Nuclear Theory·nucl-th

Monday·December 9, 2019

11 papers—8 primary·3 cross-listed

09
Crystallization of the outer crust of a non-accreting neutron star
A. F. Fantina🇫🇷 · S. De Ridder🇧🇪 · N. Chamel🇧🇪 · F. Gulminelli🇫🇷
The interior of a neutron star (NS) is usually assumed to be made of cold catalyzed matter. However, the outer layers are unlikely to remain in full equilibrium during the formation of the star and its cooling, especially after crystallization. We study the cooling and equilibrium composition of the outer layers of a NS down to crystallization. Here the impurity parameter, usually a free parameter in cooling simulations, is calculated self-consistently using a microscopic model for which a unified equation of state has recently been determined. We follow the evolution of the nuclear distributions of the multi-component Coulomb liquid plasma (MCP) fully self-consistently, adapting a general formalism originally developed for the description of supernova cores. We calculate the impurity parameter at the crystallization as determined in the one-component plasma (OCP) approximation. Our analysis shows that the sharp changes in composition obtained in the OCP approximation are smoothed out when a full nuclear distribution is allowed. The Coulomb coupling parameter at melting is found to be reasonably close to the canonical value of 175, except for specific pressures for which supercooling occurs in the OCP approximation. Our MCP treatment leads to non-monotonic variations of the impurity parameter with pressure. Its values can change by several orders of magnitude reaching about 50, suggesting that the crust may be composed of an alternation of pure (highly conductive) and impure (highly resistive) layers. The results presented here complement the recent unified equation of state obtained with the same model. Our self-consistent approach to hot MCP shows that the presence of impurities in the outer crust of a NS is non-negligible and may have a sizeable impact on transport properties. In turn, this may have important implications for the cooling of NS and their magneto-rotational evolution.
↳ astro-ph.HEnucl-thAstron.Astrophys.(2020)·48 citations
10
Electromagnetic properties of $^{21}$ O for benchmarking nuclear Hamiltonians
S. Heil · M. Petri · K. Vobig · D. Bazin · J. Belarge · P. Bender · B. A. Brown · R. Elder · B. Elman · A. Gade · T. Haylett · J. D. Holt and 16 other authors
The structure of exotic nuclei provides valuable tests for state-of-the-art nuclear theory. In particular electromagnetic transition rates are more sensitive to aspects of nuclear forces and many-body physics than excitation energies alone. We report the first lifetime measurement of excited states in $^{21}$ O, finding $τ_{1/ 2^{+}} = 42 0_{- 32}^{+ 35} (stat)_{- 12}^{+ 34} (sys)$ \,ps. This result together with the deduced level scheme and branching ratio of several $γ$ -ray decays are compared to both phenomenological shell-model and ab initio calculations based on two- and three-nucleon forces derived from chiral effective field theory. We find that the electric quadrupole reduced transition probability of $B (E2; 1/ 2^{+} \to 5/ 2_{g.s.}^{+}) = 0.7 1_{- 0.06 - 0.06}^{+ 0.07 + 0.02}$ ~e $^{2}$ fm $^{4}$ , derived from the lifetime of the $1/ 2^{+}$ state, is smaller than the phenomenological result where standard effective charges are employed, suggesting the need for modifications of the latter in neutron-rich oxygen isotopes. We compare this result to both large-space and valence-space ab initio calculations, and by using multiple input interactions we explore the sensitivity of this observable to underlying details of nuclear forces.
↳ nucl-exnucl-thPLB(2020)·12 citations
11
Exact Multi-Instanton Solutions to Selfdual Yang-Mills Equation on Curved Spaces
Jun Nian🇺🇸 · Yachao Qian🇺🇸
We find exact multi-instanton solutions to the selfdual Yang-Mills equation on a large class of curved spaces with $S O (3)$ isometry, generalizing the results previously found on $R^{4}$ . The solutions are featured with explicit multi-centered expressions and topological properties. As examples, we demonstrate the approach on several different curved spaces, including the Einstein static universe and $R \times$ dS $_{3}^{E}$ , and show that the exact multi-instanton solutions exist on these curved backgrounds.
↳ hep-thmath-phmath.MPnucl-thInt.J.Mod.Phys.A(2021)·2 citations

Affiliations

first authorsco-authorsvia INSPIRE

Crystallization of the outer crust of a non-accreting neutron star

Electromagnetic properties of 21O for benchmarking nuclear Hamiltonians

Exact Multi-Instanton Solutions to Selfdual Yang-Mills Equation on Curved Spaces

Affiliations

Electromagnetic properties of $^{21}$ O for benchmarking nuclear Hamiltonians