Null energy condition violation and beyond Horndeski physics in light of DESI DR2 data

Understand

Inflation and dark energy (DE), both featuring accelerated expansion, are crucial components of modern cosmology.

• As indicated by singularity theorems, null energy condition (NEC) violation is essential for resolving the initial singularity of inflation.
• The latest DESI DR2 results show that the DE equation of state evolves from $w_{\rm DE} < -1$ at redshift $z \lesssim 1$ to $w_{\rm DE} > -1$ today, reinforcing interest in testing NEC violation in the observable Universe.
• Within a unified effective field theory framework that applies to both inflation and DE, we use DESI DR2 data and a non-parametric reconstruction approach to test, for the first time, the ``beyond Horndeski'' physics known to support fully stable NEC violation in nonsingular cosmology.