Chern-Simons gravity coupled to the scalar sector through a generic coupling function f ( \phi ) can be tested at the very high energies of the inflationary period .
In ref . [ ] , we computed the theoretical parity breaking signatures of the \left \langle \gamma \gamma \zeta \right \rangle primordial bispectrum which mixes two gravitons and one scalar curvature perturbation .
We defined a parameter \Pi which measures the level of parity breaking of the corresponding bispectrum .
In this work we forecast the expected 1 \sigma error on \Pi using the cosmic microwave background ( CMB ) angular bispectra .
We find that , given the angular resolution of an experiment like Planck , \Pi \sim 10 ^ { 6 } is detectable via the measurement of BBT or BBE angular bispectra if the tensor-to-scalar ratio r = 0.01 .
We also show that , from the theoretical point of view , \Pi can be greater than 10 ^ { 6 } .
Thus , our conclusion is that BBT or BBE CMB angular bispectra can become an essential observable for testing Chern-Simons gravity in the primordial universe .