Probing the Coupling between Dark Components of the Universe Zong-Kuan Guo

Probing the Coupling between Dark Components of the Universe

• Zong-Kuan Guo

• Department of Physics,

• Kinki University

Outline

• Introduction

• Coupled Dark Energy with Dark Matter (physical motivations)

• Observational Constraints

• Summary

Abstract

• Recent observations of SN Ia suggest that the universe has entered a stage of an accelerated expansion.

• Given this, a dark energy component with negative pressure was suggested to account for the invisible fuel that drives the current accelerated expansion.

• However, in the LCDM model there exists a theoretical problem of cosmic coincidence: why is the vacuum density comparable with the critical density at the present epoch in the long history of the universe?

Abstract

• Cosmological models with a coupling between dark energy and dark matter could provide a phenomenological explanation to the cosmic coincidence problem.

• We place observational constraints on a coupling between dark energy and dark matter by using SNLS data, CMB shift parameter and BAO.

• Our results indicate that the uncoupled LCDM model still remains a good fit to the data, but the negative coupling with a phantom equation of state of dark energy is slightly favored over the LCDM model.

The Gold Sample of 157 SNe Ia

The Supernova Legacy Survey (SNLS)

Components of the Universe

• Dark energy ( ~72% )

• Dark matter ( ~23.8% )

• Baryons, photons and others( ~4.2% )

Three Components

Evolutions of Components

Dark Energy Models

• Cosmological Constant

• Dynamical Dark Energy, Quintessence

• Many other ideas……

Problems of Dark Energy

• The Fine-tuning Problem

• The Cosmic Coincidence Problem

The Cosmic Coincidence Problem

Coupled Dark Energy with Dark Matter

Observational Data

• 71 SN Ia from the Supernova Legacy Survey (SNLS) [arXiv:astro-ph/0510447]

• the baryon acoustic oscillation (BAO) peak found in the Sloan Digital Sky Survey (SDSS)

• [arXiv:astro-ph/0501171]

• The cosmic microwave background (CMB) shift parameter from the 3-year Wilkinson Microwave Anisotropy Probe (WMAP)

• [arXiv:astro-ph/0604051]

Theχ2 Statistic Method

Model I

Model II

Summary

• The CMB shift parameter provides a stringent constraint on the coupling.

• Our results indicate that the uncoupled LCDM model is still remains a good fit to the data.

• Perturbation of the coupled dark energy (under consideration).

• Construction of the coupling between dark components (under consideration).

Future Directions for Cosmology

• To release more and more precise observational data and to probe new observable effects.

• Based on fundamental physics to propose new models or to find new physics.

• To differentiate some models, to exclude some by using current data, and to find new observable effects that can be tested at least by the future experiments.

Thank You!