496 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
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
A Realistic Particle Physics Dark Energy Model
We present a realistic dark energy model derived from particle physics. Our
model has essentially no free parameters and has an equivalent fit to the
observational data (CMB, SN1a and LSS) as LCDM and a better fit than the best
effective model. With the lack of a clear determination of the
cosmological parameters theoretical considerations should be taken seriously to
distinguish between dark energy models.Comment: 5 pages, RevTex, 6 figure
Interacting Tachyon: generic cosmological evolution for a tachyon and a scalar field
We study the cosmological evolution of a tachyon scalar field T with a
Dirac-Born-Infeld type lagrangian and potential V(T) coupled to a canonically
normalized scalar field \phi with an arbitrary interaction term B(T,\phi) in
the presence of a barotropic fluid \rb, which can be matter or radiation. The
force between the barotropic fluid and the scalar fields is only gravitational.
We show that the dynamics is completely determine by only three parameters L1 =
- V_T/ V^{3/2}, L2= - B_T /B^{3/2} and L3 =-B_{\phi}/B. We determine
analytically theconditions for \lm_i under which the energy density of T,
\phi and \rb have the same redshift. We study the behavior of T and \phi in
the asymptotic limits for L_i and we show the numerical solution for different
interesting cases.
The effective equation of state for the tachyon field changes due to the
interaction with the scalar field and we show that it is possible for a tachyon
field to redshift as matter in the absence of an interaction term B and as
radiation when B is turned on. This result solves then the tachyonic matter
problem.Comment: 13 pages, 5 figure
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