Nuclear Theory·nucl-th

Thursday·July 12, 2018

11 papers—5 primary·6 cross-listed

01
[Submitted on 11 Jul 2018]
Better insight into the Strutinsky method (published version)
B. Mohammed-Azizi🇩🇿
Strutinsky's method is reviewed through a new understanding. This method depends on two free parameters: The smoothing parameter and the order of the curvature correction. It turns out that this method is nothing but a compromise between two fundamental conditions which are the so-called asymptotic limit which comes from the so-called remainder which imposes a small as possible smoothing parameter and the smoothing condition which forces that parameter to be, at least, slightly larger than the inter shell spacing. In this paper, to find the best value of the smoothing parameter, a new criterion is proposed instead of the plateau condition . This new criterion is much more clear and free from ambiguities of the usual plateau condition. It is also found, that the second free parameter, i.e., the order of the curvature correction, plays an accessory role since, it is connected intimately to the smoothing parameter, when the smoothing is realized. This paper provides a new and definitive insight into Strutinsky's method and its relationship with semi-classical methods.
Comments:
16 pages, 4 Figures, 3 Tables
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1807.04006 [pdf]
PRC(2019)·4 citations
02
[Submitted on 11 Jul 2018]
Consolidating the concept of low-energy magnetic dipole decay radiation
J. E. Midtbø · A. C. Larsen · T. Renstrøm · F. L. Bello Garrote · E. Lima
We have made a thorough study of the low-energy behaviour of the $γ$ -ray strength function within the framework of the shell model. We have performed large-scale calculations spanning isotopic and isotonic chains over several mass regions, with the purpose of studying the systematic behavior of the low-energy enhancement (LEE) for $M 1$ transitions. There are clear trends in the calculations: From being all but absent in the lowest mass region, the LEE becomes steeper and more pronounced as the mass number increases, and for a given mass region it further increases towards shell closures. Moreover, the LEE is found to be steeper in regions near doubly-magic nuclei where proton particles couple to neutron holes. These trends enable us to consolidate several previous works on the LEE into a single, consistent concept. We compare the inferred trends to the available experimental data from the Oslo method, and find suppport for the systematic behaviour. Lastly we have compared the calculations to strength functions compiled from discrete, experimental lifetimes, and find excellent agreement; the discrete data are consistent with a LEE, and indicate that the slope varies as function of mass number.
Comments:
11 pages, 13 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1807.04036 [pdf]
PRC(2018)·43 citations
03
[Submitted on 11 Jul 2018]
Beyond--mean--field effective masses in the nuclear Fermi liquid from axial breathing modes
M. Grasso🇫🇷 · D. Gambacurta🇷🇴 · O. Vasseur🇫🇷
Axial breathing modes are studied within the nuclear energy--density--functional theory to discuss the modification of the nucleon effective mass produced beyond the mean--field approximation. This analysis is peformed with the subtracted second random--phase--approximation (SSRPA) model applied to two nuclei, $^{48}$ Ca and $^{90}$ Zr. Analyzing the centroid energies of axial breathing modes obtained with the mean--field--based random--phase approximation and with the beyond--mean--field SSRPA model, we estimate the modification (enhancement) of the effective mass which is induced beyond the mean field. This is done by employing a relation, obtained with the Landau's Fermi liquid theory, between the excitation frequency of axial modes to $m / m^{*}$ , where $m$ ( $m^{*}$ ) is the bare (effective) mass. Such an enhancement of the effective mass is discussed in connection with the renormalization of single--particle excitation energies generated by the energy--dependent SSRPA self-energy correction. We find that the effective beyond--mean--field compression of the single--particle spectrum produced by the self--energy correction is coherent with the increase of the effective mass estimated from the analysis of axial breathing modes.
Comments:
5 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1807.04039 [pdf]
PRC(2018)·12 citations
04
[Submitted on 11 Jul 2018]
Transport phenomena with chiral fermions in strong magnetic fields
Koichi Hattori🇨🇳
I discuss the electrical conductivity, bulk viscosity, and heavy-quark diffusion coefficient in strong magnetic fields putting emphasis on consequences of the chirality conservation on the perturbative relaxation dynamics.
Comments:
Prepared for the proceedings of Quark Matter 2018 in Venice
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
1807.04150 [pdf]
NPA(2019)·2 citations
05
[Submitted on 11 Jul 2018]
Viscous hydrodynamics for nonconformal anisotropic fluids
Mike McNelis🇺🇸 · Dennis Bazow🇺🇸 · Ulrich Heinz🇺🇸
A new formulation of (3+1)-dimensional anisotropic hydrodynamics is presented that accounts nonperturbatively for the large longitudinal-transverse pressure anisotropy and bulk viscous pressure in heavy-ion collisions. The initialization of the anisotropic hydrodynamic stage is discussed, and a comparison to standard viscous hydrodynamics for (0+1)- dimensional Bjorken expansion is presented.
Comments:
4 pages, 3 figures, Quark Matter 2018
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1807.04223 [pdf]
NPA(2019)·1 citation
06
[Submitted on 10 Jul 2018] (cross-list from hep-ph)
Constraining unintegrated gluon distributions from inclusive photon production in proton-proton collisions at the LHC
Sanjin Benić🇯🇵 · Kenji Fukushima🇯🇵 · Oscar Garcia-Montero🇩🇪 · Raju Venugopalan🇺🇸
We compute the leading order (LO) $q g \to q γ$ and next-to-leading order (NLO) $g g \to q q ˉ γ$ contributions to inclusive photon production in proton-proton (p+p) collisions at the LHC. These channels provide the dominant contribution at LO and NLO for photon transverse momenta $k_{γ ⊥}$ corresponding to momentum fractions of $x \leq 0.01$ in the colliding protons. Our computations, performed in the dilute-dense framework of the Color Glass Condensate effective field theory (CGC EFT), show that the NLO contribution dominates at small- $x$ because it is sensitive to $k_{⊥}$ -dependent unintegrated gluon distributions in both of the protons. We predict a maximal $10%$ modification of the cross section at low $k_{γ ⊥}$ as a direct consequence of the violation of $k_{⊥}$ -factorization. The coherence effects responsible for this modification are enhanced in nuclei and can be identified from inclusive photon measurements in proton-nucleus collisions. We provide numerical results for the isolated inclusive photon cross section for $k_{γ ⊥} \leq 20$ GeV in p+p collisions that can be tested in the future at the LHC.
Comments:
9 pages, 5 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1807.03806 [pdf]
PLB(2019)·41 citations
07
[Submitted on 11 Jul 2018] (cross-list from cond-mat.quant-gas)
The pseudogap regime in the unitary Fermi gas
S. Jensen🇺🇸 · C. N. Gilbreth🇺🇸 · Y. Alhassid🇺🇸
We discuss the pseudogap regime in the cold atomic unitary Fermi gas, with a particular emphasis on the auxiliary-field quantum Monte Carlo (AFMC) approach. We discuss possible signatures of the pseudogap, review experimental results, and survey analytic and quantum Monte Carlo techniques before focusing on AFMC calculations in the canonical ensemble. For the latter method, we discuss results for the heat capacity, energy-staggering pairing gap, spin susceptibility, and compare to experiment and other theoretical methods.
Comments:
19 pages, 14 figures, review in a special issue of the European Journal of Physics: Special Topics, dedicated to the conference on Frontiers of Quantum and Mesoscopic Thermodynamics (FQMT'17)
Subjects:
Quantum Gases (cond-mat.quant-gas); Superconductivity (cond-mat.supr-con); Nuclear Theory (nucl-th)
arXiv:
1807.03913 [pdf]
Eur.Phys.J.ST(2019)·17 citations
08
[Submitted on 11 Jul 2018] (cross-list from hep-ph)
Simplified Bethe-Salpeter Description of Basic Pseudoscalar-Meson Features
Wolfgang Lucha🇦🇹
We assess a description of pseudoscalar mesons as pseudo-Goldstone bosons by its compatibility with some Gell-Mann-Oakes-Renner-type relation.
Comments:
5 pages, 1 figure, contributed to "QCD@Work 2018 - International Workshop on Quantum Chromodynamics: Theory and Experiment" (25 - 28 June 2018, Matera, Italy)
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1807.04066 [pdf]
EPJ Web Conf.(2018)·0 citations
09
[Submitted on 11 Jul 2018] (cross-list from hep-ph)
Energy and system size dependence of subnucleonic fluctuations
Heikki Mäntysaari🇫🇮 · Björn Schenke🇺🇸
The energy evolution of the fluctuating proton structure is studied by solving the JIMWLK renormalization group equation. The initial condition at moderate $x$ is obtained by fitting the charm reduced cross section data from HERA, requiring that the proton size remains compatible with the diffractive vector meson production measurements. Additionally, we show that the nucleon shape fluctuations are visible in exclusive vector meson production off nuclei.
Comments:
4 pages, 4 figures. Quark Matter 2018 proceedings
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1807.04088 [pdf]
NPA(2019)·0 citations
10
[Submitted on 11 Jul 2018] (cross-list from hep-ph)
NNNLO pressure of cold quark matter: leading logarithm
Tyler Gorda🇫🇮 · Aleksi Kurkela🇨🇭 · Paul Romatschke🇺🇸 · Saga Säppi🇫🇮 · Aleksi Vuorinen🇫🇮
At high baryon chemical potential $μ_{B}$ , the equation of state of QCD allows a weak-coupling expansion in the QCD coupling $α_{s}$ . The result is currently known up to and including the full next-to-next-to-leading order (NNLO) $α_{s}^{2}$ . Starting at this order, the computations are complicated by the modification of particle propagation in a dense medium, which necessitates non-perturbative treatment of the scale $α_{s}^{1/2} μ_{B}$ . In this work, we apply a Hard-Thermal-Loop scheme for capturing the contributions of this scale to the weak-coupling expansion, and use it to determine the leading-logarithm contribution to NNNLO: $α_{s}^{3} ln^{2} α_{s}$ . This result is the first improvement to the equation of state of massless cold quark matter in 40 years. The new term is negligibly small, and thus significantly increases our confidence in the applicability of the weak-coupling expansion.
Comments:
8 pages with appendix, 2 figures; v3: Added footnote to point out minus sign error in final result
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Astrophysical Phenomena (astro-ph.HE); Nuclear Theory (nucl-th)
arXiv:
1807.04120 [pdf]
PRL(2018)·159 citations
11
[Submitted on 11 Jul 2018] (cross-list from hep-lat)
Lattice Improvement in Lattice Effective Field Theory
Nico Klein🇩🇪 · Dean Lee🇺🇸 · Ulf-G. Meißner🇩🇪
Lattice calculations using the framework of effective field theory have been applied to a wide range few-body and many-body systems. One of the challenges of these calculations is to remove systematic errors arising from the nonzero lattice spacing. Fortunately, the lattice improvement program pioneered by Symanzik provides a formalism for doing this. While lattice improvement has already been utilized in lattice effective field theory calculations, the effectiveness of the improvement program has not been systematically benchmarked. In this work we use lattice improvement to remove lattice errors for a one-dimensional system of bosons with zero-range interactions. We construct the improved lattice action up to next-to-next-to-leading order and verify that the remaining errors scale as the fourth power of the lattice spacing for observables involving as many as five particles. Our results provide a guide for increasing the accuracy of future calculations in lattice effective field theory with improved lattice actions.
Comments:
10 pages, 8 figures
Subjects:
High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th); physics.atm-clus (physics.atm-clus)
arXiv:
1807.04234 [pdf]
EPJA(2018)·13 citations

Affiliations

first authorsco-authorsvia INSPIRE