Periodic Reporting for period 3 - GEODESI (Theoretical and observational consequences of the Geometrical Destabilization of Inflation)
Periodo di rendicontazione: 2021-02-01 al 2022-07-31
The GEODESI project aims at interpreting current and forthcoming cosmological observations in a renewed theoretical framework about cosmological inflation, a primordial phase of the universe in which the latter expanded exponentially. The simplest toy models of inflation economically explain all current data, leaving no observational clue to guide theorists towards a finer physical understanding. In this context, the PI unveiled an hitherto unnoticed instability at play in the primordial universe that potentially affects all inflationary models and drastically modifies the interpretation of cosmological observations in terms of fundamental physics. The so-called Geometrical Destabilization of inflation reshuffles our understanding of the origin of structures in the universe and promises precision constraints on high-energy physics. It is crucial to develop this fresh look before a host of high-quality data from large-scale structure surveys and cosmic microwave background observations become available within the 5 year timescale of the project.
We determined the fate of the geometrical destabilization of inflation, reaching the conclusion that this phenomenon does not end inflation, but that the latter continues in an unusual manner. We studied this so-called sidetracked phase of inflation in detail, including the properties of the primordial density fluctuations it generates. New types of inflationary attractors with strongly non-geodesic motion in field space have been identified: they allow to inflate on steep potentials, they offer interesting prospects for embedding inflation in realistic high-energy physics theories, and leave peculiar observational imprints, like unusual, flattened-type, deviations from Gaussianity of the statistics of primordial fluctuations. We also suggested a new, top-down motivated and model-independent mechanism to generate primordial black holes that is specific to multifield dynamics and offers interesting observational prospects. We gave a new insight into the question of the non-Gaussianities generated from realistic models of inflation with multiple degrees of freedom by generalizing Maldacena’s computation to such setups, highlighting the observable effects that derive from a curved field space. We have shown that the departure of inflation from an exact de Sitter phase, as well as Planck-suppressed derivative operators, play a decisive role in (de)stabilizing the Higgs during inflation. Using methods from nonequilibrium quantum field theory, we derived for the first time a manifestly covariant general theory of multifield stochastic inflation. Eventually, we showed how features of the density power spectrum manifest themselves as specific oscillatory patterns in the frequency profile of the scalar-induced stochastic gravitational wave background, offering a new probe of inflation on small scales and motivating new target signals for gravitational wave observatories.
We have identified new types of inflationary attractors with strongly non-geodesic motion. They have attracted the attention of cosmologists and high-energy physicists as they offer the prospect of evading well-known constraints, and leave interesting observational signatures. In this context, we have also underlined the natural appearance of unusual effective field theories characterized by transient instabilities, which had been unexplored before and are now under scrutiny. Building on this, we proposed a new top-down motivated mechanism to generate primordial black holes that is specific to multifield scenarios, overcomes single-field bounds on the growth rate of the power spectrum, and offers new targets for gravitational wave detectors. More generally, we unveiled the potential of the stochastic gravitational wave background to probe small-scale primordial features, offering a precious new probe of physics beyond vanilla inflationary models. Our results that revisit non-Gaussianities in models of inflation with multiple fields unify and generalize previous studies, and offer interesting new prospects for the cosmological collider program. Eventually, our derivation of a general theory of stochastic inflation solves important conceptual problems, it will allow us to determine quantum diffusion effects in models of inflation with curved field space, and to make non-perturbative predictions for the probability density function of the curvature perturbation in such realistic models.