The greatest shortcoming of SU(5) (Grand Unified Theory) is the failure of its proton decay prediction. After 20 years observation, no single proton decay case was recorded. The low limit for the proton lifetime is now set at about 10^33 years, which is incredibly longer than the age of the universe.

It is good news that proton don't decay. Otherwise, lives would have difficulty remaining alive. But, why won't proton decay under the current condition? SU(5) (Grand Unified Theory) does not have an answer but the Prequark Model does.

• First, we should review the differences between the two models about the neutron decay.
  • In Standard Model, neutron decay starts out from some probability that one of the down quark of neutron transforms into an up quark, which is mediated by a virtual W- boson.
    
  • In Prequark Model, things are very simple.
    1. The spacetime vacuum energy produces a down quark (d - d bar) pair.
    2. This d - d bar pair captures a down quark of neutron to form a three-quark mixture.
    3. Then, a d - d bar pair transforms into a u - u bar pair.
    4. Finally, by exchanging an Angultron and a Vacutron completes the decaying process.
    It is the spacetime vacuum energy driving the neutron to decay. Although the fluctuation amplitude of spacetime vacuum energy can be non-zero, the spacetime vacuum energy itself is always equal to zero; thus, it will not make any energy contribution to the system. However, the entropy of the end system will increase because of its involvement.
• Second, the proton decay mode of Prequark Model is shown in graph below. The proton decays into a positron and a pion (zero) [a d - d bar pair]. This decay mode is significantly different from the neutron decay mode in the following ways.
  1. This is an internal decay. That is, it does not require any external helps.
  2. Because it is an internal decaying process, the spacetime vacuum energy can produce zillion pairs of d quark or up quark and dance around the proton all day long but still cannot influence the proton decaying process one bit.
  3. Although both sides of proton decaying process are electric charge conserved and color charge balanced, the left hand side has much lower energy, and thus much stabler.
  4. That the only way to force the left side moves to the right side is when the spacetime vacuum energy could capture a proton's quark, that is, a high enough energy to break up the proton.
  5. That is, the Prequark Model can calculate the proton's decay rate with the following equation:
     Proton's decay rate equals the probability that the fluctuation amplitude of spacetime vacuum energy equals to the breaking up proton energy.
     Note: This level of spacetime vacuum fluctuation might exist during the Big Bang period.

• I: Prequark Representations
• II: Examples of Prequark Chromodynamics
• III: Proton's stability and its decay mode
• IV: Experimental evidence
• V: Prequark Superstring Model gives rise to biological life
• VI: Why Prequark Superstring Model?
• Frequently Asked Questions