Bounds on isocurvature perturbations from cosmic microwave background and large scale structure data

Area of Science:

• Cosmology
• Astrophysics
• Particle Physics

Background:

• Primordial fluctuations are key to understanding the Universe's evolution.
• Isocurvature perturbations, alongside adiabatic ones, are potential contributors to these fluctuations.
• Cosmic Microwave Background (CMB) and large-scale structure (LSS) data offer powerful probes of the early Universe.

Purpose of the Study:

• To derive stringent bounds on various isocurvature contributions (cold dark matter, baryon, neutrino density, neutrino velocity) to primordial fluctuations.
• To test the validity of different cosmological models, including the curvaton model.
• To constrain the correlated adiabatic and isocurvature components.

Main Methods:

• Bayesian likelihood analysis incorporating nine free parameters.
• Utilizing recent Cosmic Microwave Background (CMB) and large-scale structure (LSS) observational data.
• Neglecting spatial curvature, tensor perturbations, and reionization effects for model simplification.

Main Results:

• The amplitude of cold dark matter isocurvature cannot exceed 31% (at 2 sigma).
• Baryon, neutrino density, and neutrino velocity isocurvature modes are constrained to 91%, 76%, and 60% respectively.
• Cross-correlation coefficients between adiabatic and isocurvature components are strongly constrained, disfavoring maximally correlated models.

Conclusions:

• The study establishes robust upper limits on isocurvature contributions from different components.
• These constraints significantly impact and limit the viability of certain cosmological models, such as the curvaton model.
• The findings underscore the power of CMB and LSS data in refining our understanding of the Universe's fundamental properties.