Constraints on compensated isocurvature perturbations from BOSS DR12 galaxy data

We use the BOSS DR12 galaxy power spectrum to constrain compensated isocurvature perturbations (CIP), which are opposite-sign primordial baryon and dark matter perturbations that leave the total matter density unchanged. Long-wavelength CIP sigma(x) enter the galaxy density contrast as delta g(x) D b sigma sigma (x), with b sigma the linear CIP galaxy bias parameter. We parameterize the CIP spectra as P sigma sigma = A2PRR and P sigma R = xi VP sigma sigma PRR, where A is the CIP amplitude and xi is the correlation with the curvature perturbations R. We find a significance of detection of Ab sigma =6 0 of 1.8 sigma for correlated CIP (xi = 1), consistent with no detection. For uncorrelated CIP (xi = 0), the constraints are instead more significantly shifted away from zero, although this may be due to large-scale data systematics which have a bigger impact on these type of CIP. The constraints on A depend on the assumed priors for the b sigma parameter, which we estimate using separate universe simulations. Assuming b sigma values representative of all halos we find sigma A = 145 for correlated CIP and sigma|A| = 475 for uncorrelated CIP. Our strongest uncorrelated CIP constraint is for b sigma representative of the 33% most concentrated halos, sigma|A| = 197, which is better than the current CMB bounds |A| $ 360. We also discuss the impact of the local primordial non-Gaussianity parameter fNL in CIP constraints. Our results demonstrate the power of galaxy data to place tight constraints on CIP, and motivate works to understand better the impact of data systematics, as well as to determine theory priors for b sigma.

Automated summary

We place constraints on compensated isocurvature perturbations (CIP) using the BOSS DR12 galaxy power spectrum and find that galaxy data is powerful in constraining CIP.