Speaker
Description
Quantum Chromodynamics (QCD) is the theoretical framework to study hadrons by means of their fundamental degrees of freedom, i.e.~quarks and gluons, collectively referred to as partons. QCD defines many types of distributions describing a given hadron in terms of partons. For the purposes of this talk, we are interested in the so-called generalized parton distributions (GPDs) which are off-forward matrix elements of quark and gluon operators and are typically accessed in exclusive Compton scattering. Convolutions of GPDs with coefficient functions describing the interaction of photons with the partons in the hadron are named Compton form factors (CFFs). Real and imaginary parts of CFFs are related by subtracted'' dispersion relations, i.e.~the difference between the real and imaginary parts is given by a constant. This subtraction constant can be written by means of the so-called $D$-term, which is one of the functions that parameterize the GPDs. The $D$-term is of special interest in hadron physics as it is the bridge connecting the subtraction constant (accessible in experiments by measurements of the CFFs) to the internal distribution of pressure in the hadron. The latter is given the gravitational form factor (GFF) $C$. These GFFs are functions which parameterize the QCD energy-momentum tensor and can be related tomechanical'' properties of the hadron such as mass, pressure or shear forces. In this talk, we propose a dispersion relation valid to all-orders in perturbation theory and up to kinematic twist four accuracy in order to study the $D$-term and its implications in the subtraction constant and the pressure inside the hadron.
