Position-dependent power spectrum: a new observable in the large-scale structure

Understand

We present a new observable, position-dependent power spectrum, to measure the large-scale structure bispectrum in the squeezed configuration, where one wavenumber is much smaller than the other two.

• The squeezed-limit bispectrum measures how the small-scale power spectrum is modulated by a long-wavelength overdensity, which is due to gravitational evolution and possibly inflationary physics.
• We divide a survey into small subvolumes, compute the local power spectrum and the mean overdensity in each subvolume, and measure the correlation between them.
• The correlation measures the integral of the bispectrum, which is dominated by squeezed configurations if the scale of the local power spectrum is much smaller than the subvolume size.