Nuclear Theory·nucl-th

Friday·May 22, 2020

9 papers—4 primary·5 cross-listed

01
Quark spin and orbital angular momentum from proton GPDs
Adam Freese🇺🇸 · Ian C. Cloët🇺🇸
We calculate the leading-twist helicity-dependent generalized parton distributions (GPDs) of the proton at finite skewness in the Nambu--Jona-Lasinio (NJL) model of quantum chromodynamics (QCD). From these (and previously calculated helicity-independent GPDs) we obtain the spin decomposition of the proton, including predictions for quark intrinsic spin and orbital angular momentum. The inclusion of multiple species of diquarks is found to have a significant effect on the flavor decomposition, and resolving the internal structure of these dynamical diquark correlations proves essential for the mechanical stability of the proton. At a scale of $Q^{2} = 4$ GeV $^{2}$ we find that the up and down quarks carry an intrinsic spin and orbital angular momentum of $S_{u} = 0.534$ , $S_{d} = - 0.214$ , $L_{u} = - 0.189$ , and $L_{d} = 0.210$ , whereas the gluons have a total angular momentum of $J_{g} = 0.151$ . The down quark is therefore found to carry almost no total angular momentum due to cancellations between spin and orbital contributions. Comparisons are made between these spin decomposition results and lattice QCD calculations.
nucl-thhep-phPRC(2021)·24 citations
02
alpha+28Si and 16O+16O molecular states, and their isoscalar monopole strengths
M. Kimura · Y. Taniguchi
The properties of the alpha+28Si and 16O+16O molecular states which are embedded in the excited states of 32S and can have an impact on the stellar reactions are investigated using the antisymmetrized molecular dynamics. From the analysis of the cluster spectroscopic factors, the candidates of alpha+28Si and 16O+16O molecular states are identified close to and above the cluster threshold energies. The calculated properties of the alpha+28Si molecular states are consistent with those reported by the alpha+28Siresonant scattering experiments. On the other hand, the 16O+16O molecular state, which is predicted to be identical to the superdeformation of 32S, is inconsistent with the assignment proposed by an alpha inelastic scattering experiment. Our calculation suggests that the monopole transition from the ground state to the 16O+16O molecular state is rather weak and is not strongly excited by the alpha inelastic scattering.
nucl-thnucl-exPRC(2020)·3 citations
03
Neutron stars with large quark cores
Márcio Ferreira🇵🇹 · Renan Câmara Pereira🇵🇹 · Constança Providência🇵🇹
We describe charge-neutral neutron star matter in $β -$ equilibrium using hybrid equations of state, where a first-order phase transition from hadronic to quark matter is realized. The hadronic matter is described in a model-independent way by a Taylor expansion around saturation density $n_{0}$ , while the three-flavor NJL model is used for the quark matter. Exploring the present uncertainty on the empirical parameters of nuclear matter and the parameter space of the NJL model, we construct two datasets of thermodynamically consistent and causal hybrid EoSs, compatible with astrophysical observations. We conclude that, to sustain a considerable quark core size, the intensity of the phase transition from hadron to quark matter cannot be strong, having a energy density gap below $200$ MeV/fm $^{3}$ , and must occur at baryon densities not above four times the saturation density. A non zero but not too strong quark vector-isoscalar term and a weak vector isovector quark term are required. Large quark cores carrying almost half of the star mass are possible inside neutron stars with a maximum mass $\approx 2.2 M_{⊙}$ . To get a considerable number of hybrid EoS predicting quark matter already inside neutron stars with a mass $\sim 1.4 M_{⊙}$ , we require that the onset of quarks occurs in the range $1.3 n_{0}$ and $2.5 n_{0}$ . Neutron stars with large quark cores corresponding to more than one fourth of the total star mass, are possible if the energy density gap and the pressure at transition are below 100 MeV/fm $^{3}$ . However, under these constraints, the maximum neutron star mass is limited to $≲ 2.06 M_{⊙}$ . No strong signatures from quark matter were found on the radius and the tidal deformability for neutron star masses below $1.8 M_{⊙}$ .
nucl-thastro-ph.HEhep-phPRD(2020)·53 citations
04
Anomalous Internal Pair Creation
Péter Kálmán🇭🇺 · Tamás Keszthelyi🇭🇺
In recent electron-positron angular correlation measurements the observed significant enhancements relative to the internal pair creation at large angles was interpreted as indication of the creation of $J^{π} = 1^{+}$ boson called X17 particle. In this paper it is brought up that such enhancements can be generated by higher order processes. It is found that nuclear transitions, the transition energy of which is significantly lower than the whole transition energy, can cause peaked angle dependence in electron-positron angular correlation.
nucl-thEPJA(2020)·5 citations

Affiliations

first authorsco-authorsvia INSPIRE

Quark spin and orbital angular momentum from proton GPDs

alpha+28Si and 16O+16O molecular states, and their isoscalar monopole strengths

Neutron stars with large quark cores

Anomalous Internal Pair Creation

Affiliations