Effects of inflationary bubbles on the polarization and temperature anisotropies of the cosmic microwave background

We predict the imprint of linear bubbly perturbations on the polarization and temperature anisotropies of the cosmic microwave background (CMB). We analytically model a bubbly density perturbation at the beginning of the radiation dominated era and we apply the linear theory of cosmological perturbations to compute its time evolution. At decoupling, it uniquely signs the CMB polarization and temperature anisotropy sky. During evolution the perturbation propagates beyond the size of the bubble and reaches the CMB sound horizon at the time considered. Therefore, its signal appears as a series of concentric rings, each characterized by its own amplitude and sign, on the scale of 1^{o} on the sky, even if the real seed size is much smaller. Polarization and temperature rings are strictly correlated. As expected for linear perturbations with size L and density contrast \delta at decoupling, \delta T/T is roughly \delta (L/H^{-1})^{2}; the polarization is about 10% of the temperature anisotropy. We predict the impact of a distribution of bubbles on the CMB polarization and temperature power spectra. Considering models containing both CDM Gaussian and bubbly non-Gaussian fluctuations, we simulate and analyze 10^{o} x 10^{o} sky patches with angular resolution of about 3.5^{'}. The CMB power associated with the bubbles is entirely on sub-degree angular scales (200<= l<=1000), that will be explored by the forthcoming high resolution CMB experiments with the percent precision. Depending on the parameters of the bubbly distribution we find extra-power with respect to the ordinary CDM Gaussian fluctuations; we infer simple analytical scalings of the power induced by bubbly perturbations and we constrain our parameters with the existing data.Comment: 12 pages, 9 figures (two with nice colors), accepted for publication by MNRA

Early time perturbations behaviour in scalar field cosmologies

We consider the problem of the initial conditions and behaviour of the perturbations in scalar field cosmology with general potential. We use the general definition of adiabatic and isocurvature conditions to set the appropriate initial values for the perturbation in the scalar field and in the ordinary matter and radiation components. In both the cases of initial adiabaticity and isocurvature, we solve the Einstein and fluid equation at early times and on superhorizon scales to find the initial behaviour of the relevant quantities. In particular, in the isocurvature case, we consider models in which the initial perturbation arises from the matter as well as from the scalar field itself, provided that the initial value of the gauge invariant curvature is zero. We extend the standard code to include all these cases, and we show some results concerning the power spectrum of the cosmic microwave background temperature and polarization anisotropies. In particular, it turns out that the acoustic peaks follow opposite behaviours in the adiabatic and isocurvature regimes: in the first case their amplitude is higher than in the corresponding pure cold dark matter model, while they make the opposite thing for pure isocurvature initial perturbations.Comment: 21 pages, 8 figures, accepted for publication in Phys.Rev.

Cosmic microwave background constraints on dark energy dynamics: analysis beyond the power spectrum

We consider the distribution of the non-Gaussian signal induced by weak lensing on the primary total intensity cosmic microwave background (CMB) anisotropies. Our study focuses on the three point statistics exploiting an harmonic analysis based on the CMB bispectrum. By considering the three multipoles as independent variables, we reveal a complex structure of peaks and valleys determined by the re-projection of the primordial acoustic oscillations through the lensing mechanism. We study the dependence of this system on the expansion rate at the epoch in which the weak lensing power injection is relevant, probing the dark energy equation of state at redshift corresponding to the equivalence with matter or higher ($w_\infty$). We evaluate the impact of the bispectrum observable on the CMB capability of constraining the dark energy dynamics. We perform a maximum likelihood analysis by varying the dark energy abundance, the present equation of state $w_0$ and $w_\infty$. We show that the projection degeneracy affecting a pure power spectrum analysis in total intensity is broken if the bispectrum is taken into account. For a Planck-like experiment, assuming nominal performance, no foregrounds or systematics, and fixing all the parameters except $w_0$, $w_\infty$ and the dark energy abundance, a percent and ten percent precision measure of $w_0$ and $w_\infty$ is achievable from CMB data only. These results indicate that the detection of the weak lensing signal by the forthcoming CMB probes may be relevant to gain insight into the dark energy dynamics at the onset of cosmic acceleration.Comment: 14 pages, 9 figures. Matching version accepted by Physical Review D. High resolution figures available upon request to the author

Extended Quintessence: imprints on the cosmic microwave background spectra

We describe the observable features of the recently proposed Extended Quintessence scenarios on the Cosmic Microwave Background (CMB) anisotropy spectra. In this class of models a scalar field $\phi$, assumed to provide most of the cosmic energy density today, is non-minimally coupled to the Ricci curvature scalar $R$. We implement the linear theory of cosmological perturbations in scalar tensor gravitational theories to compute CMB temperature and polarization spectra. All the interesting spectral features are affected: on sub-degree angular scales, the acoustic peaks change both in amplitude and position; on larger scales the low redshift dynamics enhances the Integrated Sachs Wolfe effect. These results show how the future CMB experiments could give information on the vacuum energy as well as on the structure of the gravitational Lagrangian term.Comment: 4 pages including 1 figure, to be published in the proceedings of the COSMO99 meeting, held in Trieste, September 199

Extended Quintessence

We study Quintessence cosmologies in the context of scalar-tensor theories of gravity, where a scalar field $\phi$, assumed to provide most of the cosmic energy density today, is non-minimally coupled to the Ricci curvature scalar $R$. Such `Extended Quintessence' cosmologies have the appealing feature that the same field causing the time (and space) variation of the cosmological constant is the source of a varying Newton's constant \`a la Jordan-Brans-Dicke. We investigate here two classes of models, where the gravitational sector of the Lagrangian is $F(\phi)R$ with $F(\phi )=\xi\phi^{2}$ (Induced Gravity, IG) and $F(\phi)=1+\xi\phi^{2}$ (Non-Minimal Coupling, NMC). As a first application of this idea we consider a specific model, where the Quintessence field, $\phi$, obeying the simplest inverse power potential, has $\Omega_{\phi}=0.6$ today, in the context of the Cold Dark Matter scenario, with scale-invariant adiabatic initial perturbations. We find that, if $\xi\lesssim 5\times 10^{-4}$ for IG and $\xi\lesssim 5\times 10^{-3}(\sqrt{G}\phi_{0})^{-1}$ for NMC ($\phi_{0}$ is the present Quintessence value) our Quintessence field satisfies the existing solar system experimental constraints. Using linear perturbation theory we then obtain the polarization and temperature anisotropy spectra of the Cosmic Microwave Background (CMB) as well as the matter power-spectrum. The perturbation behavior possesses distinctive features, that we name `QR-effects', regarding acoustic peak location and height, late time integrated Sachs-Wolfe effect, as well as turnover and amplitude in the matter power spectrum. These features could be detected in the upcoming observations on CMB and large-scale structure.Comment: 19 pages including 10 figures, final version to be published in Phys.Rev.

La indeterminación, los estudios de ensamblaje y la tecnología educativa: el replanteamiento de la causalidad y la revitalización de la política

This article examines underdetermination as a key theoretical assumption in an emerging body of educational research. Underdetermination is described as a broad philosophical position that assumes that social, scientific and technological phenomena cannot be reduced to linear relationships between antecedents and consequences, for instance through the canonical progression from scientific hypotheses to experimentation and then empirical truths. Rather, phenomena are underdetermined by constellations of social and material influences that make the choice of univocal explanations problematic. The principle of underdetermination is implicit in a recent strand of educational research that critiques orthodox interpretations of scientific practices, innovation processes and policy dynamics, recasting them as social, material and political “assemblages”. In the article, I analyse the philosophical and epistemological tenets of underdetermination, in order to clarify its nature as a “first principle” in this emerging body of research. By doing so, the article brings into view a broader theoretical debate that has great bearing on future research efforts. The article critically considers the continued theoretical relevance of underdetermination, whilst acknowledging critical arguments mounted against it, namely ontological relativism and political weakness. Some supplementing theoretical ideas are explored in the conclusion.Este artículo examina la indeterminación como una premisa teórica clave dentro de un cuerpo emergente de la investigación educativa. La indeterminación se describe como una postura filosófica amplia en la que se asume que los fenómenos sociales, científicos y tecnológicos no se pueden reducir a relaciones lineales entre antecedentes y consecuencias, por ejemplo, mediante la progresión canónica desde las hipótesis científicas a la experimentación y más tarde hasta las verdades empíricas. Por el contrario, los fenómenos están indeterminados por constelaciones de influencias sociales y materiales debido a las cuales resulta problemática la elección de explicaciones unívocas. El principio de la indeterminación se encuentra implícito en una corriente reciente de la investigación educativa que critica las interpretaciones ortodoxas de las prácticas científicas, los procesos de innovación y las dinámicas relativas a las políticas, remodelándolas como “ensamblajes” sociales, materiales y políticos. En el artículo, analizo los postulados filosóficos y epistemológicos de la indeterminación con el propósito de aclarar su naturaleza como un “primer principio” en este cuerpo de investigación emergente. Al hacerlo, el presente artículo pone el foco en un debate teórico más amplio que tiene un gran peso de cara a los esfuerzos de investigación en el futuro. El artículo aborda de manera crítica la relevancia teórica continuada de la indeterminación, al tiempo que reconoce argumentos críticos que se aducen contra ella, concretamente el relativismo ontológico y la debilidad política. En la conclusión se exploran algunas ideas teóricas adicionales

Polarized Foregrounds Power Spectra vs CMB

We briefly review our work about the polarized foreground contamination of the Cosmic Microwave Background maps. We start by summarizing the main properties of the polarized cosmological signal, resulting in "electric" (E) and "magnetic" (B) components of the polarization tensor field on the sky. Then we describe our present understanding of sub-degree anisotropies from Galactic synchrotron and from extra-Galactic point sources. We discuss their contamination of the cosmological E and B modes.Comment: six pages including 2 figures, to appear in S. Cecchini et al., Astrophysical Polarized Backgrounds, AIP Conf. Proceeding