The stacked ISW signal of rare superstructures in ΛCDM

A detection of the stacked integrated Sachs-Wolfe (ISW) signal in the CMB of rare superstructures identified in the SDSS Luminous Red Galaxy catalogue has been reported at very high statistical significance. The magnitude of the observed signal has previously been argued to be more than 3 standard deviations larger than the theoretical CDM expectation. However, this calculation was made in the linear approximation, and relied on assumptions that may potentially have caused the CDM expectation to be underestimated. Here we update the theoretical model calculation and compare it with an analysis of ISW maps obtained from N-body simulations of a CDM universe. The differences between model predictions and the map analyses are found to be small and cannot explain the discrepancy with observation, which remains at >3 s. d. significance. We discuss the cosmological significance of this anomaly and speculate on the potential of alternative models to explain it.