Papers › Anchors no more: Using peculiar velocities to constrain H₀ and the primordial Universe...
Anchors no more: Using peculiar velocities to constrain H₀ and the primordial Universe without calibrators
Davide Piras, Francesco Sorrenti, Ruth Durrer, Martin Kunz
We develop a novel approach to constrain the Hubble parameter H₀ and the primordial power spectrum amplitude Aₛ using supernovae type Ia (SNIa) data. By considering SNIa as tracers of the peculiar velocity field, we can model their distance and their covariance as a function of cosmological parameters without the need of calibrators like Cepheids; this yields a new independent probe of the large-scale structure based on SNIa data without distance anchors. Crucially, we implement a differentiable pipeline in JAX, including efficient emulators and affine sampling, reducing inference time from years to hours on a single GPU. We first validate our method on mock datasets, demonstrating that we can constrain H₀ and log10¹⁰Aₛ within ∼10% using ∼10³ SNIa. We then test our pipeline with SNIa from an N-body simulation, obtaining 7%-level unbiased constraints on H₀ with a moderate noise level. We finally apply our method to Pantheon+ data, constraining H₀ at the 10% level without Cepheids when fixing Aₛ to its Planck value. On the other hand, we obtain 15%-level constraints on log10¹⁰Aₛ in agreement with Planck when including Cepheids in the analysis. In light of upcoming observations of low redshift SNIa from the Zwicky Transient Facility and the Vera Rubin Legacy Survey of Space and Time, surveys for which our method will develop its full potential, we make our code publicly available.
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