  The hedgehog lattice, a three-dimensional periodic array of magnetic
monopoles and antimonopoles, is known to be realized in the presence of the
Dzyaloshinskii-Moriya (DM) interaction. Here, we demonstrate by means of Monte
Carlo simulations that the hedgehog lattice is induced by not the DM
interaction but frustration in classical Heisenberg antiferromagnets on the
breathing pyrochlore lattice. In the model, the breathing bond-alternation is
characterized by the ratio of the nearest-neighbor (NN) antiferromagnetic
exchange interaction for large tetrahedra to that for small ones, J1'/J1. A
quadruple-q state with the ordering vector of q=(\pm 1/2,\pm 1/2,\pm 1/2),
which is realized for a large third NN antiferromagnetic interaction along the
bond direction J3, turns out to become the hedgehog-lattice state in the
breathing case of J1'/J1 <1, while in the uniform case of J1'/J1 =1, it is a
collinear state favored by thermal fluctuations. It is also found that in a
magnetic field, the structure of the (1/2,1/2,1/2) hedgehog lattice is changed
from cubic to tetragonal, resulting in a nonzero net spin chirality which in a
metalic system, should yield a characteristic topological Hall effect.
