Magnetic fields in the quark-gluon plasma: Flow contribution, initial conditions, and CP-odd domains

Abstract

In heavy-ion collisions, two beams of ionized heavy atoms (typically gold or lead) are collided into each other at velocities close to that of light. Whenever a collision between two atoms occurs, the protons and neutrons caught in the region of overlap are broken down into their constituent particles, quarks and gluons. These form a novel form of matter called the Quark-Gluon Plasma (QGP), which expands and cools until the quarks and gluons within are able to recombine into new particles. QGP exists at the frontier of known physics and presents an excellent place to look for new particles, discover previously unknown laws of physics, and understand the early universe by experimentally recreating the conditions present immediately after the Big Bang. Heavy-ion collisions also produce the strongest electromagnetic fields in nature - rivalled only by the fields present in the early universe. Because QGP plays host to charged particles, these fields play a significant role in the evolution of QGP. In this thesis, I review the current state of research pertaining to electromagnetic fields in QGP and heavy-ion collisions and detail my own contributions to the field. In particular, I examine the electromagnetic response of QGP which arises from the velocity of QGP expansion and compare it to the fields which arise from the external “wounded” nuclei. I also present models of the electric and magnetic fields during QGP lifetime that satisfy the physically motivated initial conditions. Finally, I examine the effects that CP-odd domains with constant topological charge density will have on photons incident on the surface of those domains and find highly non-trivial effects arising from the existence of sharp boundaries between the normal matter and the topologically charged medium. These effects can in principle be observed, and I outline what an experiment ought to look for in order to find these domains.