Nuclear Theory·nucl-th

Wednesday·September 4, 2019

18 papers—6 primary·12 cross-listed

01
Magic numbers of cylindrical symmetry
Andriana Martinou · Dennis Bonatsos
In nuclear physics a magic number is defined as the nucleon number, which is separated by a significantly large single-particle energy gap from the next nucleon. Magic numbers define the nuclear shells, which are considered to be active, only if they are partially occupied by nucleons. As a consequence the single particle interactions of the valence nucleons lead to the description of the collective properties of the whole nucleus in the shell model theory. But phenomena as the island of inversion, the shape coexistence and the break down of the N=20 magic number reveal that the above definition of a magic number is deficient. A complementary definition should rely on the selection rules of the single particle interactions. Specifically the selection rules of the quadrupole-quadrupole interaction lead to two sets of magic numbers, namely the harmonic oscillator magic numbers 2, 8 20, 40, 70, 112, ... and the spin-orbit SO-like magic numbers 2, 6, 14, 28, 50, 82, 126, ... The underlying symmetries are respectively the spherical symmetry of the 3D isotropic harmonic oscillator and the cylindrical symmetry of the 3D anisotropic harmonic oscillator with two frequencies equal. The above two sets of magic numbers along with the Elliott SU(3) symmetry framework predict long standing and puzzling phenomena in nuclear physics.
nucl-th2 citations
02
The Shape of the Correlation Function
Jakub Cimerman🇨🇿 · Boris Tomášik🇸🇰 · Christopher Plumberg🇸🇪
The correlation function measured in ultrarelativistic nuclear collisions is non-Gaussian. By making use of models we discuss and assess how much various effects can influence its shape. In particular, we focus on the parametrisations expressed with the help of Lévy-stable distributions. We show that the Lévy index may deviate substantially from 2 due to non-critical effects such as non-spherical shape, resonance decays, event-by-event fluctuations and functional dependence on $Q_{in v}$ or similar.
nucl-thhep-phnucl-exPhys.Part.Nucl.(2020)·6 citations
03
Color transparency in $p ˉ d \to π^{-} π^{0} p$ reaction
A.B. Larionov🇩🇪 · M. Strikman🇺🇸
We consider exclusive two-pion production in antiproton-deuteron interactions at the beam momenta around 10 GeV/c in the kinematics with large momentum transfer in the underlying hard process $p ˉ n \to π^{-} π^{0}$ . The calculations are performed taking into account the antiproton and pion soft rescattering on the spectator proton in the framework of the generalized eikonal approximation. We focus on the color transparency effect that is modeled by introducing the dependence of rescattering amplitudes on the relative position of the struck and spectator nucleons along the momentum of a fast particle. As a consequence of the interplay between the impulse approximation and rescattering amplitudes the nuclear transparency ratio reveals a pretty complicated behaviour as a function of the transverse momentum of the spectator proton and the relative azimuthal angle between the $π^{-}$ -meson and the proton. Color transparency significantly suppresses rescattering amplitudes which leads to substantial modifications of the nuclear transparency ratio moving it closer to the value obtained in the impulse approximation. By performing the Monte-Carlo analysis we determine that this effect can be studied at PANDA with a reasonable statistics.
nucl-thhep-exhep-phnucl-exEPJA(2020)·7 citations
04
Effective interactions in the sd shell
Nadezda A. Smirnova🇫🇷 · Bruce R. Barrett🇺🇸 · Youngman Kim🇰🇷 · Ik Jae Shin🇰🇷 · Andrey M. Shirokov🇺🇸 · Erdal Dikmen🇹🇷 · Pieter Maris🇺🇸 · James P. Vary🇺🇸
We perform a quantitative study of the microscopic effective shell-model interactions in the valence sd shell, obtained from modern nucleon-nucleon potentials, chiral N3LO, JISP16 and Daejeon16, using No-Core Shell-Model wave functions and the Okubo-Lee-Suzuki transformation. We investigate the monopole properties of those interactions in comparison with the phenomenological universal sd-shell interaction, USDB. Theoretical binding energies and low-energy spectra of O isotopes and of selected sd-shell nuclei, are presented. We conclude that there is a noticeable improvement in the quality of the effective interaction when it is derived from the Daejeon16 potential. We show that its proton-neutron centroids are consistent with those from USDB. We then propose monopole modifications of the Daejeon16 centroids in order to provide an adjusted interaction yielding significantly improved agreement with the experiment. A spin-tensor decomposition of two-body effective interactions is applied in order to extract more information on the structure of the centroids and to understand the reason for deficiencies arising from our current theoretical approximations. The issue of the possible role of the three-nucleon forces is addressed.
nucl-thPRC(2019)·37 citations
05
The quest of shape coexistence in Zr isotopes
J.E. Garcia-Ramos · K. Heyde
The mass region with A~100 and Z~40 is known to experience a sudden onset of deformation. The presence of the subshell closure $Z = 40$ makes feasible to create particle-hole excitations at a moderate excitation energy and, therefore, likely intruder states could be present in the low-lying spectrum. In other words, shape coexistence is expected to be a key ingredient to understand this mass region. The aim of this work is to describe excitation energies, transition rates, radii, and two-neutron separation energies for the even-even 94-110Zr nuclei and, moreover, to obtain information about wave functions and deformation. The interacting boson model with configuration mixing will be the framework to study the even-even Zr nuclei, considering only two types of configurations: 0particle-0hole and 2p-2h excitations. On one hand, the parameters appearing in the Hamiltonian and in the E2 transition operator are fixed trough a least-squares fit to the whole available experimental information. On the other hand, once the parameters have been fixed, the calculations allow to obtain a complete set of observables for the whole even-even Zr chain of isotopes. Spectra, transition rates, radii, $ρ^{2} (E 0)$ , and two-neutron separation energies have been calculated and a good agreement with the experimental information has been obtained. Moreover, a detailed study of the wave function has been conducted and mean-field energy surfaces and deformation have been computed too. The importance of shape coexistence has been shown to correctly describe the A~100 mass area for even-even Zr nuclei. This work confirmed the rather spherical nature of the ground state of 94-98Zr and its deformed nature for 100-110Zr isotopes. The sudden onset of deformation in 100Zr is owing to the rapid lowering of a deformed (intruder) configuration which is high-lying in lighter isotopes.
nucl-thnucl-exPRC(2019)·58 citations
06
Complex phase structure of the meson-baryon $T$ -matrix
Shahab Razavi🇺🇸 · K. Nakayama🇺🇸
The full complex phase structure of the meson-baryon reaction amplitude in coupled channels approach is investigated, including also the photon-baryon channel. The result may be viewed as a generalization of the well-known Watson's theorem. Furthermore, the complex phase structure is exhibited for the pole and nonpole parts of the reaction amplitude in such a way that it will serve as a convenient common starting point for constructing models with different levels of approximation, in particular, for building isobar models where the basic properties of the $S$ -matrix can be maintained. Such models should be useful, especially, in coupled multichannel calculations, where a large amount of experimental data are considered in resonance analyses, a situation encountered in modern baryon spectroscopy. In particular, it is shown that the unitarity of the pole part of the $T$ -matrix arises automatically from the dressing mechanism inherent in the basic scattering equation. This implies that no separate conditions are required for making this part of the resonance amplitude unitary as it has been done in some of the existing isobar models.
nucl-thPRD(2019)·1 citation
07
Low- $Q^{2}$ empirical parametrizations of the $N^{*}$ helicity amplitudes
G. Ramalho🇧🇷
The data associated with the electromagnetic excitations of the nucleon ( $γ^{*} N \to N^{*}$ ) are usually parametrized by helicity amplitudes at the resonance $N^{*}$ rest frame. The properties of the $γ^{*} N \to N^{*}$ transition current at low $Q^{2}$ can be, however, better understood when expressed in terms of structure form factors, particularly near the pseudothreshold, when the magnitude of the photon three-momentum vanishes ( $∣ q ∣ = 0$ ). At the pseudothreshold the invariant four-momentum square became $q^{2} = (M_{R} - M_{N})^{2}$ , well in the timelike region $Q^{2} = - q^{2} < 0$ [ $M_{N}$ and $M_{R}$ are the mass of the nucleon and of the resonance, respectively]. In the helicity amplitude representation, the amplitudes have well-defined dependences on $∣ q ∣$ , near the pseudothreshold, and there are correlations between different amplitudes. Those constraints are often ignored in the empirical parametrizations of the helicity amplitudes. In the present work, we show that the structure of the transition current near the pseudothreshold has an impact on the parametrizations of the data. We present a method which modifies analytic parametrizations of the data at low $Q^{2}$ , in order to take into account the constraints of the transition amplitudes near the pseudothreshold. The model dependence of the parametrizations on the low- $Q^{2}$ data is studied in detail.
↳ hep-phhep-exnucl-exnucl-thPRD(2019)·16 citations
08
Improved pion mean fields and masses of singly heavy baryons
June-Young Kim🇰🇷 · Hyun-Chul Kim🇰🇷
A singly heavy baryon can be viewed as $N_{c} - 1$ ( $N_{c}$ as the number of colors) light valence quarks bound by the pion mean fields that are created by the presence of the $N_{c} - 1$ valence quarks self-consistently, while the heavy quark inside a singly heavy baryon is regarded as a static color source. We investigate how the pion mean fields are created by the presence of $N_{c}$ , $N_{c} - 1$ , and $N_{c} - 2$ light valence quarks, which correspond to the systems of light baryons, singly heavy baryons, and doubly heavy baryons. As the number of color decreases from $N_{c}$ to $N_{c} - 1$ , the pion mean fields undergo changes. As a result, the valence-quark contributions to the moments of inertia of the soliton become larger than the case of the $N_{c}$ valence quarks, whereas the sea-quark contributions decrease systematically. On the other hand, the presence of the $N_{c} - 2$ valence quarks is not enough to produce the strong pion mean fields, which leads to the fact that the classical soliton can not be formed. It indicates that the pion mean-field approach is not suitable to describe doubly heavy baryons. We show that the mass spectra of the singly heavy baryons are better described by the improved pion mean fields, compared with the previous work in which the pion mean fields are assumed to be intact with $N_{c}$ varied.
↳ hep-phhep-exnucl-thPTEP(2020)·15 citations
09
Relaxation time for quark spin and thermal vorticity alignment in heavy-ion collisions
Alejandro Ayala🇲🇽 · David de la Cruz🇲🇽 · S. Hernández-Ortíz🇲🇽 · L. A. Hernández🇲🇽 · Jordi Salinas🇲🇽
We compute the relaxation time for quark/antiquark spin and thermal vorticity alignment in a quark-gluon plasma at finite temperature and quark chemical potential. We model the interaction of quark/antiquark spin with thermal vorticity as driven by a phenomenological modification of the elementary quark interaction with gluons. We find that in a scenario where the angular velocity of the quark-gluon plasma produced in a peripheral heavy-ion collision is small, quarks/antiquarks take a long time to align their spin with the vorticity. However, when the angular velocity created in the reaction is large, the alignment is efficient and well within the lifetime of the system created in the reaction. The relaxation time is larger for antiquarks which points out to a difference for the polarization of hadrons and antihadrons when this alignment is preserved during hadronization.
↳ hep-phnucl-thPLB(2020)·38 citations
10
Coupled-channel approach in hadron-hadron scattering
J.A. Oller🇪🇸
Coupled-channel dynamics for scattering and production processes in partial-wave amplitudes is discussed from a perspective that emphasizes unitarity and analyticity. We elaborate on several methods that have driven to important results in hadron physics, either by themselves or in conjunction with effective field theory. We also develop and compare with the use of the Lippmann-Schwinger equation in near-threshold scattering. The final(initial)-state interactions are discussed in detail for the elastic and coupled-channel case. Emphasis has been put in the derivation and discussion of the methods presented, with some applications examined as important examples of their usage.
↳ hep-phcond-mat.quant-gasnucl-thPPNP(2020)·77 citations
11
Nucleon axial, tensor and scalar charges and $σ$ -terms in lattice QCD
C. Alexandrou (Univ. of Cyprus & The Cyprus Inst.) · S. Bacchio (The Cyprus Inst.) · M. Constantinou (Temple Univ.) · K. Hadjiyiannakou (The Cyprus Inst.) · K. Jansen (DESY-Zeuthen) · G. Koutsou (The Cyprus Inst.) · A. Vaquero Aviles-Casco (Univ. of Utah)
We determine the nucleon axial, scalar and tensor charges within lattice Quantum Chromodynamics including all contributions from valence and sea quarks. We analyze three gauge ensembles simulated within the twisted mass formulation at approximately physical value of the pion mass. Two of these ensembles are simulated with two dynamical light quarks and lattice spacing $a = 0.094$ ~fm and the third with $a = 0.08$ ~fm includes in addition the strange and charm quarks in the sea. After comparing the results among these three ensembles, we quote as final values our most accurate analysis using the latter ensemble. For the nucleon isovector axial charge we find $1.286 (23)$ in agreement with the experimental value. We provide the flavor decomposition of the intrinsic spin $\frac{1}{2} Δ Σ^{q}$ carried by quarks in the nucleon obtaining for the up, down, strange and charm quarks $\frac{1}{2} Δ Σ^{u} = 0.431 (8)$ , $\frac{1}{2} Δ Σ^{d} = - 0.212 (8)$ , $\frac{1}{2} Δ Σ^{s} = - 0.023 (4)$ and $\frac{1}{2} Δ Σ^{c} = - 0.005 (2)$ , respectively. The corresponding values of the tensor and scalar charges for each quark flavor are also evaluated providing valuable input for experimental searches for beyond the standard model physics. In addition, we extract the nucleon $σ$ -terms and find for the light quark content $σ_{π N} = 41.6 (3.8)$ ~MeV and for the strange $σ_{s} = 45.6 (6.2)$ ~MeV. The y-parameter that is used in phenomenological studies we find $y = 0.078 (7)$ .
↳ hep-lathep-exhep-phnucl-ex+1PRD(2020)·158 citations
12
Analytic self-gravitating $4$ -Baryons, traversable NUT-AdS wormholes, flat space-time multi-Skyrmions at finite volume and a novel transition in the $S U (3)$ -Skyrme model
Eloy Ayón-Beato🇲🇽 · Fabrizio Canfora🇨🇱 · Marcela Lagos🇨🇱 · Julio Oliva🇨🇱 · Aldo Vera🇨🇱
We construct the first analytic self-gravitating Skyrmions with higher Baryon charge in four dimensions for the $S U (3)$ -Skyrme-Einstein- $Λ$ theory by combining the generalized hedgehog ansatz with the approach developed by Balachandran et al. to describe the first (numerical) example of a non-embedded solution. These are genuine $S U (3)$ analytic solutions instead of trivial embeddings of $S U (2)$ into $S U (3)$ and its geometry is that of a Bianchi IX Universe. The Skyrme ansatz is chosen in such a way that the Skyrme field equations are identically satisfied in the sector with Baryon charge 4. The field equations reduce to a dynamical system for the three Bianchi IX scale factors. Particular solutions are explicitly analyzed. Traversable wormholes with NUT-AdS asymptotics supported by a topologically non-trivial $S U (3)$ -sigma soliton are also constructed. The self-gravitating solutions admit also a suitable flat limit giving rise to Skyrmions of charge 4 confined in a box of finite volume maintaining the integrability of the $S U (3)$ Skyrme field equations. This formalism discloses a novel transition at finite Baryon density arising from the competition between embedded and non-embedded solutions in which the non-embedded solutions prevail at high density while are suppressed at low densities.
↳ hep-thgr-qchep-phnucl-thEPJC(2020)·38 citations
13
Temperatures and chemical potentials at kinetic freeze-out in relativistic heavy ion collisions from coarse grained transport simulations
Gabriele Inghirami🇫🇮 · Paula Hillmann🇩🇪 · Boris Tomášik🇸🇰 · Marcus Bleicher🇩🇪
Using the UrQMD/coarse graining approach we explore the kinetic freeze-out stage in central Au + Au collisions at various energies. These studies allow us to obtain detailed information on the thermodynamic properties (e.g. temperature and chemical potential) of the system during the kinetic decoupling stage. We explore five relevant collision energies in detail, ranging from $s_{N N} = 2.4 GeV$ (GSI-SIS) to $s_{N N} = 200 GeV$ (RHIC). By adopting a standard Hadron Resonance Gas equation of state, we determine the average temperature $⟨ T ⟩$ and the average baryon chemical potential $⟨ μ_{B} ⟩$ on the space-time hyper-surface of last interaction. The results highlight the nature of the kinetic freeze-out as a continuous process. This differential decoupling is an important aspect often missed when summarizing data as single points in the phase diagram as e.g. done in Blast-Wave fits. We compare the key properties of the system derived by using our approach with other models and we briefly review similarities and differences.
↳ hep-phnucl-exnucl-thJ.Phys.G(2020)·15 citations
14
Hermitizing the HAL QCD potential in the derivative expansion
Sinya Aoki🇯🇵 · Takumi Iritani🇯🇵 · Koichi Yazaki🇯🇵
A formalism is given to hermitize the HAL QCD potential, which needs to be non-hermitian except the leading order (LO) local term in the derivative expansion as the Nambu-Bethe-Salpeter (NBS) wave functions for different energies are not orthogonal to each other. It is shown that the non-hermitian potential can be hermitized order by order to all orders in the derivative expansion. In particular, the next-to-leading order (NLO) potential can be exactly hermitized without approximation. The formalism is then applied to a simple case of $ΞΞ (^{1} S_{0})$ scattering, for which the HAL QCD calculation is available to the NLO. The NLO term gives relatively small corrections to the scattering phase shift and the LO analysis seems justified in this case. We also observe that the local part of the hermitized NLO potential works better than that of the non-hermitian NLO potential. The hermitian version of the HAL QCD potential is desirable for comparing it with phenomenological interactions and also for using it as a two-body interaction in many body systems.
↳ hep-latnucl-thPTEP(2020)·4 citations
15
Chiral-spin symmetry of the meson spectral function above $T_{c}$
C. Rohrhofer🇯🇵 · Y. Aoki🇯🇵 · L. Ya. Glozman🇦🇹 · S. Hashimoto🇯🇵
Recently, via calculation of spatial correlators of $J = 0, 1$ isovector operators using a chirally symmetric Dirac operator within $N_{F} = 2$ QCD, it has been found that QCD at temperatures $T_{c} - 3 T_{c}$ is approximately $S U (2)_{C S}$ and $S U (4)$ symmetric. The latter symmetry suggests that the physical degrees of freedom are chirally symmetric quarks bound by the chromoelectric field into color singlet objects without chromomagnetic effects. This regime of QCD has been referred to as a Stringy Fluid. Here we calculate correlators for propagation in time direction at a temperature slightly above $T_{c}$ and find the same approximate symmetries. This means that the meson spectral function is chiral-spin and $S U (4)$ symmetric.
↳ hep-lathep-phhep-thnucl-thPLB(2020)·51 citations
16
Non-Newtonian gravity in strange quark stars and constraints from the observations of PSR J0740+6620 and GW170817
Shu-Hua Yang🇨🇳 · Chun-Mei PI🇨🇳 · Xiao-Ping Zheng🇨🇳 · Fridolin Weber🇺🇸
We investigate the effects of non-Newtonian gravity on the properties of strange quark stars (QSs) and constrain the parameters of the standard MIT bag model used to describe strange quark matter (SQM) by employing the mass of PSR J0740+6620 and the tidal deformability of GW170817. We find that, for the standard MIT bag model, these mass and tidal deformability observations would rule out the existence of QSs if non-Newtonian gravity effects are ignored. For a strange quark mass of $m_{s} = 95$ MeV, we find that QSs can exist for values of the non-Newtonian gravity parameter $g^{2} / μ^{2}$ in the range of 1.37 GeV $^{- 2} \leq g^{2} / μ^{2} \leq$ 7.28 GeV $^{- 2}$ and limits on the bag constant and the strong interaction coupling constant of the SQM model given by 141.3 MeV $\leq B^{1/4} \leq$ 150.9 MeV and $α_{S} \leq 0.56$ . For a strange quark mass of $m_{s} = 150$ MeV, QSs can exist for 1.88 GeV $^{- 2} \leq g^{2} / μ^{2} \leq$ 6.27 GeV $^{- 2}$ and limits on the parameters of the SQM model given by 139.7 MeV $\leq B^{1/4} \leq$ 147.3 MeV and $α_{S} \leq 0.49$ .
↳ astro-ph.HEnucl-thApJ(2020)·20 citations
17
QCD at finite isospin density: chiral perturbation theory confronts lattice data
Prabal Adhikari🇺🇸 · Jens O. Andersen🇳🇴
We consider the thermodynamics of three-flavor QCD in the pion-condensed phase at nonzero isospin chemical potential ( $μ_{I}$ ) and vanishing temperature using chiral perturbation theory in the isospin limit. The transition from the vacuum phase to a superfluid phase with a Bose-Einstein condensate of charged pions is shown to be second order and takes place at $μ_{I} = m_{π}$ . We calculate the pressure, isospin density, and energy density to next-to-leading order in the low-energy expansion. Our results are compared with recent high-precision lattice simulations as well as previously obtained results in two-flavor chiral perturbation theory. The agreement between the lattice results and the predictions from three-flavor chiral perturbation theory is very good for $μ_{I} < 200$ MeV. For larger values of $μ_{I}$ , the agreement between lattice data and the two-flavor predictions is surprisingly good and better than with the three-flavor predictions. Finally, in the limit $m_{s} ≫ m_{u} = m_{d}$ , we show that the three-flavor observables reduce to the two-flavor observables with renormalized parameters. The disagreement between the results for two-flavor and three-flavor $χ$ PT can largely be explained by the differences in the measured low-energy constants.
↳ hep-phnucl-thPLB(2020)·50 citations
18
Cooling binary neutron star remnants via nucleon-nucleon-axion bremsstrahlung
Tim Dietrich🇳🇱 · Katy Clough🇬🇧
The QCD axion is a hypothetical particle motivated by the Strong CP problem of particle physics. One of the primary ways in which its existence can be inferred is via its function as an additional cooling channel in stars, with some of the strongest constraints coming from the supernova observation SN1987A. Multimessenger observations of binary neutron star mergers (such as those of GW170817, AT2017gfo, and GRB170817A) may provide another scenario in which such constraints could be obtained. In particular, the axion could potentially alter the lifetime, the ejection of material, and the emitted gravitational wave signal of the postmerger remnant. In this article, we perform numerical relativity simulations of a binary neutron star merger, including a phenomenological description of the nucleon-nucleon-axion bremsstrahlung to quantify the effects of such a cooling channel on the dynamical evolution. While our simulations show a difference in the temperature profile of the merger remnant, the imprint of the axion via nucleon-nucleon-axion bremsstrahlung on the emitted gravitational wave signal and the ejecta mass is too small to improve constraints on the axion mass with current or future planned detectors. Whilst we consider a limited number of cases, and a simplified cooling model, these broadly represent the "best case" scenario, thus, a more thorough investigation is unlikely to change the conclusions, at least for this particular interaction channel.
↳ gr-qcastro-ph.HEhep-phnucl-thPRD(2019)·40 citations

Affiliations

first authorsco-authorsvia INSPIRE