77,535 research outputs found
Large angle magnetization dynamics measured by time-resolved ferromagnetic resonance
A time-resolved ferromagnetic resonance technique was used to investigate the
magnetization dynamics of a 10 nm thin Permalloy film. The experiment consisted
of a sequence of magnetic field pulses at a repetition rate equal to the
magnetic systems resonance frequency. We compared data obtained by this
technique with conventional pulsed inductive microwave magnetometry. The
results for damping and frequency response obtained by these two different
methods coincide in the limit of a small angle excitation. However, when
applying large amplitude field pulses, the magnetization had a non-linear
response. We speculate that one possible cause of the nonlinearity is related
to self-amplification of incoherence, known as the Suhl instabilities.Comment: 23 pages, 8 figures, submitted to PR
Meson decay in the Fock-Tani Formalism
The Fock-Tani formalism is a first principle method to obtain effective
interactions from microscopic Hamiltonians. Usually this formalism was applied
to scattering, here we introduced it to calculate partial decay widths for
mesons.Comment: Presented at HADRON05 XI. "International Conference on Hadron
Spectroscopy" Rio de Janeiro, Brazil, August 21 to 26, 200
Zeno effect for quantum computation and control
It is well known that the quantum Zeno effect can protect specific quantum
states from decoherence by using projective measurements. Here we combine the
theory of weak measurements with stabilizer quantum error correction and
detection codes. We derive rigorous performance bounds which demonstrate that
the Zeno effect can be used to protect appropriately encoded arbitrary states
to arbitrary accuracy, while at the same time allowing for universal quantum
computation or quantum control.Comment: Significant modifications, including a new author. To appear in PR
Dynamical Lorentz and CPT symmetry breaking in a 4D four-fermion model
In a 4D chiral Thirring model we analyse the possibility that radiative
corrections may produce spontaneous breaking of Lorentz and CPT symmetry. By
studying the effective potential, we verified that the chiral current
may assume a nonzero vacuum expectation
value which triggers the Lorentz and CPT violations. Furthermore, by making
fluctuations on the minimum of the potential we dynamically induce a bumblebee
like model containing a Chern-Simons term.Comment: Small modifications in the text and new references added, 12 pages, 4
figures, revtex4. To appear in Phys. Rev.
Flag-Dipole Spinor Fields in ESK Gravities
We consider the Riemann-Cartan geometry as a basis for the
Einstein-Sciama-Kibble theory coupled to spinor fields: we focus on and
conformal gravities, regarding the flag-dipole spinor fields, type-(4) spinor
fields under the Lounesto classification. We study such theories in specific
cases given for instance by cosmological scenarios: we find that in such
background the Dirac equation admits solutions that are not Dirac spinor
fields, but in fact the aforementioned flag-dipoles ones. These solutions are
important from a theoretical perspective, as they evince that spinor fields are
not necessarily determined by their dynamics, but also a discussion on their
structural (algebraic) properties must be carried off. Furthermore, the
phenomenological point of view is shown to be also relevant, since for
isotropic Universes they circumvent the question whether spinor fields do
undergo the Cosmological Principle.Comment: 18 pages, improved versio
On the radiative corrections in the Horava-Lifshitz z=2 QED
We calculate one-loop contributions to the two and three point spinor-vector
functions in z=2 Horava-Lifshitz QED. This allows us to obtain the anomalous
magnetic moment.Comment: 10 pages, minor correction
Graded-index optical fiber emulator of an interacting three-atom system: illumination control of particle statistics and classical non-separability
We show that a system of three trapped ultracold and strongly interacting
atoms in one-dimension can be emulated using an optical fiber with a
graded-index profile and thin metallic slabs. While the wave-nature of single
quantum particles leads to direct and well known analogies with classical
optics, for interacting many-particle systems with unrestricted statistics such
analoga are not straightforward. Here we study the symmetries present in the
fiber eigenstates by using discrete group theory and show that, by spatially
modulating the incident field, one can select the atomic statistics, i.e.,
emulate a system of three bosons, fermions or two bosons or fermions plus an
additional distinguishable particle. We also show that the optical system is
able to produce classical non-separability resembling that found in the
analogous atomic system.Comment: 14 pages, 5 figure
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