Commutative deformations of general relativity: nonlocality, causality, and dark matter

Hopf algebra methods are applied to study Drinfeld twists of (3+1)-diffeomorphisms and deformed general relativity on \emph{commutative} manifolds. A classical nonlocality length scale is produced above which microcausality emerges. Matter fields are utilized to generate self-consistent Abelian Drinfeld twists in a background independent manner and their continuous and discrete symmetries are examined. There is negligible experimental effect on the standard model of particles. While baryonic twist producing matter would begin to behave acausally for rest masses above $\sim1-10$ TeV, other possibilities are viable dark matter candidates or a right handed neutrino. First order deformed Maxwell equations are derived and yield immeasurably small cosmological dispersion and produce a propagation horizon only for photons at or above Planck energies. This model incorporates dark matter without any appeal to extra dimensions, supersymmetry, strings, grand unified theories, mirror worlds, or modifications of Newtonian dynamics.Comment: 47 pages including references, 0 figures, 0 tables Various typos/omissions correcte

Is Green the new Gold? ESG’s Influence on the Financial Performance of the Energy and Mining Industries

The demand for Environment, Social, and Governance (ESG) reporting has increased in recent years. As the concern for climate change has moved to the forefront of the investment process, companies have needed to prioritize ESG in their operations. Previous literature addresses how ESG has benefited companies’ financial performance and increased shareholder value. The pandemic has proven to have positively impacted ESG reporting as social priorities shifted. However, studies have also shown that ESG reporting is too ambiguous to concretely display any relationship with financial performance. This thesis will analyze the impact of ESG and environmental data reporting on the Return on Assets (ROA) and Return on Equity (ROE) for the energy and mining industries over the past 4 years (2018-2023). The regressions were split into pre- and post-COVID in hopes of seeing a shift in ESG reporting impacts on ROA and ROE. The results reinforced the unclear relationship between the variables with most regressions being statistically insignificant. Potential limitations could be due to the paucity of ESG research

In_(0.75)Ga_(0.25)As on GaAs submicron rings and their application for coherent nanoelectronic devices

Electron-phase modulation in magnetic and electric fields will be presented in In_(0.75)Ga_(0.25)As Aharonov-Bohm (AB) rings. The zero Schottky barrier of this material made it possible to nanofabricate devices with radii down to below 200 nm without carrier depletion. We shall present a fabrication scheme based on wet and dry etching that yielded excellent reproducibility, very high contrast of the oscillations and good electrical gating. The operation of these structures is compatible with closed-cycle refrigeration and suggests that this process can yield coherent electronic circuits that do not require cryogenic liquids. The InGaAs/AlInAs heterostructure was grown by MBE on a GaAs substrate [1], and in light of the large effective g-factor and the absence of the Schottky barrier is a material system of interest for the investigation of spin-related effects [2-4]} and the realization of hybrid superconductor/semiconductor devices [5].Comment: 7 pages, 4 figures, to appear in Physica

Scattering Matrix Theory For Nonlinear Transport

We report a scattering matrix theory for dynamic and nonlinear transport in coherent mesoscopic conductors. In general this theory allows predictions of low frequency linear dynamic conductance, as well as weakly nonlinear DC conductance. It satisfies the conditions of gauge invariance and electric current conservation, and can be put into a form suitable for numerical computation. Using this theory we examine the third order weakly nonlinear DC conductance of a tunneling diode

Diffusive conductors as Andreev interferometers

We present a novel mechanism of phase-dependent electric transport in diffusive normal metal-superconductor structures. We provide a detailed theoretical and numerical analysis of recent unexplained experiments essentially explaining them.Comment: Self extracting file, 7 pages latex and 4 postscript figures. The paper is also available at http://www.tn.tudelft.nl/tn/thspap.html In this revision we resolved some printing problems concerning figures 2 and

Density of States in Superconductor - Normal Metal - Superconductor Junctions

We consider the chi_0 dependence of the density of states inside the normal metal of a superconductor - normal metal - superconductor (SNS) junction.Here chi_0 is the phase difference of two superconductors of the junction. It is shown that in the absence of electron-electron interaction the energy dependence of the density of states has a gap which decreases as chi_0 increases and closes at chi_0= pi. Both the analytical expressions for the chi_0 dependence of the density of states and the results of numerical simulations are presented.Comment: 7 pages with 4 included epsf figures, published version with small change

Weakly Nonlinear AC Response: Theory and Application

We report a microscopic and general theoretical formalism for electrical response which is appropriate for both DC and AC weakly nonlinear quantum transport. The formalism emphasizes the electron-electron interaction and maintains current conservation and gauge invariance. It makes a formal connection between linear response and scattering matrix theory at the weakly nonlinear level. We derive the dynamic conductance and predict the nonlinear-nonequilibrium charge distribution. The definition of a nonlinear capacitance leads to a remarkable scaling relation which can be measured to give microscopic information about a conductor

Time-Dependent Current Partition in Mesoscopic Conductors

The currents at the terminals of a mesoscopic conductor are evaluated in the presence of slowly oscillating potentials applied to the contacts of the sample. The need to find a charge and current conserving solution to this dynamic current partition problem is emphasized. We present results for the electro-chemical admittance describing the long range Coulomb interaction in a Hartree approach. For multiply connected samples we discuss the symmetry of the admittance under reversal of an Aharonov-Bohm flux.Comment: 22 pages, 3 figures upon request, IBM RC 1971