1,721,029 research outputs found
Suppressed diffusion around cosmic ray sources and impact on galactic propagation
No full textAt the beginning of the 20th century a variety of observations found that the Earth is constantly bombarded by charged high energy particles from space. These cosmic rays mainly consist of protons, but also contain heavier elements. Over a large range in energy from MeV to EeV they resemble a power law. At GeV energies their arrival directions are nearly isotropic, since charged particles get deflected in the turbulent magnetic fields in the Galaxy. This prevents a direct tracking of the particles back to their sources. From the ratios of hadronic cosmic rays it is possible to deduce that particles must propagate diffusively throughout the Galaxy. Thereby, the parameters of models we fit to these data are galactic averages. In contrast, high energy -rays are produced by cosmic rays and directly point back to their origin. With this it is possible to indirectly probe the distribution of comic rays within the Galaxy. Recent observations of -rays around pulsars and supernova remnants, both potential sources, indicate that diffusion in these regions is more than two orders of magnitude lower than in the galactic average. This indicates that the conditions within the Galaxy are far from homogeneous. In this thesis, we investigate whether cosmic rays themselves can produce the suppressed diffusion. The basic idea is that in the vicinity of the source the strong spatial gradient of the cosmic ray density gives rise to the resonant streaming-instability. This produces magnetic waves upon which they scatter, a process called self-confinement. We make use of finite-difference codes to investigate the surroundings of supernova remnants. We extend existing models below and show that suppressed diffusion can exist for up to after the supernova. The same mechanism was proposed to explain TeV--ray-halos around pulsars. We implement the cascade of turbulence in existing models and show that the effectivity of the streaming-instability crucially depends on the large scale magnetic field. Our calculations indicate, that the streaming instability alone is not able to explain the observations around the pulsar Geminga. Additionally, we investigate the effects of suppressed diffusion in the galactic disk on hadronic cosmic ray ratios. The basic idea is that unstable particles are confined within the disk for longer if the diffusion coefficient is smaller. Then, the ratio of unstable to stable nuclei is increased compared to standard predictions. We develop a semi-analytical two-zone model of the Galaxy with a reduced diffusion coefficient in the galactic disk compared to the galactic halo and show that this model can be constrained by recent AMS-02 data. For the case that the diffusion coefficient in the disk represents an average over zones of low and high diffusion, we investigate the filling fraction of the suppression zones with stochastic differential equations. Finally, we highlight the impact of different spallation cross-section parametrisations on our findings
Measurement of the high-energy astrophysical neutrino energy spectrum combining muon tracks and cascades measured at the IceCube Neutrino Observatory
No full textCosmic rays were discovered more than a century ago, yet the sources of the highest energy particles remain unknown. Today, measurements of different messenger particles are used and combined to study the acceleration mechanisms and source candidates. One of these messenger particles is the neutrino whose high energy flux of astrophysical origin has first been observed a decade ago by the IceCube Neutrino Observatory. Since then, this diffuse neutrino flux of extra-galactic origin has been confirmed in multiple detection channels focusing on different event topologies, e.g., through-going muon tracks and contained cascades. In this thesis, 10 years of complementary muon track and cascade neutrino data from the IceCube Neutrino Observatory are combined into a high statistics analysis. Key to this combined fit is the consistent modeling of all signal and background flux components including systematic uncertainties. For this, a novel simulation technique is used where the detector response is continuously varied during simulation. This method and approach for combining different samples are presented and verified. It is then applied to an analysis of high-energy neutrino data for the first time resulting in a measurement of the energy spectrum of the astrophysical neutrino flux with unprecedented precision. For the first time, evidence for a spectral shape beyond the single power-law model is obtained: a broken power-law astrophysical neutrino flux is favored with . The measured neutrino energy spectrum steepens from spectral index to at a break energy of . In addition to the spectral shape measurement, detailed studies on the robustness of the result and the compatibility of the two high-energy event selections, muon tracks and cascades, are presented
Insight on the dark universe from cosmological perturbations
No full textCosmology presents the best hope of measuring the sum of neutrino masses in the future. The Cosmic Microwave Background (CMB) has already been a treasure trove of information; from Planck, BICEP/KECK, and their predecessors; and will continue to provide ever more precise information with upcoming or proposed CMB experiments, such as LiteBird, CMB-S4, CORE and PICO. These missions will have great synergy with other branches of cosmology. In particular, massive neutrinos leave a distinct imprint on the matter distribution of the universe, which upcoming large-scale structure experiments such as Euclid and the Square Kilometre Array will observe with unprecedented levels of precision. The uncertainty in modelling of non-linear structure formation is often neglected in other forecasts, or scales corresponding to this regime are entirely removed. In this work, we take into account that our understanding of non-linear modelling is imperfect. We show that a neutrino mass sum measurement is all but guaranteed from cosmology in the next decade and that this statement is robust to choice of cosmological model or modelling of non-linear effects
Exploring atmospheric neutrino fluxes : seasonal variations and prompt neutrino search in the IceCube Neutrino Observatory
No full textHigh-energy atmospheric neutrinos, generated through cosmic-ray interactions with atmospheric nuclei, provide an intriguing window into fundamental particle interactions. This study employs the IceCube Neutrino Observatory data to investigate the properties of atmospheric neutrinos. It focuses on the neutrino and their parent meson production mechanisms. We establish a correlation with temperature fluctuations by examining seasonal variations in the atmospheric neutrino flux and illustrating the impact of atmospheric conditions on neutrino production. Additionally, we search for prompt atmospheric neutrinos originating from charmed meson decays in the energy spectrum of neutrinos. The results help to constrain the production of rare and heavy mesons in proton-air collisions. Additionally, the results refine atmospheric neutrino models and help differentiate between the atmospheric and astrophysical neutrino spectrums. Although challenges remain in thoroughly characterizing the production of atmospheric neutrinos, our findings contribute to a broader understanding of the high-energy neutrino flux and support ongoing efforts in neutrino astronomy with the IceCube Neutrino Observatory
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
Study for large acceptance electron analysis with the Alpha Magnetic Spectrometer on the International Space Station
No full textThe solar wind strongly affects the fluxes and arrival directions of charged cosmic rays at all energies. The activity of the Sun and therefore its impact on cosmic rays shows both short- and long-term time structures. While the long-term variation seems to follow the 11 year solar cycle, the short-term structures are caused by individual solar events. The AMS-02 collaboration has published electron and positron fluxes with a 27 day time resolution, which allows studying of the long-term structures. Studies of individual solar events require a better time resolution, which is limited by the available statistics. In this thesis, I present a novel way to determine the cosmic ray electron flux with the AMS-02 experiment. This analysis differs from the previously published ones by using events that do not enter the electromagnetic calorimeter (ECAL). This allows a significantly larger acceptance resulting in higher statistics, which allows for a daily time resolution. The main challenges for this analysis are the energy scale and particle identification. The tracker resolution is poorer than the ECAL energy resolution, which results in larger migration effects. Accurate determination of selection efficiencies requires redundant particle identification capability, which is more challenging without the ECAL. Preliminary results for the monthly and daily electron fluxes from 20 May 2011 to 30 October 2019 for rigidities between 1.07 and 61.7 GV are presented. Significant short-term variations are visible in the daily fluxes up to ~20 GV, which had not been observed previously in cosmic ray electrons in this energy range. 19 individual Forbush decrease events have been analysed in detail. The intensity of the decrease shows an exponential dependency on rigidity for some of these events and a linear one for others. The duration of the event is consistent with a constant for some events and shows a linear decrease with rigidity for others
Observation of high-energy neutrinos from the galaxy and beyond
No full textThe IceCube Neutrino Observatory has measured a diffuse neutrino flux of astrophysical origin above ~ 50TeV. The magnitude of the flux is close to the Waxman-Bahcall bound, suggesting a connection to ultra-high-energy cosmic-rays above 10^19 eV and therefore an extragalactic origin. However, below PeV energies, a fraction of the flux is expected to originate from the decay of charged pions created in interactions of cosmic rays (CR)with matter in the Milky Way. This diffuse galactic neutrino flux is closely related to the diffuse galactic gamma-ray flux, and carries information about the properties of galactic CR transport. At the highest energies, an important tool in measuring the properties of the astrophysical neutrino flux is the resonant W- production in anti-electron-neutrino - electron interactions (Glashow Resonance) at 6.3PeV. Apart from increasing the anti-electron-neutrino-matter cross-section by two orders of magnitudes and thus increasing the effective area for neutrino detection, the Glashow Resonance enables discrimination of neutrino and anti-neutrino fluxes, giving insight to the neutrino production processes. The first part of this thesis is dedicated to a search for the diffuse galactic neutrino emission using two different emission models. Both model tests result in overfluctuations with significances below 2 sigma. The resulting upper-limits constrain the pion component of galactic diffuse emission in an energy range currently not accessible to -ray measurements. The second part of this thesis is dedicated to the analysis of a Glashow-Resonance candidate event. Details about the directional and energy reconstruction of this event will be presented. For the first time, a measurement of the astrophysical anti-electron-neutrino flux is performed
Anomalies in cosmological data and probes of the dark sector
No full textModern cosmology has entered a new age of precision. An incredible wealth of data has already been collected and will be measured in the near future. However, this new era of data also presents large challenges to the LambdaCDM paradigm. In particular, one observes large tensions in parameters inferred through different cosmological probes. To ease these tensions a large wealth of models have been proposed, focusing especially on modifications of the dark sector. In this thesis I set out to investigate these anomalies with independent data sets, to probe the various dark sector models that have been proposed to ease the tensions, and to forecast the sensitivity to the parameters of these models from future probes. First, I give a brief review of the theoretical background required to deeply understand both the proposed dark sector models and the cosmological probes I investigate. Second, I introduce the cosmological tensions under consideration as well as several probes that are commonly used in modern cosmology. I focus in particular on a combination of observables derived from Big Bang Nucleosynthesis and the Baryonic Acoustic Oscillations I have recently investigated, and I show that this combination allows to put strong and robust constraints on the current expansion rate independent of the anisotropies of the cosmic microwave background. Further, I present the tight constraints I have derived from the latest release of Lyman-alpha data on the neutrino masses and on the mass of a simple thermal relic. Afterwards, I focus on the various dark sector models that have been proposed to ease the cosmological tensions. I describe a few standard results such as the freeze-out of dark relics, and then focus on two models I have investigated on their ability to ease the cosmological tension. The first is a cannibalistic dark matter model, for which I show that it has great potential to ease the clustering tension. The second is a model of dark matter simultaneously interacting with multiple different particle species. In this case I show that a combination of dark matter photon and dark radiation interactions allows to significantly reduce the Hubble tension as well as the clustering tension. Moreover, I describe how future observations of spectral distortions of the cosmic microwave background will aid in constraining various models of dark matter. I find large improvements compared to current data sets for most of the considered models. Finally, I conclude by discussing how these spectral distortions can also put exciting constraints on the shape of the inflationary potential
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