Thermal properties of the scalar glueballs from holography

TL;DR

This paper uses a holographic QCD model combined with machine learning to analyze scalar glueballs' thermal properties across temperatures, revealing behaviors consistent with lattice simulations and providing insights into their spectral functions and quasi-normal modes.

Contribution

It introduces a systematic holographic framework with machine learning to study scalar glueballs' thermal properties from zero to finite temperature, including spectral functions and quasi-normal modes.

Findings

Pole masses remain near vacuum values at low T and decrease as T approaches T_c.

Pole masses increase above T_c, aligning with recent lattice results.

Thermal widths increase monotonically with temperature.

Abstract

Based on a machine learning holographic QCD model, we construct a systematical framework to investigate the properties of the scalar glueballs continuously from zero temperature to finite temperature. By using both the quasi-normal frequencies and the spectral functions, we extract the pole masses, thermal widths, screening masses and dispersion relation of the scalar glueballs in hot medium. It is shown that the pole masses almost remain the vacuum values at temperatures far below the critical temperature $T_c$ , and then decrease with the increasing of temperature until a temperature lower than $T_c$. This result qualitatively agrees with earlier lattice simulations. While the pole masses increase monotonically above the critical temperature $T_c$, which agrees with recent lattice calculation. Meanwhile, it is shown that the thermal widths increase monotonically with temperature, which also agrees with the near $T_c$ lattice simulations. The screening mass exhibits a similar temperature-dependent behavior to the pole mass, while the dispersion relation increasingly deviates from the relativistic one as the temperature rises. It is interesting to note that we obtain the imaginary corrections in the thermal correlators, which contains both the temperal and spatial information and might be helpful for the four-dimensional calculations. Furthermore, by comparing the quasi-normal modes and the spectral functions, we note that it requires more careful analysis when applying the spectral functions in studying thermal hadrons from holography, since there could be other types of quasi-normal modes which are not related with bound states while they may contribute to the peaks of the spectral functions.