| 1. |
- Brink, Lars, 1943
(författare)
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Stanley Mandelstam and me and life on the light-cone
- 2017
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Ingår i: Memorial Volume For Stanley Mandelstam. - : WORLD SCIENTIFIC. - 9789813207851 ; , s. 97-111
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Stanley Mandelstam has always been one of my heroes in physics. Here I will describe my meetings with Stanley over the years and how our respective work sometimes coincided.
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| 2. |
- Persson, Daniel, 1978
(författare)
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Arithmetic and Hyperbolic Structures in String Theory
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis consists of an introductory text followed by two separate parts which may be read independently of each other. In Part I we analyze certain hyperbolic structures arising when studying gravity in the vicinity of spacelike singularities (the BKL-limit). In this limit, spatial points decouple and the dynamics exhibits ultralocal behaviour which may be mapped to an auxiliary problem given in terms of a (possibly chaotic) hyperbolic billiard. In all supergravities arising as low-energy limits of string theory or M-theory, the billiard dynamics takes place within the fundamental Weyl chambers of certain hyperbolic Kac-Moody algebras, suggesting that these algebras generate hidden infinite-dimensional symmetries of gravity. We investigate the modification of the billiard dynamics when the original gravitational theory is formulated on a compact spatial manifold of arbitrary topology, revealing fascinating mathematical structures known as galleries. We further use the conjectured hyperbolic symmetry E10 to generate and classify certain cosmological (S-brane) solutions in eleven-dimensional supergravity. Finally, we show in detail that eleven-dimensional supergravity and massive type IIA supergravity are dynamically unified within the framework of a geodesic sigma model for a particle moving on the infinite-dimensional coset space E10/K(E10). Part II of the thesis is devoted to a study of how (U-)dualities in string theory provide powerful constraints on perturbative and non-perturbative quantum corrections. These dualities are typically given by certain arithmetic groups G(Z) which are conjectured to be preserved in the effective action. The exact couplings are given by moduli-dependent functions which are manifestly invariant under G(Z), known as automorphic forms. We discuss in detail various methods of constructing automorphic forms, with particular emphasis on a special class of functions known as (non-holomorphic) Eisenstein series. We provide detailed examples for the physically relevant cases of SL(2,Z) and SL(3,Z), for which we construct their respective Eisenstein series and compute their (non-abelian) Fourier expansions. We also discuss the possibility that certain generalized Eisenstein series, which are covariant under the maximal compact subgroup K(G), could play a role in determining the exact effective action for toroidally compactified higher derivative corrections. Finally, we propose that in the case of rigid Calabi-Yau compactifications in type IIA string theory, the exact universal hypermultiplet moduli space exhibits a quantum duality group given by the Picard modular group SU(2,1;Z[i]). To verify this proposal we construct an SU(2,1;Z[i])-invariant Eisenstein series, and we present preliminary results for its Fourier expansion which reveals the expected contributions from D2-brane and NS5-brane instantons.
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| 3. |
- Scott, Pat, 1982-
(författare)
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Searches for Particle Dark Matter : Dark stars, dark galaxies, dark halos and global supersymmetric fits
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The identity of dark matter is one of the key outstanding problems in both particle and astrophysics. In this thesis, I describe a number of complementary searches for particle dark matter. I discuss how the impact of dark matter on stars can constrain its interaction with nuclei, focussing on main sequence stars close to the Galactic Centre, and on the first stars as seen through the upcoming James Webb Space Telescope. The mass and annihilation cross-section of dark matter particles can be probed with searches for gamma rays produced in astronomical targets. Dwarf galaxies and ultracompact, primordially-produced dark matter minihalos turn out to be especially promising in this respect. I illustrate how the results of these searches can be combined with constraints from accelerators and cosmology to produce a single global fit to all available data. Global fits in supersymmetry turn out to be quite technically demanding, even with the simplest predictive models and the addition of complementary data from a bevy of astronomical and terrestrial experiments; I show how genetic algorithms can help in overcoming these challenges.
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| 4. |
- Dall` Olio, Daria, 1981
(författare)
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Magnetic fields around massive protostars as traced by masers and dust emission
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- It is not fully clear how the magnetic field acts during the first stages of star formation. A possible way to clarify its role is to observe the polarized light coming from masers and thermal dust emission. By measuring linear polarization angles and Zeeman splitting of different maser species it is possible to study the magnetic field morphology and strength in different parts of the protostar. Polarized emission of thermal dust has also been used extensively to probe the magnetic field at the onset of star formation. In this thesis we study the magnetic field properties of two well-known sources: the massive protostar IRAS18089-1732, showing a hot core chem- istry and a disc-outflow system, and the high-mass star forming complex G9.62+0.19, presenting several cores at different evolutionary stages. We also investigate the polarization properties of selected methanol masers, con- sidering newly-calculated methanol g-factors and hyperfine components. We compare our results with previous maser observations and we evaluate the contribution of preferred hyperfine pumping and non-Zeeman effects. We make use of MERLIN and ALMA observations and we analyse the polarized emission by 6.7 GHz methanol masers and thermal dust. Simulations were run using the radiative transfer code CHAMP for different magnetic field values, hyperfine components and pumping efficiencies. We observe that the large scale field probed by dust continuum emission is consistent with the small scale magnetic field probed by masers. Moreover, in the G9.62+0.19 complex we resolved several cores showing polarized emission. We propose an evolutionary sequence of magnetic field in this complex, where the less evolved stellar embryo exhibits a magnetic field stronger than the more evolved one. From our simulations, we find that preferred hyperfine pumping can explain some high levels of linear and circular polarization. We also notice that non-Zeeman effects need to be considered in magnetic field studies. In conclusion, our work indicates that there is a link between the magnetic field at different scales. More masers observations will help in evaluating the relevance of non-Zeeman effects and obtain good estimates of magnetic fields close to the protostar. Future multi-wavelength and multi-scale observations, aimed at detecting polarized light from masers, thermal dust and thermal molecular lines, will help to constrain magnetic field properties around massive protostars.
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| 5. |
- Urdshals, Einar, 1995
(författare)
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Dark matter electron interactions in detector materials
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Dark Matter (DM) makes up 85% of the matter content of the universe, and its gravitational effects are seen on scales ranging from that of cosmology to that of galactic astrophysics. The nature of DM is, however, unknown. Study- ing DM in the lab with a class of experiments called direct detection (DD) experiments is key to understanding its properties. For decades, experiments have been attempting to do this through searches for DM induced nuclear recoils. These have not been found, and a possible reason for this is that the hypothetical DM particle is too light to induce nuclear recoils. Therefore, in the last decade experiments have been built to study DM through electron recoils instead. As the electron is 4 orders of magnitude lighter than the nu- cleus, electron recoils can be induced by DM down to 4 orders of magnitude lighter than the lightest DM particle probeable with nuclear recoils. In order to understand current and upcoming results from experiments searching for DM induced electron recoils, a theoretical understanding of DM electron scatterings in detector materials is needed. When modelling such electron interactions, one need input both from DM and material physics. This thesis improves the theoretical understanding by both improving the material description using density functional theory (DFT), and by extending the DM description using non-relativistic effective theory (NR-EFT) tools. The improvement gives not only a more accurate description of the DM- electron interactions that the experiments are expected to see; it also vastly extends the forms of DM that can be studied in direct detection experiments. Before this extension, one typically focused on a benchmark case of DM, the so called dark photon model. With this extension, one can cover all forms of gravitationally bound DM with spins of 0, 1/2 or 1. In the included works, advances are made in the description of DM-electron interactions in common detector materials such as liquid xenon, silicon and germanium, as well as to materials in the research and development phase, such as graphene and carbon nanotubes (CNTs).
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| 6. |
- Zema, Vanessa, 1991
(författare)
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Unveiling the nature of dark matter with direct detection experiments
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The desire of discovery is an anthropic need which characterises and connects the human being over the eras. In particular, observing the sky is an instinctive drive exerted by the curiosity of the mysteries which it retains. At the present time, the tremendous advances in the exploration of space have opened even more challenges than back in the days. One of the most urgent question is unveiling the nature of dark matter (DM). As stated by Neta A. Bahcall (Professor at Princeton University), "Cosmology has revealed an amazing universe, filled with a "dark sector" that composes 95% of the energy density of our cosmos [...]" ( Dark matter universe , PNAS, 2015). About one-third of this dark sector is associated to an invisible and still undetected form of matter, the so-called dark matter, whose gravitational effect manifests at all cosmological scales. Both theoretical and experimental observations based on ordinary gravity reinforced the evidences for the existence of DM, since its first appearance in the pioneering calculations of F. Zwicky (1933). This PhD project explores the hypothesis that DM is made of new particles beyond the standard model. More specifically, it focuses on those DM particles which are trapped into the galactic gravitational field and populate the galactic halo. If DM interacts with ordinary particles, extremely sensitive detectors operating in very low-background environments, are expected to detect galactic DM particles scattering off their target material. This widely employed experimental technique is known as DM direct detection and it is the focus of my studies, where I consider the further hypothesis that DM interacts with atomic nuclei. The research I conducted during my PhD program consists of two main parts: the first part focused on purely phenomenology aspects of the DM direct detection (namely on the DM annual modulation treated using a non-relativistic effective theory and on the scattering of spin-1 DM particles off polarised nuclei) and the second one is more closely connected to experimental applications. The latter has been strongly stimulated by my collaboration with the two DM direct detection experiments CRESST and COSINUS. For CRESST, I compute the DM-nucleus cross-section for the conventional spin-dependent interactions, used to analyse the data collected with a prototype Li-based detector module, and I derive some prospects for a time dependent analysis of CRESST-III data, using a statistical frequentist approach based on Monte Carlo simulations. For COSINUS, I provide a significant extension of the pulse shape model currently used by CRESST and COSINUS in order to explain experimental observations related to the COSINUS detector response. Finally, I contribute to ongoing studies on the phonon propagation in NaI crystals based on solid state physics. This PhD thesis has been oriented to fill the gap between theoretical and experimental efforts in the DM field. This approach has facilitated the exchange of expertise, has driven the trend of my research and has stimulated the development of the ideas and methods described in this PhD thesis.
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| 7. |
- Arnadottir, Anna, et al.
(författare)
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Universums mörka hemlighet
- 2018
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Konstnärligt arbete (övrigt vetenskapligt/konstnärligt)abstract
- Here we follow the exciting exploration of dark matter, from the Big Bang to its anticipated discovery at the Large Hadron Collider. The first hints of dark matter were wound by Fritz Zwicky, the scientist who coined the term. We get to see the astral choreography witnessed by Vera Rubin in the Andromeda galaxy and then plummet deep underground to see the most sensitive dark matter detector on Earth, housed in a former gold mine.From there, we journey across space and time to the Large Hadron Collider at CERN, speeding alongside particles before they collide in visually stunning explosions of light and sound, while learning how scientists around the world are collaborating to track down the constituents of dark matter.
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| 8. |
- Forsberg, Mats, 1978-
(författare)
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Gravitational perturbations in plasmas and cosmology
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Gravitational perturbations can be in the form of scalars, vectors or tensors. This thesis focuses on the evolution of scalar perturbations in cosmology, and interactions between tensor perturbations, in the form of gravitational waves, and plasma waves. The gravitational waves studied in this thesis are assumed to have small amplitudes and wavelengths much shorter than the background length scale, allowing for the assumption of a flat background metric. Interactions between gravitational waves and plasmas are described by the Einstein-Maxwell-Vlasov, or the Einstein-Maxwell-fluid equations, depending on the level of detail required. Using such models, linear wave excitation of various waves by gravitational waves in astrophysical plasmas are studied, with a focus on resonance effects. Furthermore, the influence of strong magnetic field quantum electrodynamics, leading to detuning of the gravitational wave-electromagnetic wave resonances, is considered. Various nonlinear phenomena, including parametric excitation and wave steepening are also studied in different astrophysical settings. In cosmology the evolution of gravitational perturbations are of interest in processes such as structure formation and generation of large scale magnetic fields. Here, the growth of density perturbations in Kantowski-Sachs cosmologies with positive cosmological constant is studied.
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| 9. |
- Georgieva, Iskra, 1987
(författare)
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A Cosmic Quest for New Worlds. Characterising Exoplanet Signals via Radial Velocity and Transit Photometry.
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Since the first unambiguous detection of a planet around a Sun-like star, 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. 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 the planet’s bulk density. This is a powerful quantity, which allows us to construct models and make predictions about the structure and composition of a planet’s interior, as well as its atmosphere. Zeroing in on the latter two is currently one of the biggest challenges for exoplanet characterisation. 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. This is then followed by the ideal theoretical approach, which 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. I then discuss the biggest nemesis to planet discovery, particularly in radial velocity timeseries – stellar activity, and the problem of its often stochastic manifestation. A special focus is given to one method for its mitigation – modelling the radial velocities alongside activity indicators. This is the core concept of multi-dimensional Gaussian process regression, particularly with the quasi-periodic covariance function, which is used in a large part of this work. Finally, the last part if the thesis shows that while the ideal planet case can sometimes be applicable for quiet stars, as is the case of the TOI-2196 system, extending to non-parametric models, such as Gaussian processes, can help us to detect planets in complicated datasets, as demonstrated by the cases of the TOI-1260, TOI-733, TOI-776 and TOI-1416 systems.
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| 10. |
- Enestarre, Carina, et al.
(författare)
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The Library Treasure Hunt: Reach for the Stars. Introducing First Year Students to the Landscape of Scientific Information
- 2015
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Ingår i: ASP Conference Series. - 9781583818688 - 9781583818695 ; 492, s. 248-253
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- One important task for the librarians at Physics and Astronomy Library at Lund University is to teach the students about the library and its resources. The traditional lectures and tours of the library just weren’t working. The library competes with many other introductory activities, such as general orientation, and social events. The aim of the Treasure Hunt is to present the library in a useful and amusing way for new students at the start of their studies. Divided into small groups, the students carry out various tasks at stations in the participating libraries. The hunt takes about two hours and a treasure (a goody bag) waits for them at the end. The evaluations show that the treasure hunt is highly appreciated by the students. They become familiar with the librarians and get to know essential aspects of the library resources. The treasure hunt is important in the students’ later studies as it paves the way for further development of their information retrieval skills. A crucial factor to success of the Treasure Hunt is the cooperation of committed teachers. A challenge for the future is to have the Treasure Hunt integrated in all courses as a compulsory element.
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