According to the book Quarks, by Nambu, the Weak Force, via charged W^+/-, allows the inter-conversion between quarks & leptons:

 

[math]d + \bar{u} \rightarrow W^{-} \rightarrow e^{-} + \bar{\nu}_e[/math]

and inter-conversions, between "generations" of particles:

 

[math]s + \bar{u} \rightarrow W^{-} \rightarrow e^{-} + \bar{\nu}_e[/math]

 

[math]\mu^{-} + \bar{\nu}_{\mu} \rightarrow W^{-} \rightarrow e^{-} + \bar{\nu}_e[/math]

Note that the "decay", of a strange quark s, into an up quark u (and some leptons), may be imaginable, as an s quark, initially bound into a baryon (say), breaking a "gluon string" bond, with a neighboring quark, so that the gluon "splits" into [math]s \approx u \; \rightarrow \; s \approx \bar{u} + u \approx u[/math]. Then, the [math]s \approx \bar{u}[/math] meson emerges from the nucleon, similar to a [math]\pi^{-}[/math] meson emission; and then "implodes" into a W^- boson, which decays into leptons, i.e. [math]s \approx \bar{u} \; \rightarrow \; W^{-} \; \rightarrow \; e^{-} + \bar{\nu}_e[/math], which race away.

 

 

QUESTION: If the Weak Force already allows inter-conversions "up down & across" the Standard Model particle table, then why doesn't the Weak Force already serve as a "unifying force", i.e. at 100 GeV, i.e. 10¹⁵K, (W boson rest-mass) "everything can become anything" (albeit by particle pairs, via W bosons) ? Perhaps at 100 GeV, when particles were colorless-leptons as often as quarks, then the 'Quark-Gluon-Plasma' really would "vaporize", and stop behaving like a "cold liquid", and more like the expected "hot gas", cp. RHIC only generates temperatures of 4TK ~ few tenths GeV ??

 

I see no reason, for imparsimoniously proposing additional, hypothetical, bosons & forces, e.g. having hypothetical charges of +4/3, when "already on-the-shelf, already known-to-exist" bosons & forces, can already account, for all desired inter-particle conversions.

Allowing for particles to react into particles with different names is not what is usually considered the defining property of a "unifying force".

If Weak Force bosons allow all fundamental "particle" quanta, to inter-convert amongst themselves; then, perhaps above the Electro-Weak Unification Temperature ~100GeV, all of those quanta would exist, in an equilibrium state, where they, collectively, were equally likely, to be "anything & everything". Such would be a "quark-gluon-lepton-W-boson-photon-plasma". That would not represent a state, in which all fundamental Forces were effectively unified ?