GWxLSS

GWxLSS is a numerical tool designed to compute auto and cross-tomographic angular power spectra for Large-Scale Structure (LSS) and Gravitational Waves (GW). Specifically, it supports:

• GCph: Galaxy Clustering (photometric)
• WL: Weak Lensing
• GWC: Gravitational Wave Clustering
• GWWL: Gravitational Wave Weak Lensing

To utilize the full LSSxGW cross-correlation, it is necessary to use the latest version of MGCAMB, where the source terms for Gravitational Waves will be soon included. In the meantime the GWs features are available in GW-MGCAMB

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Features

• Likelihood: LSSxGW built as an external Cobaya module.
• Theory Module compute_obs_source.py : Computes the Angular power spectra ($C_\ell$).
• Sampling: Interfaced with MCMC and Nautilus samplers via Cobaya.
• Fisher Analysis: Built-in Fisher matrix analysis for forecasting.
• Examples: Jupyter notebooks for synthetic data and analysis.

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Installation

Requirements

Ensure you have the following dependencies installed: numpy, scipy, cobaya, nautilus, getdist, pandas.

Quick Start

To set up the environment and compile the necessary theory code:

#Clone the repository
git clone https://github.com/chiaradeleo1/GWxLSS.git
cd GWxLSS
# Install dependencies
pip install -r requirements.txt 

Then install MGCAMB (required for GW observables)

Data

The raw data are not included in this repository. Please refer to the following guide to manage your datasets:

• Synthetic Data Generation: You can generate your own synthetic data by defining specifications in gal_specs and gw_specs. Refer to the Example.ipynb notebook for a step-by-step guide.

How to Run the Code

All analyses are controlled via a YAML settings file. You can execute a run using the provided runner.py script:

python runner.py settings_file.yaml

Each YAML settings file must define the following parameters to ensure the likelihood and theory modules work correctly:

• output: name of the output file

• likelihood_settings:

  • data_path: path/to/synthetic/data
  • settings:
    • case: Define which relativistic effects to include: ['redshift', 'lensing', 'velocity', 'potential', 'lsd', 'evolve', 'gradpotential', 'ISW', 'SW', 'volume']. If set to None, no additional effects are added.
    • extra: Extra arguments passed directly to CAMB.
    • obs_used: A list of the observables you want to use. The auto and cross-spectra not specified here are automatically removed from both the covariance matrix and the data vector (see likelihood.py for implementation details).
    • scale_cut: [method, value] If using any GW observables, you must specify the maximum multipole $\ell_{\rm max}$. Note: The code currently forces a single $\ell_{\rm max}$ for the analysis. Because galaxies are expected to have a higher $\ell_{\rm max}$, theoretical values are computed up to the galaxy limit, and all auto and cross-spectra involving GWs are subsequently cut at your specified $\ell_{\rm max}$.

• use_noiseless_cls: Set to True for noiseless spectra, or False for noisy spectra.

• sampler: Choose the sampling method: nautilus (examples available in paper_settings/), mcmc, Fisher (examples available in paper_settings/ and Example.ipynb)

Reproducing Paper Results: To reproduce the results in De Leo et. al 2026, follow these steps:

• Download Data: Download the synthetic data provided on Zenodo.
• Access Chains: The chains used in the paper are also available on Zenodo.
• Use Settings: Use the input files located in the paper_settings/ folder to run your analysis.

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Citation

If you use this code in your work, please cite:

@article{De Leo_2026,
doi = {10.1088/1475-7516/2026/05/038},
url = {https://doi.org/10.1088/1475-7516/2026/05/038},
year = {2026},
month = {may},
publisher = {IOP Publishing},
volume = {2026},
number = {05},
pages = {038},
author = {De Leo, C. and Cañas-Herrera, G. and Balaudo, A. and Martinelli, M. and Silvestri, A. and Baker, T.},
title = {Illuminating the dark sector: understanding modified gravity signatures with cross-correlations of Gravitational Waves and Large-Scale Structure},
journal = {Journal of Cosmology and Astroparticle Physics},
}