  Motivated by recent numerical and experimental studies of the spin-1/2
Heisenberg antiferromagnet on kagome, we formulate a many-body model for
fermionic spinons introduced by us earlier [Phys. Rev. Lett. 103, 187203
(2009)]. The spinons interact with an emergent U(1) gauge field and experience
strong short-range attraction in the S=0 channel. The ground state of the model
is generically a $Z_2$ liquid. We calculate the edge of the two-spinon
continuum and compare the theory to the slave-fermion approach to the
Heisenberg model.
