Beyond21: A Global Framework for Cosmic Dawn and Reionization Within and Beyond the Standard Model

TL;DR

Beyond21 is an open-source Python framework that models cosmic dawn and reionization, integrating star formation, radiation backgrounds, and new physics to interpret early universe observations efficiently.

Contribution

It introduces a flexible, self-consistent pipeline for simulating cosmic dawn and reionization, including novel physics like millicharged dark matter effects.

Findings

Fast global evolution simulations (~0.1 s) enable extensive parameter studies.

Modular design allows easy updates and new physics integration.

Demonstrated impact of millicharged dark matter on baryon cooling.

Abstract

Observations of the Cosmic Dawn (CD) and Epoch of Reionization (EoR) are steadily improving, opening new opportunities to study early galaxies through complementary probes. To enable consistent interpretation of these observations, we present Beyond21, a fully open-source Python package that implements flexible prescriptions for Pop II and Pop III star formation and computes the resulting radiation backgrounds and their impact on the intergalactic medium. From this coupled evolution, Beyond21 predicts the global 21-cm signal, UV luminosity functions (UVLFs), the ionization history, and the contribution to the observed cosmic X-ray background (CXB) within a single, self-consistent pipeline. A full global evolution run executes in $\sim0.1 \ {\rm s}$ on a single CPU core, enabling broad, high-resolution parameter exploration. The modular architecture facilitates straightforward modification of astrophysical prescriptions and the incorporation of new physics. As an illustrative example, we implement a scenario in which a small fraction of dark matter is millicharged, leading to baryon cooling through elastic interactions.