Fundamental Physics

Due to the difficulties of finding superconformal Lagrangian theories for multiple M2-branes, we will in this paper instead focus on the field equations. By relaxing the requirement of a Lagrangian formulation we can explore the possibility of having structure constants $f^{ABC}{}_D$ satisfying the fundamental identity but which are not totally antisymmetric. We exemplify this discussion by making use of an explicit choice of a non-antisymmetric $f^{ABC}{}_D$ constructed from the Lie algebra structure constants $f^{ab}{}_c$ of an arbitrary gauge group. Although this choice of $f^{ABC}{}_D$ does not admit an obvious Lagrangian description, it does reproduce the correct SYM theory for a stack of $N$ D2-branes to leading order in $g_{YM}^{-1}$ upon reduction and, moreover, it sheds new light on the centre of mass coordinates for multiple M2-branes.

We investigate half-supersymmetric domain wall solutions of four maximally supersymmetric D = 9 massive supergravity theories obtained by Scherk-Schwarz reduction of D = 10 IIA and IIB supergravity. One of the theories does not have a superpotential and does not allow domain wall solutions preserving any supersymmetry. The other three theories have superpotentials leading to half-supersymmetric domain wall solutions, one of which has zero potential but non-zero superpotential. The uplifting of these domain wall solutions to ten dimensions leads to three classes of half-supersymmetric type IIB 7-brane solutions. All solutions within each class are related by SL(2, R) transformations. The three classes together contain solutions carrying all possible (quantized) 7-brane charges. One class contains the well-known D7brane solution and its dual partners and we provide the explicit solutions for the other two classes. The domain wall solution with zero potential lifts up to a half-supersymmetric conical spacetime.

We construct maximal D = 8 gauged supergravities by the reduction of D = 11 supergravity over threedimensional group manifolds. Such manifolds have been classified by Bianchi. We divide the corresponding gauged supergravities into two classes: class A (with a Lagrangian) and class B (without a Lagrangian).

We construct five massive deformations of the unique nine-dimensional N = 2 supergravity, each with two parameters. All of these deformations have a higher-dimensional origin via Scherk-Schwarz reduction and correspond to gauged supergravities. The gauge groups we encounter are SO(2), SO(1, 1) + , R, R + and the unique two-dimensional non-Abelian Lie group CR 1 , which consists of scalings and translations in one dimension.

We investigate the accelerating phases of cosmologies supported by a metric, scalars and a single exponential scalar potential. The different solutions can be represented by trajectories on a sphere and we find that quintessence happens within the 'arctic circle' of the sphere. Furthermore, we obtain multiexponential potentials from 3D group manifold reductions of gravity, implying that such potentials can be embedded in gauged supergravities with an Mtheory origin. We relate the double exponential case to flux compactifications on maximally symmetric spaces and S-branes. In the triple exponential case our analysis suggests the existence of two exotic S(D − 3)-branes in D dimensions.

Performing a Scherk-Schwarz dimensional reduction of D = 11 supergravity on a three-dimensional group manifold we construct five D = 8 gauged maximal supergravities whose gauge groups are the three-dimensional (non-)compact subgroups of SL(3, R). These cases include the Salam-Sezgin SO(3) gauged supergravity. We construct the most general half-supersymmetric domain wall solutions to these five gauged supergravities. The generic form is a triple domain wall solution whose truncations lead to double and single domain wall solutions. We find that one of the single domain wall solutions has zero potential but nonzero superpotential. Upon uplifting to 11 dimensions each domain wall becomes a purely gravitational 1/2 BPS solution. The corresponding metric has a 7 + 4 split with a Minkowski 7-metric and a 4-metric that corresponds to a gravitational instanton. These instantons generalize the SO(3) metric of Belinsky, Gibbons, Page and Pope (which includes the Eguchi-Hanson metric) to the other Bianchi types of class A.

We construct the most general non-extremal spherically symmetric instanton solution of a gravity-dilaton-axion system with SL(2, R) symmetry, for arbitrary euclidean spacetime dimension D ≥ 3. A subclass of these solutions describe completely regular wormhole geometries, whose size is determined by an invariant combination of the SL(2, R) charges. Our results can be applied to four-dimensional effective actions of type II strings compactified on a Calabi-Yau manifold, and in particular to the universal hypermultiplet coupled to gravity. We show that these models contain regular wormhole solutions, supported by regular dilaton and RR scalar fields of the universal hypermultiplet.

We construct maximal D = 8 gauged supergravities by the reduction of D = 11 supergravity over three-dimensional group manifolds. Such manifolds are classified into two classes, A and B, and eleven types. This Bianchi classification carries over to the gauged supergravities. The class A theories have 1/2 BPS domain wall solutions that uplift to purely gravitational solutions consisting of 7D Minkowski and a 4D Euclidean geometry. These geometries are generically singular. The two regular exceptions correspond to the nearhorizon limit of the single-or double-centre Kaluza-Klein monopole. In contrast, the class B supergravities are defined by a set of equations of motion that cannot be integrated to an action and allow for no 1/2 BPS domain walls.

Abstract In recent years dramatic progress has been made in the understanding of the nonperturbative structure of superstring theory and M-theory. Central to this progress are non-perturbative, solitonic objects collectively referred to as p-branes. In this thesis, comprising an introductory text and three appended research papers, we are going to briefly review superstring theory and M-theory. Emphasis will be given to the dynamics of p-branes, which is the subject of Papers I-III.

Abstract We will start by reviewing some aspects of bosonic string theory and then move on to the fermionic supersymmetric string, ie the so called superstring. The focus will here be on the veri cation of the supersymmetry of the action. In chapter 3 we will consider eleven-dimensional supergravity and in particular solve the Bianchi identities. We will in chapter 4 nally examine the p= 2 brane in eleven-dimensional supergravity and the emphasis will here be on the {-symmetry of the action. i

Sodium-ion batteries (SIBs) are currently being considered for large-scale energy storage. Optimisation of SIB electrolytes is, however, still largely lacking. Here we exhaustively evaluate NaPF 6 in diglyme as an electrolyte of choice-both physico-chemical properties and extensive electrochemical tests including half as well as full cells. Fundamentally, the ionic conductivity is found to be quite comparable to carbonate based electrolytes and obeying the fractional Walden rule with viscosity. We find Na metal to work well as a reference electrode and the electrochemical stability, evaluated potentiostatically for various electrodes and corroborated by DFT calculations, to be satisfactory in the entire voltage range of 0-4.4 V. Galvanostatic cycling at C/10 of half and full cells using Na 3 V 2 (PO 4) 3 (NVP) or Na 3 V 2 (PO 4) 2 F 3 (NVPF) as cathodes and hard carbon (HC) as anodes indicate rapid capacity fading in cells with HC anodes, possibly originating in a lack of a stable SEI or by trapping of sodium. Aiming to understand this capacity fade further, we conducted a GC/MS analysis to determine electrolyte reduction products and to propose reduction pathways, concluding that oligomer and/or alkoxide formation is possible. Overall, the promising results should warrant further investigations of diglyme based electrolytes for modern SIB development, albeit avoiding HC anodes.

For storing energy in future sustainable energy systems, sodium-ion batteries (SIB) have emerged as an alternative to the current state-of-the-art lithium-ion batteries (LIBs), since SIBs are potentially cheaper. For LIBs and SIBs alike, the development of stable systems depends on employing stable or metastable electrolytes, forming a SEI. Ether compounds have earlier been investigated for use in electrolytes, due to a presumed high reductive stability. In this project diglyme, an ether solvent, mixed with 1 M NaPF6 has been evaluated for use with Na-metal reference electrodes and a SIB electrode platform comprising Na3V2(PO4)2F3 (NVPF) and hard carbon (HC), and with a model system using Na3V2(PO4)3 (NVP) at both electrodes. Furthermore, this electrolyte has been investigated for electrochemical stability, and for possible degradation mechanisms. Techniques used are galvanostatic cycling (GCPL), cyclic voltammetry (CV) and electrical impedance spectroscopy (EIS), coupling these to ...

A crystalline, silicon, microelectronic, cryogenic, thermal detector for single quanta of low energy radiation and high resolution spectroscopy is being developed. Its volume is less than 0.1 mm 3. The constituent parts of the detector are integrated in one unit by micromacbming . The dependence of the resistance of the thermistor on temperature (R-T characteristics) has been studied experimentally. The influence of changes in the implantation dose of the thermistor on the R-T characteristics has also been studied. To obtain the best energy resolution of the detector the optimal implantation dose of the thermistor has been determined . The amplified detector pulses were fed into a Macintosh computer via an especially developed computer interface. The operation of the detector was tested by sampling gamma, X-ray and electron spectra from a i°9Cd source .

Fabrication of a thermal detector designed for high resolution spectroscopy of low-energy radiation is described. Details of the micromachining of pure silicon are given including the etching of the 0.1 mm 3 absorber and the doping process to obtain the temperature sensing thermistor which is an integrated part of the absorber. The cryogenic system, the signal processing at working temperatures around 50 mK and the data acquisition system are discussed. Theoretical aspects of the intrinsic resolving power are presented. The relation between the intrinsic detector resolution and particle energy at different working temperatures is derived. Measured resistance vs temperature is shown for thermistors made with different dopings on wafers with different initial wafer resistivity. The influence of the initial wafer purity on the R-T characteristic curves is discussed. The optimal implantation dose was determined for thermistors implanted in high purity wafers .