Kick it like DESI: PNGB quintessence with a dynamically generated initial velocity

Understand

Motivated by the hint for time-dependent dynamical dark energy from an analysis of the DESI Baryon Accoustic Oscillation (BAO) data together with information from the Cosmic Microwave Background (CMB) and Supernovae (SN), we relax the assumption of a vanishing initial velocity for a quintessence field.

• In particular we focus on pseudo-Nambu-Goldstone-Boson (PNGB) quintessence in the form of an axion like particle, that can arise as the phase of a complex scalar and could possess derivative couplings to fermions or topological couplings to abelian gauge fields, without upsetting the necessary flatness of its potential.
• We discuss mechanisms from the aforementioned interactions for sourcing an initial axion field velocity $\dot{\theta_i}$ at redshifts $3\leq z\leq 10$, that will "kick" it into motion.
• Driven by this initial velocity the axion will first roll up in its potential, similar to "freezing" dark energy.