Investigating the Combo correlation of gamma-ray bursts as a tracer of dynamical dark energy

Abstract

The Dark Energy Spectroscopic Instrument (DESI) collaboration recently presented results indicating that dark energy (DE) may exhibit dynamical behavior. Calibrated gamma-ray burst (GRB) correlations can be employed to verify or reject a time evolution of the DE equation of state (EoS), ω(z), up to redshifts of z∼ 9. We used the most updated catalog of GRBs fulfilling the Combo correlation; we improved its calibration by employing three catalogs of type Ia supernovae at redshifts of złeq0.075 and the Bézier interpolation of the Hubble rate as an alternative to the cosmographic series that cannot be constrained at high redshifts. To test the evolution of ω(z), we adopted a model-independent, redshift-binned DE parameterization. In both the calibration and the DE reconstruction analyses, the impact of the spatial curvature on the results was explored. The calibrated Combo correlation yields a Hubble constant of H_0 km/s/Mpc, which alleviates the existing Hubble tension and is broadly consistent with current measurements, although the uncertainties prevent a high-precision measurement. Regarding the reconstruction of ω(z), at złesssim0.55 we find a clear (gtrsim2 sigma) departure towards ω<-1 from the cosmological constant value. However, the shortage of GRBs in this redshift interval, together with possible population and selection effects, prevents us from drawing a robust conclusion about this trend. At z>0.55, the reconstructed DE EoS is statistically compatible with ω=-1. The Combo correlation alleviates the Hubble tension, suggesting that GRBs, as distance indicators, are broadly consistent with the current cosmic distance ladder. Overall, our results do not provide robust evidence of dynamical DE; they highlight a low-redshift phantom behavior whose interpretation requires a larger and better characterized sample of nearby GRBs.