Spectrum of scalar and pseudoscalar glueballs from functional methods

Area of Science:

• Theoretical particle physics
• Quantum chromodynamics
• Non-perturbative field theory

Background:

• Glueballs are hypothetical particles composed solely of gluons.
• Understanding glueball spectra is crucial for probing the non-perturbative regime of quantum chromodynamics (QCD).
• Previous theoretical approaches often relied on approximations or external inputs.

Purpose of the Study:

• To calculate the spectrum of scalar and pseudoscalar glueballs in pure Yang-Mills theory.
• To provide parameter-free predictions for glueball masses.
• To validate the employed theoretical framework against lattice QCD results.

Main Methods:

• Utilizing a parameter-free, self-contained truncation of Dyson-Schwinger equations (DSEs) and Bethe-Salpeter equations (BSEs).
• Fixing the single input scale by comparison with existing lattice QCD calculations.
• Ensuring the self-consistency of the truncation for reliable predictions.

Main Results:

• Obtained ground state masses for scalar and pseudoscalar glueballs as M_scalar = 2.70(11) GeV and M_pseudoscalar = 2.67(10) GeV.
• Calculated first excited state masses at M_scalar_ex1 = 4.16(16) GeV and M_pseudoscalar_ex1 = 4.10(15) GeV.
• Predicted second excited state masses at M_scalar_ex2 = 5.1(2) GeV and M_pseudoscalar_ex2 = 5.0(2) GeV.

Conclusions:

• The calculated glueball masses show very good quantitative agreement with available lattice QCD results.
• The independence of masses from the ghost propagator's infrared behavior supports the non-perturbative gauge completion.
• The self-consistent truncation provides a reliable method for studying glueball properties in the absence of dynamical quarks.