Cosmological constraints on physics beyond general relativity

Abstract

The standard cosmological model, ΛCDM, has long been successful in explaining the Universe’s evolution. However, as observational precision has advanced, significant tensions, such as the Hubble tension and the S8,0 tension, have emerged, challenging the model’s validity and hinting at the potential need for theories beyond General Relativity. Among these alternatives, Teleparallel Gravity, where gravity is described through torsion rather than curvature, offers a promising avenue. In particular, the Teleparallel Equivalent of General Relativity (TEGR) is considered, a formulation that replicates General Relativity’s field equations but uses the torsion scalar T as the primary contributor to the gravitational Lagrangian. To explore the potential of this framework in addressing these tensions, generalised functions such as f(T) and f(T, B) gravity models are investigated. Consequently, in this work a comprehensive suite of cosmological datasets are utilised. The Pantheon compilation of Type Ia Supernovae (SNe Ia) provides precise luminosity distance measurements, constraining the expansion history. Cosmic Chronometers (CC) data offer model-independent estimates of the Hubble parameter based on differential age dating of galaxies. Baryon Acoustic Oscillations (BAO) measurements probe the imprint of sound waves in the early Universe, refining constraints on the late-time expansion. Redshift Space Distortions (RSD) trace the growth of cosmic structures, offering insights into large-scale structure formation. Additionally, the BICEP/Keck BB-spectrum enables exploration of primordial gravitational waves, shedding light on early Universe physics. Alongside these datasets advanced techniques like Gaussian Processes (GPs) for reconstructing the arbitrary function, and Markov Chain Monte Carlo (MCMC) for constraining the parameters of these models are employed. The results establish f(T) gravity as a promising alternative to ΛCDM, capable of addressing persistent tensions such as H0 and S8,0. The models provide observationally consistent solutions for late-time cosmic acceleration, the growth of structures, and primordial gravitational waves. These findings present the most comprehensive constraints on f(T) gravity to date, underscoring its potential as a viable framework and enhance our understanding of the Universe’s evolution, offering valuable insights into the late- and early-time Universe. As a result, this work contributes to the growing body of research exploring alternatives to ΛCDM and highlighting the potential of modified gravity models as viable solutions.