$\mathcal{H}$-EFTCAMB: A Cobaya-Integrated, Python-Wrapped Extension of EFTCAMB for Covariant Horndeski Gravity

TL;DR

A new Horndeski module is introduced that supports computing cosmology for an arbitrary input covariant Horndeski Lagrangian in the EFT framework as well as directly solving for the scalar field equations of motion derived from the covariant Lagrangian.

Abstract

We present $\mathcal{H}\mathtt{-EFTCAMB}$, the official successor to $\mathtt{EFTCAMB}$. The original $\mathtt{EFTCAMB}$ is designed as a consistent and numerically stable implementation of the effective field theory (EFT) of dark energy in the Einstein-Boltzmann code $\mathtt{CAMB}$. On top of this, $\mathcal{H}\mathtt{-EFTCAMB}$ introduces a new Horndeski module that supports computing cosmology for an arbitrary input covariant Horndeski Lagragian. $\mathcal{H}\mathtt{-EFTCAMB}$ supports both mapping the Horndeski theory to an EFT lagrangian to solve in the EFT framework as well as directly solving for the scalar field equations of motion derived from the covariant Lagrangian. The latter approach also works for the cases when the Horndeski field experiences turn-overs, e.g. oscillation, where the EFT approach breaks down. The Horndeski module has been validated by comparing internally with existing models in the original $\mathtt{EFTCAMB}$ and externally with $\mathtt{hi\_class}$. $\mathcal{H}\mathtt{-EFTCAMB}$ features a flexible Python wrapper that is seamlessly integrated into the widely utilized cosmological sampler $\mathtt{Cobaya}$. \heft~is publicly available and serves as a comprehensive tool for testing gravity against the precision data from current and next-generation surveys.

Figures (7)

• Figure 1: The flag tree for $\mathcal{H}-$EFTCAMB. The main branch tree displays the flag structure for model selection in $\mathcal{H}-$EFTCAMB. The separate tree in the bottom left lists the flags used to specify functions.
• Figure 2: The physical model structure of $\mathcal{H}-$EFTCAMB. The first column refers to whether a model is defined by specifying an EFT or covariant Lagrangian. The second column indicates whether the background is input (Designer) or derived from the corresponding Larangian (Solve Background). The parenthesis in the third column indicates the flags to select the corresponding model.
• Figure 3: The TT, EE, and TE angular power spectra of the CMB, together with the matter power spectrum at $z=0$ for four different sets of SCG model parameters along with the relative difference between the result from the new Horndeski module in $\mathcal{H}-$EFTCAMB and that from the original implementation of SCG in EFTCAMB.
• Figure 4: Similar to Fig. \ref{['fig:Compare_SCG']}. Comparison of the results of the JBD model with $\omega_{\rm bd} = \{10,30,100,1000\}$ from $\mathcal{H}-$EFTCAMB and hi_class.
• Figure 5: Similar to Fig. \ref{['fig:Compare_SCG']}. Comparison of the results of the $\alpha_i=c_i\Omega_{\rm DE}$ parametrization from $\mathcal{H}-$EFTCAMB and hi_class.