1,679 research outputs found
Hadronic Light-by-Light Scattering in the Muonium Hyperfine Splitting
We consider an impact of hadronic light-by-light scattering on the muonium
hyperfine structure. A shift of the hyperfine interval is calculated with the light-by-light scattering approximated
by exchange of pseudoscalar and pseudovector mesons. Constraints from the
operator product expansion in QCD are used to fix parameters of the model
similar to the one used earlier for the hadronic light-by-light scattering in
calculations of the muon anomalous magnetic moment. The pseudovector exchange
is dominant in the resulting shift, . Although the effect is tiny it is useful in understanding
the level of hadronic uncertainties.Comment: 16 pages, 7 figures, a reference adde
Models of G time variations in diverse dimensions
A review of different cosmological models in diverse dimensions leading to a
relatively small time variation of the effective gravitational constant G is
presented. Among them: 4-dimensional general scalar-tensor model,
multidimensional vacuum model with two curved Einstein spaces, multidimensional
model with multicomponent anisotropic "perfect fluid", S-brane model with
scalar fields and two form field etc. It is shown that there exist different
possible ways of explanation of relatively small time variation of the
effective gravitational constant G compatible with present cosmological data
(e.g. acceleration): 4-dimensional scalar-tensor theories or multidimensional
cosmological models with different matter sources. The experimental bounds on
G-dot may be satisfied ether in some restricted interval or for all allowed
values of the synchronous time variable.Comment: 27 pages, Late
On Possible Measurement of Gravitational Interaction Parameters on Board a Satellite
The recently suggested SEE (Satellite Energy Exchange) method of measuring
the gravitational constant , possible equivalence principle violation
(measured by the E\"{o}tv\"{o}s parameter ) and the hypothetic 5th force
parameters and on board a drag-free Earth's satellite is
discussed and further developed. Various particle trajectories near a heavy
ball are numerically simulated. Some basic sources of error are analysed. The
measurement procedure is modelled by noise insertion to a ``true''
trajectory. It is concluded that the present knowledge of (for
m) and can be improved by at least two orders of
magnitude.Comment: (only two misprints on title page) 7 page
Anharmonic coherent dynamics of the soft phonon mode of a PbTe crystal
We investigate the ultrafast optical response of PbTe to an intense
single-cycle terahertz pulse, resonant with the soft transverse optical (TO)
phonon mode of the crystal. We detect multifrequency oscillations of the
reflectance anisotropy, which we associate with nonlinear motion of the TO
phonon oscillator excited directly by the terahertz pulse. Our observation of
monotonically decaying optical anisotropy together with second harmonic
oscillations of the TO mode is an evidence of a transient non-centrosymmetric
state of the crystal lattice that can be accompanied by the ferroelectric
order. We suppose that this state is induced in the PbTe crystal by the intense
terahertz pulse via alignment of the local polar nanodomains. This hypothesis
is partially supported by the observation of coherent phonons near the
satellite phonon mode frequency that are impulsively generated by a femtosecond
laser pulse and are considerably enhanced by a synchronous terahertz pulse.Comment: 7 pages, 5 figure
Influence of Sintering Conditions on Specific Electrical Conductivity in Aluminum-Graphene Composite
Dependence of specific electrical resistance on temperature (20 - 1600 ∘C) and processing method in an aluminum-graphene (up to 2wt.%) composite is investigated. It is established that spark plasma sintering (SPS) under pressure 40 MPа does not influence on electrical resistance, whereas SPS at low pressure (<10 MPa) reduces electrical resistance at a room temperature on 6 orders. Lower values of electrical resistance (up to 90 Ω *mm) received at sintering in hot pressing set at radiating heating. It is supposed that the reason of sharp decrease in electrical resistance at the lowered pressure is presence of current pulsations during SPS. They induces magnetic fields in graphene flake which lead to their moving and forming of particles to electroconductive chains or their capture in arched cells at applied pressure.
Keywords: composite, aluminum, graphene, electrical resistance, temperature dependence
Hadronic light-by-light scattering contribution to the muon anomalous magnetic moment revisited
We discuss hadronic light-by-light scattering contribution to the muon
anomalous magnetic moment a_\mu^{\rm lbl}, paying particular attention to the
consistent matching between the short- and the long-distance behavior of the
light-by-light scattering amplitude. We argue that the short-distance QCD
imposes strong constraints on this amplitude overlooked in previous analyses.
We find that accounting for these constraints leads to approximately 50 per
cent increase in the central value of a_\mu^{\rm lbl}, compared to existing
estimates. The hadronic light-by-light scattering contribution becomes
a_\mu^{\rm lbl}=136(25) \times 10^{-11}, thereby shifting the Standard Model
prediction closer to the experimental value.Comment: 16 pages, 2 figure
Magneto-optical properties of Au upon the injection of hot spin-polarized electrons across Fe/Au(001) interfaces
We demonstrate a novel method for the excitation of sizable magneto-optical
effects in Au by means of the laser-induced injection of hot spin-polarized
electrons in Au/Fe/MgO(001) heterostructures. It is based on the energy- and
spin-dependent electron transmittance of Fe/Au interface which acts as a spin
filter for non-thermalized electrons optically excited in Fe. We show that
after crossing the interface, majority electrons propagate through the Au layer
with the velocity on the order of 1 nm/fs (close to the Fermi velocity) and the
decay length on the order of 100 nm. Featuring ultrafast functionality and
requiring no strong external magnetic fields, spin injection results in a
distinct magneto-optical response of Au. We develop a formalism based on the
phase of the transient complex MOKE response and demonstrate its robustness in
a plethora of experimental and theoretical MOKE studies on Au, including our ab
initio calculations. Our work introduces a flexible tool to manipulate
magneto-optical properties of metals on the femtosecond timescale that holds
high potential for active magneto-photonics, plasmonics, and spintronics
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