Dark Energy models

class camb.dark_energy.DarkEnergyModel

Abstract base class for dark energy model implementations.

class camb.dark_energy.DarkEnergyEqnOfState

Bases: camb.dark_energy.DarkEnergyModel

Abstract base class for models using w and wa parameterization with use w(a) = w + (1-a)*wa parameterization, or call set_w_a_table to set another tabulated w(a). If tabulated w(a) is used, w and wa are set to approximate values at z=0.

See model.CAMBparams.set_initial_power_function() for a convenience constructor function to set a general interpolated P(k) model from a python function.

Variables:

• w – (float64) w(0)
• wa – (float64) -dw/da(0)
• cs2 – (float64) fluid rest-frame sound speed squared
• use_tabulated_w – (boolean) using an interpolated tabulated w(a) rather than w, wa above

set_params(w=-1.0, wa=0, cs2=1.0)

Set the parameters so that P(a)/rho(a) = w(a) = w + (1-a)*wa

Parameters:

• w – w(0)
• wa – -dw/da(0)
• cs2 – fluid rest-frame sound speed squared

set_w_a_table(a, w)

Set w(a) from numerical values (used as cublic spline). Note this is quite slow.

Parameters:

• a – array of scale factors
• w – array of w(a)

Returns:

self

class camb.dark_energy.DarkEnergyFluid

Bases: camb.dark_energy.DarkEnergyEqnOfState

Class implementing the w, wa or splined w(a) parameterization using the constant sound-speed single fluid model (as for single-field quintessense).

class camb.dark_energy.DarkEnergyPPF

Bases: camb.dark_energy.DarkEnergyEqnOfState

Class implementating the w, wa or splined w(a) parameterization in the PPF perturbation approximation (arXiv:0808.3125) Use inherited methods to set parameters or interpolation table.

class camb.dark_energy.Quintessence

Bases: camb.dark_energy.DarkEnergyModel

Abstract base class for single scalar field quintessence models.

For each model the field value and derivative are stored and splined at sampled scale factor values.

To implement a new model, need to define a new derived class in Fortran, defining Vofphi and setting up initial conditions and interpolation tables (see TEarlyQuintessence as example).

Variables:

• DebugLevel – (integer)
• astart – (float64)
• integrate_tol – (float64)
• sampled_a – (float64 array)
• phi_a – (float64 array)
• phidot_a – (float64 array)

class camb.dark_energy.EarlyQuintessence

Bases: camb.dark_energy.Quintessence

Example early quintessence (axion-like, as arXiv:1908.06995) with potential

V(phi) = m^2f^2 (1 - cos(phi/f))^2 + Lambda_{cosmological constant}

Variables:

• n – (float64) power index for potential
• f – (float64) f/Mpl (sqrt(8piG)f); only used for initial search value if use_zc is True
• m – (float64) mass parameter in reduced Planck mass units; only used for initial search value of use_zc is True
• theta_i – (float64) phi/f initial field value
• frac_lambda0 – (float64) fraction of dark energy in cosmologicla constant today (approximated as 1)
• use_zc – (boolean) solve for f, m to get specific critical reshidt zc and fde_zc
• zc – (float64) reshift of peak fractional early dark energy density
• fde_zc – (float64) fraction of early dark energy density to total at peak
• npoints – (integer) number of points for background integration spacing
• min_steps_per_osc – (integer) minimumum number of steps per background oscillation scale
• fde – (float64 array) after initialized, the calculated backgroundearly dark energy fractions at sampled_a

class camb.dark_energy.AxionEffectiveFluid

Bases: camb.dark_energy.DarkEnergyModel

Example implementation of a specifc (early) dark energy fluid model (arXiv:1806.10608). Not well tested, but should serve to demonstrate how to make your own custom classes.

Variables:

• w_n – (float64) effective equation of state parameter
• fde_zc – (float64) energy density fraction at z=zc
• zc – (float64) decay transition redshift (not same as peak of energy density fraction)
• theta_i – (float64) initial condition field value