This thesis aims at using novel machine learning techniques to test the dynamics of the Universe via the cosmological redshift-distance test. Currently, one of the most outstanding questions in cosmology is the physical cause of the accelerating cosmic expansion observed with supernovae. Simultaneously, tensions in measurements of the Hubble expansion parameter $H_0$ are emerging. Measuring the Universe expansion with next generation galaxy imaging surveys, such as provided by the Vera Rubin Observatory, offers the opportunity to discover new physics governing the Universe dynamics. In this thesis, with the long-term goal to unravel these peculiarities, we create a deep generative model in the form of a convolutional variational auto-encoder (VAE), trained with a "Variational Mixture of Posteriors" prior (VampPrior) and high-resolution galaxy images from the simulation project \texttt{TNG-50}. Our model is able to learn a prior on the visual features of galaxies and can generate synthetic galaxy images which preserve the coarse features (shape, size, inclination, and surface brightness profile), but not finer morphological features, such as spiral arms. The generative model for galaxy images is applicable to uses outside the scope of this thesis and is thus a contribution in itself. We next implement a cosmological pinhole camera model, taking angular diameter changes with redshift into account, to forward simulate the actual observation on a telescope detector. Building upon the hypothesis that certain features of galaxies should be of proper physical sizes, we use probabilistic triangulation to find the comoving distance $r(z,\Omega)$ to these in a flat ($K=0$) Universe. Using a sample of high-resolution galaxy images from redshifts $z\in[0.05,0.5]$ from \texttt{TNG-50}, we demonstrate that the implemented Bayesian inference approach successfully estimates $r(z)$ within $1\sigma$-error ($\Delta r_{\text{est}} = 140$ $(580)$ Mpc for $z=0.05$ $(0.5)$). Including the surface brightness attenuation and utilizing the avalanche of upcoming galaxy images could significantly lower the uncertainties. This thesis thus shows a promising path forward utilizing novel machine learning techniques and massive next-generation imaging data to improve and generalize the traditional cosmological angular-diameter test, which in turn has the potential to increase our understanding of the Universe. / Denna avhandling syftar till att använda nya maskininlärningstekniker för att testa universums dynamik via det kosmologiska rödförskjutningsavståndstestet. För närvarande är en av de mest framstående frågorna inom kosmologi den fysiska orsaken till den accelererande kosmiska expansionen som observerats med supernovor. Samtidigt uppstår spänningar i mätningar av Hubble-expansionsparametern $H_0$. Att mäta universums expansion med nästa generations galaxundersökningar, såsom de som ska genomföras av Vera Rubin Observatory, ger möjlighet att upptäcka ny fysik som styr universums dynamik. I den andan skapar vi i den här avhandlingen en djup generativ modell i form av en "convolutional variational auto-encoder" (VAE), tränad med en "Variational Mixture of Posteriors" prior (VampPrior) och högupplösta galaxbilder från simuleringsprojektet \texttt{TNG-50}. Vår modell kan lära sig en "prior" om galaxernas visuella egenskaper och kan generera syntetiska galaxbilder som bevarar de grova dragen (form, storlek, lutning och ytans ljusprofil), men inte finare morfologiska egenskaper, såsom spiralarmar. Den generativa modellen för galaxbilder är tillämplig på användningar som inte omfattas av denna avhandling och är därmed ett bidrag i sig. Därefter implementerar vi en kosmologisk hålkameramodell, med vilken hänsyn till förändringar i vinkelstorleken med rödförskjutning tas, för att framåt-simulera den faktiska observationen på en teleskopdetektor. Med utgångspunkt från hypotesen att galaxer i grunden borde ha gemensamma egenskaper med liknande fysiska storlekar, använder vi probabilistisk triangulering för att hitta avståndet (s.k. "comoving distance") $ r (z, \Omega) $ till dessa i ett platt ($ K = 0 $) universum. Med hjälp av ett urval av högupplösta galaxbilder från rödförskjutningar $ z \in [0.05,0.5] $ från \texttt {TNG-50} visar vi att den implementerade "Bayesian inference"-metoden framgångsrikt uppskattar $ r (z) $ inom $ 1 \sigma $ felmarginaler ($ \Delta r _ {\text{est}} = 140 $ $ (580) $ Mpc för $ z = 0,05 $ $ (0,5) $). Att inkludera dämpning i ytljusstyrka med rödförskjutning och att använda den massiva mängd av kommande galaxbilder skulle kunna minska den erhållna osäkerheten betydligt. Denna avhandling visar således en lovande väg framåt med nya maskininlärningstekniker och kommande enorma mängder av galaxbilder för att förbättra och generalisera det traditionella kosmologiska vinkeldiametertestet, vilket i sin tur har potentialen att öka vår förståelse om universum.

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京都大学 / 新制・課程博士 / 博士(理学) / 甲第24405号 / 理博第4904号 / 新制||理||1700(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 鶴 剛, 教授 井岡 邦仁, 教授 永江 知文 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

The detection of high-energy neutrinos in the EeV range requires new detection techniques to cope with the small expected flux. The radio detection method, utilizing Askaryan emission, can be used to detect these neutrinos in polar ice. The propagation of the radio pulses has to be modeled carefully to reconstruct the energy, direction, and flavor of the neutrino from the detected radio signals. This thesis outlines the effect of birefringence in ice, which splits up the radio pulse into two orthogonal polarization components with slightly different propagation speeds. The signatures resulting from birefringence can help to reconstruct the energy and direction of the neutrino. In this thesis, the effect of birefringence is derived from first principles where the only free parameter of the model is the dielectric tensor as a function of depth and direction. The introduced model can propagate full RF waveforms which for the first time allows for the accounting of interference due to changing polarization eigenvectors during propagation. The model is available open-source through the NuRadioMC framework. The predictions of the model are compared to in-situ calibration data from the ARA and ARIANNA experiments and the implications for neutrino detection are discussed. / Detektionen av högenergetiska neutriner inom EeV-intervallet kräver nya detektionsmetoder för att handskas med flödet av neutriner, som förväntas vara mycket lågt. Radiodetektormetoden, som nyttjar Askaryanemission, kan användas för att detektera dessa neutriner i polarisarna. Radiopulsernas propagering måste modelleras noggrant för att rekonstruera energin, riktningen och smaken av neutrinon från detektorns radiosignaler. Denna avhandling beskriver effekten av dubbelbrytning i is, vilket delar upp radiopulsen i två ortogonala polarisationskomponenter med något annorlunda propageringshastigheter. De signaturer som uppstår av dubbelbrytning kan hjälpa till att rekonstruera energin och riktningen hos neutrinon. I denna avhandling härleds effekterna av dubbelbrytning från grunden, där den enda fria parametern i modellen är den dielektriska tensorn som funktion av djup och riktning. Modellen som introduceras kan propagera fullständiga RF-vågformer, vilket för första gången möjliggör hänsynstagandet av interferensen som orsakas av förändrade polarisationsegenvektorer som uppstår under propageringen. Modellen är tillgänglig som öppen källkod via NuRadioMC-ramverket. Modellens förutsägelser jämförs med in-situ kalibreringsdata från experimenten ARA och ARIANNA, och vilka implikationer som modellen har för neutrinodetektion diskuteras.

<p>  Present WIMP Dark Matter search strategies are mainly focused on possible direct detection through elastic or inelastic scatterings on atomic nuclei, or with electrons. This approach<br> becomes insensitive to M(DM) < 10 GeV. Indirect DM detection refers to the search for DM-DM or DM-M annihilation, decay debris from DM particles, or other particle production,<br> resulting in detectable species. </p> <p><br>    New physics processes, initiated by cosmic ray or dark matter interactions may be observable in underground indirect search experiments by excess high multiplicity neutron<br> production in nuclear targets. Even for M(DM) < 10 GeV, DM-M interaction is capable of<br> producing large signals, >200 neutrons if the energy is deposited in a Pb target.</p> <p><br></p> <p>  The NMDS-II detector, located at an underground laboratory within the Pyhasälmi<br> complex metal mine in central Finland, collated data for 6504 ± 1 hours at 583 m.w.e.<br> and for 1440 ± 1 hours at 1166 m.w.e.. The detector system consists of a 30 cm cube<br> Pb-target surrounded by 60 He-3 proportional tubes and a two layer Geiger Counter muon<br> detection system. The lead target is used to interact with potential dark matter particles, and<br> neutron numbers are measured with He-3 tubes. The neutron event multiplicity production is<br> compared to Geant4 simulations, starting with the well measured absolute muon momentum<br> and angular distribution flux rate at sea level, then propagating the muon flux through rock<br> while preserving the momentum-angular correlation to a depth 4m above the the detector at<br> the two depth locations. The muon flux modeling is compared to the uncorrelated Miyake<br> model at each depth as verification of the muon propagation simulation. Finally, the Geant4<br> fully simulates the passage of the muon and its induced showers through a model universe<br> 10000 m^2 x 12 m depth, and the simulated response of the detector to the calculated muon<br> flux, is compared with the data. <br>  </p> <p>  The Geant4 prediction and the observed data neutron event multiplicity distributions<br> have matching power law shapes, k × n^(-p), and do not have exponential shapes. For the<br> data collected at 583 m.w.e., p=2.36±0.10 with χ2/DoF = 0.76 and for the simulation<br> p=2.34±0.01 with χ2/DoF = 1.05. At 1166 m.w.e., p=2.29±0.007 for the simulation with  χ2/DoF = 1.16. And for the data the collection with only 6 detected events above multiplicity 5, yields p=2.50 ± 0.35 predicted by the Maximum Likelihood Estimatation method. </p> <p><br></p> <p>  The DM acceptance as a function of mass is found using a proton-Pb spallation model.<br> The dark matter mass is assumed to be equal to the proton kinetic energy and to interact<br> uniformly over the volume of the lead target. The number of excess events is found to be<br> -6.1 ± 5.1, that is no excess events are observed. The upper limit with 90% confidence<br> level is then found assuming 2.3 events. The Poisson estimation then yielding search limits<br> 1.1×10^(-44) cm^(-2) for 10 GeV deposited energy, 1.9×10^(-45) cm^(-2) at 1 GeV and 3.0×10^(-45) cm^(-2) for 500 MeV deposited energy and no acceptance at 100 MeV.<br> </p> <p>    An indirect dark matter search was conducted based on DM-M interactions depositing<br> energy in a Pb-target allowing DM masses to be probed in a region 100 MeV < M(DM) <<br> 10 GeV not accessible to direct dark matter searches. Limits are placed on DM-M energy<br> deposition independent of the DM-M interaction. <br>  <br>  <br>  <br>  </p>

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Solar wind shocks and the intracluster medium comprise hot, low-density plasmas with few Coulomb collisions. Electrons there are not fluid and so gain and exchange energy by interaction with a variety of plasma waves. We explore two mechanisms for electron energization in such plasmas. In 2D kinetic simulations of solar wind shocks with low beta (magnetic pressure greater than thermal pressure), fast-mode / oblique-whistler waves accelerate electrons in bulk via proton-scale parallel electric fields; electrons’ bulk kinetic energy then converts to heat via magnetic field-aligned electrostatic wave scattering. We show and measure the heating for 2D shocks of varying magnetic obliquity and Mach number, and we qualitatively map the mechanism’s shock parameter regime. Next, consider the intracluster medium: a high-beta plasma (thermal pressure greater than magnetic pressure) in which Megaparsec-scale motions promptly trigger nanoparsec-scale plasma waves, which in turn can scatter 1–100 MeV cosmic ray electrons. Small-scale scattering combined with large-scale motion can heat electrons, and this process is called magnetic pumping. We use 1D simulations of plasma subjected to continuous bulk compression to measure the efficiency of magnetic pumping upon cosmic ray electrons. It is speculated that magnetic pumping may help re-accelerate MeV electrons to radio-emitting energies and so help explain the origin of diffuse, MHz–GHz radio halos enshrouding some clusters of galaxies.

Silicates analogous to cosmic dust were synthesized, modified, and analyzed utilizing ion-beam techniques with Rutherford backscattering spectrometry (RBS) and x-ray diffraction (XRD). Silicate dust is a common constituent in interstellar space, with an estimated 50% of dust produced in the stellar winds of M class Asymptotic Giant Branch (AGB) stars. Silicate dust acts as a surface upon which other chemicals may form (water ice for example), increasing significance in the cosmochemistry field, as well as laboratory astrophysics. Silicate formation in the stellar winds of AGB stars was simulated in the laboratory environment. Three sequential ion implantations of Fe-, MgH2-, and O- with thermal annealing were used to synthesize a mixture appropriate to silicate dust in the surface layers of a p-type Si substrate. Post implantation He+ irradiation was shown to preferentially induce crystalline formation in the analogue prior to thermal annealing. This effect is believed to originate in the ion-electron interaction in the Si substrate. The effects of ionization and ion energy loss due to electronic stopping forces is believed to precipitate nucleation in the amorphous media. For annealing temperatures of 1273 K, predominant quartz formation was found in the substrate, whereas lower annealing temperatures of 1000 K formed enstatite without post-implantation He+ irradiation, and olivine with He+ irradiation. Post annealed crystalline phase modification was investigated via x-ray diffraction and elemental compositions were investigated utilizing RBS. Finally, the interdiffusion of Fe and Mg at temperatures of 900-1100 K was investigated with RBS, and activation energies for interdiffusion were extracted for the transition from amorphous to crystalline phase in the silicate analogues. Fe had an interdiffusion energy of 1.8 eV and Mg 1.5eV. The produced analogues have similar properties to those inferred from infrared spectroscopy of the stellar winds of M-class AGB stars with an oxygen-rich outflow. This work established a method of silicate production using ion beam modifications, explored He+ irradiation effects in the annealed structures, and derived interdiffusion activation energies for Fe and Mg in the amorphous structure. Grain sizes were <100 nm with the observed formation of quartz, enstatite, and olivine.

京都大学 / 新制・課程博士 / 博士(理学) / 甲第24407号 / 理博第4906号 / 新制||理||1701(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 鶴 剛, 准教授 細川 隆史, 教授 永江 知文 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM