arXiv subjects
Publications and source records attributed to C. Rubano.
We show that it is impossible to determine the state equation of quintessence models on the basis of pure observational SNIa data. An independent estimate of $Ω_{M0}$ is necessary. Also in this most favourable case the situation can be problematic.
We present the first results of the analysis of data collected during the 1998-99 observational campaign at the 1.3 meter McGraw-Hill Telescope, towards the Andromeda galaxy (M31), aimed to the detection of gravitational microlensing effects as a probe of the presence of dark matter in our and in M31 halo. The analysis is performed using the pixel lensing technique, which consists in the study of flux variations of unresolved sources and has been proposed and implemented by the AGAPE collaboration. We carry out a shape analysis by demanding that the detected flux variations be achromatic and compatible with a Paczynski light curve. We apply the Durbin-Watson hypothesis test to the residuals. Furthermore, we consider the background of variables sources. Finally five candidate microlensing events emerge from our selection. Comparing with the predictions of a Monte Carlo simulation, assuming a standard spherical model for the M31 and Galactic haloes, and typical values for the MACHO mass, we find that our events are only marginally consistent with the distribution of observable parameters predicted by the simulation.
We present general exact solutions for two classes of exponential potentials in scalar field models for quintessence. The coupling is minimal and we consider only dust and scalar field. To some extent, it is possible to reproduce experimental results from supernovae.
The supernovae Ia data are used to analyze two general exact solutions for quintessence models. The best fit values for $Ω_{m0}$ are smaller than in the $Λ$-term model, but still acceptable. With present-day data, it is not possible to discriminate among the various situations.
We join quintessence cosmological scenarios with the duality simmetry existing in string dilaton cosmologies. Actually, we consider the tracker potential type $V = V_0/ϕ^α$ and show that duality is only established if $α= - 2$.
We extend the concept of quintessence to a flat nonminimally coupled scalar - tensor theories of gravity. By means of Noether's symmetries for the cosmological pointlike Lagrangian L, it is possible to exhibit exact solutions for a class of models depending on a free parameter s. This parameter comes out in the relationship existing between the coupling F(ϕ) and the potential V(ϕ) because of such a symmetry for L. When inverse power law potentials are taken in account, a whole family of exact solutions parametrized by such an s is proposed as a class of tracker fields, and some considerations are made about them.
SLOTT-AGAPE (Systematic Lensing Observation at Toppo Telescope - Andromeda Gravitational Amplification Pixel Lensing Experiment) is a new collaboration project among international partners from England, France, Germany, Italy and Switzerland that intends to perform microlensing observation by using M31 as target. The MACHOs search is made thanks to the pixel lensing technique.