612 research outputs found
Probing axion-like particles with the ultraviolet photon polarization from active galactic nuclei in radio galaxies
The mixing of photons with axion-like particles (ALPs) in the large-scale
magnetic field changes the polarization angle of a linearly polarized
photon beam from active galactic nuclei in radio galaxies as it propagates over
cosmological distances. Using available ultraviolet polarization data
concerning these sources we derive a new bound on the product of the photon-ALP
coupling times . We find
GeV nG for ultralight ALPs with eV. We compare
our new bound with the ones present in the literature and we comment about
possible improvements with observations of more sources.Comment: v2: one typo corrected. Added a few comments, matches published
versio
Revisiting cosmological bounds on radiative neutrino lifetime
Neutrino oscillation experiments and direct bounds on absolute masses
constrain neutrino mass differences to fall into the microwave energy range,
for most of the allowed parameter space. As a consequence of these recent
phenomenological advances, older constraints on radiative neutrino decays based
on diffuse background radiations and assuming strongly hierarchical masses in
the eV range are now outdated. We thus derive new bounds on the radiative
neutrino lifetime using the high precision cosmic microwave background spectral
data collected by the Far Infrared Absolute Spectrophotometer instrument on
board of Cosmic Background Explorer. The lower bound on the lifetime is between
a few x 10^19 s and 5 x 10^20 s, depending on the neutrino mass ordering and on
the absolute mass scale. However, due to phase space limitations, the upper
bound in terms of the effective magnetic moment mediating the decay is not
better than ~ 10^-8 Bohr magnetons. We also comment about possible improvements
of these limits, by means of recent diffuse infrared photon background data. We
compare these bounds with pre-existing limits coming from laboratory or
astrophysical arguments. We emphasize the complementarity of our results with
others available in the literature.Comment: 7 pages, 3 figures. Minor changes in the text, few references added.
Matches the published versio
Conversion of TeV photons in realistic extragalactic magnetic field
13th Patras Workshop on Axions, WIMPs and WISPs, Patras 2017, Thessaloniki, Greece, 15 May 2017 - 19 May 2017; Hamburg : Verlag Deutsches Elektronen-Synchrotron, DESY-PROC, (2018). doi:10.3204/DESY-PROC-2017-0
Stochastic conversions of TeV photons into axion-like particles in extragalactic magnetic fields
Very-high energy photons emitted by distant cosmic sources are absorbed on
the extragalactic background light (EBL) during their propagation. This effect
can be characterized in terms of a photon transfer function at Earth. The
presence of extragalactic magnetic fields could also induce conversions between
very high-energy photons and hypothetical axion-like particles (ALPs). The
turbulent structure of the extragalactic magnetic fields would produce a
stochastic behaviour in these conversions, leading to a statistical
distribution of the photon transfer functions for the different realizations of
the random magnetic fields. To characterize this effect, we derive new
equations to calculate the mean and the variance of this distribution. We find
that, in presence of ALP conversions, the photon transfer functions on
different lines of sight could have relevant deviations with respect to the
mean value, producing both an enhancement or a suppression in the observable
photon flux with respect to the expectations with only absorption. As a
consequence, the most striking signature of the mixing with ALPs would be a
reconstructed EBL density from TeV photon observations which appears to vary
over different directions of the sky: consistent with standard expectations in
some regions, but inconsistent in others.Comment: v2: 22 pages, 5 eps figures. Minor changes. A reference added.
Matches the version published on JCA
Food Selectivity in Children with Autism: Guidelines for Assessment and Clinical Interventions
Autisms Spectrum Disorders (ASD) are characterized by core symptoms (social communication and restricted and repetitive behaviors) and related comorbidities, including sensory anomalies, feeding issues, and challenging behaviors. Children with ASD experience significantly more feeding problems than their peers. In fact, parents and clinicians have to manage daily the burden of various dysfunctional behaviors of children at mealtimes (food refusal, limited variety of food, single food intake, or liquid diet). These dysfunctional behaviors at mealtime depend on different factors that are either medical/sensorial or behavioral. Consequently, a correct assessment is necessary in order to program an effective clinical intervention. The aim of this study is to provide clinicians with a guideline regarding food selectivity concerning possible explanations of the phenomenon, along with a direct/indirect assessment gathering detailed and useful information about target feeding behaviors. Finally, a description of evidence-based sensorial and behavioral strategies useful also for parent-mediated intervention is reported addressing food selectivity in children with ASD
Mirizzi syndrome associated with hepatic artery pseudoaneurysm: a case report.
INTRODUCTION: This is the first case report of Mirizzi syndrome associated with hepatic artery pseudoaneurysm. CASE PRESENTATION: A 54-year-old man presented with painful obstructive jaundice and weight loss. Computed tomography showed a hilar mass in the liver. Following an episode of haemobilia, angiography demonstrated a pseudoaneurysm of a branch of the right hepatic artery that was embolised. At surgery, a gallstone causing Mirizzi type II syndrome was found to be responsible for the biliary obstruction and a necrotic inflammatory mass and haematoma were found to be extending into the liver. The mass was debrided and drained, the obstructing stones removed and the bile duct drained with a t-tube. The patient made a full recovery. CONCLUSION: This case highlights another situation where there may be difficulty in differentiating Mirizzi syndrome from biliary tract cancer.Published versio
New cosmological mass limit on thermal relic axions
Observations of the cosmological large-scale structure provide
well-established neutrino mass limits. We extend this argument to thermal relic
axions. We calculate the axion thermal freeze-out temperature and thus their
cosmological abundance on the basis of their interaction with pions. For
hadronic axions we find a new mass limit eV (95% CL), corresponding
to a limit on the axion decay constant of GeV. For other
models this constraint is significantly weakened only if the axion-pion
coupling is strongly suppressed. For comparison we note that the same approach
leads to eV (95% CL) for neutrinos.Comment: (17 pages, 12 eps figures
Flavour-dependent radiative correction to neutrino-neutrino refraction
In the framework of the Standard Model we calculate the flavour non-universal
correction for neutrino refraction in a neutrino background and verify a
similar previous result for the case of ordinary-matter background. The
dominant term arises at loop level and involves tau leptons circulating in the
loop. These O(G_F m_tau^2) corrections to the tree-level potential provide the
dominant refractive difference between nu_mu and nu_tau unless the medium
contains mu or tau leptons. Our results affect the flavour evolution of dense
neutrino gases and may be of interest for collective three-flavour oscillations
of supernova neutrinos. We spell out explicitly how these non-universal
neutrino-neutrino interactions enter the flavour oscillation equations.Comment: 15 pages, 6 figures; updated reference lis
Tailoring the thermal conductivity of rubber nanocomposites by inorganic systems: Opportunities and challenges for their application in tires formulation
The development of effective thermally conductive rubber nanocomposites for heat management represents a tricky point for several modern technologies, ranging from electronic devices to the tire industry. Since rubber materials generally exhibit poor thermal transfer, the addition of high loadings of different carbon‐based or inorganic thermally conductive fillers is mandatory to achieve satisfactory heat dissipation performance. However, this dramatically alters the mechanical behavior of the final materials, representing a real limitation to their application. Moreover, upon fillers’ incorporation into the polymer matrix, interfacial thermal resistance arises due to differences between the phonon spectra and scattering at the hybrid interface between the phases. Thus, a suitable filler functionalization is required to avoid discontinuities in the thermal transfer. In this challenging scenario, the present review aims at summarizing the most recent efforts to improve the thermal conductivity of rubber nanocomposites by exploiting, in particular, inorganic and hybrid filler systems, focusing on those that may guarantee a viable transfer of lab-scale formulations to technological applicable solutions. The intrinsic relationship among the filler’s loading, structure, morphology, and interfacial features and the heat transfer in the rubber matrix will be explored in depth, with the ambition of providing some methodological tools for a more profitable design of thermally conductive rubber nanocomposites, especially those for the formulation of tires
Revisiting the SN1987A gamma-ray limit on ultralight axion-like particles
We revise the bound from the supernova SN1987A on the coupling of ultralight
axion-like particles (ALPs) to photons. In a core-collapse supernova, ALPs
would be emitted via the Primakoff process, and eventually convert into gamma
rays in the magnetic field of the Milky Way. The lack of a gamma-ray signal in
the GRS instrument of the SMM satellite in coincidence with the observation of
the neutrinos emitted from SN1987A therefore provides a strong bound on their
coupling to photons. Due to the large uncertainty associated with the current
bound, we revise this argument, based on state-of-the-art physical inputs both
for the supernova models and for the Milky-Way magnetic field. Furthermore, we
provide major amendments, such as the consistent treatment of
nucleon-degeneracy effects and of the reduction of the nuclear masses in the
hot and dense nuclear medium of the supernova. With these improvements, we
obtain a new upper limit on the photon-ALP coupling: g_{a\gamma} < 5.3 x
10^{-12} GeV^{-1}, for m_a < 4.4 x 10^{-10} eV, and we also give its dependence
at larger ALP masses. Moreover, we discuss how much the Fermi-LAT satellite
experiment could improve this bound, should a close-enough supernova explode in
the near future.Comment: Accepted for publication in JCAP (December 22nd, 2014
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