1,397 research outputs found
AX-GADGET: a new code for cosmological simulations of Fuzzy Dark Matter and Axion models
We present a new module of the parallel N-Body code P-GADGET3 for
cosmological simulations of light bosonic non-thermal dark matter, often
referred as Fuzzy Dark Matter (FDM). The dynamics of the FDM features a highly
non-linear Quantum Potential (QP) that suppresses the growth of structures at
small scales. Most of the previous attempts of FDM simulations either evolved
suppressed initial conditions, completely neglecting the dynamical effects of
QP throughout cosmic evolution, or resorted to numerically challenging
full-wave solvers. The code provides an interesting alternative, following the
FDM evolution without impairing the overall performance. This is done by
computing the QP acceleration through the Smoothed Particle Hydrodynamics (SPH)
routines, with improved schemes to ensure precise and stable derivatives. As an
extension of the P-GADGET3 code, it inherits all the additional physics modules
implemented up to date, opening a wide range of possibilities to constrain FDM
models and explore its degeneracies with other physical phenomena. Simulations
are compared with analytical predictions and results of other codes, validating
the QP as a crucial player in structure formation at small scales.Comment: 18 page
On Nori's Fundamental Group Scheme
We determine the quotient category which is the representation category of
the kernel of the homomorphism from Nori's fundamental group scheme to its
\'etale and local parts. Pierre Deligne pointed out an error in the first
version of this article. We profoundly thank him, in particular for sending us
his enlightning example reproduced in Remark 2.4 2).Comment: 29 page
Investigation on sound propagation for the measurement of diffusion in microporous solids.
The basic definitions of micropore diffusivities and the experimental techniques applied for their measurement are reviewed. Through a historical perspective, the techniques are briefly described, with an emphasis on the measured property, the theoretical and practical limitations. As a result the need for a novel experimental technique has been identified. The extension of the frequency response (FR) method to frequencies in the audible sound range is proposed. A detailed mathematical model is presented to describe the propagation of sound between two parallel adsorbing plates. The main body of the thesis is the description and derivation of a model that relates an acoustic quantity (i.e. propagation constant) to adsorption parameters (i.e. diffusivity and equilibrium constant) in microporous solids. The theoretical analysis describes the ranges of physical parameters where the complete model reduces to simplified versions: classical absorption isothermal limit equilibrium control temperature control. Based on the theoretical study a prototype apparatus has been designed and constructed. The system allows for flexibility in the loading of adsorbent material, geometrical properties and gas used. Preliminary experimental results are reported and interpreted based upon the theory of acoustics described above
Quantum interference from sums over closed paths for electrons on a three-dimensional lattice in a magnetic field: total energy, magnetic moment, and orbital susceptibility
We study quantum interference effects due to electron motion on a
three-dimensional cubic lattice in a continuously-tunable magnetic field of
arbitrary orientation and magnitude. These effects arise from the interference
between magnetic phase factors associated with different electron closed paths.
The sums of these phase factors, called lattice path-integrals, are
``many-loop" generalizations of the standard ``one-loop" Aharonov-Bohm-type
argument. Our lattice path integral calculation enables us to obtain various
important physical quantities through several different methods. The spirit of
our approach follows Feynman's programme: to derive physical quantities in
terms of ``sums over paths". From these lattice path-integrals we compute
analytically, for several lengths of the electron path, the half-filled
Fermi-sea ground-state energy of noninteracting spinless electrons in a cubic
lattice. Our results are valid for any strength of the applied magnetic field
in any direction. We also study in detail two experimentally important
quantities: the magnetic moment and orbital susceptibility at half-filling, as
well as the zero-field susceptibility as a function of the Fermi energy.Comment: 14 pages, RevTe
The dynamical Casimir effect in superconducting microwave circuits
We theoretically investigate the dynamical Casimir effect in electrical
circuits based on superconducting microfabricated waveguides with tunable
boundary conditions. We propose to implement a rapid modulation of the boundary
conditions by tuning the applied magnetic flux through superconducting quantum
interference devices (SQUIDs) that are embedded in the waveguide circuits. We
consider two circuits: (i) An open waveguide circuit that corresponds to a
single mirror in free space, and (ii) a resonator coupled to a microfabricated
waveguide, which corresponds to a single-sided cavity in free space. We analyze
the properties of the dynamical Casimir effect in these two setups by
calculating the generated photon-flux density, output-field correlation
functions, and the quadrature squeezing spectra. We show that these properties
of the output field exhibit signatures unique to the radiation due to the
dynamical Casimir effect, and could therefore be used for distinguishing the
dynamical Casimir effect from other types of radiation in these circuits. We
also discuss the similarities and differences between the dynamical Casimir
effect, in the resonator setup, and downconversion of pump photons in
parametric oscillators.Comment: 18 pages, 14 figure
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