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Chong Qi

Publications and source records attributed to Chong Qi.

At least 19 recordsLinked to original sources
arXiv2026

Human population dynamics as a Bayesian inverse transport problem

Many open problems across physical, biological, and engineered systems involve non-equilibrium transport processes where the governing conservation laws are known, but the underlying constitutive relations remain latent and time-varying. Conventional data-driven approaches like deep neural networks capture statistical patterns but routinely violate fundamental mass conservation. Here, we introduce a unified Bayesian inverse transport framework that resolves this by embedding Bayesian Neural Networks (BNNs) directly within exact partial differential equations in age-time space. By evaluating this framework on complex, real-world human cohort advection across China, Japan, and South Korea, we demonstrate that this physical constraint enables consistent uncertainty propagation and missing-data reconstruction from sparse observations. Beyond demography, this framework provides a generalizable foundation for observing and forecasting non-equilibrium boundary dynamics across various fields.

physics.soc-ph↗
arXiv2026

Global systematics and theoretical interpretation of $l$-forbidden $M1$ transitions in odd-$A$ nuclei

The $l$-forbidden magnetic dipole ($M1$) transitions, characterized by a change in orbital angular momentum ($\Delta \ell = 2$), serve as sensitive probes of higher-order effects, including configuration mixing and meson-exchange currents. In this work, we present a comprehensive systematic study of all experimentally known $l$-forbidden $M1$ transitions, covering odd-$A$ nuclei with neutron numbers $27 \leq N \leq 126$. To interpret these global systematics, we apply a theoretical framework based on the relativistic Dirac wave function. This approach directly links the $l$-forbidden $M1$ transition amplitudes between pseudospin-partner orbitals to experimental single-particle magnetic moments. We perform a global comparison across isotopic chains by substituting unknown magnetic moments with rescaled Schmidt estimates. Focusing on dominant transition groups, including $p_{3/2} \rightarrow f_{5/2}$, $s_{1/2} \rightarrow d_{3/2}$, and $d_{5/2} \rightarrow g_{7/2}$, our analysis establishes a robust linear correlation between the transition amplitudes $\sqrt{B(M1)}$ and the corresponding empirical single-particle matrix elements $M_{\mathrm{sp}}$. The proportionality coefficient $\rho$ serves as an empirical measure of single-particle strength fragmentation and quantifies the role of configuration mixing in driving $l$-forbidden transitions across the nuclear chart.

nucl-th↗
arXiv2026

A Four-Section Bracket for the 48-team World Cup

The expansion of the FIFA World Cup to 48 teams in 2026 introduces structural challenges in tournament design. To populate a 32-team knockout bracket from 12 groups of four, the current FIFA rules select the eight best third-placed teams using a global ranking across all groups. This global coupling creates several major problems: a combinatorial explosion of 495 possible bracket configurations; a fundamentally biased and unequal selection of third-placed qualifiers; lack of a clear path for group winners; vulnerability to collusion and ranking manipulation; and no guarantee of same-group separation beyond the first knockout round. We propose a simple unified solution called the four-section bracket (FSB) rule: split the 12 groups into four sections of three groups. All group winners, runners-up, and the two best third-placed teams in each section advance. Group winners remain in their home sections as local anchors, while lower-ranked qualifiers are transferred to other sections according to a fixed, symmetric rule. This structure guarantees same-group separation until the semifinal, protects the top eight group winners with a predictable knockout path, and reduces bracket complexity from 495 configurations to just one invariant topology per section, recovering the symmetry of the traditional 32-team format. We show substantial improvements in competitive fairness and scheduling predictability.

physics.soc-ph↗
arXiv2026

Simultaneous $\alpha\beta$ Decay: A New Mode of Nuclear Instability

We propose simultaneous $\alpha\beta$ decay as a novel mode of nuclear instability that involves the strong and weak interactions in a single quantum transition. We develop a theoretical framework to predict its branching ratios and $\alpha$-energy spectra, establishing exclusive and inclusive criteria based on whether the individual $\alpha$ and $\beta$ channels are closed or open. A global survey of the nuclear chart identifies five exclusive $\alpha\beta^-$ candidates, all predicted to be experimentally inaccessible, and ranks the leading inclusive candidates for both the $\alpha\beta^-$ and $\alpha\beta^+$ modes. Remarkably, six of the top $\alpha\beta^+$ candidates coincide with known $\beta$-delayed-$\alpha$ precursors. The observed $\alpha$ spectra are naturally accounted for by simultaneous $\alpha\beta^+$ emission, suggesting direct decay as the dominant underlying mechanism. Our findings establish simultaneous $\alpha\beta$ decay as a distinct radioactive process and a sensitive probe of the interplay between the strong and weak interactions.

nucl-th↗
arXiv2026

Hierarchical Neural Filtering of Nuclear Mass Residuals and Spectral Signatures of Quantum Chaos

In complex quantum many-body systems such as atomic nuclei, the interplay between regular collective motion and irregular intrinsic dynamics gives rise to fluctuations that cannot be fully captured by existing global theoretical models. Nuclear mass, which exhibits smooth trends across the nuclear chart together with localized deviations, provides a sensitive observable for investigating such irregular dynamics. In this work, we employ a variety of neural network architectures, which serve as controlled nonlinear filters within a Hierarchical Residual Decomposition framework to progressively extract and suppress the chaotic many-body signature (characterized by $1/f$ spectral correlations) in nuclear mass residuals. The resulting Physics-Informed Neural Ensemble (PINE) model combines multiple mass models and neural network architectures, enabling a systematic suppression of coherent and chaotic components, after which the remaining fluctuations are analyzed using Fourier-based spectral diagnostics across different mass regions. Our results show that hierarchical neural residual learning efficiently removes the dominant low-frequency correlations and suppresses the quantum-chaotic spectral rigidity, driving the residuals toward the uncorrelated white-noise limit. This systematic suppression provides a quantitative diagnostic of the underlying scale-dependent complexity and many-body correlation structure of nuclear mass deviations.

nucl-th↗
arXiv2026

Quantum tunneling, global phases and the limits of classical action reconstructions

It was proposed recently that the Schr\"odinger wave function can be reconstructed exactly from a discrete superposition of classical action branches weighted by associated classical densities, without semiclassical approximations. We examine this construction for quantum tunneling through finite potential barriers and for quantum phase phenomena. Although formally consistent when the Hamilton-Jacobi equation admits globally defined real branches, the construction breaks down in classically forbidden regions where no real classical action exists. Using rectangular and Coulomb barrier tunneling in alpha decay and nuclear fusion, we show that the wave function requires either a non-vanishing quantum potential or complex-valued action. The growing barrier component fixed by global boundary conditions is essential for transmission and cannot arise from local real classical trajectories alone. Berry phase, flux quantization, Josephson tunneling, and dc SQUID interference likewise impose global phase constraints absent from local classical action transport.

quant-ph↗
arXiv2026

Asymmetric reformulation of draw rules in chess and its implications for game theory: Repetition as loss for White

Repetition-based draw rules in deterministic games like chess ensure termination but introduce strategic artifacts, allowing players to enforce draws independent of positional value. We propose an asymmetric modification: threefold repetition results in a loss for White if it is responsible for initiating it. This rule directly targets the persistent first-move advantage and removes low-effort draw strategies available to White. The new rule is expected to reduce draw rates, re-balance first-move advantage, and promote exploration in both human and artificial play. We outline a computational framework with existing and newly designed neural-network chess engines for the empirical validation of the proposal and analyze it from the perspectives of game theory and graph dynamics.

cs.GT↗
arXiv2026

Generalized gauge-space rotations in atomic nuclei: A critical insight

We critically reexamine the concepts of pairing rotations and moments of inertia in gauge space extracted from experimental binding energies. Our analysis focuses on pairing correlations among like nucleons, neutron-proton pairing, and $\alpha$-type correlations. By investigating $\alpha$ separation energies and binding-energy differences along chains of fixed isospin projection and subtracting macroscopic contributions, we reveal a remarkably smooth and nearly universal behavior in the residual $\alpha$ correlation energy. These results exhibit the parabolic trends characteristic of collective rotations in gauge space. We demonstrate that the standard definition of the gauge-space moment of inertia for like-nucleon pairing is dominated by macroscopic contributions from Coulomb and symmetry energies. Once these are removed, the remaining moment of inertia becomes negative. This suggests that the observed behavior reflects the loss of correlation energy due to Pauli-blocking effect. Our results indicate that $\alpha$ correlations constitute a genuine collective mode associated with quartetting dynamics arising from the coherent coupling of two superfluid components.

nucl-th↗
arXiv2026

Partial conservation of seniority in semi-magic nuclei

The concept of seniority plays a central role in nuclear structure physics by classifying many-body states according to the number of unpaired nucleons. While exact seniority conservation holds in single-$j$ systems with $j \leq 7/2$, deviations arise for higher-$j$ orbitals where residual interactions can mix states of different seniority. Surprisingly, certain states in systems with $j \geq 9/2$ exhibit partial conservation of seniority, remaining solvable even when the symmetry is expected to break. This paper reviews the theoretical foundation of the seniority scheme, its connection to pairing interactions and coefficients of fractional parentage, and the conditions under which solvability persists. Particular emphasis is placed on the $j=9/2$ case, where two $v=4$ states with $I=4$ and $I=6$ remain unmixed under arbitrary interactions. We discuss analytical proofs of their existence, numerical studies, and supporting experimental evidence from semi-magic nuclei across five regions of the nuclear chart. Extensions to symbolic shell-model approaches are also presented, highlighting their utility in exploring wave functions and symmetries in many-body systems.

nucl-th↗
arXiv2026

Three-Body Barrier Dynamics of Double-Alpha Decay in Heavy Nuclei

The simultaneous emission of two $\alpha$ particles--double-$\alpha$ decay--represents a long-predicted but unobserved mode of nuclear radioactivity. Here we formulate this process as a genuine three-body problem within the hyperspherical coordinate framework and evaluate decay probabilities by numerically solving the corresponding hyperradial Schr\"{o}dinger equation, combined with large-scale random sampling of the potential parameters; the latter treatment ensures that the present results are more convincing. Inspired by this, we demonstrate that the penetrability ratio between simultaneous and sequential $\alpha$ emission exhibits a strikingly linear dependence on $ZQ_{\alpha\alpha}^{-1/2}$, extending the barrier penetration dynamics into the correlated few-body regime. The nuclei $^{108}$Xe, $^{218}$Ra, $^{224}$Pu, $^{222}$U, $^{216}$Rn, and $^{220}$Th are suggested as the most promising candidates for the observation of double-$\alpha$ decay, with predicted half-lives potentially accessible within present detection limits. Our results provide a unified framework for multi-$\alpha$ decay and open a pathway to probing nuclear clustering and few-body correlations in heavy nuclei.

nucl-th↗
arXiv2025

The $B(E2)$ anomaly: Evidence for a low-lying mixed-symmetry collective excitation mode

Exceptionally low values of the ratio of electric quadrupole transition rates, $B_{4/2}\equiv B(E2;4^+_1\rightarrow2^+_1)/B(E2;2^+_1\rightarrow0^+_{\mathrm{gs}})<1$, have been observed in neutron-deficient nuclei near $N\approx94$ (W, Os, Pt) and $N\approx62$ (Te, Xe) with few and comparable numbers of valence nucleons outside closed shells. Remarkably, the suppressed $B_{4/2}$ ratios coincide with low-lying energy level patterns characteristic of collective motion. Standard approaches, including large-scale shell model, collective models, and density functional theory, fail to reproduce this behavior, commonly referred to as the $B{4/2}$ (or $B(E2)$) anomaly. Recent work has reproduced the effect in selected Pt and Os isotopes via mapping a triaxial rotor Hamiltonian onto the interacting boson model (IBM), attributing it to triaxial rotational motion. However, this interpretation is unexpected as collectivity typically emerges first through vibrational modes with increasing valence nucleon number along isotopic chains. Here, we address this discrepancy using an extended IBM Hamiltonian across nuclei exhibiting the anomaly, benchmarked against large-scale shell model calculations, and propose that the $B(E2)$ anomaly arises from a low-lying mixed-symmetry collective mode that bridges single-particle and collective dynamics.

nucl-th↗
arXiv2025

Anomalous collective modes in atomic nuclei within the proton-neutron interacting boson model

Novel collective modes characterized by a $B_{4/2}$ ratio ($\equiv B(E2;4_1^+\rightarrow 2_1^+)/B(E2;2_1^+\rightarrow 0_1^+)$) less than 1.0 that were observed recently have been identified within the proton-neutron interacting boson model (IBM-2) using the consistent-$Q$ Hamiltonian. These modes are shown to give rise to triaxial spectral features, including significant band mixing. The results provide a compelling explanation for the deeply suppressed $B_{4/2}$ ratio observed in $^{166}$W, $^{168,170}$Os, and $^{172}$Pt, offering new insights into the $B(E2)$ anomaly phenomenon in neutron-deficient nuclei.

nucl-th↗
arXiv2025

Triaxial rotor modes in finite-N boson systems

We propose an algebraic approach to elucidate the dynamic characteristics of triaxial rotor modes in nuclei by mapping a triaxial rotor Hamiltonian to the interacting boson model (IBM) one within a finite-$N$ framework. Our method unveils striking features not observed in conventional modes, exemplified by the $B(E2)$ anomaly, characterized by $B(E2;4_1--2_1^+)/B(E2;2_1--0_1^+)<<1$. Using specific examples, we demonstrate that the peculiar properties of low-lying states in both neutron-rich and neutron-deficient Os nuclei can be comprehensively understood through the proposed Hamiltonian, which incorporates both rigid and soft triaxial rotor modes. This algebraic method not only offers fresh insights into triaxial dynamics but also showcases its capability in uncovering emergent exotic collective modes in nuclear structure.

nucl-th↗
arXiv2025

Shell model description of the $N=82$ isotonic chain with a new effective interaction

In this work, we present a systematic study of low-lying states and electromagnetic properties of the semi-magic $N = 82$ isotonic chain with proton number $Z=51$-77, using the full configuration interaction shell model with a newly developed high-quality effective interaction. The calculations are performed in a large model space that includes all proton orbitals between $Z = 50$ and 82: $0g_{7/2}$, $1d_{5/2}$, $1d_{3/2}$, $2s_{1/2}$, and $0h_{11/2}$. The effective interaction is derived through the principal component analysis approach, starting from 160 two-body matrix elements and 5 single-particle energies and considering up to 30 degrees of freedom. Those are optimized by fitting to 204 available experimental energy levels. The resulting root-mean-square deviation is as low as 102 keV. The new interaction successfully reproduces the binding energies, low-lying spectra, electric quadrupole transition probabilities $B(E2)$, and magnetic dipole moments across both even-even and odd-mass isotones. The nuclear structure of low-lying states is analyzed in detail. Additionally, predictions are made for several more proton-rich nuclei beyond current experimental reach, including $^{155}\mathrm{Ta}$, $^{156}\mathrm{W}$, $^{157}\mathrm{Re}$, $^{158}\mathrm{Os}$, and $^{159}\mathrm{Ir}$.

nucl-th↗
arXiv2025

The $\beta$-decay properties of $N=Z$ nuclei: Role of neutron-proton pairing and the shell model interpretation

We study the recently measured beta-decay of $^{70}$Kr into $^{70}$Br within the framework of the large-scale shell model. The enhancement in the Gamow-Teller (GT) transition strength in $^{70}$Br compared to the $\beta$-decay of the lighter $^{62}$Ge was suggested as an indication for increased neutron-proton ($np$) pairing correlation. To explore the $np$ correlations in nuclei, we systematically examined the $\beta$-decay properties of the even-even nuclei $A=58,62,66,$ and $70$ into $N=Z$ odd-odd nuclei. By employing an interaction involving solely $J=1, T=0$ and $J=0, T=1$ pairing matrix elements, we observe that the pairing does not necessarily lead to an enhancement in the GT strength for the same coupling strength. But with the inclusion of the $g_{9/2}$ orbital, the GT strength can be increased with increasing $np$ pairing in connection with the enhanced contribution from the $g_{9/2}$ orbital. We further compare those results with realistic calculations in the $fp$ and $f_{5/2}pg_{9/2}$ model space to gauge the contribution from $f_{7/2}$ and $g_{9/2}$ orbitals in the GT strengths. With the JUN45 interaction, there is an increment for the yrast $1^+$ state for the decay of $^{70}$Kr as compared to the decay of $^{62}$Ge due to increased $g_{9/2}$ contribution. Additionally, we probe the effect of $np$ pairing on $B_{\rm GT}$ by modifying the single-particle energies and the $T = 0$ matrix elements of the interaction responsible for the decay transition strength. In calculations with realistic interaction, we find that the accumulated transition strength can increase with enhanced $np$ pairing.

nucl-th↗
arXiv2025

Monopole and Seniority Truncations in the Large-Scale Configuration Interaction Shell Model Approach

This paper addresses the challenges of solving the quantum many-body problem, particularly within nuclear physics, through the configuration interaction (CI) method. Large-scale shell model calculations often become computationally infeasible for systems with a large number of valence particles, requiring truncation techniques. We propose truncation methods for the nuclear shell model, in which angular momentum is conserved and rotational symmetry is restored. We introduce the monopole-interaction-based truncation and seniority truncation strategies, designed to reduce the dimension of the calculations. These truncations can be established by considering certain partitions based on their importance and selecting physically meaningful states. We examine these truncations for Sn, Xe, and Pb isotopes, demonstrating their effectiveness in overcoming computational limits. These truncations work well for systems with either a single type of valence nucleon or with both types. With these truncations, we are able to achieve good convergence for the energy at a very small portion of the total dimension.

nucl-th↗