  Universal Extra Dimension (UED) is a well-motivated and well-studied
scenario. One of the main motivations is the presence of a dark matter (DM)
candidate namely, the lightest level-1 Kaluza-Klein (KK) particle (LKP), in the
particle spectrum of UED. The minimal version of UED (mUED) scenario is highly
predictive with only two parameters namely, the radius of compactification and
cut-off scale, to determine the phenomenology. Therefore, stringent constraint
results from the WMAP/PLANCK measurement of DM relic density (RD) of the
universe. The production and decays of level-1 quarks and gluons in UED
scenarios give rise to multijet final states at the Large Hadron Collider (LHC)
experiment. We study the ATLAS search for multijet plus missing transverse
energy signatures at the LHC with 13 TeV center of mass energy and 139 inverse
femtobarn integrated luminosity. In view of the fact that the DM RD allowed
part of mUED parameter-space has already been ruled out by the ATLAS multijet
search, we move on to a less restricted version of UED namely, the non-minimal
UED (nmUED), with non-vanishing boundary-localized terms (BLTs). The presence
of BLTs significantly alters the dark matter as well as the collider
phenomenology of nmUED. We obtain stringent bounds on the BLT parameters from
the ATLAS multijet plus missing transverse energy search.
