discrete symmetry forbids violation of baryon number ($B$) minus lepton number ($L$) by one unit. Accepting $R$-parity conservation, however, severely narrows one’s view of the SUSY phenomenological landscape. This is because the lightest supersymmetric particle (LSP) in $R$-parity conserving theories is stable and, therefore, must be neutral due to cosmological considerations.

Perhaps the most appealing candidates for a deeper origin for $R$-parity, models with gauged $U(1)_{B-L}$, are based on the observation that $R$-parity is a discrete subgroup of $U(1)_{B-L}$. In such models, $R$-parity is a good symmetry as long as $U(1)_{B-L}$ is. However, once $U(1)_{B-L}$ is broken, the $B-L$ number of the field that breaks $U(1)_{B-L}$ determines the fate of $R$-parity: an even $B-L$ field leads to automatic $R$-parity conservation (RPC) [@Mohapatra:1986su; @Krauss:1988zc; @Font:1989ai; @Martin:1992mq] (for more recent studies see  [@Aulakh:1999cd; @Aulakh:2000sn; @Babu:2008ep; @Feldman:2011ms; @FileviezPerez:2011dg]) , while an odd $B-L$ field triggers spontaneous $R$-parity violation (RPV) [@Aulakh:1982yn; @Hayashi:1984rd; @Mohapatra:1986aw; @Masiero:1990uj][^1]. Typically, spontaneous $R$-parity violation is safe in the sense that only lepton number violation is generated at tree level, leaving the proton as stable as it would be with RPC.

As one might expect, the approach in these early $B-L$ studies was to introduce a new “Higgs” sector (that is, 