A new class of neutrino dark energy models is presented. The new models are characterized by the lack of exotic particles or couplings that violate the standard model symmetry. It is shown that these models lead to several concrete predictions for th
e dark energy equation of state, as well as possible effects on the cosmic structure formation. These predictions, can be verified (or disproved) with future experiments. At this point, the strongest constraints on these models are obtained from big bang nucleosynthesis, and lead to new bounds on the mass of the lightest neutrino.
Adopting Diracs brane variation prescription, the energy-momentum tensor of a brane gets supplemented by a geometrical (embedding originated) dark component. While the masslessness of the graviton is preserved, and the Newton force law is recovered,
the corresponding Newton constant is necessarily lower than the one which governs FRW cosmology. This has the potential to puzzle out cosmological dark matter, a subsequent conjecture concerning galactic dark matter follows.
We point out that modern brane theories suffer from a severe vacuum energy problem. To be specific, the Casimir energy associated with the matter fields confined to the brane, is stemming from the one and the same localization mechanism which forms t
he brane itself, and is thus generically unavoidable. Possible practical solutions are discussed, including in particular spontaneously broken supersymmetry, and quantum mechanically induced brane tension.
We analyze, within the framework of unified brane gravity, the weak-field perturbations caused by the presence of matter on a 3-brane. Although deviating from the Randall-Sundrum approach, the masslessness of the graviton is still preserved. In parti
cular, the four-dimensional Newton force law is recovered, but serendipitously, the corresponding Newton constant is shown to be necessarily lower than the one which governs FRW cosmology. This has the potential to puzzle out cosmological dark matter. A subsequent conjecture concerning galactic dark matter follows.
A novel scalar field free approach to cosmic inflation is presented. The inflationary Universe and the radiation dominated Universe are shown, within the framework of unified brane cosmology, to be two different phases governed by one and the same en
ergy density. The phase transition of second order (the Hubble constant exhibits a finite jump) appears naturally and serves as the exit mechanism. No re-heating is needed. The required number of e-folds is achieved without fine tuning.
