This project contains the code necessary to produce some of the numerical results in the paper arXiv:1508.06489 (journal link), in which we extrapolate the power spectrum to superhorizon scales and show that the presence of the background density dipole, in the presence of large enough local type non-Gaussianity, generates a power asymmetry in the CMB power spectrum.

The basic idea is very simple: generate a large number of CMB maps with the Sachs-Wolfe spectrum (including the dipole term C_1, which is usually dropped, as the temperature dipole measured is dominated by the Doppler dipole). Then, assume local type non-Gaussianity and generate non-Gaussian temperature fluctuation maps. This is simple when only working in a Sachs-Wolfe universe. This couples the small scale power spectrum with the background dipole and one therefore gets a power asymmetry whose strength depends on (i) the strength of the non-linearity (fNL), and (ii) the magnitude of the background dipole (which depends on the particular realization of the modes for a CMB sky)

The following are some useful files:

• swmaps.py generates the necessary Gaussian maps and calculates the relevant data: asymmetry amplitudes, background dipole in each map etc

• ngsachswolfe.py contains a useful class SachsWolfeMap that is used for the calculations done in swmaps

• cmbutils.py some utilities for use in the above two files but that may be useful at other places later.

• padists.py contains a class called PowerAsymmetryDistribution that can read the data generated by swmaps.py to generate useful plots

• generate_plots.py script to generate some useful plots