Could galactic magnetic fields be generated by charged ultra-light boson dark matter?

Abstract

We study the possibility that large-scale magnetic fields observed in galaxies could be produced by a dark matter halo made of charged ultra-light bosons, that arise as excitations of a complex scalar field described by the Klein-Gordon equation with local U (1) symmetry which introduces electromagnetic fields that minimally couple to the complex scalar current and act as dark virtual photons. These virtual photons have an unknown coupling constant with real virtual photons. We constrain the final interaction using the observed magnetic fields in galaxies. We use classical solutions of the Klein-Gordon-Maxwell system to describe the density profile of dark matter and magnetic fields in galaxies. We consider two cases assuming spherical and dipolar spatial symmetries. For the LSB spherical galaxy F563-V2, we test the sensitivity of the predicted rotation curves in the charged Scalar Field Dark Matter (cSFDM) model to variations of the electromagnetic coupling and using the Fisher matrix error estimator, we set a constraint over that coupling by requiring that theoretical rotation curves lay inside the 1σ confidence region of observational data. We find that cSFDM haloes generate magnetic fields of the order of μG and reproduce the observed rotation curves of F563-V2 if the ultra-light boson has a charge ∼< 10 −13 e for the monopole-like density profile and ∼< 10 −14 e for the dipolelike one.

The quantum character of the Scalar Field Dark Matter

“…On cosmological scales we do not see that dark matter can be charged, we do not have any evidence of it, so we conclude that the charge can only be generated as a fluctuation that we consider to be small, due to observations in galaxies. This charge could be the origin of the magnetic field observed in galaxies, as speculated in [41]. In this work, using the ansatz (51) and (52) we were able to integrate the perturbed field equations in terms of the two background functions a and n 0 , which can be easily integrated numerically.…”

“…But to elucidate the physical behavior of the system, as in the previous example, it is not necessary to solve the system, we will make a toy model to see its behavior, but now with an electromagnetic field. Galaxies generally contain a complicated magnetic field, it has been speculated in [41] that this field could be a consequence of SFDM with the Lagrangian (4), so the solution of Maxwell's equations could be very complicated for a real magnetic field of a scalar field fluctuation. In addition, the magnetic field does not have a determining influence on the gravitational field of a fluctuation, it is generally very weak in the galaxy.…”

“…In the general case we have to add the equations (44) and (48). Here we remark that the electromagnetic field is not essential for the development of the fluctuations, it is essential in the final fluctuation to explain the magnetic field of the galaxies ( [41]) and the FB, and for the purpose of this work we can also neglect the proper interactions λ. So, let's substitute B µ = 0 and take the scalar field potential as V = m 2 ΦΦ * .…”