QCD phase diagram and its application in compact stars: A holographic hardwall approach

Abstract

Matter making up the interior of stars consists of an interacting soup of nucleons and photons. Calculating the equations of state of this nuclear matter at high densities and temperatures is complicated by the strong nature of the interactions among the nucleons and the multiple energy scales involved. A radical new approach to these systems called AdS holography tries to obtain the equations of state via gravity calculations in higher spacetime dimensions. In this thesis, we have obtained the equations of state and a phase diagram of QCD-like theories at large densities and low temperatures by using a particular version of holography termed the hardwall model. We have generalized the hardwall model to 10-d with D7-branes which allowed us to compute the phases at finite temperatures for various quark masses. This approach produces phenomenologically interesting inequalities, also at nonzero density. However, we had to return to the 5D hardwall models to study the nature of a suitable hologram of the low density confined phase. An important contribution of our work is the use of modified IR boundary conditions which incorporate phenomenology. Furthermore, we analyzed baryonic condensates within these confined phases. Interestingly, we find that condensing operators have a restricted range of scaling dimensions. The equations of state derived in these phases are then utilized to calculate the mass radius relation of compact stars. We conclude that the cores of compact stars will exhibit condensates at low temperatures and supranuclear densities.