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
06
[Submitted on 30 Apr 2020] (cross-list from hep-th)
The Dielectric Skyrme model
C. Adam🇪🇸 · K. Oles🇵🇱 · A. Wereszczynski🇵🇱
We consider a version of the Skyrme model where both the kinetic term and the Skyrme term are multiplied by field-dependent coupling functions. For suitable choices, this "dielectric Skyrme model" has static solutions saturating the pertinent topological bound in the sector of baryon number (or topological charge) $B = \pm 1$ but not for higher $∣ B ∣$ . This implies that higher charge field configurations are unbound, and loosely bound higher skyrmions can be achieved by small deformations of this dielectric Skyrme model. We provide a simple and explicit example for this possibility. Further, we show that the $∣ B ∣ = 1$ BPS sector continues to exist for certain generalizations of the model like, for instance, after its coupling to a specific version of the BPS Skyrme model, i.e., the addition of the sextic term and a particular potential.
Comments:
Latex file, 13 pages, no figures
Subjects:
High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
arXiv:
2005.00018 [pdf]
PLB(2020)·19 citations
07
[Submitted on 1 May 2020] (cross-list from hep-ph)
Kinetic theory with spin: From massive to massless fermions
Xin-Li Sheng🇨🇳 · Qun Wang🇨🇳 · Xu-Guang Huang🇨🇳
We find that the recently developed kinetic theories with spin for massive and massless fermions are smoothly connected. By introducing a reference-frame vector, we decompose the dipole-moment tensor into electric and magnetic dipole moments. We show that the axial-vector component of the Wigner function contains a contribution from the transverse magnetic dipole moment which accounts for the transverse spin degree of freedom (DOF) and vanishes smoothly in the massless limit. As a result, the kinetic equations, describing four DOF for massive fermions, becomes smoothly the chiral kinetic equations describing two DOF in the massless limit. We also confirm the small-mass behavior of the Wigner function by explicit calculation using a Gaussian wave packet.
Comments:
12 pages, no figure
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
arXiv:
2005.00204 [pdf]
PRD(2020)·31 citations
08
[Submitted on 30 Apr 2020] (cross-list from hep-ph)
Open charm and charmonium states in strong magnetic fields
Amruta Mishra🇮🇳 · S.P.Misra🇮🇳
The mass modifications of the open charm ( $D$ and $D^{*}$ ) mesons, and their effects on the decay widths $D^{*} \to D π$ as well as of the charmonium state, $Ψ (3770)$ to open charm mesons ( $Ψ (3770) \to D D ˉ$ ), are investigated in the presence of strong magnetic fields. These are studied accounting for the mixing of the pseudoscalar ( $P$ ) and vector ( $V$ ) mesons ( $D - D^{*}$ , $η_{c}^{'} - Ψ (3770)$ mixings), with the mixing parameter, $g_{P V}$ of a phenomenological three-point ( $P V γ$ ) vertex interaction determined from the observed radiative decay width of $V \to P γ$ . For charged $D - D^{*}$ mixing, this parameter is dependent on the magnetic field, because of the Landau level contributions to the vacuum masses of these mesons. The masses of the charged $D$ and $D^{*}$ mesons modified due to $P V$ mixing, in addition, have contributions from the lowest Landau levels in the presence of a strong magnetic field. The effects of the magnetic field on the decay widths are studied using a field theoretic model of composite hadrons with quark (and antiquark) consittuents. The parameter for the charged $D - D^{*}$ mixing is observed to increase appreciably with increase in the magnetic field. This leads to dominant modifications to their masses, and hence the decay widths of charged $D^{*} \to D π$ as well as $Ψ (3770) \to D^{+} D^{-}$ at large values of the magnetic field. The modifications of the masses and decay widths of the open and hidden charm mesons in the presence of strong magnetic fields should have observable consequences on the production of the open charm ( $D$ and $D^{*}$ ) mesons as well as of the charmonium states resulting from non-central ultrarelativistic heavy ion collision experiments.
Comments:
25 pages, 3 figures, version to be published in Int. Jour. Mod. Phys. E. arXiv admin note: text overlap with arXiv:2004.01007, arXiv:2006.03478
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2005.00354 [pdf]
IJMPE(2021)·22 citations
09
[Submitted on 1 May 2020] (cross-list from nucl-ex)
Precision measurement of the magnetic octupole moment in $^{45}$ Sc as a test for state-of-the-art atomic- and nuclear-structure theory
R. P. de Groote · J. Moreno · J. Dobaczewski · I. Moore · M. Reponen · B. K. Sahoo · C. Yuan
We report on measurements of the hyperfine $A, B$ and $C$ -constants of the $3 d 4 s^{2}^{2} D_{5/2}$ and $3 d 4 s^{2}^{2} D_{3/2}$ atomic states in $^{45}$ Sc. High-precision atomic calculations of the hyperfine fields of these states and second-order corrections are performed, and are used to extract $C_{5/2} = - 0.06 (6)$ kHz and $C_{3/2} = + 0.04 (3)$ kHz from the data. These results are one order of magnitude more precise than the available literature. From the combined analysis of both atomic states, we infer the nuclear magnetic octupole moment $Ω = - 0.07 (53) μ_{N} b$ , including experimental and atomic structure-related uncertainties. With a single valence proton outside of a magic calcium core, scandium is ideally suited to test a variety of nuclear models, and to investigate in-depth the many intriguing nuclear structure phenomena observed within the neighboring isotopes of calcium. We perform nuclear shell-model calculations of $Ω$ , and furthermore explore the use of Density Functional Theory for evaluating $Ω$ . From this, mutually consistent theoretical values of $Ω$ are obtained, which are in agreement with the experimental value. This confirms atomic structure calculations possess the accuracy and precision required for magnetic octupole moment measurements, and shows that modern nuclear theory is capable of providing meaningful insight into this largely unexplored observable.
Subjects:
Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
2005.00414 [pdf]
PLB(2022)·14 citations

Affiliations

first authorsco-authorsvia INSPIRE