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Advances in Astronomy
Volume 2012 (2012), Article ID 528243, 6 pages
Research Article

Constraints on a Vacuum Energy from Both SNIa and CMB Temperature Observations

Department of Physics, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka City 812-8581, Japan

Received 28 February 2012; Accepted 1 May 2012

Academic Editor: Rob Ivison

Copyright © 2012 Riou Nakamura et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


We investigate the cosmic thermal evolution with a vacuum energy which decays into photon at the low redshift. We assume that the vacuum energy is a function of the scale factor that increases toward the early universe. We put on the constraints using recent observations of both type Ia supernovae (SNIa) by Union-2 compilation and the cosmic microwave background (CMB) temperature at the range of the redshift 0.01<z<3. From SNIa, we find that the effects of a decaying vacuum energy on the cosmic expansion rate should be very small but could be possible for z<1.5. On the other hand, we obtain the severe constraints for parameters from the CMB temperature observations. Although the temperature can be still lower than the case of the standard cosmological model, it should only affect the thermal evolution at the early epoch.