Cosmological magnetic fields by parametric resonance?

We investigate the possibility that electromagnetic fluctuations are amplified in expanding universe by parametric resonance, during the oscillatory regime of a scalar field to which they are coupled. We consider scalar electrodynamics and we find that electromagnetic fluctuations undergo exponential instabilities. This mechanism could have some relevance for the problem of large scale primordial magnetic fields.Comment: 4 pages, no figures. Talk given at COSMO 99: 3rd International Conference on Particle Physics and the Early Universe, Trieste, Italy, 27 Sep - 3 Oct 199

Spectra of primordial fluctuations in two-perfect-fluid regular bounces

We introduce analytic solutions for a class of two components bouncing models, where the bounce is triggered by a negative energy density perfect fluid. The equation of state of the two components are constant in time, but otherwise unrelated. By numerically integrating regular equations for scalar cosmological perturbations, we find that the (would be) growing mode of the Newtonian potential before the bounce never matches with the the growing mode in the expanding stage. For the particular case of a negative energy density component with a stiff equation of state we give a detailed analytic study, which is in complete agreement with the numerical results. We also perform analytic and numerical calculations for long wavelength tensor perturbations, obtaining that, in most cases of interest, the tensor spectral index is independent of the negative energy fluid and given by the spectral index of the growing mode in the contracting stage. We compare our results with previous investigations in the literature.Comment: 11 pages, 5 figure

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.

On the Spectrum of Fluctuations in an Effective Field Theory of the Ekpyrotic Universe

We consider the four-dimensional effective field theory which has been used in previous studies of perturbations in the Ekpyrotic Universe, and discuss the spectrum of cosmological fluctuations induced on large scales by quantum fluctuations of the bulk brane. By matching cosmological fluctuations on a constant energy density hypersurface we show that the growing mode during the very slow collapsing pre-impact phase couples only to the decaying mode in the expanding post-impact phase, and that hence no scale-invariant spectrum of adiabatic fluctuations is generated. Note that our conclusions may not apply to improved toy models for the Ekpyrotic scenario.Comment: 8 pages, few sentences added. Conclusions unchanged. Added references. Missing name added to Ref. 5

Adiabatic regularization of the graviton stress-energy tensor in de Sitter space-time

We study the renormalized energy-momentum tensor of gravitons in a de Sitter space-time. After canonically quantizing only the physical degrees of freedom, we adopt the standard adiabatic subtraction used for massless minimally coupled scalar fields as a regularization procedure and find that the energy density of gravitons in the E(3) invariant vacuum is proportional to H^4, where H is the Hubble parameter, but with a positive sign. According to this result the scalar expansion rate, which is gauge invariant in de Sitter space-time, is increased by the fluctuations. This implies that gravitons may then add to conformally coupled matter in driving the Starobinsky model of inflation.Comment: 5 pages, revtex, final version accepted for publication in PR

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

Primordial density perturbations with running spectral index: impact on non-linear cosmic structures

(abridged) We explore the statistical properties of non-linear cosmic structures in a flat $\Lambda$CDM cosmology in which the index of the primordial power spectrum for scalar perturbations is allowed to depend on the scale. Within the inflationary paradigm, the running of the scalar spectral index can be related to the properties of the inflaton potential, and it is hence of critical importance to test it with all kinds of observations, which cover the linear and non-linear regime of gravitational instability. We focus on the amount of running $\alpha_{\mathrm{S},0}$ allowed by an updated combination of CMB anisotropy data and the 2dF Galaxy Redshift Survey. Our analysis constrains $\alpha_{\mathrm{S},0} = -0.051^{+0.047}_{-0.053}$ $(-0.034^{+0.039}_{-0.040})$ at 95% Confidence Level when (not) taking into account primordial gravitational waves in a ratio as predicted by canonical single field inflation, in agreement with other works. For the cosmological models best fitting the data both with and without running we studied the abundance of galaxy clusters and of rare objects, the halo bias, the concentration of dark matter halos, the Baryon Acoustic Oscillation, the power spectrum of cosmic shear, and the Integrated Sachs-Wolfe effect. We find that counting galaxy clusters in future X-ray and Sunyaev-Zel'dovich surveys could discriminate between the two models, more so if broad redshift information about the cluster samples will be available. Likewise, measurements of the power spectrum of cosmological weak lensing as performed by planned all-sky optical surveys such as EUCLID could detect a running of the primordial spectral index, provided the uncertainties about the source redshift distribution and the underlying matter power spectrum are well under control.Comment: 17 pages, 14 figures, 4 tables. Accepted for publication on MNRA