Browsing by Subject "Quantum field theory"

One of the main questions in nuclear astrophysics is whether deconfined quark matter exists inside neutron stars. In order to answer this, the equation of state (EoS) of cold and dense quark matter, which plays an essential role in finding the equation of state of strongly interacting matter (QCD matter) inside neutron stars, needs to be determined as accurately as possible [14, 25]. The equation of state, or the pressure, of cold and dense quark matter was evaluated to the full three-loop order in perturbation theory back in 1977 by Freedman and McLerran [9, 10] and recently the contributions of the soft momentum scale to the four-loop pressure were evaluated in [13, 14, 15]. What is missing from the full four-loop pressure is the contribution of the hard momentum scale μ. In this thesis we shall first evaluate the known result for one three-loop Feynman diagram contributing to the three-loop pressure. After this, we derive a new result for a fermionic four-loop master integral at zero temperature and finite quark chemical potentials, which directly contributes to the yet unknown hard sector of the four-loop pressure of cold and dense quark matter.