Nuclear Theory

We compute the charge radii of even-mass neon and magnesium isotopes from neutron number N = 8 to the dripline. Our calculations are based on nucleon-nucleon and three-nucleon potentials from chiral effective field theory that include delta isobars. These potentials yield an accurate saturation point and symmetry energy of nuclear matter. We use the coupled-cluster method and start from an axially symmetric reference state. Binding energies and two-neutron separation energies largely agree with data and the dripline in neon is accurate. The computed charge radii have an estimated uncertainty of about 2-3% and are accurate for many isotopes where data exist. Finer details such as isotope shifts, however, are not accurately reproduced. Chiral potentials correctly yield the subshell closure at N = 14 and also a decrease in charge radii at N = 8 (observed in neon and predicted for magnesium). They yield a continued increase of charge radii as neutrons are added beyond N = 14 yet underestimate the large increase at N = 20 in magnesium.

Background: The electric giant-dipole resonance (GDR) is the most established collective vibrational mode of excitation. A charge-exchange analog, however, has been poorly studied in comparison with the spin (magnetic) dipole resonance (SDR). Purpose: I investigate the role of deformation on the charge-exchange dipole excitations and explore the generic features as an isovector mode of excitation. Methods: The nuclear energy-density functional method is employed for calculating the response functions based on the Skyrme--Kohn--Sham--Bogoliubov method and the proton-neuton quasiparticle-random-phase approximation. Results: The deformation splitting into K=0 and K=±1 components occurs in the charge-changing channels and is proportional to the magnitude of deformation as is well known for the GDR. For the SDR, however, a simple assertion based on geometry of a nucleus cannot be applied for explaining the vibrational frequencies of each K -component. A qualitative argument on the strength distributions for each component is given based on the non-energy-weighted sum rules taking nuclear deformation into account. The concentration of the electric dipole strengths in low energy and below the giant resonance is found in neutron-rich unstable nuclei. Conclusions: The deformation splitting occurs generically for the charge-exchange dipole excitions as in the neutral channel. The analog pygmy dipole resonance can emerge in deformed neutron-rich nuclei as well as in spherical systems.

In this work, we mainly explore the possibility of charged rho superconductor (CRS) in the presence of parallel magnetic field and rotation within three-flavor Nambu--Jona-Lasino model. By following similar schemes as in the previous studies of charged pion superfluid (CPS), the CRS is found to be favored for both choices of Schwinger phase in Minkovski and curved spaces. Due to the stability of the internal spin structure, charged rho begins to condensate at a smaller threshold of angular velocity than charged pion for the given large magnetic fields. Even the axial vector meson condensation is checked -- the conclusion is that CRS is the robust ground state at strong magnetic field and fast rotation, which actually sustains to very large angular velocity.

Born in the aftermath of core collapse supernovae, neutron stars contain matter under extraordinary conditions of density and temperature that are difficult to reproduce in the laboratory. In recent years, neutron star observations have begun to yield novel insights into the nature of strongly interacting matter in the high-density regime where current theoretical models are challenged. At the same time, chiral effective field theory has developed into a powerful framework to study nuclear matter properties with quantified uncertainties in the moderate-density regime for modeling neutron stars. In this article, we review recent developments in chiral effective field theory and focus on many-body perturbation theory as a computationally efficient tool for calculating the properties of hot and dense nuclear matter. We also demonstrate how effective field theory enables statistically meaningful comparisons between nuclear theory predictions, nuclear experiments, and observational constraints on the nuclear equation of state.

Within the framework of Dyson--Schwinger equations of QCD, we study the effect of finite volume on the chiral phase transition in a sphere with the MIT boundary condition. We find that the chiral quark condensate ⟨ ψ ¯ ψ⟩ and pseudotransition temperature T pc of the crossover decreases as the volume decreases, until there is no chiral crossover transition at last. We find that the system for R=∞ \ fm is indistinguishable from R=10 fm and there is a significant decrease in T pc with R as R<4 fm. When R<1.5 fm, there is no chiral transition in the system.

Three-nucleon force and continuum play important roles in reproducing the properties of atomic nuclei around driplines. Therefore it is valuable to build up a theoretical framework where both effects can be taken into account to solve the nuclear Schrödinger equation. To this end, in this letter, we have expressed the chiral three-nucleon force within the continuum Berggren representation, so that bound, resonant and continuum states can be treated on an equal footing in the complex-momentum space. To reduce the model dimension and computational cost, the three-nucleon force is truncated at the normal-ordered two-body level and limited in the sd -shell model space, with the residual three-body term being neglected. We choose neutron-rich oxygen isotopes as the test ground because they have been well studied experimentally, with the neutron dripline determined. The calculations have been carried out within the Gamow shell model. The quality of our results in reproducing the properties of oxygen isotopes around the neutron dripline shows the relevance of the interplay between three-nucleon force and the coupling to continuum states. We also analyze the role played by the chiral three-nucleon force, by dissecting the contributions of the 2π exchange, 1π exchange and contact terms.

We have studied, for the first time, the influence of the collective quantum effects in the nuclear wave functions on the azimuthal anisotropy coefficients ϵ 2,3 in the central Pb+Pb collisions at the LHC energies. With the help of the energy weighted sum rule we demonstrate that the classical treatment with the Woods-Saxon nuclear density overestimates the mean square quadrupole moment of the 208 Pb nucleus by a factor of ∼2.2 . The Monte-Carlo Glauber simulation of the central Pb+Pb collisions accounting for the restriction on the quadrupole moment leads to ϵ 2 / ϵ 3 ≈0.8 which allows to resolve the v 2 -to- v 3 puzzle.

Collective flow of the final-state hadrons observed in ultrarelativistic heavy-ion collisions or even in smaller systems formed in high-multiplicity pp and p/d/ 3 He-nucleus collisions is one of the most important diagnostic tools to probe the initial state of the system and to shed light on the properties of the short-lived, strongly-interacting many-body state formed in these collisions. Limited, in the initial years, to the study of mainly the directed and elliptic flows -- the first two Fourier harmonics of the single-particle azimuthal distribution -- this field has evolved in recent years into a much richer area of activity. This includes not only higher Fourier harmonics and multiparticle cumulants, but also a variety of other related observables, such as the ridge seen in two-particle correlations, flow decorrelation, symmetric cumulants and event-plane correlators which measure correlations between the magnitudes or phases of the complex flows in different harmonics, coefficients that measure the nonlinear hydrodynamic response, statistical properties, such as the non-Gaussianity of the flow fluctuations, etc. We present a Tutorial Review of the modern flow picture and the various aspects of the collectivity -- an emergent phenomenon in quantum chromodynamics.

In this paper, the NJL-type model is used to investigate the color superconductivity. The four-fermion interactions of the NJL-type model are Fierz-transformed into two different classes, i.e., the quark-antiquark and the quark-quark interaction channels, associated with the chiral symmetry breaking and color superconductivity respectively. We conclude that the weighting factor between quark-antiquark and quark-quark interaction channels has significance on the phase structure when the mean-field approximation is employed, and the baryon number density gives a tight constraint on the weighting factor of quark-antiquark interaction channels. Besides, the susceptibilities show that the color superconducting phase transition is of the second-order and takes place before the chiral crossover transition as quark number density increases. In the end, we study the critical temperatures T c of the color superconductivity and it agrees with the perturbative result of diquark condensate Δ≈0.57 T c .

Song et al. [Phys. Rev. C 102, 065208 (2020)] presented results for the ? c N interaction based on an extrapolation of lattice simulations by the HAL QCD Collaboration at unphysical quark masses to the physical point via covariant chiral effective field theory. We point out that their predictions for the 3 D 1 partial wave disagree with available lattice results. We discuss the origin of that disagreement and present a comparison with predictions from conventional (non-relativistic) chiral effective field theory.