Phys.Rev. D67 (2003) 027301 We investigate the robustness of some recent results obtained for homogeneous
and isotropic cosmological models with conformally coupled scalar fields. For
this purpose, ...we investigate anisotropic homogeneous solutions of the models
described by the action $$ S=\int d^4x \sqrt{-g}\left\{F(\phi)R -
\partial_a\phi\partial^a\phi -2V(\phi) \right\}, $$ with general $F(\phi)$ and
$V(\phi)$. We show that such a class of models leads generically to geometrical
singularities if for some value of $\phi$, $F(\phi)=0$, rendering previous
cosmological results obtained for the conformal coupling case highly unstable.
We show that stable models can be obtained for suitable choices of $F(\phi)$
and $V(\phi)$. Implications for other recent results are also discussed.
We show that Einstein's gravity coupled to a non-minimally coupled scalar field is stable even for high values of the scalar field, when the sign of the Einstein-Hilbert action is reversed. We also ...discuss inflationary solutions and a possible new mechanism of reheating.
We discuss how an extended foreground of the cosmic microwave background (CMB) can account for the anomalies in the low multipoles of the CMB anisotropies. The distortion needed to account for the ...anomalies is consistent with a cold spot with the spatial geometry of the Local Supercluster (LSC) and a temperature quadrupole of order DeltaT_2^2 ~ 50 microK^2. If this hypothetic foreground is subtracted from the CMB data, the amplitude of the quadrupole (l=2) is substantially increased, and the statistically improbable alignment of the quadrupole with the octopole (l=3) is substantially weakened, increasing dramatically the likelihood of the "cleaned" maps. By placing the foreground on random locations and then computing the likelihood of the cleaned maps we can estimate the most likely place for this foreground. Although the 1-year WMAP data clearly points the location of this hypothetical foreground to the LSC or its specular image (i.e., the vicinity of the poles of the cosmic dipole axis), the three-year data seems to point to these locations as well as the north ecliptic pole. We show that this is consistent with the symmetries of the cosmic quadrupole. We also discuss a possible mechanism that could have generated this foreground: the thermal Sunyaev-Zeldovich effect caused by hot electrons in the LSC. We argue that the temperature and density of the hot gas which are necessary to generate such an effect, though in the upper end of the expected range of values, are marginally consistent with present observations of the X-ray background of spectral distortions of the CMB.
We study the CMB constraints on two Dark Energy models described by scalar fields with different Lagrangians, namely a Klein-Gordon and a Born-Infeld field. The speed of sound of field fluctuations ...are different in these two theories, and therefore the predictions for CMB and structure formation are different. Employing the WMAP data on CMB, we make a likelihood analysis on a grid of theoretical models. We constrain the parameters of the models and compute the probability distribution functions for the equation of state. We show that the effect of the different sound speeds affects the low multipoles of CMB anisotropies, but is at most marginal for the class of models studied here.
We investigate the robustness of some recent results obtained for homogeneous and isotropic cosmological models with conformally coupled scalar fields. For this purpose, we investigate anisotropic ...homogeneous solutions of the models described by the action $$ S=\int d^4x \sqrt{-g}\left\{F(\phi)R - \partial_a\phi\partial^a\phi -2V(\phi) \right\}, $$ with general \(F(\phi)\) and \(V(\phi)\). We show that such a class of models leads generically to geometrical singularities if for some value of \(\phi\), \(F(\phi)=0\), rendering previous cosmological results obtained for the conformal coupling case highly unstable. We show that stable models can be obtained for suitable choices of \(F(\phi)\) and \(V(\phi)\). Implications for other recent results are also discussed.
We investigate the large scale anomalies in the angular distribution of the cosmic microwave background radiation as measured by WMAP using several tests. These tests, based on the multipole vector ...expansion, measure correlations between the phases of the multipoles as expressed by the directions of the multipole vectors and their associated normal planes. We have computed the probability distribution functions for 46 such tests, for the multipoles l=2-5. We confirm earlier findings that point to a high level of alignment between l=2 (quadrupole) and l=3 (octopole), but with our tests we do not find significant planarity in the octopole. In addition, we have found other possible anomalies in the alignment between the octopole and the l=4 (hexadecupole) components, as well as in the planarity of l=4 and l=5. We introduce the notion of a total likelihood to estimate the relevance of the low-multipoles tests of non-gaussianity. We show that, as a result of these tests, the CMB maps which are most widely used for cosmological analysis lie within the ~ 10% of randomly generated maps with lowest likelihoods.
