93 research outputs found
Nonlinear superhorizon perturbations of non-canonical scalar field
We develop a theory of non-linear cosmological perturbations at superhorizon
scales for a scalar field with a Lagrangian of the form , where
and is the scalar field. We
employ the ADM formalism and the spatial gradient expansion approach to obtain
general solutions valid up to the second order in the gradient expansion. This
formulation can be applied to, for example, DBI inflation models to investigate
superhorizon evolution of non-Gaussianities. With slight modification, we also
obtain general solutions valid up to the same order for a perfect fluid with a
general equation of state .Comment: 14 page
Conditions for large non-Gaussianity in two-field slow-roll inflation
We study the level of primordial non-Gaussianity in slow-roll two-field
inflation. Using an analytic formula for the nonlinear parameter f_nl in the
case of a sum or product separable potential, we find that it is possible to
generate significant non-Gaussianity even during slow-roll inflation with
Gaussian perturbations at Hubble exit. In this paper we give the general
conditions to obtain large non-Gaussianity and calculate the level of
fine-tuning required to obtain this. We present explicit models in which the
non-Gaussianity at the end of inflation can exceed the current observational
bound of |f_nl|<100.Comment: 16 pages, 6 figures, 1 table, v2: typos corrected and references
added, matches version accepted by JCA
Cosmological constraints on extended Galileon models
The extended Galileon models possess tracker solutions with de Sitter
attractors along which the dark energy equation of state is constant during the
matter-dominated epoch, i.e. w_DE = -1-s, where s is a positive constant. Even
with this phantom equation of state there are viable parameter spaces in which
the ghosts and Laplacian instabilities are absent. Using the observational data
of the supernovae type Ia, the cosmic microwave background (CMB), and baryon
acoustic oscillations, we place constraints on the tracker solutions at the
background level and find that the parameter s is constrained to be s=0.034
(-0.034,+0.327) (95% CL) in the flat Universe. In order to break the degeneracy
between the models we also study the evolution of cosmological density
perturbations relevant to the large-scale structure (LSS) and the
Integrated-Sachs-Wolfe (ISW) effect in CMB. We show that, depending on the
model parameters, the LSS and the ISW effect is either positively or negatively
correlated. It is then possible to constrain viable parameter spaces further
from the observational data of the ISW-LSS cross-correlation as well as from
the matter power spectrum.Comment: 17 pages, 9 figures, uses RevTeX4-
Constraints on generating the primordial curvature perturbation and non-Gaussianity from instant preheating
We analyse models of inflation in which isocurvature perturbations present
during inflation are converted into the primordial curvature perturbation
during instant preheating. This can be due to an asymmetry between the fields
present either during inflation or during preheating. We consider all the
constraints that the model must satisfy in order to be theoretically valid and
to satisfy observations. We show that the constraints are very tight in all of
the models proposed and special initial conditions are required for the models
to work. In the case where the symmetry is strongly broken during inflation the
non-Gaussianity parameter f_NL is generally large and negative.Comment: 13 pages, 2 figures, v2: notation clarified, Refs added, typo in (21)
corrected, matches version accepted for publication in JCA
Potential-driven Galileon inflation
For the models of inflation driven by the potential energy of an inflaton
field , the covariant Galileon Lagrangian
generally works to slow down the evolution of the field. On the other hand, if
the Galileon self-interaction is dominant relative to the standard kinetic
term, we show that there is no oscillatory regime of inflaton after the end of
inflation. This is typically accompanied by the appearance of the negative
propagation speed squared of a scalar mode, which leads to the
instability of small-scale perturbations. For chaotic inflation and natural
inflation we clarify the parameter space in which inflaton oscillates
coherently during reheating. Using the WMAP constraints of the scalar spectral
index and the tensor-to-scalar ratio as well, we find that the self coupling
of the potential is constrained to be very
much smaller than 1 and that the symmetry breaking scale of natural
inflation cannot be less than the reduced Planck mass . We also
show that, in the presence of other covariant Galileon Lagrangians, there are
some cases in which inflaton oscillates coherently even for the self coupling
of the order of 0.1, but still the instability associated with
negative is generally present.Comment: 22 pages, 15 figure
Evolution of fNL to the adiabatic limit
We study inflationary perturbations in multiple-field models, for which zeta
typically evolves until all isocurvature modes decay--the "adiabatic limit". We
use numerical methods to explore the sensitivity of the nonlinear parameter fNL
to the process by which this limit is achieved, finding an appreciable
dependence on model-specific data such as the time at which slow-roll breaks
down or the timescale of reheating. In models with a sum-separable potential
where the isocurvature modes decay before the end of the slow-roll phase we
give an analytic criterion for the asymptotic value of fNL to be large. Other
examples can be constructed using a waterfall field to terminate inflation
while fNL is transiently large, caused by descent from a ridge or convergence
into a valley. We show that these two types of evolution are distinguished by
the sign of the bispectrum, and give approximate expressions for the peak fNL.Comment: v1: 25 pages, plus Appendix and bibliography, 6 figures. v2: minor
edits to match published version in JCA
The Imperfect Fluid behind Kinetic Gravity Braiding
We present a standard hydrodynamical description for non-canonical scalar
field theories with kinetic gravity braiding. In particular, this picture
applies to the simplest galileons and k-essence. The fluid variables not only
have a clear physical meaning but also drastically simplify the analysis of the
system. The fluid carries charges corresponding to shifts in field space. This
shift-charge current contains a spatial part responsible for diffusion of the
charges. Moreover, in the incompressible limit, the equation of motion becomes
the standard diffusion equation. The fluid is indeed imperfect because the
energy flows neither along the field gradient nor along the shift current. The
fluid has zero vorticity and is not dissipative: there is no entropy
production, the energy-momentum is exactly conserved, the temperature vanishes
and there is no shear viscosity. Still, in an expansion around a perfect fluid
one can identify terms which correct the pressure in the manner of bulk
viscosity. We close by formulating the non-trivial conditions for the
thermodynamic equilibrium of this imperfect fluid.Comment: 23 pages plus appendices. New version includes extended discussion on
diffusion and dynamics in alternative frames, as well as additional
references. v3 reflects version accepted for publication in JHEP: minor
comments added regarding suitability to numerical approache
Primordial fluctuations and non-Gaussianities from multifield DBI Galileon inflation
We study a cosmological scenario in which the DBI action governing the motion
of a D3-brane in a higher-dimensional spacetime is supplemented with an induced
gravity term. The latter reduces to the quartic Galileon Lagrangian when the
motion of the brane is non-relativistic and we show that it tends to violate
the null energy condition and to render cosmological fluctuations ghosts. There
nonetheless exists an interesting parameter space in which a stable phase of
quasi-exponential expansion can be achieved while the induced gravity leaves
non trivial imprints. We derive the exact second-order action governing the
dynamics of linear perturbations and we show that it can be simply understood
through a bimetric perspective. In the relativistic regime, we also calculate
the dominant contribution to the primordial bispectrum and demonstrate that
large non-Gaussianities of orthogonal shape can be generated, for the first
time in a concrete model. More generally, we find that the sign and the shape
of the bispectrum offer powerful diagnostics of the precise strength of the
induced gravity.Comment: 34 pages including 9 figures, plus appendices and bibliography.
Wordings changed and references added; matches version published in JCA
Monocytes and neutrophils expressing myeloperoxidase occur in fibrous caps and thrombi in unstable coronary plaques
<p>Abstract</p> <p>Background</p> <p>Myeloperoxidase (MPO) -containing macrophages and neutrophils have been described at sites of plaque rupture. The presence of these cells in precursor lesions to acute rupture (thin cap atheroma, or vulnerable plaque) and within thrombi adjacent to ruptures has not been described, nor an association with iron-containing macrophages within unstable plaques.</p> <p>Methods</p> <p>We studied 61 acute ruptures, 15 organizing ruptures, 31 thin cap fibroatheromas, and 28 fibroatheromas from 72 sudden coronary death victims by immunohistochemical and histochemical techniques. Inflammatory cells were typed with anti-CD68 (macrophages), anti-BP-30 (neutrophil bactericidal glycoprotein), and anti-MPO. Iron was localized by Mallory's Prussian blue stain. In selected plaques alpha smooth muscle actin (DAKO, Carpinteria, CA, clone M0851) was performed.</p> <p>Results</p> <p>MPO positive cells were present in 79% of ruptured caps, 28% of thin cap fibroatheroma, and no fibroatheromas; neutrophils were present in 72% of ruptures, 8% of thin cap fibroatheromas, and no fibroatheromas. Iron containing foam cells were present in the caps of 93% of acute ruptures, of 85% of organizing ruptures, 20% of thin cap atheromas, and 10% of fibroatheromas. MPO positive cells were more frequent in occlusive than non-occlusive thrombi adjacent to ruptures (p = .006) and were more numerous in diabetics compared to non-diabetics (p = .002)</p> <p>Conclusion</p> <p>Unstable fibrous caps are more likely to contain MPO-positive cells, neutrophils, and iron-containing macrophages than fibrous caps of stable fibroatheromas. MPO-positive cells in thrombi adjacent to disrupted plaques are associated with occlusive thrombi and are more numerous in diabetic patients.</p
Spectral Index and Non-Gaussianity in Supersymmetric Hybrid Inflation
We consider a supersymmetric hybrid inflation model with two inflaton fields.
The superpotential during inflation is dominated by W=(\kappa S+\kappa' S')M^2,
where S, S' are inflatons carrying the same U(1)_R charge, \kappa, \kappa' are
dimensionless couplings, and M (\sim 10^{15-16} GeV) is a dimensionful
parameter associated with a symmetry breaking scale. One light mass eigenstate
drives inflation, while the other heavier mass eigenstate is stuck to the
origin. The smallness of the lighter inflaton mass for the scalar spectral
index n_s\approx 0.96, which is the center value of WMAP7, can be controlled by
the ratio \kappa'/\kappa through the supergravity corrections. We also discuss
the possibility of the two field inflation and large non-Gaussianity in this
setup.Comment: 17 pages, 2 figures, version published in Eur. Phys. J.
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