9,206 research outputs found
General Relativity as an Attractor in Scalar-Tensor Stochastic Inflation
Quantum fluctuations of scalar fields during inflation could determine the
very large-scale structure of the universe. In the case of general
scalar-tensor gravity theories these fluctuations lead to the diffusion of
fundamental constants like the Planck mass and the effective Brans--Dicke
parameter, . In the particular case of Brans--Dicke gravity, where
is constant, this leads to runaway solutions with infinitely large
values of the Planck mass. However, in a theory with variable we find
stationary probability distributions with a finite value of the Planck mass
peaked at exponentially large values of after inflation. We conclude
that general relativity is an attractor during the quantum diffusion of the
fields.Comment: LaTeX (with RevTex) 11 pages, 2 uuencoded figures appended, also
available on WWW via http://star.maps.susx.ac.uk/index.htm
False Vacuum Decay after Inflation
Inflation is terminated by a non-equilibrium process which finally leads to a
thermal state. We study the onset of this transition in a class of hybrid
inflation models. The exponential growth of tachyonic modes leads to
decoherence and spinodal decomposition. We compute the decoherence time, the
spinodal time, the size of the formed domains and the homogeneous classical
fields within a single domain.Comment: Latex2e, 11 pages, 4 figure
Hybrid Inflation Exit through Tunneling
For hybrid inflationary potentials, we derive the tunneling rate from field
configurations along the flat direction towards the waterfall regime. This
process competes with the classically rolling evolution of the scalar fields
and needs to be strongly subdominant for phenomenologically viable models.
Tunneling may exclude models with a mass scale below 10^12 GeV, but can be
suppressed by small values of the coupling constants. We find that tunneling is
negligible for those models, which do not require fine tuning in order to
cancel radiative corrections, in particular for GUT-scale SUSY inflation. In
contrast, electroweak scale hybrid inflation is not viable, unless the
inflaton-waterfall field coupling is smaller than approximately 10^-11.Comment: 17 pages, 2 figure
Prevention of glucocorticoid induced-apoptosis of osteoblasts and osteocytes by protecting against endoplasmic reticulum (ER) stress
poster abstractIncreased oxidative stress, such as with excess of glucocorticoids (GC) or during aging, has been associated with endoplasmic reticulum (ER) stress, due to accumulation of misfolded or unfolded proteins, leading to cellular apoptosis. The double-stranded RNA-activated protein kinase-like ER kinase (PERK) is activated to alleviate ER stress and phosphorylates the eukaryotic translation initiation factor 2 alpha subunit (eIF2α). Phosphorylated eIF2α in turn inhibits global protein translation to provide time to the ER to recover from the unfolded protein load, promoting cell viability. We hypothesized that the pro-apoptotic effect of GC on osteoblasts and osteocytes are at least in part due to induction of ER stress. To test this hypothesis, we used MLO-Y4 osteocytic cells, OB-6 osteoblastic cells, and primary osteoblastic cells derived from neonatal murine calvaria. We found that the synthetic GC dexamethasone (DEX) significantly increased the percentage of apoptotic cells in cultures of MLO-Y4, OB-6, and primary osteoblastic cells. Similarly, the specific ER-stress inducing agents brefeldin A, an inhibitor of ER-golgi apparatus vesicle transport, and tunicamycin, a protein glycosylation inhibitor, significantly increased OB-6 cell apoptosis. We then tested the effect of salubrinal, an agent that protects against ER stress by inhibiting the dephosphorylation of eIF2α, on bone cell apoptosis. Salubrinal blocked apoptosis induced by the ER stressors brefeldin A and tunicamycin in OB-6 cells. Salubrinal was also effective in blocking apoptosis induced by DEX in MLO-Y4, OB-6 and primary osteoblastic cells. Optimal responses were found at 10 μM salubrinal, after either 6 or 24 h. Guanabenz, another inhibitor of eIF2α dephosphorylation, also blocked DEX and tunicamycin-induced apoptosis of primary osteoblastic cells. Furthermore, addition of DEX to mineralizing OB-6 or primary osteoblastic cells markedly decreased mineral deposition and hydroxyapatite formation. In contrast, treatment with guanabenz increased mineralization of OB-6 cell cultures and prevented the inhibitory effect of DEX. We conclude that part of the pro-apoptotic actions of GC on osteoblastic cells are mediated through ER stress and that interventions that prevent dephosphorylation of eIF2α could potentially prevent the deleterious effects of GC on bone
The evolution of AGN activity in brightest cluster galaxies
Artículo escrito por un elevado número de autores, solo se referencian el que aparece en primer lugar, el nombre del grupo de colaboración, si le hubiere, y los autores pertenecientes a la UAMWe present the results of an analysis of Wide-field Infrared Survey Explorer (WISE) observations of the full 2500 deg2 South Pole Telescope (SPT)-Sunyaev-Zel'dovich cluster sample. We describe a process for identifying active galactic nuclei (AGN) in brightest cluster galaxies (BCGs) based on WISE mid-IR color and redshift. Applying this technique to the BCGs of the SPT-SZ sample, we calculate the AGN-hosting BCG fraction, which is defined as the fraction of BCGs hosting bright central AGNs over all possible BCGs. Assuming an evolving single-burst stellar population model, we find statistically significant evidence (>99.9%) for a mid-IR excess at high redshift compared to low redshift, suggesting that the fraction of AGN-hosting BCGs increases with redshift over the range of 0 1. Last, this work confirms that the runaway cooling phase, as predicted by the classical cooling-flow model, in the Phoenix cluster is extremely rare and most BCGs have low (relative to Eddington) black hole accretion rate
Coupled Negative magnetocapacitance and magnetic susceptibility in a Kagome staircase-like compound Co3V2O8
The dielectric constant of the Kagome staircase-like Co3V2O8 polycrystalline
compound has been measured as function of temperature and magnetic field up to
14T. It is found that the application of an external magnetic field suppresses
the anomaly for the dielectric constant beyond 6.1K. Furthermore, its magnetic
field dependence reveals a negative magnetocapacitance which is proportional to
the magnetic susceptibility, suggesting a common magnetostrictive origin for
the magnetic field dependence of the two quantities. This result is very
different from that obtained from the isostructural compound Ni3V2O8 that
presents a peak in the dielectric constant at the incommensurate magnetic phase
transition coupled to a sign change of the magnetocapacitance
STATIONARY SOLUTIONS IN BRANS-DICKE STOCHASTIC INFLATIONARY COSMOLOGY
In Brans-Dicke theory the Universe becomes divided after inflation into many
exponentially large domains with different values of the effective
gravitational constant. Such a process can be described by diffusion equations
for the probability of finding a certain value of the inflaton and dilaton
fields in a physical volume of the Universe. For a typical chaotic inflation
potential, the solutions for the probability distribution never become
stationary but grow forever towards larger values of the fields. We show here
that a non-minimal conformal coupling of the inflaton to the curvature scalar,
as well as radiative corrections to the effective potential, may provide a
dynamical cutoff and generate stationary solutions. We also analyze the
possibility of large nonperturbative jumps of the fluctuating inflaton scalar
field, which was recently revealed in the context of the Einstein theory. We
find that in the Brans--Dicke theory the amplitude of such jumps is strongly
suppressed.Comment: 19 pages, LaTe
Direct cell-to-cell interactions between osteocytes and multiple myeloma (MM) cells up-regulate Sost and down-regulate OPG expression in osteocytes: evidence for osteocytic contributions to MM-induced bone disease
poster abstractOsteocytes are the most abundant bone cells, comprising more than 95% of the cells in bone. They are embedded into the bone matrix, but extensively communicate among themselves and with cells on the bone surface and the bone marrow through the osteocytic lacunar-canalicular network. Osteocytes secrete sclerostin, the product of the Sost gene, an antagonist of Wnt signaling that potently inhibits bone formation. Osteocytes are also a major source of pro- and anti-osteoclastogenic cytokines that
regulate osteoclastogenesis and bone resorption, including RANKL and osteoprotegerin (OPG). Recent evidence suggests that the bone remodeling compartment is disrupted in multiple myeloma (MM) allowing close contact of MM cells with bone cells including osteocytes. However, the consequences of these interactions and the contribution of osteocytes to MM bone disease are unclear. Therefore, we determined if interactions between MM cells and osteocytes regulate osteocytic gene expression. We found that co-culture of murine MLO-A5 osteocytic cells with human JJN3 MM cells up-regulated murine Sost mRNA expression 2-3 fold as early as 4h, which remained elevated up to 24h. Consistent with Sost up-regulation induced by MM cells, the expression of OPG, a Wnt target gene, was decreased by 30-50% in MLO-A5 cells, resulting in an increased RANKL/OPG at 4h. Culture of JJN3 cells in the top and MLO-A5 cells in the bottom of Boyden chambers abolished both up-regulation of Sost and down-regulation of OPG mRNA expression in osteocytic cells, demonstrating the requirement of direct contact between MM cells and osteocytic cells. Human Sost and OPG mRNA transcripts were not detected in any of these experiments, demonstrating lack of contribution of MM JJN3 cells. These findings demonstrate that direct interactions between osteocytes and MM cells up-regulate the expression of the bone formation inhibitor Sost in osteocytes, which in turn decreases Wnt signaling, reduces osteocytic OPG expression increasing the RANKL/OPG ratio. We propose that increased Sost/Sclerostin expression contributes to
the exacerbated bone resorption and the decreased bone formation that characterizes MM induced bone disease
Galaxy correlations and the BAO in a void universe: structure formation as a test of the Copernican Principle
A suggested solution to the dark energy problem is the void model, where
accelerated expansion is replaced by Hubble-scale inhomogeneity. In these
models, density perturbations grow on a radially inhomogeneous background. This
large scale inhomogeneity distorts the spherical Baryon Acoustic Oscillation
feature into an ellipsoid which implies that the bump in the galaxy correlation
function occurs at different scales in the radial and transverse correlation
functions. We compute these for the first time, under the approximation that
curvature gradients do not couple the scalar modes to vector and tensor modes.
The radial and transverse correlation functions are very different from those
of the concordance model, even when the models have the same average BAO scale.
This implies that if void models are fine-tuned to satisfy average BAO data,
there is enough extra information in the correlation functions to distinguish a
void model from the concordance model. We expect these new features to remain
when the full perturbation equations are solved, which means that the radial
and transverse galaxy correlation functions can be used as a powerful test of
the Copernican Principle.Comment: 12 pages, 8 figures, matches published versio
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