710 research outputs found
The Fate of the Universe: Dark Energy Dilution?
We study the possibility that dark energy decays in the future and the
universe stops accelerating. The fact thatthe cosmological observations prefer
an equation of state of dark energy smaller than -1 can be a signal that dark
energy will decay in the future. This conclusion is based in interpreting a
w<-1 as a signal of dark energy interaction with another fluid. We determine
the interaction through the cosmological data and extrapolate it into the
future. The resulting energy density for dark energy becomes
rho=a^{-3(1+w)}e^{-\beta(a-1)}, i.e. it has an exponential suppression for a >>
a_o=1. In this scenario the universe ends up dominated by this other fluid,
which could be matter, and the universe stops accelerating at some time in the
near future.Comment: 5 pages, 3 figure
Interacting Dark Energy: Decay into Fermions
A dark energy component is responsible for the present stage of acceleration
of our universe. If no fine tuning is assumed on the dark energy potential then
it will end up dominating the universe at late times and the universe will not
stop this stage of acceleration. On the other hand, the equation of state of
dark energy seems to be smaller than -1 as suggested by the cosmological data.
We take this as an indication that dark energy does indeed interact with
another fluid (we consider fermion fields) and we determine the interaction
through the cosmological data and extrapolate it into the future. We study the
conditions under which a dark energy can dilute faster or decay into the
fermion fields. We show that it is possible to live now in an accelerating
epoch dominated by the dark energy and without introducing any fine tuning
parameters the dark energy can either dilute faster or decaying into fermions
in the future. The acceleration of the universe will then cease.Comment: 10 page
Inflation from superstrings
We investigate the possibility of obtaining inflationary solutions of the
slow roll type from a low energy Lagrangian coming from superstrings. The
advantage of such an approach is that in these theories the scalar potential
has only one free parameter (the Planck scale) and therefore no unnatural fine
tuning may be accommodated. We find that in any viable scheme the dilaton and
the moduli fields have to be stabilized and that before this happens, no other
field may be used as the inflaton. Then inflation may occur due to chiral
matter fields. Demanding that the potential terms associated with the chiral
fields do not spoil the dilaton and moduli minimization leads to severe
constraints on the magnitude of the density fluctuations.Comment: 22 pages, no figures, latex file We have corrected the magnitude of
the density fluctuations, which become smaller than the COBE ones. Some
references have also been added, and a few misprints correcte
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