Nuclear Theory·nucl-th

Wednesday·February 28, 2018

8 papers—4 primary·4 cross-listed

01
Pion and kaon valence-quark quasiparton distributions
Shu-Sheng Xu🇨🇳 · Lei Chang🇨🇳 · Craig D. Roberts🇺🇸 · Hong-Shi Zong🇨🇳
Algebraic Ansaetze for the Poincaré-covariant Bethe-Salpeter wave functions of the pion and kaon are used to calculate their light-front wave functions (LFWFs), parton distribution amplitudes (PDAs), quasi-PDAs (qPDAs), valence parton distribution functions (PDFs), and quasi-PDFs (qPDFs). The LFWFs are broad, concave functions; and the scale of flavour-symmetry violation in the kaon is roughly 15%, being set by the ratio of emergent masses in the $s$ -and $u$ -quark sectors. qPDAs computed with longitudinal momentum $P_{z} = 1.75$ GeV provide a semiquantitatively accurate representation of the objective PDA; but even with $P_{z} = 3$ GeV, they cannot provide information about this amplitude's endpoint behaviour. On the valence-quark domain, similar outcomes characterise qPDFs. In this connection, however, the ratio of kaon-to-pion $u$ -quark qPDFs is found to provide a good approximation to the true PDF ratio on $0.3 ≲ x ≲ 0.8$ , suggesting that with existing resources computations of ratios of quasi-parton-distributions can yield results that support empirical comparison.
nucl-thhep-lathep-phnucl-exPRD(2018)·89 citations
02
Elliptic flow from Coulomb interaction and low density elastic scattering
Yuliang Sun🇨🇳 · Qingfeng Li🇨🇳 · Fuqiang Wang🇨🇳
In high energy heavy ion collisions and interacting cold atom systems, large elliptic flow anisotropies have been observed. For the large opacity ( $ρ σ L \sim 1 0^{3}$ ) of the latter hydrodynamics is a natural consequence, but for the small opacity ( $ρ σ L \sim 1$ ) of the former hydrodynamic description is questionable. To shed light onto the situation, we simulate the expansion of a low density Argon ion (or atom) system, initially trapped in an elliptical region, under the Coulomb interaction (or elastic scattering). Significant elliptic anisotropy is found in both cases, and the anisotropy depends on the initial spatial eccentricity and the density of the system. The results may provide insights into the physics of anisotropic flow in high energy heavy ion collisions and its role in the study of quantum chromodynamics.
nucl-thnucl-exPRC(2018)·0 citations
03
Hot and Dense Homogeneous Nucleonic Matter Constrained by Observations, Experiment, and Theory
Xingfu Du (1) · Andrew W. Steiner (1,2) · Jeremy W. Holt (3) ((1) Tennessee U., (2) Oak Ridge Natl. Lab., (3) Texas A-M, Cyclotron Inst. & Texas A-M)
We construct a new class of phenomenological equations of state for homogeneous matter for use in simulations of hot and dense matter in local thermodynamic equilibrium. We construct a functional form which respects experimental, observational and theoretical constraints on the nature of matter in various density and temperature regimes. Our equation of state matches (i) the virial coefficients expected from nucleon-nucleon scattering phase shifts, (ii) experimental measurements of nuclear masses and charge radii, (iii) observations of neutron star radii, (iv) theory results on the equation of state of neutron matter near the saturation density, and (v) theory results on the evolution of the EOS at finite temperatures near the saturation density. Our analytical model allows one to compute the variation in the thermodynamic quantities based on the uncertainties in the nature of the nucleon-nucleon interaction. Finally, we perform a correction to ensure the equation of state is causal at all densities, temperatures, and electron fractions.
nucl-thastro-ph.HEastro-ph.SRPRC(2019)·29 citations
04
Spin-Isospin Properties of $N = Z$ Odd-Odd Nuclei from a Core+ $p n$ Three-Body Model including Core Excitations
Futoshi Minato · Yusuke Tanimura
For $N = Z$ odd-odd nuclei, a three-body model assuming two valence particles and an inert core can provide an understanding of pairing correlations in the ground state and spin-isospin excitations. However, since residual core-nucleon interactions can have a significant impact on these quantities, the inclusion of core excitations in the model is essential for useful calculation to be performed. The effect of core excitations must be included in order to gain a detailed understanding of both the ground state and spin-isospin properties of these systems. To this end, we include the vibrational excitation of the core nucleus in our model. We solve the three-body core-nucleon-nucleon problem including core vibrational states to obtain the nuclear ground state as well as spin-isospin excitations. The spin-isospin excitations are examined from the point of view of SU(4) multiplets. By including the effect of core excitation, several experimental quantities of $N = Z$ odd-odd nuclei are better described, and the root mean square distances between proton and neutron and that between the center of mass of proton and neutron and core nucleus increase. Large $B$ ( $M 1$ ) and $B$ (GT) observed for $^{18}$ F and $^{40}$ Ca were explained in terms of the SU(4) symmetry. The core nucleus is meaningfully broken by the residual core-nucleon interactions, and various quantities concerning spin-isospin excitations as well as the ground state become consistent with experimental data. Including the core excitation in the three-body model is thus important for a more detailed understanding of nuclear structure.
nucl-thnucl-exEPJA(2020)·3 citations
05
QCD Shear Viscosity at (almost) NLO
Jacopo Ghiglieri🇨🇭 · Guy D. Moore🇩🇪 · Derek Teaney🇺🇸
We compute the shear viscosity of QCD with matter, including almost all next-to-leading order corrections -- that is, corrections suppressed by one power of $g$ relative to leading order. We argue that the still missing terms are small. The next-to-leading order corrections are large and bring $η / s$ down by more than a factor of 3 at physically relevant couplings. The perturbative expansion is problematic even at $T ≃ 100$ GeV. The largest next-to-leading order correction to $η / s$ arises from modifications to the qhat parameter, which determines the rate of transverse momentum diffusion. We also explore quark number diffusion, and shear viscosity in pure-glue QCD and in QED.
↳ hep-phnucl-thJHEP(2018)·121 citations
06
Inclusive prompt photon production in electron-nucleus scattering at small x
Kaushik Roy🇺🇸 · Raju Venugopalan🇺🇸
We compute the differential cross-section for inclusive prompt photon production in deeply inelastic scattering (DIS) of electrons on nuclei at small $x$ in the framework of the Color Glass Condensate (CGC) effective theory. The leading order (LO) computation in this framework resums leading logarithms in $x$ as well as power corrections to all orders in $Q_{s, A}^{2} / Q^{2}$ , where $Q_{s, A} (x)$ is the nuclear saturation scale. This LO result is proportional to universal dipole and quadrupole Wilson line correlators in the nucleus. In the soft photon limit, the Low-Burnett-Kroll theorem allows us to recover existing results on inclusive DIS dijet production. The $k_{⊥}$ and collinearly factorized expressions for prompt photon production in DIS are also recovered in a leading twist approximation to our result. In the latter case, our result corresponds to the dominant next-to-leading order (NLO) perturbative QCD contribution at small $x$ . We next discuss the computation of the NLO corrections to inclusive prompt photon production in the CGC framework. In particular, we emphasize the advantages for higher order computations in inclusive photon production, and for fully inclusive DIS, arising from the simple momentum space structure of the dressed quark and gluon "shock wave" propagators in the "wrong" light cone gauge $A^{-} = 0$ for a nucleus moving with $P_{N}^{+} \to \infty$ .
↳ hep-phnucl-exnucl-thJHEP(2018)·42 citations
07
The impact of domain walls on the chiral magnetic effect in hot QCD matter
Kirill Tuchin🇺🇸
The Chiral Magnetic Effect (CME) -- the separation of positive and negative electric charges along the direction of the external magnetic field in quark-gluon plasma and other topologically non-trivial media -- is a consequence of the coupling of electrodynamics to the topological gluon field fluctuations that form metastable $C P$ -odd domains. In phenomenological models it is usually assumed that the domains are uniform and the influence of the domain walls on the electric current flow is not essential. This paper challenges the latter assumption. A simple model consisting of a uniform spherical domain in a uniform time-dependent magnetic field is introduced and analytically solved. It is shown that (i) no electric current flows into or out of the domain, (ii) the charge separation current, viz. the total electric current flowing inside the domain in the external field direction, is a dissipative Ohm current, (iii) the CME effect can be produced either by the anomalous current or by the boundary conditions on the domain wall and (iv) the charge separation current oscillates in plasma long after the external field decays. These properties are qualitatively different from the CME in an infinite medium.
↳ hep-phnucl-thPRC(2018)·8 citations
08
Re-examining the transition into the N=20 island of inversion: structure of $^{30}$ Mg
B. Fernández-Domínguez🇬🇧 · B. Pietras🇬🇧 · W.N. Catford🇬🇧 · N.A. Orr🇫🇷 · M. Petri🇬🇧 · M. Chartier🇬🇧 · S. Paschalis🇬🇧 · N. Patterson🇬🇧 · J .S. Thomas🇬🇧 · M. Caamaño🇪🇸 · T. Otsuka🇯🇵 · A. Poves🇪🇸 and 25 other authors
Intermediate energy single-neutron removal from $^{31}$ Mg has been employed to investigate the transition into the N=20 island of inversion. Levels up to 5~MeV excitation energy in $^{30}$ Mg were populated and spin-parity assignments were inferred from the corresponding longitudinal momentum distributions and $γ$ -ray decay scheme. Comparison with eikonal-model calculations also permitted spectroscopic factors to be deduced. Surprisingly, the 0 $_{2}^{+}$ level in $^{30}$ Mg was found to have a strength much weaker than expected in the conventional picture of a predominantly $2 p - 2 h$ intruder configuration having a large overlap with the deformed $^{31}$ Mg ground state. In addition, negative parity levels were identified for the first time in $^{30}$ Mg, one of which is located at low excitation energy. The results are discussed in the light of shell-model calculations employing two newly developed approaches with markedly different descriptions of the structure of $^{30}$ Mg. It is concluded that the cross-shell effects in the region of the island of inversion at Z=12 are considerably more complex than previously thought and that $n p - nh$ configurations play a major role in the structure of $^{30}$ Mg.
↳ nucl-exnucl-thPLB(2018)·18 citations

Affiliations

first authorsco-authorsvia INSPIRE