# DarkHistory: A code package for calculating modified cosmic ionization and thermal histories with dark matter and other exotic energy injections

## TL;DR

DarkHistory is a Python package that models how dark matter and exotic energy injections influence the early universe's ionization and temperature history, enabling detailed studies of their cosmological impacts.

## Contribution

It introduces a self-consistent, flexible code for calculating the effects of dark matter annihilation and decay on cosmic ionization and thermal evolution, including backreaction effects.

## Key findings

- Demonstrates the code's ability to handle arbitrary dark matter parameters.
- Shows how to incorporate astrophysical and exotic energy sources.
- Provides examples of impact on 21cm signals and reionization.

## Abstract

We present a new public Python package, DarkHistory, for computing the effects of dark matter annihilation and decay on the temperature and ionization history of the early universe. DarkHistory simultaneously solves for the evolution of the free electron fraction and gas temperature, and for the cooling of annihilation/decay products and the secondary particles produced in the process. Consequently, we can self-consistently include the effects of both astrophysical and exotic sources of heating and ionization, and automatically take into account backreaction, where modifications to the ionization/temperature history in turn modify the energy-loss processes for injected particles. We present a number of worked examples, demonstrating how to use the code in a range of different configurations, in particular for arbitrary dark matter masses and annihilation/decay final states. Possible applications of DarkHistory include mapping out the effects of dark matter annihilation/decay on the global 21cm signal and the epoch of reionization, as well as the effects of exotic energy injections other than dark matter annihilation/decay. The code is available at https://github.com/hongwanliu/DarkHistory with documentation at https://darkhistory.readthedocs.io . Data files required to run the code can be downloaded at https://doi.org/10.7910/DVN/DUOUWA .