The goal of this paper is twofold: to explore the response of classical charges to electromagnetic force at the level of unity in natural units and to establish a criterion that determines physical parameters for which the related radiation-reaction effects are detectable. In pursuit of this goal, the Landau-Lifshitz equation is solved analytically for an arbitrary (transverse) electromagnetic pulse. A comparative study of the radiation emission of an electron in a linearly polarized pulse for the Landau-Lifshitz equation and for the Lorentz force equation reveals the radiation-reaction-dominated regime, in which radiation-reaction effects overcome the influence of the external fields. The case of a relativistic electron that is slowed down by a counterpropagating electromagnetic wave is studied in detail. We further show that when the electron experiences acceleration of order unity, the dynamics of the Lorentz force equation, the Landau-Lifshitz equation and the Lorentz-Abraham-Dirac equation all result in different radiation emission that could be distinguished in experiment. Finally, our analytic and numerical results are compared with those appearing in the literature.

We discuss the inverse β-decay of accelerated protons in the context of neutrino flavor superpositions (mixings) in mass Eigenstates. The process p → nℓ + ν ℓ is kinematically allowed because the accelerating field provides the rest energy difference between initial and final states. The rate of p → n conversions can be evaluated in either the laboratory frame (where the proton is accelerating) or the co-moving frame (where the proton is at rest and interacts with an effective thermal bath of ℓ and ν ℓ due to the Unruh effect). By explicit calculation, we show the rates in the two frames disagree when taking into account neutrino mixings, because the weak interaction couples to charge eigenstates whereas gravity couples to neutrino mass eigenstates [1]. The contradiction could be resolved experimentally, potentially yielding new information on the origins of neutrino masses. 25.75.Dw,25.75.Nq

We consider dynamics of vacuum decay and particle production in the context of short pulse laser experiments. We identify and evaluate the invariant "materialization time," τ , the timescale for the conversion of an electromagnetic field energy into particles, and we compare to the laser related time scales.In the past decade high intensity short pulse laser technology has advanced rapidly [1], pulses achieved intensities of 10 26 W/m 2 [2,3]. With subsequent concentration by coherent harmonic focusing allowing a further gain in intensity of around six orders of magnitude [4], laser technology is nearing the scale of rapid vacuum instability, cǫ 0 E 2 0 /4π = 4.65×10 33 W/m 2 , where E 0 ≡ m 2 c 3 /e = 1.32 × 10 18 V/m. The study of vacuum instability with laser pulses involves dynamics on a timescale set by the pulse length, which at optical frequencies implies that the fields are in existence for ∼ 10 −15 s, and may reach ∼ 10 −18 s when coherent harmonic focusing is used.The vacuum state of quantum electrodynamics (QED) is metastable in the presence of electrical fields of any strength, but only in proximity of E 0 does the effect occur on an observable time scale [5,6], as we exhibit below. Specifically, we investigate whether the laser pulse timescale allows the vacuum in strong fields to relax, thereby admitting the new vacuum to experimental investigation using pulsed lasers. The dynamics of 'false' vacuum decay have been studied in the context of spontaneous positron creation in heavy ion collisions [7,8,9] and cosmological models [10,11,12]. The QED vacuum decay has not been directly observed in heavy ion collision experiments, due to the relatively long time scale of vacuum decay dynamics as compared to competing processes. However, particle production in strong fields has found a fertile field in quantum chromodynamics [13,14].Considerable effort went into generalizing the Euler-Heisenberg-Schwinger (EHS) [5,6] pair production mechanism for a variety of large-scale (compared toλ e = /m e c = 3.86 × 10 −13 m) space-and time-dependent field configurations [15,16,17] and to incorporating back reaction [13,18,19,20,21]. A stable, modified vacuum state has only been obtained when the field fills a finite spacetime domain [18]. The perturbative vacuum is also stable for an ideal plane wave (laser) field of arbitrary strength, and thus many investigations have focused on understanding pair production in optimized pulsed laser field configurations [22,23,24,25,26,27,28,29,30,31,32]. More recently it has been also noted that in the interaction of laser pulses with thin foils, the charge seperation effect due to a much greater electron mobility helps in achieving longitudinal electrical fields of comparable strength as are present in the laser pulse, a phenomenon used in laser-ion acceleration [33]. We thus address in this work the general circumstance of a spatially homogeneous electrical field.In all laboratory experiments supercritical fields (fields capable of spontaneous particle production) will be strongl...

Quasi-constant external fields in nonlinear electromagnetism generate a contribution to the energy-momentum tensor with the form of dark energy. To provide a thorough understanding of the origin and strength of the effects, we undertake a complete theoretical and numerical study of the energy-momentum tensor T µν for nonlinear electromagnetism. The Euler-Heisenberg nonlinearity due to quantum fluctuations of spinor and scalar matter fields is considered and contrasted with the properties of classical nonlinear Born-Infeld electromagnetism. We also address modifications of charged particle kinematics by strong background fields.

We study the low energy effective theory describing gravity with broken spatial diffeomorphism invariance. In the unitary gauge, the Goldstone bosons associated with broken diffeomorphisms are eaten and the graviton becomes a massive spin-2 particle with 5 well-behaved degrees of freedom. In this gauge, the most general theory is built with the lowest dimension operators invariant under only temporal diffeomorphisms. Imposing the additional shift and SO(3) internal symmetries, we analyze the perturbations on a FRW background. At linear perturbation level, the observables of this theory are characterized by five parameters, including the usual cosmological parameters and one additional coupling constant for the symmetry-breaking scalars. In the de Sitter and Minkowski limit, the three Goldstone bosons are supermassive and can be integrated out, leaving two massive tensor modes as the only propagating degrees of freedom. We discuss several examples relevant to theories of massive gravity.