Nuclear Theory·nucl-th

Wednesday·February 28, 2018

8 papers—4 primary·4 cross-listed

05
[Submitted on 26 Feb 2018] (cross-list from hep-ph)
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.
Comments:
36 pages plus appendices, 11 figures. The main results are summarized in the introduction (Fig. 1)
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1802.09535 [pdf]
JHEP(2018)·121 citations
06
[Submitted on 26 Feb 2018] (cross-list from hep-ph)
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 $P_{N}^{+} \to \infty$ .
Comments:
33 pages, 19 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1802.09550 [pdf]
JHEP(2018)·42 citations
07
[Submitted on 26 Feb 2018] (cross-list from hep-ph)
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.
Comments:
16 pages, 6 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1802.09629 [pdf]
PRC(2018)·8 citations
08
[Submitted on 27 Feb 2018] (cross-list from nucl-ex)
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.
Comments:
Physics Letters B, Volume 779, 10 April 2018, Pages 124-129
Subjects:
Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1802.09986 [pdf]
PLB(2018)·18 citations

Affiliations

first authorsco-authorsvia INSPIRE

QCD Shear Viscosity at (almost) NLO

Inclusive prompt photon production in electron-nucleus scattering at small x

The impact of domain walls on the chiral magnetic effect in hot QCD matter

Re-examining the transition into the N=20 island of inversion: structure of 30Mg

Affiliations

Re-examining the transition into the N=20 island of inversion: structure of $^{30}$ Mg