3,036 research outputs found
Unparticle constraints from SN1987A
The existence of an unparticle sector, weakly coupled to the standard model,
would have a profound impact on supernova (SN) physics. Emission of energy into
the unparticle sector from the core of SN1987A would have significantly
shortened the observed neutrino burst. The unparticle interaction with
nucleons, neutrinos, electrons and muons is constrained to be so weak that it
is unlikely to provide any missing-energy signature at colliders. One important
exception are models where scale invariance in the hidden sector is broken by
the Higgs vacuum expectation value. In this case the SN emission is suppressed
by threshold effects.Comment: 4 pages, 1 figur
Axion hot dark matter bounds after Planck
We use cosmological observations in the post-Planck era to derive limits on
thermally produced cosmological axions. In the early universe such axions
contribute to the radiation density and later to the hot dark matter fraction.
We find an upper limit m_a < 0.67 eV at 95% C.L. after marginalising over the
unknown neutrino masses, using CMB temperature and polarisation data from
Planck and WMAP respectively, the halo matter power spectrum extracted from
SDSS-DR7, and the local Hubble expansion rate H_0 released by the Carnegie
Hubble Program based on a recalibration of the Hubble Space Telescope Key
Project sample. Leaving out the local H_0 measurement relaxes the limit
somewhat to 0.86 eV, while Planck+WMAP alone constrain the axion mass to 1.01
eV, the first time an upper limit on m_a has been obtained from CMB data alone.
Our axion limit is therefore not very sensitive to the tension between the
Planck-inferred H_0 and the locally measured value. This is in contrast with
the upper limit on the neutrino mass sum, which we find here to range from 0.27
eV at 95% C.L. combining all of the aforementioned observations, to 0.84 eV
from CMB data alone.Comment: 20 pages, 8 figures, matches version published in JCAP 1310 (2013)
02
Cosmological axion bounds
We discuss current cosmological constraints on axions, as well as future
sensitivities. Bounds on axion hot dark matter are discussed first, and
subsequently we discuss both current and future sensitivity to models in which
axions play the role as cold dark matter, but where the Peccei-Quinn symmetry
is not restored during reheating.Comment: 4 pages, 2 figures, To appear in the proceedings of 5th Patras
Workshop on Axions, WIMPs and WISPs, Durham 13-17 July 200
Cosmology seeking friendship with sterile neutrinos
Precision cosmology and big-bang nucleosynthesis mildly favor extra radiation
in the universe beyond photons and ordinary neutrinos, lending support to the
existence of low-mass sterile neutrinos. We use the WMAP 7-year data,
small-scale CMB observations from ACBAR, BICEP and QuAD, the SDSS 7th data
release, and measurement of the Hubble parameter from HST observations to
derive credible regions for the assumed common mass scale m_s and effective
number N_s of thermally excited sterile neutrino states. Our results are
compatible with the existence of one or perhaps two sterile neutrinos, as
suggested by LSND and MiniBooNE, if m_s is in the sub-eV range.Comment: 4 pages, 1 figure, matches version published in PR
Future cosmological sensitivity for hot dark matter axions
We study the potential of a future, large-volume photometric survey to
constrain the axion mass in the hot dark matter limit. Future surveys
such as Euclid will have significantly more constraining power than current
observations for hot dark matter. Nonetheless, the lowest accessible axion
masses are limited by the fact that axions lighter than eV decouple
before the QCD epoch, assumed here to occur at a temperature MeV; this leaves an axion population of such low density that its
late-time cosmological impact is negligible. For larger axion masses, eV, where axions remain in equilibrium until after the QCD phase
transition, we find that a Euclid-like survey combined with Planck CMB data can
detect at very high significance. Our conclusions are robust against
assumptions about prior knowledge of the neutrino mass. Given that the proposed
IAXO solar axion search is sensitive to eV, the axion mass
range probed by cosmology is nicely complementary.Comment: 17 pages, 5 figure
On the Validity of the 0-1 Test for Chaos
In this paper, we present a theoretical justification of the 0-1 test for
chaos. In particular, we show that with probability one, the test yields 0 for
periodic and quasiperiodic dynamics, and 1 for sufficiently chaotic dynamics
Collective dynamics in optomechanical arrays
The emerging field of optomechanics seeks to explore the interaction between
nanomechanics and light. Recently, the exciting concept of optomechanical
crystals has been introduced, where defects in photonic crystal structures are
used to generate both localized optical and mechanical modes that interact with
each other. Here we start exploring the collective dynamics of arrays
consisting of many coupled optomechanical cells. We show that such
"optomechanical arrays" can display synchronization and that they can be
described by a modified Kuramoto model that allows to explain and predict most
of the features that will be observable in future experiments.Comment: 6 pages, 5 figure
Coherent Beam-Beam Tune Shift of Unsymmetrical Beam-Beam Interactions with Large Beam-Beam Parameter
Coherent beam-beam tune shift of unsymmetrical beam-beam interactions was
studied experimentally and numerically in HERA where the lepton beam has a very
large beam-beam parameter (up to ). Unlike the symmetrical case of
beam-beam interactions, the ratio of the coherent and incoherent beam-beam tune
shift in this unsymmetrical case of beam-beam interactions was found to
decrease monotonically with increase of the beam-beam parameter. The results of
self-consistent beam-beam simulation, the linearized Vlasov equation, and the
rigid-beam model were compared with the experimental measurement. It was found
that the coherent beam-beam tune shifts measured in the experiment and
calculated in the simulation agree remarkably well but they are much smaller
than those calculated by the linearized Vlasov equation with the single-mode
approximation or the rigid-beam model. The study indicated that the single-mode
approximation in the linearization of Vlasov equation is not valid in the case
of unsymmetrical beam-beam interactions. The rigid-beam model is valid only
with a small beam-beam parameter in the case of unsymmetrical beam-beam
interactions.Comment: 32 pages, 13 figure
Reactive oxygen and nitrogen species in sepsis-induced hepatic microvascular dysfunction
OBJECTIVE AND DESIGN: Hepatic microvascular dysfunction is a critical event in the development of liver failure during sepsis. Activated blood cells and reactive oxygen and nitrogen species (RONS) have been implicated in the pathogenesis of sepsis. METHODS: Intravital-videomicroscopy was used to determine whether RONS contribute to the recruitment of leukocytes/platelets in the hepatic microvasculature during sepsis. Six hours following cecal-ligation and puncture (CLP), disturbances of the hepatic microvasculature were assessed in WT-mice (C57Bl/6 J; n = 8), in mice lacking gp91(phox)(n = 5), overexpressing superoxide-dismutase (SOD, n = 8), in WT-mice treated with a NOS-inhibitor (l-NAME, n = 5), lacking nNOS, eNOS or iNOS (n = 5 each), treated with the NO-donor DetaNO (n = 5), in WT-mice treated with gadolinium-chloride (GdCl(2), n = 5) and compared to a group of WT-mice following a sham operation (n = 8). Six hours post-CLP, the adhesion of leukocytes and platelets in terminal hepatic venules (THV) and sinusoids was quantified. RESULTS: In WT-mice, CLP elicited increases in the number of adherent leukocytes and platelets. Similar responses to CLP were noted in mice overexpressing SOD or lacking either eNOS or gp91(phox). The blood-cell recruitment was significantly blunted in septic iNOS-knockout mice and this response was reversed by pre-treatment with DetaNO. CONCLUSION: These findings suggest that iNOS-derived NO is a determinant of the pro-inflammatory phenotype assumed by the hepatic microvasculature during sepsis
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