Search for Topological Dark Matter with Atomic Clocks and GPS Constellation

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This project seeks to answer the question "what is the nature of dark matter"? Dark matter is invisible, yet it is known to exist with about five times more abundance in the universe than the ordinary matter (like stars) we can see. Although the astronomical evidence of dark matter is overwhelming, so far nobody has detected it in the laboratory, and we know almost nothing about it. Many attempts to seek dark matter as fundamental particles of nature have so far failed. Our project will search for a different possible type of dark matter known as topological defects, predicted by some models of how the universe formed. Our approach to detect topological defects is by observing their predicted effect on atomic clocks, the most precise instruments ever devised. Specifically, we will use existing data from the Global Positioning System (GPS) and seek the tiny effects of dark matter on time kept by atomic clocks connected to GPS instruments. Since the GPS system and the atomic clocks already exist and are paid for, this is a relatively low-budget project with high potential payoff. If topological defects do exist and we find them, this would help set our understanding of the universe on a more sure footing. Likewise, it would also be valuable to be able to rule out this possibility with a small margin of error, to help science focus on more likely explanations. In this way, such investigations promote the progress of science. Society also benefits in terms of new technologies that can only be made possible with the unpredictable knowledge that comes with scientific progress.Understanding the nature of dark matter remains one of top outstanding problems in physics today. Some models predict dark matter in a form of stable configurations of light fields, the topological defects (TD). The presence of TDs may lead to occasional transient changes of particle masses and coupling constants, thus giving a distinct signature that can be searched for with the network of sensitive atomic clocks. This project will use atomic clocks of the existing GPS satellite constellation and ground station network as a 50,000 km-aperture sensor array. Data from this detector have been accumulated over 15 years and are publicly available. The PI, an expert in precision positioning and timing, will conduct the GPS data processing by customizing the NASA/JPL software GIPSY/OASIS of which he is a co-author. The output will be a time series of clock phase for all GPS satellites and ground stations, which we have demonstrated can be monitored with a precision of ~0.1 ns. If DM exists in the form of macroscopic TDs, then there is a chance to discover this with this macroscopic experiment. Assuming TDs exist in sufficient abundance, then the Earth would pass through these TDs occasionally. For TDs that pass through the GPS system at galactic speeds ~300 km/sec, TDM-SM coupling would lead to transients in fundamental physical constants, which would cause a sequence of transients in atomic clock frequency, hence producing step-like functions in clock phase across an aperture of ~200 s for the GPS constellation, and ~40 s for ground stations. Since GPS carrier phase data is routinely acquired with few-mm precision at intervals of 1 s, detecting ~1 ns signals in the atomic clock phase over a 200-s aperture is easily achievable. Observing such a signature would provide decisive evidence of the existence of TDs with a high confidence level, as there is no known mechanism for background events that would mimic such a signature. Non-observation will place constraints on certain new-physics couplings.