Oscillations of Ultralight Dark Photon into Gravitational Waves

The discovery of gravitational waves (GWs) opens a new window for exploring the physics of the early universe. Identifying the source of GWs and their spectra today turn out to be the important tasks so as to assist the experimental detection of stochastic GWs. In this paper, we investigate the oscillations of the ultralight dark photon (ULDP) into GWs in the dark halo. Assuming dark matter is composed of the ULDP and there are primordial dark magnetic fields (PDMFs) arising from the axion inflation and/or the dark phase transition, then the ULDP can oscillate into the GW when it passes through an environment of PDMFs. We derive the local energy density of GWs in the galaxy cluster induced by the instaneous oscillation of ULDP in the PDMFs. These stochastic local GWs exhibit a pulse-like spectrum, with frequency depending on the mass of the ULDP, and can be detected in Pulsar Timing Arrays (PTAs) or future space-based interferometers. We also find that the low-frequency GW signal observed by the NANOGrav collaboration and other PTA experiments can be explained by the oscillation of the ULDP in the PDMFs in the early universe.Comment: 7 pages, 3 figure

Poly[[bis­(2,2-bipyridine)­bis­[μ6-5-(carboxyl­atometh­oxy)benzene-1,3-dicarboxyl­ato]trimanganese(II)] monohydrate]

The title compound, {[Mn3(C10H5O7)2(C10H8N2)2]·H2O}n, was synthesized under hydro­thermal conditions. Six carboxyl­ate groups of six 5-(carboxyl­atometh­oxy)benzene-1,3-dicarboxyl­ate anions (OABDC3−) join three MnII ions into a trinuclear centrosymmetric [Mn3(μ2-COO)6] unit with one Mn site situated on a centre of inversion. The latter MnII ion exhibits a distorted MnO6 coordination, whereas the other MnII ion has a trigonal–bipyramidal MnN2O3 coordination environment resulting from three carboxylate O atoms and the two N atoms of the bipyridine ligand. Adjacent units are linked to each other by OABDC3− ligands into a layer parallel to (010). Within the layer, O—H⋯O hydrogen-bonding inter­actions involving the uncoordinated and half-occupied water mol­ecule and the free carboxyl­ate O atoms are observed. The layers stack along [010], constructing a three-dimensional structure through π–π inter­actions between adjacent pyridine rings, with a centroid–centroid distance of 3.473 (5) Å