The Evolution of the Angle Between the Magnetic Moment and the Rotation Axis of Radio Pulsars with the Small-Scale Magnetic Field and the Superfluid Core

We investigate the evolution of the inclination angle between magnetic moment and rotational axis of neutron stars taking into account the surface small-scale magnetic fields and the superfluid neutrons in the neutron star core. We assume that pulsar angular momentum losses are the sum of magneto-dipolar and current losses. The neutron star is treated as a two-component system consisting of a charged component (including the crust and the core protons, electrons and normal neutrons) and a core superfluid neutron component. The components interact through the mutual friction force. We assume that the charged component rotates as a rigid body. The neutron superfluid velocity field calculated directly from linearized hydrodynamical equations. It is shown that the superfluid core accelerates the evolution of inclination angle and makes all pulsars evolve to orthogonal state. But as it is known from observations the rate of the angle evolution is not very high. Therefore, a small size of superfluid cores are more likely.