Simple dark matter models are built by electromagnetically interacting particles. Gravitational models are complex and built on many dogmatic theories for acceptance. Occam's razor states "when you have two competing theories that make exactly the same predictions, the simpler one is the better." Isaac Newton said "admit no more causes of natural things than what is true and sufficient to explain it."
Dark Matter Violates Occam's Razor:
Example 1: Scientist Kouvaris has invented millicharged dark matter particles to carry electric currents around neutron stars. Spin rates are slowing down faster than by magnetic fields alone, so an additional breaking effect they attribute to dark matter electric charges. In their paper
"Can Millicharged Dark Matter Explain the Braking Index of Neutron Stars" Kouvaris writes "The rate of rotation of a neutron star drops steadily as a function of time. The deceleration of the rotation is due to torque that are applied on the star impeding it's motion. There are basically two components for the torque: 1) An Orthogonal component that maximizes when the magnetic moment of the neutron star is perpendicular to the rotation axis of the star. Angular momentum is lost through emission of magnetic dipole radiation. 2) An Aligned component maximized when the rotation and the magnetic axis of the star are aligned. The torque is produced by the
electric current created by escaping charged particles that follow the open field lines of the neutron star magnetosphere. If the electric charge is sufficiently large an enhanced number of "Millicharged dark matter particles" may follow the magnetic field lines in the magnetosphere within the light cylinder and cross the surface of the star with much higher accretion rate. Accretion of Millicharged dark matter onto the neutron star can lead to an excess of electric charge that is expelled from the caps, providing this way an extra component of electric current. The total electric current has two current components.
There is no need to have dark matter. Electrical charged plasma particles constitutes 99.9% of the universe, and is a good conductor of electricity. Electric currents are in the interstellar medium from gas motions, NASA has reported.
Feature story Newscientist "Clingy Dark Matter May Slow Neutron Star Spin"Toroidal electric field around an iron core, a common supernova ejected element.
Two components of electric current in the total current.
Ampere's law applied to a toroidal solenoid.
Example 2: Robert Schererville and Chi Man Ho in their paper
"Anapole Dark Matter" say their fictional invented anapole is the only allowed electromagnetic moment for majorana dark matter. The interaction operator for the anapole moment is related to but different from that for the toroidal dipole moment. The toroidal dipole moment reduces to the anapole moment in the limit X1=X2 when the incoming and outgoing particles are the same the toroidal dipole moment coincides with the Anapole moment.
"New Simple Theory May Explain Dark Matter" (Feature Vanderbilt story)
Chasing Ghosts of Dark Matter:
Electric Universe Thunderbolts explains electric currents in cosmic plasmas, two current interacting filaments in spiral galaxies, and how dark matter is arbitrarily placed wherever it is needed in their models. In these examples dark matter is the smoking gun.
Electric currents and magnetic fields are associated together in an electromagnetic cosmic ray driven "cosmic toroidal dynamo" involving plasmas, superfluids, and phase changes.
Related story: "Pulsars Are the Unknown Dark Matter Detected by AMES"