Nuclear Theory·nucl-th

Thursday·January 24, 2019

9 papers—5 primary·4 cross-listed

01
Coupling between superfluid neutrons and superfluid protons in the elementary excitations of neutron star matter
M. Baldo🇮🇹 · C. Ducoin🇫🇷
Several phenomena occurring in neutron stars are affected by the elementary excitations that characterize the stellar matter. In particular, low-energy excitations can play a major role in the emission and propagation of neutrinos, neutron star cooling and transport processes. In this paper, we consider the elementary modes in the star region where both proton and neutron components are superfluid. We study the overall spectral functions of protons, neutrons and electrons on the basis of the Coulomb and nuclear interactions. This study is performed in the framework of the Random Phase Approximation, generalized to superfluid systems. The formalism we use ensures that the Generalized Ward's Identities are satisfied. We focus on the coupling between neutrons and protons. On one hand this coupling results in collective modes that involve simultaneously neutrons and protons, on the other hand it produces a damping of the excitations. Both effects are especially visible in the spectral functions of the different components of the matter. At high density while the neutrons and protons tend to develop independent excitations, as indicated by the spectral functions, the neutron-proton coupling still produces a strong damping of the modes.
nucl-thPRC(2019)·3 citations
02
Neutron drip line in the Ca region from Bayesian model averaging
Léo Neufcourt · Yuchen Cao · Witold Nazarewicz · Erik Olsen · Frederi Viens
The region of heavy calcium isotopes forms the frontier of experimental and theoretical nuclear structure research where the basic concepts of nuclear physics are put to stringent test. The recent discovery of the extremely neutron-rich nuclei around $^{60}$ Ca [Tarasov, 2018] and the experimental determination of masses for $^{55 - 57}$ Ca (Michimasa, 2018] provide unique information about the binding energy surface in this region. To assess the impact of these experimental discoveries on the nuclear landscape's extent, we use global mass models and statistical machine learning to make predictions, with quantified levels of certainty, for bound nuclides between Si and Ti. Using a Bayesian model averaging analysis based on Gaussian-process-based extrapolations we introduce the posterior probability $p_{e x}$ for each nucleus to be bound to neutron emission. We find that extrapolations for drip-line locations, at which the nuclear binding ends, are consistent across the global mass models used, in spite of significant variations between their raw predictions. In particular, considering the current experimental information and current global mass models, we predict that $^{68}$ Ca has an average posterior probability $p_{e x} \approx 76$ % to be bound to two-neutron emission while the nucleus $^{61}$ Ca is likely to decay by emitting a neutron ( $p_{e x} \approx 46$ %).
nucl-thstat.MLPRL(2019)·148 citations
03
The critical notes to the solutions of the "puzzle" of hyperfine structure in 82+ and 80+ $^{209}$ Bi ions
F. F. Karpeshin · M. B. Trzhaskovskaya
Some aspects of description of the Bohr-Weisskopf effect in hyperfine splitting of the H- and Li-like ions of 209Bi are considered by application of the surface and volume models of the nuclear currents. Extension of these models, used in internal conversion theory, to description of the HFS allows one to successfully describe the effect, without resorting to the specific differences. The latters are shown not to be needed at all. Moreover, they turn out to depend on the nuclear model even stronger than the HFS values themselves. Comparison of the calculated HFS values to experiment shows a satisfactory agreement. Both models provide equally good description of the effect. However, they result in different values of the retrieved rms radius of the nuclear magnetization. In this respect, situation resembles the proton radius puzzle. Prospects of future research are discussed.
nucl-thPRC(2019)·4 citations
04
The algebraic molecular model in $^{12}$ C and its application to the $α$ + $^{12}$ C scattering: from densities and transition densities to optical potentials and nuclear formfactors
A. Vitturi · J. Casal · L. Fortunato · E. G. Lanza
The algebraic molecular model is used in $^{12}$ C to construct densities and transition densities connecting low-lying states of the rotovibrational spectrum, first and foremost those belonging to the rotational bands based on the ground and the Hoyle states. These densities are then used as basic ingredients to calculate, besides electromagnetic transition probabilities, nuclear potentials and formfactors to describe elastic and inelastic $α$ + $^{12}$ C scattering processes. The calculated densities and transition densities are also compared with those obtained by directly solving the problem of three interacting alpha's within a three-body approach where continuum effects, relevant in particular for the Hoyle state, are properly taken into account.
nucl-thAIP Conf.Proc.(2019)·3 citations
05
Electron versus muon neutrino induced cross sections in charged current quasi-elastic processes
Alexis Nikolakopoulos🇧🇪 · Natalie Jachowicz🇧🇪 · Nils Van Dessel🇧🇪 · Kajetan Niewczas🇧🇪 · Raúl González-Jiménez🇪🇸 · José Manuel Udías🇪🇸 · Vishvas Pandey🇺🇸
Differences between $ν_{e}$ and $ν_{μ}$ quasielastic cross sections are essential in neutrino oscillation analyses and CP violation searches for experiments such as DUNE and T2HK. The ratio of these is however poorly known experimentally and for certain kinematic regions theoretical models give contradictory answers. We use two independent mean-field based models to investigate this ratio using $^{40}$ Ar and $^{12}$ C targets. We demonstrate that a proper treatment of the final nucleon's wave function confirms the dominance of $ν_{μ}$ over $ν_{e}$ induced cross sections at forward lepton scattering.
nucl-thPRL(2019)·51 citations
06
$Z_{c} (4430)$ and $Z_{c} (4200)$ as triangle singularities
S. X. Nakamura (Univ. Science and Technology of China)🇨🇳 · K. Tsushima (Univ. Cruzeiro do Sul)🇧🇷
$Z_{c} (4430)$ discovered by the Belle and confirmed by the LHCb in $B ˉ^{0} \to ψ (2 S) K^{-} π^{+}$ is generally considered to be a charged charmonium-like state that includes minimally two quarks and two antiquarks. $Z_{c} (4200)$ found in $B ˉ^{0} \to J / ψ K^{-} π^{+}$ by the Belle is also a good candidate of a charged charmonium-like state. We demonstrate that kinematical singularities in triangle loop diagrams induce a resonance-like behavior that can consistently explain the properties (mass, width, and Argand plot) of $Z_{c} (4430)$ and $Z_{c} (4200)$ from the experimental analyses. The triangle diagrams include only experimentally well-established hadrons. Applying this idea to $Λ_{b}^{0} \to J / ψ p π^{-}$ , we also identify triangle singularities that behave like $Z_{c} (4200)$ , but no triangle diagram is available for $Z_{c} (4430)$ . This is consistent with the LHCb's finding that their description of the $Λ_{b}^{0} \to J / ψ p π^{-}$ data is significantly improved by including a $Z_{c} (4200)$ contribution while $Z_{c} (4430)$ seems to hardly contribute. Even though the proposed mechanisms have uncertainty in the absolute strengths which are currently difficult to estimate, they are certainly a compelling alternative to tetraquark-based interpretations of $Z_{c} (4430)$ and $Z_{c} (4200)$ .
↳ hep-phhep-exnucl-thPRD(2019)·32 citations
07
Degeneracy in Studying the Supranuclear Equation of State and Modified Gravity with Neutron Stars
Lijing Shao🇨🇳
It is generally acknowledged that an extrapolation in physics from a well-known scale to an unknown scale is perilous. This prevents us from using laboratory experience to gain precise information for the supranuclear matter inside neutron stars (NSs). With operating and upcoming astronomical facilities, NSs' equation of state (EOS) is expected to be determined at a new level in the near future, under the assumption that general relativity (GR) is the correct theory for gravitation. While GR is a reasonable working assumption yet still an extrapolation, there could be a large uncertainty due to the not-so-well-tested strong gravitational field inside NSs. Here we review some recent theoretical efforts towards a better understanding of the degeneracy between the supranuclear EOS and alternative gravity theories.
↳ gr-qcastro-ph.HEnucl-exnucl-thAIP Conf.Proc.(2019)·33 citations
08
Towards a better understanding of the symmetry energy within neutron stars
C.Y. Tsang · M.B. Tsang · P. Danielewicz · W.G. Lynch · F.J. Fattoyev
The LIGO-Virgo collaboration ground-breaking detection of the binary neutron-star merger event, GW170817, has expanded efforts to understand the Equation of State (EoS) of nuclear matter. These measurements provide new constraints on the overall pressure, but do not, by itself, elucidate its microscopic origins, including the pressure arising from the symmetry energy, that governs much of the internal structure of a neutron star. To correlate microscopic constraints from nuclear measurements to the GW170817 constraints, we calculate neutron star properties with more than 200 Skyrme energy density functionals that describe properties of nuclei. Calculated neutron-star radii (R) and the tidal deformabilities which show a strong correlation with pressure at twice saturation density. By combining the neutron star EoS extracted from the GW170817 event and the EoS of symmetric matter from nucleus-nucleus collision experiments, we extract the density dependence of the symmetry pressure from 1.2 to 4.5 times saturation density. While the uncertainties in the symmetry pressure are large, they can be reduced with new experimental and astrophysical results.
↳ nucl-exnucl-th8 citations
09
Higher-order corrections to heavy-quark jet quenching
Boris Blok🇮🇱 · Konrad Tywoniuk🇳🇴
We calculate higher-order corrections to the quenching factor of heavy-quark jets due to hard, in-medium splittings in the framework of the BDMPS-Z formalism. These corrections turn out to be sensitive to a single mass-scale $m_{*} = (q^L)^{1/2}$ , where $q^$ is the medium transport coefficient and $L$ the path length, and allow to draw a distinction between the way light, with $m < m_{*}$ (in contrast to massless $m = 0$ ), and genuinely heavy, with $m > m_{*}$ , quark jets are quenched in the medium. We show that the corrections to the quenching factor at high energies are double-logarithmic and qualitatively of the same order as for the massless quark jet.
↳ hep-phnucl-thEPJC(2019)·11 citations

Affiliations

first authorsco-authorsvia INSPIRE