344 research outputs found
Spinflation
We study the cosmological implications of including angular motion in the DBI
brane inflation scenario. The non-canonical kinetic terms of the
Dirac-Born-Infeld action give an interesting alternative to slow roll
inflation, and cycling branes can drive periods of accelerated expansion in the
Universe. We present explicit numerical solutions demonstrating brane inflation
in the Klebanov-Strassler throat. We find that demanding sufficient inflation
takes place in the throat is in conflict with keeping the brane's total energy
low enough so that local gravitational backreaction on the Calabi-Yau manifold
can be safely ignored. We deduce that spinflation (brane inflation with angular
momentum) can ease this tension by providing extra e-foldings at the start of
inflation. Cosmological expansion rapidly damps the angular momentum causing an
exit to a more conventional brane inflation scenario. Finally, we set up a
general framework for cosmological perturbation theory in this scenario, where
we have multi-field non-standard kinetic term inflation.Comment: 29 pages, 6 figures, minor changes, typos fixed, to appear in JCA
Tgfbi/Bigh3 silencing activates ERK in mouse retina.
BIGH3 is a secreted protein, part of the extracellular matrix where it interacts with collagen and integrins on the cell surface. BIGH3 can play opposing roles in cancer, acting as either tumor suppressor or promoter, and its mutations lead to different forms of corneal dystrophy. Although many studies have been carried out, little is known about the physiological role of BIGH3. Using the cre-loxP system, we generated a mouse model with disruption of the Bigh3 genomic locus. Bigh3 silencing did not result in any apparent phenotype modifications, the mice remained viable and fertile. We were able to determine the presence of BIGH3 in the retinal pigment epithelium (RPE). In the absence of BIGH3, a transient decrease in the apoptotic process involved in retina maturation was observed, leading to a transient increase in the INL thickness at P15. This phenomenon was accompanied by an increased activity of the pro-survival ERK pathway
Cosmic acceleration from Abelian symmetry breaking
We discuss a consistent theory for a self-interacting vector field, breaking an Abelian symmetry in such a way to obtain an interesting behavior for its longitudinal polarization. In an appropriate decoupling limit, the dynamics of the longitudinal mode is controlled by Galileon interactions. The full theory away from the decoupling limit does not propagate ghost modes, and can be investigated in regimes where non-linearities become important. When coupled to gravity, this theory provides a candidate for dark energy, since it admits de Sitter cosmological solutions characterized by a technically natural value for the Hubble parameter. We also consider the homogeneous evolution when, besides the vector, additional matter in the form of perfect fluids is included. We find that the vector can have an important role in characterizing the universe expansion
Characterizing the cosmological gravitational wave background: Anisotropies and non-Gaussianity
A future detection of the stochastic gravitational wave background (SGWB) with gravitational wave (GW) experiments is expected to open a new window on early universe cosmology and on the astrophysics of compact objects. In this paper we study SGWB anisotropies, that can offer new tools to discriminate between different sources of GWs. In particular, the cosmological SGWB inherits its anisotropies both (i) at its production and (ii) during its propagation through our perturbed universe. Concerning (i), we show that it typically leads to anisotropies with order one dependence on frequency. We then compute the effect of (ii) through a Boltzmann approach, including contributions of both large-scale scalar and tensor linearized perturbations. We also compute for the first time the three-point function of the SGWB energy density, which can allow one to extract information on GW non-Gaussianity with interferometers. Finally, we include nonlinear effects associated with long wavelength scalar fluctuations, and compute the squeezed limit of the 3-point function for the SGWB density contrast. Such limit satisfies a consistency relation, conceptually similar to that found in the literature for the case of cosmic microwave background perturbations
Multimessenger Cosmology: correlating CMB and SGWB measurements
Characterizing the physical properties of the stochastic gravitational waves
background (SGWB) is a key step towards identifying the nature of its possible
origin. We focus our analysis on SGWB anisotropies. The existence of a
non-trivial primordial scalar-tensor-tensor (STT) correlation in the squeezed
configuration may be inferred from the effect that a long wavelength scalar
mode has on the gravitational wave power spectrum: an anisotropic contribution.
Crucially, such contribution is correlated with temperature anisotropies in the
cosmic microwave background (CMB). We show that, for inflationary models that
generate suitably large STT non-Gaussianities, cross-correlating the CMB with
the stochastic background of gravitational waves is a very effective probe of
early universe physics. The resulting signal can be a smoking-gun for
primordial SGWB anisotropies.Comment: 5 pages, 2 figure
Cosmology in massive gravity
We argue that more cosmological solutions in massive gravity can be obtained
if the metric tensor and the tensor defined by
St\"{u}ckelberg fields take the homogeneous and isotropic form. The standard
cosmology with matter and radiation dominations in the past can be recovered
and CDM model is easily obtained. The dynamical evolution of the
universe is modified at very early times.Comment: 4 pages, 1 figure,add more reference
A non-Gaussian landscape
Primordial perturbations with wavelengths greater than the observable universe shift the effective background fields in our observable patch from their global averages over the inflating space. This leads to a landscape picture where the properties of our observable patch depend on its location and may significantly differ from the expectation values predicted by the underlying fundamental inflationary model. We show that if multiple fields are present during inflation, this may happen even if our horizon exit would be preceded by only a few e-foldings of inflation. Non-Gaussian statistics are especially affected: for example models of local non-Gaussianity predicting |f_NL|>> 10 over the entire inflating volume can have a probability up to a few tens of percent to generate a non-detectable bispectrum in our observable patch |fNL^{obs.}|<10. In this work we establish systematic connections between the observable local properties of primordial perturbations and the global properties of the inflating space which reflect the underlying high energy physics. We study in detail the implications of both a detection and non-detection of primordial non-Gaussianity by Planck, and discover novel ways of characterising the naturalness of different observational configurations
Anisotropic Friedmann-Robertson-Walker universe from nonlinear massive gravity
In the scope of the nonlinear massive gravity, we study fixed points of
evolution equations for a Bianchi type--I universe. We find a new attractor
solution with non-vanishing anisotropy, on which the physical metric is
isotropic but the Stuckelberg configuration is anisotropic. As a result, at the
background level, the solution describes a homogeneous and isotropic universe,
while a statistical anisotropy is expected from perturbations, suppressed by
smallness of the graviton mass.Comment: 4 pages, 1 figure, REVTeX4; V2 with minor revison, and to appear on
PL
Anisotropies and non-Gaussianity of the cosmological gravitational wave background
The stochastic gravitational wave background (SGWB) is expected to be a key observable for gravitational wave (GW) interferometry. Its detection will open a new window to early Universe cosmology and to the astrophysics of compact objects. Using a Boltzmann approach, we study the angular anisotropies of the GW energy density, which is an important tool to disentangle the different cosmological and astrophysical contributions to the SGWB. Anisotropies in the cosmological background are imprinted both at its production and by GW propagation through the large-scale scalar and tensor perturbations of the Universe. The first contribution is not present in the cosmic microwave background radiation (as the Universe is not transparent to photons before recombination), causing an order 1 dependence of the anisotropies on frequency. Moreover, we provide a new method to characterize the cosmological SGWB through its possible deviation from Gaussian statistics. In particular, the SGWB will become a new probe of the primordial non-Gaussianity of the large-scale cosmological perturbations
Gravitational wave anisotropies from primordial black holes
An observable stochastic background of gravitational waves is generated whenever primordial black holes are created in the early universe thanks to a small-scale enhancement of the curvature perturbation. We calculate the anisotropies and non-Gaussianity of such stochastic gravitational waves background which receive two contributions, the first at formation time and the second due to propagation effects. The former contribution can be generated if the distribution of the curvature perturbation is characterized by a local and scale-invariant shape of non-Gaussianity. Under such an assumption, we conclude that a sizeable magnitude of anisotropy and non-Gaussianity in the gravitational waves would suggest that primordial black holes may not comply the totality of the dark matter.An observable stochastic background of gravitational waves is generated whenever primordial black holes are created in the early universe thanks to a small-scale enhancement of the curvature perturbation. We calculate the anisotropies and non-Gaussianity of such stochastic gravitational waves background which receive two contributions, the first at formation time and the second due to propagation effects. The former contribution can be generated if the distribution of the curvature perturbation is characterized by a local and scale-invariant shape of non-Gaussianity. Under such an assumption, we conclude that a sizeable magnitude of anisotropy and non-Gaussianity in the gravitational waves would suggest that primordial black holes may not comply the totality of the dark matter
- âŠ