Physics Letters B 760 (2016) 552–557
Contents lists available at ScienceDirect
Physics Letters B
www.elsevier.com/locate/physletb
Multi-pair states in electron–positron pair creation
Anton Wöllert, Heiko Bauke
∗
, Christoph H. Keitel
Max-Planck-Institut für Kernphysik, Saupfercheckweg 1, 69117 Heidelberg, Germany
a r t i c l e i n f o a b s t r a c t
Article history:
Received
11 April 2016
Received
in revised form 27 June 2016
Accepted
14 July 2016
Available
online 19 July 2016
Editor:
A. Ringwald
Ultra strong electromagnetic fields can lead to spontaneous creation of single or multiple electron–
positron
pairs. A quantum field theoretical treatment of the pair creation process combined with numer-
ical
methods provides a description of the fermionic quantum field state, from which all observables of
the multiple electron–positron pairs can be inferred. This allows to study the complex multi-particle dy-
namics
of electron–positron pair creation in-depth, including multi-pair statistics as well as momentum
distributions and spin. To illustrate the potential benefit of this approach, it is applied to the intermediate
regime of pair creation between nonperturbative Schwinger pair creation and perturbative multiphoton
pair creation where the creation of multi-pair states becomes nonnegligible but cascades do not yet set
in. Furthermore, it is demonstrated how spin and helicity of the created electrons and positrons are
affected by the polarization of the counterpropagating laser fields, which induce the creation of electron–
positron
pairs.
© 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license
(http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP
3
.
1. Introduction
Relativistic quantum field theory predicts the possibility of
electron–positron pair creation from the vacuum in the presence of
a strong electromagnetic field. Initiated by the pioneering works by
Sauter, Heisenberg, and Euler [1,2] many theoretical [3–14] and ex-
perimental
[15–17] efforts have been undertaken to study pair cre-
ation;
see Refs. [9,18] for recent reviews. Spontaneous pair creation
by static fields is expected to set in at the Schwinger critical field
strength of E
S
=1.3 ×10
18
V/m, which cannot be reached even by
the strongest laser facilities available today. However, pair creation
may be assisted by time- and space-dependent electromagnetic
fields. Novel light sources envisage to provide field intensities in
excess of 10
20
W/cm
2
and field frequencies in the X-ray domain
[19–23]. The ELI-Ultra High Field Facility, for example, aims to
reach intensities exceeding even 10
23
W/cm
2
corresponding to a
field strength of about 10
15
V/m, which may be sufficient to ob-
serve
pair creation [24–30].
Pair
creation in time-dependent electromagnetic fields can
be characterized via the classical nonlinearity parameter ξ =
eE/(m
0
cω) as nonperturbative Schwinger pair creation (ξ 1)
*
Corresponding author.
E-mail
addresses: woellert@mpi-hd.mpg.de (A. Wöllert),
heiko.bauke@mpi-hd.mpg.de (H. Bauke).
or perturbative multiphoton pair creation (ξ 1), where m
0
de-
notes
the electron mass, c the speed of light, e the elementary
charge, E the electric field’s peak strength, and ω its angular fre-
quency.
Both regimes are accessible by different analytical meth-
ods.
Experimentally the nonperturbative Schwinger regime may be
realized by high-intensity optical lasers and has attracted a consid-
erable
amount of theoretical research, e. g., predicting pair-creation
cascades by semi-classical methods [31–38]. In this regime, pair-
creation
can be understood as a tunneling process [39,40], which
is exponentially suppressed for subcritical fields. In the other ex-
treme
regime which is relevant for weaker intensities but ultra
high photon energies, perturbative multiphoton pair creation has
been approached experimentally [16,41]. New directions in pair
production have also been proposed [42–45] by combining both
regimes leading to the dynamically assisted Schwinger effect.
The
intermediate regime, i. e., nonperturbative multiphoton pair
creation
1
with ξ ≈ 1, however, is less studied [41,47–51] and a
comprehensible physical picture is missing. Despite this, many in-
teresting
phenomena may be expected like the coherent produc-
tion
of multiple pairs [4,5,52], quantum statistical influences [5,53],
Pauli exclusion effects [5,54] and a mixture of signatures known
from pure tunneling and multiphoton processes [10,39,45,50]. This
1
This is very similar to the intermediate domain of strong-field ionization be-
tween
the tunneling and multiphoton regimes, as studied in [46].
http://dx.doi.org/10.1016/j.physletb.2016.07.037
0370-2693/
© 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by
SCOAP
3
.
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