4,406 research outputs found
Inflation and Large Internal Dimensions
We consider some aspects of inflation in models with large internal
dimensions. If inflation occurs on a 3D wall after the stabilization of
internal dimensions in the models with low unification scale (M ~ 1 TeV), the
inflaton field must be extremely light. This problem may disappear In models
with intermediate (M ~10^{11} GeV) to high (M ~ 10^{16} GeV) unification scale.
However, in all of these cases the wall inflation does not provide a complete
solution to the horizon and flatness problems. To solve them, there must be a
stage of inflation in the bulk before the compactification of internal
dimensions.Comment: 4 pages, revtex, minor modification
From inflation to a zero cosmological constant phase without fine tuning
We show that it is possible to obtain inflation and also solve the
cosmological constant problem. The theory is invariant under changes of the
Lagrangian density to . Then the constant part of a scalar field
potential cannot be responsible for inflation. However, we show that
inflation can be driven by a condensate of a four index field strength. A
constraint appears which correlates this condensate to . After a conformal
transformation, the equations are the standard GR equations with an effective
scalar field potential which has generally an absolute minimum
independently of and without fine tuning. We also show that,
after inflation, the usual reheating phase scenario (from oscillations around
the absolute minimum) is possible.Comment: revised version containes an improved model where fine tuning is not
needed for transition to a zero cosmological constant phase. 5 pages. To
appear in Phys. Rev.
Inflation from Extra Dimensions
The radial mode of n extra compact dimensions (the radion, b) can cause
inflation in theories where the fundamental gravity scale, M, is smaller than
the Planck scale M_P. For radion potentials V(b) with a simple polynomial form,
to get the observed density perturbations, the energy scale of V(b) must
greatly exceed M ~ 1 TeV: V(b)^{1/4} = M_v ~ 10^{-4} M_P. This gives a large
radion mass and reheat temperature ~ 10^9 GeV, thus avoiding the moduli
problem. Such a value of M_v can be consistent with the classical treatment if
the new dimensions started sufficiently small. A new possibility is that b
approaches its stable value from above during inflation. The same conclusions
about M_v may hold even if inflation is driven by matter fields rather than by
the radion.Comment: 4 pages, 4 figures, uses epsf.te
Cosmological term as a source of mass
In the spherically symmetric case the dominant energy condition together with
the requirements of regularity at the center, asymptotic flatness and
fineteness of the ADM mass, defines the family of asymptotically flat globally
regular solutions to the Einstein minimally coupled equations which includes
the class of metrics asymptotically de Sitter at approaching the regular
center. The source term corresponds to an r-dependent cosmological term given
by the second rank symmetric tensor invariant under boosts in the radial
direction and evolving from de Sitter vacuum in the origin to Minkowski vacuum
at infinity. Space-time symmetry changes smoothly from the de Sitter group at
the center to the Lorentz group at infinity through the radial boosts in
between. The standard formula for the ADM mass relates it to the de Sitter
vacuum replacing a central singularity at the scale of symmetry restoration.
For masses exceeding a certain critical value m_{crit} de Sitter-Schwarzschild
geometry describes a vacuum nonsingular black hole, while beyond m_{crit} it
describes a G-lump which is a vacuum selfgravitating particlelike structure
without horizons. Quantum energy spectrum of G-lump is shifted down by the
binding energy, and zero-point vacuum mode is fixed at the value corresponding
to the Hawking temperature from the de Sitter horizon.Comment: 8 pages, revtex, 8 figures incorporated, to appear in Classical and
Quantum Gravit
Reconstructing a model of quintessential inflation
We present an explicit cosmological model where inflation and dark energy
both could arise from the dynamics of the same scalar field. We present our
discussion in the framework where the inflaton field attains a nearly
constant velocity (where
is the e-folding time) during inflation. We show that the model
with and can easily satisfy inflationary constraints,
including the spectral index of scalar fluctuations (),
tensor-to-scalar ratio () and also the bound imposed on
during the nucleosynthesis epoch (). In our
construction, the scalar field potential always scales proportionally to the
square of the Hubble expansion rate. One may thereby account for the two vastly
different energy scales associated with the Hubble parameters at early and late
epochs. The inflaton energy could also produce an observationally significant
effective dark energy at a late epoch without violating local gravity tests.Comment: 18 pages, 7 figures; added refs, published versio
Cosmological Constant, Dark Matter, and Electroweak Phase Transition
Accepting the fine tuned cosmological constant hypothesis, we have recently
proposed that this hypothesis can be tested if the dark matter freeze out
occurs at the electroweak scale and if one were to measure an anomalous shift
in the dark matter relic abundance. In this paper, we numerically compute this
relic abundance shift in the context of explicit singlet extensions of the
Standard Model and explore the properties of the phase transition which would
lead to the observationally most favorable scenario. Through the numerical
exploration, we explicitly identify a parameter space in a singlet extension of
the standard model which gives order unity observable effects. We also clarify
the notion of a temperature dependence in the vacuum energy.Comment: 58 pages, 10 figure
Power-law inflation with a nonminimally coupled scalar field
We consider the dynamics of power-law inflation with a nonminimally coupled
scalar field . It is well known that multiple scalar fields with
exponential potentials lead to an inflationary solution even if the each scalar field is not
capable to sustain inflation. In this paper, we show that inflation can be
assisted even in the one-field case by the effect of nonminimal coupling. When
is positive, since an effective potential which arises by a conformal
transformation becomes flatter compared with the case of for ,
we have an inflationary solution even when the universe evolves as
non-inflationary in the minimally coupled case. For the negative , the
assisted inflation can take place when evolves in the region of
\.Comment: 12 pages, 6 figures, to appear in Phys. Rev.
Infrared behaviour of the pressure in g\phi^3 theory in 6 dimensions
In an earlier paper Almeida and Frenkel considered the calculation of the
pressure in g\phi^3 theory in 6 dimensions via the Schwinger--Dyson equation.
They found, under certain approximations, that a finite result ensues in the
infrared limit. We find this conclusion to remain true with certain variations
of these approximations, suggesting the finiteness of the result to be fairly
robust.Comment: 6 pages, 4 figures, uses revtex
Interaction of Low - Energy Induced Gravity with Quantized Matter -- II. Temperature effects
At the very early Universe the matter fields are described by the GUT models
in curved space-time. At high energies these fields are asymptotically free and
conformally coupled to external metric. The only possible quantum effect is the
appearance of the conformal anomaly, which leads to the propagation of the new
degree of freedom - conformal factor. Simultaneously with the expansion of the
Universe, the scale of energies decreases and the propagating conformal factor
starts to interact with the Higgs field due to the violation of conformal
invariance in the matter fields sector. In a previous paper \cite{foo} we have
shown that this interaction can lead to special physical effects like the
renormalization group flow, which ends in some fixed point. Furthermore in the
vicinity of this fixed point there occur the first order phase transitions. In
the present paper we consider the same theory of conformal factor coupled to
Higgs field and incorporate the temperature effects. We reduce the complicated
higher-derivative operator to several ones of the standard second-derivative
form and calculate an exact effective potential with temperature on the anti de
Sitter (AdS) background.Comment: 12 pages, LaTex - 2 Figure
DEFROST: A New Code for Simulating Preheating after Inflation
At the end of inflation, dynamical instability can rapidly deposit the energy
of homogeneous cold inflaton into excitations of other fields. This process,
known as preheating, is rather violent, inhomogeneous and non-linear, and has
to be studied numerically. This paper presents a new code for simulating scalar
field dynamics in expanding universe written for that purpose. Compared to
available alternatives, it significantly improves both the speed and the
accuracy of calculations, and is fully instrumented for 3D visualization. We
reproduce previously published results on preheating in simple chaotic
inflation models, and further investigate non-linear dynamics of the inflaton
decay. Surprisingly, we find that the fields do not want to thermalize quite
the way one would think. Instead of directly reaching equilibrium, the
evolution appears to be stuck in a rather simple but quite inhomogeneous state.
In particular, one-point distribution function of total energy density appears
to be universal among various two-field preheating models, and is exceedingly
well described by a lognormal distribution. It is tempting to attribute this
state to scalar field turbulence.Comment: RevTeX 4.0; 16 pages, 9 figure
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