Constraining the cosmology of the phantom brane using distance measures

Abstract

The phantom brane has several important distinctive features: (i) Its equation of state is phantomlike, but there is no future ``big rip'' singularity, and (ii) the effective cosmological constant on the brane is dynamically screened, because of which the expansion rate is smaller than that in $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ at high redshifts. In this paper, we constrain the Phantom braneworld using distance measures such as type-Ia supernovae (SNeIa), baryon acoustic oscillations (BAO), and the compressed cosmic microwave background (CMB) data. We find that the simplest braneworld models provide a good fit to the data. For instance, $\mathrm{BAO}+\mathrm{SNeIa}$ data can be accommodated by the braneworld for a large region in parameter space $0\ensuremath{\le}{\mathrm{\ensuremath{\Omega}}}_{\ensuremath{\ell}}\ensuremath{\lesssim}0.3$ at $1\ensuremath{\sigma}$. The Hubble parameter can be as high as ${H}_{0}\ensuremath{\lesssim}78\text{ }\text{ }\mathrm{km}\text{ }{\mathrm{s}}^{\ensuremath{-}1}\text{ }{\mathrm{Mpc}}^{\ensuremath{-}1}$, and the effective equation of state at present can show phantomlike behavior with ${w}_{0}\ensuremath{\lesssim}\ensuremath{-}1.2$ at $1\ensuremath{\sigma}$. We note a correlation between ${H}_{0}$ and ${w}_{0}$, with higher values of ${H}_{0}$ leading to a lower, and more phantomlike, value of ${w}_{0}$. Inclusion of CMB data provides tighter constraints ${\mathrm{\ensuremath{\Omega}}}_{\ensuremath{\ell}}\ensuremath{\lesssim}0.1$. (Here ${\mathrm{\ensuremath{\Omega}}}_{\ensuremath{\ell}}$ encodes the ratio of the five- and four-dimensional Planck mass.) The Hubble parameter in this case is more tightly constrained to ${H}_{0}\ensuremath{\lesssim}71\text{ }\text{ }\mathrm{km}\text{ }{\mathrm{s}}^{\ensuremath{-}1}\text{ }{\mathrm{Mpc}}^{\ensuremath{-}1}$, and the effective equation of state to ${w}_{0}\ensuremath{\lesssim}\ensuremath{-}1.1$. Interestingly, we find that the Universe is allowed to be closed or open, with $\ensuremath{-}0.5\ensuremath{\lesssim}{\mathrm{\ensuremath{\Omega}}}_{\ensuremath{\kappa}}\ensuremath{\lesssim}0.5$, even on including the compressed CMB data. There appears to be some tension in the low and high-$z$ BAO data which may either be resolved by future data, or act as a pointer to interesting new cosmology.