States of low energy in bouncing inflationary scenarios in loop quantum cosmology

Anomalies in the Cosmic Microwave Background and Their Non-Gaussian Origin in Loop Quantum Cosmology

“…As the inset in the plot shows, inflation occurs at late time, when a |R/6| √ grows exponentially fast. Regarding scalar perturbations, they are in an adiabatic regime before the bounce, and we choose them to start in an adiabatic vacuum at those early times [see e.g., (Agullo, 2015;Agullo and Morris, 2015;de Blas and Olmedo, 2016;Ashtekar and Gupt, 2017;Elizaga Navascués et al, 2019;Martín-Benito et al, 2021) for other choices of initial state]. As perturbations evolve across the bounce, modes with wavenumbers k ≲ k LQC are excited.…”

“…Interestingly, although the inflationary phase is responsible for the primordial perturbations, certain features from the pre-inflationary bounce may survive if the inflationary era is not too long, and be imprinted in the CMB. Numerous studies have examined the way the bounce predicted by LQC modifies the primordial power spectra of scalar and tensor perturbations (Bojowald et al, 2009;Bojowald and Calcagni, 2011;Agullo et al, 2012;Agullo et al, 2013a;Agullo et al, 2013b;Fernández-Méndez et al, 2013;Fernández-Méndez et al,2014;Agullo and Morris, 2015;Barrau et al, 2015;de Blas and Olmedo, 2016;Martínez and Olmedo, 2016;Ashtekar and Gupt, 2017;Agullo et al, 2017b;Castelló Gomar et al, 2017;Zhu et al, 2017;Agullo, 2018;Agullo et al, 2020a;Agullo et al, 2020b;Li et al, 2020a;Li et al, 2020b;Ashtekar et al, 2020;Martín-Benito et al, 2021) and the non-Gaussianity (Agullo, 2015;Agullo et al, 2018;Zhu et al, 2018;Sreenath et al, 2019) at large angular scales, and showed that at smaller scales in the CMB the predictions are indistinguishable from those of standard inflation with Bunch-Davies initial conditions. Hence, if at all early Universe scenarios such as LQC were to leave any imprints on the CMB, they would be expected at the longest observable scales, or equivalently, at the lowest angular multipoles.…”

Non-oscillatory power spectrum from States of Low Energy in kinetically dominated early universes

“…In a previous work [1], we have proposed the States of Low Energy (SLEs) introduced in [2] as viable candidates for the vacuum state of cosmological perturbations in Loop Quantum Cosmology (LQC). We were motivated by the fact that they were proven to be Hadamard states that minimized the regularized energy density when smeared along the time-like curve of an isotropic observer via a test function.…”

“…Furthermore, they had been shown to provide a qualitative behavior in the ultraviolet (UV) and infrared regimes of the primordial power spectra of scalar and tensor perturbations that agrees with observations in models where a period of kinetic dominance precedes inflation [3], which is the case in LQC. However, in [1] we have only considered test functions that could be seen as natural choices within LQC, namely, ones with support on the high curvature regime. As long as this is the case, we have shown that the ambiguity in the introduction of the test function is surpassed in this context, in the sense that the resulting SLE and power spectra seem to be very insensitive to its shape and support, provided it is wide enough.…”

“…This manuscript is organized as follows. In Section II we review the application of SLEs in LQC as presented in [1]. In Section III we explore the consequence of excluding the high curvature regime from the test function, computing the corresponding SLEs and power spectra at the end of inflation.…”