On Wednesday, February 28, 2018 at 8:24:59 PM UTC, Lawrence Crowell wrote:   
   > The graviton with respect to fermions is a bit odd. A four vertex   
   > interaction of fermions with parallel spins can carry the same   
   > quantum number as a graviton if this is charge neutral and massless.   
   > A graviton interacting with a fermion results in something odd. A   
   > spin 1/2 particle that absorbs a graviton with spin 2 then has   
   > either spin 3/2 or 5/2. The first of these is a Rarita-Shwinger   
   > field, and we know electrons etc do not convert into this in a   
   > gravity field. The RS field can only be an off-shell field that   
   > decays back into the fermion and graviton. The spin 5/2 is not   
   > physical. What saves the day for there being a single three vertex   
   > interaction is supersymmetry. A fermion is associated with a spin   
   > 1 particle in the (1/2, 1) SUSY doublet. Now the graviton can   
   > interact with the fermion through its superpartner. So a fermion   
   > quantum fluctuates into being a spin 1 boson that can absorb a   
   > graviton. We may then have a nice 3-vertex interaction.   
   >   
   > LC   
      
   4 Vertex interaction:  of two photons and two electrons seems IMO so   
   unlikely, like lightning striking twice in the same place, it's much more   
   likely that it would be three different electrons involved in a 3 vertex   
   interaction with 2 photons.  So 4-vertex seems not to be viable to me as a   
   main method of gravitational attraction.   
      
   Rarita-Shwinger field:  this is new to me.  It seems a fine idea for a   
   fermion of spin 3/2 either for a hypothetical elementary particle [easy to   
   make out of preons] or a composite particle, albeit as a short-lived off-   
   shell particle; or two entangled particles.  I am unclear why the 5/2 spin   
   is not physical:  definitely not physical, or the theory not yet worked out?   
      
   I followed Susskind's online SUSY course. The physics and grassman maths   
   seemed OK to me.  Susskind kept apologising for the weirdness of the fields   
   but they fitted in very nicely with my mindset of a preon approach. Preons   
   allow fermions and bosons to mix and so do SUSY fields.  However, I did not   
   see the need for unique superpartners.  IMO there can be multiple   
   superpartners depending on which of any number of superfields is present.   
      
   How does the spin 1 SUSY return to a spin 1/2 electron after entanglement   
   ends? Doesn't that need an appropriate superfield occurring at the final   
   vertex.  Isn't a juxtaposition of three entities of appropriate superfield,   
   target particle, and entangled graviton low in probability?  I have modeled   
   all SM particle interactions and decays using two incoming entities so, to   
   me,   
   requiring three incoming entities seems strange.  Of course if various SUSY   
   fields are ubiquitous, like the higgs, then it would not be low probability.   
      
   If a SUSY spin 1 happened to change to a spin 1/2 in mid flight then it   
   would have an off-shell short lifetime and presumably decay quickly back to   
   the SUSY spin 1.  That would be a mechanism to maintain the spin 2 graviton.   
      
   I am not clear what happens to the electron which becomes a SUSY   
   spin 1.  Is this a case of quantum gravitational kidnapping rather than   
   tunnelling.  Doesn't the electron just disappear from its environment and   
   get deposited at the end vertex? Not something you would want to happen in   
   every gravitational interaction?   
      
   (I am so far behind this that I do not know what the three vertices   
   are.  But I don't want to cause you bother by explaining.  Thank you very   
   much for your comments.)   
      
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