9,923 research outputs found
A new gravitational wave background from the Big Bang
The reheating of the universe after hybrid inflation proceeds through the
nucleation and subsequent collision of large concentrations of energy density
in the form of bubble-like structures moving at relativistic speeds. This
generates a significant fraction of energy in the form of a stochastic
background of gravitational waves, whose time evolution is determined by the
successive stages of reheating: First, tachyonic preheating makes the amplitude
of gravity waves grow exponentially fast. Second, bubble collisions add a new
burst of gravitational radiation. Third, turbulent motions finally sets the end
of gravitational waves production. From then on, these waves propagate
unimpeded to us. We find that the fraction of energy density today in these
primordial gravitational waves could be significant for GUT scale models of
inflation, although well beyond the frequency range sensitivity of
gravitational wave observatories like LIGO, LISA or BBO. However, low-scale
models could still produce a detectable signal at frequencies accessible to BBO
or DECIGO. For comparison, we have also computed the analogous background from
some chaotic inflation models and obtained similar results to those of other
groups. The discovery of such a background would open a new observational
window into the very early universe, where the details of the process of
reheating could be explored. Thus, it could also serve as a new experimental
tool for testing the Inflationary Paradigm.Comment: 20 pages, 8 figures, to appear in the Proceedings of JGRG17, Nagoya
(Japan), 3-7 December 200
The Decay of the Standard Model Higgs after Inflation
We study the nonperturbative dynamics of the Standard Model (SM) after
inflation, in the regime where the SM is decoupled from (or weakly coupled to)
the inflationary sector. We use classical lattice simulations in an expanding
box in (3+1) dimensions, modeling the SM gauge interactions with both global
and Abelian-Higgs analogue scenarios. We consider different post-inflationary
expansion rates. During inflation, the Higgs forms a condensate, which starts
oscillating soon after inflation ends. Via nonperturbative effects, the
oscillations lead to a fast decay of the Higgs into the SM species,
transferring most of the energy into and bosons. All species are
initially excited far away from equilibrium, but their interactions lead them
into a stationary stage, with exact equipartition among the different energy
components. From there on the system eventually reaches equilibrium. We have
characterized in detail, in the different expansion histories considered, the
evolution of the Higgs and of its dominant decay products, until equipartition
is established. We provide a useful mapping between simulations with different
parameters, from where we derive a master formula for the Higgs decay time, as
a function of the coupling constants, Higgs initial amplitude and
postinflationary expansion rate.Comment: Minor changes to match the PRD published version. Modulation of the
Higgs amplitude removed for in Sec. V, due to improving the time
resolution in the Higgs equation of motion. Results unaffecte
Gravitational wave production from the decay of the Standard Model Higgs field after inflation
During or towards the end of inflation, the Standard Model (SM) Higgs forms a
condensate with a large amplitude. Following inflation, the condensate
oscillates, decaying non-perturbatively into the rest of the SM species. The
resulting out-of-equilibrium dynamics converts a fraction of the energy
available into gravitational waves (GW). We study this process using classical
lattice simulations in an expanding box, following the energetically dominant
electroweak gauge bosons and . We characterize the GW spectrum as a
function of the running couplings, Higgs initial amplitude, and
post-inflationary expansion rate. As long as the SM is decoupled from the
inflationary sector, the generation of this background is universally expected,
independently of the nature of inflation. Our study demonstrates the efficiency
of GW emission by gauge fields undergoing parametric resonance. The initial
energy of the Higgs condensate represents however, only a tiny fraction of the
inflationary energy. Consequently, the resulting background is very suppressed,
with an amplitude today. The
amplitude can be boosted to , if
following inflation the universe undergoes a kination-domination stage; however
the background is shifted in this case to high frequencies . In all cases the signal is out of the range of current or
planned GW detectors. This background will therefore remain, most likely, as a
curiosity of the SM.Comment: 16 pages, 6 figures. Minor changes to match version published in PR
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Affective Suffixes in Spanish: evidence for morphological generalizations
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
Characterization of TrxC, an Atypical Thioredoxin Exclusively Present in Cyanobacteria
Cyanobacteria form a diverse group of oxygenic photosynthetic prokaryotes considered to be the antecessor of plant chloroplast. They contain four different thioredoxins isoforms, three of them corresponding to m, x and y type present in plant chloroplast, while the fourth one (named TrxC) is exclusively found in cyanobacteria. TrxC has a modified active site (WCGLC) instead of the canonical (WCGPC) present in most thioredoxins. We have purified it and assayed its activity but surprisingly TrxC lacked all the classical activities, such as insulin precipitation or activation of the fructose-1,6-bisphosphatase. Mutants lacking trxC or over-expressing it were generated in the model cyanobacterium Synechocystis sp. PCC 6803 and their phenotypes have been analyzed. The ΔtrxC mutant grew at similar rates to WT in all conditions tested although it showed an increased carotenoid content especially under low carbon conditions. Overexpression strains showed reduced growth under the same conditions and accumulated lower amounts of carotenoids. They also showed lower oxygen evolution rates at high light but higher Fv’/Fm’ and Non-photochemical-quenching (NPQ) in dark adapted cells, suggesting a more oxidized plastoquinone pool. All these data suggest that TrxC might have a role in regulating photosynthetic adaptation to low carbon and/or high light conditions.España, MINECO BIO2016-75634-PJunta de Andalucía P12-BIO-1119 , BIO-28
Cosmic Microwave Background temperature and polarization anisotropies from the large-N limit of global defects
We determine the full C_l spectra and correlation functions of the
temperature and polarization anisotropies in the CMB, generated by a source
modeled by the large N limit of spontaneously broken global O(N)-theories. We
point out a problem in the standard approach of treating the radiation-matter
transition by interpolating the eigenvectors of the unequal-time correlators of
the source energy-momentum tensor. This affects the CMB predictions from all
type of cosmic defects. We propose a method to overcome this difficulty, and
find that in the large-N global model that we study, differences in the final
CMB power spectra amplitudes reach up to 25%, when compared to implementations
of the eigenvector interpolation technique. We discuss as well how to optimally
search for the contribution in the CMB from active sources such as cosmic
defects, in experiments like Planck, COrE and PRISM.Comment: 16+4 pages, 13 figures (Version 2: minor changes to match published
version in PRD
The local B-polarization of the CMB: a very sensitive probe of cosmic defects
We present a new and especially powerful signature of cosmic strings and
other topological or non-topological defects in the polarization of the cosmic
microwave background (CMB). We show that even if defects contribute 1% or less
in the CMB temperature anisotropy spectrum, their signature in the local
-polarization correlation function at angular scales of tens of arc
minutes is much larger than that due to gravitational waves from inflation,
even if the latter contribute with a ratio as big as to the
temperature anisotropies. We show that when going from non-local to local
-polarization, the ratio of the defect signal-to-noise with respect
to the inflationary value increases by about an order of magnitude. Proposed
B-polarization experiments, with a good sensitivity on arcminute scales, may
either detect a contribution from topological defects produced after inflation
or place stringent limits on them. Even Planck should be able to improve
present constraints on defect models by at least an order of magnitude, to the
level of \ep <10^{-7}. A future full-sky experiment like CMBpol, with
polarization sensitivities of the order of K-arcmin, will be able to
constrain the defect parameter \ep=Gv^2 to a few , depending
on the defect model.Comment: Version Published in Physics Letters
Aplidin (plitidepsin) is a novel anti-myeloma agent with potent anti-resorptive activity mediated by direct effects on osteoclasts
Despite recent progress in its treatment, Multiple Myeloma (MM) remains incurable and its associated bone disease persists even after complete remission. Thus, identification of new therapeutic agents that simultaneously suppress MM growth and protect bone is an unmet need. Herein, we examined the effects of Aplidin, a novel anti-cancer marine-derived compound, on MM and bone cells. In vitro, Aplidin potently inhibited MM cell growth and induced apoptosis, effects that were enhanced by dexamethasone (Dex) and bortezomib (Btz). Aplidin modestly reduced osteocyte/osteoblast viability and decreased osteoblast mineralization, effects that were enhanced by Dex and partially prevented by Btz. Further, Aplidin markedly decreased osteoclast precursor numbers and differentiation, and reduced mature osteoclast number and resorption activity. Moreover, Aplidin reduced Dex-induced osteoclast differentiation and further decreased osteoclast number when combined with Btz. Lastly, Aplidin alone, or suboptimal doses of Aplidin combined with Dex or Btz, decreased tumor growth and bone resorption in ex vivo bone organ cultures that reproduce the 3D-organization and the cellular diversity of the MM/bone marrow niche. These results demonstrate that Aplidin has potent anti-myeloma and anti-resorptive properties, and enhances proteasome inhibitors blockade of MM growth and bone destruction
The Galactic Center as a point source of neutrons at EeV energies
The central region of our Galaxy is a very peculiar environment, containing
magnetic fields in excess of 100 mG and gas densities reaching ~ 10^4cm^-3.
This region was observed as a strong source of GeV and TeVs gammas, what
suggests that a mechanism of proton-neutron conversion could be taking place
therein. We propose that the Galactic Center must also be a source of EeV
neutrons due to the conversion of ultra high energy cosmic ray protons into
neutrons via p-p interactions inside this region. This scenario should be
falsifiable by the Pierre Auger Observatory after a few years of full exposure
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