1,721,073 research outputs found
Dynamical evolution of axion condensates under stimulated decays into photons
No full textDark matter axion condensates may experience stimulated decays into photon pairs. This effect has been often interpreted as a parametric resonance of photons from the axion-photon coupling, leading to an exponential growth of the photon occupation number in a narrow instability band. Most of the previous literature does not consider the possible evolution of the axion field due to the photon growth. We revisit this effect presenting a mean field solution of the axion-photon kinetic equations, in terms of number of photons and pair correlations. We study the limit of no axion depletion, recovering the known instability. Moreover, we extend the results including a possible depletion of the axion field. In this case we find that the axion condensate exhibits the behavior of an inverted pendulum. We discuss the relevance of these effects for two different cases: a homogeneous axion field at recombination and a localized axion clump and discuss constraints that could result from the induced photon background
Model-independent diagnostic of self-induced spectral equalization versus ordinary matter effects in supernova neutrinos
No full textSelf-induced flavor conversions near the supernova (SN) core can make the fluxes for different neutrino species become almost equal, potentially altering the dynamics of the SN explosion and washing out all further neutrino oscillation effects. We present a new model-independent analysis strategy for the next galactic SN signal that will distinguish this flavor equalization scenario from a matter-effects-only scenario during the SN accretion phase. Our method does not rely on fitting or modeling the energy-dependent fluences of the different species to a known function, but rather uses a model-independent comparison of charged-current and neutral-current events at large next-generation underground detectors. Specifically, we advocate that the events due to elastic scattering on protons in a scintillator detector, which is insensitive to oscillation effects and can be used as a model-independent normalization, should be compared with the events due to inverse beta decay of νe in a water Cherenkov detector and/or the events due to charged-current interactions of νe in an argon detector. The ratio of events in these different detection channels allow one to distinguish a complete flavor equalization from a pure matter effect, for either of the neutrino mass orderings, as long as the spectral differences among the different species are not too small
Concomitant use of proton pump inhibitors and dual antiplatelet therapy for cardiovascular outcomes
No full textINTRODUCTION: The aim of this review is to discuss the consequences of potential pharmacokinetic interactions between proton pump inhibitors (PPIs) and antiplatelet therapy on cardiovascular (CV) outcomes and provide guidance on the management of concomitant use of PPIs in patients on dual antiplatelet therapy (DAPT). EVIDENCE ACQUISITION: DAPT combining aspirin and oral P2Y12 receptor inhibitors increases the risk of gastrointestinal (GI) bleeding, with higher rates of morbidity and mortality in patients undergoing percutaneous coronary intervention (PCI). PPIs are recommended in patients at risk of bleeding to reduce the risk of GI hemorrhage. PPIs can reduce the metabolism of Clopidogrel by competing with CYP450 enzymes, mostly CYP2C19 isoform. The clinical significance of this pharmacological interaction is not uniform in observational studies. The only randomized clinical trial assessing the clinical relevance of clopidogrel-omeprazole interaction showed that the use of omeprazole was associated with a reduction in GI bleeding, without any differences in CV outcomes. EVIDENCE SYNTHESIS: Several systematic reviews and meta-analyses suggest an increased risk of major adverse cardiovascular events (MACE), but not of mortality in patients with concomitant use of PPIs and Clopidogrel. Two metaanalysis studying the interactions between individual PPIs and Clopidogrel failed to demonstrate any strong relationships with adverse CV outcomes. CONCLUSIONS: PPIs should be administered in patients on DAPT at risk for GI bleeding. However the uncertain benefit of PPIs in patients who are not at risk of GI bleeding and the unclear risk in MACE suggest that caution should be used when prescribing PPIs in these patients
Self-induced temporal instability from a neutrino antenna
No full textIt has been recently shown that the flavor composition of a self-interacting neutrino gas can spontaneously acquire a time-dependent pulsating component during its flavor evolution. In this work, we perform a more detailed study of this effect in a model where neutrinos are assumed to be emitted in a two-dimensional plane from an infinite line that acts as a neutrino antenna. We consider several examples with varying matter and neutrino densities and find that temporal instabilities with various frequencies are excited in a cascade. We compare the numerical calculations of the flavor evolution with the predictions of linearized stability analysis of the equations of motion. The results obtained with these two approaches are in good agreement in the linear regime, while a dramatic speed-up of the flavor conversions occurs in the non-linear regime due to the interactions among the different pulsating modes. We show that large flavor conversions can take place if some of the temporal modes are unstable for long enough, and that this can happen even if the matter and neutrino densities are changing, as long as they vary slowly
The Initial Mass-Final Luminosity Relation of Type II Supernova Progenitors: Hints of New Physics?
No full textWe revise the theoretical initial mass-final luminosity relation for progenitors of Type IIP and IIL supernovae. The effects of the major uncertainties, such as those due to the treatment of convection, semiconvection, rotation, mass loss, nuclear reaction rates, and neutrinos production rates, are discussed in some detail. The effects of mass transfer between components of close-binary systems are also considered. By comparing the theoretical predictions to a sample of Type II supernovae for which the initial mass of the progenitors and the pre-explosive luminosity are available, we conclude that stellar rotation may explain a few progenitors that appear brighter than expected in the case of nonrotating models. In the most extreme case, SN 2012ec, an initial rotational velocity up to 300 km s-1 is required. Alternatively, these objects could be mass-losing components of close binaries. However, most of the observed progenitors appear fainter than expected. This occurrence seems to indicate that the Compton and pair neutrino energy-loss rates, as predicted by the standard electro-weak theory, are not efficient enough and that an additional negative contribution to the stellar energy balance is required. We show that axions coupled with parameters accessible to currently planned experiments, such as IAXO and, possibly, BabyIAXO and axion-like particles, may account for the missing contribution to the stellar energy loss
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Axion-like particles from primordial black holes shining through the Universe
No full textWe consider a cosmological scenario in which the very early Universe experienced a transient epoch of matter domination due to the formation of a large population of primordial black holes (PBHs) with masses M ≲ 109 g, that evaporate before Big Bang nucleosynthesis. In this context, Hawking radiation would be a non-thermal mechanism to produce a cosmic background of axion-like particles (ALPs). We assume the minimal scenario in which these ALPs couple only with photons. In the case of ultralight ALPs (m a ≲ 10-9 eV) the cosmic magnetic fields might trigger ALP-photon conversions, while for masses m a ⪆ 10 eV spontaneous ALP decay in photon pairs would be effective. We investigate the impact of these mechanisms on the cosmic X-ray background, on the excess in X-ray luminosity in Galaxy Clusters, and on the process of cosmic reionization
Bounds on axionlike particles from the diffuse supernova flux
Full text linkThe cumulative emission of axionlike particles (ALPs) from all past core-collapse supernovae (SNe) would lead to a diffuse flux with energies O(50) MeV. We use this to constrain ALPs featuring couplings to photons and to nucleons. ALPs coupled only to photons are produced in the SN core via the Primakoff process and then converted into gamma rays in the Galactic magnetic field. We set a bound on gaγ≲5×10-10 GeV-1 for ma≲10-11 eV, using recent measurements of the diffuse gamma-ray flux observed by the Fermi-LAT telescope. However, if ALPs couple also with nucleons, their production rate in SN can be considerably enhanced due to the ALPs nucleon-nucleon bremsstrahlung process. Assuming the largest ALP-nucleon coupling phenomenologically allowed, bounds on the diffuse gamma-ray flux lead to a much stronger gaγ≲6×10-13 GeV-1 for the same mass range. If ALPs are heavier than ∼keV, the decay into photons becomes significant, leading again to a diffuse gamma-ray flux. In the case of only photon coupling, we find, e.g., gaγ≲5×10-11 GeV-1 for ma∼5 keV. Allowing for a (maximal) coupling to nucleons, the limit improves to the level of gaγ≲10-19 GeV-1 for ma∼20 MeV, which represents the strongest constraint to date
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