Why is the theoretical half life of a proton so high compared to half lifes of other subatomic particles?
If protons decay they would have to have very long half lives and it has never been observed.
Many of the known subatomic particles decay. Some however are stable because conservation laws don't allow them to decay into anything else.
First of all there are two types of subatomic particles bosons and fermions. Fermions are further subdivided into leptons and hadrons.
Bosons obey the Bose-Einstein statistics. More than one boson can occupy the same energy level and they are force carriers like the photon and W and Z.
Fermions obey the Fermi-Dirac statistics. Only one fermion can occupy an energy level and they are the particles of matter. Leptons are indivisible fermions and hadrons consist of two or more bound quarks.
Boson and fermion numbers can only change in multiples of two. Charge must also be conserved. Lepton and quark numbers are also conserved.
Photons are the lightest uncharged bosons and are stable because there is nothing they can decay into.
Electron neutrinos are the lightest uncharged fermions and are stable because there is nothing they can decay into. They are also leptons.
Gluons are the lightest charged bosons. They are stable because there is nothing they can decay into.
Electrons are the lightest charged fermions. They are stable because there is nothing they can decay into. They are also leptons.
Pions are the lightest hadrons, but as they consist of a quark and an antiquark, they are highly unstable. They typically decay into two photons or an electron and an electron antineutrino, or a positron and an electron neutrino. The particle antiparticle pair decay preserves lepton numbers.
The proton is the lightest charged hadrons which has three quarks. Conservation laws require it to be stable with nothing they can decay into.
Some theories allow conservation laws to be broken under certain circumstances. Such theories allow for proton decay. If proton decay does occur it has never been observed and the half life must be very long.