Intergalactic magnetic field strength and correlation length are unknown

Determine the magnitude B and the correlation length lambda_B of the intergalactic magnetic field, whose values are currently not known, to enable more precise constraints on the graviton charge from gravitational-wave propagation and detector phase differences.

Background

The bounds on the graviton charge derived in the paper depend on the strength B and coherence length lambda_B of intergalactic magnetic fields. The authors note that increasing B and lambda_B tightens the bounds, but emphasize that their true values are not known; only lower limits exist from observations such as non-detection of GeV gamma rays from blazar-induced cascades.

Because of this uncertainty, the analysis adopts conservative choices for B and lambda_B. Firm measurements or tighter lower limits on these parameters would directly improve the precision of graviton charge constraints obtained from gravitational-wave observations and Aharonov–Bohm type phase differences.