The Gaia-ESO Survey: Exploring the complex nature and origins of the
  Galactic bulge populations
  Abridged: We used the fourth internal data release of the Gaia-ESO survey to
characterize the bulge chemistry, spatial distribution, kinematics, and to
compare it chemically with the thin and thick disks. The sample consist on
~2500 red clump stars in 11 bulge fields ($-10^\circ\leq l\leq+8^\circ$ and
$-10^\circ\leq b\leq-4^\circ$), and a set of ~6300 disk stars selected for
comparison. The bulge MDF is confirmed to be bimodal across the whole sampled
area, with metal-poor stars dominating at high latitudes. The metal-rich stars
exhibit bar-like kinematics and display a bimodality in their magnitude
distribution, a feature which is tightly associated with the X-shape bulge.
They overlap with the metal-rich end of the thin disk sequence in the [Mg/Fe]
vs. [Fe/H] plane. Metal-poor bulge stars have a more isotropic hot kinematics
and do not participate in the X-shape bulge. With similar Mg-enhancement
levels, the position of the metal-poor bulge sequence "knee" is observed at
[Fe/H]$_{knee}=-0.37\pm0.09$, being 0.06 dex higher than that of the thick
disk. It suggests a higher SFR for the bulge than for the thick disk. Finally,
we present a chemical evolution model that suitably fits the whole bulge
sequence by assuming a fast ($<1$ Gyr) intense burst of stellar formation at
early epochs. We associate metal-rich stars with the B/P bulge formed from the
secular evolution of the early thin disk. On the other hand, the metal-poor
subpopulation might be the product of an early prompt dissipative collapse
dominated by massive stars. Nevertheless, our results do not allow us to firmly
rule out the possibility that these stars come from the secular evolution of
the early thick disk. This is the first time that an analysis of the bulge MDF
and $\alpha$-abundances has been performed in a large area on the basis of a
homogeneous, fully spectroscopic analysis of high-resolution, high S/N data.
