Gauged Baryon and Lepton Number in MSSM_4 Brane Worlds

Understand

A recent D-brane model designed to accommodate a phenomenologically acceptable fourth generation of chiral fermions was noted to produce an unexpected additional unbroken nonanomalous U(1) gauge group at the string scale.

• We show that the corresponding charges acting on MSSM fields count baryon and lepton numbers.
• If broken spontaneously at lower scales, these U(1)_B and U(1)_L symmetries provide potential avenues for preserving baryogenesis while nonetheless explaining the suppression of proton decay (without the need for R parity), as well as the smallness of right-handed neutrino Majorana masses compared to the string scale.