2023-10-20 15:00  Online

Chasing dark matter with pulsar experiments

Dr. Nataliya Porayko

Pulsars are rapidly rotating, highly-magnetized neutron stars which emit electromagnetic radiation in the form of highly collimated beams, mainly observed in the radio wavelength regime. They possess a number of extraordinary properties which makes them not only immensely peculiar objects in the sky but also the laboratories for probing a wide range of astrophysical problems. Pulsars can be instrumental in solving the puzzle, which has perplexed the minds of the scientific community for almost a century – dark matter. During this talk I will cover two viable dark matter hypotheses that can be tested with pulsar experiments: i) fuzzy dark matter formed by axion-like particles; ii) and dark matter constituted by primordial black holes (PBHs). Fuzzy dark matter consisting of bosons with extremely low masses of m ∼ 10^(−22) eV, is one of the compelling dark matter candidates, which solves some of the problems of the conventional cold dark matter hypothesis. It was shown by Khmelnitsky and Rubakov that fuzzy dark matter in the Milky Way induces oscillating gravitational potentials, leaving characteristic imprints in the time of arrivals of radio pulses from pulsars. PBHs have been considered as cold dark matter alternatives for almost fifty years, and are among the few dark matter candidates that do not invoke the existence of a new particle beyond the Standard Model. One of the viable hypotheses of PBH formation is through the collapse of primordial density perturbations in the radiation dominated stage of the Universe. It has been shown (e.g. Ananda et al. 2007) that these density perturbations can effectively generate GWs in the 2nd order of perturbation theory that can be probed by pulsar timing arrays. The traces of 2nd-order gravitational waves and fuzzy dark matter in the Galaxy are searched in the latest European Pulsar Timing Array dataset that contains the times of arrival of 25 pulsars regularly monitored for more than two decades. The results and obtained limits will be summarized in the talk. Other possible ways of constraining dark matter with pulsar experiments as well as prospects of dark matter detection with future radio astronomical facilities are discussed.