# The First Billion Years in Seconds: An Effective Model for the 21-cm Signal with Population III Stars

**Authors:** Hector Afonso G. Cruz, Julian B. Munoz, Nashwan Sabti, Marc Kamionkowski  
**arXiv:** [2407.18294](https://arxiv.org/abs/2407.18294)  
**Date:** 2024-07-25  
**Summary page:** https://www.summarizepaper.com/en/paper/2407.18294v1/

## Key points

- Authors Hector Afonso G. Cruz, Julian B. Munoz, Nashwan Sabti, and Marc Kamionkowski focus on cosmic dawn and the 21-cm signal.
- They introduce an innovative analytic model using Zeus21 to study the impact of early stars on the 21-cm signal.
- The model includes Population III (Pop III) stars in low-mass molecular-cooling galaxies with distinct spectral characteristics.
- Feedback mechanisms like $H_2$-dissociating Lyman-Werner radiation and dark matter-baryon relative velocities are considered to suppress star formation in small halos.
- Their improved Zeus21 predicts global 21-cm signals accurately and is computationally efficient—three orders of magnitude faster than traditional methods.
- This advancement enables efficient parameter inference during cosmic dawn studies and opens new possibilities for researchers to explore cosmic evolution within seconds.

## Summary

In their paper titled "The First Billion Years in Seconds: An Effective Model for the 21-cm Signal with Population III Stars," authors Hector Afonso G. Cruz, Julian B. Munoz, Nashwan Sabti, and Marc Kamionkowski delve into the realm of cosmic dawn by exploring observations of the 21-cm signal. This signal provides a unique insight into the epoch when the first stars in the universe began to form. The authors introduce an innovative approach using an effective and fully analytic model to study how the presence of early stars impacts the 21-cm signal. Their methodology leverages Zeus21, a modular code that incorporates an analytic prescription of the star formation rate density (SFRD) to capture nonlinear and nonlocal correlations crucial for determining the 21-cm signal. One key aspect of their model is the inclusion of Population III (Pop III) stars, which inhabited low-mass molecular-cooling galaxies with distinct spectral characteristics compared to later Pop II stars. Additionally, feedback mechanisms such as $H_2$-dissociating Lyman-Werner (LW) radiation and dark matter-baryon relative velocities are accounted for in suppressing star formation in small halos. The long mean free path of LW photons introduces scale-dependence on SFRD fluctuations while relative velocities introduce spatial "wiggles" in the distribution of the 21-cm signal. Their improved version of Zeus21 not only predicts global 21-cm signals and power spectra with high accuracy but also boasts remarkable computational efficiency—being at least three orders of magnitude faster than traditional methods. This advancement represents a significant step towards enabling efficient and flexible parameter inference during cosmic dawn studies. Overall, this public code opens up new possibilities for researchers to explore and predict critical aspects of cosmic evolution during the first billion years of our universe within seconds—a feat previously unattainable with conventional simulation techniques.