Story on Proton decay 물리 이야기

It is usually expected that proton does have a finite life time in the generic theory of Grand unification. The main physical reason of proton's mortality comes from the mixing between quarks and leptons when they are ultimately combined in a single, basic object - a gauge multiplet - in GUT's. In that sense, proton's immortality -experimentally tested lower bound of its life time is now longer than 10^32 yrs or so- might indicate that there is no GUT upto very very high energy, say 10^16 GeV or so.

We may have available parameter spaces in supersymmetric GUT's where the life time of proton could exceed the experimental lower bound but still it is expected that proton must die in some time. That's not found yet. In any case, it is extremely important to understand why proton is so stable in any kind of theories where quarks and letptons are ultimately unified so it will be really appreciated if some of our experimentalist friends could find if proton really does decay.

In higher dimensional theories, there could be a simple reason why proton is so stable. It is simply because quarks and leptons are spatially separated in the extra dimensions. But still it is questionable to ask if quarks and leptons could be unified and separated simultaneously.

There is an old adage, "Every thing born will die (生者必滅)" and so I would say that GUT has been predicted since many years ago in oriental world.


\begin{eqnarray} \hbar c =197.3 \text{MeV fm}\\ (\hbar c)^2=0.389 \rm{GeV}^2 \rm{mb}\\ 1.0{\rm pb}=\frac{2.568\times 10^{-3}}{\rm TeV^2}\\ =10^{-40} {\rm m}^2 \end{eqnarray}

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