CMB-S4 forecasts for constraints on fNL through μ -distortion anisotropy
Abstract
Diffusion damping of the cosmic microwave background (CMB) power spectrum results from imperfect photon-baryon coupling in the pre-recombination plasma. Energy release at redshifts 5 ×104<z <2 ×106 can create μ -type spectral distortions of the CMB. These μ distortions trace the underlying photon density fluctuations, probing the primordial power spectrum in short-wavelength modes kS over the range 50 Mpc-1≲k ≲104 Mpc-1. Small-scale power modulated by long-wavelength modes kL from squeezed-limit non-Gaussianities introduces cross correlations between CMB temperature anisotropies and μ distortions. Under single-field inflation models, μ ×T correlations measured from an observer in an inertial frame should vanish up to a factor of (kL/kS)2≪1 . Thus, any measurable correlation rules out single-field inflation models. We forecast how well the next-generation ground-based CMB experiment CMB-S4 will be able to constrain primordial squeezed-limit non-Gaussianity, parametrized by fNL, using measurements of CℓμT as well as CℓμE from CMB E modes. Using current experimental specifications and foreground modeling, we expect σ (fNL)≲1000 . This is roughly 4 times better than the current limit on fNL using μ ×T and μ ×E correlations from Planck and is comparable to what is achievable with LiteBIRD, demonstrating the power of the CMB-S4 experiment. This measurement is at an effective scale of k ≈740 Mpc-1 and is thus highly complementary to measurements at larger scales from primary CMB and large-scale structure.
- Publication:
-
Physical Review D
- Pub Date:
- November 2023
- DOI:
- 10.1103/PhysRevD.108.103536
- arXiv:
- arXiv:2303.00916
- Bibcode:
- 2023PhRvD.108j3536Z
- Keywords:
-
- Astrophysics - Cosmology and Nongalactic Astrophysics;
- General Relativity and Quantum Cosmology
- E-Print:
- 19 pages, 6 figures