3,224 research outputs found

    Electric charge is a magnetic dipole when placed in a background magnetic field

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    It is demonstrated, owing to the nonlinearity of QED, that a static charge placed in a strong magnetic field\ BB\ is a magnetic dipole (besides remaining an electric monopole, as well). Its magnetic moment grows linearly with BB 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 BB 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

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    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

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    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 dd-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

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    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

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    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

    The beautiful and the political

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    Competing and polarised positions related to the possible political nature of material in contemporary music are exemplified by the work of postmodern composers and of post-war modernist composers. Whilst the former argue for the political nature of their compositions by the inclusion of contemporary issues and imagery, the latter argue for the political nature of their manipulation of otherwise politically neutral musical material. This opposition can be understood as a dialectic between content and form, and is expressed by Adorno as the opposition between representational and ‘committed’ work. This paper examines one example of each type of work—Luigi Nono’s Il Canto Sospeso (1955-56) and Johannes Kreidler’s Audioguide—and their relationship to a conception of the ‘beautiful’ in music. These expressions of the ‘political’ offer a framework through which the musically beautiful can be interrogated in the opposition of committed and autonomous artworks, and understood as an experience of alienation. Eco's exploration of Entfremdung and Kristeva's concept of abjection can both be employed to argue that the ‘political’ dimension of autonomous works offers the potential for a radical experience of beauty as a transcendence derived from present conditions, whilst committed works negate beauty as a condition of re-presenting the present

    Nigerian scam e-mails and the charms of capital

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    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