Nuclear Theory·nucl-th

Wednesday·May 26, 2021

7 papers—1 primary·6 cross-listed

01
Coupling of pairing and triaxial shape vibrations in collective states of $γ$ -soft nuclei
K. Nomura · D. Vretenar · Z. P. Li · J. Xiang
In addition to shape oscillations, low-energy excitation spectra of deformed nuclei are also influenced by pairing vibrations. The simultaneous description of these collective modes and their coupling has been a long-standing problem in nuclear structure theory. Here we address the problem in terms of self-consistent mean-field calculations of collective deformation energy surfaces, and the framework of the interacting boson approximation. In addition to quadrupole shape vibrations and rotations, the explicit coupling to pairing vibrations is taken into account by a boson-number non-conserving Hamiltonian, specified by a choice of a universal density functional and pairing interaction. An illustrative calculation for $^{128}$ Xe and $^{130}$ Xe shows the importance of dynamical pairing degrees of freedom, especially for structures built on low-energy $0^{+}$ excited states, in $γ$ -soft and triaxial nuclei.
nucl-thnucl-exPRC(2021)·11 citations
02
Analytic multi-Baryonic solutions in the SU(N)-Skyrme model at finite density
Sergio L. Cacciatori🇮🇹 · Fabrizio Canfora🇨🇱 · Marcela Lagos🇨🇱 · Federica Muscolino🇮🇹 · Aldo Vera🇨🇱
We construct explicit analytic solutions of the $S U (N)$ -Skyrme model (for generic $N$ ) suitable to describe different phases of nuclear pasta at finite volume in $(3 + 1)$ dimensions. The first type are crystals of Baryonic tubes (nuclear spaghetti) while the second type are smooth Baryonic layers (nuclear lasagna). Both, the ansatz for the spaghetti and the ansatz for the lasagna phases, reduce the complete set of Skyrme field equations to just one integrable equation for the profile within sectors of arbitrary high topological charge. We compute explicitly the total energy of both configurations in terms of the flavor number, the density and the Baryonic charge. Remarkably, our analytic results allow to compare explicitly the physical properties of nuclear spaghetti and lasagna phases. Our construction shows explicitly that, at lower densities, configurations with $N = 2$ light flavors are favored while, at higher densities, configurations with $N = 3$ are favored. Our construction also proves that in the high density regime (but still well within the range of validity of the Skyrme model) the lasagna configurations are favored while at low density the spaghetti configurations are favored. Moreover, the integrability property of the present configurations is not spoiled by the inclusion of the subleading corrections to the Skyrme model arising in the 't Hooft expansion. Finally, we briefly discuss the large $N$ limit of our configurations.
↳ hep-thastro-ph.HEhep-phnucl-thJHEP(2021)·28 citations
03
Gauge invariance of meson photo- and electroproduction currents revisited
Helmut Haberzettl🇺🇸
An exact expression is derived for the meson production current off the nucleon for real and virtual photons which cleanly separates, in a model-independent manner, a tree-level expression that manifestly preserves local gauge invariance in terms of a generalized Ward-Takahashi identity from transverse final-state-interaction (FSI) terms. As discussed in some detail, this exact formulation is particularly well suited for implementing approximation schemes of exchange-current and FSI contributions (which in practice generally will be necessary) at any level of sophistication without violating local gauge invariance.
↳ hep-phnucl-thPRD(2021)·8 citations
04
Efimov effect evaporation after confinement
E. Garrido🇺🇸 · A.S. Jensen🇩🇰
The continuous confinement of quantum systems can be described by means of the $d$ -method, where the dimension $d$ is taken as a continuous parameter. In this work we describe in detail how this method can be used to obtain the root mean square radii for a squeezed three-body system. These observables are used to investigate the disappearance of the Efimov states around the two-body threshold during a progressive confinement of the system from three to two dimensions. We illustrate how the disappearance takes place through the loss of one of the particles, whereas the other two remain bound.
↳ quant-phnucl-thphysics.atm-clusFew Body Syst.(2021)·3 citations
05
The structure of the X(3872) as explained by a Diffusion Monte Carlo calculation
M.C. Gordillo🇪🇸 · F. De Soto🇪🇸 · J. Segovia🇪🇸
Two decades after its unexpected discovery, the properties of the $X (3872)$ exotic resonance are still under intense scrutiny. In particular, there are doubts about its nature as an ensemble of mesons or having any other internal structure. We use a Diffusion Monte Carlo method to solve the many-body Schrödinger equation that describes this state as a $c c ˉ n n ˉ$ ( $n = u$ or $d$ quark) system. This approach accounts for multi-particle correlations in physical observables avoiding the usual quark-clustering assumed in other theoretical techniques. The most general and accepted pairwise Coulomb $+$ linear-confining $+$ hyperfine spin-spin interaction, with parameters obtained by a simultaneous fit of around 100 masses of mesons and baryons, is used. The $X (3872)$ contains light quarks whose masses are given by the mechanism responsible of the dynamical breaking of chiral symmetry. The same mechanisms gives rise to Goldstone-boson exchange interactions between quarks that have been fixed in the last 10-20 years reproducing hadron, hadron-hadron and multiquark phenomenology. It appears that a meson-meson molecular configuration is preferred but, contrary to the usual assumption of $D^{0} D ˉ^{* 0}$ molecule for the $X (3872)$ , our formalism produces $ω J / ψ$ and $ρ J / ψ$ clusters as the most stable ones, which could explain in a natural way all the observed features of the $X (3872)$ .
↳ hep-phhep-exhep-latnucl-ex+1PRD(2021)·16 citations
06
Three-particle finite-volume formalism for $π^{+} π^{+} K^{+}$ and related systems
Tyler D. Blanton🇺🇸 · Stephen R. Sharpe🇺🇸
We consider three-particle systems consisting of two identical particles and a third that is different, with all being spinless. Examples include $π^{+} π^{+} K^{+}$ and $K^{+} K^{+} π^{+}$ . We derive the formalism necessary to extract two- and three-particle infinite-volume scattering amplitudes from the spectrum of such systems in finite volume. We use a relativistic formalism based on an all-orders diagrammatic analysis in generic effective field theory, adopting the methodology used recently to study the case of three nondegenerate particles. We present both a direct derivation, and also a cross-check based on an appropriate limit and projection of the fully nondegenerate formalism. We also work out the threshold expansions for the three-particle K matrix that will be needed in practical applications, both for systems with two identical particles plus a third, and also for the fully nondegenerate theory.
↳ hep-latnucl-thPRD(2021)·65 citations
07
The pion-nucleon sigma term from lattice QCD
Rajan Gupta🇺🇸 · Sungwoo Park🇺🇸 · Martin Hoferichter🇨🇭 · Emanuele Mereghetti🇺🇸 · Boram Yoon🇺🇸 · Tanmoy Bhattacharya🇺🇸
We present an analysis of the pion-nucleon $σ$ -term, $σ_{π N}$ , using six ensembles with 2+1+1-flavor highly improved staggered quark action generated by the MILC collaboration. The most serious systematic effect in lattice calculations of nucleon correlation functions is the contribution of excited states. We estimate these using chiral perturbation theory ( $χ$ PT), and show that the leading contribution to the isoscalar scalar charge comes from N $π$ and N $π π$ states. Therefore, we carry out two analyses of lattice data to remove excited-state contamination, the standard one and a new one including N $π$ and N $π π$ states. We find that the standard analysis gives $σ_{π N} = 41.9 (4.9)$ MeV, consistent with previous lattice calculations, while our preferred $χ$ PT-motivated analysis gives $σ_{π N} = 59.6 (7.4)$ MeV, which is consistent with phenomenological values obtained using $π$ N scattering data. Our data on one physical pion mass ensemble was crucial for exposing this difference, therefore, calculations on additional physical mass ensembles are needed to confirm our result and resolve the tension between lattice QCD and phenomenology.
↳ hep-lathep-phnucl-thPRL(2021)·90 citations

Affiliations

first authorsco-authorsvia INSPIRE

Coupling of pairing and triaxial shape vibrations in collective states of γ-soft nuclei

Analytic multi-Baryonic solutions in the SU(N)-Skyrme model at finite density

Gauge invariance of meson photo- and electroproduction currents revisited

Efimov effect evaporation after confinement

The structure of the X(3872) as explained by a Diffusion Monte Carlo calculation

Three-particle finite-volume formalism for π+π+K+ and related systems

The pion-nucleon sigma term from lattice QCD

Affiliations

Coupling of pairing and triaxial shape vibrations in collective states of $γ$ -soft nuclei

Three-particle finite-volume formalism for $π^{+} π^{+} K^{+}$ and related systems