Solving the Cosmic Coincidence Problem: The Locally Pumped Dark Energy Model

Abstract

We propose the Locally Pumped Dark Energy (LPDE) mechanism in which cosmic acceleration is triggered by the emergence of non-linear dark matter structure. In an effective-field-theory description, coarse-graining over the density contrast profile, whose short-wavelength modes grow during halo formation, induces a shift in the local equilibrium point of a second, sufficiently heavy scalar field $χ$. At early times, the pump mechanism is negligible and $χ$ remains fixed at the origin, contributing no DE. As structures form, the equilibrium value of $χ$ is locally displaced within halos, generating a vacuum energy whose global contribution, in a mean-field picture, is controlled by the halo volume filling factor. If the $χ$ field is sufficiently heavy, with a Compton wavelength limited by halo scales, its response is localised, and spatial gradients are exponentially suppressed on large scales. After volume-averaging over the halo population, the resulting contribution on large scales behaves as a homogeneous DE component. Using the halo mass function of a fiducial $Λ$CDM cosmology, we show that vacuum-energy domination generically emerges at $z\sim\mathcal{O}(1)$, naturally correlating cosmic acceleration with structure formation. For reference, we present an explicit realisation of such a mechanism and show that, by naturally featuring a transient acceleration epoch, it can be in excellent agreement with the most recent cosmological data, including the Dark Energy Spectroscopic Instrument (DESI).

Figures (6)

• Figure 1: Illustration of the pump mechanism. The local equilibrium position shifts as non-linear structures form. The DE field $\chi$ tracks the evolving minimum adiabatically.
• Figure 2: Collapsed fraction (top) and volume filling fraction (bottom) as a function of redshift for a representative PLANCK-like cosmology calculated using the Sheth-Tormen parametrisation for the halo mass function.
• Figure 3: LPDE predictions (purple dash-dotted line) for $f_V(z)$ (top-left panel), $f_{\rm DE}(z)$ (bottom-left panel), $Om(z)$ (top-centre panel), the (normalised) Hubble parameter $h(z) \equiv H(z)/H_0$ normalized to the $\Lambda$CDM value (bottom-centre panel), the (effective) EoS parameter $w_{\rm eff}(z)$ (top-right panel), and the deceleration parameter $q(z)$ (bottom-right panel) as functions of redshift (see main text for the definitions of these quantities) for $p_{\chi} = 1/2$, $M_{\rm Min} = 10^{8} M_{\odot}$, $M_{\rm Min} = 10^{18}M_{\odot}$. In these plots, the colourful cyan bands represent the 1 to 3$\sigma$ (in progressively lighter shades of cyan) constraints from DESI:2025fii (see main text) and, for reference, dark grey dashed lines are used to highlight the $\Lambda$CDM predictions.
• Figure 4: Acceleration ratio $\mathcal{G}(r)$ (left column) and density ratio $\rho_\chi/\rho_{\rm DM}$ (right column) for two representative galactic halo with Einasto profiles parameters $\alpha=0.15$, $r_s=20\,{\rm kpc}$, $c_{200}=5$, (top row) and $\alpha=0.15$, $r_s=4\,{\rm kpc}$, $c_{200}=20$, (bottom row), both corresponding to $c_{200}/c_\chi=20$. Both the amplitude-dominated (solid blue lines) and the gradient-dominated (dashed orange) profiles are shown.
• Figure 5: Same plots as in Fig. \ref{['fig:cosmo_summary']}, but varying $M_{\rm min}$ in the range $[10^{5} M_{\odot}, 10^{12} M_{\odot}]$. The other parameters are fixed to $p_{\chi} = 1/2$ and $M_{\rm max} = 10^{18} M_{\odot}$.