Features and new physical scales in primordial observables: Theory and observation

Abstract

June 22, 20152 All cosmological observations to date are consistent with adiabatic, Gaussian and nearly scale invariant initial conditions. These findings provide strong evidence for a particular symmetry breaking pattern in the very early universe (with a close to vanishing order parameter, ), widely accepted as conforming to the predictions of the simplest realizations of the inflationary paradigm. However, given that our observations are only privy to perturbations, in inferring something about the background that gave rise to them, it should be clear that many different underlying constructions project onto the same set of cosmological observables. Features in the primordial correlation functions, if present, would offer a unique and discriminating window onto the parent theory in which the mechanism that generated the initial conditions is embedded. In certain contexts, simple linear response theory allows us to infer new characteristic scales from the presence of features that can break the aforementioned degeneracies among different background models, and in some cases can even offer a limited spectroscopy of the heavier degrees of freedom that couple to the inflaton. In this review, we offer a pedagogical survey of the diverse, theoretically well grounded mechanisms which can imprint features into primordial correlation functions in addition to reviewing the techniques one can employ to probe observations. These observations include cosmic microwave background anisotropies and spectral distortions as well as the matter two and three point functions as inferred from large-scale structure and potentially, 21 cm surveys.

BeyondΛCDM: Problems, solutions, and the road ahead

“…CMB spectral distortions probe the primordial power spectrum on a range of scales that is wider than for the primary CMB anisotropies. Since the large majority of singlefield models in current agreement with CMB observations cannot induce modifications on the smaller scales probed by CMB spectral distortions [416], this is another promising avenue to test the possibility of multi-field dynamics during inflation [417,418].…”

Lagrange multiplier and Wess-Zumino variable as extra dimensions in the torus universe

“…On the other hand, these forms of commutators and the corresponding quantum mechanics can be investigated in quantum cosmology, especially in inflation model and primordial universe [73,74]. Moreover, highest energy processes which are observed in astrophysics makes us capable to study such a kind of nonommutativity, where the noncommutative parameter affects the dispersion of gamma rays of far astrophysical sources [76,77].…”

Multi-field inflation and cosmological perturbations

“…Note that if a hierarchy of scales is present in the mass matrix, then we can compute a fairly reliable effective single field theory: see [45] for a concrete review on this subject. If we do not have any light mode other than R, we can integrate out the heavy isocurvature modes F by performing formally the path integral over F. Writing (5.49) schematically as…”