Baryon Acoustic Oscillations in the Lyman-alpha forest of BOSS quasars

I will present the measurement of baryon acoustic oscillations (BAO) using Lyman-alpha forests of BOSS quasars. The Lyman-alpha absorption in quasar spectra traces the matter distribution along the quasar lines of sight. Using 160,000 high-redshift quasars, the BAO scale is measured at 3{\%} level in the flux correlation function. This translates into a 3{\%} accuracy measurement of the expansion rate at z $=$ 2.3, unique at this redshift. Combined with the local expansion rate, this result requires cosmological models with a dark energy component, as also inferred by previous supernovae studies.