Generalized cardassian expansion: a model in which the universe is flat, matter dominated, and accelerating
✍ Scribed by Katherine Freese
- Publisher
- Elsevier Science
- Year
- 2003
- Tongue
- English
- Weight
- 467 KB
- Volume
- 124
- Category
- Article
- ISSN
- 0920-5632
No coin nor oath required. For personal study only.
✦ Synopsis
The Cardassian universe is a proposed modification to the Friedmann Robertson Walker equation (FRW) in which the universe is flat, matter dominated, and accelerating. In this presentation, we generalize the original Cardassian proposal to include additional variants on the FRW equation; specific examples are presented.
In the ordinary FRW equation, the right hand side is a linear function of the energy density, Hz -p. Here, instead, the right hand side of the FRW equation is a diierent function of the energy density, H2 -g(p). This function returns to ordinary FRW at early times, but modifies the expansion at a late epoch of the universe. The only ingredients in this universe are matter and radiation: in particular, there is NO vacuum contribution. Currently the modification of the FRW equation is such that the universe accelerates; we call this period of acceleration the Cardassian era. The universe can be flat and yet consist of only matter and radiation, and still be compatible with observations. The energy density required to close the universe is much smaller than in a standard cosmology, so that matter can be sufficient to provide a flat geometry. The new term required may arise, e.g., as a consequence of our observable universe living as a 3dimensional brane in a higher dimensional