Nuclear Theory·nucl-th

Tuesday·December 31, 2024

23 papers—8 primary·15 cross-listed

09
Semi-Classical Spin Hydrodynamics in Flat and Curved Spacetime: Covariance, Linear Waves, and Bjorken Background
Annamaria Chiarini🇩🇪 · Julia Sammet🇩🇪 · Masoud Shokri🇩🇪
We explore various aspects of semi-classical spin hydrodynamics, where hydrodynamic currents are derived from an expansion in the reduced Planck constant $ℏ$ , incorporating both flat and curved spacetimes. After establishing covariant definitions for angular momentum currents, we demonstrate that the conservation of the energy-momentum tensor requires modifications involving the Riemann curvature and the spin tensors. We also revise pseudo-gauge transformations to ensure their applicability in curved spacetimes. Key assumptions for semi-classical spin hydrodynamics are introduced, enabling studies without explicitly invoking quantum kinetic theory. We derive and analyze the linearized semi-classical spin hydrodynamic equations, proving that spin and fluid modes decouple in the linear regime. As a concrete example, we study the ideal-spin approximation in a dissipative fluid with shear viscosity. This analysis confirms our general result: the damping of spin waves is governed solely by spin relaxation time coefficients, independent of linear fluid perturbations. We also examine the Gibbs stability criterion and reveal its limitations at first order in $ℏ$ , signaling the inherent anisotropy of the equilibrium state, which remains unaddressed in current semi-classical spin hydrodynamics formulations. Finally, within a conformal Bjorken flow background and using the slow-roll approximation attractor for the fluid sector, we show that the relaxation of the spin potential is governed by spin relaxation time coefficients, mirroring the damping behavior of spin waves in the linear regime.
↳ gr-qchep-phhep-thnucl-thPRD(2026)·10 citations
10
Moments from Momentum Derivatives in Lattice QCD
Zhuoyi Pang🇨🇳 · Jian-Hui Zhang🇨🇳 · Dian-Jun Zhao🇨🇳
We show that the traditional moments approach in lattice QCD, based on operator product expansion (OPE), can be realized in a way that utilizes derivatives in momentum rather than in distance. This also avoids power divergent mixings, and thus allows to extract moments order by order, to all orders in principle. Moreover, by exploiting the symmetry of lattice matrix elements,we can determine the even and odd moments separately. As a demonstrative example, we determine the first three moments beyond the tensor charge gT of the isovector quark transversity distribution in the nucleon.
↳ hep-lathep-phhep-thnucl-ex+1CPC(2025)·5 citations
11
Pion fragmentation functions from a quark-jet model in a functional approach
Roberto Correa da Silveira🇧🇷 · Fernando E. Serna🇨🇴 · Bruno El-Bennich🇧🇷
The elementary fragmentation function that describes the process $q \to π$ is predicted applying crossing and charge symmetry to the cut diagram of the pion valence quark distribution function. This elementary probability distribution defines the ladder-kernel of a quark jet fragmentation equation, which is solved self-consistently to obtain the full pion fragmentation function. The hadronization into a pion employs the complete Poincaré invariant Bethe-Salpeter wave function, though the overwhelming contribution to the fragmentation function is due the leading Bethe-Salpeter amplitude. Compared to a Nambu--Jona-Lasinio model prediction, the fragmentation function we obtain is enhanced in the range $z ≲ 0.8$ but otherwise in good qualitative agreement. The full pion fragmentation function is overall greater than the elementary fragmentation function below $z ≲ 0.6$ .
↳ hep-phhep-exnucl-exnucl-thPRC(2025)·3 citations
12
Gauge covariance of the gap equation: from the rainbow truncation to gauge symmetry constraints
Bruno El-Bennich🇧🇷
The gauge covariance of the quark gap equation is compared for three quark-gluon vertices: the bare vertex, a Ball-Chiu like vertex constrained by the corresponding Slavnov-Taylor identity, and a full vertex including the transverse components derived from transverse Slavnov-Taylor identities. The covariance properties are verified with the chiral quark condensate and the pion decay constant in the chiral limit.
↳ hep-phhep-latnucl-thSymmetry(2025)·1 citation
13
The nucleon properties in finite temperature and density with vector meson
Bingtao Li🇨🇳 · Yiming Lyu🇨🇳 · Song Shu🇨🇳 · PeiXin Weng🇨🇳 · Hui Zhang🇨🇳
We introduce the vector meson $ω$ into the Quark Meson model, and study the impact of vector interactions on the properties of static hadrons using the mean-field approximation. The short-range repulsive force associated with vector interactions leads to an expansion of the root mean square radius of nucleons. While the mass of hadrons increases, the gap between this mass and the energy of the three free constituent quarks decreases, resulting in the instability of hadrons. Our study of nucleon mass and radius at finite temperature and density has potential applications for particle yield in heavy ion collisions and the mass-radius relationship in compact stars.
↳ hep-phhep-thnucl-th2 citations
14
The nucleon properties in finite temperature and density with Gaussian fluctuations
Peixin Weng🇨🇳 · Bingtao Li🇨🇳 · Yiming Lyu🇨🇳 · Song Shu🇨🇳 · Hui Zhang🇨🇳
We investigate the properties of nucleons at finite temperature and density using a two-flavor quark meson model with Gaussian fluctuations that extend beyond the mean-field approximation. Our findings suggest that Gaussian fluctuations lead to a non-monotonic behavior of the nucleon mass as a function of temperature and density, which may play an important role in the study of the hadronization process of relativistic heavy-ion collisions. Moreover, we observe an increase in the nucleon radius due to Gaussian fluctuations, suggesting an effective repulsive force akin to the Casimir effect, as observed in the gold-bromobenzene-silica system. This study offers new insights into how temperature, density, and quantum fluctuations affect the structure and properties of nucleons under extreme conditions.
↳ hep-thhep-phnucl-thPLB(2025)·1 citation
15
The Spectra of $p Λ ˉ$ and $p Σ ˉ$ Hexaquark States
Xuan-Heng Zhang🇨🇳 · Sheng-Qi Zhang🇨🇳 · Cong-Feng Qiao🇨🇳
Motivated by the observation of the $J^{P} = 1^{+}$ resonance $X (2085)$ in the $p Λ ˉ$ system by the BESIII collaboration, we studied the molecular states of hexaquarks $p Λ ˉ$ and $p Σ ˉ$ with baryon-antibaryon structures within the framework of the QCD sum rules. Non-perturbative contributions up to dimension 13 were considered in our analysis. The results indicate the existence of six possible molecular states $p Λ ˉ$ and $p Σ ˉ$ , with quantum numbers $J^{P} = 0^{-}, 0^{+}, 1^{-}$ . Consequently, the current sum rule results do not support the interpretation of $X (2085)$ as a $p Λ ˉ$ or $p Σ ˉ$ molecular state. On the other hand, we find that the masses of the proposed $p Λ ˉ$ and $p Σ ˉ$ structures with $J^{P} = 1^{-}$ are in the vicinity of observed $X (2075)$ , which implies that the nature of this state needs more invistigations. Moreover, the possible decay modes of the concerned hexaquark states are analyzed.
↳ hep-phhep-exnucl-thEPJC(2025)·11 citations
16
Spectral sum rules and phase transition in strongly coupled QCD
Yi-Lun Du🇨🇳 · Nan Su · Konrad Tywoniuk🇳🇴
By incorporating contributions from both the (chromo)electric scale $g T$ and (chromo)magnetic scale $g^{2} T$ , we establish spectral sum rules of quarks for strongly coupled QCD that respect Fermi-Dirac statistics as required by quantum mechanics. In sharp contrast to QED and weakly coupled QCD whose spectral functions consist of discontinuous zero-dimensional (poles) and one-dimensional (branch cuts) non-analytic contributions from real energy $p_{0} \in R$ , the derived spectral function for strongly coupled quarks features continuous but non-analytic contributions from complex energy $p_{0} \in C$ that are two-dimensional in nature. In light of the novel sum rules, we uncover an intrinsic QCD transition between a three-mode phase at small coupling and a one-mode phase at large coupling. The transition is induced by the magnetic scale that generates a massless hydro-like mode with the genuine non-Abelian feature of positivity violation and serving as the Goldstone mode of the Lorentz symmetry breaking. The thermal mass serves as an order parameter of the transition and vanishes at large coupling in line with phenomenological predictions from Dyson-Schwinger equations and gauge/gravity duality. This result provides novel insights into the mechanism of the QCD deconfinement transition.
↳ hep-thhep-lathep-phnucl-th2 citations
17
Flavour-Dependent Chemical Freeze-Out of Light Nuclei in Relativistic Heavy-Ion Collisions
Rishabh Sharma🇮🇳 · Fernando Antonio Flor🇺🇸 · Sibaram Behera🇮🇳 · Chitrasen Jena🇮🇳 · Helen Caines🇺🇸
We study the production of light nuclei in Au+Au collisions at $s_{NN}$ = 7.7 - 200 GeV and Pb+Pb collisions at $s_{NN}$ = 2.76 and 5.02 TeV within a flavour-dependent freeze-out framework, assuming different flavoured hadrons undergo separate chemical freeze-out. Using the Thermal-FIST package, thermal parameters extracted from fits to various sets of hadron yields, including and excluding light nuclei, are used to calculate the ratios of the yields of light nuclei, namely, $d / p$ , $d ˉ / p ˉ$ , $t / p$ , and $t / d$ . A comparison with data from the STAR and ALICE collaborations shows that a sequential freeze-out scenario provides a better description of light nuclei yield ratios than the traditional single freeze-out approach. These results suggest the flavour-dependent chemical freeze-out for final state light-nuclei production persists in heavy-ion collisions at both RHIC and LHC energies.
↳ hep-phhep-exnucl-thEPJC(2025)·2 citations
18
Possible scenario of dynamical chiral symmetry breaking in the instanton liquid
Yamato Suda🇯🇵 · Daisuke Jido🇯🇵
Based on simulations of the interacting instanton liquid model (IILM) with three-flavor quarks, we compute the free energy density of the QCD vacuum as a function of the quark condensate. We then evaluate the second derivative of the free energy density with respect to the quark condensate at the origin. This evaluation allows us to investigate whether chiral symmetry breaking in the IILM occurs in an anomaly-driven way. Such a breaking pattern of chiral symmetry has been proposed in a previous study to connect the QCD vacuum structure with meson properties, such as the mass of the sigma meson. We also perform the quenched simulations, in which no dynamical quarks interact with instantons. Comparing these results with the full calculations provides a better understanding of the pattern of chiral symmetry breaking in the IILM. We find that in the full IILM, chiral symmetry is dynamically broken in anomaly-driven way, whereas in the quenched IILM, it is broken through the ordinary mechanism. Based on these results, we suggest that chiral symmetry breaking in real QCD could also occur in an anomaly-driven way. Consequently, in phenomena where chiral symmetry breaking plays a crucial role, the anomaly effect may also have significant influence.
↳ hep-phnucl-thPoS(2025)·0 citations
19
Response of superfluid fermions at finite temperature
Sumit Bhattacharjee · Elena Litvinova
A consistent finite-temperature microscopic theory for the response of strongly coupled superfluid fermionic systems is formulated. We start from the general many-body Hamiltonian with the vacuum (bare) two-fermion interaction and derive the equation of motion (EOM) for the thermally averaged two-time two-fermion correlation function, which determines the spectrum of the system under study. The superfluidity is introduced via the Bogoliubov transformation of the fermionic field operators, and the entire formalism is carried out in the basis of Bogoliubov's quasiparticles, keeping the complete 4x4 block matrix structure of the two-fermion EOM. Fully correlated static and dynamical interaction kernels of the resulting EOM are discussed. A special focus is then placed on the latter kernel, which is advanced to a factorized form, enabling a minimal truncation of the many-body problem while keeping important effects of emergent collectivity and mapping to the quasiparticle-vibration coupling (qPVC). As in the zero-temperature and non-superfluid cases, the qPVC can be associated with a new order parameter, qPVC vertex. In the thermal superfluid theory, the latter vertex, as well as the components of the dynamical kernel, acquire an extended form including thermally unblocked transition amplitudes.
↳ cond-mat.quant-gasnucl-th1 citation
20
Emergence, Formation and Dynamics of Hot QCD Matter
Bruno Sebastian Scheihing-Hitschfeld🇺🇸
In this thesis, we make progress in two concrete directions in the vast landscape of hot QCD physics. The first one is quarkonium transport inside quark-gluon plasma (QGP), the high temperature phase of QCD. Over the past two decades it has been realized that a significant fraction of quarkonium suppression in high energy heavy ion collisions comes from dynamic dissociation and recombination processes, instead of static screening of the interaction potential as originally proposed by Matsui and Satz. Our contribution is the formulation of the precise correlation functions in QCD at finite temperature that describe the dissociation and recombination processes of heavy quarkonium in QGP, as well as their calculation in weakly coupled QCD and strongly coupled $N = 4$ supersymmetric Yang-Mills theory. We also formulate the Euclidean version of these correlation functions so that they may be calculated using Lattice QCD techniques. The second contribution we make is the development of tools to understand the process of hydrodynamization in QCD kinetic theory and their application to a simplified description where only a subset of the QCD scattering mechanisms are included. By doing this, we learn that the process of hydrodynamization in this theory, and specifically, how memory of the initial condition is lost, follows the recently proposed Adiabatic Hydrodynamization scenario. Concretely, hydrodynamization proceeds through a sequential process in which a monotonously shrinking set of low-energy states dominate the dynamics, where the opening of an energy gap relative to the ground state(s) signals the start of each stage of this process. The hydrodynamic attractor is reached when only one low-energy state remains as the ground state, and the system approaches local thermal equilibrium following the adiabatic evolution of this low-energy state.
↳ hep-phhep-thnucl-th2 citations
21
Constraining the $f$ -mode oscillations frequency in Neutron Stars through Universal Relations in the realm of Energy-Momentum Squared Gravity
Sayantan Ghosh🇮🇳
Neutron stars (NSs), superdense objects with exceptionally strong gravitational fields, provide an ideal laboratory for probing general relativity (GR) in the high-curvature regime. They also present an exciting opportunity to explore new gravitational physics beyond the traditional framework of GR. Thus, investigating alternative theories of gravity in the context of superdense stars is intriguing and essential for advancing our understanding of gravitational phenomena in extreme environments. Energy-Momentum Squared Gravity (EMSG) is a modified theory of gravity that extends GR by including nonlinear terms involving the energy-momentum tensor $T_{μν}$ . This study examines the effects of EMSG on the properties and behaviour of NSs by varying the free parameter $α$ . The hydrostatic equilibrium equations in the EMSG framework are derived and solved numerically to obtain mass-radius relations for soft, stiff, and intermediate equations of state (EOS). Observational measurements of NS masses and radii are used to constrain the fundamental-mode ( $f$ -mode) oscillation frequency through its universal relation with the tidal Love number and compactness. Results indicate that the Stiff EOS undergoes a phase transition at the highest energy densities and pressures, followed by the Intermediate and Soft EOSs, highlighting the distinctive characteristics of these models. Additionally, the study explores the impact of EOS choice on the sound speed profile of NSs, reaffirming the physical validity of the models across varying $α$ values.
↳ gr-qcastro-ph.HEnucl-thGen.Rel.Grav.(2025)·6 citations
22
Femtoscopic study of the $S = - 1$ meson-baryon interaction: $K^{-} p$ , $π^{-} Λ$ and $K^{+} Ξ^{-}$ correlations
P. Encarnación🇪🇸 · A. Feijoo🇩🇪 · V. Mantovani Sarti🇩🇪 · A. Ramos🇪🇸
We study the femtoscopic correlation functions of meson-baryon pairs in the strangeness $S = - 1$ sector, employing unitarized s-wave scattering amplitudes derived from the chiral Lagrangian up to next-to-leading order. For the first time, we deliver predictions on the $π^{-} Λ$ and $K^{+} Ξ^{-}$ correlation functions which are feasible to be measured at the Large Hadron Collider. We also demonstrate that the employed model is perfectly capable of reproducing the $K^{-} p$ correlation function data measured by the same collaboration, without the need to modify the coupling strength to the $K ˉ^{0} n$ channel, as has been recently suggested. In all cases, the effects of the source size on the correlation are tested. In addition, we present detailed analysis of the different coupled-channel contributions, together with the quantification of the relative relevance of the different terms in the interaction. These calculations require the knowledge of the so-called production weights, for which we present two novel methods to compute them.
↳ hep-phnucl-thPRD(2025)·24 citations
23
Weak nuclear decays deep-underground as a probe of axion dark matter
Jorge Alda🇮🇹 · Carlo Broggini🇮🇹 · Giuseppe Di Carlo🇮🇹 · Luca Di Luzio🇮🇹 · Denise Piatti🇮🇹 · Stefano Rigolin🇮🇹 · Claudio Toni🇮🇹
We investigate the time modulation of weak nuclear decays as a method to probe axion dark matter. To this end, we develop a theoretical framework to compute the $θ$ -dependence of weak nuclear decays, including electron capture and $β$ decay, which enables us to predict the time variation of weak radioactivity in response to an oscillating axion dark matter background. As an application, we recast old data sets, from the weak nuclear decays of $^{40} K$ and $^{137} Cs$ taken at the underground Gran Sasso Laboratory, in order to set constraints on the axion decay constant, specifically in the axion mass range from few $1 0^{- 23}$ eV up to $1 0^{- 19}$ eV. We finally propose a new measurement at the Gran Sasso Laboratory, based on the weak nuclear decay of $^{40} K$ via electron capture, in order to explore even shorter timescales, thus reaching sensitivities to axion masses up to $1 0^{- 9}$ eV.
↳ hep-phhep-exnucl-exnucl-thPRD(2025)·17 citations

Affiliations

first authorsco-authorsvia INSPIRE