Hypernuclear matter in strong magnetic field
  Compact stars with strong magnetic fields (magnetars) have been
observationally determined to have surface magnetic fields of order of
10^{14}-10^{15} G, the implied internal field strength being several orders
larger. We study the equation of state and composition of dense hypernuclear
matter in strong magnetic fields in a range expected in the interiors of
magnetars. Within the non-linear Boguta-Bodmer-Walecka model we find that the
magnetic field has sizable influence on the properties of matter for central
magnetic field B \ge 10^{17} G, in particular the matter properties become
anisotropic. Moreover, for the central fields B \ge 10^{18} G, the magnetized
hypernuclear matter shows instability, which is signaled by the negative sign
of the derivative of the pressure parallel to the field with respect to the
density, and leads to vanishing parallel pressure at the critical value B_{\rm
cr} \simeq 10^{19} G. This limits the range of admissible homogeneously
distributed fields in magnetars to fields below the critical value B_{\rm cr}.
