🚀 go-pugleaf

In article <8AUG199217160900@zeus.tamu.edu> dwr2560@zeus.tamu.edu (RING, DAVID WAYNE) writes:

> matt@physics.berkeley.edu writes...
> >This just means that non-supersymmetric SU(5) theories are ruled out,
> >right?  My understanding was that there were still a number of viable
> >SO(10) and E(6) models.  
> 
> You're probably right, it's so hard to keep up on these things. There are
> of course many models which are not ruled out. But do any of them make any 
> real predictions?

Well, yes and no.  The big advantage of the original Georgi-Glashow
SU(5) model was that it had essentially no free parameters (well, the
Higgs masses, but that doesn't make it any worse than the Standard
Model): all low-energy predictions can be expressed in terms of the
GUT mass M_X, which, in turn, can be deduced from low-energy
measurements of the gauge coupling constants.  This simplicity is what
made it attractive, and is also what allowed it to be ruled out.

Any time you add more parameters, as with SO(10), or SUSY SU(5), or
whatever, you lose some of that predictive power.  So it's a lot
harder to rule these models out.

Still, I think it's fair to say that they do make real predictions.
SO(10), for example, predicts the existence of a new heavy neutral
gauge boson (i.e., a Z'), and predicts the existence of right-handed
neutrinos.  It doesn't say anything about their mass, but, well, you
can't have everything.
--
Matthew Austern              I dreamt I was being followed by a roving band 
(510) 644-2618               of young Republicans, all wearing the same suit,
matt@physics.berkeley.edu    taunting me and shouting, "Politically correct
austern@theorm.lbl.gov       multiculturist scum!"... They were going to make
austern@lbl.bitnet	     me kiss Jesse Helms's picture when I woke up.