Hadron phenomenology using holographic light-front Quantum Chromodynamics

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There are four known fundamental interactions in Nature and this proposal investigates one of the them: the strong interaction which is responsible for binding quarks together in hadrons and nucleons together in atomic nuclei. It is thus the underlying interaction for both hadronic and nuclear physics. We do have a fundamental theory for the strong interaction: Quantum Chromodynamics (QCD) and it tells us how quarks interact by exchanging gluons and also how gluons interact between themselves by exchanging other gluons. However, the equations of QCD are extremely difficult to solve exactly when the coupling between the interacting particles is strong. Experimentally, isolated quarks (or gluons) are never observed, i.e. our detectors only see hadrons. Understanding the permanent confinement of quarks and gluons inside hadrons from first principles in QCD remains to this day an open problem. Consequently, hadronic physics remain largely phenomenological. But phenomenology is what allows theory and experiment to mutually guide and reinforce each other, it is a key element to progress in science. New insights into strongly-coupled QCD comes from conjecture, proposed by Juan Maldacena (Princeton) in the late nineties, of a mathematical equivalence between special classes of quantum theory (without gravity) in 4-dimensional spacetime and a classical (not quantum) gravity theory in a higher dimensional spacetime. The usefulness of this equivalence is due to the fact that if the quantum theory is strongly-coupled, its gravity dual is weakly-coupled. Hence, one can obtain information on the hard-to-solve quantum theory by solving instead its easy-to-solve gravity dual. Unfortunately, the gravity dual to QCD is not known. But gravity duals to approximate versions of QCD are known and one of them is referred to as light-front holographic QCD. This research focuses on the phenomenology of light-front holographic QCD to understand hadronic structure and how the latter affects the physics of rare decays of the B meson. Such decays are extraordinarily sensitive probes to new physics beyond the Standard Model (SM). In the recent years, a number of discrepancies between SM predictions and experimental data have been observed at the Large Hadron Collider (LHC) in Europe. A better understanding of hadronic structure will shed light on these discrepancies. At the same time, this research will serve to interpret and guide future experiments on hadronic structure from other facilities like the Jefferson Lab in the US. This research contributes to the training of the next generation of Canadian researchers by introducing them to highly sophisticated mathematics and computational tools and giving them the opportunity to use real world data coming from particle colliders around the world. It also sustains the prominent Canadian role at the forefront of world-class research in addressing one of the most fundamental questions in contemporary particle physics.