The observable universe is made up mostly of protons and neutrons — collectively known as nucleons — the fundamental building blocks of atomic nuclei. According to our current understanding, rooted in the theory of Quantum Chromodynamics (QCD), nucleons are not simple objects. They are intricate assemblies of quarks and gluons, collectively known as partons. Unraveling how these quarks and gluons shaped the universe, from the hot, dense soup that followed the Big Bang to the mass we observe today, is one of the most exciting challenges in modern science.

For decades, experiments have helped us probe the structure of nucleons by measuring distribution functions, which are essentially maps of how quarks and gluons behave inside nucleons. While we have made significant progress in understanding the one-dimensional distributions of quarks and gluons, we are still missing the full picture. To truly understand nucleons, we need to explore their internal dynamics in multiple dimensions, raising questions like:

• How do the spin and orbital motion of quarks and gluons contribute to the overall spin of the nucleon?

• What accounts for the mass of nucleons and other hadrons?

• How do quarks and gluons generate internal forces like pressure, and how do these forces shape nucleons?

Addressing these questions requires a concerted effort that combines theoretical and experimental approaches. Facilities like the Electron-Ion Collider (EIC) at Brookhaven National Laboratory will play a crucial role in probing the partonic structure of nucleons, and my research focuses on providing the theoretical groundwork necessary for answering these questions, as well as interpreting and guiding experimental efforts.