Axion-like particle effects on the polarization of cosmic high-energy gamma sources

Various satellite-borne missions are being planned whose goal is to measure the polarization of a large number of gamma-ray bursts (GRBs). We show that the polarization pattern predicted by current models of GRB emission can be drastically modified by the existence of very light axion-like particles (ALPs), which are present in many extensions of the Standard Model of particle physics. Basically, the propagation of photons emitted by a GRB through cosmic magnetic fields with a domain-like structure induces photon-ALP mixing, which is expected to produce a strong modification of the original photon polarization. Because of the random orientation of the magnetic field in each domain, this effect strongly depends on the orientation of the photon line of sight. As a consequence, photon-ALP conversion considerably broadens the original polarization distribution. Searching for such a peculiar feature through future high-statistics polarimetric measurements is therefore a new opportunity to discover very light ALPs.Comment: Final version (21 pages, 8 eps figures). Matches the version published on JCAP. Added a Section on the effects of cosmic expansion on photon-ALP conversions. Figures modified to take into account this effect. References updated. Conclusions unchanged

Search for solar axion emission from 7Li and D(p,gamma)3He nuclear decays with the CAST gamma-ray calorimeter

We present the results of a search for a high-energy axion emission signal from 7Li (0.478 MeV) and D(p,gamma)3He (5.5 MeV) nuclear transitions using a low-background gamma-ray calorimeter during Phase I of the CAST experiment. These so-called "hadronic axions" could provide a solution to the long-standing strong-CP problem and can be emitted from the solar core from nuclear M1 transitions. This is the first such search for high-energy pseudoscalar bosons with couplings to nucleons conducted using a helioscope approach. No excess signal above background was found.Comment: 20 pages, 8 figures, final version to be published in JCA

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

Zearalenone production and growth in drinking water inoculated with Fusarium graminearum

Production of the mycotoxin zearalenone (ZEN) was examined in drinking water inoculated with Fusarium graminearum. The strain employed was isolated from a US water distribution system. ZEN was purified with an immunoaffinity column and quantified by high-performance liquid chromatography (HPLC) with fluorescence detection. The extracellular yield of ZEN was 15.0 ng l−1. Visual growth was observed. Ergosterol was also indicative of growth and an average of 6.2 μg l−1 was obtained. Other compounds were also detected although remain unidentified. There is no equivalent information available. More work is required on metabolite expression in water as mycotoxins have consequences for human and animal health. The levels detected in this study were low. Water needs to be accepted as a potential source as it attracts high quality demands in terms of purity.Fundação para a Ciência e a Tecnologia (FCT

Signatures of photon and axion-like particle mixing in the gamma-ray burst jet

Photons couple to Axion-Like Particles (ALPs) or more generally to any pseudo Nambu-Goldstone boson in the presence of an external electromagnetic field. Mixing between photons and ALPs in the strong magnetic field of a Gamma-Ray Burst (GRB) jet during the prompt emission phase can leave observable imprints on the gamma-ray polarization and spectrum. Mixing in the intergalactic medium is not expected to modify these signatures for ALP mass > 10^(-14) eV and/or for < nG magnetic field. We show that the depletion of photons due to conversion to ALPs changes the linear degree of polarization from the values predicted by the synchrotron model of gamma ray emission. We also show that when the magnetic field orientation in the propagation region is perpendicular to the field orientation in the production region, the observed synchrotron spectrum becomes steeper than the theoretical prediction and as detected in a sizable fraction of GRB sample. Detection of the correlated polarization and spectral signatures from these steep-spectrum GRBs by gamma-ray polarimeters can be a very powerful probe to discover ALPs. Measurement of gamma-ray polarization from GRBs in general, with high statistics, can also be useful to search for ALPs.Comment: 17 pages, 3 figures. Accepted for publication in JCAP with minor change

Cosmological mass limits on neutrinos, axions, and other light particles

The small-scale power spectrum of the cosmological matter distribution together with other cosmological data provides a sensitive measure of the hot dark matter fraction, leading to restrictive neutrino mass limits. We extend this argument to generic cases of low-mass thermal relics. We vary the cosmic epoch of thermal decoupling, the radiation content of the universe, and the new particle's spin degrees of freedom. Our treatment covers various scenarios of active plus sterile neutrinos or axion-like particles. For three degenerate massive neutrinos, we reproduce the well-known limit of m_nu < 0.34 eV. In a 3+1 scenario of 3 massless and 1 fully thermalized sterile neutrino we find m_nu < 1.0 eV. Thermally produced QCD axions must obey m_a < 3.0 eV, superseding limits from a direct telescope search, but leaving room for solar eV-mass axions to be discovered by the CAST experiment.Comment: 15 pages, 6 figures, matches version in JCA

Cosmological constraints on neutrino plus axion hot dark matter

We use observations of the cosmological large-scale structure to derive limits on two-component hot dark matter consisting of mass-degenerate neutrinos and hadronic axions, both components having velocity dispersions corresponding to their respective decoupling temperatures. We restrict the data samples to the safely linear regime, in particular excluding the Lyman-alpha forest. Using standard Bayesian inference techniques we derive credible regions in the two-parameter space of m_a and sum(m_nu). Marginalising over sum(m_nu) provides m_a < 1.2 eV (95% C.L.). In the absence of axions the same data and methods give sum(m_nu) < 0.65 eV (95% C.L.). We also derive limits on m_a for a range of axion-pion couplings up to one order of magnitude larger or smaller than the hadronic value.Comment: 13 pages, 2 figures, uses iopart.cl

Exploring nu signals in dark matter detectors

We investigate standard and non-standard solar neutrino signals in direct dark matter detection experiments. It is well known that even without new physics, scattering of solar neutrinos on nuclei or electrons is an irreducible background for direct dark matter searches, once these experiments each the ton scale. Here, we entertain the possibility that neutrino interactions are enhanced by new physics, such as new light force carriers (for instance a "dark photon") or neutrino magnetic moments. We consider models with only the three standard neutrino flavors, as well as scenarios with extra sterile neutrinos. We find that low-energy neutrino--electron and neutrino--nucleus scattering rates can be enhanced by several orders of magnitude, potentially enough to explain the event excesses observed in CoGeNT and CRESST. We also investigate temporal modulation in these neutrino signals, which can arise from geometric effects, oscillation physics, non-standard neutrino energy loss, and direction-dependent detection efficiencies. We emphasize that, in addition to providing potential explanations for existing signals, models featuring new physics in the neutrino sector can also be very relevant to future dark matter searches, where, on the one hand, they can be probed and constrained, but on the other hand, their signatures could also be confused with dark matter signals.Comment: 38 pages, 8 figures, 1 table; v3: eq 3 and nuclear recoil plots corrected, footnote added, conclusions unchange

Statistical analysis plan for the ‘Triple Antiplatelets for Reducing Dependency after Ischaemic Stroke’ (TARDIS) trial

Rationale: Antiplatelet agents such as aspirin, clopidogrel and dipyridamole are effective in reducing the risk of recurrence after a stroke. Importantly, the risk of recurrence is highest immediately after the index event while antiplatelets cause bleeding. Aims and/or hypothesis: The ‘Triple Antiplatelets for Reducing Dependency after Ischaemic Stroke’ (TARDIS) trial is testing whether short-term intensive antiplatelet therapy is safe and effective in reducing the early risk of recurrence as compared with standard guideline-based therapy. Design: TARDIS is an international multi-center prospective randomized open-label blinded–end-point trial, with funding from the UK Health Technology Assessment program. Patients with acute ischemic stroke or transient ischemic attack are randomized within 48 h to intensive/triple antiplatelet therapy or guideline antiplatelets taken for one-month. Patients or relatives give written informed (proxy) consent and all sites have research ethics approval. Analyses will be done by intention-to-treat. Study Outcome: The primary outcome is shift in stroke recurrent events and their severity, assessed using the modified Rankin Scale, at three-months. Discussion: This paper and attachment describe the trial’s statistical analysis plan, as developed from the protocol during recruitment and prior to unblinding of data. The statistical analysis plan contains design and methods for analyses, and unpopulated tables and figures for the primary and baseline publications. The data from the trial will provide the first large-scale randomized evidence for the use of intensive antiplatelet therapy for preventing recurrence after acute stroke and transient ischemic attack