| 1. |
- Ahrens, Maryon
(författare)
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Investigating the potential of current and future neutrino detectors to identify the sources of the astrophysical neutrinos seen by IceCube
- 2018
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- High energy neutrino astronomy aims to view the universe with a new messenger, the neutrino. This messenger provides another window onto the universe, complementing what we can learn from photons, cosmic rays, and gravitational waves. The neutrino constitutes together with these other messengers the so-called multi-messenger approach to studying the universe.Recently, an all-sky diffuse flux of astrophysical neutrinos has been observed by the IceCube neutrino detector. However, the origins of these astrophysical neutrinos have not yet been clearly identified. Since neutrinos traverse large distances unimpeded, neutrinos from distant and individually faint sources are likely to dominate the extragalactic neutrino flux. This complicates the prospects of identifying the sources of astrophysical neutrinos.This thesis explores the requirements that different source classes put on a generic neutrino detector, in order for such a detector to be able to resolve individual sources of neutrinos, and investigates which kinds of source classes might be detectable with current and future detectors.While starburst galaxies may be difficult to resolve if they are the main source of the astrophysical neutrino flux, blazars and active galactic nuclei are promising sources that could be resolved with IceCube or next generation neutrino detectors such as IceCube Gen2.
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| 2. |
- Beise, Jakob
(författare)
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Exploring the potentials of next-generation, wavelength-shifting, optical sensors for IceCube
- 2023
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The IceCube Neutrino Observatory has sensitivity to MeV electron antineutrinos from core-collapse supernovae through an excess of the detection rate over the background. Wavelength-shifting sensors have the potential to greatly increase photon collection making it a promising candidate for improving the measurement of the supernova neutrino light curve in IceCube-Gen2. For high-energy neutrino reconstruction, the competing effect of increased photon collection and the broader time distribution necessitate detailed simulations to determine the impact. In this thesis, we investigate the sensitivity gain caused by wavelength shifters in a future IceCube-Gen2 detector regarding the detection of faint modulations of the supernova neutrino lightcurve. Furthermore, we lay the groundwork for a future high-energy reconstruction through the implementation and integration of wavelength-shifting sensors into the IceCube simulation framework.
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| 3. |
- Farias Osses, Juan Pablo, 1987
(författare)
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Th Dynamics of Star Cluster Formation
- 2018
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A major question in astrophysics is how star clusters form. These objects are important, since they are the birth sites of most stars, perhaps including our own Sun. There are different theoretical models of cluster formation and our main goal is to examine how they may affect the dynamical evolution of the stars in the system, including those stars that are ejected from the cluster. In particular, we set up cluster formation models with global initial conditions of the Turbulent Clump Model, which has been proposed as a description of gas structures within molecular clouds. We then investigate how global star formation efficiency from such a natal gas clump, overall clump density, degree of primordial mass segregation, degree of primordial binarity and binary population properties affect the subsequent dynamical evolution. In a second paper, after a major code development that allows modeling of gradual star formation, we investigate how the rate of star cluster formation affects its dynamical evolution, which is the first time such a study has been conducted for realistic clusters that have realistic binary properties. We show througth this thesis that star clusters that formed fast, i.e., during about one free-fall time, show quite different properties than star clusters that forms in a slow quasi-equilibirum fashion. Quickly-formed clusters tend to expand much faster compared to slow-formed clusters, thus requiring higher initial densities to agree with observations. Creation of the runaway stellar population is also sensitive to the rate of cluster formation. Future directions of this work, adding greater degrees of realism are also discussed. Finally, we carry out an example study of how the observed properties of a particular set of runaway stars can constrain properties of the dynamical ejection event, with implications for the closest region of massive star formation in the Orion Nebula Cluster.
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| 4. |
- Gray, Taylor, 1996
(författare)
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Producing Dark Matter at Particle Accelerators: Extending the landscape and performing global fits of Light Dark Matter theories
- 2024
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- There is overwhelming evidence for the existence of an unknown and dark mass in the universe from several different observations. This missing mass has been coined dark matter (DM), with one hypothesis being that its nature is a new type of particle which interacts minimally with ordinary matter. Major experimental efforts attempting to search for interactions between DM and ordinary matter are currently in place, with no convincing evidence of discovery so far. These experiments have largely been geared for DM with masses O(GeV-TeV), with the main search channel being nuclear recoils from DM scattering. However, DM with lighter masses, O(MeV-GeV), have been gaining significant interest recently since they can account for the measured cosmological DM relic abundance while evading nuclear recoil direct detection constraints. Since such light DM does not carry enough momentum to be probed optimally via nuclear recoils, other search strategies such as direct detection via electron recoils and accelerators are ideal for this mass range. Here we study the vast theory potential of accelerator based experiments, in particular fixed target experiments, on motivated sub-GeV DM models. In Paper I, we consider two theoretical frameworks for spin-1 sub-GeV DM, so called simplified and SIMP models, both of which are testable by current and future experiments such as the upcoming (Light Dark Matter eXperiment) LDMX. We find that simplified models are subject to strong bounds from experiments, cosmological observations, and unitarity. However SIMPs, a more sophisticated framework for spin-1 DM, are not subject to unitarity violations and current experimental constraints, while being consistent with the relic abundance measurement and in reach of near future experimental sensitivities. There is a growing number of constraints from laboratory experiments and astrophysical and cosmological observations on sub-GeV DM, each giving information on the viable parameter space not yet excluded. In Paper II, we compare these observations with the predictions of two sub-GeV DM models (Dirac fermion and complex scalar DM). We perform this comparison within frequentist and Bayesian global analyses using the Global And Modular BSM Inference Tool (GAMBIT) extended in this work. We infer the regions of parameter space preferred by current data, and compare with projections of near future experiments.
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| 5. |
- Jansson, Matti, 1982-
(författare)
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Geometry Calibration of IceCube : using Photon Timing from Downgoing Muons
- 2022
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The IceCube Neutrino Observatory at the South Pole has instrumented one cu-bic kilometer of ice by deploying digital optical modules (DOMs) in 86 drillholes, each containing a string of DOMs. So far IceCube has used the locationof the drill tower for the positions of DOMs in the transverse directions (x andy) to the vertical direction (z). Attempts to improve on this have so far failed.This thesis presents a new method for calibrating the positions of the DOMs.For a large selection of muon tracks, a maximum likelihood-based approach isused to determine the positions of DOMs. As a proof of concept, four centralstrings are studied to keep systematics uncertainties as low as possible. Themethod can find x and y (z) positions to 0.2m (0.5m) as found using simulationcorresponding to four days of data. In four days of real data we find that thereconstructed z position has a systematic offset of around 5m, which is not aphysical shift as the positions are known to 0.2m. For the x and y positions theresults are consistent with nominal positions except for string 36. As string 36is a string at the center of the IceCube array, it should be the most symmet-ric and an accurate estimate could indicate that the method has found a realdeviation.
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| 6. |
- Morå, Knut Dundas, 1989-
(författare)
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A Search for Dark Matter Lines with H.E.S.S. II
- 2016
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Most of the matter in the universe, ~80% is thought to be dark matter- particles that have small or no interactions with standard model particles. Dark matter is an integral part of the current understanding of cosmology, and leaves signs in the movements of stars and galaxies, as well as the Cosmic Microwave Background. The erakly interacting massive particle (WIMP) is a well-studied dark matter model that would be expected to have a mass around the weak scale, 100 GeV. WIMPs annihilating in the galactic center could give rise to mono- energetic gamma-rays in addition to a more extended spectrum. This thesis details a search for a dark matter line in a region 1.5° west of the galactic center using the High Energy Stereoscopic System (H.E.S.S.) imaging air Cherenkov telescope. The inclusion of a fifth telescope in the array enabled the analysis to extend the HESS energy range down to 100 GeV for a spectral line search. At 130 GeV, a limit of 1.38 10^-27 cm^3/s on the velocity-weighted cross-section at 95% confidence limit could be set using15.2 hours of data. The analysis is the first paper using all five telescopes of H.E.S.S. II. The main subject of the thesis has been in optimization of this analysis as well as future H.E.S.S. pointings.
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| 7. |
- Valtonen-Mattila, Nora
(författare)
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Extending the observational reach of core-collapse supernovae for IceCube using high-energy neutrinos
- 2022
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Neutrino telescopes such as IceCube monitor for low-energy neutrinos O(10 MeV) produced in nuclear processes during core-collapse in supernovae. The detection horizon to the neutrino burst is 50 kpc, the distance to the Magellanic Clouds. However, this limits the number of supernovae accessible through low-energy neutrino detection, as the Galactic rate is only 2 per century. Some models predict the production of high-energy O(>GeV) neutrinos through acceleration mechanisms, such as the ejecta colliding with the circumstellar material or relativistic jets in the stellar envelope. This thesis examines how these high-energy neutrinos could be exploited with neutrino telescopes like IceCube to extend the detection horizon to core-collapse supernovae past the Magellanic clouds. To examine the detection horizon for IceCube, we use two data samples, one utilizing muon tracks which provide good sensitivity in the northern sky, and the other all flavor starting events, which provide good sensitivity in the southern sky. We demonstrate that extending the reach past 50 kpc and well into the 10s of Mpc is possible, where the expected rate is more than two core-collapse supernovae per year.
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| 8. |
- Georgieva, Iskra, 1987
(författare)
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From Photons to Worlds: An odyssey in exoplanet detection and characterisation
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Since the first unambiguous detection of a planet around a Sun-like, the interest in the new and exciting field of exoplanets has grown immensely. New and exciting developments are seen at a pace unparalleled for most subfields of astronomy and astrophysics. In this thesis, I describe the two most successful techniques for exoplanet detection and characterisation - transits and radial velocities - and the challenges commonly encountered in extracting the planets from the data. Transit photometry allows us to measure the planet radius, while radial velocity measurements give us the planet's minimum mass. These methods' true strength, however, manifests in their combination as it allows us to estimate the true mass, which together with the radius gives us an estimate of a planet's bulk density. This is a powerful quantity, which allows us to speculate about the structure and composition of a planet's interior and atmosphere. I describe the process of detecting a planet in a stellar light curve, and how transits and radial velocities are modelled together in order to determine the planet parameters. I demonstrate how the ideal theoretical approach can be used to study a system in practice. However, the current challenges in exoplanet characterisation surpass the ideal case, leading us to explore more complex models. Finally, I show how by extending the ideal planet approach with non-parametric models, we can detect planets in complicated datasets, as demonstrated by the case of the TOI-1260 multi-planet system.
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| 9. |
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| 10. |
- Otto, Ernst, 1971
(författare)
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Direct Write Technology of SIN Tunnel Junctions for Thermometry and Microwave Devices
- 2008
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis concerns development of SIN junction technology for thermometry and microwave detectors, as well as technology of a planar phase switch as a part of integratedmicrowave receiver.Cold-Electron Bolometer (CEB) is a sensitive detector of a microwave radiation, in which SIN tunnel junctions are used for temperature measurement of a nanoscale absorber in thesame way as in SIN thermometers. A novel direct-write trilayer technology and a Ti-based technology were developed for the CEB and thermometry.The trilayer technology is based on in-situ evaporation of the superconductive electrode followed by the oxidation and the normal counter-electrode as a first step and deposition of a normal-metal absorber as a second one. The junctions were characterized as temperature sensors, and a thermometer responsivity of 52 mV/K was observed for an array of 100junctions in series with a temperature resolution of ± 5μK.A novel Ti-based direct-write technology for fabrication of Ti-TiO2-Al tunnel junctions has another advantages related to thickness of the absorber. In particular, a very thin andcompletely flat absorber can be created with no bending parts. The key point of this technology is deposition of Ti film as a base electrode and deposition of Al electrode after oxidation of Ti.The junctions are to be used for fabrication of microwave receivers for sensitive measurements in new generation of telescopes, e.g. CLOVER project including polarizationCosmic Microwave Background (CMB) radiation measurements, BOOMERANG and OLIMPO balloon telescope project which is dedicated to measuring the Sunyaev-Zeldovich effect in clusters of Galaxies.A planar phase switch operating at 97-225 GHz has been developed, fabricated, and tested. The system makes it possible to modulate the microwave signal or switch it between two branches of a circuit with low losses and high speed. The proposed fully planar design allowsthe switch to be integrated into the detector circuit.The phase modulation scheme will be used in high-precision astrophysical experiments such as the investigation of the polarization of the cosmic microwave background.Keywords: SIN tunnel junction, direct write technology, Cold-Electron Bolometer, cryogenicthermometry, phase switch, microwave device, noise equivalent power
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