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Senast publicerade

Classical ghosts - A literature study of the Batalin-Vilkovisky formalism
Andersson, Leo
Gauge symmetry appears in many physical theories and is often handled by just imposing gauge choices, i.e. removing the gauge symmetry as it consists of unphysical degrees of freedom. This approach may fail when symmetries do not close on-shell and obscures underlying structure of the theory. The Batalin-Vilkovisky formalism describes the connected structure of (higher) gauge symmetries, their corresponding (higher) Noether identities and equations of motion, by introducing a plethora of extra fields called ghosts, antifields and antighosts to represent these. This literature study starts with the introduction of graded structures, from graded vector spaces to Q-manifolds and their duals L∞-algebras, whereafter the physical phenomena and problems that motivates the BV formalism are explained. These phenomena and the formalism itself are then formulated in terms of the introduced mathematical framework. The extra fields are regarded as elements or sections of a symplectic Q-manifold. Central for the BV formalism is an action S that through the symplectic structure induces a differential which in turn gives the equations of motion, gauge transformation etc. when it acts upon the corresponding field. In the L∞-dual description the gauge symmetries etc. are formulated in terms of higher products that generalise the Lie bracket, while equivalence between physical theories corresponds to quasi-isomorphisms. After some minor examples and calculations the thesis ends by revisiting a BV formulation of 10D supersymmetric Yang-Mills, with the help of bosonic spinors and weight partition functions.
Investigation of the influence of coating and drying methods of catalytic inks on the structure of resulting electrodes for Proton Exchange Membrane Fuel Cells
(2024) Nair, Sandeep Jayaprakash
In the decal transfer process of making catalyst electrode coatings for Proton Exchange Membrane Fuel Cells (PEMFCs), understanding the coating and drying parts of the process is important to get desired final electrode structures. Coating and drying are also important manufacturing steps and must be optimized for this as well. The structural evolution during drying from ink microstructure to the electrode microstructure yields the resulting pore structure at a micro scale, and at a larger length scale the crack morphology. To achieve the desired structures, we need to make both a well dispersed catalyst ink with good interaction of components and provide favorable drying conditions. In this study, different solvent combinations and dry weights in ink, and different drying conditions of temperature and vapor pressures were explored. Qualitative inspection of digital microscope images of the electrodes was used to analyze dried structure and cracks. Critical Crack Thickness (CCT), the height up to which a coating can inhibit cracks well, and the maximum catalyst loading in each setting was monitored. Results showed that 1-propanol rich solvent matrix with water gave the least cracks and highest CCTs in comparison to ethanol and tert-butanol for the studied catalyst and ionomer. Higher temperatures did not have a strong impact on crack morphology or CCT for the same ink recipes but reduced the drying time. Higher vapor pressure of alcohol above the wet ink coating led to slower drying and enabled higher CCTs. The experiments enabled us to achieve coatings with a loading of 0.7 mg/cm2 and a CCT of 250 microns, robust to higher temperature drying conditions, which was not possible before with recipes described by suppliers. The results here are promising for making high performance electrodes in-house and has set a foundation for future work on fuel cells for a variety of applications, helping the green energy transition.
Cooper Pair Spectroscopy for Odd-Frequency Superconductors
(2026) Hermansson, Johan
In conventional spin-singlet superconductors with even parity, the anomalous pairing amplitude is even in frequency. Odd-frequency superconductivity is an unconventional superconducting state in which the pair amplitude is odd under exchange of time coordinates. Since superconducting pairing is encoded in two-particle correlations, double photoelectron spectroscopy provides a natural framework for probing such states through the simultaneous detection of two photoemitted electrons. When applied to superconducting samples, this approach is commonly referred to as Cooper pair spectroscopy. In this thesis, a Green’s-function formulation of Cooper pair spectroscopy for odd-frequency superconductors is developed by extending the theoretical structure of angle-resolved photoemission spectroscopy to the doublephotoemission case. Starting from an expansion of the S-matrix, the double-photoelectron counting rate is derived to second order, which is the lowest order giving a non-vanishing contribution. The result separates into an anomalous contribution, expressed through greater anomalous Green’s functions, and a normal contribution, expressed through lesser normal Green’s functions. The anomalous part describes correlated emission associated with a single Cooper pair, while the normal part describes contributions from ordinary single-particle correlations. The main result is that odd-frequency pairing leads to a different momentum structure in the anomalous contribution than conventional even-frequency pairing. In particular, the odd-frequency kernel contains a difference of screened Coulomb potentials, whereas the even-frequency case contains their sum. Consequently, for a symmetric screened Coulomb potential, the momentum dependence of the electron– photon coupling becomes essential for obtaining a finite odd-frequency anomalous contribution. The derived expression therefore identifies a key formal distinction between even- and odd-frequency superconductors in double photoelectron spectroscopy and provides a basis for future numerical and experimental investigations.
Modeling Human-Drone Proxemics in an Augmented Reality Environment
Malm, Vilmer; Raimer, Hugo
As drones increasingly move into human-occupied spaces, they must be able to navigate in ways that are not only safe but also socially acceptable. This thesis investigates human-drone proxemics in an augmented reality (AR) environment, with the aim of modeling the interpersonal distances people prefer when approached by a social drone. Building on prior two-dimensional rubber-sheet models from human-robot proxemics, this work extends the approach into a three-dimensional “rubber-bubble” model suitable for drones. A user study was conducted in Sweden and Vietnam (N = 69), where participants interacted with a virtual drone approaching from 21 different angles in an area in front of them. Participants indicated when the drone reached their preferred stopping distance, producing a dataset used to evaluate approach-angle effects, demographic variables as predictors, cultural differences, and various degrees of personalization. The methodology combined statistical testing, polynomial rubber-bubble models, linear mixed models, and Bayesian modeling for an exhaustive and exploratory analysis. The results show that rubber-bubble models can represent individualized proxemic preferences within the observed frontal zone, suggesting usefulness for autonomous drone navigation. Gender and culture both showed potential in predicting stopping distances. In summary, this work contributes with an extension of 2D rubber-sheet to 3D rubber-bubble modeling, a thorough analysis of demographics and culture as potential predictors for human-drone proxemics, and an open-source AR environment for safe and repeatable human-drone research.
Maelstrom Crawler: A feedback-driven web vulnerability scanner - Improving web vulnerability scanning with dynamic strategies
Morisbak Olsson, Oscar; Mert Tekin, Roj
Web application vulnerability scanners rely on crawlers to explore applications and discover potential attack surfaces. The effectiveness of these scanners is therefore heavily influenced by the crawler’s ability to navigate diverse applications. Most existing crawlers use a fixed navigation strategy, despite different strategies often being more effective in different contexts. This thesis investigates whether a crawler that dynamically switches between navigation strategies based on feedback it receives at runtime can improve web application vulnerability scanning. To address this problem, we design and implement the Maelstrom Crawler, a feedback driven extension of the open-source Black Widow vulnerability scanner. Maelstrom dynamically alternates between randomised BFS and randomised DFS exploration using feedback channels that monitor the progress during execution and suggest when to switch strategy. An initial set of nine candidates for feedback channels was analysed using principal component analysis and an ablation study, resulting in five selected channels: growth, duplicate candidates, URL diversity, error rate, and novel code. These channels together guide the strategy-switching decisions through a majority voting based mechanism. To prevent excessive switching and thrashing, the design includes comparison and baseline windows together with a cooldown period. The final design was evaluated on three open-source applications: OsCommerce, WordPress, and Kanboard. Results show that Maelstrom Crawler achieved an average code coverage improvement of 9.63% compared to Black Widow, 91.68% compared to OWASP ZAP, and 70.74% compared to EvoCrawl. Internal experiments further demonstrated that feedback-driven strategy switching outperformed purely random switching. However, the improved code coverage did not consistently translate into increased vulnerability discovery, highlighting a gap between exploration effectiveness and vulnerability detection. The results indicate that feedback-driven strategy adaptation can improve crawler exploration efficiency and code coverage in web applications. Furthermore, they suggest that dynamically combining multiple navigation strategies is a promising direction for future web vulnerability scanners.