Quantum electron self-interaction in a strong laser field

The quantum state of an electron in a strong laser field is altered if the interaction of the electron with its own electromagnetic field is taken into account. Starting from the Schwinger-Dirac equation, we determine the states of an electron in a plane-wave field with inclusion, at leading order, of its electromagnetic self-interaction. On the one hand, the electron states show a pure "quantum" contribution to the electron quasi-momentum, conceptually different from the conventional "classical" one arising from the quiver motion of the electron. On the other hand, the electron self-interaction induces a distinct dynamics of the electron spin, whose effects are shown to be measurable in principle with available technology.Comment: 5 pages, 2 figure

Building Consensus. An introduction to a rhetorical approach

The contemporary debate on democracy shows two points of view: the \u201cdeliberative\u201d one and the \u201cagonistic\u201d one. The first one is related to the classical tradition that considers Habermas as its reference point. It emphasizes the role of rational deliberation as a means to produce a legitimate and binding consensus. In contrast, the second one draws its inspiration from C. Schmitt, and considers conflict and disagreement as unavoidable conditions of democratic life. Despite their obvious differences, these two theoretical models have a conception of rhetoric in common that is subjected to, or at least excluded from, the full exercise of argumentative rationality. We propose an interpretation of rhetoric that includes the logical-argumentative dimension in the rhetorical domain is possible. In this way, the recovery of rhetoric, considered both as a practice and as a theory of persuasive speech, may shed light on the role of discursive processes in building consensus, and thus may allow a revision of the dialectical tension between the pairs of concepts that the debate tends to focus on: normative/descriptive, rational/irrational, agreement/conflict

Entre théorie et pratique. Aristote et le strabisme de la techne

The Aristotelian reflection on the epistemological status of techne, and more specifically on the definition of rhetoric as a techne, can help us to rethink the very actual cleavage between theory and practice. A good techne, as the rhetoric has to be according to Aristotle, has not to choose between theory and practice, between the universal and the particular, but should be able to look simultaneously in both directions and to keep them together. We will try to show that may be worth to rediscover and to introduce the Aristotelian notion of techne into the contemporary epistemological and philosophical debate

Improved local-constant-field approximation for strong-field QED codes

The local-constant-field approximation (LCFA) is an essential theoretical tool for investigating strong-field QED phenomena in background electromagnetic fields with complex spacetime structure. In our previous work [Phys.~Rev.~A~\textbf{98}, 012134 (2018)] we have analyzed the shortcomings of the LCFA in nonlinear Compton scattering at low emitted photon energies for the case of a background plane-wave field. Here, we generalize that analysis to background fields, which can feature a virtually arbitrary spacetime structure. In addition, we provide an explicit and simple implementation of an improved expression of the nonlinear Compton scattering differential probability that solves the main shortcomings of the standard LCFA in the infrared region, and is suitable for background electromagnetic fields with arbitrary spacetime structure such as those occurring in particle-in-cell simulations. Finally, we carry out a systematic procedure to calculate the probability of nonlinear Compton scattering per unit of emitted photon light-cone energy and of nonlinear Breit-Wheeler pair production per unit of produced positron light-cone energy beyond the LCFA in a plane-wave background field, which allows us to identify the limits of validity of this approximation quantitatively.Comment: 15 pages, 3 figure

Implementing nonlinear Compton scattering beyond the local constant field approximation

In the calculation of probabilities of physical processes occurring in a background classical field, the local constant field approximation (LCFA) relies on the possibility of neglecting the space-time variation of the external field within the region of formation of the process. This approximation is widely employed in strong-field QED as it allows to evaluate probabilities of processes occurring in arbitrary electromagnetic fields starting from the corresponding quantities computed in a constant electromagnetic field. Here, we demonstrate in the case of nonlinear single Compton scattering that the LCFA is quantitatively and qualitatively insufficient for describing the low-energy part of the emitted photon probability. In addition, we provide a simple recipe to implement an improved expression of the photon emission probability beyond the LCFA in numerical codes, which are an essential tool to interpret present and upcoming experiments in strong-field QED.Comment: 12 pages, 3 figur

Citizens, citizenship and European Union: an open bet? The culture of legality

Although the meanings of citizenship, active citizenship and organized crime are still open to debate, we try to show the evaluation of the culture of legality and the investments in social, economic and cultural programs for youth as a major defense for such a capillary phenomenon. There is also general agreement that EU programs for endorsing citizenship and active citizenship represent an effective tool for creating transnational networks of young people committed to EU values. Thus, they perceive the culture of legality as the best form of protection against arbitrary violence with references not only to a developed (and eventually harmonized) system of legal sanctions, but also to the fulfillment of individual and collective freedom. We try to shed light on these concept by teh tools provided by political science and philosophy of language

Electron-positron annihilation into two photons in an intense plane-wave field

The process of electron-positron annihilation into two photons in the presence of an intense classical plane wave of an arbitrary shape is investigated analytically by employing light-cone quantization and by taking into account the effects of the plane wave exactly. We introduce a general description of second-order 2-to-2 scattering processes in a plane-wave background field, indicating the necessity of considering the localization of the colliding particles and achieving that by means of wave packets. We define a local cross section in the background field, which generalizes the vacuum cross section and which, though not being directly an observable, allows for a comparison between the results in the plane wave and in vacuum without relying on the shape of the incoming wave packets. Two possible cascade or two-step channels have been identified in the annihilation process and an alternative way of representing the two-step and one-step contributions via a "virtuality" integral has been found. Finally, we compute the total local cross section to leading order in the coupling between the electron-positron field and the quantized photon field, excluding the interference between the two leading-order diagrams arising from the exchange of the two final photons, and express it in a relatively compact form. In contrast to processes in a background field initiated by a single particle, the pair annihilation into two photons, in fact, also occurs in vacuum. Our result naturally embeds the vacuum part and reduces to the vacuum expression, known in the literature, in the case of a vanishing laser field.Comment: 26 pages, 2 figure

Pair production in a strong slowly varying magnetic field: the effect of a background gravitational field

The production probability of an $e^--e^+$ pair in the presence of a strong, uniform and slowly varying magnetic field is calculated by taking into account the presence of a background gravitational field. The curvature of the spacetime metric induced by the gravitational field not only changes the transition probabilities calculated in the Minkowski spacetime but also primes transitions that are strictly forbidden in absence of the gravitational field.Comment: 56 pages, no figure