Probing Time-Dependent Physics with Phase-Folding CMB Maps

TL;DR

This paper introduces a phase-folding mapmaking method that enhances the sensitivity of CMB observations to time-dependent signals, expanding the frequency range from microhertz to hundreds of hertz, enabling new cosmological tests.

Contribution

The authors develop a novel phase-folding mapmaking framework that allows targeted searches for periodic signals in CMB data at higher frequencies than traditional methods.

Findings

Extended CMB sensitivity from microhertz to 100 Hz frequencies.

Demonstrated constraints on stochastic gravitational wave backgrounds.

Proposed search for oscillating polarization rotation from axion-like particles.

Abstract

Time-resolved observations of the Cosmic Microwave Background (CMB) offer a powerful probe of time-dependent cosmological signals, such as a stochastic gravitational wave background passing through Earth, which imprints a time-varying deflection on the CMB, and time-dependent cosmic birefringence, which induces an oscillating polarization rotation. However, analyses based on time-division CMB maps are fundamentally limited by the mapmaking cadence, restricting sensitivity to frequencies below $\sim 10^{-5}$ Hz. In this paper we develop a phase-folding mapmaking framework to enable targeted searches of such periodic cosmological signals with frequencies up to the detector sampling rate of $O(100)$ Hz. We demonstrate the power of this framework with two cosmological applications: (1) constraining a stochastic gravitational wave background via its time-dependent lensing signature, and (2) the search for an oscillating polarization rotation from axion-like particles. We show that this technique transforms CMB experiments into broadband probes of the oscillating sky, extending their constraining power from the microhertz regime up to $O(100)$ Hz-an expansion of over seven orders of magnitude in frequency. This provides a new observational window, complementary to other approaches by probing under-explored frequency ranges for gravitational waves and axion-like particles.