# Local measurement of H0¶

Synopsis

Prototype class for local Hubble parameter measurements

Author

This is a simple gaussian likelihood for the latest local $$H_0$$ measurements using a combination of different data.

It defines the following likelihoods

• H0.riess2018a: A legacy local measurement of $$H_0$$, used in the analysis of Planck data for the Planck 2018 release. (arXiv:1801.01120)

• H0.riess2018b: Updated local measurement of $$H_0$$. (arXiv:1804.10655)

• H0.riess201903: Riess et al. 2019 constraint (arXiv:1903.07603)

• H0.riess2020: Riess et al. 2020 constraint (arXiv:2012.08534)

• H0.freedman2020: Freedman et al. 2020 constraint (arXiv:2002.01550)

The above are all based on simple Gaussian posteriors for the value of H0 today, which is not what is directly measured. It can be more accurate to put a constraint on the intrinsic magnitude, which can then be combined with Supernovae constraints to relate to the expansion. An example is provided in

which should be run in combination with sn.pantheon with use_abs_mag: True (contributed by Pablo Lemos).

## Using a different measurement¶

If you would like to use different values for the $$H_0$$ constraint, as a mean and a standard deviation, simply add the following likelihood, substituting mu_H0 and sigma_H0 for the respective values:

likelihood:
my_H0:
external: 'lambda _self: -0.5 * (_self.provider.get_param("H0") - mu_H0)**2 / (sigma_H0)**2'
requires: ["H0"]