When an ultrarelativistic electron beam collides with a sufficiently intense laser pulse, radiationreaction 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.PACS numbers: 12.20. Ds, A deep understanding of the dynamics of electric charges driven by electromagnetic fields is one of the most fundamental problems in physics, as it has implications in different fields, including accelerator, radiation and high-energy physics. Apart from its impact on practical issues, as the construction of new experimental devices (e.g., quantum x-free electron lasers [1]), the investigation of the dynamics of electric charges (electrons, for definiteness) is also of pure theoretical interest, as it involves in general a coupled dynamics of the electrons and of their own electromagnetic field.In the realm of classical electrodynamics, radiationreaction (RR) effects stem from the back reaction on the electron dynamics of the electromagnetic field generated by the electron itself while being accelerated by a background electromagnetic field [2,3]. The LandauLifshitz (LL) equation has been recently identified as the classical equation of motion of an electron, with mass m and charge e < 0, which includes RR effects selfconsistently [2][3][4][5][6][7], although alternative models have been suggested [8,9]. The analytical solution of the LL equation in a plane-wave field [10] shows that if an electron impinges with initial four-momentum p µ 0 onto a planewave field (electric-field amplitude E 0 , central angular frequency ω 0 and propagating along the direction n), RR effects substantially affect the electron dynamics, if the parameter R c = αχ 0 ξ 0 is of the order of unity (see also [11]). Here, α = e 2 is the fine-structure constant, χ 0 = ((np 0 )/m)E 0 /E cr is the so-called quantum nonlinearity parameter, with n µ = (1, n) and E cr = m 2 /|e| = 1.3 × 10 16 V/cm , and ξ 0 = |e|E 0 /mω 0 is the classical nonlinearity or relativistic parameter (units with = c = 1 are used throughout). It is worth noting that, although χ 0 is much smaller than unity in the realm of classical electrodynamics [2], the parameter R c can be of the order of unity [4,10,11]. The parameter R c represents the average energy radiated by the electron in one laser period in units of the initial electron energy, and for an ultrarelativistic electron initially counterpropagating with respect to the laser field with en-, ...

We show that magnetic fields significantly enhance a new tunneling mechanism in quantum field theories with photons coupling to fermionic minicharged particles (MCPs). 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 MCPs with masses in and below the meV regime as suggested by new-physics extensions of the standard model.

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.

We show that magnetic fields have the potential to significantly enhance a recently proposed light-shining-through-walls scenario in quantum-field theories with photons coupling to minicharged particles. Suggesting a dedicated laboratory experiment, we demonstrate that this particular tunneling scenario could provide access to a parameter regime competitive with the currently best direct laboratory limits on minicharged fermions below the meV regime. With present day technology, such an experiment has the potential to even overcome the best model-independent cosmological bounds on minicharged fermions with masses below O(10 −4 )eV.

Laser pulses traveling through a plasma can feature group velocities significantly differing from the speed of light in vacuum. This modifies the well-known Volkov states of an electron inside a strong laser-field from the vacuum case and consequently all quantum electrodynamical effects triggered by the electron. Here we present an in-depth study of the basic process of photon emission by an electron scattered from an intense short laser pulse inside a plasma, labeled nonlinear Compton scattering, based on modified Volkov solutions derived from first principles. Consequences of the nonlinear, plasma-dressed laser dispersion on the Compton spectra of emitted photons and implications for high-intensity laser-plasma experiments are pointed out.