arXiv subjects

Christos Iona

Publications and source records attributed to Christos Iona.

6 recordsLinked to original sources

arXiv2026

Spin and momentum fraction carried by partons in the nucleon

We determine the momentum fraction and angular momentum carried by quarks and gluons in the proton in lattice QCD. We use four ensembles simulated with up, down, strange and charm quarks with their masses tuned to their physical values. These ensembles have similar physical volume and different lattice spacings allowing us to take the continuum limit directly at the physical pion mass point. We extract the quark and gluon momentum fractions and total angular momentum in the continuum limit as well as the intrinsic quark spin and orbital angular momentum contributions to the proton spin. We find the total momentum fraction $\langle x_N \rangle= 0.995(60)(29)$ and the total spin $J_N = 0.507(43)(65)$, showing that both the momentum and spin sum rules are satisfied. We compare our results to those extracted from phenomenological analyses.

hep-lat↗

arXiv2026

Nucleon unpolarized second Mellin moments using lattice QCD ensembles with physical quark masses and in the continuum limit

We compute the matrix elements of the energy-momentum tensor of the nucleon using four ensembles of twisted mass clover-improved fermions with the up, down, strange and charm quark masses tuned to approximately their physical values. The four ensembles have similar physical volume and lattice spacings $a=0.080$~fm, $0.068$~fm, $0.057$~fm, and $0.049$ fm, allowing us to take the continuum limit directly at the physical pion mass point. We compute both connected and disconnected quark contributions as well as gluon contributions. All renormalization functions, including the mixing of the quark singlet with the gluon, are determined non-perturbatively. We extract the gravitational form factors in the continuum limit at $Q^2=0$ and evaluate the contribution of quarks and gluons to the momentum and angular momentum of the proton. Using the values of the intrinsic quark spin computed using the same gauge ensembles we also determine the orbital angular momentum for each quark flavor.

hep-lat↗

arXiv2026

Nucleon strange electromagnetic form factors using $N_f=2+1+1$ twisted-mass fermions at the physical point

We present the strange electromagnetic form factors of the nucleon using lattice QCD with $N_f=2+1+1$ twisted mass clover-improved fermions and quark masses tuned to their physical values. Using four ensembles with lattice spacings of $a=0.080$ fm, $0.068$ fm, $0.057$ fm and $0.049$ fm, and similar physical volume, we obtain the continuum limit directly at the physical pion mass. The disconnected strange contributions are computed using high statistics two-point functions combined with stochastic noise mitigation techniques, such as spin-color dilution and hierarchical probing in the estimation of the quark loop. From the momentum dependence of the form factors, we provide the strange electric and magnetic radii, as well as the strange magnetic moment in the continuum limit.

hep-lat↗

arXiv2026

Nucleon strange electromagnetic form factors from $N_f=2+1+1$ lattice QCD

We present the nucleon strange electromagnetic form factors using four lattice QCD ensembles with $N_f=2+1+1$ twisted mass clover-improved fermions and quark masses tuned to approximately their physical values. The four ensembles have similar physical volume and lattice spacings of $a=0.080$ fm, $0.068$ fm, $0.057$ fm and $0.049$ fm allowing us to take the continuum limit directly at the physical pion mass point. We compute nucleon three-point correlation functions with high statistics, where the disconnected fermion loops are evaluated stochastically with spin-color dilution and hierarchical probing. We find non-zero values for both electric and magnetic form factors. We extract the strange electric and magnetic radii, as well as the strange magnetic moment in the continuum limit by studying the momentum dependence of the form factors. We also compute the charm electromagnetic form factors within the same setup, which we find to be consistent with zero within the statistical precision of our data.

hep-lat↗

arXiv2026

Strangeness of nucleons from $N_f=2+1+1$ lattice QCD

We present the strange electromagnetic form factors of the nucleon using lattice QCD simulations with degenerate light, a strange, and a charm quark in the sea with masses tuned to their physical values. For the first time, the strange electromagnetic form factors are computed at the continuum limit using only ensembles simulated with physical quark masses, eliminating the need for chiral extrapolations and their associated systematic uncertainty. We obtain the momentum transfer dependence of the form factors using the $z$-expansion and provide the strange electric and magnetic radii, as well as the strange magnetic moment. When combining our statistical errors and systematic uncertainties stemming from the momentum transfer dependence fit, our errors are an order of magnitude smaller than those associated with experimental determinations of the strange electromagnetic form factor.

hep-lat↗

arXiv2025

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

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 $σ_{πN}=41.9(8.1)$ 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.

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