Population synthesis of pulsars: Magnetic field effects

New results based on methods of population synthesis, concerning magnetic f ield effects on the evolution of pulsars, are reported. The present study c onfirms that models with timescales for the magnetic field decay longer tha n the pulsar lifetime are in better agreement with the data. These new simu lations indicate that the diagram log(P(P)over dot)log(t(s)) alone cannot b e used to test field decay models. The dispersion of the values of the init ial period and magnetic field can explain the observed behaviour of the dat a points in such a diagram. The simulations also indicate that the statisti cal properties of anomalous X-ray pulsars and soft-gamma repeaters (magneta r candidates) are compatible with those derived for objects born in the hig h side tail of the magnetic field distribution. The predicted birth rate of neutron stars having field strengths in excess of 10(14) G is one object b orn each 750 yr.