Abstract:
We consider the phantom braneworld model in the context of the maximum turnaround radius, RTA;max,
of a stable, spherical cosmic structure with a given mass. The maximum turnaround radius is the point
where the attraction due to the central inhomogeneity gets balanced with the repulsion of the ambient dark
energy, beyond which a structure cannot hold any mass, thereby giving the maximum upper bound on the
size of a stable structure. In this work we derive an analytical expression of RTA;max for this model using
cosmological scalar perturbation theory. Using this we numerically constrain the parameter space,
including a bulk cosmological constant and the Weyl fluid, from the mass versus observed size data for
some nearby, nonvirial cosmic structures. We use different values of the matter density parameter Ωm, both
larger and smaller than that of the Λ cold dark matter, as the input in our analysis. We show in particular,
that (a) with a vanishing bulk cosmological constant the predicted upper bound is always greater than what
is actually observed; a similar conclusion holds if the bulk cosmological constant is negative (b) if it is
positive, the predicted maximum size can go considerably below than what is actually observed and owing
to the involved nature of the field equations, it leads to interesting constraints on not only the bulk
cosmological constant itself but on the whole parameter space of the theory.
