Motivated by the successes of relativistic theories in studies of atomic/molecular and nuclear systems and the need for a relativistic chiral force in relativistic nuclear structure studies, we explore a new relativistic scheme to construct the nucleon-nucleon interaction in the framework of covariant chiral effective field theory. The chiral interaction is formulated up to leading order with covariant power counting and a Lorentz invariant chiral Lagrangian.We find that the relativistic scheme induces all six spin operators needed to describe the nuclear force. A detailed investigation of the partial wave potentials shows a better description of the;S——0 and;P;phase shifts than the leading order Weinberg approach, and similar to that of the next-to-leading order Weinberg approach. For the other partial waves with angular momenta J≥1, the relativistic results are almost the same as their leading order non-relativistic counterparts.
Recently,a relativistic chiral nucleon-nucleon interaction was formulated up to leading order,which provides a good description of the phase shifts of J≤1 partial waves[Chin.Phys.C 42(2018)014103].Nevertheless,a separable regulator function that is not manifestly covariant was used in solving the relativistic scattering equation.In the present work,we first explore a covariant and separable form factor to regularize the kernel potential and then apply it to study the simplest but most challenging ^(1)S_(0) channel which features several lowenergy scales.In addition to being self-consistent,we show that the resulting relativistic potential can describe quite well the unique features of the ^(1)S_(0) channel at leading order,in particular the pole position of the virtual bound state and the zero amplitude at the scattering momentum ~340 MeV,indicating that the relativistic formulation may be more natural from the viewpoint of effective field theories.
The N = 28 shell gap in sulfur, argon, calcium and titanium isotopes is investigated in the framework of relativistic continuum Hartree-Bogoliubov （RCHB） theory. The evolutions of neutron shell gap, separation energy, single particle energy and pairing energy are analyzed, and it is found that the N = 28 shell gap is quenched in sulfur isotopes but persists in argon, calcium and titanium isotopes. The evolution of the N = 28 shell gap in the N = 28 isotonic chain is discussed, and the erosion of the N = 28 shell gap is understood with the evolution of potential with proton number.
The superheavy nucleus256Rf,where rotational band and multi-quasiparticle isomer have been observed recently,has been investigated using total Routhian surface calculations and configuration-constrained calculations of potential energy surface,with the inclusion of b6deformation.The experimental moment of inertial is well reproduced,indicating that the alignment is delayed due to the b6deformation.A K p=5-or 8-state could form a two-quasiparticle isomer that is calculated to have higher fission barrier than the ground state.
Based on relativistic mean field（RMF） models, we study finite A-hypernuclei and massive neutron stars. The effective N-N interactions PK1 and TM1 are adopted, while the N-A interactions are constrained by reproducing the binding energy of A-hyperon at 1 s orbit of Λ^40Ca. It is found that the A-meson couplings follow a simple relation, indicating a fixed A potential well for symmetric nuclear matter at saturation densities, i.e., around VΛ=-29.786 MeV. With those interactions, a large mass range of Λ-hypernuclei can be described well. Furthermore,the masses of PSR J1614-2230 and PSR J0348＋0432 can be attained adopting the Λ-meson couplings gσΛ/gσN≥0.73,gωΛ/gωN≥0.80 for PK1 and gσΛ/gσN≥0.81,gωΛ/gωN≥0.90 for TM1, respectively. This resolves the hyperon puzzle without introducing any additional degrees of freedom.
