GPS.ELF: Update on the search for exotic low-mass field emission from the binary neutron star merger (GW170817) using GPS atomic clocks*

Exotic low-mass fields (ELF) are plausible dark matter candidates appearing as potential solutions to the strong-CP and hierarchy problems. Powerful astrophysical events, such as binary neutron star and binary black hole mergers can potentially emit ELFs which leads to an intriguing possibility for a novel, exotic physics, modality in multi-messenger astronomy [Nature Astronomy 5, 150 (2021)]. In our ELF search, we use the data from atomic clocks of the Global Positioning System (GPS) making it a quantum sensor network. It is expected that ELFs imprint an anti-chirp transient across the GPS sensor network. Our search targets the August 17, 2017 GW170817 binary neutron star merger event detected by LIGO. The search is carried out by comparing the clock excess noise before and after the LIGO gravitational wave trigger. We present the progress of our search for such feebly interacting ELFs using three days of data for clock excess noise comparison. We found an intriguing excess in the clock noise post LIGO gravitational wave trigger. Potentially the excess noise could be explained away by the increased solar electron flux on August 17, 2017. While analysing the data we discovered anomalies in Block II-F GPS satellite clocks that may degrade their suitability as sensors of exotic physics.