Hunting for topological dark matter with atomic clocks

Abstract

The cosmological applications of atomic clocks 1‐3 so far have been limited to searches for the uniform-in-time drift of fundamental constants 4 . We point out that a transient-in-time change of fundamental constants can be induced by darkmatter objects that have large spatial extent, such as stable topologicaldefects 5 builtfromlightnon-StandardModelfields. Networks of correlated atomic clocks, some of them already in existence 6 , such as the Global Positioning System, can be used as a powerful tool to search for topological defect dark matter,thusprovidinganotherimportantfundamentalphysics application for the ever-improving accuracy of atomic clocks. During the encounter with an extended dark-matter object, as itsweepsthroughthenetwork,initiallysynchronizedclockswill becomedesynchronized.Timediscrepanciesbetweenspatially separated clocks are expected to exhibit a distinct signature, encoding the defect’s space structure and its interaction strength with atoms. Despite solid evidence for the existence of dark matter ( 25% of the global energy budget in the Universe and DM’0.3GeVcm 3 in the neighbourhood of the Solar system 7 ), its relationship to particles and fields of the Standard Model (SM) remains a mystery. Although searches for particle dark matter (DM) are being actively pursued 8 , there is also significant interest in alternatives, among which is DM composed from very light fields. Depending on the initial field configuration at early cosmological times, such light fields could lead to dark matter via coherent oscillations around the minimum of their potential, and/or form non-trivial stable field configurations in physical three-dimensional space if their potential allows such a possibility. This latter option, which we will generically refer to as topological defects (TDs), is the main interest of our paper. The light masses of fields forming the TDs could lead to a large, indeed macroscopic, size for a defect. Their encounters with the Earth, combined with the DMSM coupling, can lead to novel signatures of dark matter expressed generically in terms of ‘transient eects’. These eects, coherent on the scale of individual detectors, are temporary shifts in the frequencies and phases of measuring devices, rather than large energy depositions as is the case for microscopic DM. In this paper we suggest the possibility of a new search technique for the topological defect dark matter (TDM), based on a network of atomic clocks. Atomic clocks are arguably the most accurate scientific instruments ever built, reaching a 10 18 fractional inaccuracy 1,2 .