  We propose a novel, higher-derivative, Weyl-invariant and generally-covariant
theory for the cosmological constant. This theory is a mimetic construction
with gauge fields playing the role of dynamical variables. These fields compose
the Chern-Simons current instead of the vector field used in the Henneaux and
Teitelboim formulation of the unimodular gravity. The equations of motion
exactly reproduce the traceless Einstein equations. We demonstrate that,
reformulated in Weyl-invariant variables, this novel theory reduces to standard
general relativity with the cosmological constant as a Lagrange multiplier.
This Lagrange multiplier has an axion-like coupling.
