Can an Anti-de Sitter Vacuum in the Dark Energy Sector Explain JWST High-Redshift Galaxy and Reionization Observations?

TL;DR

The JWST-detected abundance of UV-bright galaxies at $z>10$ challenges canonical $\Lambda$CDM. The authors test a beyond-$\Lambda$CDM framework featuring an AdS vacuum in the dark-energy sector implemented via a CPL scalar field with $w_\phi(z)=w_0+w_a\frac{z}{1+z}$ and a negative $\Lambda$, coupled to a self-consistent semi-analytic model of galaxy evolution and reionization. They find that cosmological modifications can boost early structure formation but cannot simultaneously satisfy CMB and low-redshift constraints, implying some evolution in high-$z$ galaxy properties is necessary. The results emphasize holistic testing of beyond-$\Lambda$CDM proposals and motivate integrating the framework with fast semi-numerical codes to predict a broader set of observables for current and upcoming surveys.

Abstract

The unexpectedly large abundance of UV-bright galaxies at $z>10$ discovered by the James Webb Space Telescope poses a significant challenge to the standard $Λ$CDM cosmology. This work tests whether modifying the cosmological background, and thereby the growth of structures, can resolve this tension without invoking significant evolution in the astrophysical properties of early galaxies. We investigate an alternative framework featuring an anti-de Sitter vacuum in the dark energy sector, which naturally arises in quantum gravity models like string theory and can enhance early structure formation. Using a self-consistent semi-analytical model that couples galaxy evolution with reionization, we confront this scenario with a wide range of observations. We show that while a model tailored to fit the high-$z$ UV luminosity functions (UVLFs) appears promising, it is in strong tension with cosmological constraints from the CMB and other low-redshift probes. Conversely, models within this framework that satisfy these constraints provide only a modest boost to structure formation and fail to reproduce the observed galaxy abundances at $z>10$. Although these models remain consistent with the cosmic reionization history, we find that this class of cosmological modifications is insufficient on its own to explain the galaxy excess. Our study underscores the importance of holistic testing for any beyond-$Λ$CDM proposal; apparent success in one observational regime does not guarantee overall viability. By demonstrating the limitations of a purely cosmological solution, our results strengthen the case that evolving astrophysical properties are a necessary ingredient for solving the challenge of early galaxy formation.

Figures (13)

• Figure 1: The evolution of the linear growth factor (top panel) and the Hubble expansion rate $H(z)$ relative to $\Lambda$CDM (bottom panel) as a function of redshift for different cosmological models with dynamical dark energy.
• Figure 2: The effect of dynamical dark energy models, featuring a scalar field with a redshift-dependent equation of state described by equation (\ref{['eq:cpl_eos']}) and a negative cosmological constant $\Lambda$, on the dark matter halo mass functions at high redshifts ($z=7, 10,$ and $13$). Here, we only vary $\Omega_\Lambda$ while keeping the equation of state parameters of the scalar field $\phi$ fixed ($w_0 = -1.05$, $w_a = 0.7$).
• Figure 3: The galaxy UV luminosity functions at nine different redshifts (with their respective mean values $\langle z \rangle$ mentioned in the upper left corner) for 200 random samples drawn from the MCMC chains of the fiducial CPL$\bm{n\Lambda}$CDM case. In each panel, the solid dark-violet line corresponds to the best-fitting model, while the colored data points show the different observational constraints Bouwens2021Donnan2023Harikane2023Bouwens2023McLeod2024Donnan2024 used in the likelihood analysis. The prediction from a model within the $\bm{\Lambda}$CDM (Planck 2018) cosmology that best matches the observational measurements at $z < 10$ and does not assume any evolution in the UV efficiency parameters above $z \sim 10$ is also shown using black dotted lines.
• Figure 4: The evolution of the globally averaged intergalactic neutral hydrogen fraction as a function of redshift for 200 random samples drawn from the MCMC chains of the fiducial CPL$\bm{n\Lambda}$CDM case. The colored data points represent the observational measurements of $Q_{\rm HI}$($z$) used in the analysis.
• Figure 5: Comparison of the evolution of energy densities and expansion rates across different cosmological models. The top panel shows the redshift evolution of the matter density (solid lines) and the total dark energy density (dashed lines). The bottom panel presents the ratio of the Hubble parameter in our fiducial CPL$n\Lambda$CDM model to that in the $\Lambda$CDM model, as a function of redshift.