The mass fraction of halo stars contributed by the disruption of
  globular clusters in the E-MOSAICS simulations
  Globular clusters (GCs) have been posited, alongside dwarf galaxies, as
significant contributors to the field stellar population of the Galactic halo.
In order to quantify their contribution, we examine the fraction of halo stars
formed in stellar clusters in the suite of 25 present-day Milky Way-mass
cosmological zoom simulations from the E-MOSAICS project. We find that a median
of $2.3$ and $0.3$ per cent of the mass in halo field stars formed in clusters
and GCs, defined as clusters more massive than $5\times 10^3$ and
$10^5~M_{\odot}$, respectively, with the $25$-$75$th percentiles spanning
$1.9$-$3.0$ and $0.2$-$0.5$ per cent being caused by differences in the
assembly histories of the host galaxies. Under the extreme assumption that no
stellar cluster survives to the present day, the mass fractions increase to a
median of $5.9$ and $1.8$ per cent. These small fractions indicate that the
disruption of GCs plays a sub-dominant role in the build-up of the stellar
halo. We also determine the contributed halo mass fraction that would present
signatures of light-element abundance variations considered to be unique to
GCs, and find that clusters and GCs would contribute a median of $1.1$ and
$0.2$ per cent, respectively. We estimate the contributed fraction of GC stars
to the Milky Way halo, based on recent surveys, and find upper limits of
$2$-$5$ per cent (significantly lower than previous estimates), suggesting that
models other than those invoking strong mass loss are required to describe the
formation of chemically enriched stellar populations in GCs.
