Strangeness and anisotropic phases in dense nuclear matter in the chiral transition region

Abstract

The theory of Quantum Chromodynamics presents a rich phase structure. However, while the low temperature and intermediate density region is a key piece in understanding the physics of neutron stars, it is also elusive from ab-initio methods and experiments. In this thesis we discuss two different models that explore the phase diagram of Quantum Chromodynamics. In the first part we construct a model for dense matter based on low-density nuclear matter properties that exhibits a chiral phase transition and includes strangeness through hyperonic degrees of freedom. Along with empirical constraints from nuclear matter we require that at asymptotically large densities the chirally restored phase contains strangeness and the speed of sound approaches the conformal limit, resulting in a high-density phase that resembles deconfined quark matter. Additionally, the model is required to reproduce sufficiently massive compact stars. We also find that for the allowed parameter range strangeness does not appear in the chirally broken phase and that the chiral transition is of first order. In the second part we employ a simpler version of this model to discuss the competition between isotropic and anisotropic phases. Assuming isotropy, the model exhibits a chiral phase transition which is a crossover. This observation crucially depends on the presence of the nucleonic vacuum contribution, an important addition to this model. Allowing for an anisotropic phase in the form of a chiral density wave can disrupt the smooth crossover. We identify the regions in the parameter space of the model where a chiral density wave is energetically preferred. A high-density re-appearance of the chiral density wave demonstrating unphysical behavior, is avoided by a suitable renormalization scheme. We find that, within our model, the chiral density wave is only realized for baryon densities of at least about 6 times nuclear saturation density. As an introduction, the necessary tools and concepts are presented. In the end, possible extensions of this work are discussed.

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Identifiers

ORCID for Savvas Pitsinigkos: orcid.org/0000-0001-8674-4876

ORCID for Andreas Schmitt: orcid.org/0000-0003-2858-4450

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