  The effect of in-medium dinucleon bound states on self-consistent
single-particle fields in Brueckner, Bethe and Goldstone theory is investigated
in symmetric nuclear matter at zero temperature. To this end, dinucleon bound
state occurences in the $^1S_0$ and ${}^3SD_1$ channels are explicitly
accounted for -within the continuous choice for the auxiliary fields- while
imposing self-consistency in Brueckner-Hartree-Fock approximation calculations.
Searches are carried out at Fermi momenta in the range
$0<k_F\leq1.75$~fm$^{-1}$, using the Argonne $v_{18}$ bare nucleon-nucleon
potential without resorting to the effective mass approximation. As a result,
two distinct solutions meeting the self-consistency requirement are found with
overlapping domains in the interval $0.130\;\textrm{fm}^{-1} \leq k_F \leq
0.285\;\textrm{fm}^{-1}$, corresponding to mass densities between $10^{11.4}$
and $10^{12.4}$ g cm$^{-3}$. Effective masses as high as three times the
nucleon mass are found in the coexistence domain. The emergence of
superfluidity in relationship with BCS pairing gap solutions is discussed.
