Nuclear Theory·nucl-th

Tuesday·February 11, 2025

11 papers—4 primary·7 cross-listed

05
Nucleon axial, tensor, and scalar charges and $σ$ -terms in lattice QCD
Constantia Alexandrou🇨🇾 · Simone Bacchio🇨🇾 · Jacob Finkenrath🇨🇾 · Christos Iona🇨🇭 · Giannis Koutsou🇨🇾 · Yan Li🇨🇾 · Gregoris Spanoudes🇨🇾
We determine the nucleon axial, scalar and tensor charges at the continuum limit by analyzing three $N_{f} = 2 + 1 + 1$ twisted mass fermion ensembles with all quark masses tuned to approximately their physical values. We include all contributions from valence and sea quarks. We use the Akaike Information Criterion to evaluate systematic errors due to excited states and the continuum extrapolation. For the nucleon isovector axial charge we find $g_{A}^{u - d} = 1.250 (24)$ , in agreement with the experimental value. We compute the axial, tensor and scalar charges for each quark flavor. The axial charge provides crucial information on the intrinsic spin carried by quark in the nucleon and the the latter two provide input for experimental searches of physics beyond the standard model. Moreover, we extract the nucleon $σ$ -terms and find $σ_{π N} = 41.9 (8.1)$ MeV, for the strange $σ_{s} = 30 (17)$ MeV and for the charm $σ_{c} = 82 (29)$ MeV. We also present preliminary results on the isovector quantities using a fourth ensemble at smaller lattice spacing.
↳ hep-lathep-exhep-phnucl-thPoS(2025)·4 citations
06
Spin alignment of quarkonia in vortical quark-gluon plasma
Yuhao Liang🇨🇳 · Shu Lin🇨🇳
The spin alignment of $J / ψ$ with respect to event plane in relativistic heavy ion collisions exhibits a significant signal. We propose a possible mechanism for spin alignment through spin dependent dissociation of quarkonia in a vortical quark-gluon plasma. The spin dependent dissociation is realized through inelastic scattering between constituents of quarkonium and those of quark-gluon plasma polarized by the vorticity. The spin dependent dissociation rate is found to depend on the directions of vorticity, quantization axis, and quark momentum. We implement our results in a dissociation dominated evolution model for quarkonia in the Bjorken flow, finding the spin $0$ state is slightly suppressed compared to the average of the other two, which is consistent with the sign found in experiments. We also find absence of logarithmic enhancement in binding energy in the vortical correction to dissociation rate, which is understood from the requirement that a spin dependent dissociation can only come from quark coupling to a pair of chromomagnetic and chromoelectric field.
↳ hep-phnucl-exnucl-thCPC(2025)·7 citations
07
Insights into the $γ^{(*)} + N (940) \frac{1}{2}^{+} \to Δ (1700) \frac{3}{2}^{-}$ transition
L. Albino🇪🇸 · G. Paredes-Torres🇲🇽 · K. Raya🇪🇸 · A. Bashir🇲🇽 · J. Segovia🇪🇸
We report novel theoretical results for the $γ^{(*)} + N (940) \frac{1}{2}^{+} \to Δ (1700) \frac{3}{2}^{-}$ transition, utilizing a symmetry-preserving treatment of a vector $\otimes$ vector contact interaction (SCI) within the Dyson-Schwinger equations (DSEs) formalism. In this approach, both nucleon, $N (940) \frac{1}{2}^{+}$ , and $Δ (1232)$ 's parity partner, $Δ (1700) \frac{3}{2}^{-}$ , are treated as quark-diquark composites, with their internal structures governed accordingly by a tractable truncation of the Poincaré-covariant Faddeev equation. Nonpointlike quark+quark (diquark) correlations within baryons, which are deeply tied to the processes driving hadron mass generation, are inherently dynamic in the sense that they continually break apart and recombine guided by the Faddeev kernel. For the nucleon, isoscalar-scalar and isovector-axial-vector diquarks dominate, while the $Δ (1700) \frac{3}{2}^{-}$ state only includes contributions from isovector-axial-vector diquarks because the SCI-interaction excludes isovector-vector diquarks. Once the Faddeev wave function of the baryons involved in the electromagnetic transition is normalized taking into account that its elastic electric form factor must be one at the on-shell photon point, we compute the transition form factors that describe the $γ^{(*)} + N (940) \frac{1}{2}^{+} \to Δ (1700) \frac{3}{2}^{-}$ reaction and, using algebraic relations, derive the corresponding helicity amplitudes. When comparing with experiment, our findings highlight a strong sensitivity of these observables to the internal structure of baryons, offering valuable insights. Although the SCI-framework has obvious limitations, its algebraic simplicity provides analytical predictions that serve as useful benchmarks for guiding more refined studies within QCD-based DSEs frameworks.
↳ hep-phhep-exhep-latnucl-ex+1PRD(2025)·5 citations
08
Pseudoscalar Screening Mass at Finite Temperature and Magnetic Field from Lattice QCD with Physical Quark Masses
Rishabh Thakkar🇨🇳 · Heng-Tong Ding🇨🇳 · Jin-Biao Gu🇨🇳 · Sheng-Tai🇨🇳
Understanding the screening mass of pseudoscalar mesons at finite temperature and magnetic field is crucial for comprehending the behavior of strongly interacting matter under extreme conditions, such as those found in the early universe or inside neutron stars. Additionally, in heavy ion collisions, strong magnetic fields are generated, which could significantly influence the properties of the quark-gluon plasma. The study of these screening masses provides insight into the modifications of mesonic properties in such environments, which is essential for the theoretical understanding of Quantum Chromodynamics (QCD) phase transitions and the properties of the quark-gluon plasma. Here, we present continuum estimated lattice QCD results on the screening mass of neutral pseudoscalar mesons at finite temperatures and nonzero magnetic fields. The simulations used (2+1)-flavor lattice QCD simulations using physical quark masses employing the HISQ/tree action. The continuum estimation was carried out using lattices having temporal extents $N_{τ}$ = 8, 12, and 16, all having aspect ratio $N_{σ} / N_{τ}$ = 4. The investigated temperature ranges from 145 MeV to 166 MeV, while the magnetic field strength varies from 0 to 1 GeV $^{2}$ . We discuss the dependence of the screening masses of various neutral pseudoscalar mesons on temperature, magnetic field strength, and quark mass.
↳ hep-lathep-phnucl-thPoS(2025)·1 citation
09
Gauge Dependence of ccbar Potential from Nambu-Bethe-Salpeter Wave Function in Lattice QCD
Tianchen Zhang (RCNP, Osaka University)🇯🇵 · Noriyoshi Ishii (RCNP, Osaka University)🇯🇵
We study the gauge dependence of $c c ˉ$ potentials extracted from Nambu-Bethe-Salpeter (NBS) wave functions. The potentials are obtained using the HAL QCD potential method, with an extension introduced by Kawanai and Sasaki for self-consistent determination of the charm quark mass. A systematic comparison is conducted between results obtained in the Coulomb and Landau gauges. The numerical calculations are performed using 2+1 flavor QCD gauge configurations with the charm quark treated in the quenched approximation. We find that the central potentials in both gauges show excellent agreement at short distances but exhibit discrepancies at large distances. We attribute these discrepancies to insufficient suppression of excited-state contamination in the Landau gauge, which affects the linear-rising behavior of the potential at large distance.
↳ hep-lathep-phnucl-thPoS(2025)·0 citations
10
Axialvector diqaurk Mass and quark-diquark potential in Sigma_c
Soya Nishioka (RCNP Osaka university)🇯🇵 · Noriyoshi Ishii (RCNP Osaka university)🇯🇵
The axialvector diquark is studied by using 2+1 flavor Lattice QCD. Being a two-quark object, diquark has a non-neutral color charge. Hence the two-point correlators of diquark fields do not have a particle pole due to the color confinement of QCD, and it is not straightforward to study the diquark mass by lattice QCD by using an exponential fit of a temporal two-point correlator. In order to avoid this difficulty, our strategy is to regard the diquark mass as a mass parameter of an effective quark-diquark model which is constructed by using an extended HAL QCD method based on equal-time quark-diquark Nambu-Bethe-Salpeter (NBS) wave functions. We attempt to calculate the axial-vector diquark mass and the quark-diquark potentials between a charm quark and an axial-vector diquark in the $Σ_{c}$ baryon. Lattice QCD Monte Carlo calculation is performed by using the 2+1 flavor QCD gauge configurations generated on $3 2^{3} \times 64$ lattice by PACS-CS Collaboration which corresponds to the pion mass of about 700 MeV. As a result, a quark-diquark central potential of Cornell-type and a short-ranged spin-dependent potential are obtained. However, from a quantitative point of view, the ground state convergence of the NBS wave functions are not sufficient so that we obtain a larger string tension and a smaller axial-vector diquark mass than we have expected phenomenologically.
↳ hep-lathep-phnucl-thPoS(2025)·2 citations
11
Probing the QCD $θ ˉ$ term with paramagnetic molecules
Heleen Mulder🇳🇱 · Rob Timmermans🇳🇱 · Jordy de Vries🇳🇱
The experimental search for CP violation in paramagnetic atomic and molecular systems has made impressive progress in recent years. This has led to strong upper limits on the electron electric dipole moment. The same measurements can also be used to constrain hadronic sources of CP violation through CP-violating interactions between the electrons and the nucleus. We employ heavy-baryon chiral perturbation theory to compute such CP-violating semileptonic electron-nucleus interactions arising from the QCD theta term. We sharpen earlier results by determining the relevant short-distance effects and by an explicit two-loop calculation of meson-photon diagrams. We derive a bound of $∣ θ ˉ ∣ < 1.5 \cdot 1 0^{- 8}$ at $90%$ confidence, based on HfF $^{+}$ experiments at JILA. A further experimental improvement of one to two orders of magnitude would make paramagnetic molecular electric dipole moment experiments competitive with the neutron and diamagnetic atom program in constraining strong CP violation and higher-dimensional CP-odd quark-gluon operators.
↳ hep-phnucl-thphysics.atom-phJHEP(2025)·11 citations

Affiliations

first authorsco-authorsvia INSPIRE

Nucleon axial, tensor, and scalar charges and σ-terms in lattice QCD

Spin alignment of quarkonia in vortical quark-gluon plasma

Insights into the γ(∗)+N(940)21​+→Δ(1700)23​− transition

Pseudoscalar Screening Mass at Finite Temperature and Magnetic Field from Lattice QCD with Physical Quark Masses

Gauge Dependence of ccbar Potential from Nambu-Bethe-Salpeter Wave Function in Lattice QCD

Axialvector diqaurk Mass and quark-diquark potential in Sigma_c

Probing the QCD θˉ term with paramagnetic molecules

Affiliations

Nucleon axial, tensor, and scalar charges and $σ$ -terms in lattice QCD

Insights into the $γ^{(*)} + N (940) \frac{1}{2}^{+} \to Δ (1700) \frac{3}{2}^{-}$ transition

Probing the QCD $θ ˉ$ term with paramagnetic molecules