1,720,981 research outputs found
Model independent limits on an ultralight gravitino from supernovae
No full textWe revisit astrophysical constraints on models with an ultralight gravitino, in particular extending the analysis to more general models and the case of R-parity breaking. These constraints allow us to restrict the value of the gravitino mass depending on the masses of scalar moduli. We perform both a frequentist and a Bayesian analysis and we find comparable results, even if the Bayesian analysis is in part affected by volume effects. Only a small window of gravitino masses can be excluded by the supernova constraints in a model-independent way, while limits obtained with a definite assumption on the scalar masses are more stringent
Solar reflection of light dark matter with heavy mediators
Get PDFThe direct detection of sub-GeV dark matter particles is hampered by their low energy deposits. If the maximum deposit allowed by kinematics falls below the energy threshold of a direct detection experiment, it is unable to detect these light particles. Mechanisms that boost particles from the Galactic halo can therefore extend the sensitivity of terrestrial direct dark matter searches to lower masses. Sub-GeV and sub-MeV dark matter particles can be efficiently accelerated by colliding with thermal nuclei and electrons of the solar plasma, respectively. This process is called "solar reflection."In this paper, we present a comprehensive study of solar reflection via electron and/or nuclear scatterings using Monte Carlo simulations of dark matter trajectories through the Sun. We study the properties of the boosted dark matter particles, obtain exclusion limits based on various experiments probing both electron and nuclear recoils, and derive projections for future detectors. In addition, we find and quantify a novel, distinct annual modulation signature of a potential solar reflection signal which critically depends on the anisotropies of the boosted dark matter flux ejected from the Sun. Along with this paper, we also publish the corresponding research software
Dark Matter in the Earth and the Sun:Simulating Underground Scatterings for the Direct Detection of Low-Mass Dark Matter
No full textAstrofysiske observationer giver overbevisende tegn på, at størstedelen af stof i universet er mørkt. Dette mørke stof (DM) viser ingen observationelle interaktioner med elektromagnetisk stråling, og dets natur og oprindelse er stadig ukendt. Direkte detektionseksperimenter søger efter interaktioner mellem DM fra galaksehaloen og atomkerner i en detektor. Hidtil har eksperimenter kun været i stand til at sætte strenge grænser i DM parameterrummet. Disse begrænsninger løsnes for sub-GeV DM-masser, da lette partikler ikke har nok energi til at udløse en måling i de fleste detektorer. Ny eksperimentel indsats skifter fokus mod lavere masser, for eksempel ved at lede efter uelastiske sammenstød mellem DM og elektroner.Hvis sammenstød mellem DM og almindeligt stof antages at ske i detektoren, vil kollisioner også finde sted i hovedparten af planeter og stjerner. For tilstrækkeligt store tværsnit kan disse sammenstød forekomme i Jorden eller Solen, endda før de måles i detektoren. I denne afhandling undersøger vi virkningen af disse prædetektor sammenstød i direkte søgninger af let DM ved brug af Monte Carlo (MC) simuleringer. Ved at simulere baner og sammenstød af mange individuelle DM-partikler gennem Jorden eller Solen bestemmer vi de lokale forvrængninger i de statistiske egenskaber af DM forårsaget af elastiske DM-atomkernekollisioner i en given detektor.Sammenstød inde i Jorden ændrer den underjordiske DM-densitet og hastighedsfordeling. Enhver detektor bevæger sig periodisk gennem disse inhomogenitetermens planeten roterer, og den forventede hændelsesrate vil variere i løbet af en siderisk dag. Ved hjælp af MC-simuleringer kan vi bestemme den nøjagtige amplitude og fase af denne døgnmodulering i givent eksperiment. For endnu højere sammenstødssandsynligheder begynder sammenstød i lagene ovenover det underjordiske eksperiment at dæmpe den indkommende DM-flux. Vi bestemmer det kritiske tværsnit, hvor et eksperiment mister følsomheden overfor DM for en række atomkerne- og elektronspredningsforsøg samt forskellige typer interaktioner.Desuden udvikler vi ideen om, at sub-GeV DM-partikler kan trænge ind i Solen, få kinetisk energi ved at kollidere med varme atomkerner og blive reflekteret med høje hastigheder. Vi udleder analytiske udtryk for partikelfluxen fra solreflektion via et enkelt sammenstød og demonstrerer udsigterne for fremtidige eksperimenter til at lede efter reflekteret DM og udvide følsomheden over for lavere masser end hvad der er tilgængelig ved halo-DM alene. Vi præsenterer de første MC-resultater. Vi inkluderer refleksion efter flere sammenstød, som forstærker den reflekterede DM-flux og derved potentialet ved solreflektion til direkte søgninger efter let DM.Astrophysical and cosmological observations provide compelling evidence that the majority of matter in the Universe is dark. Showing no interactions with electromagnetic radiation, this dark matter (DM) eludes direct observations, and its nature and origin remains unknown to this day. Direct detection experiments search for interactions between halo DM and nuclei inside a detector. So far, a variety of experiments were only able to set stringent limits on the DM parameter space. These constraints weaken for sub-GeV DM masses, as light particles are not energetic enough to trigger most detectors. New experimental efforts shift the focus towards lower masses, for example by looking for inelastic DM-electron scatterings.If scatterings between DM and ordinary matter are assumed to occur in a detector’s target material, collisions will naturally take place inside the bulk of planets and stars as well. For sufficiently large cross sections, these scatterings might occur in the Earth or Sun even prior to the detection. In this thesis, we study the impact of these pre-detection scatterings on direct searches of light DM with the use of Monte Carlo (MC) simulations. By simulating the trajectories and scatterings of many individual DM particles through the Earth or Sun, we determine the local distortions of the statistical properties of DM at any detector caused by elastic DM-nucleus collisions.Scatterings inside the Earth distort the underground DM density and velocity distribution. Any detector moves periodically through these inhomogeneities due to the Earth’s rotation, and the expected event rate will vary throughout a sidereal day. Using MC simulations, we can determine the exact amplitude and phase of this diurnal modulation for any experiment. For even higher scattering probabilities, collisions in the overburden above the typically underground detectors start to attenuate the incoming DM flux. The critical cross section above which an experiment loses sensitivity to DM itself is determined for a variety of DM-nucleus and DM-electron scattering experiments and different types of interactions.Furthermore, we develop the idea that sub-GeV DM particles can enter the Sun, gain kinetic energy by colliding on hot nuclei and get reflected with great speeds. By deriving an analytic expressions for the particle flux from solar reflection via a single scattering, we demonstrate the prospects of future experiments to probe reflected DM and extend their sensitivity to lower masses than accessible by halo DM alone. We present first results for MC simulations of solar reflections. Including reflection after multiple scatterings greatly amplifies the reflected DM flux and thereby the potential of solar reflection for direct searches for light DM
Electron recoils from terrestrial upscattering of inelastic dark matter
No full textThe growing interest in the interactions between dark matter particles and electrons has received a further boost by the observation of an excess in electron recoil events in the XENON1T experiment. Of particular interest are dark matter models in which the scattering process is inelastic, such that the ground state can upscatter into an excited state. The subsequent exothermic downscattering of such excited states on electrons can lead to observable signals in direct detection experiments and gives a good fit to the XENON1T excess. In this work, we study terrestrial upscattering, i.e., inelastic scattering of dark matter particles on nuclei in the Earth, as a plausible origin of such excited states. Using both analytical and Monte Carlo methods, we obtain detailed predictions of their density and velocity distribution. These results enable us to explore the time dependence of the flux of excited states resulting from the rotation of the Earth. For the case of XENON1T, we find the resulting daily modulation of the electron recoil signal to be at the level of 10% with a strong dependence on the dark matter mass
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
How blind are underground and surface detectors to strongly interacting dark matter?
Get PDFAbove a critical dark matter-nucleus scattering cross section any terrestrial direct detection experiment loses sensitivity to dark matter, since the Earth crust, atmosphere, and potential shielding layers start to block off the dark matter particles. This critical cross section is commonly determined by describing the average energy loss of the dark matter particles analytically. However, this treatment overestimates the stopping power of the Earth crust. Therefore the obtained bounds should be considered as conservative. We perform Monte Carlo simulations to determine the precise value of the critical cross section for various direct detection experiments and compare them to other dark matter constraints in the low mass regime. In this region we find parameter space where typical underground and surface detectors are completely blind to dark matter. This "hole" in the parameter space can hardly be closed with an increase in the detector exposure. Dedicated surface or high-altitude experiments may be the only way to directly probe this part of the parameter space.</p
obscura: A modular C++ tool and library for the direct detection of (sub-GeV) dark matter via nuclear and electron recoils
No full textVersion 1.0.0 to be published alongside the JOSS software paper
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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