The chiral phase transition via stochastic hydrodynamics

Atoms are the building blocks of nature as we see it everyday, but they are not indivisible as scientists once thought. Within the center of each atom is a nucleus, composed of protons and neutrons. What holds these particles together? It turns out that they are made up of quarks, glued together by gluons. The force holding the quarks and gluons together is a fundamental force of nature, known as the strong nuclear force. In order to study the strong force in detail, physicists crash together gold ions at the Relativistic Heavy Ion Collider (RHIC) in Brookhaven National Laboratory and lead ions at the Large Hadron Collider (LHC) in CERN. The highly energetic collisions produce, for a very short period of time, a new state of matter known as the Quark Gluon Plasma (QGP). Studying this exotic state of matter is interesting not only because it tells us how nuclei are glued together, but also because we can learn about the early history of our universe. In fact, according to our current understanding, QGP was produced during the first few microseconds after the Big Bang. Physicists have observed that when the material produced by these collisions cools and expands, it is in fact undergoing a phase transition. A phase transition is when matter changes state. Water becoming ice at the freezing point is a well-known example of a phase transition from a liquid to a solid phase. The phase transition studied in the LHC and RHIC is known as the chiral phase transition. Particles can come in two forms: left or right-handed. Chirality is a property which tells you if the left-handed particles are the same as the right-handed ones. The chiral phase transition is when matter goes from a chiral to a non-chiral phase. Although much work has been done, the exact nature of the chiral phase transition still proves elusive. One way to make progress in understanding the chiral phase transition can be to use another well- known fact about the QGP, namely that it behaves like a fluid. Physicists have observed this peculiar feature of the QGP in experiments at the LHC and RHIC, noting that in many ways the QGP behaves very much like the most perfect fluid that nature has ever seen. A clear example of the fluidity of the QGP is its low viscosity. Viscosity is a measure of the sluggishness with which a liquid flows: the lower the viscosity, the better the flow. Honey, for instance, has a higher viscosity than water. Surprisingly, the QGP is one of the least viscous fluids that we have encountered. As a result, a useful theoretical shortcut is to model the complicated QGP-producing collisions as a fluid. The theory underpinning this approach is known as stochastic relativistic hydrodynamics, which can be used to shed light on the chiral phase transition.

Atoms are the building blocks of nature as we see it everyday. Within the center of each atom is a nucleus, filled with protons and neutrons, which in turn are made up of quarks, 'glued' together by gluons. The quarks and gluons are held together by the strong nuclear force, a fundamental force of nature. To study the strong force, physicists smash together gold ions at the Relativistic Heavy Ion Collider (RHIC) and lead ions at the Large Hadron Collider (LHC). The highly energetic collisions produce, for a fleeting instant, a new state of matter called the Quark Gluon Plasma (QGP). Studying this exotic state of matter is interesting not only because it tells us about how matter is held together, but also because we can learn about the early history of our universe. According to our current understanding, QGP was produced during the first few microseconds after the Big Bang. Physicists have observed that when the material produced by these collisions cools and expands, it undergoes a phase transition. A phase transition is when matter changes state, like water becoming ice at the freezing point, going from a liquid to a solid phase. The phase transition studied in the LHC and RHIC is known as the chiral phase transition. Particles can come in two forms: left or right-handed. Chirality is a property which tells you if the left-handed particles are the same as the right-handed ones. The chiral phase transition is when matter goes from a chiral to a non-chiral phase. Although much work has been done, the exact nature of the chiral phase transition still proves elusive. One way to make progress in understanding the chiral phase transition is to use the fluid-like nature of QGP. Physicists have observed this peculiar feature in experiments at the LHC and RHIC, noting that in many ways the QGP behaves very much like the most 'perfect' fluid that nature has ever seen. A clear example of the fluidity of the QGP is its low viscosity. Viscosity is a measure of the sluggishness with which a liquid flows: the lower the viscosity, the better the flow. Honey, for instance, has a higher viscosity than water. Surprisingly, the QGP is one of the least viscous fluids that we have encountered. As a result, a useful theoretical approach is to model the complicated QGP-producing collisions as a fluid. The theory underpinning this approach is known as stochastic relativistic hydrodynamics, which can be used to shed light on the chiral phase transition. As part of my research, I have determined the leading contribution to the QGP viscosity, arising from effects associated to the chiral phase transition in a number of relevant analytic and numerical models.