Nuclear Theory·nucl-th

Tuesday·March 9, 2021

9 papers—5 primary·4 cross-listed

01
Deep learning stochastic processes with QCD phase transition
Lijia Jiang🇩🇪 · Lingxiao Wang🇩🇪 · Kai Zhou🇩🇪
It is non-trivial to recognize phase transitions and track dynamics inside a stochastic process because of its intrinsic stochasticity. In this paper, we employ the deep learning method to classify the phase orders and predict the damping coefficient of fluctuating systems under Langevin's description. As a concrete set-up, we demonstrate this paradigm for the scalar condensation in QCD matter near the critical point, in which the order parameter of chiral phase transition can be characterized in a $1 + 1$ -dimensional Langevin equation for $σ$ field. In a supervised learning manner, the Convolutional Neural Networks(CNNs) accurately classify the first-order phase transition and crossover based on $σ$ field configurations with fluctuations. Noise in the stochastic process does not significantly hinder the performance of the well-trained neural network for phase order recognition. For mixed dynamics with diverse dynamical parameters, we further devise and train the machine to predict the damping coefficients $η$ in a broad range. The results show that it is robust to extract the dynamics from the bumpy field configurations.
nucl-thnucl-exphysics.data-anPRD(2021)·34 citations
02
The decline rate of the production cross-section of superheavy nuclei with $Z = 114 - 117$ at high excitation energies
J. Hong🇰🇷 · G. G. Adamian🇷🇺 · N. V. Antonenko🇷🇺 · P. Jachimowicz🇵🇱 · M. Kowal🇵🇱
The production cross sections of superheavy nuclei with charge numbers $114 - 117$ are predicted in the $(5 - 9) n$ -evaporation channels of the $^{48}$ Ca-induced complete fusion reactions for future experiments. The estimates of synthesis capabilities are based on a uniform and consistent set of input nuclear data provided by the multidimensional macroscopic-microscopic approach. The contributions of various factors to the final production cross section are discussed. As shown, the specific interplay between survival and fusion probabilities unexpectedly leads to a relatively slow decline of the total cross-sections with increasing excitation energy. This effect is supported by a favorable arrangement of fission barriers protecting the compound nucleus against splitting concerning energetic thresholds for the emission of successive neutrons. In particular, the probabilities of the formation of superheavy nuclei in the $5 n$ -, $6 n$ -, and in some cases even in $7 n$ -evaporation channels are still promising. This may offer a new opportunity for the future synthesis of unknown neutron-deficient superheavy isotopes.
nucl-thPRC(2021)·9 citations
03
Global study of separable pairing interaction in covariant density functional theory
S. Teeti🇺🇸 · A. V. Afanasjev🇺🇸
A systematic global investigation of pairing properties based on all available experimental data on pairing indicators has been performed for the first time in the framework of covariant density functional theory. It is based on separable pairing interaction of Ref. [1]. The optimization of the scaling factors of this interaction to experimental data clearly reveals its isospin dependence in neutron subsystem. However, the situation is less certain in proton subsystem since similar accuracy of the description of pairing indicators can be achieved both with isospin-dependent and mass-dependent scaling factors. The differences in the functional dependencies of scaling factors lead to the uncertainties in the prediction of proton and neutron pairing properties which are especially pronounced at high isospin and could have a significant impact on some physical observables. For a given part of nuclear chart the scaling factors for spherical nuclei are smaller than those for deformed ones; this feature exists also in non-relativistic density functional theories. Its origin is traced back to particle-vibration coupling in odd- $A$ nuclei which is missing in all existing global studies of pairing. Although the present investigation is based on the NL5(E) covariant energy density functional (CEDF), its general conclusions are expected to be valid also for other CEDFs built at the Hartree level.
nucl-thPRC(2021)·18 citations
04
Bayesian inference on the isospin splitting of nucleon effective mass from giant resonances in $^{208}$ Pb
Zhen Zhang🇨🇳 · Xue-Bin Feng🇨🇳 · Lie-Wen Chen🇨🇳
From a Bayesian analysis of the electric dipole polarizability, the constrained energy of isovector giant dipole resonance, the peak energy of isocalar giant quadrupole resonance and the constrained energy of isocalar giant monopole resonance in $^{208}$ Pb, we extract the isoscalar and isovector effective masses in nuclear matter at saturation density $ρ_{0}$ as $m_{s, 0}^{*} / m = 0.8 7_{- 0.04}^{+ 0.04}$ and $m_{v, 0}^{*} / m = 0.7 8_{- 0.05}^{+ 0.06}$ at $90%$ confidence level. The obtained constraints on $m_{s, 0}^{*}$ and $m_{v, 0}^{*}$ lead to a positive isospin splitting of nucleon effective mass in asymmetric nuclear matter of isospin asymmetry $δ$ at $ρ_{0}$ as $m_{n - p}^{*} / m = (0.2 0_{- 0.14}^{+ 0.15}) δ$ . In addition, the symmetry energy at the subsaturation density $ρ^{*} = 0.05 fm^{- 3}$ is determined to be $E_{sym} (ρ^{*}) = 16.7 \pm 1.3$ MeV at $90%$ confidence level.
nucl-thCPC(2021)·19 citations
05
Derivation of the nonlocal collision term in the relativistic Boltzmann equation for massive spin-1/2 particles from quantum field theory
Nora Weickgenannt🇩🇪 · Enrico Speranza🇩🇪 · Xin-li Sheng🇨🇳 · Qun Wang🇨🇳 · Dirk H. Rischke🇩🇪
We derive the Boltzmann equation and the collision kernel for massive spin-1/2 particles, using the Wigner-function formalism and employing an expansion in powers of $ℏ$ . The phase space is enlarged to include a variable related to the spin degrees of freedom. This allows to reduce the transport equations of the independent components of the Wigner function to one scalar equation. To next-to-leading order in $ℏ$ , we find that the collision kernel contains both local and nonlocal terms. We show that off-shell contributions cancel in the Boltzmann equation. Our framework can be used to study spin-polarization phenomena induced by vorticity as recently observed in heavy-ion collisions and in condensed-matter systems.
nucl-thhep-phPRD(2021)·128 citations
06
Distribution amplitudes of light diquarks
Ya Lu🇨🇳 · Daniele Binosi🇮🇹 · Minghui Ding🇮🇹 · Craig D. Roberts🇨🇳 · Hui-Yu Xing🇨🇳 · Chang Xu🇨🇳
Accumulating evidence indicates that soft quark+quark (diquark) correlations play an important role in the structure and interactions of hadrons constituted from three or more valence-quarks; so, it is worth developing insights into diquark structure. Using a leading-order truncation of those equations needed to solve continuum two-valence-body bound-state problems, the leading-twist two-parton distribution amplitudes (DAs) of light-quark scalar and pseudovector diquarks are calculated. The diquark DAs are narrower and taller than the asymptotic profile that characterises mesons. Consequently, the valence quasiparticles in a diquark are less likely to carry a large light-front fraction of the system's total momentum than those in a meson. These features may both influence the form of baryon DAs and be transmitted to diquark distribution functions (DFs), in which case their impact will be felt, e.g. in the proton's $u$ and $d$ valence-quark DFs.
↳ hep-phhep-exhep-latnucl-ex+1EPJA(2021)·16 citations
07
Neutron interferometry and tests of short-range modifications of gravity
J. M. Rocha🇧🇷 · F. Dahia🇧🇷
We consider tests of short-distance modifications of gravity based on neutron interferometry in the scenario of large extra dimensions. Avoiding the non-computability problem in the calculation of the internal gravitational potential of extended sources, typical of models with zero-width brane, we determine the neutron optical potential associated with the higher-dimension gravitational interaction between the incident neutron and a material medium in the context of thick brane theories. Proceeding this way, we identify the physical quantity of the extra dimension model that the neutron interferometry is capable of constraining. We also consider interferometric experiments in which the phase shifter is an electric field, as in the test of the Aharanov-Casher effect. We argue that this experiment, with this non-baryonic source, can be viewed as a test of the short-range behavior of Post-Newtonian parameters that measure the capacity of the pressure and the internal energy for producing gravity.
↳ gr-qcnucl-thquant-phPRD(2021)·11 citations
08
On the light front surfaces in the phase space of hadrons in heavy-ion collisions
Rahul Ramachandran Nair🇵🇱
Surfaces corresponding to the constant values of the light front variable forms paraboloids in the phase space of the inclusively produced hadrons in heavy-ion collisions. In this paper, it is demonstrated with the simulated Au-Au collisions at $s = 200$ GeV using the UrQMD event generator that the paraboloidal surface defined by a certain constant value of the light front variable divides the particles in the phase space into two groups such that the distributions of the square of the transverse momentum, the polar angle and the light front variable of particles belonging to one among them can be described with the Boltzmann distribution parameterised by the mass-dependent temperature.
↳ hep-phnucl-th1 citation
09
Improved $K_{e 3}$ radiative corrections sharpen the $K_{μ 2}$ -- $K_{l 3}$ discrepancy
Chien-Yeah Seng🇩🇪 · Daniel Galviz🇩🇪 · Mikhail Gorchtein🇩🇪 · Ulf-G. Meißner🇩🇪
The measurements of $V_{u s}$ in leptonic $(K_{μ 2})$ and semileptonic $(K_{l 3})$ kaon decays exhibit a $3 σ$ disagreement, which could originate either from physics beyond the Standard Model or some large unidentified Standard Model systematic effects. Clarifying this issue requires a careful examination of all existing Standard Model inputs. Making use of a newly-proposed computational framework and the most recent lattice QCD results, we perform a comprehensive re-analysis of the electroweak radiative corrections to the $K_{e 3}$ decay rates that achieves an unprecedented level of precision of $1 0^{- 4}$ , which improves the current best results by almost an order of magnitude. No large systematic effects are found, which suggests that the electroweak radiative corrections should be removed from the ``list of culprits'' responsible for the $K_{μ 2}$ -- $K_{l 3}$ discrepancy.
↳ hep-phhep-exhep-latnucl-ex+1JHEP(2021)·40 citations

Affiliations

first authorsco-authorsvia INSPIRE