Evidence for quark-diquark structure of baryons from fluctuations of conserved charges

TL;DR

This paper provides thermodynamic evidence supporting a string quark-diquark model of baryons in QCD, by comparing hadronic spectra derived from string theory with lattice QCD fluctuations of conserved charges.

Contribution

It introduces a string-based hadronic spectrum model with quark-diquark endpoints and demonstrates its consistency with lattice QCD data on conserved charge fluctuations.

Findings

Hagedorn spectrum fits lattice QCD data without extra parameters

Net-baryon fluctuations are underestimated by traditional models

String quark-diquark picture aligns with observed thermodynamics

Abstract

We study fluctuations and correlations of conserved charges in QCD using a string-based description of the hadronic mass spectrum. Mesons and baryons are modeled as open relativistic strings with quark-antiquark and quark-diquark endpoints, respectively, leading to an exponential Hagedorn growth of states with a limiting temperature fixed by the string tension. We find that continuous Hagedorn spectra constrained by experimentally established hadrons underestimate net-baryon number fluctuations obtained in lattice QCD calculations. By extracting the Hagedorn string spectrum directly from lattice QCD through a fit to the second-order net-baryon number susceptibility, we obtain a consistent description of a broad set of fluctuations of conserved charges from LQCD with the Hagedorn temperature $T_H \simeq 323~$MeV, without introducing additional free parameters. Our results provide thermodynamic evidence in support of a string quark-diquark picture of baryons in the confined phase of QCD.