Nuclear Theory·nucl-th

Friday·December 16, 2022

9 papers—2 primary·7 cross-listed

01
Beyond-Mean-Field with an Effective Hamiltonian Mapped from an Energy Density Functional
J. Ljungberg · J. Boström · B. G. Carlsson · A. Idini · J. Rotureau
A method for beyond-mean-field calculations based on an energy density functional is described. The main idea is to map the energy surface for the nuclear quadrupole deformation, obtained from an energy density functional at the mean-field level, into an effective Hamiltonian expressed as a many-body operator. The advantage of this procedure is that one avoids the problems with density dependence which can arise in beyond-mean-field methods. The effective Hamiltonian is then used in a straightforward way in the generator-coordinate-method with the inclusion of projections onto good particle numbers and angular momentum. In the end, both spectra and wave functions are obtained. As an example of the method, calculations for the nucleus $^{62}$ Zn is performed with three different parametrizations of the Skyrme functional. The results are compared with experiment.
nucl-thJ.Phys.Conf.Ser.(2023)·4 citations
02
Coexistence of quartets and pairs in even-even $N > Z$ nuclei
M. Sambataro · N. Sandulescu · D. Gambacurta
We analyse the structure of the ground states of even-even $N > Z$ nuclei with nucleons moving in the same major shell and interacting via realistic two-body forces of shell-model type. We express the ground states of these nuclei as a product of a quartet term, which represents the $N = Z$ subsystem, and a pair condensate built with the excess neutrons. The accuracy of this approximation is discussed for nuclei with valence nucleons in the $s d$ and $p f$ major shells.
nucl-thNPA(2023)·2 citations
03
Rigorous bounds on transport from causality
Michal P. Heller🇧🇪 · Alexandre Serantes🇪🇸 · Michał Spaliński🇫🇮 · Benjamin Withers🇬🇧
We use causality to derive a number of simple and universal constraints on dispersion relations, which describe the location of singularities of retarded two-point functions in relativistic quantum field theories. We prove that all causal dissipative dispersion relations have a finite radius of convergence. We then give two-sided bounds on all transport coefficients in units of this radius, including an upper bound on diffusivity.
↳ hep-thcond-mat.stat-mechgr-qcmath-ph+2PRL(2023)·81 citations
04
Cancellation of the sigma mode in the thermal pion gas by quark Pauli blocking
David Blaschke🇵🇱 · Alexandra Friesen🇷🇺 · Yuriy Kalinovsky🇷🇺
We calculate the pressure of the interacting pion gas using the Beth-Uhlenbeck approach to the relativistic virial expansion with Breit-Wigner phase shifts for the $σ$ - and $ϱ$ - meson resonances. The repulsive phase shift $δ_{0}^{2}$ is taken from quark interchange model of Barnes and Swanson [Phys. Rev. D 46 (1992) 131] in very good agreement with experimental data. In this work we show that the cancellation of the attractive (I = 0) and repulsive (I = 2) isospin channel contributions to the scalar $π - π$ interaction in the low-energy region that is known for the vacuum phase shifts, takes place also at finite temperature. This happens despite the strong medium dependence of these phase shifts that enters our model by the temperature dependence of the $σ$ - meson and constituent quark masses because for these masses the relation $m_{σ} (T) \approx 2 m_{q} (T)$ holds and the scattering length approximation is valid as long as the strong decay channel $σ \to π π$ is open. Exploiting the Nambu--Jona-Lasinio model for describing the dynamical breaking of chiral symmetry in the vacuum and its restoration at finite temperature, we justify with our approach that the $σ$ -meson should be absent from the hadron resonance gas description at low temperatures because the above cancellation holds. However, since this cancellation breaks down in the vicinity of the hadronization transition, where due to chiral symmetry restoration the decay channel $σ \to π π$ closes and the $σ$ - meson becomes a good resonance, the latter should be included into the statistical model description of chemical freeze-out in heavy-ion collisions.
↳ hep-phnucl-thSymmetry(2023)·0 citations
05
Dynamics and Equation of State Dependencies of Relevance for Nucleosynthesis in Supernovae and Neutron Star Mergers
H.-Thomas Janka (1) · Andreas Bauswein (2) ((1) MPI for Astrophysics, Garching, (2) GSI, Darmstadt)
Neutron stars (NSs) and black holes (BHs) are born when the final collapse of the stellar core terminates the lives of stars more massive than about 9 Msun. This can trigger the powerful ejection of a large fraction of the star's material in a core-collapse supernova (CCSN), whose extreme luminosity is energized by the decay of radioactive isotopes such as 56Ni and 56Co. When evolving in close binary systems, the compact relics of such infernal catastrophes spiral towards each other on orbits gradually decaying by gravitational-wave emission. Ultimately, the violent collision of the two components forms a more massive, rapidly spinning remnant, again accompanied by the ejection of considerable amounts of matter. These merger events can be observed by high-energy bursts of gamma rays with afterglows and electromagnetic transients called kilonovae, which radiate the energy released in radioactive decays of freshly assembled rapid neutron-capture elements. By means of their mass ejection and the nuclear and neutrino reactions taking place in the ejecta, both CCSNe and compact object mergers (COMs) are prominent sites of heavy-element nucleosynthesis and play a central role in the cosmic cycle of matter and the chemical enrichment history of galaxies. The nuclear equation of state (EoS) of NS matter, from neutron-rich to proton-dominated conditions and with temperatures ranging from about zero to ~100 MeV, is a crucial ingredient in these astrophysical phenomena. It determines their dynamical processes, their remnant properties even at the level of deciding between NS or BH, and the properties of the associated emission of neutrinos, whose interactions govern the thermodynamic conditions and the neutron-to-proton ratio for nucleosynthesis reactions in the innermost ejecta. This chapter discusses corresponding EoS dependent effects of relevance in CCSNe as well as COMs. (slightly abridged)
↳ astro-ph.HEgr-qchep-phnucl-th19 citations
06
Pion and photon beam initiated backward charmonium or lepton pair production
Bernard Pire🇫🇷 · Kirill M. Semenov-Tian-Shansky🇰🇷 · Alisa A. Shaikhutdinova🇷🇺 · Lech Szymanowski🇵🇱
Hard exclusive reactions initiated by pion or photon beams within the near-backward kinematical regime specified by the small Mandelstam variable $- u$ can be studied to access pion-to-nucleon and photon-to-nucleon Transition Distribution Amplitudes (TDAs). Checking the validity of collinear factorized description of pion and photon induced reactions in terms of TDAs allows to test the universality of TDAs between the space-like and time-like regimes that is the indispensable feature of the QCD collinear factorization approach. In this short review we consider the exclusive pion- and photo-production off nucleon of a highly virtual lepton pair (or heavy quarkonium) in the near-backward region. We first employ a simplistic cross channel nucleon exchange model of pion-to-nucleon TDAs to estimate the magnitude of the corresponding cross sections for the kinematical conditions of J-PARC. We then illustrate the flexibility of our approach by building a two parameter model for the photon-to-nucleon TDAs based on preliminary results for near threshold $J / ψ$ photoproduction at JLab and provide our estimates for near-backward $J / ψ$ photoproduction and Timelike Compton Scattering cross sections for the kinematical conditions of JLab and of future EIC and EicC.
↳ hep-phhep-exnucl-exnucl-thAAPPS Bull.(2023)·11 citations
07
$C$ and $C P$ violation in effective field theories
Hakan Akdag🇩🇪 · Bastian Kubis🇩🇪 · Andreas Wirzba🇩🇪
The quest for new sources of the simultaneous violation of $C$ and $C P$ symmetry was popular in the 1960s and has since been mostly neglected for more than half a century. In this work we revisit fundamental quark-level operators that break $C$ and $C P$ up to and including mass dimension 8 for flavor-conserving transitions, relying on the complete operator sets of the so-called Standard Model effective field theory and the low-energy effective field theory. With the formalism of chiral perturbation theory, we match these quark operators to light-meson physics, derive $C$ - and $C P$ -odd Lagrangians for several processes in the $η$ , $η^{'}$ , and pion sectors, and furthermore, as a proof of principle, give estimates for the respective observables in explicit dependence of the underlying high-energy scale for new physics.
↳ hep-phnucl-thJHEP(2023)·17 citations
08
Can the two-pole structure of the $D_{0}^{*} (2300)$ be understood from recent lattice data?
Anuvind Asokan🇩🇪 · Meng-Na Tang🇨🇳 · Feng-Kun Guo🇨🇳 · Christoph Hanhart🇩🇪 · Yuki Kamiya🇩🇪 · Ulf-G. Meißner🇩🇪
It was demonstrated in a series of papers employing unitarized chiral perturbation theory that the phenomenology of the scalar open-charm state, the $D_{0}^{*} (2300)$ , can be understood as the interplay of two poles, corresponding to two scalar-isospin doublet states with different SU(3) flavor content. Within this formalism the lightest open charm positive parity states emerge as being dynamically generated from the scattering of the Goldstone-boson octet off $D$ mesons, a picture that at the same time solves various problems that the experimental observations posed. However, in recent lattice studies of $D π$ scattering at different pion masses only one pole was reported in the $D_{0}^{*}$ channel, while it was not possible to extract reliable parameters of a second pole from the lattice data. In this paper we demonstrate how this seeming contradiction can be understood and that imposing SU(3) constraints on the fitting amplitudes allows one to extract information on the second pole from the lattice data with minimal bias. The results may also be regarded as a showcase how approximate symmetries can be imposed in the $K$ -matrix formalism to reduce the number of parameters.
↳ hep-phhep-exhep-latnucl-thEPJC(2023)·26 citations
09
Three-Body Unitary Coupled-Channel Analysis on $η (1405/1475)$
S. X. Nakamura (Univ. of Science and Technology of China)🇨🇳 · Q. Huang (Nanjing Normal Univ.)🇨🇳 · J. -J. Wu (Univ. of Chinese Academy of Sciences)🇨🇳 · H. P. Peng (Univ. of Science and Technology of China)🇨🇳 · Y. Zhang (Univ. of Science and Technology of China)🇨🇳 · Y. C. Zhu (Univ. of Science and Technology of China)🇨🇳
The recent BESIII data on $J / ψ \to γ (K_{S} K_{S} π^{0})$ , which is significantly more precise than earlier $η (1405/1475)$ -related data, enables quantitative discussions on $η (1405/1475)$ at the previously unreachable level. We conduct a three-body unitary coupled-channel analysis of experimental Monte-Carlo outputs for radiative $J / ψ$ decays via $η (1405/1475)$ : $K_{S} K_{S} π^{0}$ Dalitz plot distributions from the BESIII, and branching ratios of $γ (η π^{+} π^{-})$ and $γ (γ π^{+} π^{-})$ final states relative to that of $γ (K K ˉ π)$ . Our model systematically considers (multi-)loop diagrams and an associated triangle singularity, which is critical in making excellent predictions on $η (1405/1475) \to π π π$ lineshapes and branching ratios. The $η (1405/1475)$ pole locations are revealed for the first time. Two poles for $η (1405)$ are found on different Riemann sheets of the $K^{*} K ˉ$ channel, while one pole for $η (1475)$ . The $η (1405/1475)$ states are described with two bare states dressed by continuum states. The lower bare state would be an excited $η^{'}$ , while the higher one could be an excited $η^{(')}$ , hybrid, glueball, or their mixture. This work presents the first-ever pole determination based on a manifestly three-body unitary coupled-channel framework applied to experimental three-body final state distributions (Dalitz plots).
↳ hep-phhep-exnucl-thPRD(2023)·13 citations

Affiliations

first authorsco-authorsvia INSPIRE