Re: Could there be new forces found due to SUSY?

Hi John,

You're right to realize that the SUSY theory predicts SUSY force carriers: the photino, wino, bino for the electroweak force, the gluino for the strong force, and the gravitino for gravity. And several higgsinos.

However, these do not really carry "new forces". Gluons and gluinos, for example, interact with any QCD colored particle, i.e. both quarks and squarks. Photons and photinos both interact with any charged particle. Winos, binos, Ws and Zs interact with anything, and always with the peculiar "weak" coupling strength. So, no, the new bosons don't carry NEW forces; they carry the same old forces, but with new mediators. On the surface, the new carriers will make the forces look very different. That's the theory, anyway.

Theory aside: we already know, experimentally, that SUSY particles (or whatever makes up dark matter) don't interact very strongly with one another. How do we know? Because the dark matter clouds don't seem to collapse the same way that gas clouds do. If SUSY particles bumped into each other as easily as electrons and protons do, then the spherical ball of dark matter surrounding our galaxy would have settled into a disk, as all of the stars have; large galaxy clusters would have to be more spherical than they are; waves in the early-universe gas that emitted the "Cosmic Microwave Background" would have propagated differently. This sort of argument has been used to limit "self-interacting dark matter"---type that into Google and you will find some papers on the topic.

Sometimes we think of SUSY as "mirror matter": an exact copy of the standard model with only the spins changed. This is true at the level of group theory: the organization of the SUSY world is the same as that of the Standard Model world. But we call SUSY a "broken symmetry". If the symmetry were exact, then the SUSY particles would have the same masses (and mixings?) of the standard model particles. For some reason, probably "spontaneous symmetry breaking", the SUSY particles are all very heavy. This has all sorts of practical effects; most importantly, the only SUSY particle surviving in the Universe today is the lightest one, usually called the LSP. The heavier ones (all of the squarks, selectrons, etc. that would be easy to see and study) decay very quickly into the LSP, plus a bunch of standard model particles. Therefore, even if squarks, sleptons, and winos do have lots of new interactions, these interactions are not going on in the modern universe. The LSP is the only thing left.

Hope this helps. I'm glad you asked; your question prompted a useful discussion of photino interactions among my labmates.

-Ben