Stochastic Properties of Ultralight Scalar Field Gradients

Abstract

Ultralight axion-like particles are well-motivated dark matter candidates that are the target of numerous direct detection efforts. In the vicinity of the Solar System, such particles can be treated as oscillating scalar fields. The velocity dispersion of the Milky Way determines a coherence time of about 10^6 oscillations, beyond which the amplitude of the axion field fluctuates stochastically. Any analysis of data from an axion direct detection experiment must carefully account for this stochastic behavior to properly interpret the results. This is especially true for experiments sensitive to the gradient of the axion field that are unable to collect data for many coherence times. Indeed, the direction, in addition to the amplitude, of the axion field gradient fluctuates stochastically. We present the first complete stochastic treatment for the gradient of the axion field, including multiple computationally efficient methods for performing likelihood-based data analysis, which can be applied to any axion signal, regardless of coherence time. Additionally, we demonstrate that ignoring the stochastic behavior of the gradient of the axion field can potentially result in failure to discover a true axion signal.

16 pages, figures

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• Small-scale structure in vector dark matter
• Search for oscillations of fundamental constants using molecular spectroscopy
• Laboratory Constraints on the Neutron-Spin Coupling of feV-scale Axions
• Spectral signatures of axionlike dark matter
• Search for dark-photon dark matter in the SuperMAG geomagnetic field dataset
• On the Sensitivity of Spin-Precession Axion Experiments
• A torsion-balance search for ultra low-mass bosonic dark matter
• Intensity interferometry for ultralight bosonic dark matter detection
• Dissecting axion and dark photon with a network of vector sensors
• Towards an electrostatic storage ring for fundamental physics measurements
• On the single classical field description of interacting scalar fields