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Physics Nuclear Theory

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Sunday 4 October

Nuclear Theory

Nuclear mass table in deformed relativistic Hartree-Bogoliubov theory in continuum, III: nuclei with $8 \leq Z \leq 120$

DRHBc Mass Table Collaboration: Peng Guo, Xiaojie Cao, Kangmin Chen et al. (+89 more)

The mass table in the deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc) with the PC-PK1 density functional has been established for nuclei with $8 \leq Z \leq 120$, extended from the previous works for even-even nuclei [Zhang et al. (DRHBc mass table collaboration), At. Data Nucl. Data Tables 144, 101488 (2022)] and for even-$Z$ nuclei [Guo et al. (DRHBc mass table collaboration), At. Data Nucl. Data Tables 158, 101661 (2024)]. The calculated binding energies, two- and one-nucleon separation energies, root-mean-square (rms) radii of neutron, proton, matter, and charge distributions, quadrupole deformations, neutron and proton Fermi surfaces, and the blocked neutron (proton) orbitals of odd-$N$ ($Z$) nuclei are tabulated and compared with the available experimental data. A total of 9495 nuclei are predicted to be bound, with an rms deviation of 1.444 MeV from the 2380 mass data. Good agreement with the available experimental pairing gaps, $\alpha$ decay energies, and charge radii is also achieved. The accuracies of the calculated nuclear masses and nucleon separation energies as well as the prediction for drip lines are compared with those obtained by other relativistic and nonrelativistic density functional calculations. It turns out that the DRHBc theory with PC-PK1 provides one of the best microscopic descriptions for nuclear masses. The systematics of nucleon separation energies, pairing gaps, pairing energies, two-nucleon gaps, $\alpha$ decay energies, rms radii, quadrupole deformations, potential energy curves, neutron density distributions, and neutron mean-field potentials are discussed.
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All authors DRHBc Mass Table Collaboration: Peng Guo, Xiaojie Cao, Kangmin Chen, Qibo Chen, Myung-Ki Cheoun, Yongbeom Choi, Wenmin Deng, Jianmin Dong, Pengxiang Du, Xiaokai Du, Kangda Duan, Xiaohua Fan, Wei Gao, Lisheng Geng, Xi Guo, Yixin Guo, Eunja Ha, Xiao-Tao He, Jinniu Hu, Rongyan Hu, Jingke Huang, Kun Huang, Yanan Huang, Zidan Huang, Xiaofei Jiang, Seonghyun Kim, Youngman Kim, Chang-Hwan Lee, Jenny Lee, Jian Li, Minglong Li, Zhipan Li, Zhengzheng Li, Zhanjiang Lian, Haozhao Liang, Boran Liu, Lang Liu, Xiao Lu, Chenjun Lv, Jie Meng, Myeong-Hwan Mun, Yifei Niu, Zhongming Niu, Cong Pan, Panagiota Papakonstantinou, Jing Peng, Xiaoying Qu, Tianshuai Shang, Xinle Shang, Caiwan Shen, Guofang Shen, Ting Sun, Tingting Sun, Wei Sun, Xiang-Xiang Sun, Chen Wang, Peng Wang, Sibo Wang, Yiran Wang, Yuanyuan Wang, Yumeng Wang, Jiawei Wu, Liang Wu, Xinhui Wu, Xuewei Xia, Yingfeng Xu, Yonghe Xue, Jiangming Yao, Yaochen Yang, Guixiang Ye, Lian Ye, To Chung Yiu, Jianghan Yu, Yangyang Yu, Wentao Zeng, Kaiyuan Zhang, Jinzhe, Zhang, Ning Zhang, Shijie Zhang, Shuangquan Zhang, Wei Zhang, Xiaoyan Zhang, Yanxin Zhang, Ying Zhang, Yingxun Zhang, Zhenhua Zhang, Qiang Zhao, Ruyou Zheng, Chang Zhou, Shan-Gui Zhou, Lianjian Zou

Nuclear Theory · Cross-listed from physics.flu-dyn

Landau damping and mode-selective instability of a vortex gas

H. Terças, J. L. Figueiredo, J. T et al. (+1 more)

We show that a collisionless point-vortex gas behaves as a genuine Vlasov system. Starting from the non-canonical Hamiltonian structure of point-vortex dynamics, we derive a reduced Klimontovich equation and the corresponding Vlasov description directly on the physical plane, without introducing auxiliary momentum variables. The theory predicts a rich spectrum of collective phenomena, including vortex Rossby-like waves, global oscillations, resonant critical layers, and a dielectric response operator analogous to that of plasmas and self-gravitating systems. For smooth vortex distributions, differential rotation gives rise to a vortex analogue of Landau damping, whereby collective modes transfer energy and angular momentum to resonant vortex annuli in the absence of collisions or dissipation. Remarkably, differential rotation acts as a stringent mode-selection mechanism: for a Gaussian vortex cloud, only a single quadrupolar quasi-mode survives, while all higher multipoles are destroyed by phase mixing. We further predict a vortex counterpart of the beam–plasma instability, in which a thin vortex ring orbiting an Onsager patch selectively excites Kelvin modes with an azimuthal symmetry controlled by the ring population. These results establish kinetic theory as a natural framework for collective vortex dynamics and suggest new mechanisms for vortex transport, vortex avalanches, and rotational glitches in neutron-star superfluids.
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All authors H. Terças, J. L. Figueiredo, J. T, Mendonça

Saturday 3 October

Nuclear Theory

Radii and Scaling Relations of Dark-Matter-Admixed Neutron Stars

Zhi-yao Li, Wei-zhou Jiang and Dian Sun

The radius of a neutron star is closely related to the equation of state (EOS) of asymmetric nuclear matter, particularly to the nuclear symmetry energy. At fixed stellar mass, the neutron-star radius and the nuclear-matter pressure near saturation density approximately satisfy a pressure–radius (R-P) scaling relation, linking stellar geometry to strong-interaction matter. In the presence of dark matter (DM), changes in the stellar geometry can modify this relation. We investigate how GeV- and sub-GeV-scale DM affects the R-P relation in DM-admixed neutron stars (DANSs) within a gravity-only two-fluid framework. We extend the Buchdahl analytic solution to a two-fluid configuration to demonstrate this scaling and then use 21 nuclear EOSs to fit the relation $R_{\rm NM}=\bar C P_{\rm NM}^{\eta}$ for $1M_\odot$ and $1.4M_\odot$ DANSs. The exponent $\eta$ and coefficient $\bar C$ jointly quantify the DM-induced modification and depend on the DM particle mass, stellar DM content, and self-interaction strength. For bosonic DM, changes in $\eta$ and $\bar C$ occur mainly in the sub-GeV range, whereas significant fermionic-DM effects persist up to about 1.5 GeV. Increasing the DM content or strengthening a repulsive self-interaction generally increases $\eta$ and decreases $\bar C$. The modified R-P relation therefore encodes information about the DM particle mass, abundance, and self-interaction, and affect the extraction of the nuclear EOS from celestial observations. At DM masses of several hundred MeV, both fermionic and bosonic DM can also produce DM-dominated low-mass ($1M_\odot$) DANSs with large radial extensions, for which the conventional scaling relation ceases to apply.
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Friday 2 October

Nuclear Theory

Emulation of coupled-channels scattering for strongly deformed nuclei

M. Catacora-Rios, Kyle Beyer, Jin Lei et al. (+1 more)

Nucleon scattering off strongly deformed nuclei such as the actinides requires coupled-channels (CC) calculations in which several members of the ground-state rotational band are coupled explicitly, which makes Bayesian uncertainty quantification of deformed global optical potentials costly. We reformulate the direct boundary matching method (DBMM) by imposing its outgoing-wave boundary condition through a generalized Bloch operator; the resulting Bloch-DBMM solver converges as fast as the modern R-matrix method and extends to charged projectiles on targets with deformed charge distributions. On top of it we build a reduced-basis emulator, CCB-ROM, whose basis vectors span all channels of a $J^\pi$ block simultaneously, and generalize the coupled-channels empirical interpolation method to arbitrary non-affine deformed interactions. For $n,p+{}^{232}$Th inelastic scattering with the ground-state band coupled through the $8^+$ state, at 4 and 35 MeV, the Bloch-DBMM solver is benchmarked against Frescox, and the emulator replaces a 2700-dimensional system by one of dimension $N_b\le200$, with a cost of $\mathcal{O}(N_b^3)$ independent of the number of channels, reproducing the exact solver calculations for all five band members with speed-ups of over two orders of magnitude. CCB-ROM thus delivers differential cross sections, transmission coefficients and reaction cross sections from one calculation, at a cost compatible with Bayesian calibration of deformed optical potentials for neutrons and protons alike, and extends naturally to closed channels and to compound-nucleus reaction codes.
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All authors M. Catacora-Rios, Kyle Beyer, Jin Lei, Filomena Nunes

Nuclear Theory · Cross-listed from hep-ph

No Einstein Relation, No Problem: How Relativistic Weakly Coupled Heavy Quarks Equilibrate Beyond Leading Logarithm Anyway

Jean F. Du Plessis and Bruno Scheihing-Hitschfeld

Relativistic heavy quarks equilibrate even when their microscopic drag and momentum diffusion violate the Einstein relation. We investigate how equilibration proceeds as a function of the coupling and compared to simplified Fokker-Planck models. To do this, we present a detailed calculation of the momentum-transfer kernel in weakly coupled non-Abelian plasmas through strict $\mathcal{O}(g^4)$, and study the resulting dynamics at leading order in the inverse heavy-quark mass. Beyond leading logarithm, its non-Gaussian structure plays a crucial role in equilibration. We examine closely the analytic structure of the evolution kernel, determine the large-order asymptotics of the momentum-transfer cumulants, and show how the kernel's bounded analytic domain fixes asymmetric exponential tails at the level of the momentum transfer probability. Strongly coupled $\mathcal{N}=4$ SYM also features an approximately Gaussian core and exponential tails, but differs in the nature of the kernel's singularities and the velocity dependence of the transport coefficients and tail exponents. These differences have distinct dynamical consequences: for the parameters studied, the persistence of the relativistic population in steeply falling spectra is largely explained by drag alone at very weak coupling, whereas fluctuation-induced survivor bias produces a large relative enhancement at strong coupling. Nevertheless, the shared qualitative structure between weak and strong coupling points the way towards a practical phenomenological description of heavy quarks anchored in first-principles field theory.
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Nuclear Theory

Ab initio Green's function theory of superfluid neutron matter

F. Marino, W. G. Jiang, C. Barbieri et al. (+1 more)

At the low densities encountered in the inner crust of neutron stars, neutron matter becomes superfluid, directly influencing macroscopic phenomena such as star cooling. However, a precise quantitative understanding of this system has been hindered by uncontrolled many-body approximations. In this letter, we exploit the nonperturbative Gorkov algebraic diagrammatic construction method to provide a unified ab initio description of the equation of state and the single-particle spectral functions of homogeneous neutron matter, spanning from the dilute regime to saturation density. We identify clear microscopic signatures of superfluidity in the excitation spectrum and quantify the pairing gaps associated with realistic chiral Hamiltonians, estimating for the first time their sensitivity to the many-body truncation. Our robust handling of both dynamical and pairing correlations paves the way for exploring electroweak processes across the regimes relevant to neutron stars.
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All authors F. Marino, W. G. Jiang, C. Barbieri, G. Colò

Nuclear Theory · Cross-listed from physics.chem-ph

Bogoliubov self-consistent $GW$ and second-order Green's function methods for attractive fermionic interactions

Mauricio Rodríguez-Mayorga, Johannes Tölle and Pierre-François Loos

Describing fermionic systems with attractive interactions, such as superconductors and atomic nuclei, beyond the mean-field level remains a central challenge. In this work, we investigate the performance of Bogoliubov fully self-consistent $GW$ (Bog.~sc$GW$) and second-order Green's function (Bog.~scGF2) methods, implemented within a unified imaginary-time and imaginary-frequency framework. Using the attractive Hubbard model as a benchmark against full configuration interaction (FCI), we find that Bog. scGF2 provides a more accurate description than Bog.~sc$GW$. In particular, Bog.~sc$GW$ systematically overestimates the correlation energy, with errors increasing rapidly as the attractive interaction strength grows. These results highlight the importance of exchange contributions in strongly correlated fermionic systems, even when exchange effects are included only at low order in perturbation theory.
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Nuclear Theory

Total angular momentum distributions of fission fragments at scission in a 2-center basis

Paul Carpentier, Nathalie Pillet and Pablo Nieto-Gallego

In this article, we propose a new method to calculate the angular momentum distribution of fis- sion fragments adapted to the case of 2-center axial basis used to solve the Hartree-Fock-Bogoliubov equations in view of fission studies. As a first application, we have studied the properties of the fission fragment angular momentum distribution in the scission area of 240Pu using the Gogny D1S interaction. Here, a one dimensional asymmetric and adiabatic path (the lowest in energy), gener- ated by the newly proposed Link and Drop methods, has been considered. The major result of this study is the appearance of an odd-even angular momentum staggering in both fragments when going through scission. The odd-J components are progressively suppressed as the fragments separate, leading to an increasing dominance of even-J components. This behavior is systematically correlated with the rapid reduction of the intrinsic octupole deformation of the fragments, asso- ciated with the restoration of a more nearly reflection-symmetric shape. Finally, particle-number projection reveals the role of shell effects associated with specific fragment configurations in shaping the fragment angular momentum distributions.
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Nuclear Theory · Cross-listed from astro-ph.HE

Twins in the Shadow: Phase Transitions in Proto-Neutron Stars

Jannik Milthaler, Jan-Erik Christian, Pia Jakobus et al. (+1 more)

We study the impact of a first-order phase transition from hadronic to deconfined quark matter on the evolution of proto-neutron stars. To maximize the applicability of our results, we construct an equation of state that is highly parameterizable, where we use a relativistic mean field approach to model hadronic matter and a constant speed of sound approach to model quark matter. We approximate the cooling behavior of proto-neutron stars as a sequence of decreasing entropy at constant baryonic mass. Some parameterizations lead to so-called "twin-stars", where two neutron stars have the same (gravitational) mass but different radii. Detecting them is regarded as a smoking gun signal for phase transition. We find, however, that proto-neutron star evolution suggests that gravitational twin stars are only possible if the hybrid star does not have, in addition, a baryonic twin. This rules out most twin star pairs, especially if the phase transition occurs at large densities. In a mass-radius diagram the unpopulated hybrid branch appears to be "in the shadow" of the hadronic branch.
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All authors Jannik Milthaler, Jan-Erik Christian, Pia Jakobus, Stephan Rosswog

Nuclear Theory

Energy-Resolved Spin and Parity Distributions of Fission Fragments

Petar Marević, Nicolas Schunck, Antonio Bjelčić et al. (+1 more)

Fission fragments are born rotating rapidly, but the evolution of this spin with excitation energy and its impact on fission observables remain largely unknown. Combining state-of-the-art microscopic and statistical reaction theory, we simulate the full fission process - from the initial state, through scission, to fragment decay - and report the first microscopic, energy-resolved spin and parity distributions of the fragments produced in $^{239}$Pu(n,f). From thermal energy to $E_n = 10$ MeV, the spin of individual fragments evolves non-monotonically, tracking their deformation. The parity content, strongly non-statistical at thermal energy, remains correlated with spin throughout this range. For the first time, we quantify the impact of microscopic spin-parity distributions on prompt photon multiplicities, demonstrating the predictive potential of parameter-free microscopic inputs.
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All authors Petar Marević, Nicolas Schunck, Antonio Bjelčić, Guillaume Scamps

Nuclear Theory

Precise description of spontaneous fission half-lives of Rutherfordium isotopes within the relativistic Hartree-Bogoliubov theory

Jie Zhao

I investigate the spontaneous-fission (SF) half-lives of $^{254,256}$Rf within the multidimensionally constrained relativistic Hartree-Bogoliubov (MDC-RHB) model combined with the local quasiparticle random-phase approximation (LQRPA) method. The collective inertia is evaluated using the finite-amplitude method (FAM), which enables a fully self-consistent treatment of dynamical residual effects beyond the conventional cranking approximation. The effective collective potential is constructed by subtracting both the vibrational zero-point energy and rotational energy correction from the deformation energy surface. The SF half-lives are evaluated within the Wentzel-Kramers-Brillouin (WKB) approximation. Compared with the nonperturbative and perturbative cranking approximation, the FAM-LQRPA collective inertia is significantly enhanced, especially around the ground-state minimum, due to the dynamical residual interaction included in the QRPA. As a consequence, the predicted SF half-lives increase by several orders of magnitude and become consistent with experimental data. The calculated SF half-lives are 5.65 $\mu$s for $^{254}$Rf and 0.95 ms for $^{256}$Rf, both within approximately two orders of magnitude of the corresponding experimental values. These results indicate that a self-consistent treatment of dynamical residual effects and beyond mean-field correlations is crucial for quantitative microscopic descriptions of SF within covariant density functional theory.
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Nuclear Theory · Cross-listed from physics.comp-ph

AI-Assisted GPU optimization of the Stochastic Variational Method for Few-Body Boson System

Noritaka Shimizu, Shigeyoshi Aoyama, Yusuke Tsunoda et al. (+1 more)

The stochastic variational method (SVM) is one of the most powerful methods to solve quantum few-body systems precisely in various fields, such as nuclear and atomic physics. To the best of our knowledge, no SVM code optimized for GPUs has been reported. We developed a parallel SVM code for few-body clusters of $^4$He atoms and optimized it for two GPU architectures, NVIDIA GH200 and AMD Instinct MI300A, with the entire code written by an AI coding agent. On the algorithmic side, we introduce the secular-equation method with the Gu–Eisenstat prescription for solving the generalized eigenvalue problem within the SVM framework. The main part of the code tuning is to batch the many small matrices so that the GPUs are used efficiently, together with an array layout in memory optimized for coalesced addressing. For the five-body system with 4800 SVM basis states, the tuned SVM code runs 16.2 (14.7) times faster on the NVIDIA GH200 (AMD MI300A) than the same tuned code on the Intel Xeon Max CPU system, and 168 (153) times faster than the first working CPU implementation. The achieved performance brings 6-body and larger cluster systems within reach.
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All authors Noritaka Shimizu, Shigeyoshi Aoyama, Yusuke Tsunoda, Akira Nukada

Nuclear Theory

Real-time decay dynamics of the low-lying $1/2^+$ state in $^9$Be: Signatures of virtual-state behavior

Yuma Kikuchi, Kiyoshi Katō and Takayuki Myo

The low-lying $1/2^+$ state of $^9$Be has been interpreted either as a near-threshold resonance or as an $^8$Be+$n$ virtual state. Because both pictures can produce a pronounced threshold enhancement, its nature is difficult to determine from energy-domain observables alone. We investigate the low-lying $1/2^+$ state through its real-time decay dynamics and compare its behavior with that of the well-established $5/2^+$ resonance. A wave packet produced by electric-dipole excitation of the $^9$Be ground state is propagated in an $\alpha+\alpha+n$ three-body model. We analyze the survival probability, the fit-window dependence of the effective decay width, and time-dependent densities in different Jacobi-coordinate representations. The $1/2^+$ survival dynamics are further compared with an $s$-wave effective-range description motivated by the dominant $^8$Be+$n$ component found in our previous three-body studies. The $5/2^+$ channel shows approximately exponential late-time decay, with an effective width of $0.264$ MeV, close to the complex-scaled pole width of $0.285$ MeV. In contrast, the $1/2^+$ effective width decreases as the fitting interval is shifted to later times, and no stationary decay width is obtained. Its late-time survival probability is well described by the effective-range spectral distribution. The density evolution develops an $^8$Be+$n$-like asymptotic configuration while retaining a localized $p_{3/2}$ $\alpha n$ component suggestive of a $^5$He+$\alpha$-like configuration in the internal region. The $1/2^+$ decay differs qualitatively from resonance-like exponential decay and is consistent with near-threshold virtual-state dynamics. The distinct internal and asymptotic configurations revealed by the time-dependent densities provide complementary structural information beyond that contained in a single decay width.
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Thursday 1 October

Nuclear Theory

The causal diamond of relativistic hydrodynamics

L. Gavassino

The convergence of hydrodynamics is commonly investigated by Taylor-expanding the gapless dispersion relations $\omega(k)$ around $k=0$. We show that this diagnostic can fail arbitrarily close to the hydrodynamic limit: sound modes can collide at arbitrarily small wave number, rendering $\omega(k)$ nonanalytic, while the relationship between densities and fluxes remains analytic there. We instead formulate the gradient expansion off-shell (i.e. in the presence of external forces), directly at the level of the constitutive relations. For causal theories with relaxational spectra, we establish convergence for $|i\omega|+w|ik|<1/\tau_g$, where $w$ is the maximal information speed and $1/\tau_g$ the nonhydrodynamic gap. On the naturally Lorentzian $\{i\omega,ik\}$ plane, this region is a causal diamond, whose boundary marks the first possible encounter with nonhydrodynamic modes. Beyond it, analytic continuation reveals the nonhydrodynamic spectrum through singularities of the resummed constitutive relations. Thus, hydrodynamics is aware of the degrees of freedom beyond hydrodynamics, but this information becomes fully accessible only off-shell.
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Nuclear Theory

Under the spell of chiral symmetry

Vicente Vento

In this reflection, I want to look back over more than thirty years, from 1978 to 2008, of my professional and personal relationship with Mannque Rho. I will briefly describe some of the original ideas that emerged from our collaboration: the Little Bag, the Cheshire Cat principle, and Skyrmion matter. I do not intend to be exhaustive, neither in content nor in references, which can be found in our published works. Instead, I want to retrace the path we took together through physics, accompanied by many good friends.
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Nuclear Theory · Cross-listed from hep-ph

How Quantum Is Bottomonium in the Quark-Gluon Plasma?

Nora Brambilla and Tom Magorsch

We study how much quantum structure bottomonium retains during its evolution in the quark-gluon plasma. Within the open quantum system framework, we simulate the Lindblad equation obtained from potential nonrelativistic QCD in the quantum Brownian regime. From the resulting real-time evolution of the bottomonium density matrix, we compute the Wigner transform and study its negativity as a measure of nonclassicality and a test of a key condition underlying classical Langevin-type approximations. We find that the medium suppresses the negativity, which nevertheless approaches a finite plateau close to that of the $1\mathrm{S}$ state. The overlaps with the excited $2\mathrm{S}$ and $3\mathrm{S}$ states arise from near-canceling positive and negative phase-space contributions, driven by negative regions in the Wigner transforms of the bound-state projectors, while the $1\mathrm{S}$ overlap is insensitive to such contributions. We further show that the position-space coherence is similarly suppressed and plateaus close to the 1S value. We trace the finite residual quantum structure to conditional purification: the medium preferentially dissolves weakly bound and unbound modes with large $\langle r^2\rangle$, driving the surviving singlet $\mathrm{S}$-wave ensemble toward the $1\mathrm{S}$ state. More broadly, these results reveal that classicalization is partial and observable dependent, a feature that is relevant across applications of open quantum system methods in fundamental physics.
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Nuclear Theory · Cross-listed from quant-ph

Unitary Schur Sampling of Qudits via Random SWAP Tests: Hunt for Antisymmetry

Shrigyan Brahmachari, David Jakab, Henry D. Pfister et al. (+1 more)

Schur sampling is a fundamental primitive for extracting permutation-invariant information from many-body quantum systems and has broad applications in quantum information science. Circuit-based implementations typically rely on coherent representation-theoretic operations such as Clebsch-Gordan transforms, generalized phase estimation, or quantum Fourier transforms over the symmetric group. We show that unitary Schur sampling of arbitrary permutation-invariant mixed states on $n$ $d$-dimensional qudits can instead be implemented using only pairwise SWAP tests, namely, two-qudit projective measurements onto the symmetric and antisymmetric subspaces. Our protocol achieves error $\epsilon$ in diamond distance using $O(n\min\{n,d\}^{3}\log^2(n/\epsilon))$ random SWAP tests. The central idea is to repeatedly identify and extract the largest antisymmetric subsystem. This turns unitary Schur sampling into a search for antisymmetry and gives the algorithm a natural interpretation as a stochastic traversal of a Young diagram. The protocol preserves the $\mathrm{SU}(d)$-irrep state while preparing a canonical pure state in the multiplicity subsystem. As an application, we consider quantum purity amplification (QPA), in which multiple noisy copies of a pure quantum state are combined to produce a state of higher purity. We show that the optimal purified state can be obtained by retaining a single designated output qudit and discarding the rest.
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All authors Shrigyan Brahmachari, David Jakab, Henry D. Pfister, Iman Marvian

Nuclear Theory

Trace-anomaly decomposition and universal dark matter scaling in compact stars

Adamu Issifu, Constança Providência and Tobias Frederico

We investigate how dark matter (DM) admixture modifies the conformal properties and phase structure of dense neutron-star matter within a self-consistent single-fluid framework, with the global DM fraction $F_\chi=N_\chi/N_B$ fixing the local relation $n_\chi=F_\chi n_B$. We derive an exact decomposition of the total trace anomaly, $\Delta_{\rm tot}$, into microscopic contributions. For collider-motivated Higgs-portal benchmarks, explicit Higgs, vector-mediator, and contact-interaction contributions are negligible, while heavy nonrelativistic DM has an intrinsic trace anomaly close to the nonrelativistic limit, $\Delta_\chi\simeq1/3$. Consequently, the DM rest-mass energy fraction dominates the DM-induced modification of $\Delta_{\rm tot}$, producing a smooth upward shift of up to $\sim0.1$ for $F_\chi\sim0.2\%$. In the pressureless, comoving heavy-WIMP regime, we further identify a universal dark-sector scaling governed by the mass-loading parameter $\lambda=F_\chi m_\chi/m_N$: numerical calculations with different $(F_\chi,m_\chi)$ pairs at fixed $\lambda$ exhibit overlapping trace-anomaly, sound-speed, and mass–radius responses for a given baryonic equation of state. In hybrid stars, DM leaves the coexistence pressure and chemical potential essentially unchanged, whereas first-order hadron–quark deconfinement produces sharp discontinuities in the squared sound speed $c_s^2$, $\Delta_{\rm tot}$, and $\Delta_{\rm tot}-\Delta_B$. The combined softening substantially reduces the maximum stellar mass, placing $F_\chi\sim0.2\%$ in tension with the observed $2\,M_\odot$ neutron stars. These results show that the trace anomaly and its density evolution provide a sensitive diagnostic for distinguishing smooth DM-induced modifications of dense matter from genuine first-order deconfinement.
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Nuclear Theory · Cross-listed from hep-ph

Confronting $K^-d$ dynamics with kaonic atom measurements within a novel unitary framework

Albert Feijoo, Àngels Ramos and Juan Torres-Rincon

We study the low-energy interaction of negative kaons with deuterons using chiral $\bar{K}N$ interaction models (OR and BCN) as input. The three-body $K^-d$ amplitude is constructed within the Fixed-Center Approximation to the Faddeev equations, where the unitary constraints missing in the conventional approach are formally implemented with the incorporation of coherent multiple-scattering processes. The unitary procedure is extended to coupled channels including charge-exchange processes, as well as isospin-breaking effects through the use of physical particle masses. This provides a consistent description of the low-energy $K^-d$ amplitude and allows for the determination of the scattering length and the effective range. The resulting framework is then used to assess the compatibility of the BCN $\bar{K}N$ interaction model with the recent SIDDHARTA-2 measurements of kaonic hydrogen and kaonic deuterium through a bootstrap analysis. The procedure leads to a readjustment of the BCN parameterization which produces visible effects in several isospin-sensitive $\bar{K}N$ scattering observables, hence highlighting the additional information provided by the new kaonic-atom measurements to better constrain the poorly known isovector component of the ${\bar K}N$ interaction.
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Nuclear Theory · Cross-listed from hep-ph

Generalized fluctuation-dissipation theorem and Einstein relation in rotating equilibrium

Shuo Fang and Shi Pu

We derive a generalized fluctuation-dissipation theorem (FDT) for vector fields in rotating thermal equilibrium from an exact phase-space Kubo-Martin-Schwinger (KMS) relation. The resulting FDT contains rotation-induced tensorial contributions beyond a scalar thermal factor. In the local transport limit, we obtain a model-independent generalized Einstein relation with rotation in which, through second order in thermal vorticity, symmetric momentum diffusion depends on low-frequency spectral information beyond that encoded in the rotation-dependent dissipative drag. Remarkably, we find a new Einstein-type relation linking zero modes in the spectral function to the nonrotating drag coefficient. These zero modes underlie a new mechanism for the orbital polarization of heavy quarkonium. The same FDT constraint yields a modified detailed-balance relation whose first-order vortical correction is governed by transition polarization, without explicit dependence on the bath model. Our findings establish microscopic equilibrium constraints for studying rotating quantum matter in various fields.
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Nuclear Theory

Thermodynamic signatures do not uniquely identify deconfinement in neutron stars

Yong-Liang Ma and Jia-Ying Xiong

The smallness of polytropic index $\Gamma_\varepsilon \lesssim 1.75$ and near conformality of sound velocity $c_s^2 \approx 1/3$ in neutron star matter are usually referred to as signals of the emergence of quark matter. We construct a density-resolved nucleonic reference domain in the \((P/P_{\rm free},\Gamma_\varepsilon)\) plane using nucleonic EoSs jointly constrained by nuclear matter properties and neutron star mass, radius and tidal data, and found that the domain extends unambiguously below \(\Gamma_\varepsilon=1.75\). Crucially, the nucleonic domain becomes stable against the truncation order only after \(Z_0\) and \(Z_{sym}\) are included, showing that the higher-order density dependence controls the extrapolation from finite nuclei to neutron-star matter. These findings therefore provide concrete targets for finite-nucleus and heavy-ion experiments, while linking terrestrial nuclear physics directly to multimessenger observations. We compare the domain with smooth equations of state generated by neural networks without phase labels and represented by symbolic regression. Among these reconstructions, \(35.29\%\) have complete trajectories inside the nucleonic domain over \(0.5\leq n/n_0\leq8\). Within the EoS sample obtained after minimizing the multimessenger loss, the smallest value of \(\max_n c_s^2(n)\) is 0.38, above the conformal value $1/3$. In conclusion, we convert microscopic interpretation into a falsifiable, density-resolved null-hypothesis test and show quantitatively that current observations do not reject the nucleonic null over much of the admissible space of equation of state.
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Nuclear Theory

Properties of rapidly rotating hot neutron stars within Brueckner theory

Hong-Ming Liu, Bo-Xiu Zhou, Zeng-Hua Li et al. (+2 more)

We study the properties of hot rapidly rotating neutron stars using various equations of state based on the Brueckner-Hartree-Fock approach at finite temperature. The temperature dependence of gravitational mass, equatorial radius, Kepler frequency, moment of inertia are analysed in detail and universal relations are examined.
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All authors Hong-Ming Liu, Bo-Xiu Zhou, Zeng-Hua Li, Jin-Biao Wei, H.-J. Schulze

Nuclear Theory · Cross-listed from hep-ph

Gravitational D-form factors of the nucleon and pion with mixing between two-quark and four-quark states

Mamiya Kawaguchi, Yao Ma and Yong-Liang Ma

We investigate the gravitational $D$-form factors of the nucleon and pion within an extended linear sigma model (eLSM) that incorporates both two-quark and four-quark states, as well as nucleon fields. Within the scalar-meson-dominance picture, we find that meson mixing between two-quark and four-quark states suppresses the nucleon $D$-form factor and leads to agreement with the lattice-QCD results. Interestingly, a quantitatively similar suppression was previously found in the parity doublet model (PDM) as a consequence of a nonzero chiral invariant component of the nucleon mass. This suggests that the effects of meson mixing and the chiral invariant mass are difficult to distinguish from the nucleon $D$-form factor alone. We therefore examine the pion $D$-form factor in the chiral limit. While its value in the forward limit remains fixed at $-1$ in both the eLSM and the PDM, meson mixing modifies its momentum-transfer dependence. In contrast, the chiral invariant mass does not directly affect the pion $D$-form factor. These results suggest that a combined analysis of the nucleon and pion $D$-form factors can provide further insight into the mass decomposition of the nucleon and the quark composition of mesons.
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Nuclear Theory

Hadronization into Nuclei: Does Size Matter?

Anton Andronic, Peter Braun-Munzinger, Hjalmar Brunßen et al. (+1 more)

We investigate an extension of the statistical hadronization model (SHM) that takes (hyper)nucleus sizes into account. The spatial extent of nuclear wave functions relative to the fireball volume is used to calculate a size correction, which describes the suppression with respect to a point-like treatment of the (hyper)nucleus at hadronization. For several species of light nuclei (d, ${}^{3}\mathrm{H}$, ${}^{3}\mathrm{He}$) and for the hypernucleus ${}^{3}_{\Lambda}\mathrm{H}$, the predicted effects of the size correction on SHM yields are compared to yield measurements in pp, p-Pb, and Pb-Pb collisions in the ALICE experiment. The experimental data suggest that this size correction, based on applying final-state wave functions at chemical freeze-out, does not give a consistent description of (hyper)nucleus production in nuclear and hadronic collisions. By contrast, the SHM without a nuclear-size correction provides a substantially better description of the data. This result lends further support to the interpretation that such nuclear states are formed from initially compact (multi-quark) configurations which after hadronization expand to their final-state wave functions.
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All authors Anton Andronic, Peter Braun-Munzinger, Hjalmar Brunßen, Johanna Stachel

Nuclear Theory

Microscopic Insights into the Quarkyonic Hadron–Quark Crossover: Lessons from Ultracold Fermi Gases

Hiroyuki Tajima

In neutron-star and dense quantum chromodynamics (QCD) physics, it is important to understand how baryonic matter evolves into quark matter at high density. A continuous hadron–quark crossover is one of the most attractive candidates because it can reconcile the comparatively soft equation of state around nuclear density with the rapid stiffening required to support massive neutron stars. Recent neutron-star observations motivate equations of state that stiffen rapidly across the intermediate-density regime, while quarkyonic-matter descriptions feature a shell-like baryon momentum distribution there. In this paper, we review our recent work on the microscopic description and interpretation of these phenomena by drawing an analogy with the Bose–Einstein condensate (BEC) to Bardeen–Cooper–Schrieffer (BCS) crossover in ultracold Fermi gases and two-color QCD. As pairing fluctuations play a crucial role in the BEC–BCS crossover, we discuss the role of its three-body counterpart, that is, tripling fluctuations associated with baryon formation in the hadron–quark crossover. In terms of a phase-shift representation of tripling fluctuations, the interplay between a three-body bound-state pole and the scattering continuum suppresses low-momentum baryonic occupation, generates a baryonic momentum shell, and reduces the density susceptibility, thereby producing a peak in the speed of sound. We review the demonstration of this mechanism in a one-dimensional three-component Fermi gas, its relativistic extension, and its connection to phenomenological quarkyonic equations of state.
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Wednesday 30 September

Nuclear Theory

Dispersive optical model description of the CaFe experiment

R. A. Ramon, M. C. Atkinson and W. H. Dickhoff

High-momentum ratios measured in the CaFe experiment using high-energy electron scattering off the CaFe nuclei $(i.e.~ {}^{40}\mathrm{Ca}, {}^{48}\mathrm{Ca}, {}^{54}\mathrm{Fe})$ have revealed a surprising correlation between the nuclear shell structure and the high-momentum components generated by short-range and tensor correlations (SRC). The non-local dispersive optical model (DOM) successfully describes the experimentally measured high-momentum ratios while simultaneously describing the nuclear bound-state properties and scattering observables for these CaFe nuclei. The experimentally measured average high-momentum ratio of ${}^{48}\mathrm{Ca}$/${}^{40}\mathrm{Ca}$ and ${}^{54}\mathrm{Fe}$/${}^{48}\mathrm{Ca}$ are $1.10~\pm~0.02$ and $1.49~\pm~0.03$, respectively. The corresponding DOM results are $1.05~\pm~0.05$ and $1.52~\pm~0.08$, which is the first successful description of these experimental results. The present DOM analysis of CaFe nuclei relied on an extended version of the DOM incorporating a shrinkable geometry to provide a more localized and stronger volume absorption at higher missing energies to correctly represent the SRC physics. The success of the DOM can be attributed to its simultaneous treatment of structure and reaction data, the latter requiring a depletion of the mean-field accompanied by the proper admixture of high-momentum components in the respective ground states.
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Nuclear Theory

A Two-Component Exciton Model for $\beta$-Delayed Neutron Emission

Nico Braukman, Toshihiko Kawano, Robert Grzywacz et al. (+1 more)

A model for $\beta$-delayed neutron emission is presented in which the emission of neutrons is allowed to occur before states populated in $\beta^-$ decay have reached equilibrium in the so-called "compound nucleus" picture. The pre-equilibrium neutron spectra are computed using a two-component exciton model, where neutron and proton, particle and hole degrees of freedom are treated independently. This model is implemented in the code BeoH to supplement the existing Hauser-Feshbach model for statistical decay of compound-nucleus states. The effect of a pre-equilibrium component in the total neutron spectrum on the single- and multi-neutron emission probabilities $P_{xn}$ is investigated for $\beta$-decay precursor nuclei in the regions $47\leq Z\leq 49,~83\leq N\leq 86$ and $54\leq Z\leq 58,~N=125,126$. An absolute change in the $P_{xn}$ values of up to 5-10% is observed in the $N=126$ region when including pre-equilibrium emission compared to the values predicted by the Hauser-Feshbach model alone.
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All authors Nico Braukman, Toshihiko Kawano, Robert Grzywacz, Zhengyu Xu

Nuclear Theory

Coexistence of strange quark stars and neutron stars: metastability and nucleation in proto-neutron stars

Mirco Guerrini, Giuseppe Pagliara, Luca Passarella et al. (+1 more)

If strange quark matter (SQM) is absolutely stable, hadronic neutron stars (NSs) and strange quark stars (QSs) may coexist in the so-called two-families scenario. A key issue is explaining how hadronic NSs can survive as long-lived metastable objects, rather than promptly converting into stable QSs. Since all NSs are born as hot proto-neutron stars (PNSs), a necessary condition for their existence is that the conditions for conversion, triggered by the nucleation of the first critical SQM droplet, are not reached in every PNS. We investigate the thermal nucleation of critical SQM droplets under representative PNS conditions, accounting for flavor-composition fluctuations and finite-size effects on color superconductivity by suppressing pairing in droplets smaller than the diquark coherence length. We define the nucleation conditions as the thermodynamic state at which a critical SQM droplet is expected to nucleate statistically within the characteristic dynamical timescale of the system. Under these conditions, the reduced nucleation barrier is nearly universal, with $W_*/T\simeq167$ to within a few units. Exploring the SQM parameter space, we show that requiring a canonical $1.4~\rm{M}_{\odot}$ NS to survive the PNS stage sets a lower bound on the hadron-quark surface tension $\sigma\gtrsim 67$ MeVfm$^{-2}$.
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All authors Mirco Guerrini, Giuseppe Pagliara, Luca Passarella, Alessandro Drago

Nuclear Theory · Cross-listed from quant-ph

Late-Time Power Laws in Fluorescence Decays: Quantum Decay or Alternative Mechanisms?

Francesco Giacosa, Anna Kolbus, Krzysztof Kyziol et al. (+4 more)

In quantum mechanics, the properties of an unstable system are closely related to its corresponding energy distribution. One of the predictions of the theory is the emergence of a late-time power law in the survival probability $P(t)$ of the unstable state. However, in complex systems, similar effects may emerge due to other phenomena. This is the case for nonextensive statistical models, for some continuous lifetime distribution models, and also for certain energy-migration models applied to fluorescence. In this work, these alternative interpretations are confronted with data from time-resolved fluorescence spectroscopy experiments with erythrosine B and eosine Y as fluorophores. It turns out that some of the features expected within the quantum-mechanical description, such as the sharp transition from the exponential to the power-law regime, cannot be reproduced by the specific statistical and energy-migration parametrizations fitted in the analysis.
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All authors Francesco Giacosa, Anna Kolbus, Krzysztof Kyziol, Magdalena Plodowska, Milena Piotrowska, Karol Szary, Arthur Vereijken

Nuclear Theory · Cross-listed from hep-ph

Unified description of longitudinal and transverse parton dynamics in cold nuclear matter

Weiyao Ke

We present a unified description of longitudinal momentum evolution and transverse-momentum broadening in cold nuclear matter using soft collinear effective theory with Glauber gluon interactions (SCET$_{\rm G}$). In a finite nucleus, Landau–Pomeranchuk–Migdal interference couples medium-induced energy loss to the transverse scale resolved by the observable. Our framework combines RG evolution of impact-parameter-dependent energy loss with BFKL-type rapidity evolution of the collision kernel, improved by kinematical constraints and running coupling. With a common set of cold-nuclear-matter parameters, it accounts for the main nuclear modification patterns in semi-inclusive DIS and Drell–Yan production and provides predictions for TMD hadron multiplicities at the EIC. We also discuss the one-point energy correlator in DIS, whose energy weighting suppresses the leading final-state energy-loss contribution. In the EIC kinematics studied, the residual dynamical corrections are small, leaving the nuclear modification dominated by the initial-state nuclear parton distributions.
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