We predict the level of small-scale anisotropy in the cosmic microwave background ( CMB ) due to the Sunyaev–Zel ’ dovich ( SZ ) effect for the ensemble of cosmological models that are consistent with current measurements of large-scale CMB anisotropy .
We argue that the recently reported detections of the small-scale ( arcminutes ) CMB anisotropy are only marginally consistent with being the SZ effect when cosmological models are calibrated to the existing primary CMB data on large scales .
The discrepancy is at more than 2 - 2.5 \sigma , and is mainly due to a lower \sigma _ { 8 } \lesssim 0.8 favored by the primary CMB and a higher \sigma _ { 8 } \gtrsim 1 favored by the SZ effect .
A degeneracy between the optical depth to Thomson scattering and the CMB-derived value of \sigma _ { 8 } suggests that the discrepancy is reduced if the universe was reionized very early , at redshift of \sim 25 .