  The behavior of simple eigenvalues of Aharonov-Bohm operators with many
coalescing poles is discussed. In the case of half-integer circulation, a gauge
transformation makes the problem equivalent to an eigenvalue problem for the
Laplacian in a domain with straight cracks, laying along the moving directions
of poles. For this problem, we obtain an asymptotic expansion for eigenvalues,
in which the dominant term is related to the minimum of an energy functional
associated with the configuration of poles and defined on a space of functions
suitably jumping through the cracks.
  Concerning configurations with an odd number of poles, an accurate blow-up
analysis identifies the exact asymptotic behaviour of eigenvalues and the sign
of the variation in some cases. An application to the special case of two poles
is also discussed.
