Holography, the Cosmological Constant and the Upper Limit of the Number of e-foldings

If the source of the current accelerating expansion of the universe is a positive cosmological constant, Banks and Fischler argued that there exists an upper limit of the total number of e-foldings of inflation. We further elaborate on the upper limit in the senses of viewing the cosmological horizon as the boundary of a cavity and of the holographic Dbound in a de Sitter space. Assuming a simple evolution model of inflation, we obtain an expression of the upper limit in terms of the cosmological constant, the initial energy density and end energy density of inflation, and reheating temperature, and discuss how the upper limit is modified in the different evolution models of the universe. The holographic D-bound gives more high upper limit than the entropy threshold in the cavity. For the most extremal case where the initial energy density of inflation is as high as the Planck energy, and the reheating temperature is as low as the energy scale of nucleosynthesis, the former gives the upper limit as 146 and the latter as 122. For reasonable assumption in the simplest cosmology, the holographic D-bound leads to a value about 85, while the cavity model gives a value around 65 for the upper limit, which is close to the value in order to solve the flatness problem and horizon problem in the hot big bang cosmology. ∗e-mail address: [email protected]