102 research outputs found
Numerical aspects of black hole superradiance
In this work we explore a numerical technique, based on the spherical harmonic decomposition and the discretization of the radial coordinate through Čebyšëv polynomial interpolation, for the computation of quasi-bound states of linear massive scalar and vector perturbations in spinning black hole spacetimes in General Relativity. The aim is studying black hole superradiant instabilities, an energy-extraction mechanism triggered by the presence of massive bosonic fields near black holes, which finds wide applications in constraining scenarios beyond Standard Model and General Relativity. This method does not rely on any separation ansätze, thus it can have wide applications. Consequently we extend the technique so that it can be applied also to the computation of massive tensor quasi-bound states in spinning black holes in General Relativity, whose separability ansatz is currently unknown. We also apply it to spinning black holes in scalar-tensor theory non-linearly interacting with plasma, wherein the massless scalar perturbations acquires an effective mass, finding a novel way for constraining scalar-tensor theories
Noncommutative Geometry and Gauge theories on AF algebras
Non-commutative geometry (NCG) is a mathematical discipline developed in the
1990s by Alain Connes. It is presented as a new generalization of usual
geometry, both encompassing and going beyond the Riemannian framework, within a
purely algebraic formalism. Like Riemannian geometry, NCG also has links with
physics. Indeed, NCG provided a powerful framework for the reformulation of the
Standard Model of Particle Physics (SMPP), taking into account General
Relativity, in a single "geometric" representation, based on Non-Commutative
Gauge Theories (NCGFT). Moreover, this accomplishment provides a convenient
framework to study various possibilities to go beyond the SMPP, such as Grand
Unified Theories (GUTs). This thesis intends to show an elegant method recently
developed by Thierry Masson and myself, which proposes a general scheme to
elaborate GUTs in the framework of NCGFTs. This concerns the study of NCGFTs
based on approximately finite -algebras (AF-algebras), using either
derivations of the algebra or spectral triples to build up the underlying
differential structure of the Gauge Theory. The inductive sequence defining the
AF-algebra is used to allow the construction of a sequence of NCGFTs of
Yang-Mills Higgs types, so that the rank can represent a grand unified
theory of the rank . The main advantage of this framework is that it
controls, using appropriate conditions, the interaction of the degrees of
freedom along the inductive sequence on the AF algebra. This suggests a way to
obtain GUT-like models while offering many directions of theoretical
investigation to go beyond the SMPP
Electron Momentum Distributions from Strong-Field-Induced Ionization of Atoms and Molecules
High-intensity femtosecond laser pulses in the visible or infrared range can induce electron emission. This single-ionization process may be interpreted as a sequence of (nonadiabatic) tunnel ionization and subsequent acceleration of the electron by the external oscillating field in the presence of the electrostatic force between electron and parent ion. Based on the analysis of photoelectron momentum distributions from the numerical solution of the time-dependent Schrödinger equation, this thesis theoretically studies a variety of phenomena taking place in atoms as well as in molecules in strong fields. The underlying physical mechanisms are revealed by simplified models which take the nonperturbative character of the ionization process into account.
The simulation results for several settings are directly compared to measurements, offering the possibility to benchmark state-of-the-art theory and experiment against each other. One example of this is an investigation of the nonadiabatic strong-field ionization of atomic hydrogen in an attoclock setting. More generally, the deflection of the photoelectrons is analyzed in different attoclock configurations to explore the initial conditions of electrons at the tunnel exit—the position where the electron appears after tunneling. When a molecule is ionized, its orbital structure influences the liberated electron wave packet. The orbital imprint on the momentum-space phase of the wave packet, which encodes spatial information, is demonstrated and an interferometric approach to access these phases is evaluated. A characterization of the freed wave packet is crucial as it influences subsequent processes.
Such secondary processes are induced when the electron is driven back to the parent ion and scatters off. Similar to focusing of light by a lens, the Coulomb attraction forces scattered electron wave packets through focal points, causing a shift of their phase. Due to the interference of outgoing waves, these phases become visible in electron momentum distributions. For a faithful description, these focal-point effects must be included in a prefactor of the exponentiated action in semiclassical models. Furthermore, the control of electron scattering dynamics is demonstrated for low-energy electrons close to the continuum threshold by means of near-single-cycle terahertz pulses. The temporally-localized preparation of the electron wave packet by a femtosecond laser pulse at a well-defined time within the terahertz field enables a switching between different regimes of dynamics, ranging from recollision-free acceleration to extensive scattering phenomena.
In contrast to most studies in the electric dipole approximation that consider only the temporal evolution of the external electric field, various beyond-dipole effects in strong-field ionization are explored in the present work. The microscopic mechanisms of nondipole modifications are thoroughly analyzed. There, the effects of the spatially-varying electric field and of the magnetic field as well as their fingerprints on the geometry of the momentum distributions are identified. Furthermore, the subcycle time resolution of the light-induced momentum transfer in an attoclock-like setup is explored theoretically. Electron recollisions entirely change the observed nondipole effects and render the observations sensitive to the electronic target structure. The high-order above-threshold ionization caused by large-angle scattering is investigated both for exemplary atoms and for diatomic molecules through examination of nondipole shifts of the lateral momentum distribution. The phases of the electron wave packets are also altered by beyond-dipole effects. It is shown that this results in a displacement of ring-link structures known as above-threshold ionization rings that are caused by intercycle interference. In addition, the holographic structures arising from the subcycle interference of scattered and nonscattered electrons are modified
Modified Theories of Gravity and Cosmological Applications
This reprint focuses on recent aspects of gravitational theory and cosmology. It contains subjects of particular interest for modified gravity theories and applications to cosmology, special attention is given to Einstein–Gauss–Bonnet, f(R)-gravity, anisotropic inflation, extra dimension theories of gravity, black holes, dark energy, Palatini gravity, anisotropic spacetime, Einstein–Finsler gravity, off-diagonal cosmological solutions, Hawking-temperature and scalar-tensor-vector theories
Fermions coupled to solitons on low-dimensional spheres
We examine models of Dirac fermions coupled to topological solitons on the circle S1 and the sphere S2. The fermion is coupled to a pseudoscalar kink in the (1+1)-dimensional model, and to an isovector modelling a baby Skyrmion in the (2+1)-dimensional model. In each case, we solve the spectrum of the fermionic Hamiltonian exactly when the soliton field is kept fixed as a background field, and the fermion dynamics do not cause any back-reaction on the soliton field. In the (1+1)-dimensional model, we then bring the kink field out of the background, fully coupling it to the fermion field. After a change of coordinates to a set of bosonic coordinates constructed out of bispinors, we demonstrate that solutions to the bosonic dynamical system can be understood analytically via the framework of elliptic functions. We show that for a particular class of solutions with no axial charge, we can recover the underlying fermion field from the bispinor solution. In the (2+1)-dimensional model we specialise to the case of the background soliton of topological degree 1 and exploit an SU(2) symmetry to describe the fermion spectrum
Review of Particle Physics
The Review summarizes much of particle physics and cosmology. Using data from previous editions, plus 2,143
new measurements from 709 papers, we list, evaluate, and average measured properties of gauge bosons and the
recently discovered Higgs boson, leptons, quarks, mesons, and baryons. We summarize searches for hypothetical
particles such as supersymmetric particles, heavy bosons, axions, dark photons, etc. Particle properties and search
limits are listed in Summary Tables. We give numerous tables, figures, formulae, and reviews of topics such as Higgs
Boson Physics, Supersymmetry, Grand Unified Theories, Neutrino Mixing, Dark Energy, Dark Matter, Cosmology,
Particle Detectors, Colliders, Probability and Statistics. Among the 120 reviews are many that are new or heavily
revised, including a new review on Machine Learning, and one on Spectroscopy of Light Meson Resonances.
The Review is divided into two volumes. Volume 1 includes the Summary Tables and 97 review articles. Volume
2 consists of the Particle Listings and contains also 23 reviews that address specific aspects of the data presented
in the Listings.
The complete Review (both volumes) is published online on the website of the Particle Data Group (pdg.lbl.gov)
and in a journal. Volume 1 is available in print as the PDG Book. A Particle Physics Booklet with the Summary
Tables and essential tables, figures, and equations from selected review articles is available in print, as a web version
optimized for use on phones, and as an Android app.United States Department of Energy (DOE) DE-AC02-05CH11231government of Japan (Ministry of Education, Culture, Sports, Science and Technology)Istituto Nazionale di Fisica Nucleare (INFN)Physical Society of Japan (JPS)European Laboratory for Particle Physics (CERN)United States Department of Energy (DOE
Understanding Quantum Technologies 2022
Understanding Quantum Technologies 2022 is a creative-commons ebook that
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electronics, photonics, components fabs, raw materials), quantum computing
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around the world, quantum technologies societal impact and even quantum fake
sciences. The main audience are computer science engineers, developers and IT
specialists as well as quantum scientists and students who want to acquire a
global view of how quantum technologies work, and particularly quantum
computing. This version is an extensive update to the 2021 edition published in
October 2021.Comment: 1132 pages, 920 figures, Letter forma
Symmetries in Quantum Mechanics and Statistical Physics
This book collects contributions to the Special Issue entitled "Symmetries in Quantum Mechanics and Statistical Physics" of the journal Symmetry. These contributions focus on recent advancements in the study of PT–invariance of non-Hermitian Hamiltonians, the supersymmetric quantum mechanics of relativistic and non-relativisitc systems, duality transformations for power–law potentials and conformal transformations. New aspects on the spreading of wave packets are also discussed
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