  We extend the $SU(3)_c \times SU(2)_L \times U(1)_Y$ standard model by a
$U(1)_{Y'}$ gauge symmetry. Three right-handed neutrinos are introduced to
cancel the gauge anomaly. One Higgs singlet is responsible for spontaneously
breaking the $U(1)_{Y'}$ symmetry while the standard model Higgs doublet does
not carry any $U(1)_{Y'}$ charges. The down-type quarks, up-type quarks,
charged leptons and neutral neutrinos obtain their Dirac masses through four
types of dimension-5 operators constructed by the fermion doublets and singlets
with the Higgs doublet and singlet. This effective theory is realized in three
renormalizable contexts with heavy fermion singlets, scalar doublets and
fermion doublets. The heavy fermion singlets and doublets for generating the
neutrino masses also accommodate a successful Dirac leptogenesis to explain the
baryon asymmetry in the universe.
