Axion-induced birefringence effects in laser driven nonlinear vacuum interaction

The propagation of a probe electromagnetic field through a counterpropagating strong plane wave is investigated. The effects of the electromagnetic field-(pseudo)scalar axion field interaction and of the self-interaction of the electromagnetic field mediated by virtual electron-positron pairs in the effective Lagrangian approach are included. First, we show that if the strong field is circularly polarized, contrary to the leading-order nonlinear QED effects, the axion-photon interaction induces a chiral-like birefringence and a dichroism in the vacuum. The latter effect is explained by evoking the conservation of the total angular momentum along the common propagation direction of probe and the strong wave, which allows for real axion production only for probe and strong fields with the same helicity. Moreover, in the case of ultra-short strong pulses, it is shown that the absorption coefficients of probe photons depend on the form of the pulse and, in particular, on the carrier-envelope phase of the strong beam. The present results can be exploited experimentally to isolate nonlinear vacuum effects stemming from light-axion interaction, especially at upcoming ultra-strong laser facilities, where stringent constraints on the axion-photon coupling constant are in principle provided.Comment: 16 pages, 1 figur

Spin effects in strong-field laser-electron interactions

The electron spin degree of freedom can play a significant role in relativistic scattering processes involving intense laser fields. In this contribution we discuss the influence of the electron spin on (i) Kapitza-Dirac scattering in an x-ray laser field of high intensity, (ii) photo-induced electron-positron pair production in a strong laser wave and (iii) multiphoton electron-positron pair production on an atomic nucleus. We show that in all cases under consideration the electron spin can have a characteristic impact on the process properties and their total probabilities. To this end, spin-resolved calculations based on the Dirac equation in the presence of an intense laser field are performed. The predictions from Dirac theory are also compared with the corresponding results from the Klein-Gordon equation.Comment: 9 pages, 6 figure

Cultivo de ostión Crassostrea gigas: Análisis de 40 años de actividades en México

This study is the revision of the culture of the oyster Crassostrea gigas since its introduction in Mexico 40 years ago. The introduction occurred in Baja California during 1973 and then the cultures expanded to other states. There is no juvenile collection from the wild so the spat is produced in national and foreign hatcheries. Current culture systems are; hanging oysters fixed on ropes from racks, oyster trays in long-lines, and plastic mesh bags set on trestles. Mortality outbreaks have been detected since 1997 and today is known that events occur in March-April and November affecting oysters less than 50 mm long. Two diseases related to mortality outbreaks have been confirmed for C. gigas in Mexico; herpesvirus and perkinsosis. Production collapsed due to mortalities leading to a crisis of the activity; signs of recovery are seen until 2010 with a production of 2,858 tonnes. Aquatic animal health agencies as well as state oyster committees in Baja California, Baja California Sur, and Sonora have been key elements for the recovery and organization of oyster industry in the region. At present, studies in genetics are in course to produce disease-resistant oysters and there are promising results using new experimental culture systems. However, problems associated with the activity are diverse and require important efforts from all sectors involved to consolidate the cultivation of the species in the region.Se presenta una revisión sobre el cultivo del ostión Crassostrea gigas desde que fue introducido a México hace 40 años. La introducción de esta especie se hizo en Baja California durante 1973 y a partir de ahí el cultivo de la especie se extendió a otros estados. No hay captación natural de la especie en la región; toda la semilla que se utiliza proviene de laboratorios nacionales y extranjeros. Los principales sistemas de cultivo son; sartas en balsas y estantes, cajas ostrícolas en sistema suspendido y costales sobre estantes. En 1997 se empezaron a registrar mortalidades masivas de ostión y actualmente se sabe que los eventos ocurren en marzo-abril y noviembre, afectando principalmente a ostiones menores de 50 mm. Se han confirmado dos enfermedades para C. gigas en México relacionadas con las mortalidades; herpesvirus y perkinsosis. Debido a las mortalidades la producción se desplomó y puso en crisis a la actividad; hasta 2010 se empiezan a ver signos de recuperación (2,858 toneladas). Los Comités de Sanidad Acuícola así como los Comités Estatales Sistema Producto Ostión en Baja California, Baja California Sur y Sonora han sido claves para la recuperación y organización de la ostricultura en la región. Actualmente se realiza investigación en genética para producir ostiones resistentes a enfermedades y se tienen resultados alentadores usando nuevas tecnologías de cultivo. No obstante, las problemáticas asociadas a la actividad son variadas y se requieren esfuerzos importantes de todos los sectores involucrados para consolidar el cultivo de la especie en la región