Five parameters are all you need (in $\Lambda$CDM)

Understand

The standard cosmological model, with its six independent parameters, successfully describes our observable Universe.

• One of these parameters, the optical depth to reionization $\tau_\mathrm{reio}$, represents the scatterings that Cosmic Microwave Background (CMB) photons will experience after decoupling from the primordial plasma as the intergalactic medium transitions from neutral to ionized.
• $\tau_\mathrm{reio}$ depends on the neutral hydrogen fraction $x_\mathrm{HI}$, which, in turn, should theoretically depend on cosmology.
• We present a novel method to establish the missing link between cosmology and reionization timeline using symbolic regression.