Effects of a decaying cosmological fluctuation

Area of Science:

• Cosmology
• Astrophysics
• Cosmic Microwave Background Radiation

Background:

• Cosmological perturbations are crucial for understanding the early universe's structure formation.
• The behavior of decaying modes depends on the universe's fluid components.
• Previous models often assumed perfect fluid behavior, potentially oversimplifying decaying mode dynamics.

Purpose of the Study:

• To investigate the initial conditions and observable signatures of decaying cosmological perturbations.
• To analyze how non-perfect fluid components affect decaying mode evolution.
• To constrain the amplitude of decaying adiabatic fluctuations using observational data.

Main Methods:

• Theoretical modeling of decaying cosmological perturbations, considering non-perfect fluid components.
• Analysis of perturbation signatures in Cosmic Microwave Background (CMB) anisotropies.
• Examination of effects on matter power spectra.
• Utilizing data from the Wilkinson Microwave Anisotropy Probe (WMAP).

Main Results:

• Decaying adiabatic modes in universes with collisionless matter decay slower and exhibit super-Hubble oscillations compared to perfect-fluid dominated models.
• The ratio of decaying to growing modes for scale-invariant adiabatic fluctuations at matter-radiation equality is constrained.
• WMAP first-year data limit this ratio to less than 10%.

Conclusions:

• The presence of non-perfect fluid components significantly alters the decay rate and behavior of cosmological perturbations.
• Observational data, specifically from the CMB, provide stringent constraints on the amplitude of decaying fluctuations.
• These findings refine models of early universe cosmology and structure formation.