The anomaly cancellation condition for the gravitational part of the chiral anomaly (neglecting gauge charges) is simply that there are the same number of left and right moving fields
NL=NR
which in your case is
3N(1L)+N(0L)=2N(1/2R),
where N(R) indicates the number of (complex) fields in each representation. The prefactors are the (complex) dimensions of the gauge multiplets.
To determine the gauge part of the chiral anomaly, note that the SU(2) Chern-Simons level may be determined from its U(1) subgroup, so it is equivalent to determine the U(1) gauge anomaly. This anomaly cancellation condition is
∑iq2i=∑jq2j,
where i indexes left-moving charge carriers and j indexes right-moving charge carriers.
The SU(2) triplet has a charge +2 and a charge −2 carrier, the doublet has a +1 and a −1, and the singlet has no charge carriers. So the anomaly cancellation condition is
8N(1L)=2N(1/2R).
Note that this technique works for any connected compact gauge group, since the Chern-Simons levels are determined by their maximal torus. Thus, the chiral anomaly in 1+1D always comes down to a number of U(1) anomalies (plus the gravitational part) which must be checked.
This post imported from StackExchange Physics at 2020-11-08 17:29 (UTC), posted by SE-user Ryan Thorngren