Coming dissertations at Uppsala university
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Cohomologies for String Amplitudes
Link: http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-525887
In this thesis we cover methods useful for the low-energy-expansion, or α’-expansion of string amplitudes. The task of α’-expanding a string amplitude can be divided into two steps: decomposing your string amplitude into a family of integrals, and figuring out how to α’-expand each integral in these families. We review such integrals, which we call string integrals, in this thesis.
Related to string integrals, we also introduce versions of these integrals were some punctures are not integrated over. We call the resulting integrals stringy integrals, and these are going to be functions of these leftover punctures (and τ in the genus-one case). We characterize these family of stringy integrals at genus-zero and genus-one, which includes knowing what differential equations they satisfy and their α’-expansion. In fact, the differential equation of these integrals is crucial to obtain efficient α’-expansions, as generating functions of multiple polylogarithms or their elliptic counterparts, and highlight mathematical properties these integrals exhibit. We also study such generating functions of multiple polylogarithms in an abstract setting, to better understand properties of polylogarithms themselves.
We finalize with some discussion of twisted cohomology, and how it can be used to give a mathematical foundation for some of our families of stringy integrals, making them true bases of integrals. Hence, the title of the thesis. Moreover, we use twisted cohomology at genus-one to find a double-copy formula for some of our stringy integrals, and related them to generating functions of elliptic modular graph forms.
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From Quantum to Classical Scattering of Kerr Black Holes : A construction of massive higher-spin scattering amplitudes and their classical limits.
Link: http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-525178
Gravitational scattering processes involving black holes as asymptotic states can provide insight into the classical dynamics of binary black hole systems. The observed gravitational waves emitted during mergers need to be compared to high-precision theoretical predictions. By modelling black holes as massive point particles in an effective quantum field theory, one can take advantage of the advanced computational tools originally designed for collider physics. For Schwarzschild black holes the natural objects to study are scattering amplitudes involving massive scalar fields with interactions mediated by gravitons. The classical physics is extracted by considering limits of the kinematics.
Extending this effective description to rotating Kerr black holes introduces subtleties. To leading order in the post-Minkowskian perturbation scheme, there now exists candidate three-point scattering amplitudes for massive higher-spin particles that in the classical limit reproduce the Kerr metric. For small quantum spins, these are given by familiar theories of interacting massive fields which have a well-behaved massless limit. These theories are sufficient to capture the first few spin-multipole orders for the classical observables; however, to capture more orders one is required to use input from higher-spin theories. The three-point higher-spin amplitudes were originally introduced without reference to an underlying Lagrangian description. Lagrangians for interacting higher-spin fields are notoriously complicated as they necessarily describe composite fields in an effective higher-derivative theory.
This thesis explores the underlying higher-spin effective theories suitable for describing rotating black holes, and proposes a new spin-s family of Compton scattering amplitudes. We present two complementary constructions for consistent interacting higher-spin Lagrangians: the first relies on massive higher-spin gauge symmetry to remove unwanted states, and the second one manifests the correct degrees of freedom using a chiral field framework. A significant portion of the thesis discusses how to extract classical physics from quantum amplitudes, focusing on consistent treatments of the spin degrees of freedom. The resulting quantum and classical Compton amplitudes are built to be consistent with perturbations of the Kerr metric, through a combination of constraints from higher-spin considerations and classical analysis.
In addition to the black-hole amplitudes, we study the scattering of higher-spin fields in a gauge theory referred to as root-Kerr. The three point amplitudes of this gauge theory are closely related to the Kerr ones, such that it provides an instructive model for both higher-spin consistency and classical analysis. Another toy model discussed is the scattering of higher-spin superstring states on the leading Regge trajectory.
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Astrocytes in Alzheimer’s disease : Exploring the impact of amyloid-β pathology on neurotoxicity, metabolism and inflammation.
Link: http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-525110
Astrocytes play a central role in brain homeostasis, but are also tightly connected to the pathogenesis of Alzheimer’s disease (AD). Yet, their exact role in amyloid-beta (Aβ) pathology and chronic neuroinflammation is unclear. The aim of this thesis was to elucidate the impact of astrocytes in AD progression. For this purpose, astrocytes in different culture set-ups were exposed to soluble Aβ aggregates. The astrocytes engulf and process, but fail to fully degrade the Aβ aggregates, which are instead stored as large intracellular deposits. In Paper I, we show that extracellular vesicles (EVs), secreted from the Aβ-containing cells induce synaptic loss, axonal swelling and vacuolization of primary neurons, which consequently leads to apoptosis.
Astrocytes play a central role in the brain’s energy metabolism and we were therefore interested in how Aβ pathology affects their metabolism. In Paper II, we report that Aβ accumulation in astrocytes disrupts mitochondrial fission/fusion homeostasis, resulting in decreased mitochondrial respiration and altered glycolysis. Interestingly, the astrocytes switch to fatty acid β oxidation with the aid of peroxisomes to maintain stable energy production.
Another important task is to understand how astrocytes modify the ingested Aβ. In Paper III, we characterized the astrocytic Aβ inclusions by isolating them with magnetic beads. Our analysis showed that the astrocytes truncate and pack together the Aβ aggregates. Moreover, we found that astrocytes release specifically truncated forms of Aβ via different routes.
Astrocytes’ involvement in lipid metabolism and inflammation has recently gained much interest, but many questions remain about the connection between these processes. In Paper IV, we show that Aβ pathology causes lipid droplet (LD) accumulation in astrocytes. Moreover, we could show that astrocytes frequently transfer LDs to neighboring cells, both through direct cell-to-cell contacts and via secretion. Astrocytes have previously been reported to express major histocompatibility complex II (MHCII) and have the capacity to perform as professional antigen presenting cells. Interestingly, our results demonstrate that LDs contain MHCII, identifying a link between LDs and inflammation in astrocytes.
Taken together, this thesis contributes with important knowledge of the role of astrocytes in AD pathology.