assumptions about squark mixing?
In MG4 I understood what was expected in an SLHA file and what assumptions were being made: stops and sbottoms could mix, the other squarks didn't, and the blocks STOPMIX and SBOTMIX contained the mixings. It wasn't as general as possible, but at least the assumptions were very clear.
In MG5, I'm confused about what assumptions are being made. I thought the full USQMIX block defined in 0801.1800, which relates the basis (u_L, c_L, t_L, u_R, c_L, t_R) to a mass-ordered basis of all up-type squarks (and the analogous thing for down-type squarks) was being used. However, in parameters.py, it looks like only a subset of the mixing angles (RRu13, RRu16, RRu23, RRu26, RRu35, RRu44, RRu51, and RRu62) are defined, so I think implicitly the same assumption is being made that only the stops are mixing. Also, I'm confused about the ordering; 0801.1800 says that USQMIX maps the gauge/flavor eigenstate basis to a basis that is "mass-ordered," which I take to mean that, e.g., if stop1 and stop2 are lightest they are assigned codes 1000002 and 1000004, independent of the old conventions for flavor labeling, whereas if they are heaviest they are assigned codes 2000004 and 2000006. However, that looks inconsistent with the apparent assumption being made in parameters.py that the mixed states are #1 and #2 (which are mixtures of 3 and 6 in the gauge/flavor basis, i.e. of stop_L and stop_R) -- this would only be mass-ordered if the stops are the lightest.
This confusion is compounded by the relabeling of su1, su2, ... su6 as ul, cl, ... t2 defined in input/particles
Is there some documentation of the precise assumptions being made in the MG5 code? If the goal really is to read the full USQMIX matrix, then shouldn't there be parameter definitions for RRu11, RRu12, and so on? Or maybe I've just misread the code and it's more general than it appears to be at first glance.
Thanks for any help clearing up my confusion on this point.
Best regards,
Matt
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