# Is there some explanation for $y_t=1$

The Yukawa coupling of the top quark is Dirac-natural in a too excellent way, it is within one sigma experimentally, and within 99.5% in absolute value, of being equal to one. Without some symmetry, it seems too much for a quantity that is supposed to come down from GUT/Planck scale via the renormalization group. Is there some explanation for this?

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I don't know of any explanation for this but I'd be interested to hear if someone else comes up with something. –  David Z Sep 19 '11 at 17:17
Search on "large top yukawa" returns some theories... –  Mitchell Porter Sep 20 '11 at 2:28
@MitchellPorter yep, a "order one" yukawa was expected, even predicted, in some setups. But one thing is a range, say, 0.2.. 20, and a very different thing is 0.995 pm 0.005 –  arivero Sep 20 '11 at 9:33
Sounds like a question suitable for the theoreticalphysics.stackexchange.com , imo –  anna v Dec 12 '11 at 6:45
It is OK to me, if the moderators forward them to the other SE. –  arivero Dec 12 '11 at 8:47

This is a very naive answer or, in fact, it is not an answer. Among all numbers of order one, is not $y_t=1$ the most likely value, i.e., the statically expected value? Why do we need an explanation for $y_t=0.995$ and not for, say, $y_t=0.629$?