Testing Horndeski Gravity in the Era of Stage IV Surveys

by Matteo Cataneo (University of Bonn)

Thursday Oct 30, 2025, 2:15 PM → 3:45 PM Europe/Berlin

D6-135 (UHG)

This is an exceptionally exciting time for cosmology. The Euclid mission has begun mapping the Universe with unprecedented precision, and the Legacy Survey of Space and Time (LSST) will soon follow, together delivering observations that will transform our ability to test gravity and dark energy. At the same time, recent results from the Dark Energy Spectroscopic Instrument (DESI), hinting at an evolving dark energy equation of state - possibly crossing the phantom divide - have reignited interest in alternatives to the standard cosmological model, ΛCDM. The simplest extensions introduce an additional scalar field, originally motivated as a dynamical form of dark energy that could reproduce cosmic acceleration without invoking a cosmological constant. This seemingly minimal modification, however, opens a vast and intricate theory space. Horndeski gravity provides a unifying framework to organise this landscape of scalar–tensor theories and to systematically constrain departures from ΛCDM in the ongoing search for the physics driving cosmic acceleration.
Confronting these theories with data requires modelling techniques that can predict cosmological observables across a broad range of physical scales - from the linear regime of large-scale structure to the deeply non-linear scales of clusters and groups of galaxies.
In this talk, I will present a modelling strategy grounded in effective field theory and the halo model that achieves this goal for general Horndeski cosmologies. I will show how this approach streamlines both theoretical exploration and data analysis, and outline a roadmap of methodological advances designed to make the framework robust and fully deployable for forthcoming Stage IV survey analyses.

 

2025-10-30_Matteo_Cataneo.pdf