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Register a new userProbing primordial non-Gaussianity with 21 cm fluctuations from minihalos
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Added by
Toyokazu Sekiguchi Ph.D
Publication date
2018
fields
Physics
and research's language is
English
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We investigate future constraints on primordial local-type non-Gaussianity from 21 cm angular power spectrum from minihalos. We particularly focus on the trispectrum of primordial curvature perturbations which are characterized by the non-linearity parameters $tau_{rm NL}$ and $g_{rm NL}$. We show that future measurements of minihalo 21 cm angular power spectrum can probe these non-linearity parameters with an unprecedented precision of $tau_{rm NL}sim30$ and $g_{rm NL}sim2times10^3$ for Square Kilometre Array (SKA) and $tau_{rm NL}sim0.6$ and $g_{rm NL}sim8times10^2$ for Fast Fourier Transform Telescope (FFTT). These levels of sensitivity would give significant implications for models of the inflationary Universe and the origin of cosmic density fluctuations.
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We forecast ability of dedicated 21 cm intensity mapping experiments to constraint primordial non-Gaussianity using power spectrum and bispectrum. We model the signal including the non-linear biasing expansion using a generalized halo model approach. We consider the importance of foreground filtering scale and of the foreground wedge. We find that the current generation intensity mapping experiments like CHIME do not posses sufficient sensitivity to be competitive with the existing limits. On the other hand, upcoming experiments like HIRAX can improve the current constraints and the proposed PUMA experiment can substantially improve them, reaching sensitivities below $sigma (f_{rm NL})<5$ for equilateral and orthogonal configurations and $sigma( f_{rm NL}) < 1$ for the local shape if good foreground control is achieved.
Ultracompact minihalos~(UCMHs) can form after the epoch of matter-radiation equality, if the density fluctuations of dark matter have significantly large amplitude on small scales. The constraint on the UCMH abundance allows us to access such small-scale fluctuations. In this paper, we present that, through the measurement of 21-cm fluctuations before the epoch of reionization~ we can obtain a constraint on the UCMH abundance. We calculate the 21-cm signal from UCMHs and show that UCMHs provide the enhancement of the 21-cm fluctuations. We also investigate the constraint on the UCMH abundance and small-scale curvature perturbations. Our results indicate that the upcoming 21-cm observation, the Square Kilometre Array (SKA), provides the constraint on amplitude of primordial curvature power spectrum, ${cal A}_{zeta} lesssim 10^{-6}$ on $100~{rm Mpc}^{-1} lesssim k lesssim 1000~{rm Mpc}^{-1}$. Although it is not stronger than the one from the non-detection of gamma rays induced by dark matter annihilation in UCMHs, the constraint by the SKA will be important because this constraint is independent of the dark matter particle model.
Here we review the present status of modelling of and searching for primordial non-Gaussianity of cosmological perturbations. After introducing the models for non-Gaussianity generation during inflation, we discuss the search for non-Gaussian signatures in the Cosmic Microwave Background and in the Large-Scale Structure of the Universe.
Enormous information about interactions is contained in the non-Gaussianities of the primordial curvature perturbations, which are essential to break the degeneracy of inflationary models. We study the primordial bispectra for G-inflation models predicting both sharp and broad peaks in the primordial scalar power spectrum. We calculate the non-Gaussianity parameter $f_{mathrm{NL}}$ in the equilateral limit and squeezed limit numerically, and confirm that the consistency relation holds in these models. Even though $f_{mathrm{NL}}$ becomes large at the scales before the power spectrum reaches the peak and the scales where there are wiggles in the power spectrum, it remains to be small at the peak scales. Therefore, the contributions of non-Gaussianity to the scalar induced secondary gravitational waves and primordial black hole abundance are expected to be negligible.
Measuring the small primordial nonGaussianity (PNG) predicted by cosmic inflation theories may help diagnose them. The detectability of PNG by its imprint on the 21cm power spectrum from the epoch of reionization is reassessed here in terms of $f_{NL}$, the local nonlinearity parameter. We find that an optimum, multi-frequency observation by SKA can achieve $Delta f_{NL} sim 3$ (comparable to recent Planck CMB limits), while a cosmic-variance-limited array of this size like Omniscope can even detect $Delta f_{NL} sim 0.2$. This substantially revises the methods and results of previous work.
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