arXivDaily arXiv每日学术速递 周一至周五更新
2606.19829 2026-06-19 nucl-th 新提交

Parameter-free deformation variables of the proxy-SU(3) symmetry in even-even actinide, superheavy and hyperheavy nuclei with Z=82-126, N=82-258

偶偶锕系、超重和超重核中proxy-SU(3)对称性的无参数形变变量(Z=82-126, N=82-258)

Dennis Bonatsos, V. K. B. Kota, Andriana Martinou, S. K. Peroulis, D. Petrellis, P. Vasileiou, T. J. Mertzimekis, N. Minkov

AI总结 本文利用proxy-SU(3)近似,为Z=82-126、N=82-258范围内的原子核提供了无参数预测的形变变量β和γ,并给出了最高权重和次高权重不可约表示。

Comments 36 pages, 3 figures

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AI中文摘要

超重和超重核是当今核结构的前沿之一,同时许多锕系核的实验信息也相当有限。因此,能够对这些核提供无参数依赖预测的理论方法特别引人关注。其中一种方法是壳模型的proxy-SU(3)近似,该方法已在中等质量核和重核(直至稀土区)中通过实验数据得到了充分检验,并被发现能够为集体形变变量β和γ提供可靠的无参数预测。在proxy-SU(3)方法中,通过幺正变换恢复了三维谐振子的SU(3)对称性,该对称性在sd壳层之外因强自旋-轨道相互作用而被破坏。对于每个原子核,泡利原理和核子-核子相互作用的短程性质所允许的最对称不可约表示(irrep),在数学语言中称为最高权重(hw)irrep,被发现是足够的,除非hw irrep是完全对称的,此时还需要包含次高权重(nhw)irrep。本文提供了从Z=82、N=82到Z=126、N=258的所有原子核的hw和nhw irrep的完整集合,以及相应的形变变量β和γ的无参数预测。还考虑了若干实例,展示了所收集结果在研究长椭球到扁椭球形变转变、镜像对称性以及集体变量沿稳定谷演化方面的应用。

英文摘要

Superheavy and hyperheavy nuclei are one of the frontiers of nuclear structure nowadays, while also for many actinides rather limited experimental information exists. Therefore, theoretical methods providing parameter-independent predictions for these nuclei are of particular interest. Such a method is the proxy-SU(3) approximation to the shell model, which has been adequately tested against experimental data in medium-mass and heavy nuclei up to the rare earth region, and has been found to provide reliable, parameter-independent predictions for the collective deformation variables beta and gamma. Within the proxy-SU(3) approach, the SU(3) symmetry of the 3-dimensional harmonic oscillator, which is destroyed beyond the sd shell by the strong spin-orbit interaction, is restored through a unitary transformation. For each nucleus, the most symmetric irreducible representation (irrep) allowed by the Pauli principle and the short-range nature of the nucleon-nucleon interaction, called the highest-weight (hw ) irrep in mathematical language, is found to suffice, except in cases in which the hw irrep turns out to be completely symmetric, so that the next highest weight (nhw) irrep has also to be included. In this article we provide a full collection of the hw and nhw irreps, as well as of the corresponding parameter-free predictions for the deformation variables beta and gamma, for all atomic nuclei ranging from Z=82, N=82 to Z=126, N=258. Several cases exemplifying the use of the collected results for studying the prolate to oblate shape transition, mirror symmetries, as well as the evolution of the collective variables along the valley of stability are also considered.

2606.20111 2026-06-19 nucl-th astro-ph.HE astro-ph.SR hep-ph 新提交

Hybrid stars with hyperons: structure based on QCD sum rule coupling constants

含有超子的混合星:基于QCD求和规则耦合常数的结构

F. Moradi Jangal, H. R. Moshfegh, K. Azizi

AI总结 在相对论平均场框架下,利用QCD求和规则导出的耦合常数,结合MIT袋模型和NJL模型描述夸克相,通过Gibbs和Maxwell构造分析强子-夸克相变,计算混合星的质量-半径关系、潮汐Love数和无量纲潮汐形变,为多信使天体物理观测提供定量预测。

Comments 25 pages, 6 figures, 4 tables

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AI中文摘要

我们在相对论平均场框架内对由强子、轻子和夸克组成的混合星进行了全面研究。使用从QCD求和规则(QCDSR)导出的耦合常数,我们首先确定核物质的体性质,并评估核子和超子的单粒子势,以约束强子部分。然后,在β平衡下,采用σ-ω-ρ模型构建强子相的状态方程(EOS),而夸克相则分别用MIT袋模型和Nambu-Jona-Lasinio(NJL)模型描述。通过Gibbs和Maxwell构造分析了强子-夸克相变。基于得到的EOS,我们获得了混合星的质量-半径关系,研究了粒子分数及其径向分布,并计算了潮汐Love数($\mathcal{K}_{2}$)和无量纲潮汐形变($\varLambda$)。我们的结果为与当前多信使天体物理观测的比较提供了定量预测。

英文摘要

We present a comprehensive study of hybrid stars composed of hadrons, leptons, and quarks within a relativistic mean-field framework. Using coupling constants derived from QCD sum rules (QCDSR), we first determine the bulk properties of nuclear matter and evaluate the single-particle potentials of nucleons and hyperons to constrain the hadronic sector. The equation of state (EOS) under beta equilibrium is then constructed employing the $σ-ω-ρ$ model for the hadronic phase, while the quark phase is described using both the MIT bag model and the Nambu-Jona-Lasinio (NJL) model. The hadron-quark phase transition is analyzed through both Gibbs and Maxwell constructions. Based on resulting EOSs, we obtain the mass-radius relations of hybrid stars, investigate particle fractions and their radial distributions, and calculate the tidal Love number ($\mathcal{K}_{2}$) and the dimensionless tidal deformability ($\varLambda$). Our results provide quantitative predictions relevant for comparison with current multimessenger astrophysical observations.

2606.20203 2026-06-19 nucl-th gr-qc hep-ph 新提交

Trace anomaly and interior curvature of neutron stars in energy-momentum squared gravity

能动量平方引力中中子星的迹反常与内部曲率

Ratikanta Swain, Sayantan Ghosh, Bharat Kumar

AI总结 研究能动量平方引力中中子星内部迹反常与曲率的关系,发现迹反常仍能组织内部几何,但随耦合强度分裂,扩展了GR热力学-几何对应。

Comments Comments are welcome and appreciated

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AI中文摘要

在能动量平方引力(EMSG)中,中子星内部的时空由有效热力学变量驱动,这些变量不必与物理流体压力和能量密度一致。因此,一个悬而未决的问题是,致密物质的迹反常——QCD中衡量共形对称性被破坏程度的量——是否仍像在广义相对论(GR)中那样组织内部轮廓和曲率。我们采用清晰的物质-几何分离:迹反常仅由流体部分计算,而时空曲率标量由实际驱动修正的Tolman-Oppenheimer-Volkoff方程的变量构建。对于五种相对论平均场状态方程,在所有可接受的EMSG模型中,径向迹反常轮廓从核心到表面单调增加,如同在GR中一样,但随EMSG耦合强度系统性地分裂;分裂随恒星致密性增大而增大。尽管存在这种变形,曲率不变量在绘制为迹反常的函数时仍落在有组织的带上,扩展了GR热力学-几何对应。里奇收缩显示出最紧密的组织,而里奇标量仍对状态方程最敏感。对于观测上可及的恒星,EMSG效应较小,但在刚硬、超致密构型中最大,表明即使当引力与物质非线性耦合时,迹反常仍是内部几何的有用热力学标签。

英文摘要

In energy-momentum squared gravity (EMSG), the spacetime inside a neutron star is sourced by effective thermodynamic variables that need not coincide with the physical fluid pressure and energy density. It is therefore an open question whether the trace anomaly of dense matter -- the QCD measure of how strongly conformal symmetry is broken -- still organizes interior profiles and curvature in the same way it does in general relativity (GR). We adopt a clear matter-geometry separation: the trace anomaly is computed from the fluid sector alone, while spacetime curvature scalars are built from the variables that actually source the modified Tolman-Oppenheimer-Volkoff equations. For five relativistic mean-field equations of state, the radial trace-anomaly profiles increase monotonically from core to surface in all accepted EMSG models, as in GR, but split systematically with the EMSG coupling strength; the splitting grows with stellar compactness. Despite this deformation, curvature invariants still fall onto organized bands when plotted against the trace anomaly, extending the GR thermodynamic-geometric correspondence. The Ricci contraction shows the tightest organization, whereas the Ricci scalar remains the most equation-of-state sensitive. EMSG effects are modest for observationally accessible stars but largest in stiff, ultracompact configurations, indicating that the trace anomaly remains a useful thermodynamic label for interior geometry even when gravity couples nonlinearly to matter.

2606.18347 2026-06-19 hep-ph hep-ex nucl-ex nucl-th 交叉投稿

Self-Calibration of the Neutrino-Argon Cross Section with Solar Neutrinos

利用太阳中微子实现中微子-氩截面的自校准

Rasmi Hajjar, Obada Nairat, John F. Beacom

AI总结 提出利用太阳中微子数据精确测量CC ν_e+^{40}Ar截面,通过已知的^8B通量和存活概率以及跃迁角分布,在9-15 MeV能量范围内实现≤2%精度。

Comments Main text is 11 pages, with 8 figures. Comments are welcome. Please also see today's complementary study by Cheng, Hostert, Machado, Mishra, and Thompson

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AI中文摘要

DUNE的MeV物理项目的成功取决于对带电电流(CC)ν_e+^{40}Ar截面的高精度了解。虽然对于构成该截面的核跃迁存在10%水平的间接约束,但MeV范围内的唯一直接测量不确定度约为50%。我们出人意料地表明,可以利用太阳中微子数据本身精确测量该截面。这是可能的,因为独立已知的^8B通量和存活概率,以及构成截面的费米和伽莫夫-泰勒跃迁的独特角分布。我们提出了提取跃迁强度的新方法,考虑了直观分组和主成分分析。在关于探测的悲观假设下,但假设探测器不确定性得到控制,我们证明在9-15 MeV能量范围内可以实现截面≤2%的精度。这些结果将为研究高达几十MeV的截面提供重要基础,在该能量范围内由于核碎裂通道,复杂性显著增加,但减少不确定性对于超新星和大气中微子研究至关重要。

英文摘要

The success of DUNE's MeV physics program depends upon high-precision knowledge of the charged-current (CC) $ν_e+\mathrm{^{40}Ar}$ cross section. While there are indirect constraints at the 10% level for the nuclear transitions that constitute this cross section, the only direct measurement in the MeV range has an uncertainty of $\sim$50%. We show, surprisingly, that the cross section can be precisely measured using the solar-neutrino data themselves. This is possible because of independent knowledge of the $^8$B flux and survival probability, plus the distinctive angular distributions of the Fermi and Gamow-Teller transitions that comprise the cross section. We propose new methods to extract the transition strengths, considering both intuitive groupings and a Principal Component Analysis. Under pessimistic assumptions about detection, but taking detector uncertainties to be controlled, we demonstrate that a precision of $\lesssim$2% on the cross section can be achieved in the 9-15 MeV energy range. These results will be an important foundation for studying the cross section up to several tens of MeV, where the complexity increases significantly due to nuclear breakup channels but where reducing uncertainties is critical for supernova and atmospheric neutrino studies.

2606.19840 2026-06-19 hep-lat hep-ph nucl-th 交叉投稿

Scalar diquark mass and quark--diquark potential from lattice QCD using the potential method with a static quark

标量双夸克质量与夸克-双夸克势:基于静态夸克势方法的格点QCD研究

Kai-Wen Kelvin-Lee, Noriyoshi Ishii

AI总结 采用HAL QCD势方法,通过自洽确定双夸克质量并提取Cornell型夸克-双夸克势,发现弦张力与静态夸克-反夸克势结果在5%内一致。

Comments 6 pages, 3 figures

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AI中文摘要

我们通过将HAL QCD启发的势方法应用于由标量双夸克和静态夸克构成的重子系统,研究了标量双夸克质量和夸克-双夸克势。双夸克质量通过自洽方式确定,要求从两点关联函数得到的p波重子谱在势框架内得以重现。数值计算使用PACS-CS合作组生成的$2+1$味QCD规范场配置,在$L^{3} \times T = 32^{3} \times 64$格点上进行,$a^{-1} \approx 2.176$ GeV,π介子质量$m_{\pi} \approx 702$ MeV。通过分析,我们得到标量双夸克质量接近朴素组分夸克估计$(2/3)m_{N}$,同时得到Cornell型(库仑+线性)的夸克-双夸克势。从夸克-双夸克势提取的弦张力与从静态夸克-反夸克势(Wilson环)得到的结果在约5%内一致。

英文摘要

We study the scalar diquark mass and the quark--diquark potential by applying a HAL QCD-inspired potential method to a baryonic system composed of a scalar diquark and a static quark. The diquark mass is determined self-consistently by requiring that the p-wave baryonic spectrum obtained from two-point correlators be reproduced within the potential framework. Numerical calculations are performed using $2+1$ flavor QCD gauge configurations generated by the PACS-CS Collaboration on a $L^{3} \times T = 32^{3} \times 64$ lattice with $a^{-1} \approx 2.176$ GeV and the pion mass, $m_π \approx 702$ MeV. From the analysis, we obtain a scalar diquark mass which is close to the na\"ıve constituent quark estimate $ (2/3)m_{N}$, together with a quark--diquark potential of the Cornell type (Coulomb + linear). The string tension extracted from the quark--diquark potential agrees within approximately 5% with that obtained from the static quark--antiquark potential (Wilson Loop).

2606.20028 2026-06-19 nucl-ex nucl-th 交叉投稿

Probing flavor effects in the QCD parton shower using $\mathbf{{\rm D}^0}$-tagged jet angularities in proton$-$proton collisions at $\mathbf{ \sqrt{s} = 5.02}$ TeV

在质子-质子碰撞中利用 ${\rm D}^0$ 标记喷注角形度探测 QCD 部分子簇射中的味效应($\sqrt{s} = 5.02$ TeV)

ALICE Collaboration

AI总结 ALICE合作组首次测量了pp碰撞中${\rm D}^0$标记喷注的角形度,通过可调权重参数表征喷注内粒子的角分布和动量分布,发现低角权重下${\rm D}^0$标记喷注的角形度值小于包容喷注,为QCD死锥效应提供了证据,并利用PYTHIA 8模拟验证了结果。

Comments 24 pages, 6 captioned figures, 1 table, authors from page 19, submitted to PRD, figures at http://alice-publications.web.cern.ch/node/13375

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AI中文摘要

ALICE合作组首次测量了质子-质子(pp)碰撞中${\rm D}^0$标记喷注的角形度,质心能量为$\sqrt{s} = 5.02$ TeV。喷注角形度是一种强大的子结构观测量,通过可调的权重参数表征喷注内粒子的角分布和动量分布。改变喷注角形度中的角参数可以系统地探测对共线辐射和软辐射的敏感性,从而通过比较不同部分子引发的喷注来研究味依赖的碎裂和强子化。本文报告了分辨参数$R=0.4$的${\rm D}^0$标记和包容(胶子主导)带电粒子喷注角形度,在低喷注横动量范围($10 < p_{\rm T}^{\rm ch. \\, jet} < 20$ GeV/$c$)内,其中粲夸克质量效应最为显著。在低角权重(强调共线辐射)下,${\rm D}^0$标记喷注表现出比包容喷注更小的角形度值。这为大质量夸克辐射抑制——即QCD死锥效应——提供了证据。随着角权重增加(更强调大角辐射),${\rm D}^0$标记喷注与包容喷注分布之间的差异减小。这表明修正集中在喷注核心而非边缘。PYTHIA 8模拟定性地再现了${\rm D}^0$标记和包容带电粒子喷注的角形度,但对${\rm D}^0$标记喷注分布的再现优于包容喷注,为模型提供了强有力的新约束。这些结果提供了对味依赖碎裂的洞察,并为未来研究重离子碰撞中产生的夸克-胶子等离子体中的喷注修正建立了重要的基准。

英文摘要

The ALICE Collaboration presents the first measurements of ${\rm D}^0$-tagged jet angularities in proton$-$proton (pp) collisions at $\sqrt{s} = 5.02$ TeV. Jet angularities are powerful substructure observables that characterize the angular and momentum distributions of particles within jets via tunable weighting parameters. Varying the angular parameter in jet angularities allows for a systematic probe of the sensitivity to collinear and soft radiation, enabling the study of flavor-dependent fragmentation and hadronization through comparisons of jets initiated by different partons. This paper reports ${\rm D}^0$-tagged and inclusive (gluon-dominated) charged-particle jet angularities with a resolution parameter $R=0.4$ in the low jet transverse momentum range ($10 < p_{\rm T}^{\rm ch. \, jet} < 20$ GeV/$c$), where charm-quark mass effects are most significant. At low angular weight, which emphasizes collinear radiation, ${\rm D}^0$-tagged jets exhibit smaller angularity values than inclusive jets. This provides evidence for the radiation suppression from massive quarks -- a phenomenon known as the QCD dead-cone effect. As the angular weight increases, giving more emphasis to wide-angle radiation, the difference between ${\rm D}^0$-tagged and inclusive jet distributions decreases. This indicates that the modification is concentrated within the jet core rather than its edge. PYTHIA 8 simulations qualitatively reproduce both the angularity of ${\rm D}^0$-tagged and inclusive charged-particle jets, but reproduce the ${\rm D}^0$-tagged jet distributions better than those of inclusive jets, offering a powerful new constraint for models. These results provide insight into flavor-dependent fragmentation and establish an essential baseline for future studies of jet modifications in the quark-gluon plasma produced in heavy-ion collisions.

2606.20063 2026-06-19 hep-ph hep-ex nucl-ex nucl-th 交叉投稿

Toward Precision Fragmentation of $Ω_{3Q}$ Baryons: The OMG3Q1.1 Framework

迈向$\Omega_{3Q}$重子碎裂的精确化:OMG3Q1.1框架

Francesco Giovanni Celiberto

AI总结 提出OMG3Q1.1框架,结合双夸克启发输入和阈值感知DGLAP演化,首次给出$\Omega_{3Q}$重子碎裂函数的不确定性量化集,为稀有三重味重子提供精确基准。

Comments 52 pages, 7 figures, 1 table, 294 references. Includes F-MHOU and F-NPWF uncertainty replicas, threshold-aware HF-NRevo DGLAP evolution, and LHAPDF release at https://github.com/FGCeliberto/Collinear_FFs

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AI中文摘要

近年来重子领域的实验进展,包括双粲态观测,重新激发了人们对日益增重的强子系统产生机制的兴趣,并呼唤具有精度和不确定性控制的描述。我们提出用于同味全重$\Omega_{3Q}$重子在高能强子碰撞中碎裂的OMG3Q1.1框架。该构建将双夸克启发的组分重夸克和胶子道输入与HF-NRevo方案中阈值感知的DGLAP演化相结合。基于副本的策略一致地量化了微扰缺失高阶效应(F-MHOUs)和非微扰波函数不确定性(F-NPWFs),从而产生了$\Omega_{3Q}$扇区首个不确定性分辨的碎裂函数集。所得到的LHAPDF6网格被用于在(sym)JETHAD环境中研究HL-LHC和未来FCC上的半包含$\Omega_{3Q}$加喷注产生。OMG3Q1.1框架为稀有三重味重子建立了面向精确的基准,并为未来重味重子景观的研究提供了基础。

英文摘要

Recent experimental advances in the baryon sector, including the observation of doubly charmed states, have renewed interest in the production mechanisms of increasingly heavy hadronic systems, calling for precision and uncertainty-controlled descriptions. We present the OMG3Q1.1 framework for the fragmentation of same-flavor all-heavy $Ω_{3Q}$ baryons in high-energy hadronic collisions. The construction combines diquark-inspired inputs for constituent-heavy-quark and gluon channels with threshold-aware DGLAP evolution within the HF-NRevo scheme. A replica-based strategy consistently quantifies perturbative missing-higher-order effects (F-MHOUs) and nonperturbative wave-function uncertainties (F-NPWFs), yielding the first uncertainty-resolved fragmentation-function set for the $Ω_{3Q}$ sector. The resulting LHAPDF6 grids are employed to investigate semi-inclusive $Ω_{3Q}$ plus jet production at the HL-LHC and future FCC within the (sym)JETHAD environment. The OMG3Q1.1 framework establishes a precision-oriented baseline for rare triply heavy baryons and provides a foundation for future studies of the heavy-flavor baryon landscape.

2606.20362 2026-06-19 hep-ph nucl-th 交叉投稿

Revisiting the role of saturation in diffractive vector meson production

重新审视饱和在衍射矢量介子产生中的作用

Heikki Mäntysaari, Hendrik Roch, Björn Schenke, Chun Shen, Wenbin Zhao

AI总结 基于CGC框架,对γ+p和γ+Pb碰撞中的相干和非相干衍射J/ψ光产生进行全局贝叶斯分析,发现电磁离解校正显著降低了质子与核数据间的张力,实现了CGC框架内的一致描述。

Comments 8 pages, 4 figures

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AI中文摘要

我们使用基于色玻璃凝聚(CGC)的框架以及来自大型强子对撞机(LHC)的超外围碰撞数据(对预期的电磁离解(EMD)效应进行了校正),对γ+p和γ+Pb碰撞中的相干和非相干衍射J/ψ光产生进行了全局贝叶斯分析。利用底层CGC计算的高斯过程模拟器,我们从HERA和LHC测量的组合数据集中推断模型参数。我们发现,经过EMD校正的γ+Pb数据显著降低了先前观察到的质子与核数据集之间的张力,从而能够在CGC框架内一致地同时描述γ+p和γ+Pb碰撞中的衍射J/ψ产生。

英文摘要

We perform a global Bayesian analysis of coherent and incoherent diffractive $\mathrm{J}/ψ$ photoproduction in $γ+p$ and $γ+\mathrm{Pb}$ collisions using a Color Glass Condensate (CGC)-based framework and ultraperipheral collision data from the Large Hadron Collider (LHC), corrected for the expected effect of electromagnetic dissociation (EMD). Using Gaussian-process emulators of the underlying CGC calculations, we infer model parameters from a combined set of HERA and LHC measurements. We find that the $γ+\mathrm{Pb}$ data with EMD correction substantially reduce the previously observed tension between proton and nuclear datasets, enabling a consistent simultaneous description of diffractive $\mathrm{J}/ψ$ production in $γ+p$ and $γ+\mathrm{Pb}$ collisions within the CGC framework.

2606.20530 2026-06-19 hep-ph nucl-th 交叉投稿

Rotating magnetized pion gas of finite transverse size: condensation constraints and transport properties

有限横向尺寸的旋转磁化π介子气体:凝聚约束与输运性质

Ankit Kumar, Diwakar Gaur, Vinod Chandra

AI总结 研究旋转π介子气体在磁场中的电、热和热电响应,发现旋转作为有效化学势增强输运系数,克服磁场的抑制作用。

Comments 13 pages, 7 figures, two-column

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AI中文摘要

本文研究了在背景磁场中具有有限横向半径的旋转π介子气体的电、热和热电响应,其中旋转轴与磁场对齐。我们明确计算了π+凝聚的参数极限,并将工作区域严格限制在这些边界之外,以确保输运系数行为良好。值得注意的是,系统表现出凝聚不对称性,在诱导π+凝聚的参数下,π-保持未凝聚。使用弛豫时间近似下的玻尔兹曼输运方程,我们计算了纵向电导率、热导率和塞贝克系数。我们的结果揭示了磁场与旋转之间的竞争相互作用,突出了旋转对介质输运性质的显著影响:在静态介质中,磁场抑制输运系数,而旋转作为有效化学势引入能量位移,有利于输运系数的增加。超过某个角速度,这种旋转增强作用压倒了磁抑制,导致输运系数随磁场增加而增加。最后,通过洛伦兹数分析了电荷和热输运的相对重要性,进一步揭示了旋转磁化π介子介质的输运特性。

英文摘要

This work investigates the electric, thermal, and thermoelectric responses of a rotating pion gas of finite transverse radius in the presence of a background magnetic field, with the rotation axis aligned with the magnetic field. We explicitly calculate the parameter limits for $π^+$ condensation and restrict our working regime safely outside these boundaries, ensuring well-behaved transport coefficients. Notably, the system exhibits a condensation asymmetry, with $π^-$ remaining uncondensed at the parameters that induce $π^+$ condensation. Using the Boltzmann Transport Equation under the Relaxation Time Approximation, we calculate the longitudinal electrical conductivity, thermal conductivity, and the Seebeck coefficient. Our results reveal a competing interplay between the magnetic field and rotation, highlighting the substantial impact of rotation on the medium's transport properties: while the magnetic field suppresses the transport coefficients in a static medium, rotation, acting as an effective chemical potential, introduces an energy shift that favors their increase. Beyond an angular velocity, this rotational enhancement overpowers the magnetic suppression, leading to an increase in the transport coefficients with increasing magnetic field. Finally, we analyze the relative significance of charge and heat transport through the Lorenz number, providing further insight into the transport characteristics of the rotating magnetized pion medium.

2511.15385 2026-06-19 nucl-th nucl-ex 版本更新

A relativistic mechanism for the enhanced isovector spin-orbit interaction suggested by parity-violating electron scattering experiments

宇称破坏电子散射实验提示的增强同位旋矢量自旋-轨道相互作用的相对论机制

Mengying Qiu, Tong-Gang Yue, Zhen Zhang, Lie-Wen Chen

AI总结 通过相对论密度相关点耦合泛函框架,发现增强的同位旋矢量张量耦合可自然诱导强同位旋矢量自旋-轨道相互作用,为同时描述PREX-II和CREX结果提供可行途径。

Comments 19 pages, 13 figures, 5 tables. Accepted for publication in Physics Letters B

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AI中文摘要

近期对$^{208}$Pb(PREX-II)和$^{48}$Ca(CREX)的高精度宇称破坏电子散射(PVES)测量揭示,在现代核能量密度泛函(EDFs)中同时描述两者存在张力。对这些数据的分析表明,增强的同位旋矢量自旋-轨道相互作用可能有助于同时解释这两个测量结果,但其在协变密度泛函理论中的相对论起源仍有待阐明。我们证明,在协变密度相关点耦合EDF框架内,增强的同位旋矢量张量耦合可自然诱导如此强的同位旋矢量自旋-轨道相互作用。这一机制为同时描述PREX-II和CREX结果提供了一条有希望的途径,同时保持对有限核和核物质的合理描述。因此,对$^{48}$Ca的PVES为协变同位旋矢量张量相互作用提供了灵敏的探针。

英文摘要

Recent high-precision parity-violating electron scattering (PVES) measurements on $^{208}$Pb (PREX-II) and $^{48}$Ca (CREX) reveal a tension in their simultaneous description within modern nuclear energy density functionals (EDFs). Analyses of these data suggest that an enhanced isovector spin-orbit interaction may help account for both measurements, but its relativistic origin in covariant density functional theory remains to be clarified. We show that, within the framework of a covariant density-dependent point-coupling EDF, an enhanced isovector tensor coupling can naturally induce such a strong isovector spin-orbit interaction. This mechanism provides a promising route toward a simultaneous description of the PREX-II and CREX results while preserving a reasonable description of finite nuclei and nuclear matter. PVES on $^{48}$Ca thus provides a sensitive probe of the covariant isovector tensor interaction.

2602.22690 2026-06-19 nucl-th hep-ph 版本更新

Space-time regions of high baryon density and baryon stopping in heavy-ion collisions

重离子碰撞中高重子密度和重子阻止的时空区域

Yuri B. Ivanov

AI总结 使用三流体动力学模型计算中心Au+Au碰撞中高重子密度物质的四体积,发现3FD模型比JAM模型有更强的重子阻止,且高密度区域随能量单调变化,最优能量范围在3.2–8 GeV。

Comments 8 pages, 4 figures, version published in Phys.Rev.C

Journal ref Phys. Rev. C 113, 064906 (2026)

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AI中文摘要

在三流体动力学模型(3FD)中计算了四体积($V_4=$ 空间三维体积×寿命),并与JET AA微观输运模型(JAM)的结果进行了比较。计算针对中心Au+Au碰撞在能量$\sqrt{s_{NN}}=$ 3–19.6 GeV下进行。这些$V_4$指示了实现宏观高重子密度物质的最佳碰撞能量范围。发现3FD的四体积明显超过JAM中的四体积,这表明3FD模型中的重子阻止比JAM更强。论证了这种重子阻止的差异与这些模型中实现的状态方程(EoS)的硬度相关。与JAM相反,重子密度($n_B$)超过正常核密度($n_0$)三倍的四体积不随$\sqrt{s_{NN}}$呈现最大值。它随着$\sqrt{s_{NN}}$的增加单调递减,保持在相当宏观的水平(即$V_4\geq 5.5^4$ fm$^4$/c)。对于更高的重子密度,$V_4$在$\sqrt{s_{NN}}$依赖关系中呈现最大值。密度$n_B/n_0>$ 4的最佳能量范围位于$\sqrt{s_{NN}}=$ 3.2–8 GeV。即使对于$n_B/n_0>$ 6,在$\sqrt{s_{NN}}=$ 4.5–9 GeV时,四体积仍然相当宏观($V_4\geq 4^4$ fm$^4$/c),这与JAM相反。

英文摘要

Four-volumes ($V_4=$ spatial-3-volume$\times$lifetime) are calculated within the model of three-fluid dynamics (3FD) and compared with those of the the JET AA Microscopic Transport Model (JAM). The calculations are performed for central Au+Au collisions at energies $\sqrt{s_{NN}}=$ 3 -- 19.6 GeV. These $V_4$ indicate optimal collision-energy ranges for realizing macroscopic high baryon-density matter. It is found that the 3FD four-volumes noticeably exceed those in the JAM, which indicates a stronger baryon stopping in the 3FD model as compared to that JAM. It is argued that this difference in the baryon stopping correlates with stiffness of the EoS implemented in these models. Contrary to JAM, the four-volume, where a baryon density ($n_B$) exceeds three times the normal nuclear density ($n_0$), does not exhibit a maximum as a function of $\sqrt{s_{NN}}$. It decreases monotonically with increasing $\sqrt{s_{NN}}$, remaining at a fairly macroscopic level (i.e. $V_4\geq 5.5^4$ fm$^4$/c). For higher baryon densities, $V_4$ exhibits maxima in its dependence on $\sqrt{s_{NN}}$. The optimal energy range for densities $n_B/n_0>$ 4 is located at $\sqrt{s_{NN}}=$ 3.2 -- 8 GeV. Even for $n_B/n_0>$ 6, the four-volume remains quite macroscopic ($V_4\geq 4^4$ fm$^4$/c) at $\sqrt{s_{NN}}=$ 4.5 -- 9 GeV contrary to the JAM.

2410.22688 2026-06-19 nucl-ex hep-ex hep-ph nucl-th 版本更新

Azimuthal Anisotropy Scaling Functions for Identified Particle and Anti-Particle Species across Beam Energies: Insights into Baryon Junction Effects

跨束流能量的鉴别粒子与反粒子方位角各向异性标度函数:重子结效应洞察

Roy A. Lacey

AI总结 通过构建跨束流能量的方位角各向异性标度函数,分离了集体流与淬火区域,揭示了重子结驱动的净重子输运和QCD临界区附近的比剪切粘度最小值。

Comments Published version

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AI中文摘要

从Pb+Pb($\sqrt{s_{NN}}$=2.76, 5.02~TeV)和Au+Au($\sqrt{s_{NN}}$=7.7--200~GeV)碰撞中物种分辨的各向异性测量构建了方位角各向异性标度函数,以探测有限重子化学势($\mu_B$)下的重子输运和介质响应。在此数据驱动框架内,跨越集体流和淬火区域的介子和重子各向异性坍缩到共同的标度曲线上,从而能够定量分离粘性衰减、径向流和强子再散射。衰减标度$k_\beta$表现出非单调的束流能量依赖性,与低能下强子再散射的上升相一致,这与温度依赖的比剪切粘度在QCD临界区域附近接近最小值一致。在LHC能量下,有效径向流响应中电荷奇异的重子-反重子分离可忽略,但随$\sqrt{s_{NN}}$降低而增大。这种跨$p,\Lambda,\Xi,\Omega$和$d$的物种均匀、重子数标度的分离排除了纯强子起源,支持有限$\mu_B$下结驱动的净重子输运,增强了有限快速演化系统中临界动力学的实验可见性。这些结果共同确立了物种分辨的标度函数作为约束重子停止、介质不透明度和QGP输运性质的紧凑而稳健的工具。

英文摘要

Azimuthal anisotropy scaling functions are constructed from species-resolved anisotropy measurements in Pb+Pb ($\sqrt{s_{NN}}$=2.76, 5.02~TeV) and Au+Au ($\sqrt{s_{NN}}$=7.7--200~GeV) collisions to probe baryon transport and medium response at finite baryon chemical potential ($μ_B$). Within this data-driven framework, meson and baryon anisotropies spanning the collective-flow and quenching regimes collapse onto common scaling curves, enabling quantitative separation of viscous attenuation, radial flow, and hadronic re-scattering. The attenuation scale $k_β$ exhibits a non-monotonic beam-energy dependence, coincident with the low-energy rise of hadronic re-scattering, consistent with a temperature-dependent specific shear viscosity featuring a near-minimum near the QCD critical region. A charge-odd baryon--antibaryon separation in the effective radial-flow response is negligible at LHC energies but grows toward lower $\sqrt{s_{NN}}$. This species-uniform, baryon-number-scaling separation across $p,Λ,Ξ,Ω$, and $d$ disfavors a purely hadronic origin and supports junction-driven net-baryon transport at finite $μ_B$, enhancing the experimental visibility of critical dynamics in finite, rapidly evolving systems. Together, these results establish species-resolved scaling functions as a compact and robust tool for constraining baryon stopping, medium opacity, and QGP transport properties.

2506.18905 2026-06-19 hep-ph nucl-th 版本更新

Relativistic corrections to exclusive photoproduction of Quarkonia near-threshold

近阈值区域夸克偶素独家光产生的相对论修正

Sarah K. Blask, Sean Fleming, Thomas Mehen, Jyotirmoy Roy, Iain W. Stewart, Fanyi Zhao

AI总结 利用非相对论QCD在广义部分子分布框架下计算近阈值区域矢量夸克偶素独家光产生振幅的相对论修正,发现J/ψ的修正很大,导致GPD矩展开在阈值附近失效,并计算了J/ψ和Υ的截面。

Comments 17 pages, 7 figures, additional calculations and discussion added, new figures added, typographical errors fixed

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AI中文摘要

在广义部分子分布(GPD)框架内,使用非相对论QCD(NRQCD)计算近阈值区域矢量夸克偶素独家光产生振幅的相对论修正。发现对于$J/\psi$,相对论修正很大,并导致GPD矩展开在阈值附近失效。计算了$J/\psi$和$\Upsilon$的截面,并将前者与数据进行了比较。我们还证明了在远离近阈值区域时,相对论修正存在端点发散。

英文摘要

Non-relativistic QCD (NRQCD) is used to calculate the relativistic correction to the amplitude for exclusive photoproduction of vector Quarkonia in the near-threshold region within the generalized parton distribution (GPD) framework. The relativistic corrections are found to be large for $J/ψ$, and lead to a breakdown of the GPD moment expansion near threshold. Cross-sections for both $J/ψ$ and $Υ$ are calculated with the former being compared to the data. We also demonstrate the presence of endpoint divergences for the relativistic correction away from the near-threshold regime.

2507.17955 2026-06-19 hep-ph hep-ex nucl-th 版本更新

Constraints on millicharged particles from nuclear gamma-decays

核伽马衰变对毫电荷粒子的约束

Ting Gao, Maxim Pospelov

AI总结 研究核反应堆中铀-239的伽马级联产生毫电荷粒子对,计算通量并利用电子反冲实验数据导出毫电荷上限,在0.7-2 MeV质量区间内最强。

Comments 19 pages, published version

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AI中文摘要

我们考虑核伽马衰变和伽马发射反应,这些反应可以是假设的毫电荷粒子(χ)的有效来源。特别是,我们重新审视了核反应堆环境中毫电荷粒子的产生,指出$^{239}$U的伽马级联是产生χ$\bar\chi$对的被忽视但强大的来源。与以往研究相比,这导致了更高的通量。然后,我们应用新的通量估计,从靠近反应堆堆芯的各种实验中搜索的电子反冲中推导出毫电荷值ε = Q_χ/e的新限制。导出的ε限制在质量区间~0.7-2 MeV内是最强的。我们还推导了来自太阳的MCP通量,并指出了低阈值暗物质搜索实验的潜在灵敏度。

英文摘要

We consider nuclear gamma decays and $γ$-emitting reactions that can be an efficient source of hypothetical millicharged particles ($χ$). In particular, we revisit the production of millicharged particles in nuclear reactor environment, pointing out that $γ$ cascades from $^{239}$U is an overlooked yet a powerful source of $χ\barχ$ pairs. This leads to an increased flux compared to previous studies. We then apply new estimates of the flux to derive novel limits on the value of millicharge, $\varepsilon = Q_χ/e$, from the electron recoil searched for in a variety of experiments placed in proximity to the reactor cores. The derived limits on $\varepsilon$ are the strongest in the interval of masses $\sim 0.7-2$ MeV. We also derive the MCP flux from the Sun and point out potential sensitivity of the low-threshold dark matter search experiments.

2509.25098 2026-06-19 hep-ph hep-ex nucl-ex nucl-th 版本更新

New insights from the flavor dependence of quark transverse momentum distributions in the pion

从π介子中夸克横向动量分布的味道依赖性获得的新见解

Lorenzo Rossi, Alessandro Bacchetta, Matteo Cerutti, Marco Radici

AI总结 通过改进理论不确定性描述并首次探索夸克味道差异,更新了π介子中非极化夸克的横向动量分布提取。

Comments The MAP (Multi-dimensional Analysis of Partonic distributions) Collaboration; 10 pages, 7 (multiple) figures

Journal ref Phys. Lett. B 877 (2026) 140482

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AI中文摘要

我们更新了先前对π介子中非极化夸克横向动量分布的提取,通过实施更全面的理论不确定性描述,并首次探索夸克味道之间可能存在的差异。我们从所有可用的非极化π-核Drell-Yan过程数据中提取这些分布,其中截面是末态轻子对横向动量的微分。该截面涉及核子中的横向动量分布,我们一致地取自先前的研究。

英文摘要

We update our previous extraction of transverse momentum distributions of unpolarized quarks in the pion by implementing a more comprehensive description of theoretical uncertainties and, for the first time, by exploring possible differences among quark flavors. We extract such distributions from all available data for unpolarized pion-nucleus Drell-Yan processes, where the cross section is differential in the transverse momentum of the final lepton pair. The cross section involves transverse momentum distributions in the nucleon, that we consistently take from our previous studies.

2601.18882 2026-06-19 hep-ph hep-th nucl-th 版本更新

Next-to-next-to-leading power corrections to unpolarized Semi-Inclusive Deep Inelastic Scattering

非极化半单举深度非弹性散射的次次领头幂次修正

Ian Balitsky, Alexei Prokudin

AI总结 本文利用快度因子化形式,推导了非极化半单举深度非弹性散射(SIDIS)中次次领头幂次(NNLP)修正的解析表达式,包括非极化分布与碎裂函数以及Boer-Mulders函数与Collins碎裂函数的卷积,并与实验数据进行了比较。

Comments 30 pages, 15 figures, JHEP published version

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AI中文摘要

半单举深度非弹性散射(SIDIS)是通过横向动量依赖的部分子分布和碎裂函数探索核子三维结构的关键工具。虽然SIDIS截面的领头幂次贡献已得到充分研究,但次领头幂次(NLP,$1/Q$阶)和次次领头幂次(NNLP,$1/Q^2$阶)对强子张量的修正直到最近才开始被系统研究。这些修正对于现代高精度数据的可靠唯象学和解释至关重要。在作者近期的工作中,利用快度因子化形式推导了Drell-Yan过程的NNLP修正。本文将此方法推广到SIDIS,并得到了非极化结构函数的解析表达式。我们推导的NNLP修正包括非极化分布$f_1$与非极化碎裂函数$D_1$的卷积,以及Boer-Mulders函数$h_1^\perp$与Collins碎裂函数$H_1^\perp$的卷积。我们将结果与先前公式进行了比较,提供了数值研究,将预测与HERMES和COMPASS测量进行了对比,并给出了未来在Jefferson Lab和电子-离子对撞机上实验的预测。

英文摘要

Semi-Inclusive Deep Inelastic Scattering (SIDIS) is a key tool for exploring the three-dimensional structure of the nucleon through Transverse Momentum Dependent parton distributions and fragmentation functions. While leading-power contributions to the SIDIS cross-section are well established, next-to-leading (NLP) of order $1/Q$ and next-to-next-to-leading power (NNLP) corrections of order $1/Q^2$ to the hadronic tensor have only recently begun to be systematically investigated. These corrections are essential for the reliable phenomenology and interpretation of modern high-precision data. In recent papers by one of the authors, NNLP corrections to Drell-Yan process were derived using rapidity factorization formalism. In the present work we extend this approach to SIDIS and obtain analytic expressions for the unpolarized structure functions. We derive NNLP corrections that include convolutions of unpolarized distributions, $f_1$, with unpolarized fragmentation functions, $D_1$, and Boer-Mulders functions, $h_1^\perp$, with Collins fragmentation functions, $H_1^\perp$. We compare our results with previous formulations, provide numerical studies, confront our predictions with HERMES and COMPASS measurements, and present predictions for future experiments at Jefferson Lab and the Electron-Ion Collider.

2606.05305 2026-06-19 hep-lat hep-ph hep-th nucl-th 版本更新

Gauge field flow for chiral gauge theories on a disk boundary

圆盘边界上手征规范理论的规范场流

Jinlong Dang, Rohith Karur, Srimoyee Sen

AI总结 本文提出在方形格点嵌入圆盘上实现运动方程流的具体方案,并演示格点上异常流入与异常抵消机制。

Comments minor typos corrected and references updated

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AI中文摘要

最近一种$2n$维手征规范理论的非微扰表述依赖于在$2n+1$维圆盘流形的$2n$维边界上实现手征费米子。该表述还要求使用某种保持$2n$维规范不变性的流方案将边界规范构型扩展到圆盘内部。本文提出了在方形格点嵌入圆盘上运动方程流的具体实现。此外,我们将流规范场与费米子耦合,并在格点上演示了异常流入和异常抵消机制的作用。

英文摘要

A recent non-perturbative formulation of $2n$ dimensional chiral gauge theories relies on realizing chiral fermions on the $2n$ dimensional boundary of a $2n+1$ dimensional disk manifold. It also requires extending boundary gauge configurations into the interior of the disk using some flow prescription that preserves 2n dimensional gauge invariance. In this paper we propose a concrete realization of the equation of motion flow with the disk embedded on a square lattice. In addition, we couple the flow gauge field to fermions and demonstrate the mechanism of anomaly inflow and anmaly cancellation at work on the lattice.

2606.05306 2026-06-19 hep-lat hep-ph hep-th nucl-th 版本更新

Gauge field flow for chiral gauge theories on a slab

平板上的手征规范理论的规范场流

Jinlong Dang, Rohith Karur, Srimoyee Sen

AI总结 本文提出在平板几何的2n+1维欧几里得格点上,利用畴壁费米子构造手征规范理论,通过梯度流将规范场延伸到额外维度以解耦反壁上的镜像费米子,并实现了EOM流,在格点上展示了流守恒和反常流入机制。

Comments minor typo corrections, references updated

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AI中文摘要

使用平板几何的$2n+1$维欧几里得格点上的畴壁费米子来表述手征规范理论的提议,涉及位于其中一个畴壁上的$2n$维动力学规范场。通过梯度流将规范场延伸到额外维度,从而解耦反壁上的镜像费米子。我们在存在$2n$维背景规范场的情况下,在$n=1$的格点上实现了这一构造。我们还制定并实现了另一种规范场流方案,其中规范场在远离畴壁处满足$2n+1$维运动方程,称为EOM(运动方程)流。在这两种情况下,我们将规范场与费米子耦合,并在格点上演示了流守恒和反常流入如何工作。

英文摘要

The proposal to formulate chiral gauge theories using domain wall fermions on $2n+1$ dimensional Euclidean lattice with a slab geometry involves $2n$ dimensional dynamical gauge fields residing on one of the domain walls. The gauge fields are extended into the extra dimension using gradient flow decoupling the mirror fermions on the anti-wall. We implement this construction on the lattice for $n=1$ in the presence of $2n$ dimensional background gauge fields. We also formulate and implement an additional gauge field flow proposal, where the gauge fields satisfy $2n+1$ dimensional equation of motion away from the domain wall, known as the EOM (equation of motion) flow. In both cases, we couple the gauge fields to fermions and demonstrate how current conservation and anomaly inflow work on the lattice.

2606.14166 2026-06-19 hep-ph hep-ex nucl-th 版本更新

Thermal dileptons to probe the baryon-rich QCD matter in the forward region of LHC energy heavy-ion collisions

热双轻子探测LHC能量重离子碰撞前向区域富重子QCD物质

Motomi Oya, Nicholas J. Benoit, Chiho Nonaka, Azumi Sakai, Yorito Yamaguchi

AI总结 在LHC能量下,通过(3+1)维流体动力学框架研究有限重子化学势对前向快度区域热双轻子产生的影响,发现重子密度导致双轻子产额减少3-4%,但有效温度仍与早期QGP温度强相关。

Comments 11 pages, 9 figures

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AI中文摘要

我们研究了在$\sqrt{s_{\text{NN}}}=5.02~\text{TeV}$的中心Pb-Pb碰撞中,具有有限重子化学势($\mu_{\text{B}}$)的夸克-胶子等离子体(QGP)的热双轻子产生。最近的研究表明,即使在LHC能量下,前向快度区域也能达到可观的重子密度。我们将有限$\mu_{\text{B}}$纳入(3+1)维流体动力学框架,并发现$\mu_{\text{B}}$在介质演化过程中在$\eta_\text{s}=6$附近超过500 MeV。利用该框架,我们计算了宽快度范围内的热双轻子谱,并评估了有限$\mu_{\text{B}}$对双轻子产生的影响。在前向快度区域$5.2 < y < 7.2$,由于有限重子密度下夸克-反夸克丰度降低,观察到3-4%的抑制。我们进一步检查了从中间质量区域$1.2 < M_{\ell \ell} < 2.6~\text{GeV}$的双轻子质谱中提取的有效温度。有效温度与底层流体动力学温度保持强相关,并对QGP演化的早期高温阶段保持敏感性。这些结果表明,前向快度双轻子仍然是有效的温度计,同时提供了对LHC有限重子密度的敏感性。

英文摘要

We investigate thermal dilepton production from a quark-gluon plasma (QGP) with finite baryon chemical potential ($μ_{\text{B}}$) in central Pb-Pb collisions at $\sqrt{s_{\text{NN}}}=5.02~\text{TeV}$. Recent studies suggest that sizable baryon densities can be achieved at forward rapidity even at LHC energies. We incorporate finite $μ_{\text{B}}$ into a (3+1)-dimensional hydrodynamic framework and find that $μ_{\text{B}}$ exceeds 500 MeV around $η_\text{s} = 6$ during the medium evolution. Using this framework, we calculate thermal dilepton spectra over a wide rapidity range and evaluate the impact of finite $μ_{\text{B}}$ on dilepton production. A suppression of 3-4% is observed in the forward-rapidity region $5.2 < y < 7.2$ due to the reduced quark-antiquark abundance at finite baryon density. We further examine the effective temperature extracted from dilepton mass spectra in the intermediate-mass region $1.2 < M_{\ell \ell} < 2.6~\text{GeV}$ . The effective temperature remains strongly correlated with the underlying hydrodynamic temperature and retains sensitivity to the early high-temperature stage of the QGP evolution. These results demonstrate that forward-rapidity dileptons remain effective thermometers while providing sensitivity to finite baryon density at the LHC.

2512.07977 2026-06-19 nucl-th astro-ph.HE hep-ph 版本更新

Rapidly Spinning Massive Pulsars as an Indicator of Quark Deconfinement

Christoph Gärtlein, Violetta Sagun, Oleksii Ivanytskyi, David Blaschke, Ilídio Lopes

Comments Proceedings of XQCD 2025

Journal ref J. Subatomic Part. Cosmol. 5, 100286 (2026)

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英文摘要

We study rotating hybrid stars, with particular emphasis on the effect of spin on the deconfinement phase transition and star properties. Our analysis is based on a hybrid equation of state with a phase transition from hadronic matter containing hyperons to color-superconducting quark matter, where the quark phase is modeled within a relativistic density functional approach. By varying the strength of the vector repulsion and diquark pairing couplings in the microscopic quark Lagrangian, we construct a set of hybrid star sequences with different quark-matter onset densities. This framework ensures consistency with astrophysical and gravitational wave constraints on mass, radius, and tidal deformability.

2512.03876 2026-06-19 nucl-th hep-th physics.plasm-ph 版本更新

Generalized Beth--Uhlenbeck entropy formula from the $Φ-$derivable approach

David Blaschke, Gerd Röpke, Gordon Baym

Comments 10 pages, 3 figures, contribution to the special issue of "Contributions to Plasma Physics" on the occasion of the 65th birthday of Michael Bonitz

Journal ref Contributions to Plasma Physics 0, e70145 (2026)

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英文摘要

We derive a generalized Beth-Uhlenbeck formula for the entropy of a dense fermion system with strong two-particle correlations, including scattering states and bound states. We work within the $Φ-$derivable approach to the thermodynamic potential. The formula takes the form of an energy-momentum integral over a statistical distribution function times a unique spectral density. In the near mass-shell limit, the spectral density reduces, contrary to naïve expectations, not to a Lorentzian but rather to a "squared Lorentzian" shape. The relation of the Beth-Uhlenbeck formula to the $Φ$-derivable approach is exact at the two-loop level for $Φ$. The formalism we develop, which extends the Beth-Uhlenbeck approach beyond the low-density limit, includes Mott dissociation of bound states, in accordance with Levinson's theorem, and the self-consistent back reaction of correlations in the fermion propagation. We discuss applications to further systems, such as quark matter and nuclear matter.