Blue-tilted spectral running and the JWST early galaxy tension

Abstract

Recently, the James Webb Space Telescope (JWST) collaboration has found the unexpectedly large abundance of massive galaxies with stellar masses of $\sim 10^{10}{M}_{\odot }$ at high redshifts $z\simeq 6.5-9$ compared with the prediction of the standard $\Lambda$CDM model. As a possible solution to the tension, we consider a blue-tilted spectrum of density perturbations with a positive running. We find that, for ${\alpha }_s\simeq 0.02$ and ${\beta }_s\simeq 0.02$, a joint analysis with CMB observations shows that the tension can be resolved at the 1$\sigma$ confidence level. Such a blue-tilted spectrum is also plausible from the perspective for formations of primordial black holes on much smaller scales in the early Universe.

Comments: 17 pages, 4 figures, to appear in Phys. Rev. D