Thanks to CMB anisotropy measurements (especially from the WMAP and Planck satellites), we now know that primordial fluctuations are predominantly adiabatic. That is to say that photons, neutrinos, baryons, and dark matter had fluctuations in energy density that were more or less spatially in phase. Isocurvature fluctuations, on the other hand, are fluctuations in the relative energy densities of different species at fixed total density. They are now constrained to be 1% or less of the primordial density fluctuation, depending on precise assumptions. There are 3 well-motivated isocurvature modes (shown below contributing to fluctuations along with an adiabatic component). Generally speaking, isocurvature perturbations are produced by sub-dominant fields during the inflationary era. Detecting them would thus yield insight into physics at the inflationary energy scale, or even the production of baryon number, lepton number, or dark matter in the early universe.

Probing a panoply of curvaton-decay scenarios using CMB data

In the curvaton model, an energetically sub-dominant field (the curvaton) during inflation eventually begins to redshift as matter, allowing it and its decay products to later dominate the overall primordial density fluctuation (overtaking that caused by fluctuations in the inflaton itself). In this work, Tristan Smith and I systematically probed and limited the curvaton parameter […]

Search for Compensated Isocurvature Perturbations with Planck Power Spectra

One interesting feature of compensated isocurvature perturbations (CIPs) is that they have a similar effect on CMB power spectra to weak lensing of the CMB. CIPs are fluctuations in the relative number densities of dark matter and baryons. In this work (led by Johns Hopkins graduate student Julian B. Muñoz under my mentorship & supervised […]

Compensated isocurvature perturbations in the curvaton model

Compensated isocurvature perturbations (CIPs) are fluctuations in the relative density of baryons and cold dark matter (CDM) at fixed total matter density, which are detectable using CMB data as a result of a spatially varying sound speed in the baryon-photon plasma. In this work, graduate student Chen He (mentored by me & supervised by Prof. […]

Spectral distortions from isocurvature perturbations

Isocurvature perturbations are fluctuations in the relative number densities of particles at constant total density. Like adiabatic (or total density) fluctuations, primordial isocurvature perturbations will excite acoustic waves in the baryon-photon plasma. Jens Chluba and I computed the spectral distortions (deviations of the spatially averaged CMB from a perfect blackbody) generated when these acoustic waves […]

Search for compensated isocurvature perturbations using the WMAP 9-year data release

Working with Duncan Hanson,we used the WMAP 9-year maps to search for evidence of compensated isocurvature perturbations (CIPs) using the techniques outlined in arXiv:1107.5047. We find that baryons do trace dark matter at the ~10% level (expressed as a limit on the CIP amplitude). Results published in arXiv:1306.4319 (Phys. Rev. D 89, 023006). Collaborators: Duncan […]

Compensated Isocurvature Perturbations: a new CMB signature

Unlike isocurvature perturbations between photons and neutrinos, CDM, or baryons, isocurvature perturbations between dark matter and baryons are surprisingly poorly constrained. In this work, we show that such perturbations do have observable effects on the CMB due to higher-order effects that induce off-diagonal correlations and non-Gaussianity in the CMB. Results published in arXiv:1107.5047 (Phys. Rev. […]