Magnetic field dependence of Delta isobars properties in a Skyrme model

The properties of $\Delta$ isobars in a uniform magnetic field are investigated. In the weak magnetic field region, the general relations between magnetic moment of nucleons and $\Delta$ isobars are given. In the strong magnetic field region, the mass and size of $\Delta$ isobars depend on the increasing of magnetic field strength in different ways: the effective mass of $\Delta^{++}$, $\Delta^{+}$ and $\Delta^{0}$ first decreases and then increases, consequently, the size of $\Delta^{++}$, $\Delta^{+}$ and $\Delta^{0}$ first increases and then decreases; whereas, the effective mass of $\Delta^{-}$ always increases, and consequently, the size of $\Delta^{-}$ always decreases. The estimation shows in the core part of the magnetar, the equation of state for $\Delta$ isobars depends on the magnetic field, which affects the mass limit of the magnetar.