Weak gravity at micron scales from dark bubble cosmology and its cosmological consequences

TL;DR

The paper analyzes a dark bubble cosmology in 5D AdS space, deriving how gravity weakens at micron scales around $L\sim 10^{-5}$ m and detailing the observable consequences in table-top experiments. It develops a holographic framework with a cutoff hologram that reproduces 4D gravity on large scales while suppressing gravity at short distances, and extends the analysis to cosmology where high-density epochs exhibit a gravity-weakening inflation-like phase without a dedicated inflaton. A nucleation scenario in which a 5D black hole catalyzes the dark bubble’s birth yields a quantitative link to the present matter content and predicts a small positive spatial curvature $\Omega_c\sim 5\times 10^{-4}$, addressing the why-now problem. The work also discusses black-hole phenomenology, proposing black shells as potential 4D mimickers within this framework and outlining future directions for embedding AdS black shells in the dark-bubble model.

Abstract

The dark bubble model makes a positive cosmological constant natural in string theory, and predicts several new physical phenomena within reach in the near future. In this paper we study the experimental consequences of the model for the strength of gravity at scales of order $10^{-5}$m. Contrary to other models of gravity involving extra dimensions, the dark bubble model predicts gravity to become weaker rather than stronger at small scales, compared to Newtonian gravity. In particular, we provide explicit predictions of measurable deviations using table top experiments. We also show how the same effect reduces the effective force of gravity at high energy densities in cosmology, leading to a period of early inflation without the need for anything beyond radiation. We also discuss the quantum origin of the universe with a 5D black hole acting as a catalyst for the nucleation of the dark bubble and how it accounts for the present matter content in the universe. This leads to a prediction of $Ω_c \approx 5\times 10^{-4}$ for a positive curvature of the universe, suggesting an explanation of the why-now-problem of the cosmological constant. We end by speculating on how to incorporate AdS black shells as black hole mimickers within the dark bubble model.

Figures (8)

• Figure 1: A small mass resting on the dark bubble.
• Figure 2: Spacetime outside the bubble (top of the figure, in light gray) contains both the normalizable $I_2$ (decaying towards the boundary) and the non-normalizable $K_2$ (growing towards the boundary) modes, corresponding to the functions $B_+(p), A_+(p)$ respectively. Regularity at the center of the bubble requires that the inside (bottom half of the figure, in dark gray), contains only the non-normalizable $K_2$, corresponding to $A_-(p)$. The functions $f_\pm(p)$ determine how the brane is embedded into the bulk.
• Figure 3: The scale where gravity is turned off is constant on the dark bubble, but its projection in the hologram is shrinking. Thus, in the hologram gravity is turning on starting in the IR.
• Figure 4: The gravitational potential and the gravitational force (both in units of $G_4 M_4$) due to a particle of mass $M_4$, as a function of distance from the particle (in units of the AdS$_5$ length $L$). Upper curves correspond to ordinary 4D gravity, while the lower curves correspond to the the 4D universe on a dark bubble. Gravity on the dark bubble gets weaker at small distances.
• Figure 5: The active mass density for a point mass as a function of radius in units of the AdS$_5$ radius $L$.