynamical energy loss formalism can provide a basis for a state of the art QGP tomography tool - e.g. to jointly constrain the medium properties from the point of both high pt and low pt data.

The expression for the dynamical spectral structure of the density fluctuation near the QCD critical point has been derived using linear response theory within the purview of Israel-Stewart relativistic viscous hydrodynamics. The change in spectral structure of the system as it moves toward critical end point has been studied. The effects of the critical point have been introduced in the system through a realistic equation of state and the scaling behaviour of various transport coefficients and thermodynamic response functions. We have found that the Brillouin and the Rayleigh peaks are distinctly visible when the system is away from critical point but the peaks tend to merge near the critical point. The sensitivity of structure of the spectral function on wave vector ( k ) of the sound wave has been demonstrated. It has been shown that the Brillouin peaks get merged with the Rayleigh peak because of the absorption of sound waves in the vicinity of the critical point.

The past two decades have witnessed tremendous progress in the microscopic description of atomic nuclei. The Topical Review `The Future of Nuclear Structure' aims at summarizing the current state-of-the-art microscopic calculations in Nuclear Theory and to give a useful reference for young researches who wish to learn more about this exciting discipline.

The neutron star maximum mass and the radius are investigated within the framework of the relativistic mean-field (RMF) model. The variation in the radius at the canonical mass, R 1.4 , using different inner crust equation of state (EoS) with different symmetry energy slope parameter is studied. It is found that although the NS maximum mass and the corresponding radius do not vary much with different inner crust EoSs, the radius and the tidal deformability at 1.4 M ⊙ vary with the different choice of crust EoS and variation of about 1-2 km is seen in the radius at the canonical mass. For non-unified EoSs, the crust with a low symmetry energy slope parameter produces a low NS radius at the canonical mass. The properties of maximally rotating neutron stars are also studied. The variation in the radius of rotating star at the canonical mass 1.4 M ⊙ is also seen with the slope parameter. Similar to the static neutron star, the radius at 1.4 M ⊙ of rotating neutron star is affected by slope parameter of the inner crust. Other important quantities like moment of inertia, frequency, rotational kinetic energy to gravitational energy ratio are also calculated. The variation in these quantities with the crust slope parameter is found to be more proportional to the mass and the radius of NS.

The phenomenon of liquid-gas phase transition occurring in heavy ion collisions at intermediate energies is a subject of contemporary interest. In statistical models of fragmentation, the liquid drop model is generally used to calculate the ground state binding energies of the fragments. It is well known that the surface and symmetry energy of the hot fragments at the low density freeze out can be considerably modified. In addition to this, the level density parameter also has a wide variation. The effect of variation of these parameters is studied on fragmentation observables which are related to the nuclear liquid gas phase transition. The canonical thermodynamical model which has been very successful in describing the phenomenon of fragmentation is used for the study. The shift in transition temperature owing to the variation in liquid drop model parameters has been examined.

Resonances are of particular importance to the scattering of composite particles in quantum mechanics. We build an effective field theory for two-body scattering which includes a low-energy S -wave resonance. Our starting point is the most general Lagrangian with short-range interactions. We demonstrate that these interactions can be organized into various orders so as to generate a systematic expansion for an S matrix with two low-energy poles. The pole positions are restricted by renormalization at leading order, where the common feature is a non-positive effective range. We carry out the expansion explicitly to next-to-leading order and illustrate how it systematically accounts for the results of a toy model -- a spherical well with a delta shell at its border.

The effective interactions between two nuclear clusters, d+d , t+t , and α+α , are investigated within a cluster model using local nucleon-nucleon~( NN ) forces. It is shown that the interaction in the spin-aligned d+d system is repulsive for all inter-cluster distances, whereas the α+α and spin-aligned t+t systems are attractive at intermediate distances. The Pauli blocking between identical-nucleon pairs is responsible for the cluster-cluster repulsion and becomes dominant in the shallow binding limit. We demonstrate that two d -clusters could be bound if the NN force has nonzero range and is strong enough to form a deeply bound d -cluster, or if the NN force has both even-parity and odd-parity attraction. Effective dimer-dimer interactions for general quantum systems of two-component fermions are also discussed in heavy-light mass limit, where one component is much heavier than the other, and their relation to inter-cluster interactions in nuclear systems are discussed. Our findings provide a conceptual foundation for conclusions obtained numerically in the literature, that increasing the range or strength of the local part of the attractive nucleon-nucleon interaction results in a more attractive cluster-cluster interaction.