Stochasticity effects in quantum radiation reaction

When an ultrarelativistic electron beam collides with a sufficiently intense laser pulse, radiation-reaction effects can strongly alter the beam dynamics. In the realm of classical electrodynamics, radiation reaction has a beneficial effect on the electron beam as it tends to reduce its energy spread. Here, we show that when quantum effects become important, radiation reaction induces the opposite effect, i.e., the electron beam spreads out after interacting with the laser pulse. We identify the physical origin of this opposite tendency in the intrinsic stochasticity of photon emission, which becomes substantial in the full quantum regime. Our numerical simulations indicated that the predicted effects of the stochasticity can be measured already with presently available lasers and electron accelerators.Comment: 5 pages, 2 figure

Electron-beam dynamics in a strong laser field including quantum radiation reaction

The evolution of an electron beam colliding head-on with a strong plane-wave field is investigated in the framework of strong-field QED including radiation-reaction effects due to photon emission. Employing a kinetic approach to describe the electron and the photon distribution it is shown that at a given total laser fluence the final electron distribution depends on the shape of the laser envelope and on the pulse duration, in contrast to the classical predictions of radiation reaction based on the Landau-Lifshitz equation. Finally, it is investigated how the pair-creation process leads to a nonlinear coupled evolution of the electrons in the beam, of the produced charged particles, and of the emitted photons.Comment: 25 pages, 11 figure

Magnetically amplified tunneling of the 3rd kind as a probe of minicharged particles

We show that magnetic fields significantly enhance a new tunneling mechanism in quantum-field theories with photons coupling to fermionic minicharged particles. We propose a dedicated laboratory experiment of the light-shining-through-walls type that can explore a parameter regime comparable to and even beyond the best model-independent cosmological bounds. With present-day technology, such an experiment is particularly sensitive to minicharged particles with masses in and below the meV regime.Comment: 5 pages, 2 figures; some clarifications added, matches version published in PR

Relating color discrimination to photopigment genes in deutan observers

AbstractDeutan observers are a heterogeneous group, varying nearly continuously from deuteranomalous trichromats with fine chromatic discrimination in the red/green range to deuteranopes who have none. We sought to relate chromatic discriminative ability among deutans measured psychophysically (phenotypes) to observers' separation between long-wave visual pigments inferred from visual pigment genes (genotypes). If middle-wave pigment genes are assumed not to be expressed in these deutan observers there is a clear relation between phenotype and genotype

Novel aspects of radiation reaction in the classical and the quantum regime

This work is dedicated to the study of radiation reaction signatures in the framework of classical and quantum electrodynamics. Since there has been no distinct experimental validation of radiation reaction and its underlying equations so far and its impact is expected to be substantial for the construction of new experimental devices, e.g., quantum x-free electron lasers, a profound understanding of radiation reaction effects is of special interest. Here, we describe how the inclusion of quantum radiation reaction effects changes the dynamics of ultra-relativistic electron beams colliding with intense laser pulses significantly. Thereafter, the angular distribution of emitted radiation is demonstrated to be strongly altered in the quantum framework, if in addition to single photon emission also higher order photon emissions are considered. Furthermore, stimulated Raman scattering of an ultra-intense laser pulse in plasmas is examined and forward Raman scattering is found to be significantly increased by the inclusion of radiation reaction effects in the classical regime. The numerical simulations in this work show the feasibility of an experimental verification of the predicted effects with presently available lasers and electron accelerators.Comment: 13 pages, 3 figures, Proceedings of the LPHYS'13 Worksho

The Effect of Cone Opsin Mutations on Retinal Structure and the Integrity of the Photoreceptor Mosaic

Purpose. To evaluate retinal structure and photoreceptor mosaic integrity in subjects with OPN1LW and OPN1MW mutations. Methods. Eleven subjects were recruited, eight of whom have been previously described. Cone and rod density was measured using images of the photoreceptor mosaic obtained from an adaptive optics scanning light ophthalmoscope (AOSLO). Total retinal thickness, inner retinal thickness, and outer nuclear layer plus Henle fiber layer (ONL+HFL) thickness were measured using cross-sectional spectral-domain optical coherence tomography (SD-OCT) images. Molecular genetic analyses were performed to characterize the OPN1LW/OPN1MW gene array. Results. While disruptions in retinal lamination and cone mosaic structure were observed in all subjects, genotype-specific differences were also observed. For example, subjects with “L/M interchange” mutations resulting from intermixing of ancestral OPN1LW and OPN1MW genes had significant residual cone structure in the parafovea (∼25% of normal), despite widespread retinal disruption that included a large foveal lesion and thinning of the parafoveal inner retina. These subjects also reported a later-onset, progressive loss of visual function. In contrast, subjects with the C203R missense mutation presented with congenital blue cone monochromacy, with retinal lamination defects being restricted to the ONL+HFL and the degree of residual cone structure (8% of normal) being consistent with that expected for the S-cone submosaic. Conclusions. The photoreceptor phenotype associated with OPN1LW and OPN1MW mutations is highly variable. These findings have implications for the potential restoration of visual function in subjects with opsin mutations. Our study highlights the importance of high-resolution phenotyping to characterize cellular structure in inherited retinal disease; such information will be critical for selecting patients most likely to respond to therapeutic intervention and for establishing a baseline for evaluating treatment efficacy

A study of unusual Rayleigh matches in deutan deficiency

Rayleigh match data were modeled with the aim of explaining the locations of match midpoints and matching ranges, both in normal trichromats and in subjects with congenital color deficiency. Model parameters included the wavelength of peak sensitivity of cone photopigments, the effective photopigment optical density, and the noise amplitude in the red-green color channel. In order to avoid the suprathreshold, perceptual effects of extreme L:M cone ratios on color vision, selective post-receptoral amplification of cone signals is needed. The associated noise is also amplified and this causes corresponding changes in red-green threshold sensitivity. We propose that the noise amplitude and hence the size of the matching range in normal trichromats relates to the known inter-subject variation in the relative numbers of L and M cones. If this hypothesis can be shown to account for the extremes of the red-green matching range measured in normal trichromats, it is of interest to establish the extent to which it also predicts the unexpected, small matching ranges that are observed in some subjects with red-green color deficiency. A subset of subjects with deutan deficiency that exhibited less common Nagel matches were selected for genetic analysis of their cone pigment genes in order to confirm the type of deficiency, and to predict the corresponding peak wavelength separation (δλmax) of their two, long-wavelength cone pigments. The Rayleigh match model predicted accurately the midpoint and the range for the spectral differences specified by the genes. The prediction also required plausible selection of effective optical density of the cone pigments and noise. The noise needed varied, but the estimates were confined to lie within the limits established from the matching ranges measured in normal trichromats. The model predicts correctly the small matching ranges measured in some deuteranomalous subjects, principally accounted for by a low estimate of noise level in the red-green channel. The model also predicts the “normal” matches made by some subjects that rely on two hybrid genes and therefore exhibit red-green thresholds outside the normal range, typical of mild deuteranomaly

Assessing Photoreceptor Structure Associated with Ellipsoid Zone Disruptions Visualized with Optical Coherence Tomography

Purpose: To compare images of photoreceptor layer disruptions obtained with optical coherence tomography (OCT) and adaptive optics scanning light ophthalmoscopy (AOSLO) in a variety of pathologic states.Methods: Five subjects with photoreceptor ellipsoid zone disruption as per OCT and clinical diagnoses of closed-globe blunt ocular trauma (n = 2), macular telangiectasia type 2 (n = 1), blue-cone monochromacy (n = 1), or cone-rod dystrophy (n = 1) were included. Images were acquired within and around photoreceptor lesions using spectral domain OCT, confocal AOSLO, and split-detector AOSLO.Results: There were substantial differences in the extent and appearance of the photoreceptor mosaic as revealed by confocal AOSLO, split-detector AOSLO, and spectral domain OCT en face view of the ellipsoid zone.Conclusion: Clinically available spectral domain OCT, viewed en face or as B-scan, may lead to misinterpretation of photoreceptor anatomy in a variety of diseases and injuries. This was demonstrated using split-detector AOSLO to reveal substantial populations of photoreceptors in areas of no, low, or ambiguous ellipsoid zone reflectivity with en face OCT and confocal AOSLO. Although it is unclear if these photoreceptors are functional, their presence offers hope for therapeutic strategies aimed at preserving or restoring photoreceptor function

Can stimulus enhancement explain the apparent success of the model-rival technique in the domestic dog (Canis familiaris)?

The model-rival technique is a method of training whereby an animal learns the distinguishing features of a target object, such as name and colour, by observing a trainer and a potential competitor engage in conversation about these features. In this study the apparent effectiveness of the model-rival technique in training dogs to perform a selection-retrieval task by McKinley and Young McKinley, S., Young, R.J., 2003. The efficacy of the model-rival method when compared with operant conditioning for training domestic dogs to perform a retrieval-selection task. Appl. Anim. Behav. Sci. 81, 357-365 was investigated to evaluate the hypothesis that simpler forms of learning may be responsible for the results. This was tested by repeating McKinley and Young's model-rival training method and comparing the results to those of training sessions devised to include different forms of stimulus enhancement of the object to be retrieved. These training sessions involved: minimal enhancement, during which the experimenters made no interactions with the target object; indirect stimulus enhancement, during which both experimenters switched their gaze between the dog and the target object; or direct stimulus enhancement, during which one of the experimenters held the target object. It was found that only the model-rival and direct enhancement methods resulted in a significant number of dogs successfully completing the selection-retrieval test. There was also evidence to suggest that with the direct stimulus enhancement training method dogs learned quicker than with the model-rival training method. It was concluded that dogs are able to learn to retrieve a named object in a selection-retrieval task as a result of simple stimulus enhancement, without necessarily understanding the complex cognitive processes which underpin learning in the model-rival process. c 2008 Elsevier B.V. All rights reserved