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
05
How transverse thermal fluctuations disorder a condensate of chiral spirals into a quantum spin liquid
Robert D. Pisarski🇺🇸 · Alexei M. Tsvelik🇺🇸 · Semeon Valgushev🇺🇸
For a scalar theory with a global $O (N)$ symmetry, when $N = 2$ a spatially inhomogeneous condensate arises when the term in the Lagrangian with two spatial derivatives has a negative coefficient. If the condensate for such a chiral spiral includes only one mode, characterized by a momentum $k_{0} z^$ , then in perturbation theory at nonzero temperature the propagator for the static mode has a double pole when $k^{2} = k_{0}^{2}$ . We conjecture that since chiral spirals spontaneously break both global and spacetime symmetries, that such double poles are a universal property of their static transverse modes. Fluctuations from double poles generate linear infrared divergences in any number of spatial dimensions and disorder the condensate of chiral spirals, analogous to a type of quantum spin liquid. The characteristic feature of this region is that over large spatial distances the two point function is the usual exponential times an oscillatory function. We prove this at large $N$ and suggest this occurs for all $N > 2$ . Implications for four-fermion models and the phase diagram of QCD are discussed.
↳ hep-phcond-mat.stat-mechnucl-thPRD(2020)·53 citations
06
Recent developments in chiral and spin polarization effects in heavy-ion collisions
Jian-Hua Gao🇨🇳 · Guo-Liang Ma🇨🇳 · Shi Pu🇨🇳 · Qun Wang🇨🇳
We give a brief overview of recent theoretical and experimental results on the chiral magnetic effect and spin polarization effect in heavy-ion collisions. We present updated experimental results for the chiral magnetic effect and related phenomena. The time evolution of the magnetic fields in different models is discussed. The newly developed quantum kinetic theory for massive fermions is reviewed. We present theoretical and experimental results for the polarization of $Λ$ hyperons and the $ρ_{00}$ value of vector mesons.
↳ hep-phnucl-exnucl-thNucl.Sci.Tech.(2020)·132 citations
07
Analytic model studies of polarized baryon production
B. Boldizsár🇭🇺
We investigate known exact solutions of hydrodynamics and derive analytic formulas for the polarization of baryons produced at freeze-out. Such polarization (observed in high energy heavy-ion experiments) carries information on the time evolution of the quark-gluon plasma (sQGP), and our results give first analytic insight into the connection between this type of measurements and dynamical properties of the sQGP (e.g. vorticity). We present results for a rotating and acceleratingly expanding solution and also give hints on how to calculate the polarization using a rotating extension of the Buda--Lund parameterization.
↳ hep-phnucl-thPhys.Part.Nucl.(2020)·0 citations
08
Fluctuations of conserved charges, chiral spin symmetry and deconfinement in an SU(2)_color subgroup of SU(3)_color above T_c
L. Ya. Glozman🇦🇹
Above a pseudocritical temperature of chiral symmetry restoration T_c the energy and the pressure are very far from the quark-gluon-plasma limit (i.e. ideal gas of free quarks and gluons). At the same time very soon above T_c fluctuations of conserved charges behave as if quarks were free particles. Within the T_c - 3T_c interval a chiral spin symmetry emerges in QCD which is not consistent with free quarks and suggests that degrees of freedom are chirally symmetric quarks bound into the color-singlet objects by the chromoelectric field. Here we analyse temporal and spatial correlators in this interval and demonstrate that they indicate simultaneously the chiral spin symmetry as well as absence of the interquark interactions in channels constrained by a current conservation. The latter channels are responsible for both fluctuations of conserved charges and for dileptons. Assuming that a SU(2)_color subgroup of SU(3)_color is deconfined soon above T_c but confinement persits in SU(3)_color/SU(2)_color in the interval T_c - 3T_c we are able to reconcile all empirical facts listed above.
↳ hep-phhep-lathep-thnucl-thPRD(2020)·4 citations
09
Strong Coupling Lattice QCD in the Continuous Time Limit
Marc Klegrewe🇩🇪 · Wolfgang Unger🇩🇪
We present results for lattice QCD with staggered fermions in the limit of infinite gauge coupling, obtained from a worm-type Monte Carlo algorithm on a discrete spatial lattice but with continuous Euclidean time. This is obtained by sending both the anisotropy parameter $ξ = a_{σ} / a_{τ}$ and the number of time-slices $N_{τ}$ to infinity, keeping the ratio $a T = ξ / N τ$ fixed. The obvious gain is that no continuum extrapolation $N_{τ} \to \infty$ has to be carried out. Moreover, the algorithm is faster and the sign problem disappears. We derive the continuous time partition function and the corresponding Hamiltonian formulation. We compare our computations with those on discrete lattices and study both zero and finite temperature properties of lattice QCD in this regime.
↳ hep-latnucl-thPRD(2020)·15 citations

Affiliations

first authorsco-authorsvia INSPIRE