Nuclear Theory·nucl-th

Tuesday·January 24, 2017

17 papers—10 primary·7 cross-listed

01
Meson-baryon scattering to one-loop order in heavy baryon chiral perturbation theory
Bo-Lin Huang🇨🇳 · Jin-Sheng Zhang🇨🇳 · Yun-De Li🇨🇳 · Norbert Kaiser🇩🇪
We calculate the T-matrices of pseudoscalar meson octet-baryon scattering to one-loop order in SU(3) heavy baryon chiral perturbation theory. The pertinent combinations of low-energy constants are determined by fitting to phase shifts of $π N$ and $K N$ scattering and the corresponding data. By using these low-energy constants, we obtain the strong phase shift difference of $π Λ$ scattering at the $Ξ$ mass, $δ_{P} - δ_{S} = (8.8 \pm 0.2)$ degrees, in agreement with experimental results. We find that the phase shifts in the $S_{01}$ ( $π Σ$ ), $S_{01}$ ( $K Ξ$ ), $S_{01}$ ( $K N$ ), and $S_{11}$ ( $K Σ$ ) waves are so strong that resonances may be generated dynamically in all these channels. We also predict the scattering lengths and make comparisons with the results obtained from the threshold T-matrices in heavy baryon chiral perturbation theory and the method of covariant infrared regularization. The issue of convergence is also discussed in detail.
nucl-thPRD(2017)·20 citations
02
Neutron stars within relativistic central variational method
Jinniu Hu · Hong Shen · Hiroshi Toki
The properties of neutron stars are investigated within the relativistic central variational method by using a realistic nucleon-nucleon ( $N N$ ) interaction. The strong repulsion of realistic $N N$ interactions at short distances is treated by a Jastrow central correlation function, whose form is completely determined through minimization of the total energy of the nuclear many-body system. The relativistic Hartree-Fock wave functions are chosen as the trial wave function. In this framework, the equation of state of the neutron star matter in $β$ equilibrium is obtained self-consistently. We further determine the properties of neutron stars via the Tolman-Oppenheimer-Volkoff equation using Bonn A, B, and C potentials. The maximum masses of neutron stars with these realistic potentials are around $2.18 M_{⊙}$ and their corresponding radii are around $11$ km. These results are in accordance with the calculations of the relativistic Brueckner-Hartree-Fock theory with the same potentials. Furthermore, we also find that the splitting of proton-neutron effective masses will be reversed at high density in the neutron star matter, which are caused by the contribution of short-range correlation on kinetic energy.
nucl-thPRC(2017)·1 citation
03
Collective excitations of hot QCD medium in a quasi-particle description
M.Yousuf Jamal🇮🇳 · Sukanya Mitra🇮🇳 · Vinod Chandra🇮🇳
Collective excitations of a hot QCD medium are the main focus of the present article. The analysis is performed within semi-classical transport theory with isotropic and anisotropic momentum distribution functions for the gluonic and quark-antiquark degrees of freedom that constitutes the hot QCD plasma. The isotropic/equilibrium momentum distributions for gluons and quarks are based on a recent quasi-particle description of hot QCD equations of state. The anisotropic distributions are just the extensions of isotropic ones by stretching or squeezing them in one of the directions. The hot QCD medium effects in the model adopted here enter through the effective gluon and quark fugacities along with non-trivial dispersion relations leading to an effective QCD coupling constant. Interestingly, with these distribution functions the tensorial structure of the gluon polarization tensor in the medium turned out to be similar to the one for the non-interacting ultra-relativistic system of quarks/antiquarks and gluons . The interactions mainly modify the Debye mass parameter and , in turn, the effective coupling in the medium. These modifications have been seen to modify the collective modes of the hot QCD plasma in a significant way.
nucl-thPRD(2017)·38 citations
04
Hyperon-nucleon Scattering In A Covariant Chiral Effective Field Theory Approach
Kai-Wen Li🇨🇳 · Xiu-Lei Ren🇨🇳 · Li-Sheng Geng🇨🇳 · Bingwei Long🇨🇳
A recently proposed covariant chiral effective field theory approach is applied to study strangeness $S = - 1$ hyperon-nucleon interactions at leading order. 12 low energy constants are introduced by Lorentz invariance, which is different from the heavy baryon approach, where only five appear. The Kadyshevsky equation is employed to iterate the chiral potentials. A quite satisfactory description of the 36 hyperon-nucleon scattering data is obtained with $χ^{2} ≃ 17$ , which is comparable with the next-to-leading order heavy baryon approach. The results hint at a more efficient way to construct the chiral potentials.
nucl-thPoS(2017)·2 citations
05
Unexpected neutron/proton ratio and isospin effect in low-energy antiproton induced reactions
Zhao-Qing Feng🇨🇳
The inclusive spectra of preequilibrium nucleons produced in low-energy antiproton-nucleus collisions are thoroughly investigated within the framework of the Lanzhou quantum molecular dynamics model for the first time. All possible reaction channels such as elastic scattering, annihilation, charge exchange and inelastic scattering in antibaryon-baryon, baryon-baryon and meson-baryon collisions have been included in the transport model. The unexpected neutron/proton ratio in comparison to the pion and proton induced reactions is caused from the isospin effects of pion-nucleon collisions and the density dependence of symmetry energy. It is found that the $π^{-}$ -neutron collisions enhance the neutron emission in the antiproton annihilation in a nucleus. Different to heavy-ion collisions, the isospin effects are pronounced at the low kinetic energies. A soft symmetry energy with the stiffness of $γ_{s} =$ 0.5 at subsaturation densities is constrained from the available data of the neutron/proton spectra.
nucl-thPRC(2017)·5 citations
06
Superheavy toroidal nuclei in the Skyrme energy functional framework
A. Kosior · A. Staszczak · Cheuk-Yin Wong
Using the Hartree-Fock-Bogoliubov (HFB) self-consistent mean-field theory with the SkM* Skyrme energy-density functional, we study nuclear structure properties of even-even superheavy nuclei (SHN) of $Z = 120$ isotopes and $N = 184$ isotones. The shape of the nucleus along the lowest energy curve as a function of the quadrupole moment $Q_{20}$ makes a sudden transition from the oblate spheroids (biconcave discs) to the toroidal shapes, in the region of large oblate quadrupole moments.
nucl-thActa Phys.Polon.Supp.(2017)·6 citations
07
(No) neutron star maximum mass constraint from hypernuclei
M. Fortin🇵🇱 · S.S. Avancini🇧🇷 · C. Providência🇵🇹 · I. Vidaña🇵🇹
(Abridged) The recent measurement of the mass of two $2 M_{⊙}$ pulsars has raised the question whether such large masses allow for the existence of exotic degrees of freedom, such as hyperons, inside neutron stars. In the present work we will investigate how the existing hypernuclei properties may constrain the neutron star equation of state and confront the neutron star maximum masses obtained with equations of state calibrated to hypernuclei properties with the astrophysical $2 M_{⊙}$ constraint. The study is performed using a relativistic mean field approach to describe both the hypernuclei and the neutron star equations of state. A set of five models consistent with $2 M_{⊙}$ for a purely nucleonic composition are employed. The $Λ$ -meson couplings are determined for all the models considered. Hyperonic stars with the complete baryonic octet are studied, restricting the coupling of the $Σ$ and $Ξ$ hyperons to the $ω -$ , $ρ -$ and $σ -$ mesons due to the lack of experimental data, and maximum star masses calculated for unified equations of state. We conclude that the currently available hypernuclei experimental data and the lack of constraints on the asymmetric equation of state of nuclear matter at high densities do not allow to further constrain the neutron star matter equation of state using the recent $2 M_{⊙}$ observations. It is also shown that the $Λ$ potential in symmetric nuclear matter takes a value $\sim 30 - 32$ MeV at saturation for the $g_{ω Λ}$ coupling given by the SU(6) symmetry, close to values generally used in the literature. However, the $Λ$ potential in $Λ$ matter varies between -16 and -8 MeV taking for vector mesons couplings the SU(6) values, at variance with generally employed values between $- 1$ and $- 5$ MeV.
nucl-thastro-ph.HEPRC(2017)·134 citations
08
Benchmark Results for Few-Body Hypernuclei
F. Ferrari Ruffino🇮🇹 · N. Barnea🇮🇱 · S. Deflorian🇮🇹 · W. Leidemann🇮🇹 · D. Lonardoni🇺🇸 · G. Orlandini🇮🇹 · F. Pederiva🇮🇹
The Non-Symmetrized Hyperspherical Harmonics method (NSHH) is introduced in the hypernuclear sector and benchmarked with three different ab-initio methods, namely the Auxiliary Field Diffusion Monte Carlo method, the Faddeev-Yakubovsky approach and the Gaussian Expansion Method. Binding energies and hyperon separation energies of three- to five-body hypernuclei are calculated by employing the two-body $Λ$ N component of the phenomenological Bodmer-Usmani potential, and a hyperon-nucleon interaction simulating the scattering phase shifts given by NSC97f. The range of applicability of the NSHH method is briefly discussed.
nucl-thFew Body Syst.(2017)·11 citations
09
Ground-State Properties of $^{4}$ He and $^{16}$ O Extrapolated from Lattice QCD with Pionless EFT
L. Contessi🇮🇹 · A. Lovato🇺🇸 · F. Pederiva🇮🇹 · A. Roggero🇺🇸 · J. Kirscher🇺🇸 · U. van Kolck🇫🇷
We extend the prediction range of Pionless Effective Field Theory with an analysis of the ground state of $^{16}$ O in leading order. To renormalize the theory, we use as input both experimental data and lattice QCD predictions of nuclear observables, which probe the sensitivity of nuclei to increased quark masses. The nuclear many-body Schrödinger equation is solved with the Auxiliary Field Diffusion Monte Carlo method. For the first time in a nuclear quantum Monte Carlo calculation, a linear optimization procedure, which allows us to devise an accurate trial wave function with a large number of variational parameters, is adopted. The method yields a binding energy of $^{4}$ He which is in good agreement with experiment at physical pion mass and with lattice calculations at larger pion masses. At leading order we do not find any evidence of a $^{16}$ O state which is stable against breakup into four $^{4}$ He, although higher-order terms could bind $^{16}$ O.
nucl-thhep-latPLB(2017)·109 citations
10
Equations of state for real gases on the nuclear scale
Volodymyr Vovchenko🇩🇪
The formalism to augment the classical models of equation of state for real gases with the quantum statistical effects is presented. It allows an arbitrary excluded volume procedure to model repulsive interactions, and an arbitrary density-dependent mean field to model attractive interactions. Variations on the excluded volume mechanism include van der Waals (VDW) and Carnahan-Starling models, while the mean fields are based on VDW, Redlich-Kwong-Soave, Peng-Robinson, and Clausius equations of state. The VDW parameters of the nucleon-nucleon interaction are fitted in each model to the properties of the ground state of nuclear matter, and the following range of values is obtained: $a = 330 - 430$ MeV fm $^{3}$ and $b = 2.5 - 4.4$ fm $^{3}$ . In the context of the excluded-volume approach, the fits to the nuclear ground state disfavor the values of the effective hard-core radius of a nucleon significantly smaller than $0.5$ fm, at least for the nuclear matter region of the phase diagram. Modifications to the standard VDW repulsion and attraction terms allow to improve significantly the value of the nuclear incompressibility factor $K_{0}$ , bringing it closer to empirical estimates. The generalization to include the baryon-baryon interactions into the hadron resonance gas model is performed. The behavior of the baryon-related lattice QCD observables at zero chemical potential is shown to be strongly correlated to the nuclear matter properties: an improved description of the nuclear incompressibility also yields an improved description of the lattice data at $μ = 0$ .
nucl-thcond-mat.quant-gascond-mat.stat-mechhep-phPRC(2017)·55 citations
11
Parton energy loss in QCD matter
Konrad Tywoniuk🇨🇭
QCD jets, produced copiously in heavy-ion collisions at LHC and also at RHIC, serve as probes of the dynamics of the quark-gluon plasma (QGP). Jet fragmentation in the medium is interesting in its own right and, in order to extract pertinent information about the QGP, it has to be well understood. We present a brief overview of the physics involved and argue that jet substructure observables provide new opportunities for understanding the nature of the modifications.
↳ hep-phnucl-thNucl.Part.Phys.Proc.(2017)·1 citation
12
Quark matter with strong magnetic field and possibility of the third family of compact stars
Hajime Sotani🇯🇵 · Toshitaka Tatsumi🇯🇵
We consider the possibility for the existence of the third family of compact objects, considering the effect of strong magnetic fields inside the hybrid stars. As a result, we demonstrate such new sequences of stable equilibrium configurations for some hadronic equations of state. Through the analysis of the adiabatic index inside stars, we find the conditions for appearing the third family of compact objects, i.e., for hadronic stars without quarks, that the maximum mass should be small, the central density for the maximum mass should be also small, and the radius for the the maximum mass should be large. Even for soft hadronic equations of state, the two solar-mass stars might survive as the third family of compact objects, once quark matter with strong magnetic field, such as $\sim O (1 0^{19} G)$ , is taken into account. It might give a hint to solve the so-called hyperon puzzle in nuclear physics.
↳ astro-ph.HEhep-phnucl-thMNRAS(2017)·12 citations
13
Temperature oscillations and sound waves in hadronic matter
Grzegorz Wilk🇵🇱 · Zbigniew Wlodarczyk🇵🇱
Recent high energy CERN LHC experiments on transverse momenta distributions of produced particles seem to show the existence of some (small but persistent) log-periodic oscillation in the ratios $R = σ_{d a t a} (p_{T}) / σ_{f i t} (p_{T})$ . We argue that they can provide us with so far unnoticed information on the production process, which can be interpreted as the presence of some kind of sound waves formed during the collision process in the bulk of the produced high density matter.
↳ hep-phcond-mat.stat-mechnucl-thPhysica A(2017)·8 citations
14
Probing the possibility of hotspots on the central neutron star in HESS J1731-347
V.F. Suleimanov · D. Klochkov · J. Poutanen · K. Werner
The X-ray spectra of the neutron stars located in the centers of supernova remnants Cas A and HESS J1731-347 are well fit with carbon atmosphere models. These fits yield plausible neutron star sizes for the known or estimated distances to these supernova remnants. The evidence in favor of the presence of a pure carbon envelope at the neutron star surface is rather indirect and is based on the assumption that the emission is generated uniformly by the entire stellar surface. Although this assumption is supported by the absence of pulsations, the observational upper limit on the pulsed fraction is not very stringent. In an attempt to quantify this evidence, we investigate the possibility that the observed spectrum of the neutron star in HESS J1731-347 is a combination of the spectra produced in a hydrogen atmosphere of the hotspots and of the cooler remaining part of the neutron star surface. The lack of pulsations in this case has to be explained either by a sufficiently small angle between the neutron star spin axis and the line of sight, or by a sufficiently small angular distance between the hotspots and the neutron star rotation poles. As the observed flux from a non-uniformly emitting neutron star depends on the angular distribution of the radiation emerging from the atmosphere, we have computed two new grids of pure carbon and pure hydrogen atmosphere model spectra accounting for Compton scattering. Using new hydrogen models, we have evaluated the probability of a geometry that leads to a pulsed fraction below the observed upper limit to be about 8.2 %. Such a geometry thus seems to be rather improbable but cannot be excluded at this stage.
↳ astro-ph.HEastro-ph.SRnucl-thAstron.Astrophys.(2017)·17 citations
15
Harmonic decomposition of three-particle azimuthal correlations at RHIC
STAR Collaboration: L. Adamczyk · J. K. Adkins · G. Agakishiev · M. M. Aggarwal · Z. Ahammed · N. N. Ajitanand · I. Alekseev · D. M. Anderson · R. Aoyama · A. Aparin · D. Arkhipkin · E. C. Aschenauer and 336 other authors
We present measurements of three-particle correlations for various harmonics in Au+Au collisions at energies ranging from $s_{NN} = 7.7$ to 200 GeV using the STAR detector. The quantity $⟨ cos (m ϕ_{1} + n ϕ_{2} - (m + n) ϕ_{3})⟩$ is evaluated as a function of $s_{NN}$ , collision centrality, transverse momentum, $p_{T}$ , pseudo-rapidity difference, $Δ η$ , and harmonics ( $m$ and $n$ ). These data provide detailed information on global event properties like the three-dimensional structure of the initial overlap region, the expansion dynamics of the matter produced in the collisions, and the transport properties of the medium. A strong dependence on $Δ η$ is observed for most harmonic combinations consistent with breaking of longitudinal boost invariance. Data reveal changes with energy in the two-particle correlation functions relative to the second-harmonic event-plane and provide ways to constrain models of heavy-ion collisions over a wide range of collision energies.
↳ nucl-exnucl-thPRC(2018)·60 citations
16
Constraining the initial conditions and temperature dependent transport with three-particle correlations in Au+Au collisions
STAR Collaboration: L. Adamczyk · J. K. Adkins · G. Agakishiev · M. M. Aggarwal · Z. Ahammed · N. N. Ajitanand · I. Alekseev · D. M. Anderson · R. Aoyama · A. Aparin · D. Arkhipkin · E. C. Aschenauer and 336 other authors
We present three-particle mixed-harmonic correlations $\la cos (m ϕ_{a} + n ϕ_{b} - (m + n) ϕ_{c}) \ra$ for harmonics $m, n = 1 - 3$ for charged particles in $s_{N N} =$ 200 GeV Au+Au collisions at RHIC. These measurements provide information on the three-dimensional structure of the initial collision zone and are important for constraining models of a subsequent low-viscosity quark-gluon plasma expansion phase. We investigate correlations between the first, second and third harmonics predicted as a consequence of fluctuations in the initial state. The dependence of the correlations on the pseudorapidity separation between particles show hints of a breaking of longitudinal invariance. We compare our results to a number of state-of-the art hydrodynamic calculations with different initial states and temperature dependent viscosities. These measurements provide important steps towards constraining the temperature dependent transport and the longitudinal structure of the initial state at RHIC.
↳ nucl-exnucl-thPLB(2019)·14 citations
17
Rescattering effects in the hadronic-light-by-light contribution to the anomalous magnetic moment of the muon
Gilberto Colangelo🇨🇭 · Martin Hoferichter🇺🇸 · Massimiliano Procura🇨🇭 · Peter Stoffer🇩🇪
We present a first model-independent calculation of $π π$ intermediate states in the hadronic-light-by-light (HLbL) contribution to the anomalous magnetic moment of the muon $(g - 2)_{μ}$ that goes beyond the scalar QED pion loop. To this end we combine a recently developed dispersive description of the HLbL tensor with a partial-wave expansion and demonstrate that the known scalar-QED result is recovered after partial-wave resummation. Using dispersive fits to high-statistics data for the pion vector form factor, we provide an evaluation of the full pion box, $a_{μ}^{π -box} = - 15.9 (2) \times 1 0^{- 11}$ . We then construct suitable input for the $γ^{*} γ^{*} \to π π$ helicity partial waves based on a pion-pole left-hand cut and show that for the dominant charged-pion contribution this representation is consistent with the two-loop chiral prediction and the COMPASS measurement for the pion polarizability. This allows us to reliably estimate $S$ -wave rescattering effects to the full pion box and leads to our final estimate for the sum of these two contributions: $a_{μ}^{π -box} + a_{μ, J = 0}^{π π, π -pole LHC} = - 24 (1) \times 1 0^{- 11}$ .
↳ hep-phhep-exhep-latnucl-thPRL(2017)·192 citations

Affiliations

first authorsco-authorsvia INSPIRE