51 research outputs found
Super Gaussian enhancers in the Schwinger mechanism
We study the Schwinger mechanism in the presence of an additional uniformly
oriented, weak super Gaussian of integer order . Using the worldline
approach, we determine the relevant critical points to compute the leading
order exponential factor analytically. We show that increasing the parameter
gives rise to a strong dynamical enhancement. For , this effect turns
out to be larger compared to a weak contribution of Sauter type. For higher
orders, specifically, for the rectangular barrier limit, i.e. , we approach the Lorentzian case as an upper bound. Although the
mentioned backgrounds significantly differ in Minkowski spacetime, we show that
the found coincidence applies due to identical reflection points in the
Euclidean instanton plane. In addition, we also treat the background in
perturbation theory following recent ideas. By doing so, we show that the
parameter determines whether the weak contribution behaves perturbatively
or nonperturbatively with respect to the field strength ratio and, hence,
reveals an interesting dependence on the background shape. In particular, we
show that for backgrounds, for which higher orders in the field strength ratio
turn out to be relevant, a proposed integral condition is not fulfilled. In
view of these findings, the latter may serve as an indicator for the necessity
of higher order contributions.Comment: 8 pages, 5 figures, v3: text revisions, references updated, matches
journal versio
Nonlinear lepton-photon interactions in external background fields
Nonlinear phenomena of lepton-photon interactions in external backgrounds
with a generalised periodic plane-wave geometry are studied. We discuss
nonlinear Compton scattering in head-on lepton-photon collisions extended
properly to beyond the soft-photon regime. In addition, our results are applied
to stimulated lepton-antilepton pair production in photon collisions with
unrestricted energies. Derivations are considered semi-classically based on
unperturbed fermionic Volkov representations encoding the full interaction with
the background field. Closed expressions for total probabilities considering
S-matrix elements have been derived. The general formula is applied to Compton
scattering by an electron propagating in an external laser-like background. We
obtain additive contributions in the extended unconstrained result which turns
out to be stringently required in the highly nonlinear regime. A detailed
comparison of contributing harmonics is discussed for various field parameters.Comment: 39 pages, 8 figures, minor changes in introduction, references added,
a few misprints foun
Euclidean mirrors: enhanced vacuum decay from reflected instantons
We study the tunneling of virtual matter-antimatter pairs from the quantum
vacuum in the presence of a spatially uniform, time-dependent electric
background composed of a strong, slow field superimposed with a weak, rapid
field. After analytic continuation to Euclidean spacetime, we obtain from the
instanton equations two critical points. While one of them is the closing point
of the instanton path, the other serves as an Euclidean mirror which reflects
and squeezes the instanton. It is this reflection and shrinking which is
responsible for an enormous enhancement of the vacuum pair production rate. We
discuss how important features of two different mechanisms can be analysed and
understood via such a rotation in the complex plane. a) Consistent with
previous studies, we first discuss the standard assisted mechanism with a
static strong field and certain weak fields with a distinct pole structure in
order to show that the reflection takes place exactly at the poles. We also
discuss the effect of possible sub-cycle structures. We extend this reflection
picture then to weak fields which have no poles present and illustrate the
effective reflections with explicit examples. An additional field strength
dependence for the rate occurs in such cases. We analytically compute the
characteristic threshold for the assisted mechanism given by the critical
combined Keldysh parameter. We discuss significant differences between these
two types of fields. For various backgrounds, we present the contributing
instantons and perform analytical computations for the corresponding rates
treating both fields nonperturbatively. b) In addition, we also study the case
with a nonstatic strong field which gives rise to the assisted dynamical
mechanism. For different strong field profiles we investigate the impact on the
critical combined Keldysh parameter. [...]Comment: 54 pages, 23 figures, revised, restructured to improve readability,
matches journal versio
Entanglement entropy on finitely ramified graphs
We compute the entanglement entropy in a composite system separated by a
finitely ramified boundary with the structure of a self-similar lattice graph.
We derive the entropy as a function of the decimation factor which determines
the spectral dimension, the latter being generically different from the
topological dimension. For large decimations, the graph becomes increasingly
dense, yielding a gain in the entanglement entropy which, in the asymptotically
smooth limit, approaches a constant value. Conversely, a small decimation
factor decreases the entanglement entropy due to a large number of spectral
gaps which regulate the amount of information crossing the boundary. In line
with earlier studies, we also comment on similarities with certain holographic
formulations. Finally, we calculate the higher order corrections in the
entanglement entropy which possess a log-periodic oscillatory behavior.Comment: 7 pages, 3 figures, references added, to be published in PR
Entanglement entropy in holographic moving mirror and Page curve
We calculate the time evolution of entanglement entropy in two dimensional
conformal field theory with a moving mirror. For a setup modeling Hawking
radiation, we obtain a linear growth of entanglement entropy and show that this
can be interpreted as the production of entangled pairs. For a setup, which
mimics black hole formation and evaporation, we find that the evolution follows
the ideal Page curve. We perform these computations by constructing the gravity
dual of the moving mirror model via holography. We also argue that our
holographic setup provides a concrete model to derive the Page curve for black
hole radiation in the strong coupling regime of gravity.Comment: 8 pages, 7 figures, v2: references adde
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