4 research outputs found
How to Test Stringy Dark Energy?
It is suggested, by using a covariant lagrangian formalism to estimate the
equation of state , that stringy dark energy predicts , a
negative pressure larger in magnitude than that for a cosmological constant or
quintessence. This would lead to a later transition from decelerating to
accelerating cosmological expansion; is briefly considered as one
illustrative example.Comment: 4 pages LaTeX. v2. Typos correcte
Cosmon dark matter?
We investigate if the fluctuations of the scalar field mediating quintessence
-- the cosmon -- can play an important role in cosmology. Small fluctuations
with short wavelength behave similar to a relativistic gas. In contrast, the
contribution to the energy density from horizon size fluctuations may decrease
less rapidly than radiation. We discuss the possibility that the cosmon
fluctuations grow nonlinearly, form lumps and constitute the clustering dark
matter of the universe. Cosmon dark matter would lead to interesting
consequences for the equation of state and the coupling between quintessence
and dark matter.Comment: Published version,correction in appendix A, 43 pages, LaTe
Can Structure Formation Influence the Cosmological Evolution?
The backreaction of structure formation influences the cosmological evolution
equation for the homogenous and isotropic average metric. In a cold dark matter
universe this effect leads only to small corrections unless a substantial
fraction of matter is located in regions where strong gravitational fields
evolve in time. A``cosmic virial theorem'' states that the sum of gravitational
and matter pressure vanishes and therefore relates the average kinetic energy
to a suitable average of the Newtonian potential. In presence of a scalar
``cosmon'' field mediating quintessence, however, cosmology could be modified
if local cosmon fluctuations grow large. We speculate that this may trigger the
accelerated expansion of the universe after the formation of structure.Comment: new "cosmic virial theorem",new references,LaTex,11 page