140 research outputs found
Electric charge is a magnetic dipole when placed in a background magnetic field
It is demonstrated, owing to the nonlinearity of QED, that a static charge
placed in a strong magnetic field\ \ is a magnetic dipole (besides remaining
an electric monopole, as well). Its magnetic moment grows linearly with as
long as the latter remains smaller than the characteristic value of 1.2\cdot
10^{13}\unit{G} but tends to a constant as exceeds that value. The force
acting on a densely charged object by the dipole magnetic field of a neutron
star is estimated
Magnetic response to applied electrostatic field in external magnetic field
We show, within QED and other possible nonlinear theories, that a static
charge localized in a finite domain of space becomes a magnetic dipole, if it
is placed in an external (constant and homogeneous) magnetic field in the
vacuum. The magnetic moment is quadratic in the charge, depends on its size and
is parallel to the external field, provided the charge distribution is at least
cylindrically symmetric. This magneto-electric effect is a nonlinear response
of the magnetized vacuum to an applied electrostatic field. Referring to a
simple example of a spherically-symmetric applied field, the nonlinearly
induced current and its magnetic field are found explicitly throughout the
space, the pattern of lines of force is depicted, both inside and outside the
charge, which resembles that of a standard solenoid of classical
magnetostatics
Magnetic response from constant backgrounds to Coulomb sources
Magnetically uncharged, magnetic linear response of the vacuum filled with
arbitrarily combined constant electric and magnetic fields to an imposed static
electric charge is found within general nonlinear electrodynamics. When the
electric charge is point-like and external fields are parallel, the response
found may be interpreted as a field of two point-like magnetic charges of
opposite polarity in one point. Coefficients characterizing the magnetic
response and induced currents are specialized to Quantum Electrodynamics, where
the nonlinearity is taken as that determined by the Heisenberg-Euler effective
Lagrangian.Comment: The part dealing with magnetically charged responses is removed to be
a subject of another paper after revisio
Noncommutative magnetic moment, fundamental length and lepton size
Upper bounds on fundamental length are discussed that follow from the fact
that a magnetic moment is inherent in a charged particle in noncommutative (NC)
electrodynamics. The strongest result thus obtained for the fundamental lenth
is still larger than the estimate of electron or muon size achieved following
the Brodsky-Drell and Dehlmet approach to lepton compositeness. This means that
NC electrodynamics cannot alone explain the whole existing descrepancy between
the theoretical and experimental values of the muon magnetic moment. On the
contrary, as measurements and calculations are further improved, the
fundamental length estimate based on electron data may go down to match its
compositeness radius
Noncommutative magnetic moment of charged particles
It has been argued, that in noncommutative field theories sizes of physical
objects cannot be taken smaller than an elementary length related to
noncommutativity parameters. By gauge-covariantly extending field equations of
noncommutative U(1)_*-theory to the presence of external sources, we find
electric and magnetic fields produces by an extended charge. We find that such
a charge, apart from being an ordinary electric monopole, is also a magnetic
dipole. By writing off the existing experimental clearance in the value of the
lepton magnetic moments for the present effect, we get the bound on
noncommutativity at the level of 10^4 TeV.Comment: 9 pages, revtex; v2: replaced to match the published versio
Classical Noncommutative Electrodynamics with External Source
In a -noncommutative (NC) gauge field theory we extend the
Seiberg-Witten (SW) map to include the (gauge-invariance-violating) external
current and formulate - to the first order in the NC parameter -
gauge-covariant classical field equations. We find solutions to these equations
in the vacuum and in an external magnetic field, when the 4-current is a static
electric charge of a finite size , restricted from below by the elementary
length. We impose extra boundary conditions, which we use to rule out all
singularities, included, from the solutions. The static charge proves to
be a magnetic dipole, with its magnetic moment being inversely proportional to
its size . The external magnetic field modifies the long-range Coulomb field
and some electromagnetic form-factors. We also analyze the ambiguity in the SW
map and show that at least to the order studied here it is equivalent to the
ambiguity of adding a homogeneous solution to the current-conservation
equation
USA Observation of Spectral and Timing Evolution During the 2000 Outburst of XTE J1550-564
We report on timing and spectral observations of the 2000 outburst of XTE
J1550-564 made by the Unconventional Stellar Aspect (USA) Experiment on board
the Advanced Research and Global Observation Satellite (ARGOS). We observe a
low-frequency quasi-periodic oscillation (LFQPO) with a centroid frequency that
tends to increase with increasing flux and a fractional rms amplitude which is
correlated with the hardness ratio. The evolution of the hardness ratio (4--16
keV/1--4 keV) with time and source flux is examined. The hardness-intensity
diagram (HID) shows a cyclical movement in the clockwise direction and possibly
indicates the presence of two independent accretion flows. We observe a
relationship between the USA 4--16 keV count rate and radio observations and
discuss this in the context of previously observed correlations between X-ray,
radio, optical and IR data. We examine our results in the context of models
invoking two accretion flows: a thin disk and a hot sub-Keplerian flow.Comment: 11 pages, 2 figure
USA and RXTE Observations of a Variable Low-Frequency QPO in XTE J1118+480
The USA experiment on ARGOS and RXTE have exensively observed the X-ray
transient XTE J1118+480 during its recent outburst in 2000 April--June. We
present detailed monitoring of the evolution of a low frequency QPO which
drifts from 0.07 Hz to 0.15 Hz during the outburst. We examine possible
correlations of the QPO frequency with the flux and spectral characteristics of
the source, and compare this QPO to low frequency QPOs observed in other black
hole candidates.Comment: Accepted by ApJ Letters, reference added, minor revisions, 6 page
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