SPEAKER: Luca Izzo (Università di Roma `Sapienza')
ABSTRACT: Data from cosmic microwave background radiation, baryon acoustic oscillations, and supernovae Ia (SNe-Ia) support a Universe dominated by an exotic component, the "dark energy”, whose equation of state seems to be constant and negative, w0 ~ -1. This feature renders DE a “repulsive” force, very likely responsible for the observed acceleration of the universe. Measuring the evolution of w along the redshift is one of the most demanding challenges for observational cosmology. In this talk, I’ll discuss the use of gamma-ray bursts as possible probes for the high-redshift universe. In particular, after a brief introduction on GRB phenomenology, I’ll present and discuss the existence of a tight relation for GRBs, named "Combo-relation", based on characteristic parameters of GRB prompt and afterglow phenomenology. The core of the proposed method consists in a light-curve fitting procedure, similar to the SNe Ia sample, and then recover the estimate of the initial luminosity of the shallow phase, which represents "the ruler" of the proposed relation. This is used to measure $\Omega_m$ and the evolution of the dark energy equation of state w(z). I also discuss the use of a new calibration method for the same relation, which reduces the dependence on SNe Ia systematics, rendering GRBs an almost independent dataset for investigating the geometry and the content of the Universe.