Victor Dinu

Vacuum refractive indices and helicity flip in strong-field QED

Vacuum birefringence is governed by the amplitude for a photon to flip helicity or polarization state in an external field. Here, we calculate the flip and nonflip amplitudes in arbitrary plane wave backgrounds, along with the induced spacetime-dependent refractive indices of the vacuum. We compare the behavior of the amplitudes in the low energy and high energy regimes, and analyze the impact of pulse shape and energy. We also provide the first lightfront-QED derivation of the coefficients in the Heisenberg-Euler effective action.

Photon polarization in light-by-light scattering: Finite size effects

We derive a simple expression for the photon helicity and polarization-flip probabilities in arbitrary background fields, in the low-energy regime. Taking the background to model a focused laser beam, we study the impact of pulse shape and collision geometry on the probabilities and on ellipticity signals of vacuum birefringence. We find that models which do not account for pulse duration can overestimate all signals in near head-on collisions by up to an order of magnitude. Taking pulse duration into account, the flip probability becomes relatively insensitive to both angular incidence and the fine details of the pulse structure.

Quantum radiation reaction: from interference to incoherence

We investigate quantum radiation reaction in laser-electron interactions across different energy and intensity regimes. Using a fully quantum approach which also accounts exactly for the effect of the strong laser pulse on the electron motion, we identify in particular a regime in which radiation reaction is dominated by quantum interference. We find signatures of quantum radiation reaction in the electron spectra which have no classical analogue and which cannot be captured by the incoherent approximations typically used in the high-intensity regime. These signatures are measurable with presently available laser and accelerator technology.

Infrared divergences in plane wave backgrounds

We show that the emission of soft photons via nonlinear Compton scattering in a pulsed plane wave (laser field) is in general infrared divergent. We give examples of both soft and soft-collinear divergences, and we pay particular attention to the case of crossed fields in both classical and quantum theories.

Exact final state integrals for strong field QED

This paper introduces the exact, analytic integration of all final state variables for the process of nonlinear Compton scattering in an intense plane-wave laser pulse, improving upon a previously slow and challenging numerical approach. Computationally simple and insightful formulas are derived for the total scattering probability and mean energy momentum of the emitted radiation. The general form of the effective mass appears explicitly. We consider several limiting cases and present a quantum correction to Larmors formula. Numerical results are plotted and analyzed in detail.

Nonexponential decay laws in perturbation theory of near threshold eigenvalues

We consider a two channel model of the form He=[Hop00E0]+e[0W12W210] on H=Hop⊕C. The operator Hop is assumed to have the properties of a Schrodinger operator in odd dimensions, with a threshold at zero. As the energy parameter E0 is tuned past the threshold, we consider the survival probability |⟨Ψ0,e−itHeΨ0⟩|2, where Ψ0 is the eigenfunction corresponding to eigenvalue E0 for e=0. We find nonexponential decay laws for e small and E0 close to zero provided that the resolvent of Hop is not at least Lipschitz continuous at the threshold zero.

Perturbation of near threshold eigenvalues: Crossover from exponential to non-exponential decay laws

For a two-channel model of the form \begin{eqnarray*} H_\varepsilon= \left[ \begin{array}{@{}c@{\quad}c@{}} H_{\rm op} … 0\\[2pt] 0 … E_0 \end{array}\right] +\varepsilon\left[ \begin{array}{@{}c@{\quad}c@{}} 0 … W_{12}\\[2pt] W_{21} …0 \end{array}\right] \quad \text{on}\ \mathcal{H}=\mathcal{H}_{\rm op}\oplus \mathbf C, \end{eqnarray*} appearing in the study of Feshbach resonances, we continue the rigorous study, begun in our paper (J. Math. Phys.50 (2009) 013516), of the decay laws for resonances produced by perturbation of unstable bound states close to a threshold. The operator Hop is assumed to have the properties of a Schrodinger operator in odd dimensions, with a threshold at zero. We consider for e small the survival probability |〈ψ0, e-itHeΨ0〉|2, where Ψ0 is the eigenfunction corresponding to E0 for e = 0. For E0 in a small neighborhood of the origin independent of e, the survival probability amplitude is expressed in terms of some special functions related to the error function, up to error terms...

Electron distributions in nonlinear Compton scattering

Our calculation of the final electron distribution in nonlinear Compton scattering with very energetic electrons is performed for an electromagnetic pulse with finite duration. In contrast to the monochromatic case, this gives access to the the asymptotically free electrons and not to those dressed by the laser field.