Flavor structure of anomaly-free hidden photon models

Extensions of the Standard Model with an Abelian gauge group are constrained by gauge anomaly cancellation, so that only a limited number of possible charge assignments is allowed without the introduction of new chiral fermions. For flavor universal charges, couplings of the associated hidden photon to Standard Model fermions are flavor conserving at tree level. We show explicitly that even the flavor-specific charge assignments allowed by anomaly cancellation condition lead to flavor-conserving tree-level couplings of the hidden photon to quarks and charged leptons if the Cabibbo-Kobayashi-Maskawa or Pontecorvo-Maki-Nakagawa-Sakata matrix can be successfully reconstructed. Further, loop-induced flavor-changing couplings are strongly suppressed. As a consequence, the structure of the Majorana mass matrix is constrained and flavor-changing tree-level couplings of the hidden photon to neutrino mass eigenstates are identified as a means to distinguish the $U(1{)}_{B-L}$ gauge boson from any other anomaly-free extension of the Standard Model without new chiral fermions. We present a comprehensive analysis of constraints and projections for future searches for a $U(1{)}_{B-3L_i}$ gauge boson, calculate the reach of resonance searches in $B$ meson decays and comment on the implications for nonstandard neutrino interactions.

Figure 1

Loop diagrams contributing to flavor-changing couplings of the $U(1{)}_X$ gauge boson.

Figure 2

Total widths of the $U(1{)}_{B-3L_i}$ bosons normalized to the total width of the $U(1{)}_{B-L}$ boson (top left) without kinetic mixing. Branching ratios of the $U(1{)}_{B-3L_i}$ gauge bosons $X$ to different final states $\mathcal{F}$ in the case of $i=e$ (top right), $\mu$ (bottom left) and $\tau$ (bottom right) without kinetic mixing.

Figure 3

Limits on the parameter space of a $U(1{)}_{B-3L_e}$ gauge boson without kinetic mixing.

Figure 4

Limits on the parameter space of a $U(1{)}_{B-3L_{\mu }}$ gauge boson without kinetic mixing.

Figure 5

Limits on the parameter space of a $U(1{)}_{B-3L_{\tau }}$ gauge boson without kinetic mixing.