Baryons and QCD equation of state at large densities

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The physics of neutron stars has received tremendous international attention after the observation and analysis of gravitational waves from a binary-neutron-star merger event recorded as GW170817. Dedicated experiments such as NICER/ISS promise to provide interesting additional information in the near and middle future. A central object of the physics of neutron stars is the equation of state (EOS) of strongly interacting matter described by the theory of strong interactions, QCD. From a theory perspective, the EOS is not well known in the important region of intermediate densities of QCD matter. Whereas effective chiral field theories and perturbative approaches provide solid results in the low and (very) large density region, model results in the intermediate region are hampered by artefacts and systematic errors. In this project we propose to provide a high-quality equation of state (EOS) for QCD matter at small, intermediate and large densities in one and the same approach based on QCD. Our technical workhorse is a functional approach to QCD via Dyson-Schwinger and Bethe-Salpeter equations that has been successfully applied already to the physics of the QCD phase diagram, the physics of medium effects on hadrons and the physics of baryon spectra by my group. Based on this expertise we plan to focus particularly on the intermediate density region which may include the transition from a hadronic to a quark matter phase characterized by diquark condensation. The key degrees of freedom for thermodynamics in this region are fermions, i.e., baryons and quarks. In the hadronic phase we plan to determine the masses and wave functions of baryons and incorporate their effects into the EOS. We will study their fate in the coexistence region of a potential first order phase transition and in the (colour) superconducting region beyond, where quark effects are expected to dominate the EOS. The correct high density perturbative limit in our framework has been demonstrated already in previous works. If successful, we will be able to provide significant qualitative and quantitative improvements of previous determinations of the EOS with potential large impact on two timely research fields, the physics of neutron stars and the physics of heavy ion collisions.