The hot Hagedorn Universe

TL;DR

This paper reviews the historical and current role of Hagedorn temperature and the statistical bootstrap model in understanding the hot early universe, emphasizing the connection between QGP physics and cosmological observations like the CMB.

Contribution

It provides a comprehensive overview of how Hagedorn temperature insights contributed to cosmology and links early universe QGP properties with modern experimental and lattice QCD studies.

Findings

Enhanced understanding of neutrino freeze-out

Improved interpretation of CMB temperature fluctuations

Established connection between QGP in early universe and laboratory experiments

Abstract

In the context of the half-centenary of Hagedorn temperature and the statistical bootstrap model (SBM) we present a short account of how these insights coincided with the establishment of the hot big-bang model (BBM) and helped resolve some of the early philosophical difficulties. We then turn attention to the present day context and show the dominance of strong interaction quark and gluon degrees of freedom in the early stage, helping to characterize the properties of the hot Universe. We focus attention on the current experimental insights about cosmic microwave background (CMB) temperature fluctuation, and develop a much improved understanding of the neutrino freeze-out, in this way paving the path to the opening of a direct connection of quark-gluon plasma (QGP) physics in the early Universe with the QCD-lattice, and the study of the properties of QGP formed in the laboratory.