34,706 research outputs found
Minimal cut-off vacuum state constraints from CMB bispectrum statistics
In this short note we translate the best available observational bounds on
the CMB bispectrum amplitudes into constraints on a specific scale-invariant
New Physics Hypersurface (NPH) model of vacuum state modifications, as first
proposed by Danielsson, in general models of single-field inflation. As
compared to the power spectrum the bispectrum constraints are less ambiguous
and provide an interesting upper bound on the cut-off scale in general models
of single-field inflation with a small speed of sound. This upper bound is
incompatible with the power spectrum constraint for most of the parameter
domain, leaving very little room for minimal cut-off vacuum state modifications
in general single-field models with a small speed of sound.Comment: 9 pages, 1 figur
Relativistic Dissipative Hydrodynamic Equations at the Second Order for Multi-Component Systems with Multiple Conserved Currents
We derive the second order hydrodynamic equations for the relativistic system
of multi-components with multiple conserved currents by generalizing the
Israel-Stewart theory and Grad's moment method. We find that, in addition to
the conventional moment equations, extra moment equations associated with
conserved currents should be introduced to consistently match the number of
equations with that of unknowns and to satisfy the Onsager reciprocal
relations. Consistent expansion of the entropy current leads to constitutive
equations which involve the terms not appearing in the original Israel-Stewart
theory even in the single component limit. We also find several terms which
exhibit thermal diffusion such as Soret and Dufour effects. We finally compare
our results with those of other existing formalisms.Comment: 18 pages, no figures; title changed, to appear in Nucl. Phys.
The unification of inflation and late-time acceleration in the frame of -essence
By using the formulation of the reconstruction, we explicitly construct
models of -essence, which unify the inflation in the early universe and the
late accelerating expansion of the present universe by a single scalar field.
Due to the higher derivative terms, the solution describing the unification can
be stable in the space of solutions, which makes the restriction for the
initial condition relaxed. The higher derivative terms also eliminate tachyon.
Therefore we can construct a model describing the time development, which
cannot be realized by a usual inflaton or quintessence models of the canonical
scalar field due to the instability or the existence of tachyon. We also
propose a mechanism of the reheating by the quantum effects coming from the
variation of the energy density of the scalar field.Comment: LaTeX, 13 pages, 10 figure
Energy Density in Expanding Universes as Seen by Unruh's Detector
We consider the response of an Unruh detector to scalar fields in an
expanding space-time. When combining transition elements of the scalar field
Hamiltonian with the interaction operator of detector and field, one finds at
second order in time-dependent perturbation theory a transition amplitude,
which actually dominates in the ultraviolet over the first order contribution.
In particular, the detector response faithfully reproduces the particle number
implied by the stress-energy of a minimally coupled scalar field, which is
inversely proportional to the energy of a scalar mode. This finding disagrees
with the contention that in de Sitter space, the response of the detector drops
exponentially with particle energy and therefore indicates a thermal spectrum.Comment: 15 pages, 1 figur
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