Binary pulsars can be excellent probes of ultra-light dark matter. We consider the scenario where the latter is represented by a spin-2 field. The coherent oscillations of the dark matter field perturb the dynamics of binary systems, leading to secular effects for masses that resonate with the binary systems. For the range 10 −23 eV m 10 −17 eV we show that current timing data could potentially constrain the universal coupling strength of dark matter to ordinary matter at the level of α 10 −5 . :1909.13814v1 [astro-ph.HE] arXiv

Ultra-light Dark Matter (ULDM) models are suitable candidates for the cosmological Dark Matter that may leave characteristic imprints in many observables. Among other probes, signatures of ULDM can be searched for in pulsar timing data. In this work we describe the effects of spin-2 ULDM on pulsar timing arrays, extending previous results on lower spins. Spin-2 ULDM is universally coupled to standard matter with dimensionless strength α. We estimate that current data could constrain this coupling in the mass range m ≲ 4 × 10−22 eV at the 10−5 to 10−6 level, which is the most competitive constraint in this mass range. A crucial feature of the spin-2 ULDM effect on pulsar timing is its anisotropic, quadrupolar shape. This feature can be instrumental in differentiating the effects sourced by spin-2 ULDM from, for instance, scalar ULDM, and the systematics of a PTA experiment.

The layer-by-layer (LbL) method is based on sequential deposition of polycations and polyanions. Many of the properties of polyelectrolyte thin films deposited via this method depend on the nature of the topmost layer. Thus, these properties show odd-even oscillations during multilayer growth as the topmost layer alternates from polycations to polyanions. The work function of a (semi)conductive substrate modified with an LbL polyelectrolyte multilayer also displays an oscillatory behavior independent of film thickness. The topmost layer modulates the work function of a substrate buried well below the film. In agreement with previous observations, in this work, we show that the work function of a gold substrate changes periodically with the number of adsorbed layers, as different combinations of polycations and polyanions are deposited using the LbL method. For the first time, we rationalize this behavior in terms of formation of a dipole layer between the excess charge at the topmost layer and the charge of the metal substrate, and we put forward a semiquantitative model based on a continuum description of the electrostatics of the system that reproduces the experimental observations.