Hi,

In the context of Seiberg-Witten Theory, There are two types of particles:

- Mutually Local Particles: This means that at the vacuum manifold, one can use a coordinate (an Electric-Magnetic duality frame) on Coulomb branch such that all hypermultiplet have electric charges which couple to a theory written completely in terms of usual $U(1)$ photon coupled to electric sources;
- Mutually Non-Local Particles: This means that there is no such coordinate

I have several questions:

- What is non-local here? why this name?
- In the case of $SU(2)$ theory, at the two singularities it is said that a monopole and a dyon become massless, Does this particles are in BPS spectrum of theory at the original duality frame (coordinate $a$) or it is in new frame ($a_D$ for monopole and $a-2a_D$ for dyons.)?
- Where the flatness of $Sp(2r;\mathbb{Z})$ comes from (for a $r$-dimensional complex Coulomb branch)?