Cosmology

darksirens.cosmology.cosmo module

class darksirens.cosmology.cosmo.Cosmology(params)

Bases: object

camb_basis(cosmopars)

Checks for \(h\) and \(\Omega_m\) in the parameters passed and replaces them with \(H_0\) and \(\Omega_ch^2\).

Parameters

cosmopars (dictionary) – cosmological parameters passed by the user.

Returns

The modified cosmopars dictionary.

Return type

dictionary

get_cosmo_funcs(inipars)

Gets cosmological functions using camb.

Parameters

inipars (dictionary) – parameters passed to camb to get cosmological results.

Returns

Dictionary of cosmological functions.

Return type

dictionary

darksirens.cosmology.lensing module

class darksirens.cosmology.lensing.Lensing(cosmo)

Bases: object

This class manages the weak-lensing corrections to GW observations. It depends on the cosmology.

draw_magnification(z, size=None)

Randomly draws the magnification mu of an event, according to a shifted log-normal distribution. In other words, the quantity \(X = \ln(\mu - \mu_{\rm min})\) follows a normal distribution. The parameters of the distribution are chosen so as to ensure that \(\langle\mu\rangle = 1\), in agreement with the magnification theorem; and \(\langle\mu^2\rangle - \langle\mu\rangle^2 = 4 \sigma_\kappa^2\).

Parameters

• z – the redshift of the event.

• size – output shape of the distribution drawn from (np.random.normal())

get_minimal_magnification(cosmo, z_max=100, n_sample=1000)

Generates the minimal magnification up to \(z_{\rm max}\) by interpolating a sample of \(n_{\rm sample}\) elements.

Parameters

• cosmo – instance of the Cosmology class.

• z_max (float) – maximum redshift for the magnification.

• n_sample (integer) – number of elements in the sample to be interpolated.

Returns

The minimal magnification.

Return type

interp1d

pdf_magnification(mu, z)

Empirical PDF for the magnification at redshift \(z\). This is only for testing purposes.

Parameters

• mu (float) – the magnification.

• z (float) – the redshift of the event.

std_dev_convergence(z)

Standard deviation of the weak-lensing convergence. The expression is an empirical fit to the weak-lensing prediction, in the flat sky and Limber’s approximation, and with a cosmology such that \(h=0.674\), \(\Omega_m=0.315\) and \(\Omega_b=0.05\).

Warning: To be changed depending on the cosmology. Run the notebook “variance_convergence” with the cosmology of your choice and replace the best-fit parameters a, b, c, d hereafter.

Parameters

z (float) – the redshift of the event.