Abstract
Dark matter may induce apparent temporal variations in the physical "constants", including the electromagnetic fine-structure constant and fermion masses. In particular, a coherently oscillating classical dark-matter field may induce apparent oscillations of physical constants in time, while the passage of macroscopic dark-matter objects (such as topological defects) may induce apparent transient variations in the physical constants. In this paper, we point out several new signatures of the aforementioned types of dark matter that can arise due to the geometric asymmetry created by the beam-splitter in a two-arm laser interferometer. These new signatures include dark-matter-induced time-varying size changes of a freely-suspended beam-splitter and associated time-varying shifts of the main reflecting surface of the beam-splitter that splits and recombines the laser beam, as well as time-varying refractive-index changes in the freely-suspended beam-splitter and time-varying size changes of freely-suspended arm mirrors. We demonstrate that existing ground-based experiments already have sufficient sensitivity to probe extensive regions of unconstrained parameter space in models involving oscillating scalar dark-matter fields and domain walls composed of scalar fields. In the case of oscillating dark-matter fields, Michelson interferometers $-$ in particular, the GEO600 detector $-$ are especially sensitive. The sensitivity of Fabry-Perot-Michelson interferometers, including LIGO, VIRGO and KAGRA, to oscillating dark-matter fields can be significantly increased by making the thicknesses of the freely-suspended Fabry-Perot arm mirrors different in the two arms. We also discuss how small-scale Michelson interferometers, such as the Fermilab holometer, could be used to perform resonant narrowband searches for oscillating dark-matter fields with enhanced sensitivity to dark matter.
Highlights
While the existence of dark matter (DM) is well established from astrophysical and cosmological observations, the elucidation of its precise nature remains one of the most important problems in contemporary physics
Using Eqs. (4), (16), (23), and (24), we estimate the sensitivities of a single smallscale Michelson interferometer and a pair of colocated smallscale Michelson interferometers using the above narrowband approach and operating near room temperature to the linear interactions of the DM field φ with the photon and electron in Eq (1), assuming that the measurements are limited by Brownian thermal noise and that all of the dimensions of the beam-splitter are altered in a proportional manner
The estimated sensitivities of existing, modified, and future laser-interferometry experiments to oscillating DM fields and domain walls are presented in Figs. 3 and 4, respectively
Summary
While the existence of dark matter (DM) is well established from astrophysical and cosmological observations, the elucidation of its precise nature remains one of the most important problems in contemporary physics. We point out that the beam-splitter and arm mirrors of an interferometer, if freely suspended, can produce differential optical-path-length changes if one or more of the physical constants of nature vary in time (and space). The sensitivity of Fabry-Perot-Michelson interferometers, including LIGO [17], VIRGO [18], and KAGRA [19], to oscillating DM fields can be significantly increased by making the thicknesses of the freely suspended Fabry-Perot arm mirrors different in the two arms In this case, the sensitivity of these experiments to conventional gravitational-wave searches, which can be performed simultaneously with our suggested DM searches, would not necessarily be degraded. We express the interferometer output in terms of the difference of the optical path lengths in different arms of an interferometer
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