arXiv subjects

Zhuangfei Wang

Publications and source records attributed to Zhuangfei Wang.

4 recordsLinked to original sources

arXiv2024

Disentangling modified gravity from a dark force with gravitational redshift

The standard approach to test for deviations from general relativity on cosmological scales is to combine measurements of the growth rate of structure with gravitational lensing. In this study, we show that this method suffers from an important limitation with regard to these two probes: models of dark matter with additional interactions can lead to the very same observational signatures found in modified gravity and vice versa. Using synthetic data of redshift-space distortions, weak lensing, and cosmic microwave background, we demonstrate that this degeneracy is inevitable between modifications of gravity and a dark fifth force. We then show that the coming generation of surveys, in particular the Square Kilometre Array, will allow us to break the degeneracy between such models through measurements of gravitational redshift. Performing a Markov chain Monte Carlo analysis of the synthetic dataset, we quantify the extent to which gravitational redshift can distinguish between two representative classes of models, generalized Brans-Dicke (modified gravity) and coupled quintessence (fifth force).

astro-ph.CO↗

arXiv2024

Extending MGCAMB tests of gravity to nonlinear scales

Modified Growth with {\tt CAMB} ({\tt MGCAMB}) is a patch for the Einstein-Boltzmann solver {\tt CAMB} for cosmological tests of gravity. Until now, {\tt MGCAMB} was limited to scales well-described by linear perturbation theory. In this work, we extend the framework with a phenomenological model that can capture nonlinear corrections in a broad range of modified gravity theories. The extension employs the publicly available halo model reaction code {\tt ReACT}, developed for modeling the nonlinear corrections to cosmological observables in extensions of the $Λ$CDM model. The nonlinear extension makes it possible to use a wider range of data from large scale structure surveys, without applying a linear scale cut. We demonstrate that, with the 3$\times$2pt Dark Energy Survey data, we achieve a stronger constraint on the linear phenomenological functions $μ$ and $Σ$, after marginalzing over the additional nonlinear parameter $p_1$, compared to the case without the nonlinear extension and using a linear cut. The new version of {\tt MGCAMB} is now forked with {\tt CAMB} on GitHub allowing for compatibility with future upgrades.

astro-ph.CO↗

arXiv2023

New MGCAMB tests of gravity with CosmoMC and Cobaya

We present a new version of MGCAMB, a patch for the Einstein-Boltzmann solver CAMB for cosmological tests of gravity. New features include a new cubic-spline parameterization allowing for a simultaneous reconstruction of $μ$, $Σ$ and the dark energy density fraction $Ω_X$ as functions of redshift, the option to work with a direct implementation of $μ$, $Σ$ (instead of converting to $μ$, $γ$ first), along with the option to test models with a scalar field coupled only to dark matter, and the option to include dark energy perturbations when working with $w\ne -1$ backgrounds, to restore consistency with CAMB in the GR limit. This version of MGCAMB comes with a Python wrapper to run it directly from the Python interface, an implementation in the latest version of CosmoMC, and can be used with Cobaya.

astro-ph.CO↗

arXiv2023

On validity of the quasi-static approximation in scalar-tensor theories

The discovery of cosmic acceleration motivated extensive studies of dynamical dark energy and modified gravity models. Of particular interest are the scalar-tensor theories, with a scalar field dark energy non-minimally coupled to matter. Cosmological constraints on these models often employ the quasi-static approximation (QSA), in which the dynamics of the scalar field perturbations is proportional to the perturbation in the matter density. Using the QSA simplifies the physical interpretation of the phenomenology of scalar-tensor theories, and results in substantial savings of computing time when deriving parameter constraints. Focusing on the symmetron model, which is a well-motivated scalar-tensor theory with a screening mechanism, we compare the exact solution of the linearly perturbed field equations to those obtained under the QSA and identify the range of the model parameters for which the QSA is valid. We find that the evolution of background scalar field is most important, namely, whether it is dominated by the Hubble friction or the scalar field potential. This helps us derive a criterion for the symmetron model, but same argument can be applied to other scalar-tensor theories of generalized Brans-Dicke type. We consider two scenarios, one where the scalar field is only coupled to dark matter and where it couples to all of the matter.

astro-ph.CO↗