Clover

Chroma and QUDA Conventions

The Chroma convention for the unpreconditioned operator is

A - (1/2) D 

where A looks like

(Nd + M) + c. (1/8) i sigma_mu,nu F_mu,nu

with Nd being the number of dimensions, M is the mass parameter, c is the Clover coeff and sigma_mu,mu is the spin structure of the Clover term with F_mu,mu being the field strength tensor.

If you divide out (Nd + M) = 1/( 2 * kappa ) you get the more conventional:

A' - kappa D

With A' = 1+i ( kappa c )/4 sigma_mu,nu F_mu,nu. Since Chroma computes A and passes that instead of A' and the mass is embedded, at interface we can just pass a kappa=0.5 to correctly normalize the operator. Conversely, if we wanted QUDA to compute the Clover term A' with a given kappa, we would need to divide it by (2 * kappa) to change it to A.