Physics Letters B 750 (2015) 237–241
Contents lists available at ScienceDirect
Physics Letters B
www.elsevier.com/locate/physletb
Phantom metrics with Killing spinors
W.A. Sabra
Centre for Advanced Mathematical Sciences and Physics Department, American University of Beirut, Lebanon
a r t i c l e i n f o a b s t r a c t
Article history:
Received
25 July 2015
Accepted
10 September 2015
Available
online 16 September 2015
Editor:
M. Cveti
ˇ
c
We study metric solutions of Einstein–anti-Maxwell theory admitting Killing spinors. The analogue of the
IWP metric which admits a space-like Killing vector is found and is expressed in terms of a complex
function satisfying the wave equation in flat (2 + 1)-dimensional space–time. As examples, electric and
magnetic Kasner spaces are constructed by allowing the solution to depend only on the time coordinate.
Euclidean solutions are also presented.
© 2015 The Author. 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
The first systematic classification of metrics admitting super-
covariantly
constant spinors in Einstein–Maxwell theory was per-
formed
many years ago by Tod in [1]. The analysis of Tod was to
some extent motivated by the results of Gibbons and Hull [2]. The
metrics found in [1] are bosonic solutions of minimal N = 2super-
gravity
theory admitting half of the supersymmetry. In the context
of the supergravity theory, the Killing spinor equation represents
the vanishing of the gravitini supersymmetry transformation in a
bosonic background. The metrics with a time-like Killing vector are
the known Israel–Wilson–Perjés (IWP) metrics [3] with the static
limit given by the Majumdar–Papapetrou (MP) metrics [4]. The
second class of metrics with a null-Killing vector is given by plane-
wave
space–times [5]. In recent years, a considerable amount of
research activities has been devoted to the understanding and the
systematic classification of supersymmetric solutions in ungauged,
gauged and fake (de Sitter) supergravity theories in various di-
mensions
(see for example [6]). Fake de Sitter supergravity can be
obtained by analytic continuation of anti de Sitter supergravity. We
also note that de Sitter supergravities can also be obtained as gen-
uine
low energy effective theories of the so called
∗
theories of
[7]. For instance, a non-linear Kaluza Klein reduction arising of IIB
∗
string theory and M
∗
theory produce four and five-dimensional de
Sitter supergravities with vector multiplets. However these theo-
ries
have actions where some of the gauge fields kinetic terms
have the non-conventional sign [8]. Black hole solutions with anti
or phantom Maxwell fields
1
have been studied and analyzed in [9].
E-mail address: waficsabra@gmail.com.
1
There anti or phantom Maxwell field refers to an electromagnetic field of the
opposite sign from usual.
Black hole solutions with phantom fields and their relations to
astrophysics and dark matter were also considered by many au-
thors
(see [10] and references therein). However, to our knowledge
phantom solutions with Killing spinors have not yet been dis-
cussed.
In
our present work, we shall study metrics admitting Killing
spinors in gravitational theories with anti-Maxwell fields. We shall
only focus on the simplest theory of four-dimensional Einstein
gravity coupled to a Maxwell field as a first step for a future
study of supergravity theories with many anti-Maxwell and scalar
fields in various space–time dimensions. We will consider both the
Lorentzian and the Euclidean theory. The action of the theory is
given by
S =
d
4
x
√
−g
R +κ
2
F
μν
F
μν
,
(1.1)
where F
μν
is the U (1) gauge field strength. We have introduced a
parameter κ which for κ = i, corresponds to the standard Einstein–
Maxwell
theory and for κ = 1 corresponds to the Einstein–anti-
Maxwell
theory, i.e., where the Maxwell field kinetic term comes
with the wrong sign. The signature of the metric is taken to be
(−, +, +, +). For κ = 1, this action can be thought of as the
bosonic part of a fake minimal N = 2, D =4supergravity. The Ein-
stein
and gauge field equations derived from (1.1) are
R
μν
=−κ
2
2F
μρ
F
ν
ρ
−
1
2
g
μν
F
αβ
F
αβ
,
d ∗ F =0 . (1.2)
Here F is the two form representing the gauge field strength F
μν
.
The Killing spinor equation is given by
∂
μ
+
1
4
ω
μ,ν
1
ν
2
γ
ν
1
ν
2
+
κ
4
F
ν
1
ν
2
γ
ν
1
ν
2
γ
μ
ε = 0. (1.3)
http://dx.doi.org/10.1016/j.physletb.2015.09.025
0370-2693/
© 2015 The Author. 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
.