Physics Colloquium

Please note that self-served coffee and cookies will be in the seminar lounge at 3:00 pm. Abstract: From the point of view of a particle physicist, neutron stars are fascinating objects: They consist of strongly interacting matter at densities far higher than those achieved in terrestrial laboratories. They give us unique insight on the properties of quantum chromodynamics at finite densities, and a hope for a source of new physics with increasingly improving observations and theoretical descriptions. However, those theoretical descriptions provide exceptionally challenging: Lattice QCD, the usual gold-standard for theoretical information in the strongly coupled regime where neutron stars (and in particular their cores) lie ceases to work at finite density due to a fundamental obstacle known the sign problem. One of the few first-principles tools for describing dense matter is perturbative QCD. The methods of thermal field theory and effective field theories make this possible. Nevertheless, very high-order corrections are required in order to make pQCD applicable for this purpose. I will outline the computations needed for such improvements, in particular showing the diagrammatic methods needed to consistently perform finite-density computations in order to explain how advancements in recent years have made progressing even to next-to-next-to-next-to-leading order possible after a 40-year lull in progress.