  Quasinormal modes of a two-parameter family of Lorentzian wormhole
spacetimes, which arise as solutions in a specific scalar-tensor theory
associated with braneworld gravity, are obtained using standard numerical
methods. Being solutions in a scalar-tensor theory, these wormholes can exist
with matter satisfying the Weak Energy Condition. If one posits that the
end-state of stellar-mass binary black hole mergers, of the type observed in
GW150914, can be these wormholes, then we show how their properties can be
measured from their distinct signatures in the gravitational waves emitted by
them as they settle down in the post-merger phase from an initially perturbed
state. We propose that their scalar quasinormal modes correspond to the
so-called breathing modes, which normally arise in gravitational wave solutions
in scalar-tensor theories. We show how the frequency and damping time of these
modes depend on the wormhole parameters, including its mass. We derive the mode
solutions and use them to determine how one can measure those parameters when
these wormholes are the endstate of binary black hole mergers. Specifically, we
find that if a breathing mode is observed in LIGO-like detectors with design
sensitivity, and has a maximum amplitude equal to that of the tensor mode that
was observed of GW150914, then for a range of values of the wormhole
parameters, we will be able to discern it from a black hole. If in future
observations we are able to confirm the existence of such wormholes, we would,
at one go, have some indirect evidence of a modified theory of gravity as well
as extra spatial dimensions.
