arXiv subjects

Y. L. Yang

Publications and source records attributed to Y. L. Yang.

9 recordsLinked to original sources

arXiv2025

The charge radii of calcium isotopes within relativistic density functional theory: nucleon's finite-size and quadrupole shape fluctuation effects

The anomaly in the charge radii of Ca isotopes has been puzzling for nuclear theory for decades. We present the first self-consistent solution to this puzzle within the density functional theory without resorting to local parameter adjustment. By taking into account both the intrinsic electromagnetic structure of nucleons and the zero-point motions of nuclear shape, which have been often neglected in previous studies, the similar charge radii of $^{40}$Ca and $^{48}$Ca as well as an inverted parabolic behavior between them are reproduced. It is found that these effects also play crucial roles in the description of the isotonic shift between the charge radii of Sn and Cd isotopes.

nucl-th↗

arXiv2025

Next-to-leading-order prediction for the neutrinoless double-beta decay

The neutrinoless double-beta decay ($0νββ$) of two neutrons$nn \rightarrow ppee$ is the elementary subprocess of $0νββ$ decay in nuclei. Accurate knowledge of the $nn \rightarrow ppee$ amplitude is required to pin down the short-range contributions in the nuclear matrix elements of the candidate nuclei for large-scale $0νββ$ searches. In this Letter, we report the first next-to-leading-order prediction of the nn \rightarrow ppee amplitude, with Bayesian uncertainty quantification. This is made possible by the development of the relativistic chiral effective field theory, in which no unknown contact term is required up to next-to-leading order. The theory is validated by reproducing in a parameter-free way the available data on the charge independence and charge symmetry breaking contributions in the two-nucleon scattering. The present work makes an essential step towards addressing the uncertainty in the theoretical calculations of the nuclear matrix elements relevant for $0νββ$ searches.

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arXiv2024

Neutrinoless double-beta decay in a finite volume from relativistic effective field theory

The neutrinoless double-beta decay process $nn\rightarrow ppee$ within the light Majorana-exchange scenario is studied using the relativistic pionless effective field theory (EFT) in finite-volume cubic boxes with the periodic boundary conditions. Using the low-energy two-nucleon scattering observables from lattice QCD available at $m_π=300$, 450, 510, and 806 MeV, the leading-order $nn\rightarrow ppee$ transition matrix elements are predicted and their volume dependence is investigated. The predictions for the $nn\rightarrow ppee$ transition matrix elements can be directly compared to the lattice QCD calculations of the $nn\rightarrow ppee$ process at the same pion masses. In particular for the matrix element at $m_π=806$ MeV, the predictions with relativistic pionless EFT are confronted to the recent first lattice QCD evaluation. Therefore, the present results are expected to play a crucial role in the benchmark between the nuclear EFTs and the upcoming lattice QCD calculations of the $nn\rightarrow pp ee$ process, which would provide a nontrivial test on the predictive power of nuclear EFTs on neutrinoless double-beta decay.

hep-lat↗

arXiv2024

Relativistic model-free prediction for neutrinoless double beta decay at leading order

Starting from a manifestly Lorentz-invariant chiral Lagrangian, we present a model-free prediction for the transition amplitude of the process $nn\rightarrow pp e^-e^-$ induced by light Majorana neutrinos, which is a key process of the neutrinoless double beta decay ($0νββ$) in heavy nuclei employed in large-scale searches. Contrary to the nonrelativistic case, we show that the transition amplitude can be renormalized at leading order without any uncertain contact operators. The predicted amplitude defines a stringent benchmark for the previous estimation with model-dependent inputs, and greatly reduces the uncertainty of $0νββ$ transition operator in the calculations of nuclear matrix elements. Generalizations of the present framework could also help to address the uncertainties in $0νββ$ decay induced by other mechanisms. In addition, the present work motivates a relativistic {\it ab initio} calculation of $0νββ$ decay in light and medium-mass nuclei.

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arXiv2024

Reconciling light nuclei and nuclear matter: relativistic $ab\ initio$ calculations

It has been a long-standing challenge to accurately predict the properties of light nuclei and nuclear matter simultaneously in nuclear $ab\ initio$ calculations. In this Letter, we develop the relativistic quantum Monte Carlo methods for the nuclear $ab\ initio$ problem, and calculate the ground-state energies of $A\leq4$ nuclei using the two-nucleon Bonn force with an unprecedented high accuracy. For $A=3,4$ nuclei, the present relativistic results significantly outperforms the nonrelativistic results with only two-nucleon forces. Combining the present results for light nuclei and the previous results for nuclear matter with the same Bonn force, a correlation between the properties of light $A\leq4$ nuclei and the nuclear saturation is revealed, and both systems are well described simultaneously, even without introducing three-nucleon forces. This provides a quantitative understanding of the connection between the light nuclei and nuclear matter saturation properties, which has been an outstanding problem in nuclear $ab\ initio$ calculations for decades.

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arXiv2023

Shape and multiple shape coexistence of nuclei within covariant density functional theory

Shape and multiple shape coexistence of nuclei are investigated throughout the nuclear chart by calculating the low-lying spectra and the quadrupole shape invariants for even-even nuclei with $10\leq Z\leq 104$ from the proton drip line to the neutron one within a five-dimensional collective Hamiltonian based on the covariant density functional PC-PK1. The quadrupole shape invariants are implemented to characterize the quadrupole deformations of low-lying $0^+$ states and predict nuclear mass regions of shape and multiple shape coexistence. The predicted low-lying spectra and the shape or multi-shape coexisting nuclei are overall in good agreement with the available experimental results. In addition, the present work predicts a wealth of nuclei with shape or multiple shape coexistence in the neutron-rich regions. The connection between the strong $E0$ transition strength and the occurrence of shape coexistence is analyzed systemically. It is found that nuclei with pronounced shape coexistence generally have strong $E0$ transition strengths, while the reverse may not be true. The present results can serve as useful guidelines for experimental searches and theoretical studies of shape and multiple shape coexistence, especially in neutron-rich regions.

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arXiv2022

Relativistic effects and three-body interactions in atomic nuclei

Based on the leading-order covariant pionless effective field theory, a relativistic nuclear Hamiltonian is derived and solved using the variational Monte Carlo approach for $A\le 4$ nuclei by representing the nuclear many-body wave functions with a symmetry-based artificial neural network. It is found that the relativistic effects rescue the renormalizability of the theory, and overcome the energy collapse problem for $^3$H and $^4$He without promoting a repulsive three-nucleon interaction to leading order as in nonrelativistic calculations. Nevertheless, to exactly reproduce the experimental ground-state energies, a three-nucleon interaction is needed and its interplay with the relativistic effects plays a crucial role. The strongly repulsive relativistic effects suppress the energy contribution given by the three-nucleon interactions, so a strong strength for the three-nucleon interaction could be required to reproduce the experimental energies. These results shed light on a consistent understanding of relativistic effects and three-body interactions in atomic nuclei.

nucl-th↗

arXiv2022

Nuclear landscape in a mapped collective Hamiltonian from covariant density functional theory

The nuclear landscape has been investigated within the triaxial relativistic Hartree-Bogoliubov theory with the PC-PK1 density functional, and the beyond-mean-field dynamical correlation energies are taken into account by a microscopically mapped five-dimensional collective Hamiltonian without additional free parameters. The effects of triaxial deformation and dynamical correlations on the nuclear landscape are analyzed. The present results provide the best description of the experimental binding energies, in particular for medium and heavy mass regions, in comparison with the results obtained previously with other state-of-the-art covariant density functionals. The inclusion of the dynamical correlation energies plays an important role in the PC-PK1 results. It is emphasized that the nuclear landscape is considerably extended by the PC-PK1 functional in comparison with the previous results with other density functionals, which may be due to the different isovector properties in the density functionals.

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arXiv2013

A new measurement method of electrode gains for orthogonal symmetric type beam position monitor

The new beam position monitor (BPM) system of the injector at the upgrade project of Hefei Light Source (HLS II) has 19 stripline beam position monitors. Most consist of four orthogonal symmetric stripline electrodes. The differences in electronic gain and mismachining tolerance can cause the change of the beam response of the BPM electrodes. This variation will couple the two measured horizontal positions in order to bring the measuring error. To alleviate this effect, a new technique to measure the relative response of the four electrodes has been developed. It is irrelevant to the beam charge and the related coefficient can be theoretical calculated. The effect of electrodes coupling on this technique is analyzed. The calibration data is used to fit the gain for all 19 injector beam position monitors. The results show the standard deviation of the distribution of measured gains is about 5%.

physics.acc-ph↗