spectroxide: A code package for computing cosmic microwave background spectral distortions

2026-04-27

AI Summary

This work addresses the absence of efficient, accurate open-source tools for computing cosmic microwave background (CMB) spectral distortions induced by arbitrary energy injections over redshifts \( z \lesssim 5 \times 10^6 \). The authors present a physics-based open-source code package that evolves the CMB spectrum from high redshift to the present by solving the photon Boltzmann equation, fully accounting for Compton scattering, double Compton emission, and bremsstrahlung. Notably, the core solver—implemented in Rust with a Python interface—is the first in this domain to be developed with AI-assisted coding under rigorous supervision by physicists. The implementation is validated through approximately 400 automated tests and cross-checked against Green’s function tables and analytical limits. Having successfully reproduced established results with high fidelity, the software is now publicly available on GitHub, filling a critical gap in high-quality open-source resources for CMB spectral distortion studies.

Abstract

We present spectroxide, a code package for computing cosmic microwave background spectral distortions in which all ${\sim}14{,}500$ lines of Rust code, Python interface, and ${\sim}400$ automated tests were written by an AI assistant (Claude Code) under human physicist supervision. The solver evolves the photon Boltzmann equation under Compton scattering, double Compton emission, and Bremsstrahlung from $z \sim 5 \times 10^6$ to the present, computing spectral distortions from arbitrary heat and photon injection within this redshift range. No fully open-source code of this kind is publicly available; we validate against analytic limits, published spectra, and publicly available precomputed Green's function tables. We document the development as a case study in AI-assisted scientific computing, highlighting how domain expertise caught physics bugs (incorrect dimensional prefactors, near-cancellation errors) that evaded the full automated test suite, and provide recommendations for best practices in human--AI collaborative development of scientific software. We make spectroxide publicly available on GitHub.

Problem

• cosmic microwave background
• spectral distortions
• open-source code
• photon injection
• energy injection

Innovation

• AI-assisted scientific computing
• cosmic microwave background spectral distortions
• Boltzmann equation solver
• human-AI collaboration
• open-source scientific software