‘Observational’ Quantum Cosmology

Modified Saez–Ballester scalar–tensor theory from 5D space-time

“…We observe that for a matter-dominated case, our model yields two disconnected branches. 8 However, for both of the branches, by assuming a 3 0 ψ 0 > 0, the time behavior of the scalar field depends not only on the sign of the c 1 β but also on the signs of c 1 and β. We have shown that for different values of n, dependent on the signs of c 1 and β, the scalar field can whether contracts or expands with the cosmic time.…”

“…In order to investigate the vacuum solution, from relations (4.8) and (4.9), we find that the only allowed solution is obtained by setting β = 0, such that by employing (3.12), we get γ = ± W/6. Consequently, the solutions (3.14), 8 The pre-big bag cosmology [70] has been inspired by superstring theory. Such a scenario has also been constructed by a class of solutions associated to the low-energy string theory, see, e.g., the Nariai solution associated to the dust fluid in the context of the BD theory [44,71,72], such that for one of them (branch I), the scale factor contracts when t < t i and for the other (branch II) it expands for t > t i .…”

“…Higher-dimensional models of the universe have been widely studied: Kaluza-Klein (KK) theories [4][5][6], tendimensional and eleven-dimensional supergravity [7][8][9] as well as string theories [10,11]. In particular, Kaluza considered a five-dimensional space-time, under the following key assumptions [6], to bring together electromagnetism with general relativity (GR): (i) there is no ordinary matter in the higher dimensional space-time, (ii) geometrical quantities similar to those defined in GR were introduced and (iii) the cylinder condition for the extra coordinate was assumed, which implies that the derivatives with respect to the extra dimension must vanish.…”

Chaos, decoherence and quantum cosmology

“…First, we shall make no attempt to be systematic in our presentation of chaos [10,16,32,81,248,256] and decoherence [121,253,275], we shall only pinpoint those aspects of these subjects which have been found to be relevant to quantum cosmology. Most importantly, we shall neither attempt a complete presentation of quantum cosmology itself [35,36,182,270,271] . For the purposes of this review, quantum cosmology means the theory of the Wheeler-DeWitt equation restricted to Friedmann -Robertson -Walker mini super spaces (to be defined below), later enlarged to midi super spaces by including also linearized primordial fluctuations (whereby the former mini super spaces come to be regarded as quantum open systems).…”