2,880 research outputs found
Detecting photon-photon scattering in vacuum at exawatt lasers
In a recent paper, we have shown that the QED nonlinear corrections imply a
phase correction to the linear evolution of crossing electromagnetic waves in
vacuum. Here, we provide a more complete analysis, including a full numerical
solution of the QED nonlinear wave equations for short-distance propagation in
a symmetric configuration. The excellent agreement of such a solution with the
result that we obtain using our perturbatively-motivated Variational Approach
is then used to justify an analytical approximation that can be applied in a
more general case. This allows us to find the most promising configuration for
the search of photon-photon scattering in optics experiments. In particular, we
show that our previous requirement of phase coherence between the two crossing
beams can be released. We then propose a very simple experiment that can be
performed at future exawatt laser facilities, such as ELI, by bombarding a low
power laser beam with the exawatt bump.Comment: 8 pages, 6 figure
High Energy Photon-Photon Collisions at a Linear Collider
High intensity back-scattered laser beams will allow the efficient conversion
of a substantial fraction of the incident lepton energy into high energy
photons, thus significantly extending the physics capabilities of an
electron-electron or electron-positron linear collider. The annihilation of two
photons produces C=+ final states in virtually all angular momentum states. The
annihilation of polarized photons into the Higgs boson determines its
fundamental two-photon coupling as well as determining its parity. Other novel
two-photon processes include the two-photon production of charged lepton pairs,
vector boson pairs, as well as supersymmetric squark and slepton pairs and
Higgstrahlung. The one-loop box diagram leads to the production of pairs of
neutral particles. High energy photon-photon collisions can also provide a
remarkably background-free laboratory for studying possibly anomalous
collisions and annihilation. In the case of QCD, each photon can materialize as
a quark anti-quark pair which interact via multiple gluon exchange. The
diffractive channels in photon-photon collisions allow a novel look at the QCD
pomeron and odderon. Odderon exchange can be identified by looking at the heavy
quark asymmetry. In the case of electron-photon collisions, one can measure the
photon structure functions and its various components. Exclusive hadron
production processes in photon-photon collisions test QCD at the amplitude
level and measure the hadron distribution amplitudes which control exclusive
semi-leptonic and two-body hadronic B-decays.Comment: Invited talk, presented at the 5th International Workshop On
Electron-Electron Interactions At TeV Energies, Santa Cruz, California, 12-14
December 200
Beam energy measurement at linear colliders using spin precession
Linear collider designs foresee some bends of about 5-10 mrad. The spin
precession angle of one TeV electrons on 10 mrad bend is 23.2 rad and it
changes proportional to the energy. Measurement of the spin direction using
Compton scattering of laser light on electrons before and after the bend allows
determining the beam energy with an accuracy about of 10^{-5}. In this paper
the principle of the method, the procedure of the measurement and possible
errors are discussed. Some remarks about importance of plasma focusing effects
in the method of beam energy measurement using Moller scattering are given.Comment: 7 pages, Latex, 4 figures(.eps). In v.3 corresponds to journal
publication. Talk at 26-th Advanced ICFA Beam Dynamic Workshop on
Nanometre-Size Colliding Beams (Nanobeam2002), Lausanne, Switzerland, Sept
2-6, 200
The dependence of the hard diffractive photoproduction of vector meson or photon and the range of pQCD validity
We consider two coupled problems.
We study the dependence on photon virtuality for the semihard
quasi--elastic photoproduction of neutral vector mesons on a quark, gluon or
real photon (at
GeV)). To this end we calculate the corresponding amplitudes (in an
analytical form) in the lowest nontrivial approximation of perturbative QCD. It
is shown that the amplitude for the production of light meson varies very
rapidly with the photon virtuality near .
We estimate the bound of the pQCD validity region for such processes. For the
real incident photon the obtained bound for the meson production is very
high. This bound decreases fast with the increase of , and we expect that
the virtual photoproduction at HERA gives opportunity to test the pQCD results.
The signature of this region is discussed. For the hard Compton effect the pQCD
should work good at not too high , and this effect seems measurable
at HERA.Comment: ReVTeX, 36 pages, 5 Postscript figures, uses epsf.st
Electromagnetic Fields of Slowly Rotating Magnetized Gravastars
We study the dipolar magnetic field configuration and present solutions of
Maxwell equations in the internal background spacetime of a a slowly rotating
gravastar. The shell of gravastar where magnetic field penetrated is modeled as
sphere consisting of perfect highly magnetized fluid with infinite
conductivity. Dipolar magnetic field of the gravastar is produced by a circular
current loop symmetrically placed at radius at the equatorial plane.Comment: 5 pages, 2 figures, accepted for publication to Mod. Phys. Lett.
Observation of vortex dipoles in an oblate Bose-Einstein condensate
We report experimental observations and numerical simulations of the
formation, dynamics, and lifetimes of single and multiply charged quantized
vortex dipoles in highly oblate dilute-gas Bose-Einstein condensates (BECs). We
nucleate pairs of vortices of opposite charge (vortex dipoles) by forcing
superfluid flow around a repulsive gaussian obstacle within the BEC. By
controlling the flow velocity we determine the critical velocity for the
nucleation of a single vortex dipole, with excellent agreement between
experimental and numerical results. We present measurements of vortex dipole
dynamics, finding that the vortex cores of opposite charge can exist for many
seconds and that annihilation is inhibited in our highly oblate trap geometry.
For sufficiently rapid flow velocities we find that clusters of like-charge
vortices aggregate into long-lived dipolar flow structures.Comment: 4 pages, 4 figures, 1 EPAPS fil
The internal magnetic field in superconducting ferromagnets
We have measured the nonlinear response to the ac magnetic field in the
superconducting weak ferromagnet Ru-1222, at different regimes of sample
cooling which provides unambiguous evidence of the interplay of the domain
structure and the vorticity in the superconducting state. This is {\em direct}
proof of coexistence of ferromagnetic and superconductive order parameters in
high- ruthenocuprates.Comment: 9 pages, 6 figure
Gravitational Laser Back-Scattering
A possible way of producing gravitons in the laboratory is investigated. We
evaluate the cross section electron + photon electron + graviton
in the framework of linearized gravitation, and analyse this reaction
considering the photon coming either from a laser beam or from a Compton
back-scattering process.Comment: 11 pages, 2 figures (available upon request), RevTeX, IFT-P.03/9
and couplings in collision with polarized beams
The potential of e mode of linear collider to probe
and vertices is investigated through the Z boson
production from the procees . Considering the longitudinal and
transverse polarization states of the Z boson and incoming polarized beams we
find the 95% C.L. limits on the form factors , ,
and with integrated luminosity 500
and 0.5, 1, 1.5 TeV energies. It is shown that the polarization can
improve sensitivities by factors 2-3 depending on the energy.Comment: 12 pages, 8 EPS figure
Spin textures, screening and excitations in dirty quantum Hall ferromagnets
We study quantum Hall ferromagnets in the presence of a random electrostatic
impurity potential. Describing these systems with a classical non-linear sigma
model and using analytical estimates supported by results from numerical
simulations, we examine the nature of the ground state as a function of
disorder strength, , and deviation, , of the average Landau
level filling factor from unity. Screening of an impurity potential requires
distortions of the spin configuration, and in the absence of Zeeman coupling
there is a disorder-driven, zero-temperature phase transition from a
ferromagnet at small and to a spin glass at larger
or . We examine ground-state response functions and
excitations.Comment: 4 pages, 3 figure
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