We present a holographic dark-energy model in which the Newton constant G _ { N } scales in such a way as to render the vacuum energy density a true constant .
Nevertheless , the model acts as a dynamical dark-energy model since the scaling of G _ { N } goes at the expense of deviation of concentration of dark-matter particles from its canonical form and/or of promotion of their mass to a time-dependent quantity , thereby making the effective equation of state ( EOS ) variable and different from -1 at the present epoch .
Thus the model has a potential to naturally underpin Dirac ’ s suggestion for explaining the large-number hypothesis , which demands a dynamical G _ { N } along with the creation of matter in the universe .
We show that with the aid of observational bounds on the variation of the gravitational coupling , the effective-field theory IR cutoff can be strongly restricted , being always closer to the future event horizon than to the Hubble distance .
As for the observational side , the effective EOS restricted by observation can be made arbitrary close to -1 , and therefore the present model can be considered as a “ minimal ” dynamical dark-energy scenario .
In addition , for nonzero but small curvature ( | \Omega _ { k 0 } | \begin { picture } ( 1.4 , 1.0 ) \put ( 0.7 , -0.3 ) { \makebox ( 0.0 , 1.0 ) [ t ] { $ < $ } % } \put ( 0.7 , -0.3 ) { \makebox ( 0.0 , 1.0 ) [ b ] { $ \sim$ } } \end { picture } 0.003 ) , the model easily accommodates a transition across the phantom line for redshifts z \begin { picture } ( 1.4 , 1.0 ) \put ( 0.7 , -0.3 ) { \makebox ( 0.0 , 1.0 ) [ t ] { $ < $ } } \put ( 0.7 , -0.3 ) { \makebox ( 0.0 , 1.0 ) [ b ] { $ \sim$ } } \end { picture } 0.2 , as mildly favored by the data .
A thermodynamic aspect of the scenario is also discussed .