Suppression of scalar power on large scales and associated bispectra
H. V. Ragavendra, Debika Chowdhury, L. Sriramkumar
备注：
v1: 16 pages, 11 figures; v2: 30 pages, 12 figures, scalar power spectra compared with the CMB data, discussions and references added, version to be submitted for publication; v3: 25 pages, 15 figures, revised in response to referee's comments, version to appear in Phys. Rev. D
[Abridged] A sharp cut-off in the primordial scalar power spectrum on large scales has been known to improve the fit to the cosmic microwave background (CMB) data when compared to the more standard, nearly scale invariant power spectrum that arises in slow roll inflation. In an earlier work, we had numerically investigated the characteristics of the scalar bispectrum generated in models with kinetically dominated initial conditions. In this work, we compare the scenario with two other competing scenarios (viz. punctuated inflation and a model due to Starobinsky) which also suppress the scalar power in a roughly similar fashion on large scales. We further consider two other scenarios involving inflation of a finite duration, one wherein the scalar field begins on the inflationary attractor and another wherein the field starts with a smaller velocity and evolves towards the attractor. These scenarios too exhibit a sharp drop in power on large scales if the initial conditions on the perturbations for a range of modes are imposed on super-Hubble scales as in the kinetically dominated model. We compare the performance of all the models against the Planck CMB data at the level of power spectra. We also compare the amplitudes and shapes of the scalar non-Gaussianity parameter $f_{_{\rm NL}}$ in all these cases which lead to scalar power spectra of similar form. Interestingly, we find that, in the models wherein the initial conditions on the perturbations are imposed on super-Hubble scales, the consistency relation governing the scalar bispectrum is violated for the large scale modes, whereas the relation is satisfied for all the modes in the other scenarios. These differences in the behavior of the scalar bispectra can conceivably help us observationally discriminate between the various models which lead to scalar power spectra of roughly similar shape.
We compute the full bispectra, namely both auto- and cross- bispectra, of primordial curvature and tensor perturbations in the most general single-field inflation model whose scalar and gravitational equations of motion are of second order. The formulae in the limits of k-inflation and potential-driven inflation are also given. These expressions are useful for estimating the full bispectra of temperature and polarization anisotropies of the cosmic microwave background radiation.
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Recent measurements from the BICEP2 cosmic microwave background polarization experiment indicate the presence of primordial gravitational waves with surprisingly large amplitude. If these results are confirmed, they point to a discrepancy with temperature anisotropy power spectrum measurements and suggest that extensions to the standard cosmological model may be required to resolve the discrepancy. One intriguing extension is an anticorrelation between tensors and scalars to naturally suppress the temperature power. Here I examine this possibility and show that such a suppression is not possib…
Suppression of scalar perturbations due to a heavy axion
International Centre for Theoretical Physics Asia-Pacific, University of Chinese Academy of Sciences（国际理论物理中心亚太分部，中国科学院大学）；Taiji Laboratory for Gravitational Wave Universe, University of Chinese Academy of Sciences（太极引力波宇宙实验室，中国科学院大学）；Institute of Theoretical Physics, Chinese Academy of Sciences (CAS)（中国科学院理论物理研究所）；School of Physical Sciences, University of Chinese Academy of Sciences（中国科学院大学物理科学学院）；Department of Physics, Anhui Normal University（安徽师范大学物理系）；School of Fundamental Physics and Mathematical Sciences, Hangzhou Institute for Advanced Study, University of Chinese Academy of Sciences（中国科学院大学杭州高等研究院基础物理与数学学院）
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