Dynamical dark energy imprints in the Lyman- α forest

The nature of dark energy (DE) remains elusive, even though it constitutes the dominant energy-density component of the Universe and drives the late-time acceleration of cosmic expansion. By combining measurements of the expansion history from baryon acoustic oscillations, supernova surveys, and cosmic microwave background data, the Dark Energy Spectroscopic Instrument (DESI) Collaboration has inferred that the DE equation of state may evolve over time. The profound implications of a time-variable, ``dynamical'' DE (DDE) that departs from a cosmological constant motivate the need for independent observational tests. In this work, we use a focused set of cosmological hydrodynamical simulations to investigate how DDE affects the properties of the Lyman-α ``forest'' of absorption features produced by neutral hydrogen in the cosmic web. We find that DDE models consistent with the DESI constraints induce a spectral tilt in the forest transmitted flux power spectrum, imprinting a scale- and redshift-dependent signature relative to standard ΛCDM cosmologies. These models also yield higher intergalactic medium temperatures and reduced Lyman-α opacity compared to ΛCDM. We discuss the observational implications of these trends as potential avenues for independent confirmation of DDE.