Description
Christian Bernard Hall
In this talk, I will show how effective field theory can be combined with dispersion theory to provide a representation of the nucleon's electromagnetic form factors that incorporates the correct analytical structure and the dynamics of QCD at low energy. As an application, I will present how this approach contributes to the determination of the proton's charge and magnetic radii, as well as...
Nucleon electroweak form factors contain relevant details about hadronic structure and strong interactions in the nonperturbative regime. This information is encoded in their dependence on the momentum transferred to the nucleon by external probes but also in their quark-mass dependence, which is accessible by Lattice QCD (LQCD) simulations.
In our study we rely on relativistic chiral...
Chiral effective field theory has become a standard tool to analyze low-energy reactions involving pions, nucleons and external electroweak sources. I will briefly describe conceptual foundations of this method, review our recent efforts towards developing it into a precision tool for low-energy nuclear physics and discuss some of the remaining challenges.
We perform a coupled-channel dispersive analysis of $γ^{(∗)}γ^{(∗)} \to \pi\pi/\pi\eta/K\bar{K}$ using a modified Muskhelishvili–Omnès framework that enforces analyticity and unitarity, modeling the left-hand cut with pion/kaon and vector-meson pole terms. Both unsubtracted and subtracted forms are studied, the latter incorporating Adler-zero constraints. The S-wave $\pi\pi/K\bar{K}_{I = 0}$...
We analyze the processes $e^+ e^- \to \gamma^* \to J/\psi \, \pi \, \pi \, (K \bar{K})$ and $e^+ e^- \to \gamma^* \to h_c \, \pi \, \pi$ using the recently proposed Dalitz-plot decomposition approach, based on the helicity formalism for three-body decays. Within a Lagrangian-based toy model, we validate key aspects of this approach, namely the factorization of the overall rotation for all...
We present our preliminary determination of the charge radii of light mesons using the PACS10 configurations, which were generated at the physical point on large volumes of more than $(10\,\text{fm})^3$ by the PACS Collaboration. In general, charge radius calculations suffer from systematic effects due to chiral extrapolation, finite lattice spacing effect, finite volume effect, and the choice...
A key step toward a better understanding of the nucleon structure is the study of Generalized Parton Distributions (GPDs). GPDs are nowadays the object of an intense effort of research since they convey an image of the nucleon structure where the longitudinal momentum and the transverse spatial position of the partons inside the nucleon are correlated. Moreover, GPDs give access, via Ji's sum...
Generalized Parton Distributions (GPDs) provide a unified framework for exploring the three-dimensional structure of hadrons, encoding correlations between spatial and momentum distributions as well as spin and orbital angular momenta of quarks and gluons. Lattice QCD offers a first-principles approach to access these nonperturbative quantities, but long-standing challenges have limited...
Theoretical control of soft interactions is fundamental to establish TMD factorization. It is possible to sistematically include soft interactions through soft modes in bacckground field method to reach a consistente factorization of SIDIS or Drell-Yan cross sections at next-to-leading power, where all nonperturbative terms are expressed as martix elements of field operators. As a practical...
We present a one-loop perturbative study of unpolarized twist-two generalized parton distributions (GPDs) for external on-shell gluon states. A finite quark mass 𝑚 is kept throughout: it serves as an infrared regulator and, crucially, enables an explicit realization of the full trace-anomaly relation. By taking second Mellin moments, we extract the associated gravitational form factors (GFFs)...
Gluons play a central role in the proton’s structure, carrying a substantial fraction of its momentum and driving its dynamics at small Bjorken-$x$. A precise determination of the unpolarized gluon parton distribution function (PDF) from first principles is essential for understanding QCD and for reducing uncertainties in high-energy collider predictions. In this talk, we extend our work on...
We calculate the Next to Leading Order (NLO) corrections to single inclusive hadron production in DIS (SIDIS) in the forward rapidity region using the Color Glass Condensate (CGC) formalism. We then consider the kinematic region where the transverse momentum of the produced hadron is much less than the virtuality of the photon and show that there are large (Sudakov) logs originating from this...
Recent studies of spin and azimuthal asymmetries at JLab suggest that separation of different dynamical contributions may be critical for interpretation of observables in both exclusive and semi-inclusive production of hadrons in electroproduction. Measurements of multiparticle final states in multidimensional space will be needed to sort out all disagreements with theory predictions and...
The size of the proton has traditionally been defined by its charge radius, neglecting the role of gluons despite their dominance in its structure. Here we report the first global experimental extraction of the proton’s total scalar energy density, reconstructed from near-threshold $J/\psi$ production data to provide the gluonic contribution and the quark contribution from DVCS. We show that...
