70 research outputs found
Photon propagation in magnetic and electric fields with scalar/pseudoscalar couplings: a new look
We consider the minimal coupling of two photons to neutral scalar and
pseudoscalar fields, as for instance in the case of the Higgs boson and axion,
respectively. In this framework, we analyze the photon dispersion relations in
the presence of static and homogeneous external magnetic and electric fields,
by taking into account the contribution of the imaginary part of the
scalar/pseudoscalar self-energy. We show that this contribution cannot be
neglected when it is of the same order as the photon-scalar/pseudoscalar mixing
term. In addition to the usual light-like photon propagation mode, with a
refraction index n > 1, a massive mode with mass of the order of the coupled
boson mass can be induced, provided that the external field is above a
particular critical value. Depending on the values of the external field,
photon energy, and mass of the scalar/pseudoscalar particle, the
scalar/pseudoscalar width could induce a sizeable rate of photon splitting in
two photons due to a strong resonant phenomenon. This effect has no practical
laboratory applications for the Higgs physics due to the very large critical
external magnetic or electric fields involved, for a photon energy of the order
of a TeV. However, it can have relevant consequences in the axion physics or in
any other scenario where light neutral scalar/pseudoscalar fields have minimal
coupling with two photons.Comment: 40 pages, LaTeX, 5.eps Figures, new appendix and results included,
misprints corrected, conclusions unchanged. Version to appear on Phys. Rev.
Scattering of scalar and Dirac particles by a magnetic tube of finite radius
We consider the Dirac equation in cylindrically symmetric magnetic fields and
find its normal modes as eigenfunctions of a complete set of commuting
operators. This set consists of the Dirac operator itself, the -components
of the linear and the total angular momenta, and of one of the possible spin
polarization operators. The spin structure of the solution is completely fixed
independently of the radial distribution of the magnetic field which influences
only the radial modes. We solve explicitly the radial equations for the uniform
magnetic field inside a solenoid of a finite radius and consider in detail the
scattering of scalar and Dirac particles in this field. For particles with low
energy the scattering cross section coincides with the Aharonov-Bohm scattering
cross section. We work out the first order corrections to this result caused by
the fact that the solenoid radius is finite. At high energies we obtain the
classical result for the scattering cross section.Comment: LaTeX file, 17 page
Axions, their Relatives and Prospects for the Future
The observation of a non-vanishing rotation of linear polarized laser light
after passage through a strong magnetic field by the PVLAS collaboration has
renewed the interest in light particles coupled to photons. Axions are a
species of such particles that is theoretically well motivated. However, the
relation between coupling and mass predicted by standard axion models conflicts
with the PVLAS observation. Moreover, light particles with a coupling to
photons of the strength required to explain PVLAS face trouble from
astrophysical bounds. We discuss models that can avoid these bounds. Finally,
we present some ideas to test these possible explanations of PVLAS
experimentally.Comment: 11 pages, 4 figures. Contributed to the ``Third Symposium on Large
TPCs for Low Energy Rare Event Detection'' in Paris, December 200
Formation of "Lightnings" in a Neutron Star Magnetosphere and the Nature of RRATs
The connection between the radio emission from "lightnings" produced by the
absorption of high-energy photons from the cosmic gamma-ray background in a
neutron star magnetosphere and radio bursts from rotating radio transients
(RRATs) is investigated. The lightning length reaches 1000 km; the lightning
radius is 100 m and is comparable to the polar cap radius. If a closed
magnetosphere is filled with a dense plasma, then lightnings are efficiently
formed only in the region of open magnetic field lines. For the radio emission
from a separate lightning to be observed, the polar cap of the neutron star
must be directed toward the observer and, at the same time, the lightning must
be formed. The maximum burst rate is related to the time of the plasma outflow
from the polar cap region. The typical interval between two consecutive bursts
is ~100 s. The width of a single radio burst can be determined both by the
width of the emission cone formed by the lightning emitting regions at some
height above the neutron star surface and by a finite lightning lifetime. The
width of the phase distribution for radio bursts from RRATs, along with the
integrated pulse width, is determined by the width of the bundle of open
magnetic field lines at the formation height of the radio emission. The results
obtained are consistent with the currently available data and are indicative of
a close connection between RRATs, intermittent pulsars, and extreme nullers.Comment: 24 pages, no figures, references update
Electron-positron pair production in the Aharonov-Bohm potential
In the framework of QED we evaluate the cross section for electron-positron
pair production by a single photon in the presence of the external
Aharonov-Bohm potential in first order of perturbation theory. We analyse
energy, angular and polarization distributions at different energy regimes:
near the threshold and at high photon energies.Comment: LaTeX file, 13 page
Are we ready to transfer optical light to gamma-rays?
Scattering relativistic electrons with optical lasers can result in a
significant frequency upshift for the photons, potentially producing
-rays. This is what linear Compton scattering taught us. Ultra-intense
lasers offer nowadays a new paradigm where multi-photon absorption effects come
into play. These effects can result in higher harmonics, higher yields and also
electron-positron pairs. This article intends to discriminate the different
laser scenarios that have been proposed over the past years as well as to give
scaling laws for future experiments. The energy conversion from laser or
particles to high-frequency photons is addressed for both the well-known
counter propagating electron beam-laser interaction and for
Quantum-electrodynamics cascades triggered by various lasers. Constructing
bright and energetic gamma-ray sources in controlled conditions is within an
ace of seeing the light of day.Comment: 9 pages, 9 figure
Black-hole concept of a point-like nucleus with supercritical charge
The Dirac equation for an electron in the central Coulomb field of a
point-like nucleus with the charge greater than 137 is considered. This
singular problem, to which the fall-down onto the centre is inherent, is
addressed using a new approach, based on a black-hole concept of the singular
centre and capable of producing cut-off-free results. To this end the Dirac
equation is presented as a generalized eigenvalue boundary problem of a
self-adjoint operator. The eigenfunctions make complete sets, orthogonal with a
singular measure, and describe particles, asymptotically free and
delta-function-normalizable both at infinity and near the singular centre
. The barrier transmission coefficient for these particles responsible for
the effects of electron absorption and spontaneous electron-positron pair
production is found analytically as a function of electron energy and charge of
the nucleus. The singular threshold behaviour of the corresponding amplitudes
substitutes for the resonance behaviour, typical of the conventional theory,
which appeals to a finite-size nucleus.Comment: 22 pages, 5 figures, LATEX requires IOPAR
Electron spin polarization in realistic trajectories around the magnetic node of two counter-propagating, circularly polarized, ultra-intense lasers
It has recently been suggested that two counter-propagating, circularly polarized, ultra-intense lasers can induce a strong electron spin polarization at the magnetic node of the electromagnetic field that they setup (Del Sorbo et al 2017 Phys. Rev. A 96 043407). We confirm these results by considering a more sophisticated description that integrates over realistic trajectories. The electron dynamics is weakly affected by the variation of power radiated due to the spin polarization. The degree of spin polarization differs by approximately 5% if considering electrons initially at rest or already in a circular orbit. The instability of trajectories at the magnetic node induces a spin precession associated with the electron migration that establishes an upper temporal limit to the polarization of the electron population of about one laser period
- …