  Three-dimensional Weyl semimetals have pairs of topologically protected Weyl
nodes, whose projections onto the surface Brillouin zone are the end points of
zero energy surface states called Fermi arcs. At the endpoints of the Fermi
arcs, surface states extend into and are hybridized with the bulk. Here, we
consider a two-dimensional junction of two identical Weyl semimetals whose
surfaces are twisted with respect to each other and tunnel-coupled. Confining
ourselves to commensurate angles (such that a larger unit cell preserves a
reduced translation symmetry at the interface) enables us to analyze arbitrary
strengths of the tunnel-coupling. We study the evolution of the Fermi arcs at
the interface, in detail, as a function of the twisting angle and the strength
of the tunnel-coupling. We show unambiguously that in certain parameter
regimes, all surface states decay exponentially into the bulk, and the Fermi
arcs become Fermi loops without endpoints. We study the evolution of the `Fermi
surfaces' of these surface states as the tunnel-coupling strengths vary. We
show that changes in the connectivity of the Fermi arcs/loops have interesting
signatures in the optical conductivity in the presence of a magnetic field
perpendicular to the surface.
