Toward a concordance teleparallel cosmology. Part I. Background dynamics

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Assuming a spatially flat universe, we study the cosmological viability of an infrared corrected teleparallel gravity model, which accounts for late acceleration by weakening gravity at later times on cosmological distances. The theory does not introduce any additional free parameters into the cosmological model, as is commonly the case with modified gravity based cosmologies. This feature renders the cosmological model statistically comparable, on equal footing, with ΛCDM. In this context, using recent cosmological observations — Pantheon supernova Type Ia, Hubble constant H0, Baryon acoustic oscillation, redshift space distortions, Big Bang nucleosynthesis and the cosmic microwave background constraint on the decoupling acoustic scale — we show that, although the exponential infrared-corrected gravity and ΛCDM are physically different, they are phenomenologically and statistically equivalent. However, the former is more adept at fitting accurately determined observational constraints while decreasing the H0 tension without worsening the S8 tension. This calls for full examination of the empirical viability of the theory at the linear perturbation level, which is the subject of part II.