Astronomy and Astrophysics – Astrophysics
Scientific paper
2002-12-05
Astronomy and Astrophysics
Astrophysics
LaTeX 15 pages, 14 figures. Minor changes. Accepted in IJMPD
Scientific paper
We study the cosmology of canonically normalized scalar fields that lead to an equation of state parameter of w_\phi=p_\phi/\rho_\phi<-1 without violating the weak energy condition: rho=\Sigma_i\rho_i \geq 0 and \rho_i+p_i\geq 0. This kind of behavior requires a negative scalar potential V, widely predicted in particle physics. We show that the energy density \rho_\phi=E_k+V takes negative values with an equation of state with w_\phi < -1. However, the net effect of the $\phi$ field on the scale factor is to decelerate it giving a total equation of state parameter w=p/\rho> w_b=p_b/\rho_b, where \rho_b stands for any kind of energy density with -1\leq w_b \leq 1. The fact that \rho_\phi<0 allows, at least in principle, to have a small cosmological constant or quintessence today as the cancellation of high energy scales such as the electroweak or susy breaking scale. While V is negative |\rho_\phi| is smaller than the sum of all other energy densities regardless of the functional form of the potential V. We show that the existence of a negative potential leads, inevitable, to a collapsing universe, i.e. to a would be "big crunch". In this picture we would still be living in the expanding universe.
German Gabriel
la Macorra Axel de
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