Teasing bits of information out of the CMB energy spectrum

Chluba, Jens; Jeong, Donghui

doi:10.1093/mnras/stt2327

Cited by 125 publications

(221 citation statements)

References 101 publications

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“…Although the dissipation-induced average y distortion is expected to be 5 times smaller than the µ distortion (see estimate above), the experimental sensitivity to y is 5 − 10 times better [42,44]. Assuming a PRISM detection limit of y min 2 × 10 −10 , we thus infer a comparable smallest nonGaussianity parameter, …”

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confidence: 73%

Probing the scale dependence of non-Gaussianity with spectral distortions of the cosmic microwave background

et al. 2015

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Many inflation models predict that primordial density perturbations have a nonzero three-point correlation function, or bispectrum in Fourier space. Of the several possibilities for this bispectrum, the most commmon is the local-model bispectrum, which can be described as a spatial modulation of the small-scale (largewavenumber) power spectrum by long-wavelength density fluctuations. While the local model predicts this spatial modulation to be scale-independent, many variants have some scale-dependence. Here we note that this scale dependence can be probed with measurements of frequency-spectrum distortions in the cosmic microwave background (CMB), in particular highlighting Compton-y distortions. Dissipation of primordial perturbations with wavenumbers 50 Mpc −1 k 10 4 Mpc −1 give rise to chemical-potential (µ) distortions, while those with wavenumbers 1 Mpc −1 k 50 Mpc −1 give rise to Compton-y distortions. With local-model non-Gaussianity, the distortions induced by this dissipation can be distinguished from those due to other sources via their crosscorrelation with the CMB temperature T . We show that the relative strengths of the µT and yT correlations thus probe the scale-dependence of non-Gaussianity and estimate the magnitude of possible signals relative to sensitivities of future experiments. We discuss the complementarity of these measurements with other probes of squeezed-limit non-Gaussianity.

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confidence: 73%

Probing the scale dependence of non-Gaussianity with spectral distortions of the cosmic microwave background

et al. 2015

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“…The other constraints are described in the main body of the text. The reach of PIXIE corresponds to µ < 2.8 × 10 −8 and y < 2.4 × 10 −9 [63,64]. The reach including the expected impact of foregrounds, µ < 9.4 × 10 −8 [65], is shown with a dotted line.…”

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confidence: 99%

Fourth Exception in the Calculation of Relic Abundances

2017

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We propose that the dark matter abundance is set by the decoupling of inelastic scattering instead of annihilations. This coscattering mechanism is generically realized if dark matter scatters against states of comparable mass from the thermal bath. Coscattering points to dark matter that is exponentially lighter than the weak scale and has a suppressed annihilation rate, avoiding stringent constraints from indirect detection. Dark matter upscatters into states whose late decays can lead to observable distortions to the blackbody spectrum of the cosmic microwave background.Introduction: Dark Matter (DM) constitutes most of the matter in our Universe, but its origin is unknown. One of the most attractive possibilities is that DM starts in thermal equilibrium in the early Universe, and its abundance is set once its annihilations become slower than the expansion rate. This framework is insensitive to initial conditions and has the further appeal of tying the DM abundance to its (potentially observable) interactions.The most widely considered possibility is that 2-to-2 annihilations to Standard Model (SM) particles set the DM relic density. This is known as the Weakly Interacting Massive Particle (WIMP) paradigm [1-4] and points to DM particles with weak scale masses and crosssections. This theoretical framework has had considerable impact shaping experimental searches for DM.However it has long been appreciated that simple variations to the cosmology of thermal relics can have dramatic consequences. In a seminal paper, Ref.[5] enumerates three "exceptions" to thermal relic cosmology: (1) mutual annihilations of multiple species (coannihilations), (2) annihilations into heaver states (forbidden channels), and (3) annihilations near a pole in the cross section. These exceptions lead to phenomenology that can differ significantly from standard WIMPs (see for example [11][12][13]34]), while sharing their appealing theoretical features.In this letter, we introduce a fourth exception. Like Ref.[5], we assume DM begins in thermal equilibrium, has its number diluted through 2-to-2 annihilations, and has a temperature that tracks the photon temperature (for studies that relax at least one of these assumptions see for example Refs. [14][15][16][17][18][19][20][21][22][23][24][25][26][27]). We consider the presence of two states charged under the symmetry that stabilizes DM: χ and ψ, where m χ < m ψ and χ is DM. We assume that χ annihilations are suppressed, and two processes are active:

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“…7). As we discuss later, any detection of such values of µ-distortions will rule out single-field slow-roll inflation, if we assume that all the generated distortions are due to Silk damping and not to other mechanisms like, for example, decaying Dark Matter particles; 7 6 In [45] it was shown that, when also r-distortions are considered, the expected error should be larger (about σµ = 1.4 × 10 −8 ): however at the large values of αs and βs allowed by Planck, the forecasts of Tab. VI are not significantly affected.…”

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confidence: 99%

Constraints on the running of the running of the scalar tilt from CMB anisotropies and spectral distortions

et al. 2016

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We use the recent observations of Cosmic Microwave Background temperature and polarization anisotropies provided by the Planck satellite experiment to place constraints on the running αs = dns/d log k and the running of the running βs = dαs/d log k of the spectral index ns of primordial scalar fluctuations. We find αs = 0.011 ± 0.010 and βs = 0.027 ± 0.013 at 68% CL, suggesting the presence of a running of the running at the level of two standard deviations. We find no significant correlation between βs and foregrounds parameters, with the exception of the point sources amplitude at 143 GHz, A P S 143 , which shifts by half sigma when the running of the running is considered. We further study the cosmological implications of such preference for αs, βs ∼ 0.01 by including in the analysis the lensing amplitude AL, the curvature parameter Ω k , and the sum of neutrino masses mν . We find that when the running of the running is considered, Planck data are more compatible with the standard expectations of AL = 1 and Ω k = 0 but still hint at possible deviations. The indication for βs > 0 survives at two standard deviations when external datasets such as BAO and CFHTLenS are included in the analysis, and persists at ∼ 1.7 standard deviations when CMB lensing is considered. We discuss the possibility of constraining βs with current and future measurements of CMB spectral distortions, showing that an experiment like PIXIE could provide strong constraints on αs and βs.

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Teasing bits of information out of the CMB energy spectrum

Cited by 125 publications

References 101 publications

Probing the scale dependence of non-Gaussianity with spectral distortions of the cosmic microwave background

Probing the scale dependence of non-Gaussianity with spectral distortions of the cosmic microwave background

Fourth Exception in the Calculation of Relic Abundances

Constraints on the running of the running of the scalar tilt from CMB anisotropies and spectral distortions

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