  We study the expressivity and complexity of model checking linear temporal
logic with team semantics (TeamLTL). TeamLTL, despite being a purely modal
logic, is capable of defining hyperproperties, i.e., properties which relate
multiple execution traces. TeamLTL has been introduced quite recently and only
few results are known regarding its expressivity and its model checking
problem. We relate the expressivity of TeamLTL to logics for hyperproperties
obtained by extending LTL with trace and propositional quantifiers (HyperLTL
and HyperQPTL). By doing so, we obtain a number of model checking results for
TeamLTL and identify its undecidability frontier. In particular, we show
decidability of model checking of the so-called left-flat fragment of any
downward closed TeamLTL-extension. Moreover, we establish that the model
checking problem of TeamLTL with Boolean disjunction and inclusion atoms is
undecidable.
