Probing Modified Gravity with Integrated Sachs-Wolfe CMB and Galaxy Cross-correlations

TL;DR

This study tests modified gravity models against cosmic microwave background and galaxy data, finding that some models predict different ISW effects, with K-mouflage closely matching LCDM and others showing degraded fits.

Contribution

It evaluates three specific Horndeski subclass models using ISW-galaxy cross-correlations, highlighting differences in their predictions and fit quality compared to LCDM.

Findings

GGC and GCCG models predict negative ISW-galaxy correlations, unlike LCDM.

K-mouflage model closely matches LCDM predictions.

GGC and GCCG best-fit models fit the data worse than LCDM.

Abstract

We use the cross-correlation power spectrum of the integrated Sachs-Wolfe (ISW) effect in the cosmic microwave background (CMB) temperature anisotropy and galaxy fluctuations to probe the physics of late-time cosmic acceleration. For this purpose, we focus on three models of dark energy that belong to a sub-class of Horndeski theories with the speed of gravity equivalent to that of light: Galileon Ghost Condensate (GGC), Generalized Cubic Covariant Galileon (GCCG), and K-mouflage. In the GGC and GCCG models, the existence of cubic-order scalar self-interactions allows a possibility for realizing negative ISW-galaxy cross-correlations, while the K-mouflage model predicts a positive correlation similar to the $\Lambda$-cold-dark-matter (LCDM) model. In our analysis, we fix the parameters of each model to their best-fit values derived from a baseline likelihood analysis with observational data from CMB, baryon acoustic oscillations, and supernovae type Ia. Then we fit those best-fit models to the ISW-galaxy cross-correlation power spectrum extracted from a collection of photometric redshift surveys. We find that both GGC and GCCG best-fit models degrade the fit to the ISW-galaxy cross-correlation data compared to LCDM best-fit model. This is attributed to the fact that, for their best-fit values constrained from the baseline likelihood, the cubic-order scalar self-interaction gives rise to suppressed ISW tails relative to $\Lambda$CDM. The K-mouflage best-fit model is largely degenerate with the LCDM best-fit model and has a positively correlated ISW-galaxy power close to that of LCDM.