Dark photon stars: formation and role as dark matter substructure

Abstract

Any new vector boson with non-zero mass (a 'dark photon' or 'Proca boson') that is present during inflation is automatically produced at this time from vacuum fluctuations and can comprise all or a substantial fraction of the observed dark matter density, as shown by Graham, Mardon, and Rajendran. We demonstrate, utilising both analytic and numerical studies, that such a scenario implies an extremely rich dark matter substructure arising purely from the interplay of gravitational interactions and quantum effects. Due to a remarkable parametric coincidence between the size of the primordial density perturbations and the scale at which quantum pressure is relevant, a substantial fraction of the dark matter inevitably collapses into gravitationally bound solitons, which are fully quantum coherent objects. The central densities of these 'dark photon star', or 'Proca star', solitons are typically a factor 106 larger than the local background dark matter density, and they have characteristic masses of 10-16 M ⊙ (10-5 eV/m)3/2, where m is the mass of the vector. During and post soliton production a comparable fraction of the energy density is initially stored in, and subsequently radiated from, long-lived quasi-normal modes. Furthermore, the solitons are surrounded by characteristic 'fuzzy' dark matter halos in which quantum wave-like properties are also enhanced relative to the usual virialized dark matter expectations. Lower density compact halos, with masses a factor of ∼ 105 greater than the solitons, form at much larger scales. We argue that, at minimum, the solitons are likely to survive to the present day without being tidally disrupted. This rich substructure, which we anticipate also arises from other dark photon dark matter production mechanisms, opens up a wide range of new direct and indirect detection possibilities, as we discuss in a companion paper.

New Constraints on Dark Matter and Cosmic Neutrino Profiles through Gravity

“…In many theories of light DM scalars (including the QCD axion 2 ), the breaking of a high-scale U (1) symmetry [64] after inflation gives rise to large density perturbations that collapse at (or just before) matter-radiation equality [65,66], which are well-described by power-law profiles [67]; similar arguments apply to spin-1 DM candidates [68]. These overdensities are known as axion miniclusters, and they may constitute a large fraction of the total DM mass in galaxies (see, e.g., [69]).…”

i-SPin: An integrator for multicomponent Schrödinger-Poisson systems with self-interactions

“…For instance, they are present in the low-energy effective theory of vector dark matter arising from an Abelian Higgs model (with a heavy Higgs field). These interactions can lead to interesting modifications to the phenomenology of vector dark matter formation [43][44][45][46][47][48][49], blackhole superradiance [50][51][52][53], and impact nonlinear small-scale structure in such dark matter [11][12][13]54]. As discussed in [14,55], they also remove the energy degeneracy between polarized vector solitons which could potentially impact their cosmological population.…”

“…Physical systems described by Schrödinger(-like) equations are ubiquitous in many areas of physics, ranging from (ultra-)light dark matter in cosmology [1][2][3][4][5][6][7][8][9][10][11][12][13][14], to terrestrial systems in non-linear optics [15][16][17][18][19][20][21][22], water waves [23][24][25] and Bose-Einstein condensates (BEC) [26][27][28][29][30][31][32]. Apart from long-range interactions such as gravity in the astrophysical/cosmological context, or external potential in laboratory settings, the Schrödinger field can have point-like quartic selfinteractions, with its evolution determined by time-dependent Gross-Pitaevskii(-like) equations.…”

Unequal-mass boson-star binaries: initial data and merger dynamics

“…The concept of BSs, in the sense of equilibrium solutions to the Einstein equations, followed about a decade later with Kaup's pioneering work [17] on self-gravitating configurations of massive complex scalar field, dubbed as Klein-Gordon geons. Originally these configurations were devised from fundamental scalar (spin 0) fields [18,19] and later on extended to vector (spin 1) fields (aka Proca stars) [20][21][22][23][24][25][26][27][28][29][30][31] or high-spin fields [32,33]. The nature of the scalar field can be real-resulting in potentially long lived but not strictly stable compact objects commonly referred to as oscillatons (OSs) [34][35][36][37]-or complex for BSs; this latter complex case is the focus of our work.…”