Nuclear Theory·nucl-th

Monday·May 4, 2020

9 papers—5 primary·4 cross-listed

01
[Submitted on 30 Apr 2020]
The Lifshitz Regime and its Experimental Signals
R. D. Pisarski🇺🇸 · F. Rennecke🇺🇸 · A. Tsvelik🇺🇸 · S. Valgushev🇺🇸
We discuss the possibility of a Lifshitz regime, where the dispersion relation for Goldstone bosons and related fields has a minimum at nonzero momenta. Studies with the Functional Renormalization Group suggest that this occurs over a wide region in the plane of temperature and baryon chemical potential. Conversely, the FRG finds that the region in which fluctuations from a critical endpoint are significant is rather small. We suggest that this is due generically to the narrowness of the tricritical region in the chiral limit. Even if particles are produced in thermal equilibrium, a dispersion relation which is non-monotonic in momenta produces what appears to be non-thermal behavior.
Comments:
Submitted to the proceedings of Quark Matter 2019, Nucl. Phys. A
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
2005.00045 [pdf]
NPA(2021)·25 citations
02
[Submitted on 30 Apr 2020]
Ab initio Leading Order Effective Potentials for Elastic Nucleon-Nucleus Scattering
M. Burrows · R. B. Baker · Ch. Elster · S. P. Weppner · K.D. Launey · P. Maris · G. Popa
Background: Calculating microscopic effective interactions (optical potentials) for elastic nucleon-nucleus scattering has already in the past led to a large body of work. For first-order calculations a nucleon-nucleon (\textit{NN}) interaction and a one-body density of the nucleus were taken as input to rigorous calculations of microscopic full-folding calculations. Purpose: Based on the spectator expansion of the multiple scattering series we employ a chiral next-to-next-to-leading order (NNLO) nucleon-nucleon interaction on the same footing in the structure as well as in the reaction calculation to obtain an in leading-order consistent effective potential for nucleon-nucleus elastic scattering, which includes the spin of the struck target nucleon. Methods: The first order effective folding potential is computed by first deriving a nonlocal scalar density as well as a spin-projected momentum distribution. Those are then integrated with the off-shell Wolfenstein amplitudes $A$ , $C$ , and $M$ . The resulting nonlocal potential serves as input to a momentum-space Lippmann-Schwinger equation, whose solutions are summed to obtain the nucleon-nucleus scattering observables. Results: We calculate elastic scattering observables for $^{4}$ He, $^{6}$ He, $^{8}$ He, $^{12}$ C, and $^{16}$ O in the energy regime between 100 and 200 MeV projectile kinetic energy, and compare to available data. We also explore the extension down to about 70 MeV, and study the effect of ignoring the spin of the struck nucleon in the nucleus. Conclusions: In our calculations we contrast elastic scattering off closed-shell and open-shell nuclei. We find that for closed-shell nuclei the approximation of ignoring the spin of the struck target nucleon is excellent. We only see effects of the spin of the struck target nucleon when considering $^{6}$ He and $^{8}$ He, which are nuclei with a $N / Z$ ratio larger than 1.
Comments:
13 pages, 13 figures
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
2005.00111 [pdf]
PRC(2020)·38 citations
03
[Submitted on 30 Apr 2020]
Novel ansatz for charge radii in density functional theories
Rong An · Li-Sheng Geng · Shi-Sheng Zhang
Charge radii are one of the most fundamental properties of atomic nuclei characterizing their charge distributions. Though the general trend as a function of the mass number is well described by the $A^{1/3}$ rule, some fine structures, such as the evolution along the calcium isotopic chain and the corresponding odd-even staggerings, are notoriously difficult to describe both in density functional theories and ab initio methods. In this letter, we propose a novel ansatz to describe the charge radii of calcium isotopes, by adding a correction term, proportional to the number of Cooper pairs, and determined by the BCS amplitudes and a single parameter, to the charge radii calculated in the relativistic mean field model with the pairing interaction treated with the BCS method. The new ansatz yields results consistent with data not only for calcium isotopes, but also for ten other isotopic chains, including oxygen, neon, magnesium, chromium, nickel, germanium, zirconium, cadmium, tin, and lead. It is remarkable that this ansatz with a single parameter can describe nuclear charge radii throughout the periodic table, particularly the odd-even staggerings and parabolic behavior. We hope that the present study can stimulate more discussions about its nature and relation with other effects proposed to explain the odd-even staggerings of charge radii.
Comments:
6 pages, 5 figures
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
2005.00141 [pdf]
PRC(2020)·38 citations
04
[Submitted on 1 May 2020]
Light nuclei production in relativistic heavy ion collisions from the AMPT model
Kai-Jia Sun🇺🇸 · Che Ming Ko🇺🇸
Based on an improved multiphase transport (AMPT) model, which gives a good description of proton production with a smooth quark matter to hadronic matter transition in relativistic heavy ion collisions, we study deuteron and triton production from the coalescence of nucleons at the kinetic freezeout of these collisions. For Au+Au collisions at center-of-mass energies $s_{NN}$ from 7.7 GeV to 200 GeV available at the Relativistic Heavy Ion Collider (RHIC), we find that the yield ratio $N_{t} N_{p} / N_{d}^{2}$ of proton, deuteron\com{,} and triton is essentially a constant as a function of collision energy. Our result confirms the expectation that without a first-order quark to hadronic matter phase transition in the produced matter or its approach to the critical point of the QCD matter, this yield ratio does not show any non-monotonic behavior in its collision energy dependence.
Comments:
5 pages, 2 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
2005.00182 [pdf]
PRC(2021)·46 citations
05
[Submitted on 1 May 2020]
Weak charge and weak radius of $^{12}$ C
Oleksandr Koshchii🇩🇪 · Jens Erler🇩🇪 · Mikhail Gorchtein🇩🇪 · Charles J. Horowitz🇺🇸 · Jorge Piekarewicz🇺🇸 · Xavier Roca-Maza🇮🇹 · Chien-Yeah Seng🇩🇪 · Hubert Spiesberger🇩🇪
We present a feasibility study of a simultaneous sub-percent extraction of the weak charge and the weak radius of the $^{12}$ C nucleus using parity-violating electron scattering, based on a largely model-independent assessment of the uncertainties. The corresponding measurement is considered to be carried out at the future MESA facility in Mainz with $E_{beam} = 155$ MeV. We find that a combination of a $0.3%$ precise measurement of the parity-violating asymmetry at forward angles with a $10%$ measurement at backward angles will allow to determine the weak charge and the weak radius of $^{12}$ C with $0.4%$ and $0.5%$ precision, respectively. These values could be improved to $0.3%$ and $0.2%$ for a $3%$ backward measurement. This experimental program will have impact on precision low-energy tests in the electroweak sector and nuclear structure.
Comments:
7 pages, 5 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
2005.00479 [pdf]
PRC(2020)·14 citations

Affiliations

first authorsco-authorsvia INSPIRE

The Lifshitz Regime and its Experimental Signals

Ab initio Leading Order Effective Potentials for Elastic Nucleon-Nucleus Scattering

Novel ansatz for charge radii in density functional theories

Light nuclei production in relativistic heavy ion collisions from the AMPT model

Weak charge and weak radius of 12C

Affiliations

Weak charge and weak radius of $^{12}$ C