Nuclear Theory·nucl-th

Tuesday·June 15, 2021

10 papers—7 primary·3 cross-listed

01
Stiffening of matter in quark-hadron continuity
Toru Kojo🇨🇳
We discuss stiffening of matter in quark-hadron continuity. We introduce a model that relates quark wave functions in a baryon and the occupation probability of states for baryons and quarks in dense matter. In a dilute regime, the confined quarks contribute to the energy density through the masses of baryons, but do not directly contribute to the pressure; hence, the equations of state are very soft. This dilute regime continues until the low momentum states for quarks get saturated; this may happen even before baryons fully overlap, possibly at density slightly above the nuclear saturation density. After the saturation the pressure grows rapidly while changes in energy density are modest, producing a peak in the speed of sound. If we use baryonic descriptions for quark distributions near the Fermi surface, we reach a description similar to the quarkyonic matter model of McLerran and Reddy. With a simple adjustment of quark interactions to get the nucleon mass, our model becomes consistent with the constraints from 1.4-solar mass neutron stars, but the high density part is too soft to account for two-solar mass neutron stars. We delineate the relation between the saturation effects and short range interactions of quarks, suggesting interactions that leave low density equations of state unchanged but stiffen the high density part.
nucl-thastro-ph.HEhep-phhep-thPRD(2021)·85 citations
02
The Angular Correlations in the $e^{+} e^{-}$ Decay of Excited States in 8Be
A.C Hayes🇺🇸 · J.L. Friar🇺🇸 · GM. Hale🇺🇸 · GT. Garvey🇺🇸
Motivated by the recent observation of anomalous electron-positron angular correlations in the decay of the 18.15 MeV 1+ excited states in 8Be, we reexamine in detail the Standard Model expectations for these angular correlations. The 18.15 MeV state is above particle threshold, and several multipoles can contribute to its $e^{+} e^{-}$ decay. We present the general theoretical expressions for $e^{+} e^{-}$ angular distributions for nuclear decay by C0, C1, C2 M1, E1, and E2 multipoles, and we examine their relative contribution to the $e^{+} e^{-}$ decay of 8Be at 18.15 MeV. We find that this resonance is dominated by M1 and E1 decay, and that the ratio of M1 to E1 strength is a strong function of energy. This is in contract to the original analysis of the $e^{+} e^{-}$ angular distributions, where the M1/E1 ratio was assumed to be a constant over the energy region Ep = 0:8-1:2 MeV. We find that the existence of a `bump' in the measured angular distribution is strongly dependent on the assumed M1/E1 ratio, with the present analysis finding the measured large-angle contributions to the $e^{+} e^{-}$ angular distribution to be lower than expectation. Thus, in the current analysis we find no evidence for axion decay in the 18.15 MeV resonance region of 8Be.
nucl-thhep-exhep-phnucl-exPRC(2022)·20 citations
03
Axial meson contribution to proton form factors
Nikolai Korchagin🇨🇳 · Andrey Radzhabov🇷🇺
The effect of axial meson exchange on extraction of proton electromagnetic form factors in $e p$ scattering is calculated. Taking as an example $f_{1} (1285)$ meson exchange, it is quantitatively shown how it affects Rosenbluth and polarization transfer methods. The contribution of an axial meson is negligible in comparison with the traditional box-type two photon exchange and could not be responsible for difference of form factors extracted by different techniques. However, results support the idea that meson exchange could explain deviation of individual polarizations.
nucl-thhep-ph1 citation
04
Hybrid neutron stars in the mass-radius diagram
Mateusz Cierniak🇵🇱 · David Blaschke🇵🇱
We present a systematic investigation of the possible locations for the special point (SP), a unique feature of hybrid neutron stars in the mass-radius. The study is performed within the two-phase approach where the high-density (quark matter) phase is described by the constant-sound-speed (CSS) equation of state (EoS) and the nuclear matter phase around saturation density is varied from very soft (APR) to stiff (DD2 with excluded nucleon volume. Different construction schemes for the deconfinement transition are applied: Maxwell construction, mixed phase construction and parabolic interpolation. We demonstrate for the first time that the SP is invariant not only against changing the nuclear matter EoS, but also against variation of the construction schemes for the phase transition. Since the SP serves as a proxy for the maximum mass and accessible radii of massive hybrid stars, we draw conclusions for the limiting masses and radii of hybrid neutron stars.
nucl-thastro-ph.HEhep-phAstron.Nachr.(2021)·30 citations
05
Interplay between pairing and triaxial shape degrees of freedom in Os and Pt nuclei
K. Nomura · D. Vretenar · Z. P. Li · J. Xiang
The effect of coupling between pairing and quadrupole triaxial shape vibrations on the low-energy collective states of $γ$ -soft nuclei is investigated using a model based on the framework of nuclear energy density functionals (EDFs). Employing a constrained self-consistent mean-field (SCMF) method that uses universal EDFs and pairing interactions, potential energy surfaces of characteristic $γ$ -soft Os and Pt nuclei with $A \approx 190$ are calculated as functions of the pairing and triaxial quadrupole deformations. Collective spectroscopic properties are computed using a number-nonconserving interacting boson model (IBM) Hamiltonian, with parameters determined by mapping the SCMF energy surface onto the expectation value of the Hamiltonian in the boson condensate state. It is shown that, by simultaneously considering both the shape and pairing collective degrees of freedom, the EDF-based IBM successfully reproduces data on collective structures based on low-energy $0^{+}$ states, as well as $γ$ -vibrational bands.
nucl-thnucl-exPRC(2021)·11 citations
06
Comparative study of $^{6}$ He $β$ -decay based on different similarity-renormalization-group evolved chiral interactions
A. Gnech · L.E. Marcucci · R. Schiavilla · M. Viviani
We report on a study of the Gamow-Teller matrix element contributing to $^{6}$ He $β$ -decay with similarity renormalization group (SRG) versions of momentum- and configuration-space two-nucleon interactions. These interactions are derived from two different formulations of chiral effective field theory ( $χ$ EFT) -- without and with the explicit inclusion of $Δ$ -isobars. We consider evolution parameters $Λ_{SRG}$ in the range between 1.2 and 2.0 fm $^{- 1}$ and, for the $Δ$ -less case, also the unevolved (bare) interaction. The axial current contains one- and two-body terms, consistently derived at tree level (no loops) in the two distinct $χ$ EFT formulations we have adopted here. The $^{6}$ He and $^{6}$ Li ground-state wave functions are obtained from hyperspherical-harmonics (HH) solutions of the nuclear many-body problem. In $A$ = $6$ systems, the HH method is limited at present to treat only two-body interactions and non-SRG evolved currents. Our results exhibit a significant dependence on $Λ_{SRG}$ of the contributions associated with two-body currents, suggesting that a consistent SRG-evolution of these is needed in order to obtain reliable estimates. We also show that the contributions from one-pion-exchange currents depend strongly on the model (chiral) interactions and on the momentum- or configuration-space cutoffs used to regularize them. These results might prove helpful in clarifying the origin of the sign difference recently found in No-Core-Shell-Model and Quantum Monte Carlo calculations of the $^{6}$ He Gamow-Teller matrix element.
nucl-thPRC(2021)·11 citations
07
Scaling in the short-time approximation
S. Pastore · J. Carlson · S. Gandolfi · R. Schiavilla · R. B. Wiringa
We briefly review the concept of scaling and how it occurs in quasielastic electron and neutrino scattering from nuclei, and then the particular approach to scaling in the short-time approximation. We show that, while two-nucleon currents do significantly enhance the transverse electromagnetic response, they do not spoil scaling, but in fact enhance it. We provide scaling results obtained in the short-time approximation that verify this claim. The enhanced scaling is not ``accidental'' -- as claimed in Ref.~\cite{Benhar:2020jye} -- but rather reflects the dominant role played by pion exchange interactions and currents in the quasielastic regime.
nucl-th0 citations
08
Expanding Nuclear Physics Horizons with the Gamma Factory
Dmitry Budker🇩🇪 · Julian C. Berengut🇦🇺 · Victor V. Flambaum🇦🇺 · Mikhail Gorchtein🇩🇪 · Junlan Jin🇨🇳 · Felix Karbstein🇩🇪 · Mieczyslaw Witold Krasny🇫🇷 · Yuri A. Litvinov🇩🇪 · Adriana Pálffy🇩🇪 · Vladimir Pascalutsa🇩🇪 · Alexey Petrenko🇷🇺 · Andrey Surzhykov🇩🇪 and 4 other authors
The Gamma Factory (GF) is an ambitious proposal, currently explored within the CERN Physics Beyond Colliders program, for a source of photons with energies up to $\approx 400$ MeV and photon fluxes (up to $\approx 1 0^{17}$ photons per second) exceeding those of the currently available gamma sources by orders of magnitude. The high-energy (secondary) photons are produced via resonant scattering of the primary laser photons by highly relativistic partially-stripped ions circulating in the accelerator. The secondary photons are emitted in a narrow cone and the energy of the beam can be monochromatized, eventually down to the $\approx 1$ ppm level, via collimation, at the expense of the photon flux. This paper surveys the new opportunities that may be afforded by the GF in nuclear physics and related fields.
↳ nucl-exhep-exnucl-thphysics.acc-ph+1Annalen Phys.(2022)·42 citations
09
Perspective on Tsallis Statistics for Nuclear and Particle Physics
Joseph I. Kapusta🇺🇸
This is a concise introduction to the topic of nonextensive Tsallis statistics meant especially for those interested in its relation to high energy proton-proton, proton-nucleus, and nucleus-nucleus collisions. The three types of Tsallis statistics are reviewed. Only one of them is consistent with the fundamental hypothesis of equilibrium statistical mechanics. The single particle distributions associated with it, namely Boltzmann, Fermi-Dirac, and Bose-Einstein, are derived. These are not equilibrium solutions to the conventional Boltzmann transport equation which must be modified in a rather nonintuitive manner for them to be so. Nevertheless the Boltzmann limit of the Tsallis distribution is extremely efficient in representing a wide variety of single particle distributions in high energy proton-proton, proton-nucleus, and nucleus-nucleus collisions with only three parameters, one of them being the so-called nonextensitivity parameter $q$ . This distribution interpolates between an exponential at low transverse energy, reflecting thermal equilibrium, to a power law at high transverse energy, reflecting the asymptotic freedom of QCD. It should not be viewed as a fundamental new parameter representing nonextensive behavior in these collisions.
↳ hep-phnucl-thIJMPE(2021)·15 citations
10
Fully heavy multiquarks
Jean-Marc Richard🇫🇷
The existence of stable multiquarks made of heavy quarks and antiquarks is discussed in the framework of potential models. It is stressed that the few-body problem should be handled seriously and accurately. No bound state is found within the current models. But resonances are likely present in the spectrum above the lowest threshold.
↳ hep-phnucl-thFew Body Syst.(2021)·3 citations

Affiliations

first authorsco-authorsvia INSPIRE