250 research outputs found
Non-Gaussianity in Loop Quantum Cosmology
We extend the phenomenology of loop quantum cosmology (LQC) to second order
in perturbations. Our motivation is twofold. On the one hand, since LQC
predicts a cosmic bounce that takes place at the Planck scale, the second order
contributions could be large enough to jeopardize the validity of the
perturbative expansion on which previous results rest. On the other hand, the
upper bounds on primordial non-Gaussianity obtained by the Planck Collaboration
are expected to play a significant role on explorations of the LQC
phenomenology. We find that the bounce in LQC produces an enhancement of
non-Gaussianity of several orders of magnitude, on length scales that were
larger than the curvature radius at the bounce. Nonetheless, we find that one
can still rely on the perturbative expansion to make predictions about
primordial perturbations. We discuss the consequences of our results for LQC
and its predictions for the cosmic microwave background.Comment: Minor updates: current version matches the accepted PRD manuscrip
Estimation of imprints of the bounce in loop quantum cosmology on the bispectra of cosmic microwave background
Primordial non-Gaussianity has set strong constraints on models of the early
universe. Studies have shown that Loop Quantum Cosmology (LQC), which is an
attempt to extend inflationary scenario to planck scales, leads to a strongly
scale dependent and oscillatory non-Gaussianity. In particular, the
non-Gaussianity function generated in LQC,
though similar to that generated during slow roll inflation at small scales, is
highly scale dependent and oscillatory at long wavelengths. In this work, we
investigate the imprints of such a primordial bispectrum in the bispectrum of
Cosmic Microwave Background (CMB). Inspired by earlier works, we propose an
analytical template for the primordial bispectrum in LQC. We write the template
as a sum of strongly scale dependent and oscillatory part, which captures the
contribution due to the bounce, and a part which captures the scale invariant
behaviour similar to that of slow roll. We then compute the reduced bispectra
of temperature and electric polarisation and their three-point
cross-correlations corresponding to these two parts. We show that the
contribution from the bounce to the reduced bispectrum is negligible compared
to that from the scale-independent part. Thus, we conclude that the CMB
bispectra generated in LQC will be similar to that generated in slow roll
inflation. We conclude with a discussion of our results and its implications to
LQC.Comment: v1:17 pages, 8 figures; v2: 23 pages, 9 figures, improved template of
bispectrum, new subsections added, version accepted for publication in JCA
Predictions for the CMB from an anisotropic quantum bounce
We introduce an extension of the standard inflationary paradigm on which the
big bang singularity is replaced by an anisotropic bounce. Unlike in the big
bang model, cosmological perturbations find an adiabatic regime in the past. We
show that this scenario accounts for the observed quadrupolar modulation in the
temperature anisotropies of the cosmic microwave background (CMB), and we make
predictions for the remaining angular correlation functions E-E, B-B and T-E,
together with non-zero temperature-polarization correlations T-B and E-B, that
can be used to test our ideas. We base our calculations on the bounce predicted
by loop quantum cosmology, but our techniques and conclusions apply to other
bouncing models as well.Comment: 5 pages, 4 figures, minor changes to match published versio
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