  We report the discovery of a peculiar horizontal branch (HB) in NGC 6440 and
NGC 6569, two massive and metal-rich Galactic globular clusters (GGCs) located
in the Galactic bulge, within 4 kpc from the Galactic Center. In both clusters,
two distinct clumps are detected at the level of the cluster HB, separated by
only ~ 0.1 magnitudes in the Ks band. They were detected with IR photometric
data collected with the "VISTA Variables in the Via Lactea" (VVV) Survey, and
confirmed in independent IR catalogs available in the literature, and HST
optical photometry. Our analysis demonstrates that these clumps are real
cluster features, not a product of field contamination or interstellar
reddening. The observed split HBs could be a signature of two stellar
sub-populations with different chemical composition and/or age, as recently
found in Terzan 5, but it cannot be excluded that they are caused by
evolutionary effects, in particular for NGC 6440. This interpretation, however,
requires an anomalously high helium content (Y > 0.30). Our discovery suggests
that such a peculiar HB morphology could be a common feature of massive,
metal-rich bulge GGCs.
