🚀 go-pugleaf

I write...
>>Could you be more specific? If you mean the coupling constants coming
>>together, theoretically they should, and experimentally they do.

sichase@csa3.lbl.gov writes...
>I don't agree on either point.  "Theoretically they should" is questionable.
>You certainly can construct unification schemes where two of the coupling 
>constants come together at one mass scale and the combined pair comes
>together with the third at another, can't you?  As far as I understand it,

This can happen in more complicated models, but it doesn't in SU(5). When I said
theoretically they should, I was assuming SU(5).

>there is no strong reason to expect otherwise.  As far as "experimentally
>they do,"  it seems to me that this is the big open question.  The coupling
>constants run towards some kind of meeting and minimal SUSY does a 
>better job of getting them to meet at one pont than at least one simple 
>GUT (probably SU(5) was the one in the plot that got all the press).
>But I don't see how that is m9uch evidence for SUSY.

All the non-supersymmetric models are ruled out (Frampton has constructed
some which are still ok, but they are really contrived) by the couplings
not unifying correctly. Most of the SUSY ones are similarly ruled out. One
is ok. The minimal SU(5) one. It also predicts everything correctly. 

>>Do you mean the experimental result that sin^2(theta) is the predicted
>>value, or the result that proton decay is suppressed, as predicted? ;-)
>
>I will take your smily at face value and not bring up any of the so far
>completely embarassing experimental history of GUTs w.r.t. experimental
>verification.  Not that we have anything better.  Sigh...

It was more of a wink than a smiley. Most of the embarrasment was for non-
supersymmetric GUTs. There was one exception, though. Sin^2(theta) was
too low for SUSY. But the experimental value has since been corrected. ;)

I think a lot of people are sceptical because of these embarrasments you
talk about, but that is reasonable only if the new model is just one of a
series of tweaks, which adjust to fit each new experimental bound. That is
not the case here. There are independent theoretical reasons for considering
supersymmetry. And once you incorporate it into SU(5) , ALL the GUT
problems are solved! The only real objection to SUSY is: why should one
partner of each multiplet be light? I think the success of SUSY GUT weighs
somewhat heavier, because there are MANY things we don't understand and
we can't throw away theories just because our knowledge is incomplete.

BTW I think SUSY has about 60/40 chance of being correct. (Is that a
meaningful statement?)

Dave Ring
dwr2560@zeus.tamu.edu