Speaker
Description
The well-known Hubble tension is widely thought to be an indication of new physics beyond $\Lambda$CDM. Theoretical modification happening before recombination (early) seems to be more viable than post-recombination (late) ones since they are less constrained by observations. We propose the AdS-EDE model which solves the tension at 1$\sigma$ level for the first time while remaining compatible with data. Predictions of important cosmological parameters are shifted in correlation with $H_0$ in the early solutions, including EDE, from their $\Lambda$CDM values. The AdS-EDE model proves to be an ideal candidate for studying parameter shifts due to its large $H_0$ value. EDE models show a positive correlation between the scalar primordial spectrum index $n_s$ and $H_0$, and become fully compatible with a Zeldovich-Harrison ($n_s=1$) spectrum given the locally measured $H_0$ value. I will talk about the physical origin of this correlation and its profound implication on our understanding of the early Universe and inflation. The other parameter shift I will discuss is the positive $\omega_{cdm}-H_0$ correlation. The enhancement in $\omega_{cdm}$ induces a larger $S_8$, exacerbating the so called $S_8$ problem which is sometimes employed to criticize EDE. I will explain this correlation is mainly a requirement of background CMB+BAO compatibility and seems inevitable in the simplest EDE models. However, clear knowledge of the physical origin of this correlation actually tells us how to possibly restore concordance with $S_8$ and LSS in the EDE models.
