arXiv subjects

Dani de Boe

Publications and source records attributed to Dani de Boe.

5 recordsLinked to original sources

arXiv2026

Nonlinear Scales in Luminal Horndeski -- I. Halo mass function and power spectrum boost in models with Vainshtein screening

We investigate nonlinear structure formation in Horndeski gravity with luminal gravitational wave speed ($c_T = 1$), assuming Vainshtein screening within the spherical collapse model. We compute the critical and virial overdensities and evaluate the halo mass function. Building on the reaction approach, we present a framework for the computation of the reaction and the resulting nonlinear matter power spectrum using the EFTofDE formulation of Horndeski gravity. We show results for the case of EFT functions that trace the evolution of dark energy, and specialize to the cubic galileon and nDGP models for benchmarking against existing results. The framework interfaces with \texttt{EFTCAMB} for the linear evolution, though alternatives are possible. While restricted to Vainshtein-screened models, the current implementation focuses on qualitative trends and parameter dependencies. Further refinements and extensions to other screening mechanisms will be addressed in future work.

astro-ph.CO↗

arXiv2026

An efficient one-loop EFTofLSS framework for Vainshtein-screened Horndeski gravity

We present an extension of \texttt{PyBird} for one-loop large-scale structure analyses of modified gravity models. We implement support for quasi-static, Vainshtein-screened luminal Horndeski models (in EFTofDE and covariant formalisms) and nDGP, and replace the Green's function approach with a direct ODE method for computing the exact time-dependent functions entering the perturbation kernels. The new implementation improves computational efficiency while maintaining numerical consistency with the standard approach, and we validate the resulting one-loop matter power spectrum against $N$-body simulations for the $α_i\proptoΩ_{\rm DE}$ parametrization. We apply this framework to constrain the $α_i \propto a^3$ and $α_i \propto Ω_{\rm DE}$ parametrizations using Planck CMB, BOSS full-shape, and DESI DR2 BAO data, finding that full-shape information significantly tightens the constraints. We further showcase the pipeline for the cubic Galileon and nDGP models, demonstrating its applicability beyond the phenomenological amplitude parametrizations to covariant modified-gravity theories. Finally, we assess the impact of the Einstein--de Sitter approximation and find that exact time dependence can be retained at modest computational cost, which may become relevant for future large-scale structure surveys.

astro-ph.CO↗

arXiv2026

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

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.

gr-qc↗

arXiv2025

Cosmological scalar perturbations in Horndeski-like gravity

Scalar-tensor theories are promising dark energy models. A promising scalar-tensor theory, called Horndeski-like gravity, is coming from the application of the Horndeski gravity in string theory and cosmology that takes into account two dilaton fields. In this work we study the stability of the scalar sector of this theory and compare it with that coming from the previously studied tensor sector. With the first-order formalism we investigate the allowed background solutions. Focusing on the background solution with a single scalar field, the entropy coming from particle production $S_{in}$ and that of the apparent horizon $S$ will be studied, which translates into \textit{entropy bounds}. These entropy bounds are compared with the stability of the scalar and tensor sector as well. The gravitational slip (minus one) to entropy ratio is also considered as a possible replacement for the usual shear viscosity to entropy ratio for black holes.

gr-qc↗

arXiv2024

Phenomenology of Horndeski Gravity under Positivity Bounds

A set of conditions that any effective field theory needs to satisfy in order to allow for the existence of a viable UV completion has recently gained attention in the cosmological context under the name of $\textit{positivity bounds}$. In this paper we revisit the derivation of such bounds for Horndeski gravity and translate them into a complete set of viability conditions in the language of effective field theory of dark energy. We implement the latter into $\texttt{EFTCAMB}$ and explore the large scale structure phenomenology of Horndeski gravity under positivity bounds. We build a statistically significant sample of viable Horndeski models, and derive the corresponding predictions for the background evolution, in terms of $w_{\rm DE}$, and the dynamics of linear perturbations, in terms of the phenomenological functions $μ$ and $Σ$, associated to clustering and weak lensing, respectively. We find that the addition of positivity bounds to the traditional no-ghost and no-gradient conditions considerably tightens the theoretical constraints on all these functions. The most significant feature is a strengthening of the correlation $μ\simeqΣ$, and a related tight constraint on the luminal speed of gravitational waves $c^2_T\simeq1$. In anticipation of a more complete formulation of positivity conditions in cosmology, this work demonstrates the strong potential of such bounds in shaping the viable parameter space of scalar-tensor theories.

astro-ph.CO↗