Can string theory answer why the Yukawa couplings or the v.e.v.s.have the values they have in our Universe? I mean, why can string theory answer( and EXPLAIN) the question of why the top coupling to the Higgs is so big in comparison with the remaining particles? And with respect to fermions, can the Higgs coupling explain the tiny neutrino masses withour invoking Majorana conditions on the fermion fields? That is, can the Higgs sector select to be fine-tune the neutrinos to Majoranas with low couplings (excepting possible right-handed heavy neutrinos or sterile neutrinos) and heavy quarks to high couplings by some reason?

  • $\begingroup$ If a stringer presumes to tell you how the Yukawa couplings follow from string theory, somehow, anyhow, just don't believe her/him. $\endgroup$ – Cosmas Zachos Jan 21 '18 at 17:09
  • $\begingroup$ I know Cosmas, I KNOW, hehehehe...That is why ask...The landscape is terrible... $\endgroup$ – riemannium Jan 21 '18 at 17:41
  • $\begingroup$ Yukawa couplings, indeed, follow from NO symmetry in the Standard Model. And as far as I know, excepting some rough trials in SUGRA or SUSY, there is no known origin based on currently accepted symmetry principles behind the Yukawa couplings. There is a big mystery and puzzle there! $\endgroup$ – riemannium Jan 21 '18 at 17:43
  • $\begingroup$ Related physics.stackexchange.com/q/15/2451 and links therein. $\endgroup$ – Qmechanic Jan 21 '18 at 20:39
  • $\begingroup$ @Cosmas Zachos, I don't know what message you want to convey. String theory has mechanisms to produce yukawa couplings, and for some vacua they can be crudely calculated. Are you just saying that no particular class of models has emerged as the clear leader? $\endgroup$ – Mitchell Porter Jan 21 '18 at 20:46

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