Pulsar timing and polarimetry: results and perspectives

Pulsar timing, i.e. the analysis of the arrival times of pulses from a pulsar, is a powerful tool in modern astrophysics. It allows us to measure the time delays of an electromagnetic signal caused by a number of physical processes as the signal propagates from the source to the observer. Joint analysis of an ensemble of pulsars (Pulsar Timing Arrays, PTAs) can be used to address a variety of astrophysical challenges, including the problem of direct detection of space-time metric perturbations, in particular those induced by gravitational waves. Here we present a comprehensive review of the current state of research in the field of pulsar timing, with particular emphasis on recent advancements in the detection of stochastic background of nHz gravitational waves, reported by a number of international collaborations such as NANOGrav (North American Nanohertz Observatory for Gravitational Waves), European Pulsar Timing Array (EPTA), Chinese Pulsar Timing Array (CPTA) and Indian Pulsar Timing Array (InPTA), which are joining their efforts within the International PTA (IPTA). Additionally, this paper reviews contemporary constraints on scalar ultralight matter (pseudoscalar bosons), obtained from timing and polarimetry data of pulsars. The prospects for applying these tools to other problems in fundamental physics and cosmology are explored.