343 research outputs found
Heating and Trapping of Electrons in ECRIS from Scratch to Afterglow
Plasmas in Electron Cyclotron Resonance Ion Sources (ECRIS) are collisionless and can therefore be simulated by just following the motion of electrons in the confining static magnetic and oscillating microwave (MW) electric field of ECRIS. With a powerful algorithm the three-dimensional trajectories of 104 ECR-heated and confined electrons are calculated in a standard ECRIS with a deep minimum of |B| and a new ECRIS with a very flat minimum of |B|. The spatial electron (plasma) densities and electron energy densities deduced from these trajectories yield new and surprising insight in the performance of ECRIS. With computer animation we plan to present: The energy increase of certain electrons on extremely stable trajectories, the power dependence of the electron energy density up to the X-ray collapse, the time dependent build up of the electron density and energy density distributions, and the time evolution of these electron distributions under afterglow conditions
Eccentric binary black holes: Comparing numerical relativity and small mass-ratio perturbation theory
The modelling of unequal mass binary black hole systems is of high importanceto detect and estimate parameters from these systems. Numerical relativity (NR)is well suited to study systems with comparable component masses, m_1\simm_2, whereas small mass ratio (SMR) perturbation theory applies to binarieswhere 521:101:10.7$. From these we extract quantities likegravitational wave energy and angular momentum fluxes and periastron advance,and assess their accuracy. To facilitate comparison, we develop tools to mapbetween NR and SMR inspiral evolutions of eccentric binary black holes. Wederive post-Newtonian accurate relations between different definitions ofeccentricity. Based on these analyses, we introduce a new definition ofeccentricity based on the (2,2)-mode of the gravitational radiation, whichreduces to the Newtonian definition of eccentricity in the Newtonian limit.From the comparison between NR simulations and SMR results, we quantify theunknown next-to-leading order SMR contributions to the gravitational energy andangular momentum fluxes, and periastron advance. We show that in the comparablemass regime these contributions are subdominant and higher order SMRcontributions are negligible.<br
From the Feynman-Schwinger representation to the non-perturbative relativistic bound state interaction
We write the 4-point Green function in QCD in the Feynman-Schwinger
representation and show that all the dynamical information are contained in the
Wilson loop average. We work out the QED case in order to obtain the usual
Bethe-Salpeter kernel. Finally we discuss the QCD case in the non-perturbative
regime giving some insight in the nature of the interaction kernel.Comment: 25 pages, RevTex, 3 figures included, typos corrected, to appear in
Phys. Rev. D 5
Spawning rings of exceptional points out of Dirac cones
The Dirac cone underlies many unique electronic properties of graphene and
topological insulators, and its band structure--two conical bands touching at a
single point--has also been realized for photons in waveguide arrays, atoms in
optical lattices, and through accidental degeneracy. Deformations of the Dirac
cone often reveal intriguing properties; an example is the quantum Hall effect,
where a constant magnetic field breaks the Dirac cone into isolated Landau
levels. A seemingly unrelated phenomenon is the exceptional point, also known
as the parity-time symmetry breaking point, where two resonances coincide in
both their positions and widths. Exceptional points lead to counter-intuitive
phenomena such as loss-induced transparency, unidirectional transmission or
reflection, and lasers with reversed pump dependence or single-mode operation.
These two fields of research are in fact connected: here we discover the
ability of a Dirac cone to evolve into a ring of exceptional points, which we
call an "exceptional ring." We experimentally demonstrate this concept in a
photonic crystal slab. Angle-resolved reflection measurements of the photonic
crystal slab reveal that the peaks of reflectivity follow the conical band
structure of a Dirac cone from accidental degeneracy, whereas the complex
eigenvalues of the system are deformed into a two-dimensional flat band
enclosed by an exceptional ring. This deformation arises from the dissimilar
radiation rates of dipole and quadrupole resonances, which play a role
analogous to the loss and gain in parity-time symmetric systems. Our results
indicate that the radiation that exists in any open system can fundamentally
alter its physical properties in ways previously expected only in the presence
of material loss and gain
CPT-symmetric discrete square well
A new version of an elementary PT-symmetric square well quantum model is
proposed in which a certain Hermiticity-violating end-point interaction leaves
the spectrum real in a large domain of couplings . Within
this interval we employ the usual coupling-independent operator P of parity and
construct, in a systematic Runge-Kutta discrete approximation, a
coupling-dependent operator of charge C which enables us to classify our
P-asymmetric model as CPT-symmetric or, equivalently, hiddenly Hermitian alias
cryptohermitian.Comment: 12 pp., presented to conference PHHQP IX
(http://www.math.zju.edu.cn/wjd/
A versatile all-optical parity-time signal processing device using a Bragg grating induced using positive and negative Kerr-nonlinearity
The properties of gratings with Kerr nonlinearity and PT symmetry are investigated in this paper. The impact of the gain and loss saturation on the response of the grating is analysed for different input intensities and gain/loss parameters. Potential applications of these gratings as
switches, logic gates and amplifiers are also shown
Low Q^2 Jet Production at HERA and Virtual Photon Structure
The transition between photoproduction and deep-inelastic scattering is
investigated in jet production at the HERA ep collider, using data collected by
the H1 experiment. Measurements of the differential inclusive jet
cross-sections dsigep/dEt* and dsigmep/deta*, where Et* and eta* are the
transverse energy and the pseudorapidity of the jets in the virtual
photon-proton centre of mass frame, are presented for 0 < Q2 < 49 GeV2 and 0.3
< y < 0.6. The interpretation of the results in terms of the structure of the
virtual photon is discussed. The data are best described by QCD calculations
which include a partonic structure of the virtual photon that evolves with Q2.Comment: 20 pages, 5 Figure
Solitary waves in the Nonlinear Dirac Equation
In the present work, we consider the existence, stability, and dynamics of
solitary waves in the nonlinear Dirac equation. We start by introducing the
Soler model of self-interacting spinors, and discuss its localized waveforms in
one, two, and three spatial dimensions and the equations they satisfy. We
present the associated explicit solutions in one dimension and numerically
obtain their analogues in higher dimensions. The stability is subsequently
discussed from a theoretical perspective and then complemented with numerical
computations. Finally, the dynamics of the solutions is explored and compared
to its non-relativistic analogue, which is the nonlinear Schr{\"o}dinger
equation. A few special topics are also explored, including the discrete
variant of the nonlinear Dirac equation and its solitary wave properties, as
well as the PT-symmetric variant of the model
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