Nuclear Theory·nucl-th

Friday·May 10, 2019

7 papers—1 primary·6 cross-listed

02
Chiral symmetry breaking, entanglement, and the nucleon spin decomposition
Silas R. Beane🇺🇸 · Peter Ehlers🇺🇸
The nucleon is naturally viewed as a bipartite system of valence spin -- defined by its non-vanishing chiral charge -- and non-valence or sea spin. The sea spin can be traced over to give a reduced density matrix, and it is shown that the resulting entanglement entropy acts as an order parameter of chiral symmetry breaking in the nucleon. In the large- $N_{c}$ limit, the entanglement entropy vanishes and the valence spin accounts for all of the nucleon spin, while in the limit of maximal entanglement entropy, the nucleon loses memory of the valence spin and consequently has spin dominated by the sea. The nucleon state vector in the chiral basis, fit to low-energy data, gives a valence spin content consistent with experiment and lattice QCD determinations, and has large entanglement entropy.
↳ hep-phhep-latnucl-thMod.Phys.Lett.A(2019)·34 citations
03
Where we stand on structure dependence of ISGMR in the Zr-Mo region: Implications on K_\infty
K. B. Howard · U. Garg · Y. K. Gupta · M. N. Harakeh
Isoscalar giant resonances, being the archetypal forms of collective nuclear behavior, have been studied extensively for decades with the goal of constraining bulk nuclear properties of the equation of state, as well as for modeling dynamical behaviors within stellar environments. An important such mode is the isoscalar electric giant monopole resonance (ISGMR) that can be understood as a radially symmetric density vibration within the saturated nuclear volume. The field has a few key open questions, which have been proposed and remain unresolved. One of the more provocative questions is the extra high-energy strength in the $A \approx 90$ region, which manifested in large percentages of the $E 0$ sum rule in $^{92}$ Zr and $^{92}$ Mo above the main ISGMR peak. The purpose of this article is to introduce these questions within the context of experimental investigations into the phenomena in the zirconium and molybdenum isotopic chains, and to address, via a discussion of previously published and preliminary results, the implications of recent experimental efforts on extraction of the nuclear incompressibility from this data.
↳ nucl-exnucl-thEPJA(2019)·10 citations
04
A still unsettled issue in the nucleon spin decomposition problem : On the role of surface terms and gluon topology
Masashi Wakamatsu🇯🇵
In almost all the past analyses of the decomposition of the nucleon spin into its constituents, surface terms are simply assumed to vanish and not to affect the integrated sum rule of the nucleon spin. However, several authors claim that neglect of surface terms is not necessarily justified, especially owing to possible nontrivial topological configuration of the gluon field in the QCD vacuum. There also exist some arguments indicating that the nontrivial gluon topology would bring about a delta-function type singularity at zero Bjorken variable into the longitudinally polarized gluon distribution function, thereby invalidating a naive partonic sum rule for the total nucleon spin. In the present paper, we carefully examine the role of surface terms in the nucleon spin decomposition problem. We shall argue that surface terms do not prevent us from obtaining a physically meaningful decomposition of the nucleon spin. In particular, we demonstrate that nontrivial topology of the gluon field would not bring about a delta-function type singularity into the longitudinally polarized gluon distribution functions. We also make some critical comments on the recent analyses of the role of surface terms in the density level decomposition of the total nucleon angular momentum as well as that of the total photon angular momentum.
↳ hep-phnucl-thEPJA(2019)·7 citations
05
Critical end points in (2+1)-flavor QCD with imaginary chemical potential
Jishnu Goswami🇩🇪 · Frithjof Karsch🇩🇪 · Anirban Lahiri🇩🇪 · Marius Neumann🇩🇪 · Christian Schmidt🇩🇪
We present here the results from an ongoing determination of the critical quark mass in simulations of (2+1)-flavor QCD with an imaginary chemical potential. Studies with unimproved actions found the existence of a critical quark mass value at which the crossover transition ends on a second order phase transition and becomes first order for smaller values of the quark mass for the case of both vanishing and imaginary chemical potential. We use the Highly Improved Staggered Quark (HISQ) action and perform calculations in the Roberge-Weiss (RW) plane, where the value of the critical mass is expected to be largest. The lowest quark mass value used in our simulation corresponds to the pion mass $m_{π}$ , down to $40$ MeV. Contrary to calculations performed with unimproved actions we find no evidence for the occurrence of first order transitions at the smallest quark mass values explored so far. Moreover we also show that the chiral observables are sensitive to the RW transition. Our results also indicate that the RW transition and chiral transition could coincide in the chiral limit.
↳ hep-lathep-phnucl-thPoS(2019)·10 citations
06
Constraint on the maximum mass of neutron stars using GW170817 event
Masaru Shibata🇩🇪 · Enping Zhou🇩🇪 · Kenta Kiuchi🇩🇪 · Sho Fujibayashi🇩🇪
We revisit the constraint on the maximum mass of cold spherical neutron stars coming from the observational results of GW170817. We develop a new framework for the analysis by employing both energy and angular momentum conservation laws as well as solid results of latest numerical-relativity simulations and of neutron stars in equilibrium. The new analysis shows that the maximum mass of cold spherical neutron stars can be only weakly constrained as $M_{max} \alt 2.3 M_{⊙}$ . Our present result illustrates that the merger remnant neutron star at the onset of collapse to a black hole is not necessarily rapidly rotating and shows that we have to take into account the angular momentum conservation law to impose the constraint on the maximum mass of neutron stars.
↳ astro-ph.HEgr-qcnucl-thPRD(2019)·341 citations
07
Diffractive dijet production in impact parameter dependent saturation models
Farid Salazar🇺🇸 · Bjoern Schenke🇺🇸
We study coherent diffractive dijet production in electron-hadron and electron-nucleus collisions within the dipole picture. We provide semi-analytic results for the differential cross section and elliptic anisotropy in the angle between dijet transverse momentum and hadron recoil momentum. We demonstrate the direct relation between angular moments of the dipole amplitude in coordinate space and angular moments of the diffractive dijet cross sections. To perform explicit calculations we employ two different saturation models, extended to include the target geometry. In the limit of large photon virtuality or quark masses, we find fully analytic results that allow direct insight into how the differential cross section and elliptic anisotropy depend on the saturation scale, target geometry, and kinematic variables. We further provide numerical results for more general kinematics in collisions at a future electron-ion collider, and study the effects of approaching the saturated regime on diffractive dijet observables.
↳ hep-phnucl-thPRD(2019)·68 citations

Affiliations

first authorsco-authorsvia INSPIRE

Chiral symmetry breaking, entanglement, and the nucleon spin decomposition

Where we stand on structure dependence of ISGMR in the Zr-Mo region: Implications on K_\infty

A still unsettled issue in the nucleon spin decomposition problem : On the role of surface terms and gluon topology

Critical end points in (2+1)-flavor QCD with imaginary chemical potential

Constraint on the maximum mass of neutron stars using GW170817 event

Diffractive dijet production in impact parameter dependent saturation models

Affiliations