Lighting Dark Ages with Tomographic ISW Effect
arxiv(2024)
Abstract
The integrated Sachs-Wolfe effect (ISW) describes how CMB photons pick up a
net blue or redshift when traversing the time-varying gravitational potentials
between the last scattering surface and us. Deviations from its standard
amplitude could hint new physics. We show that reconstructing the amplitude of
the ISW effect as a function of the redshift may provide a unique tool to probe
the gravity sector during the era of dark ages, inaccessible via other
cosmological observables. Exploiting Planck CMB temperature, polarization and
lensing observations, we find a 2σ deviation from the standard ISW
amplitude at redshift z=500. Barrying a systematic origin, our findings could
point to either possibly new physics or a departure from the standard picture
of structure formation under the General Relativity framework. Assuming the
simplest two-redshift-bin scenario, we ensure 38σ and 2σ
evidences of the early and late ISW effects, respectively, despite a priori
possible degeneracy with the CMB lensing amplitude. Using a multiple
tomographic method, we present the first complete characterization of the ISW
effect over space and time. Future tomographic ISW analyses are therefore
crucial to probe the dark ages at redshifts otherwise unreachable via other
probes.
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