The Universe is pervaded by an invisible substance — ultralight dark matter, which doesn't collide with ordinary matter but can tremble like a taut string. Its oscillations alter the world's most fundamental properties: the electron charge, the speed of light — as if the tuning of a single cosmic note slightly drifts. Only ultrasensitive instruments can catch this quiver.
Future space antennas LISA and Taiji, designed to register gravitational waves — ripples in curved spacetime, — will also notice the fluctuations of constants. Inside the devices, gold test masses float freely; laser beams track their motion. The tremor from dark matter accelerates the masses differently than it shifts the laser's frequency, and clever algorithms extract the pure 'note' from the noise. A new local observation method compares the mass's drift relative to the housing — boosting sensitivity to effects on electrons by a factor of a thousand. It's like picking out a whisper over the roar of the surf. Thus, the Standard Model gets a chance to directly perceive the Universe's most elusive substance.
as written by the authors arXiv:2606.03478
Ultralight dark matter (ULDM) coupled to the Standard Model may effectively induce coherent oscillations of fundamental constants and thereby generate narrow-band signals in precision interferometric experiments. Here we present a systematic study of how these oscillations leave distinctive imprints on space-based laser interferometers, including LISA and Taiji. Starting from the one-way inter-spacecraft link observables, we analyze several instrument-level effects induced by ULDM, including composition-dependent acceleration of test masses, laser-frequency variations associated with cavity-length modulation, refractive-index effects, and clock-related contributions. We then propagate these signals through the standard data processing chain, including time-delay interferometry and clock-noise elimination. We show that the observability of an ULDM-induced effect is determined by the structure of its single-link response. In particular, the ULDM-driven variation in laser frequency appears in the raw link observable with the same form as laser phase noise. As a consequence, it is strongly suppressed in the final interferometry channels. In contrast, signals that possess an explicit directional pattern are not eliminated by this procedure, such as the ULDM-induced oscillations of the test masses. We further construct a local observable that isolates the differential motion between the test mass and the optical bench, and derive its sensitivity to both the dilaton--gluon coupling $$d_g$$ and the dilaton--electron coupling $$d_e$$ for LISA, Taiji, and BBO. We find that the local observable yields sensitivities comparable to the standard Michelson interferometer for $$d_g$$, but better than Michelson channel by three orders of magnitude for $$d_e$$.
The tremor frequency of dark matter depends on its mass — like strings of different thickness. Perhaps the cosmos vibrates on one such string, and we are tuning in to its note for the first time.
In Liu Cixin's 'The Three-Body Problem', dark matter is the key to interstellar travel. Its real tremors may become the first clue in unraveling this cosmic mystery.