  A number of lattices exhibit moat-like band structures, i.e. a band with
infinitely degenerate energy minima attained along a closed line in the
Brillouin zone. If such a lattice is populated with hard-core bosons, the
degeneracy prevents their condensation. At half-filling, the system is
equivalent to $s=1/2$ XY model at zero magnetic field, while absence of
condensation translates into the absence of magnetic order in the XY plane.
Here we show that the ground state breaks the time-reversal as well as
inversion symmetries. This state, which may be identified with the chiral spin
liquid, has a bulk gap and chiral gapless edge excitations. The applications of
the developed analytical theory include an explanation of recent numerical
findings and a suggestion for the chiral spin liquid realizations in
experiments with cold atoms in optical lattices.
