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[ABRIDGED] Based on high-resolution (R~42000 to 48000) and highsignal-to-noise (S/N~50 to 150) spectra obtained with UVES/VLT, we presentdetailed elemental abundances (O, Na, Mg, Al, Si, Ca, Ti, Cr, Fe, Ni, Zn, Y,and Ba) and stellar ages for 26 microlensed dwarf and subgiant stars in theGalactic bulge. The analysis is based on equivalent width measurements andstandard 1-D LTE MARCS model stellar atmospheres. We also present NLTE Liabundances based on line synthesis of the 7Li line at 670.8 nm. We show thatthe bulge metallicity distribution (MDF) is double-peaked; one peak at [Fe/H]=-0.6 and one at [Fe/H]=+0.3, and with a dearth of stars around solarmetallicity. This is in contrast to the MDF derived from red giants in Baade'swindow, which peaks at this exact value. A simple significance test shows thatit is extremely unlikely to have such a gap in the microlensed dwarf star MDFif the dwarf stars are drawn from the giant star MDF. To resolve this issue wediscuss several possibilities, but we can not settle on a conclusive solutionfor the observed differences. We further find that the metal-poor bulge dwarfstars are predominantly old with ages greater than 10\,Gyr, while themetal-rich bulge dwarf stars show a wide range of ages. The metal-poor bulgesample is very similar to the Galactic thick disk in terms of averagemetallicity, elemental abundance trends, and stellar ages. Speculatively, themetal-rich bulge population might be the manifestation of the inner thin disk.If so, the two bulge populations could support the recent findings, based onkinematics, that there are no signatures of a classical bulge and that theMilky Way is a pure-disk galaxy. Also, recent claims of a flat IMF in the bulgebased on the MDF of giant stars may have to be revised based on the MDF andabundance trends probed by our microlensed dwarf stars.

Chemical evolution of the Galactic bulge as traced by microlensed dwarf and subgiant stars. IV. Two bulge populations