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Register a new userLaser intensity effects in noncommutative QED
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We discuss a two-fold extension of QED assuming the presence of strong external fields provided by an ultra-intense laser and noncommutativity of spacetime. While noncommutative effects leave the electrons intensity induced mass shift unchanged, the photons change significantly in character: they acquire a quasi-momentum that is no longer light-like. We study the consequences of this combined noncommutative strong-field effect for basic lepton-photon interactions.
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The spectrally resolved differential cross section of Compton scattering, $d sigma / d omega vert_{omega = const}$, rises from small towards larger laser intensity parameter $xi$, reaches a maximum, and falls towards the asymptotic strong-field region. Expressed by invariant quantities: $d sigma /du vert_{u = const}$ rises from small towards larger values of $xi$, reaches a maximum at $xi_{max} = frac49 {cal K} u m^2 / k cdot p$, ${cal K} = {cal O} (1)$, and falls at $xi > xi_{max}$ like $propto xi^{-3/2} exp left (- frac{2 u m^2}{3 xi , k cdot p} right )$ at $u ge 1$. [The quantity $u$ is the Ritus variable related to the light-front momentum-fraction $s = (1 + u)/u = k cdot k / k cdot p$ of the emitted photon (four-momentum $k$, frequency $omega$), and $k cdot p/m^2$ quantifies the invariant energy in the entrance channel of electron (four-momentum $p$, mass $m$) and laser (four-wave vector $k$).] Such a behavior of a differential observable is to be contrasted with the laser intensity dependence of the total probability, $lim_{chi = xi k cdot p/m^2, xi to infty} mathbb{P} propto alpha chi^{2/3} m^2 / k cdot p$, which is governed by the soft spectral part. We combine the hard-photon yield from Compton with the seeded Breit-Wheeler pair production in a folding model and obtain a rapidly increasing $e^+ e^-$ pair number at $xi lesssim 4$. Laser bandwidth effects are quantified in the weak-field limit of the related trident pair production.
We find dispersion laws for the photon propagating in the presence of mutually orthogonal constant external electric and magnetic fields in the context of the $theta $-expanded noncommutative QED. We show that there is no birefringence to the first order in the noncommutativity parameter $% theta .$ By analyzing the group velocities of the photon eigenmodes we show that there occurs superluminal propagation for any direction. This phenomenon depends on the mutual orientation of the external electromagnetic fields and the noncommutativity vector. We argue that the propagation of signals with superluminal group velocity violates causality in spite of the fact that the noncommutative theory is not Lorentz-invariant and speculate about possible workarounds.
In this paper, we investigate the behavior of non-commutative IR divergences and will also discuss their cancellation in the physical cross sections. The commutative IR (soft) divergences existing in the non-planar diagrams will be examined in order to prove an all order cancellation of these divergences using the Weinbergs method. In non-commutative QED, collinear divergences due to triple photon splitting vertex, were encountered, which are shown to be canceled out by the non-commutative version of KLN theorem. This guarantees that there is no mixing between the Collinear, soft and non-commutative IR divergences.
Over the last Century the method of particle acceleration to high energies has become the prime approach to explore the fundamental nature of matter in laboratory. It appears that the latest search of the contemporary accelerator based on the colliders shows a sign of saturation (or at least a slow-down) in increasing its energy and other necessary parameters to extend this frontier. We suggest two pronged approach enabled by the recent progress in high intensity lasers.
Absorption covers the physical processes which convert intense photon flux into energetic particles when a high-power laser illuminates optically-thick matter. It underpins important petawatt-scale applications today, e.g., medical-quality proton beam production. However, development of ultra-high-field applications has been hindered since no study so far has described absorption throughout the entire transition from the classical to the quantum electrodynamical (QED) regime of plasma physics. Here we present a model of absorption that holds over an unprecedented six orders-of-magnitude in optical intensity and lays the groundwork for QED applications of laser-driven particle beams. We demonstrate 58% efficient gamma-ray production at $1.8times 10^{25}~mathrm{W~ cm^{-2}}$ and the creation of an anti-matter source achieving $4times 10^{24} mathrm{positrons} mathrm{cm^{-3}}$, $10^{6}~times$ denser than of any known photonic scheme. These results will find applications in scaled laboratory probes of black hole and pulsar winds, gamma-ray radiography for materials science and homeland security, and fundamental nuclear physics.
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