A model-independent reconstruction of dark energy to very high redshift

Abstract

We provide a model-independent reconstruction of dark energy from $z=0$ to $\gtrsim 10^5$. We parameterise the model by a perfect fluid with a series of physically well-motivated bins in energy-density, such that the equation of state is always $-1\le w\le 1$. Our method is capable of describing a range of theoretical models with smooth modifications to the expansion history. Combining the latest CMB, BAO, SN and local $H_0$ measurements, we obtain a large improvement of $\Delta {\chi }^2=41.3$ over LCDM, at the expense of 33 additional parameters in the fit, with dark energy contributing significantly between $z\sim 10^4-10^5$, and intriguingly with a sound speed $c_s^2\sim 1/3$. A significant part of the $\Delta {\chi }^2$ improvement comes from \Planck\ + Atacama Cosmology Telescope (\textsc{Act}) data, alleviating tension between them within LCDM. We apply a correlation prior to penalise models with unnecessary degrees of freedom and find no preference for deviations from LCDM at late-times, but moderate Bayesian evidence of an early dark energy (EDE) component. Although the model has a large amount of freedom, it is unable to reduce $S_8\equiv {\sigma }_8({\Omega }_{\mathrm{c}}/0.3{)}^{0.5}$ below that of \lcdm, to bring about full concordance with large-scale structure data.

7 pages, 3 figures

Cited by in corpus (1)

• Hot New Early Dark Energy