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

Light-amplified Landau-Zener conductivity in gapped graphene monolayers: a simulacrum of photo-catalyzed vacuum instability

Interband transitions of electrons in a gapped graphene monolayer are highly stimulated near the Fermi surface when a high-frequency electric wave of weak intensity and a strong constant electric field are superposed on its surface. We consider the situation in which the photon energy associated with the fast-oscillating field is slightly below the graphene gap so that the quantum transitions still occur through tunneling effects while being facilitated by multiphoton absorption channels. In the considered parameter regime the photo-catalyzed current linked to the described setup is shown to exceed the one driven by the strong field solely by several orders of magnitude. Optimization conditions are revealed and an asymptotic formula for the current density is derived. The robustness of our assessment supports the viability of detecting this phenomenon in graphene, which would serve as a first-principle-proof of concept of the dynamically-assisted Schwinger mechanism in QED.Comment: 12 pages, 6 figure

On the connection between Hamilton and Lagrange formalism in Quantum Field Theory

The connection between the Hamilton and the standard Lagrange formalism is established for a generic Quantum Field Theory with vanishing vacuum expectation values of the fundamental fields. The Effective Actions in both formalisms are the same if and only if the fundamental fields and the momentum fields are related by the stationarity condition. These momentum fields in general differ from the canonical fields as defined via the Effective Action. By means of functional methods a systematic procedure is presented to identify the full correlation functions, which depend on the momentum fields, as functionals of those usually appearing in the standard Lagrange formalism. Whereas Lagrange correlation functions can be decomposed into tree diagrams the decomposition of Hamilton correlation functions involves loop corrections similar to those arising in n-particle effective actions. To demonstrate the method we derive for theories with linearized interactions the propagators of composite auxiliary fields and the ones of the fundamental degrees of freedom. The formalism is then utilized in the case of Coulomb gauge Yang-Mills theory for which the relations between the two-point correlation functions of the transversal and longitudinal components of the conjugate momentum to the ones of the gauge field are given.Comment: 25 pages, 24 figures, revised and extended version with an explicit application of the formalism to Coulomb gauge QC