From: sichase@csa2.lbl.gov (SCOTT I CHASE)
Newsgroups: sci.physics
Subject: Re: Standard Model without Higgses (Was : Size of a PHOTON?)
Date: 5 Nov 1992 11:01 PST
Organization: Lawrence Berkeley Laboratory - Berkeley, CA, USA
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In article <1992Nov4.223548.8659@physics.ucla.edu>, baillie@physics.ucla.edu (Baillie) writes...
>Not wanting to detract from your well-stated point, but if you turned off
>the Higgs in the standard model, the W and Z would not be massless, because
>of _dynamical_ symmetry breaking. For instance, in a theory with two quark
>flavours, there is an SU(2)_Left x SU(2)_Right symmetry which is broken down
>by QCD to diagonal SU(2). This leaves 3 Goldstone bosons --- the pions, which
>are "eaten" by the W and Z to give them mass, in the same way that the
>unphysical Higgs bosons get "eaten" in the Standard Model.

I entirely avoided the question of alternative models of mass because
the Higgs model provided me with a nice answer to the question of "where"
the mass is.  As you point out, people should not get the impression that
the Higgs model is the only serious possibility.  Another example, popular
lately, is spontaneous symmetry breaking by a top-quark condensate.   If
the mass of the top quark if *very* large, the symmetry of the vacuum
can be broken by a bose condensate of pairs of top quarks.  The condensate
plays the role that the fundamental scalar plays in the SM. I'm afraid
that I can't tell you the details.  However, I can say that it does provide
a model with a certain "frugality," in that it accomplishes SSB without
postulating a new fundamental scalar - it merely makes use of the existing
heavy quarks.  This has some appeal from a theoretical point of view,
since the existence of the Higgs is a somewhat ad hoc assumption.

From an experimental point of view, the entire question of mass generation
is only now becoming a tractable problem.  I am sure that Matt will flame
me for lending so much credence to this, but I'll tell you anyway.  Ellis 
et.al. have done fits to the large body of LEP data on Z physics, treating
M(top) and M(Higgs) as two open parameters of the SM.  The fact that 
radiative corrections set nice limits on M(top) is well known and widely
accepted.  You find, roughly, that on the assumption that the SM is correct,
M(top) = 130+/-30 GeV.  Ellis finds that you can also now constrain the Higgs
mass, though very weakly.  If you *really* stretch things, and select your
data sets carefully, you can get down to 50 < M(Higgs) < 600 GeV.  If you
play it more "fairly," not excluding any data sets, etc., you find 
M(Higgs) < 3000 GeV, or some such large number which I may not be remembering
exactly.

The important point is that the experiments are now good enough to 
constrain the model to the point where *something* like a Higgs (of *some*
mass) is required to make things work.  I.e., the data imply that the 
Higgs, or something which acts effectively like a Higgs, MUST exist if
the rest of the SM is correct.  

This is very exciting, because it implies that as the data get better 
we will be able to address the question of mass generation in a direct
experimental manner, and end all this theoretical wrangling once and for all.

-Scott
--------------------
Scott I. Chase			"It is not a simple life to be a single cell,
SICHASE@CSA2.LBL.GOV		 although I have no right to say so, having
				 been a single cell so long ago myself that I 
				 have no memory at all of that stage of my 
				 life." - Lewis Thomas