On the discrete spectrum of spin-orbit Hamiltonians with singular interactions

We give a variational proof of the existence of infinitely many bound states below the continuous spectrum for spin-orbit Hamiltonians (including the Rashba and Dresselhaus cases) perturbed by measure potentials thus extending the results of J.Bruening, V.Geyler, K.Pankrashkin: J. Phys. A 40 (2007) F113--F117.Comment: 10 pages; to appear in Russian Journal of Mathematical Physics (memorial volume in honor of Vladimir Geyler). Results improved in this versio

From Model Specification to Simulation of Biologically Constrained Networks of Spiking Neurons.

A declarative extensible markup language (SpineML) for describing the dynamics, network and experiments of large-scale spiking neural network simulations is described which builds upon the NineML standard. It utilises a level of abstraction which targets point neuron representation but addresses the limitations of existing tools by allowing arbitrary dynamics to be expressed. The use of XML promotes model sharing, is human readable and allows collaborative working. The syntax uses a high-level self explanatory format which allows straight forward code generation or translation of a model description to a native simulator format. This paper demonstrates the use of code generation in order to translate, simulate and reproduce the results of a benchmark model across a range of simulators. The flexibility of the SpineML syntax is highlighted by reproducing a pre-existing, biologically constrained model of a neural microcircuit (the striatum). The SpineML code is open source and is available at http://bimpa.group.shef.ac.uk/SpineML

Novel techniques for alpha/beta pulse shape discrimination in Borexino

Borexino could efficiently distinguish between alpha and beta radiation in its liquid scintillator by the characteristic time profile of their scintillation pulse. This alpha/beta discrimination, first demonstrated at the tonne scale in the Counting Test Facility prototype, was used throughout the lifetime of the experiment between 2007 and 2021. With this method, alpha events are identified and subtracted from the beta-like solar neutrino events. This is particularly important in liquid scintillator as alpha scintillation is quenched many-fold. In Borexino, the prominent Po-210 decay peak was a background in the energy range of electrons scattered from Be-7 solar neutrinos. Optimal alpha-beta discrimination was achieved with a "multi-layer perceptron neural network", which its higher ability to leverage the timing information of the scintillation photons detected by the photomultiplier tubes. An event-by-event, high efficiency, stable, and uniform pulse shape discrimination was essential in characterising the spatial distribution of background in the detector. This benefited most Borexino measurements, including solar neutrinos in the \pp chain and the first direct observation of the CNO cycle in the Sun. This paper presents the key milestones in alpha/beta discrimination in Borexino as a term of comparison for current and future large liquid scintillator detectorsComment: 13 pages, 14 figure

Borexino's search for low-energy neutrinos associated with gravitational wave events from GWTC-3 database

The search for neutrino events in correlation with gravitational wave (GW) events for three observing runs (O1, O2 and O3) from 09/2015 to 03/2020 has been performed using the Borexino data-set of the same period. We have searched for signals of neutrino-electron scattering with visible energies above 250 keV within a time window of 1000 s centered at the detection moment of a particular GW event. The search was done with three visible energy thresholds of 0.25, 0.8 and 3.0 MeV.Two types of incoming neutrino spectra were considered: the mono-energetic line and the spectrum expected from supernovae. The same spectra were considered for electron antineutrinos detected through inverse beta-decay (IBD) reaction. GW candidates originated by merging binaries of black holes (BHBH), neutron stars (NSNS) and neutron star and black hole (NSBH) were analysed separately. Additionally, the subset of most intensive BHBH mergers at closer distances and with larger radiative mass than the rest was considered. In total, follow-ups of 74 out of 93 gravitational waves reported in the GWTC-3 catalog were analyzed and no statistically significant excess over the background was observed. As a result, the strongest upper limits on GW-associated neutrino and antineutrino fluences for all flavors (\nu_e, \nu_\mu, \nu_\tau) have been obtained in the (0.5 - 5.0) MeV neutrino energy range.Comment: 13 pages, 8 figure

The Hidden Sexuality of Alexandrium Minutum: An Example of Overlooked Sex in Dinoflagellates

Dinoflagellates are haploid eukaryotic microalgae in which rapid proliferation causes dense blooms, with harmful health and economic effects to humans. The proliferation mode is mainly asexual, as the sexual cycle is believed to be rare and restricted to stressful environmental conditions. However, sexuality is key to explaining the recurrence of many dinoflagellate blooms because in many species the fate of the planktonic zygotes (planozygotes) is the formation of resistant cysts in the seabed (encystment). Nevertheless, recent research has shown that individually isolated planozygotes in the lab can enter other routes besides encystment, a behavior of which the relevance has not been explored at the population level. In this study, using imaging flow cytometry, cell sorting, and Fluorescence In Situ Hybridization (FISH), we followed DNA content and nuclear changes in a population of the toxic dinoflagellate Alexandrium minutum that was induced to encystment. Our results first show that planozygotes behave like a population with an “encystment-independent” division cycle, which is light-controlled and follows the same Light:Dark (L:D) pattern as the cycle governing the haploid mitosis. Resting cyst formation was the fate of just a small fraction of the planozygotes formed and was restricted to a period of strongly limited nutrient conditions. The diploid-haploid turnover between L:D cycles was consistent with two-step meiosis. However, the diel and morphological division pattern of the planozygote division also suggests mitosis, which would imply that this species is not haplontic, as previously considered, but biphasic, because individuals could undergo mitotic divisions in both the sexual (diploid) and the asexual (haploid) phases. We also report incomplete genome duplication processes. Our work calls for a reconsideration of the dogma of rare sex in dinoflagellates.Versión del edito

First Directional Measurement of sub-MeV Solar Neutrinos with Borexino

We report the measurement of sub-MeV solar neutrinos through the use of their associated Cherenkov radiation, performed with the Borexino detector at the Laboratori Nazionali del Gran Sasso. The measurement is achieved using a novel technique that correlates individual photon hits of events to the known position of the Sun. In an energy window between 0.54 to 0.74 MeV, selected using the dominant scintillation light, we have measured 10 887þ2386 ðstatÞ � 947ðsystÞ (68% confidence interval) −2103 solar neutrinos out of 19904 total events. This corresponds to a 7Be neutrino interaction rate of 51.6þ13.9 counts=ðday · 100 tonÞ, which is in agreement with the standard solar model predictions and the −12.5 previous spectroscopic results of Borexino. The no-neutrino hypothesis can be excluded with > 5σ confidence level. For the first time, we have demonstrated the possibility of utilizing the directional Cherenkov information for sub-MeV solar neutrinos, in a large-scale, high light yield liquid scintillator detector. This measurement provides an experimental proof of principle for future hybrid event reconstruction using both Cherenkov and scintillation signatures simultaneously

Experimental Detection of the CNO Cycle

Borexino recently reported the first experimental evidence for a CNO neutrino. Since this process accounts for only about 1% of the Sun’s total energy production, the associated neutrino flux is remarkably low compared to that of the pp chain, the dominant hydrogen-burning process. This experimental evidence for the existence of CNO neutrinos was obtained using a highly radio-pure Borexino liquid scintillator. Improvements in the thermal stabilization of the detector over the last five years have allowed us to exploit a method of constraining the rate of 210Bi background. Since the CNO cycle is dominant in massive stars, this result is the first experimental evidence of a major stellar hydrogen-to-helium conversion mechanism in the Universe

Solar and geoneutrinos

Thanks to the progress of neutrino physics, today we are able of exploiting neutrinos as a tool to study astrophysical objects. The latter in turn serve as unique sources of elusive neutrinos, which fundamental properties are still to be understood. This contribution attempts to summarize the latest results obtained by measuring neutrinos emitted from the Sun and geoneutrinos produced in radioactive decays inside the Earth, with a particular focus on a recent discovery of the CNO-cycle solar neutrinos by Borexino. Comprehensive measurement of the pp-chain solar neutrinos and the first directional detection of sub-MeV solar neutrinos by Borexino, the updated 8B solar neutrino results of Super-Kamiokande, as well as the latest Borexino and KamLAND geoneutrino measurements are also discussed

Identification of the cosmogenic 11C background in large volumes of liquid scintillators with Borexino

Cosmogenic radio-nuclei are an important source of background for low-energy neutrino experiments. In Borexino, cosmogenic 11C decays outnumber solar pep and CNO neutrino events by about ten to one. In order to extract the flux of these two neutrino species, a highly efficient identification of this background is mandatory. We present here the details of the most consolidated strategy, used throughout Borexino solar neutrino measurements. It hinges upon finding the space-time correlations between 11C decays, the preceding parent muons and the accompanying neutrons. This article describes the working principles and evaluates the performance of this Three-Fold Coincidence (TFC) technique in its two current implementations: a hard-cut and a likelihood-based approach. Both show stable performances throughout Borexino Phases II (2012–2016) and III (2016–2020) data sets, with a 11C tagging efficiency of ∼90 % and ∼ 63–66 % of the exposure surviving the tagging. We present also a novel technique that targets specifically 11C produced in high-multiplicity during major spallation events. Such 11C appear as a burst of events, whose space-time correlation can be exploited. Burst identification can be combined with the TFC to obtain about the same tagging efficiency of ∼90% but with a higher fraction of the exposure surviving, in the range of ∼ 66–68 %