Nuclear Theory·nucl-th

Wednesday·May 20, 2020

7 papers—3 primary·4 cross-listed

01
The thermal conductivity of "pastas" in neutron star matter
Claudio Dorso · Jonathan Dunn · Alejandro Strachan · Guillermo Frank
This investigation explores the phononic thermal conductivity of nuclear star matter as it undergoes the "topological" transition to the "pasta" regime, and further down to the solid-liquid phase transition. The study was carried out using molecular dynamics simulations with nuclear potentials embedded in an effective (i.e. Thomas-Fermi) Coulomb potential. The thermal conductivity experiences a dramatic change within a narrow temperature interval around T=1 MeV. This change accomplishes the "pasta" breakdown during a heating process. The thermal conductivity by flipping protons' or neutrons' velocity further shows a decoupling for asymmetric nuclear star matter.
nucl-thNPA(2020)·13 citations
02
Cross-shell excitations in doubly magic 132Sn and its nearest neighbours
Sangeeta Das · M. Saha Sarkar
Large scale shell model calculations have been performed to study the excitation spectra of 132Sn and its nearest neighbours with a new cross-shell interaction constructed from two widely used interactions, sn100pn and CWG, of this mass region. A few of the two-body matrix elements have been tuned to reproduce the low-lying multiplet states of 132Sn. This is the first full scale shell model study of 132Sn energy spectra as well as transition probabilities. The excitation spectra for other nearest neighbours are reproduced reasonably well. The most important observable calculated are the E1 transition probabilities, which were so far beyond the scope of calculations with the existing interactions.
nucl-thNPA(2021)·4 citations
03
Transport in neutron star mergers
Steven P. Harris🇺🇸
After an introduction to the QCD phase diagram, the nuclear equations of state, and neutron star mergers, I discuss three projects related to transport and nuclear matter in neutron star mergers. The first is the nature of beta equilibrium in the portion of a merger that is transparent to neutrinos. We calculate the weak interaction (Urca) rates and find that the beta equilibrium condition needs to be modified by adding an additional chemical potential, which changes slightly the particle content in neutrino-transparent beta equilibrium. Secondly, we calculate the bulk viscosity in neutrino-transparent nuclear matter in conditions encountered in neutron star mergers. Bulk viscosity arises from a phase lag between the pressure and density in the nuclear matter, which is due to the finite rate of beta equilibration. When bulk viscosity is sufficiently strong, which happens when the equilibration rate nearly matches the frequency of the density oscillation, it can noticeably dampen the oscillation. We find that in certain thermodynamic conditions likely encountered in mergers, oscillations in nuclear matter can be damped on timescales on the order of 10 milliseconds, so we conclude that bulk viscosity should be included in merger simulations. Finally, we study thermal transport due to axions in neutron star mergers. We conclude that axions are never trapped in mergers, but instead escape, carrying energy away from the merger. We calculate the cooling time due to the energy carried away by axions and find that within current constraints on the axion-nucleon coupling, axions could cool fluid elements in mergers on timescales which could affect the dynamics of the merger.
nucl-thastro-ph.HEgr-qchep-phProQuest Dissertations Publishing, 2020. …·8 citations
04
Rare two-body decays of the top quark into a bottom meson plus an up or charm quark
David d'Enterria🇨🇭 · Hua-Sheng Shao🇫🇷
Rare two-body decays of the top quark into a neutral bottom-quark meson plus an up- or charm-quark: $t \to B^{0} + u, c$ ; $t \to B_{s}^{0} + c, u$ ; and $t \to Υ (n S) + c, u$ , are studied for the first time. The corresponding partials widths are computed at leading order in the non-relativistic QCD framework. The sums of all two-body branching ratios amount to $B (t \to B^{0} + jet) \approx B (t \to B_{s}^{0} + jet) \approx 4.2 \cdot 1 0^{- 5}$ and $B (t \to Υ (n S) + jet) \approx 2 \cdot 1 0^{- 9}$ , respectively. The feasibility to observe the $t \to B_{(s)}^{0} + jet$ decay is estimated in top-pair events produced in proton-proton collisions at $s = 14, 100$ TeV at the LHC and FCC, respectively. Combining many exclusive hadronic $B_{(s)}^{0}$ decays, with $J / ψ$ or $D^{0, \pm}$ final states, about 50 (16000) events are expected in 3 (20) ab $^{- 1}$ of integrated luminosity at the LHC (FCC), after typical selection criteria, acceptance, and efficiency losses. An observation of the two-body top-quark decay can also be achieved in the interesting $t \to b (jet) + c (jet)$ dijet final state, where the $B_{(s)}^{0}$ decay products are reconstructed as a jet, with 5300 and 1.4 million signal events above backgrounds expected after selection criteria at the LHC and FCC, respectively. Such unique final states provide a new direct method to precisely measure the top-quark mass via simple 2-body invariant mass analyses.
↳ hep-phhep-exnucl-thJHEP(2020)·3 citations
05
Polarization in low energy kaon-hyperon interaction
Marcelo G. L. Nogueira-Santos🇧🇷 · Celso C. Barros Jr🇧🇷
In this paper, we study the low energy kaon-hyperon interaction considering effective chiral Lagrangians that include kaons, $σ$ mesons, hyperons and the corresponding resonances. The scattering amplitudes are calculated and then we determine the angular distributions and polarizations.
↳ hep-phnucl-thIJMPE(2020)·7 citations
06
A two-neutron halo is unveiled in $^{29}$ F
S. Bagchi🇨🇦 · R. Kanungo🇨🇦 · Y. K. Tanaka🇨🇦 · H. Geissel🇩🇪 · P. Doornenbal🇯🇵 · W. Horiuchi🇯🇵 · G. Hagen🇺🇸 · T. Suzuki🇯🇵 · N. Tsunoda🇯🇵 · D. S. Ahn🇯🇵 · H. Baba🇯🇵 · K. Behr🇩🇪 and 35 other authors
We report the measurement of reaction cross sections ( $σ_{R}^{ex}$ ) of $^{27, 29}$ F with a carbon target at RIKEN. The unexpectedly large $σ_{R}^{ex}$ and derived matter radius identify $^{29}$ F as the heaviest two-neutron Borromean halo to date. The halo is attributed to neutrons occupying the $2 p_{3/2}$ orbital, thereby vanishing the shell closure associated with the neutron number $N = 20$ . The results are explained by state-of-the-art shell model calculations. Coupled-cluster computations based on effective field theories of the strong nuclear force describe the matter radius of $^{27}$ F but are challenged for $^{29}$ F.
↳ nucl-exnucl-thPRL(2020)·96 citations
07
Forward doubly-virtual Compton scattering off the nucleon in chiral perturbation theory: the subtraction function and moments of unpolarized structure functions
Jose Manuel Alarcón (Universidad Complutense de Madrid)🇪🇸 · Franziska Hagelstein (AEC Bern)🇨🇭 · Vadim Lensky🇩🇪 · Vladimir Pascalutsa (JGU Mainz)🇩🇪
The forward doubly-virtual Compton scattering (VVCS) off the nucleon contains a wealth of information on nucleon structure, relevant to the calculation of the two-photon-exchange effects in atomic spectroscopy and electron scattering. We report on a complete next-to-leading-order (NLO) calculation of low-energy VVCS in chiral perturbation theory ( $χ$ PT). Here we focus on the unpolarized VVCS amplitudes $T_{1} (ν, Q^{2})$ and $T_{2} (ν, Q^{2})$ , and the corresponding structure functions $F_{1} (x, Q^{2})$ and $F_{2} (x, Q^{2})$ . Our results are confronted, where possible, with "data-driven" dispersive evaluations of low-energy structure quantities, such as nucleon polarizabilities. We find significant disagreements with dispersive evaluations at very low momentum-transfer $Q$ ; for example, in the slope of polarizabilities at zero momentum-transfer. By expanding the results in powers of the inverse nucleon mass, we reproduce the known "heavy-baryon" expressions. This serves as a check of our calculation, as well as demonstrates the differences between the manifestly Lorentz-invariant (B $χ$ PT) and heavy-baryon (HB $χ$ PT) frameworks.
↳ hep-phhep-latnucl-exnucl-th+1PRD(2020)·18 citations

Affiliations

first authorsco-authorsvia INSPIRE

The thermal conductivity of "pastas" in neutron star matter

Cross-shell excitations in doubly magic 132Sn and its nearest neighbours

Transport in neutron star mergers

Rare two-body decays of the top quark into a bottom meson plus an up or charm quark

Polarization in low energy kaon-hyperon interaction

A two-neutron halo is unveiled in 29F

Forward doubly-virtual Compton scattering off the nucleon in chiral perturbation theory: the subtraction function and moments of unpolarized structure functions

Affiliations

A two-neutron halo is unveiled in $^{29}$ F