![]() ![]() ![]() 3 for a comprehensive list of references). This 4.2 σ disagreement, known as the “Hubble tension”, has spurred much interest in modifications of the ΛCDM model capable of resolving it (cf. In particular, the Supernovae H0 for the Equation of State (SH0ES) collaboration 2, using Cepheid calibrated supernovae Type Ia, finds a much higher value of H 0 = 73.5 ± 1.4 km/s/Mpc. Although this ΛCDM model fits many observations exquisitely well, its prediction for the present-day cosmic expansion rate, H 0 = 67.36 ± 0.54 km/s/Mpc 1, based on precise cosmic microwave background (CMB) radiation observations by the Planck satellite, do not compare well with direct measurements of the Hubble constant. ![]() We show explicitly that models which achieve a higher Hubble constant with lower values of matter density Ω m h 2 run into tension with the observations of baryon acoustic oscillations, while models with larger Ω m h 2 develop tension with galaxy weak lensing data.ĭecades of progress in observational and theoretical cosmology have led to the consensus that our universe is well described by a flat Friedman–Robertson–Lemaitre metric and is currently comprised of around 5% baryons, 25% cold dark matter (CDM), and 70% dark energy in its simplest form-the cosmological constant Λ. We demonstrate here that any model which only reduces r ⋆ can never fully resolve the Hubble tension while remaining consistent with other cosmological datasets. Many of them introduce new physics, such as early dark energy, modifications of the standard model neutrino sector, extra radiation, primordial magnetic fields or varying fundamental constants, with the aim of reducing the sound horizon at recombination r ⋆. A large number of amendments to the ΛCDM model have been proposed in order to solve this tension. The mismatch between the locally measured expansion rate of the universe and the one inferred from the cosmic microwave background measurements by Planck in the context of the standard ΛCDM, known as the Hubble tension, has become one of the most pressing problems in cosmology. ![]()
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