Inflation and Reheating in Spontaneously Generated Gravity

Inflation is studied in the context of induced gravity (IG) $\gamma \sigma^2 R$, where $R$ is the Ricci scalar, $\sigma$ a scalar field and $\gamma$ a dimensionless constant, and diverse symmetry-breaking potentials $V(\sigma)$ are considered. In particular we compared the predictions for Landau-Ginzburg (LG) and Coleman-Weinberg (CW) type potentials and their possible generalizations with the most recent data. We find that large field inflation generally leads to fewer constraints on the parameters and the shape of the potential whereas small field inflation is more problematic and, if viable, implies more constraints, in particular on the parameter $\gamma$. We also examined the reheating phase and obtained an accurate analytical solution for the dynamics of inflaton and the Hubble parameter by using a multiple scale analysis (MSA). The solutions were then used to study the average expansion of the Universe, the average equation of state for the scalar field and both the perturbative and resonant decays of the inflaton field.Comment: 15 pages, 10 figures, to be published in Phys. Rev.

Stochastic growth of quantum fluctuations during slow-roll inflation

We compute the growth of the mean square of quantum fluctuations of test fields with small effective mass during a slowly changing, nearly de Sitter stage which took place in different inflationary models. We consider a minimally coupled scalar with a small mass, a modulus with an effective mass $\propto H^2$ (with $H$ as the Hubble parameter) and a massless non-minimally coupled scalar in the test field approximation and compare the growth of their relative mean square with the one of gauge-invariant inflaton fluctuations. We find that in most of the single field inflationary models the mean square gauge invariant inflaton fluctuation grows {\em faster} than any test field with a non-negative effective mass. Hybrid inflationary models can be an exception: the mean square of a test field can dominate over the gauge invariant inflaton fluctuation one on suitably choosing parameters. We also compute the stochastic growth of quantum fluctuation of a second field, relaxing the assumption of its zero homogeneous value, in a generic inflationary model; as a main result, we obtain that the equation of motion of a gauge invariant variable associated, order by order, with a generic quantum scalar fluctuation during inflation can be obtained only if we use the number of e-folds as the time variable in the corresponding Langevin and Fokker-Planck equations for the stochastic approach. We employ this approach to derive some bounds in the case of a model with two massive fields.Comment: 9 pages, 4 figures. Added references, minor changes, matches the version to be published in Phys. Rev.

Exploring cosmic origins with CORE: Inflation

Finelli, F., Bucher, M., Achúcarro, A., Ballardini, M., Bartolo, N., Baumann, D., Clesse, S., Errard, J., Handley, W., Hindmarsh, M., Kiiveri, K., Kunz, M., Lasenby, A., Liguori, M., Paoletti, D., Ringeval, C., Väliviita, J., Tent, B.V., Vennin, V., Ade, P., Allison, R., Arroja, F., Ashdown, M., Banday, A.J., Banerji, R., Bartlett, J.G., Basak, S., De Bernardis, P., Bersanelli, M., Bonaldi, A., Borril, J., Bouchet, F.R., Boulanger, F., Brinckmann, T., Burigana, C., Buzzelli, A., Cai, Z.-Y., Calvo, M., Carvalho, C.S., Castellano, G., Challinor, A., Chluba, J., Colantoni, I., Coppolecchia, A., Crook, M., D'Alessandro, G., D'Amico, G., Delabrouille, J., Desjacques, V., Zotti, G.D., Diego, J.M., Valentino, E.D., Feeney, S., Fergusson, J.R., Fernandez-Cobos, R., Ferraro, S., Forastieri, F., Galli, S., García-Bellido, J., De Gasperis, G., Génova-Santos, R.T., Gerbino, M., González-Nuevo, J., Grandis, S., Greenslade, J., Hagstotz, S., Hanany, S., Hazra, D.K., Hernández-Monteagudo, C., Hervias-Caimapo, C., Hills, M., Hivon, E., Hu, B., Kisner, T., Kitching, T., Kovetz, E.D., Kurki-Suonio, H., Lamagna, L., Lattanzi, M., Lesgourgues, J., Lewis, A., Lindholm, V., Lizarraga, J., López-Caniego, M., Luzzi, G., Maffei, B., Mandolesi, N., Martínez-González, E., Martins, C.J.A.P., Masi, S., McCarthy, D., Matarrese, S., Melchiorri, A., Melin, J.-B., Molinari, D., Monfardini, A., Natoli, P., Negrello, M., Notari, A., Oppizzi, F., Paiella, A., Pajer, E., Patanchon, G., Patil, S.P., Piat, M., Pisano, G., Polastri, L., Polenta, G., Pollo, A., Poulin, V., Quartin, M., Ravenni, A., Remazeilles, M., Renzi, A., Roest, D., Roman, M., Rubiño-Martin, J.A., Salvati, L., Starobinsky, A.A., Tartari, A., Tasinato, G., Tomasi, M., Torrado, J., Trappe, N., Trombetti, T., Tucci, M., Tucker, C., Urrestilla, J., De Weygaert, R.V., Vielva, P., Vittorio, N., Young, K., Zannoni, M

Hemispherical power asymmetries in the WMAP 7-year low-resolution temperature and polarization maps

We test the hemispherical power asymmetry of the WMAP 7-year low-resolution temperature and polarization maps. We consider two natural estimators for such an asymmetry and exploit our implementation of an optimal angular power spectrum estimator for all the six CMB spectra. By scanning the whole sky through a sample of 24 directions, we search for asymmetries in the power spectra of the two hemispheres, comparing the results with Monte Carlo simulations drawn from the WMAP 7-year best-fit model. Our analysis extends previous results to the polarization sector. The level of asymmetry on the ILC temperature map is found to be compatible with previous results, whereas no significant asymmetry on the polarized spectra is detected. Moreover, we show that our results are only weakly affected by the a posteriori choice of the maximum multipole considered for the analysis. We also forecast the capability to detect dipole modulation by our methodology at Planck sensitivity.Comment: 7 pages, 9 figures. Accepted for publication in MNRA

Slow-roll Inflation for Generalized Two-Field Lagrangians

We study the slow-roll regime of two field inflation, in which the two fields are also coupled through their kinetic terms. Such Lagrangians are motivated by particle physics and by scalar-tensor theories studied in the Einstein frame. We compute the power spectra of adiabatic and isocurvature perturbations on large scales to first order in the slow-roll parameters. We discuss the relevance of the extra coupling terms for the amplitude and indexes of the power spectra. Beyond the consistency condition which involves the amplitude of gravitational waves, additional relations may be found in particular models based on such Lagrangians: as an example, we find an additional general consistency condition in implicit form for Brans-Dicke theory in the Einstein frame.Comment: 17 pages, 1 figure, accepted for publication in Phys. Rev.

Metric perturbations at reheating: the use of spherical symmetry

We consider decay of the inflaton with a quartic potential coupled to other fields, including gravity, but restricted to spherical symmetry. We describe analytically an early, quasilinear regime, during which inflaton fluctuations and the metric functions are driven by nonlinear effects of the decay products. We present a detailed study of the leading nonlinear effects in this regime. Results of the quasilinear approximation, in its domain of applicability, are found to be consistent with those of fully nonlinear lattice studies. We discuss how these results may be promoted to the full three dimensions.Comment: 18 pages, revtex, 2 figure

Improved CMB anisotropy constraints on primordial magnetic fields from the post-recombination ionization history

We investigate the impact of a stochastic background of Primordial Magnetic Fields (PMF) generated before recombination on the ionization history of the Universe and on the Cosmic Microwave Background radiation (CMB). Pre-recombination PMFs are dissipated during recombination and reionization via decaying MHD turbulence and ambipolar diffusion. This modifies the local matter and electron temperatures and thus affects the ionization history and Thomson visibility function. We use this effect to constrain PMFs described by a spectrum of power-law type, extending our previous study (based on a scale-invariant spectrum) to arbitrary spectral index. We derive upper bounds on the integrated amplitude of PMFs due to the separate effect of ambipolar diffusion and MHD decaying turbulence and their combination. We show that ambipolar diffusion is relevant for $n_{\rm B}>0$ whereas for $n_{\rm B}<0$ MHD turbulence is more important. The bound marginalized over the spectral index on the integrated amplitude of PMFs with a sharp cut-off is $\sqrt{\langle B^2 \rangle}<0.83$ nG. We discuss the quantitative relevance of the assumptions on the damping mechanism and the comparison with previous bounds.Comment: 11 pages, 21 figures. Minor updates to match the published versio

New constraints on parity symmetry from a re-analysis of the WMAP-7 low-resolution power spectra

8 páginas, 6 figuras, 3 tablas.-- El Pdf del archivo es la versión pre-print: arXiv:1006.1979v2 .-- et al.The parity symmetry of the cosmic microwave background (CMB) pattern as seen by Wilkinson Microwave Anisotropy Probe 7 yr (WMAP 7 yr) is tested jointly in temperature and polarization at large angular scale. A quadratic maximum likelihood (QML) estimator is applied to the WMAP 7-yr low-resolution maps to compute all polarized CMB angular power spectra. The analysis is supported by 10 000 realistic Monte Carlo realizations. We confirm the previously reported parity anomaly for TT in the range δℓ=[2, 22] at >99.5 per cent C.L. No anomalies have been detected in TT for a wider ℓ range (up to ℓmax= 40). No violations have been found for EE, TE and BB which we test here for the first time. The cross-spectra TB and EB are found to be consistent with zero. We also forecast Planck capabilities in probing parity violations on low-resolution maps.Support for LAMBDA is provided by the NASA Office of Space Science. This work was supported by ASI through ASI/INAF Agreement I/072/09/0 for the Planck LFI Activity of Phase E2.Peer reviewe

Resonance enhancement of particle production during reheating

We found a consistent equation of reheating after inflation, which shows that for small quantum fluctuations the frequencies of resonance are slighted different from the standard ones. Quantum interference is taken into account and we found that at large fluctuations the process mimics very well the usual parametric resonance but proceed in a different dynamical way. The analysis is made in a toy quantum mechanical model and we discuss further its extension to quantum field theory.Comment: 4 pages, 4 figures(eps), using RevTe