The origin of stellar populations in the Galactic bulge from chemical
  abundances
  In this work, we study the formation and chemical evolution of the Galactic
bulge with particular focus on the abundance pattern ([Mg/Fe] vs. [Fe/H]),
metallicity and age distribution functions. We consider detailed chemical
evolution models for the Galactic bulge and inner disc, with the aim of
shedding light on the connection between these components and the origin of
bulge stars. In particular, we first present a model assuming a fast and
intense star formation, with the majority of bulge stars forming on a timescale
less than 1 Gyr. Then we analyze the possibility of two distinct stellar
populations in the bulge, as suggested by Gaia-ESO and APOGEE data. These two
populations, one metal poor and the other metal rich, can have had two
different origins: i) the metal rich formed after a stop of roughly 250 Myr in
the star formation rate of the bulge, or ii) the metal rich population is made
of stars formed in the inner disc and brought into the bulge by the early
secular evolution of the bar. We also examine the case of multiple star bursts
in the bulge with consequent formation of multiple populations, as suggested by
studies of microlensed stars. After comparing model results and observations,
we suggest that the most likely scenario is that there are two main stellar
populations, both made mainly by old stars (> 10 Gyr), with the metal rich and
younger one formed from inner thin disc stars, in agreement with kinematical
arguments. However, on the basis of dynamical simulations, we cannot completely
exclude that the second population formed after a stop in the star formation
during the bulge evolution, so that all the stars formed in situ.
