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 1sigma confidence region of observational data. We find that cSFDM haloes generate magnetic fields of the order of mu G and reproduce the observed rotation curves of F563-V2 if the ultra-light boson has a charge sim <10^{-13}e for the monopole-like density profile and sim <10^{-14}e for the dipole-like one.
Highlights
The origin of large-scale magnetic fields remains as an open problem and a matter of active discussion and research
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
For the LSB spherical galaxy F563-V2, we test the sensitivity of the predicted rotation curves in the charged Scalar Field Dark Matter 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
Summary
The origin of large-scale magnetic fields remains as an open problem and a matter of active discussion and research. The classical field solutions of the KG equation describe the order parameter of a system of bosons in the relativistic regime Given that this model provides one of the strongest dark matter candidates together with unresolved question about the origin of magnetic fields at large scales, we believe that the mechanism proposed in this work must be thoroughly studied, being this work a very first step in such task. This is the reason we believe that the CMB and the MPS wouldn’t give further constrains to the charge we found but we think that the rotation curves of galaxies could give a stronger constrain to the charge of the scalar field This is exactly one of the main results of this work: in order to preserve the predictions at astrophysical scales such as the stellar rotation curves in galaxies, the electromagnetic coupling of SFDM bosons is strongly restricted to very low values.
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