The phantom brane has several important distinctive features : ( i ) Its equation of state is phantom-like , but there is no future ‘ big rip ’ singularity , ( ii ) the effective cosmological constant on the brane is dynamically screened , because of which the expansion rate is smaller than that in \Lambda 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 , BAO +SNeIa data can be accommodated by the braneworld for a large region in parameter space 0 \leq \Omega _ { \ell } \lower 3.87 pt \hbox { $ \buildrel < \over { \sim } $ } ~ { } 0.3 at 1 \sigma .
The Hubble parameter can be as high as H _ { 0 } \lower 3.87 pt \hbox { $ \buildrel < \over { \sim } $ } ~ { } 78 { km } { s } ^ { -1 } % { Mpc } ^ { -1 } , and the effective equation of state at present can show phantom-like behaviour with w _ { 0 } \lower 3.87 pt \hbox { $ \buildrel < \over { \sim } $ } ~ { } -1.2 at 1 \sigma .
We note a correlation between H _ { 0 } and w _ { 0 } , with higher values of H _ { 0 } leading to a lower , and more phantom-like , value of w _ { 0 } .
Inclusion of CMB data provides tighter constraints \Omega _ { \ell } \lower 3.87 pt \hbox { $ \buildrel < \over { \sim } $ } ~ { } 0.1 .
( Here \Omega _ { \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 } \lower 3.87 pt \hbox { $ \buildrel < \over { \sim } $ } ~ { } 71 { km } { s } ^ { -1 } % { Mpc } ^ { -1 } , and the effective equation of state to w _ { 0 } \lower 3.87 pt \hbox { $ \buildrel < \over { \sim } $ } ~ { } -1.1 .
Interestingly , we find that the universe is allowed be closed or open , with -0.5 \lower 3.87 pt \hbox { $ \buildrel < \over { \sim } $ } ~ { } \Omega _ { \kappa } \lower 3.87 % pt \hbox { $ \buildrel < \over { \sim } $ } ~ { } 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 .