The first three minutes after the birth of the world are a cosmic kitchen where nature cooked the lightest atomic nuclei. The recipe is set by gravity: it controls the cooling rate of the hot 'broth' of particles. If gravity worked differently than we are used to, the dish would have turned out different — with different amounts of helium and deuterium.
The authors took a fresh theory of spacetime curvature: it is called $f(R,G,\mathcal{T})$ and is more complex than Einstein's. In this theory, curvature depends not only on matter but also on its internal pressure, as well as on a special combination of curvatures — the so-called Gauss–Bonnet invariant. Four variants of such gravity were stress-tested against data from the 'kitchen': how much helium was cooked in the first minutes.
The constraints turned out to be no tighter than for standard cosmology. For each of the four models, wide parameter regions exist where the calculated helium abundance falls within the allowed corridor. In other words, the new gravity does not spoil the proven recipe for light nuclei: it just adds new, still permissible ingredients.
Thus, the first minutes of the universe become not only the cradle of matter but also a testing ground for the boldest theories of gravity. The same cosmic kitchen that gave us hydrogen and helium now helps verify the geometry of space itself.
as written by the authors arXiv:2607.17252
In this article, We investigate the cosmological consequences of a recently developed $$f(R,G,\mathcal{T})$$ gravitational framework, in which the action is formulated as a general function of the Ricci scalar $$R$$, the Gauss-Bonnet invariant $$G$$, and the trace of the energy-momentum tensor $$\mathcal{T}$$. As one of the most reliable probes of the physical conditions in the early universe, Big Bang nucleosynthesis offers a stringent framework for testing deviations from standard cosmology. We consider four representative models that are analyzed and constrained using observational limits on $$\left|\Delta T_f/T_f\right|$$ and the primordial helium mass fraction $$Y_p$$. The bounds obtained identify the allowed parameter regions for each model and demonstrate that significant departures from standard cosmology are compatible with nucleosynthesis observations. Our analysis shows that broad regions of the parameter space satisfy existing nucleosynthesis constraints, indicating the consistency of $$f(R,G,\mathcal{T})$$ gravity with the observed primordial light-element abundances and the established picture of the early universe preserving the observed abundances of light nuclei.
Almost all the helium that fills party balloons was not born in the Big Bang but in the interiors of stars, yet primordial helium still makes up about a quarter of all helium in the universe.