1810.03227
Parkes Pulsar Timing Array constraints on ultralight scalar-field dark matter
Porayko et al
It is widely accepted that day matter contributes about a quarter of the critical mass-energy density in our Universe. The nature of dark matter is currently unknown, with the mass of possible constituents spanning nearly one hundred orders of magnitude. The ultralight scalar fieldwork matter, consisting of extremely light bosons with m~1e-22 eV and often called "fuzzy" dark matter, provides intriguing solutions to some challenges at sub-galactic scales for the standard cold dark matter model. As shown by Khmelnitsky and Rubakov, such a scalar field in the Galaxy would produce an oscillating gravitational potential with nanohertz frequencies, resulting in periodic variations in the times of arrival of radio pulses from pulsars. The Parkes Pulsar Timing Array (PPTA) has been monitoring 20 millisecond pulsars at 2 to 3 weeks intervals for more than a decade. In addition to the detection of nanohertz gravitational waves, PPTA offers the opportunity for direct searches for fuzzy dark matter in an astrophysical feasible range of masses. Analyze the latest PPTA data set which includes timing observations for 26 pulsars made between 2004 and 2016. Perform a search in this data set for evidence of ultralight dark matter in the Galaxy using Bayesian and Frequentist methods. No statistically significant detection has been made. Therefore place upper limits on the local DM density. The limits, improving on previous searches by a factor of 2 to 5, constrain the DM density of ultralight bosons with m<=1e-23 eV to be below 6 GeV/cm^3 with 95 % CL in the Earth neighborhood. Finally, discuss the project of probing the astrophysical favored mass range m>~1e-22 eV with next-generation pulsar timing facilities.
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