Back to the features: assessing the discriminating power of future CMB missions on inflationary models

Abstract

Future Cosmic Microwave Background (CMB) experiments will deliver extremely accurate measurements of the E-modes pattern of the CMB polarization field. Given the sharpness of the E-modes transfer functions, such surveys make for a powerful detector of high-frequency signals from primordial features that may be lurking in current data sets. With a handful of toy models that increase the fit to the latest Planck data, but are of marginal statistical significance, we use a state-of-the-art forecast pipeline to illustrate the promising prospects to test primordial features in the next decade. Not only will future experiments allow us to detect such features in data, but they will also be able to discriminate between models and narrow down the physical mechanism originating them with high statistical significance. On the other hand, if the anomalies in the currently measured CMB spectra are just statistical fluctuations, all the current feature best fit candidates will be ruled out. Either way, our results show that primordial features are a clear target of forthcoming CMB surveys beyond the detection of tensor modes.

Questions on calculation of primordial power spectrum with large spikes: the resonance model case

“…refs. [96,124]). In this appendix, we explicitly show that the perturbative expansion is no longer adequate for the oscillatory feature model considered in this paper and that we have to resort to the equation of motion to get the correct shape of the tree power spectrum.…”

Primordial stochastic gravitational wave backgrounds from a sharp feature in three-field inflation. Part I. The radiation era

“…In this section we take M ss,0 = M bb,0 = ξ sb = 0, but take them nonzero in some of our numerical simulations. 3 To find the WKB approximation of the perturbations during the turn, we take the mode functions to have the form [35,45,60]…”

“…Primordial stochastic gravitational wave backgrounds (SGWBs) are an interesting candidate signal for terrestrial and space-based gravitational wave observatories, and, if detected, could reveal early-universe dynamics at much earlier times than the cosmic microwave background (CMB) [1][2][3][4][5]. Studying the implications of features in the gravitational wave spectrum will be able to shed light on a wide array of potential early-universe processes, including cosmic strings and other topological defects [6,7], primordial first-order phase transitions [8,9], nonstandard cosmic histories that amplify primordial scalar or tensor modes [10][11][12][13][14], the presence of extra spatial dimensions [15,16], cosmic inflation (see below), and post-inflationary dynamics [17].…”

“…In field spaces with sufficiently many isometries,[49] found that rapid-turn, slow-roll trajectories must have M sb ∼ (3 − )τ 3. We are unaware of any model where this parametrization of the masses is precisely valid, but take it as a natural generalization of the two-field scenario, where models with Mss an exact multiple of Ω 2 are known, e.g [59]…”

Primordial feature constraints from BOSS + eBOSS

“…There is already a plethora of analyses using WMAP [32][33][34][35][36][37][38][39] and Planck [2,8,[40][41][42][43][44] datasets. Forecasts for future CMB surveys are present in recent works [45][46][47]. Gravitational waves are one of the main byproducts of inflation; the presence of PF could also affect the stochastic gravitational wave background [48][49][50][51][52][53], and [54] showed a forecast for LISA.…”