The braneworld model proposed by Dvali, Gabadadze and Porrati (DGP) leads to an accelerated universe without cosmological constant or other form of dark energy for the positive branch $(epsilon =+1)$. For the negative branch $(epsilon =-1)$ we have investigated the behavior of a model with an holographic Ricci-like dark energy and dark matter, where the IR cutoff takes the form $alpha H^2 + beta dot{H}$, being $H$ the Hubble parameter and $alpha$, $beta$ positive constants of the model. We perform an analytical study of the model in the late-time dark energy dominated epoch, where we obtain a solution for $r_cH(z)$, where $r_c$ is the leakage scale of gravity into the bulk, and conditions for the negative branch on the holographic parameters $alpha$ and $beta$, in order to hold the conditions of weak energy and accelerated universe. On the other hand, we compare the model versus the late-time cosmological data using the latest type Ia supernova sample of the Joint Light-curve Analysis (JLA), in order to constraint the holographic parameters in the negative branch, as well as $r_cH_0$ in the positive branch, where $H_0$ is the Hubble constant. We find that the model has a good fit to the data and that the most likely values for $(r_cH_0, alpha, beta)$ lie in the permitted region found from an analytical solution in a dark energy dominated universe. We give a justification to use holographic cut-off in 4D for the dark energy in the 5 dimensional DGP model. Finally, using the Bayesian Information Criterion we find that this model it is disfavored compared with the flat $Lambda$CDM model.
We explore the cosmological constraints on the parameter w_dm of the dark matter barotropic equation of state (EoS) to investigate the warmness of the dark matter fluid. The model is composed by the dark matter and dark energy fluids in addition to the radiation and baryon components. We constrain the values of w_dm using the latest cosmological observations that measure the expansion history of the Universe. When w_dm is estimated together with the parameter w_de of the barotropic EoS of dark energy we found that the cosmological data favor a value of w_dm = 0.006 +- 0.001, suggesting a -warm- dark matter, and w_de= -1.11 +- 0.03$ that corresponds to a phantom dark energy, instead of favoring a cold dark matter and a cosmological constant (w_dm = 0, w_de = -1). When w_dm is estimated alone but assuming w_de = -1, -1.1, -0.9, we found w_dm = 0.009 +- 0.002, 0.006 +- 0.002, 0.012 +- 0.002 respectively, where the errors are at 3 sigma (99.73%), i.e., w_dm > 0 with at least 99.73% of confidence level. When (w_dm, Omega_dm0) are constrained together, the best fit to data corresponds to (w_dm=0.005 +- 0.001, Omega_dm0 = 0.223 +- 0.008) and with the assumption of w_de = -1.1 instead of a cosmological constant (i.e., w_de = -1). With these results we found evidence of w_dm > 0 suggesting a -warm- dark matter, independent of the assumed value for w_{rm de}, but where values w_de < -1 are preferred by the observations instead of the cosmological constant. These constraints on w_dm are consistent with perturbative analyses done in previous works.
In this work we address the study of null geodesics in the background of Reissner-Nordstrom Anti de Sitter black holes. We compute the exact trajectories in terms of elliptic functions of Weierstrass, obtaining a detailed description of the orbits in terms of charge, mass and the cosmological constant. The trajectories of the photon are classified using the impact parameter.
A cosmological model of an holographic dark energy interacting with dark matter throughout a decaying term of the form $Q=3(lambda_1rho_{DE} + lambda_2rho_m) H$ is investigated. General constraint on the parameters of the model are found when accelerated expansion is imposed and we found a phantom scenarios, without any reference to a specific equation of state for the dark energy. The behavior of equation of stated for dark energy is also discussed.
