2,081 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\ $B$\ is a magnetic dipole (besides remaining
an electric monopole, as well). Its magnetic moment grows linearly with $B$ 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 $B$ 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

### Particle creation from the vacuum by an exponentially decreasing electric field

We analyze the creation of fermions and bosons from the vacuum by the
exponentially decreasing in time electric field in detail. In our calculations
we use QED and follow in main the consideration of particle creation effect in
a homogeneous electric field. To this end we find complete sets of exact
solutions of the $d$-dimensional Dirac equation in the exponentially decreasing
electric field and use them to calculate all the characteristics of the effect,
in particular, the total number of created particles and the probability of a
vacuum to remain a vacuum. It should be noted that the latter quantities were
derived in the case under consideration for the first time. All possible
asymptotic regimes are discussed in detail. In addition, switching on and
switching off effects are studied.Comment: We add some references and minor comments. Version accepted for
publication in Physica Scripta as a Invited Commen

### 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

### Nigerian scam e-mails and the charms of capital

So-called '419' or 'advance-fee' e-mail frauds have proved remarkably successful. Global losses to these scams are believed to run to billions of dollars. Although it can be assumed that the promise of personal gain which these e-mails hold out is part of what motivates victims, there is more than greed at issue here. How is it that the seemingly incredible offers given in these unsolicited messages can find an audience willing to treat them as credible? The essay offers a speculative thesis in answer to this question. Firstly, it is argued, these scams are adept at exploiting common presuppositions in British and American culture regarding Africa and the relationships that are assumed to exist between their nations and those in the global south. Secondly, part of the appeal of these e-mails lies in the fact that they appear to reveal the processes by which wealth is created and distributed in the global economy. They thus speak to their readers’ attempts to map or conceptualise the otherwise inscrutable processes of that economy. In the conclusion the essay looks at the contradictions in the official state response to this phenomena

### 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

### Singular electromagnetic fields in nonlinear electrodynamics with a constant background field

When exploring equations of nonlinear electrodynamics in effective medium
formed by mutually parallel external electric and magnetic fields, we come to
special static axial-symmetric solutions of two types. The first are comprised
of fields referred to as electric and magnetic responses to a point-like
electric charge when placed into the medium. In electric case, this is a field
determined by the induced charge density. In magnetic case, this is a field
carrying no magnetic charge and determined by an induced current. Fields of
second type require presence of pseudoscalar constants for their existence.
These are singular on the axis drawn along the external fields. In electric
case this is a field of an inhomogeneously charged infinitely thin thread. In
magnetic case this is the magnetic monopole with the Dirac string supported by
solenoidal current. In both cases the necessary pseudoscalar constant is
supplied by field derivatives of nonlinear Lagrangian taken on external fields.
There is also a magnetic thread solution dual to electric thread with null
total magnetic charge.Comment: Published versio

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