Nuclear Theory·nucl-th

Tuesday·March 1, 2022

12 papers—11 primary·1 cross-listed

01
Effective field theory of pairing rotations
T. Papenbrock
Pairing rotations are the low-energy excitations of finite superfluid systems, connecting systems that differ in their number of Cooper pairs. This paper presents a model-independent derivation of pairing rotations within an effective theory that exploits the emergent breaking of U(1) phase symmetries. The symmetries are realized nonlinearly and the Nambu-Goldstone modes depend only on time because the system is finite. Semi-magic nuclei exhibit pairing rotational bands while the pairing spectrum becomes an elliptical paraboloid for open-shell nuclei. Model-independent relations between double charge-exchange reactions and alpha particle capture or knockout in open-shell nuclei are in analogy to the pair transfer reactions in a single superfluid. Odd semi-magic nuclei are described by coupling a fermion to the superfluid. The leading-order theories reproduce data for pairing rotational bands within uncertainty estimates.
nucl-thnucl-exPRC(2022)·12 citations
02
Insights into the equation of state of neutron-rich matter since GW170817
J. Piekarewicz🇺🇸
The historical detection of gravitational waves emitted from the binary neutron star merger GW170817 has opened the new era of multi-messenger astronomy. Since then, many other significant discoveries -- both on heaven and earth -- are providing new clues into the behavior of neutron-rich matter. It is the goal of this article to illustrate how the remarkable progress made during the last few years is spearheading the field into the golden age of neutron-star physics.
nucl-thgr-qcnucl-exJ.Phys.Conf.Ser.(2022)·0 citations
03
Transient Joule- and (ac) Josephson-like photon emission in one- and two- nucleon tunneling processes between superfluid nuclei: blackbody and coherent spectral functions
R. A. Broglia · F. Barranco · G. Potel · E. Vigezzi
Effective charged neutrons involved in one- and two- nucleon tunneling processes in heavy ion collisions between superfluid nuclei are expected to emit photons. Although the centroid, width and integrated energy area characterizing the associated gamma-strength functions are rather similar, the corresponding line shapes reflect the thermal equilibrated-like character of the quasiparticle transfer (1n-channel, blackbody spectral functional dependence), and the quantal coherent character of the Cooper pair transfer (2n-channel, Gaussian functional dependence) respectively. The predicted angular distributions, polarizations and analyzing power provide further insight into the profoundly different physics to be found at the basis of what can be considered a transient Joule-like and a (ac) Josephson-like nuclear processes
nucl-thPRC(2022)·8 citations
04
Non-iterative finite amplitude methods for E1 and M1 giant resonances
Hirokazu Sasaki · Toshihiko Kawano · Ionel Stetcu
The finite amplitude method (FAM) is a very efficient approach for solving the fully self-consistent random-phase approximation (RPA) equations. We use FAM to rederive the RPA matrices for general Skyrme-like functionals, calculate the electric dipole (E1) and the magnetic dipole (M1) giant resonances, and compare the results with available experimental and evaluated data. For the E1 transitions in heavy nuclei, the calculations reproduce well the resonance energy of the photoabsorption cross sections. In the case of M1 transitions, we show that the residual interaction does not affect the transition strength of double-magic nuclei, which suggests that the spin terms in the Skyrme force currently neglected in the present computation could improve the agreement between FAM and experimental data.
nucl-thastro-ph.HEnucl-exPRC(2022)·10 citations
05
A topological realization of spin polarization through vortex formation in collisions of Bose-Einstein condensates
Jian Deng🇨🇳 · Qun Wang🇨🇳 · Hong Zhang🇨🇳
The global spin polarization of hadrons in heavy ion collisions has been measured in STAR (the Solenoidal Tracker At Relativistic heavy ion collider) experiments, which opens up a new window in the study of the hottest, least viscous and most vortical fluid that has ever been produced in the laboratory. We present a different approach to spin polarization from conventional ones: a topological realization of spin polarization through quantum vortex formation in collisions of Bose-Einstein condensates (BEC). This approach is based on the observation that the vortex is a topological excitation in a superfluid in presence of local orbital angular momentum and is an analogue of spin degrees of freedom. The formation processes of vortices and vortex-antivortex pairs are investigated by solving the Gross-Pitaevskii Equation with a large-scale parallel algorithm on Graphics Processing Unit (GPU) to very high precision. In a rotating environment, the primary vortex with winding number one is stable against perturbation, which has a minimal energy and fixed orbital angular momentum (OAM), but the vortices with larger winding numbers are unstable and will decay into primary vortices through a redistribution of the energy and vorticity. The injection of OAM can also be realized in non-central collisions of self-interacting condensates, part of the OAM of the initial state will induce the formation of vortices through concentration of energy and vorticity density around topological defects. Different from a hydrodynamical description, the interference of the wave function plays an important role in the transport of energy and vorticity, reflecting the quantum nature of the vortex formation process. The study of the vortex formation may shed light on the nature of particle spin and spin-orbit couplings in strong interaction matter produced in heavy-ion collisions.
nucl-thcond-mat.quant-gashep-phPhys.Fluids(2022)·1 citation
06
Gamow shell model description of the radiative capture reaction $^{8}$ Li $(n, γ)$ $^{9}$ Li
G.X. Dong🇨🇳 · X.B. Wang🇨🇳 · N. Michel🇨🇳 · M. Płoszajczak🇫🇷
The $^{8}$ Li $(n, γ)$ $^{9}$ Li reaction plays a critical role in several reaction chains leading to the nucleosynthesis of $A > 12$ nuclei. Due to unstable nature of $^{8}$ Li and the unavailability of neutron targets, direct measurements of this reaction are exceedingly difficult. Only upper limits of this cross section, provided by the indirect experiments, have been obtained so far. In this work, we use the Gamow shell model (GSM) in the coupled-channel representation (GSM-CC) to study the properties of $^{9}$ Li and the radiative capture reaction $^{8}$ Li $(n, γ)$ $^{9}$ Li. In GSM-CC calculations, a translationally invariant Hamiltonian is used with a finite-range two-body interaction tuned to reproduce the low-energy spectra of $^{8 - 9}$ Li. In the calculation of $^{8}$ Li $(n, γ)$ $^{9}$ Li cross section, all relevant E1, M1, and E2 transitions from the initial continuum states to the final bound states $3/2_{1}^{-}$ , $1/2_{1}^{-}$ and the resonance $5/2_{1}^{-}$ of $^{9}$ Li are included. The GSM-CC approach reproduces the experimental low-energy spectrum, neutron emission threshold, and spectroscopic factors in $^{9}$ Li. The calculated reaction rate is consistent with the experimental upper limit of the reaction rate obtained in the indirect measurements at stellar energies. The GSM-CC calculations suggest that the $^{8}$ Li $(n, γ)$ $^{9}$ Li reaction can reduce heavy-element production via the main chain $^{7}$ Li( $n, γ$ ) $^{8}$ Li( $α, n$ ) $^{11}$ B( $n, γ$ ) $^{12}$ B( $β^{+}$ ) $^{12}$ C. Major contribution to the calculated cross section is given by the direct E1 transition to the ground state of $^{8}$ Li. The contribution of excited states to the reaction rate does not exceed $\sim$ 18% of the total reaction rate.
nucl-thPRC(2022)·13 citations
07
The Equation of State of Neutron-Rich Matter at Fourth Order of Chiral Effective Field Theory and the Radius of a Medium-Mass Neutron Star
Francesca Sammarruca · Randy Millerson
We report neutron star predictions based on our most recent equations of state. These are derived from chiral effective field theory, which allows for a systematic development of nuclear forces, order by order. We utilize high-quality two-nucleon interactions and include all three-nucleon forces up to fourth order in the chiral expansion. Our ab initio predictions are restricted to the domain of applicability of chiral effective field theory. However, stellar matter in the interior of neutron stars can be up to several times denser than normal nuclear matter at saturation, and its composition is essentially unknown. Following established practices, we extend our microscopic predictions to higher densities matching piecewise polytropes. The radius of the average-size neutron star, about 1.4 solar masses, is sensitive to the pressure at normal densities, and thus it is suitable to constrain ab initio theories of the equation of state. For this reason, we focus on the radius of medium-mass stars. We compare our results with other theoretical predictions and recent constraints.
nucl-thUniverse(2022)·14 citations
08
Probing the initial longitudinal density profile and electromagnetic field in ultrarelativistic heavy-ion collisions with heavy quarks
Ze-Fang Jiang🇨🇳 · Shanshan Cao🇨🇳 · Wen-Jing Xing🇨🇳 · Xiang-Yu Wu🇨🇳 · C. B. Yang🇨🇳 · Ben-Wei Zhang🇨🇳
Heavy quarks are valuable probes of the electromagnetic field and the initial condition of the quark-gluon plasma (QGP) matter produced in high-energy nuclear collisions. Within an improved Langevin model that is coupled to a (3+1)-dimensional viscous hydrodynamic model, we explore the origin of the directed flow coefficient ( $v_{1}$ ) of heavy mesons and their decay leptons, and its splitting ( $Δ v_{1}$ ) between opposite charges. We find that while the rapidity dependence of the heavy flavor $v_{1}$ is mainly driven by the titled energy density profile of the QGP with respect to the longitudinal direction at the RHIC energy, it is dominated by the electromagnetic field at the LHC energy. The $Δ v_{1}$ serves as a novel probe of the spacetime evolution profile of the electromagnetic field. Our results of $D$ mesons and their decay electrons are consistent with the available data at RHIC and LHC, and our predictions on the heavy flavor decay muons can be further tested by future measurements.
nucl-thhep-phPRC(2022)·37 citations
09
Emergent geometry and duality in the carbon nucleus
Shihang Shen🇩🇪 · Serdar Elhatisari · Timo A. Lähde🇩🇪 · Dean Lee🇺🇸 · Bing-Nan Lu · Ulf-G. Meißner🇩🇪
The carbon atom provides the backbone for the complex organic chemistry composing the building blocks of life. The physics of the carbon nucleus in its predominant isotope, $^{12}$ C, is similarly full of multifaceted complexity. Some nuclear states of $^{12}$ C can be preferentially treated as a collection of independent particles held by the mean field of the nucleus, while other states behave more as a collection of three alpha-particle clusters. But these two pictures are not mutually exclusive, and some states can be described in either fashion $^{1, 2}$ . In this work, we provide the first model-independent tomographic scan of the three-dimensional geometry of the nuclear states of $^{12}$ C using the {\it ab initio} framework of nuclear lattice effective field theory. We find that the well-known but enigmatic Hoyle state is composed of a "bent-arm" or obtuse triangular arrangement of alpha clusters. We identify all of the low-lying nuclear states of $^{12}$ C as having an intrinsic shape composed of three alpha clusters forming either an equilateral triangle or an obtuse triangle. From these basic structural formations, the various nuclear states correspond to different rotational and vibrational excitations as well as either distortions or large-amplitude displacements of the alpha clusters. The states with the equilateral triangle formation also have a dual description in terms of particle-hole excitations in the mean-field picture. We compare our theoretical calculations with experimental data for binding energies, quadrupole moments, electromagnetic transitions, charge densities, and form factors. The overall agreement is good, and further studies using higher-fidelity interactions are planned.
nucl-thhep-latnucl-exNature Commun.(2023)·77 citations
10
Time-dependent generator coordinate method study of fission: dissipation effects
Jie Zhao · Tamara Nikšić · Dario Vretenar
Starting from a quantum theory of dissipation for nuclear collective motion, the time-dependent generator coordinate method (TDGCM) is extended to allow for dissipation effects in the description of induced fission dynamics. The extension is based on a generalization of the GCM generating functions that includes excited states, and the resulting equation of motion in the collective coordinates and excitation energy. With the assumption of a narrow hamiltonian kernel, an expansion in a power series in collective momenta leads to a Schrödinger-like equation that explicitly includes a dissipation term, proportional to the momentum of the statistical wave function. An illustrative calculation is performed for induced fission of $^{228}$ Th. The three-dimensional model space includes the axially-symmetric quadrupole and octupole shape variables, and the nuclear temperature. When compared to data for photo-induced fission of $^{228}$ Th, the calculated fission yields demonstrate the important role of the additional term in the hamiltonian that explicitly takes into account the dissipation of energy of collective motion into intrinsic degrees of freedom.
nucl-thnucl-exPRC(2022)·28 citations
11
Unsupervised machine learning correlations in EoS of neutron stars
Ronaldo V. Lobato · Emanuel V. Chimanski · Carlos A. Bertulani
Neutron stars are compact objects of large interest in the nuclear astrophysics community. The extreme conditions present in such systems impose big challenges to our current microscopic models of nuclear structure. Equation of states (EoS) are frequently derived from sophisticated quantum mechanical models, such as: relativistic, non-relativistic and many mean-field approaches. Every single model, in general, contains many parameters such as the NN interaction strength, particle compositions, etc. These are particular features of each model and can be represented by numbers and categories in a machine learning context. Different choices of features will affect EoS properties leading to different macroscopic properties of the star. In this work we analyze a selection of EoS containing a variety of different physics models. One of our objectives is to develop tools that enable a better understanding of the correlations among the different model features and the outcome produced by them when employed to model neutron stars.
nucl-thastro-ph.HEPoS(2022)·6 citations

Affiliations

first authorsco-authorsvia INSPIRE