1,721,535 research outputs found
Meccanismi di sostituzione nelle Ti-flogopiti del Monte Vulture e implicazioni petrologiche
No full textStochastic backgrounds of gravitational waves from cosmological populations of astrophysical sources
No full textAstrophysical sources of gravitational radiation are likely to have been formed since the beginning of star formation. Realistic source rates of formation throughout the Universe have been estimated from an observation-based determination of the star formation rate density evolution. Both the radiation emitted during the collapse to black holes and the spin-down radiation, induced by the r-mode instability, emitted by hot, young rapidly rotating neutron stars have been considered. We have investigated the overall signal produced by the ensemble of sources exploring the parameter space and discussing its possible detectability
Baryonic Acoustic Oscillations via the Renormalization Group
Full text linkRenormalization Group techniques, successfully employed in quantum field theory and statistical physics, are applied to study the dynamics of structure formation in the Universe. A semi-analytic approach to the computation of the nonlinear power-spectrum of dark matter density fluctuations is proposed. The method can be applied down to zero redshift and to length scales where perturbation theory fails. Our predictions accurately fit the results of numerical simulations in reproducing the "acoustic oscillations" features of the power spectrum, which will be accurately measured in future galaxy surveys and will provide a probe to distinguish among different dark energy models
“Il manoscritto 249 della Biblioteca civica di Verona: una traduzione anonima del Quijote” (I, 1-5)
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Resumming Cosmic Perturbations
No full textRenormalization group (RG) techniques have been successfully employed in quantum field theory and statistical physics. Here we apply RG methods to study the non-linear stages of structure formation in the universe. Exact equations for the power spectrum, the bispectrum, and all higher order correlation functions can be derived for any underlying cosmological model. A remarkable feature of the RG flow is the emergence of an intrinsic UV cut-off, due to dark matter velocity dispersion, which improves the convergence of the equations at small scales. As a consequence, the method is able to follow the non-linear evolution of the power spectrum down to zero redshift and to length scales where perturbation theory fails. Our predictions accurately fit the results of N-body simulations in reproducing the 'baryon acoustic oscillation' features of the power spectrum, which will be accurately measured in future galaxy surveys and will provide a probe for distinguishing among different dark energy models
Gravitational-wave cosmological distances in scalar-tensor theories of gravity
Full text linkWe analyze the propagation of high-frequency gravitational waves (GW) in scalar-tensor theories of gravity, with the aim of examining properties of cosmological distances as inferred from GW measurements. By using symmetry principles, we first determine the most general structure of the GW linearized equations and of the GW energy momentum tensor, assuming that GW move with the speed of light. Modified gravity effects are encoded in a small number of parameters, and we study the conditions for ensuring graviton number conservation in our covariant set-up. We then apply our general findings to the case of GW propagating through a perturbed cosmological space-time, deriving the expressions for the GW luminosity distance dL(GW) and the GW angular distance dA(GW). We prove for the first time the validity of Etherington reciprocity law dL(GW) = (1+z)2 dA(GW) for a perturbed universe within a scalar-tensor framework. We find that besides the GW luminosity distance, also the GW angular distance can be modified with respect to General Relativity. We discuss implications of this result for gravitational lensing, focussing on time-delays of lensed GW and lensed photons emitted simultaneously during a multimessenger event. We explicitly show how modified gravity effects compensate between different coefficients in the GW time-delay formula: lensed GW arrive at the same time as their lensed electromagnetic counterparts, in agreement with causality constraints
Measuring the energy scale of inflation with large scale structures
No full textThe determination of the inflationary energy scale represents one of the first step towards the understanding of the early Universe physics. The (very mild) non-Gaussian signals that arise from any inflation model carry information about the energy scale of inflation and may leave an imprint in some cosmological observables, for instance on the clustering of high-redshift, rare and massive collapsed structures. In particular, the graviton exchange contribution due to interactions between scalar and tensor fluctuations leaves a specific signature in the four-point function of curvature perturbations, thus on clustering properties of collapsed structures. We compute the contribution of graviton exchange on two- and three-point function of halos, showing that at large scales k~ 10−3 Mpc−1 its magnitude is comparable or larger to that of other primordial non-Gaussian signals discussed in the literature. This provides a potential route to probe the existence of tensor fluctuations which is alternative and highly complementary to B-mode polarisation measurements of the cosmic microwave background radiation
Anisotropy in solid inflation
No full textIn the model of solid / elastic inflation, inflation is driven by a source that has the field theoretical description of a solid. To allow for prolonged slow roll inflation, the solid needs to be extremely insensitive to the spatial expansion. We point out that, because of this property, the solid is also rather inefficient in erasing anisotropic deformations of the geometry. This allows for a prolonged inflationary anisotropic solution, providing the first example with standard gravity and scalar fields only which evades the conditions of the so called cosmic no-hair conjecture. We compute the curvature perturbations on the anisotropic solution, and the corresponding phenomenological bound on the anisotropy. Finally, we discuss the analogy between this model and the f(φ)F2 model, which also allows for anisotropic inflation thanks to a suitable coupling between the inflaton φ and a vector field. We remark that the bispectrum of the curvature perturbations in solid inflation is enhanced in the squeezed limit and presents a nontrivial angular dependence, as had previously been found for the f(φ)F2 model. © 2013 IOP Publishing Ltd and Sissa Medialab srl
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