Physics Letters B 795 (2019) 650–656
Contents lists available at ScienceDirect
Physics Letters B
www.elsevier.com/locate/physletb
Principal tensor strikes again: Separability of vector equations with
torsion
Ramiro Cayuso
a,b
, Finnian Gray
a,b,∗
, David Kubiz
ˇ
nák
a,b
, Aoibheann Margalit
a,b
,
Renato Gomes Souza
a,b,c
, Leander Thiele
a,b
a
Perimeter Institute, 31 Caroline Street North, Waterloo, ON, N2L 2Y5, Canada
b
Department of Physics and Astronomy, University of Waterloo, Waterloo, ON, N2L 3G1, Canada
c
ICTP South American Institute for Fundamental Research, IFT-UNESP, Sao Paulo, SP, 01140-070, Brazil
a r t i c l e i n f o a b s t r a c t
Article history:
Received
28 June 2019
Accepted
3 July 2019
Available
online 5 July 2019
Editor:
M. Cveti
ˇ
c
Many black hole spacetimes with a 3-form field exhibit a hidden symmetry encoded in a torsion
generalization of the principal Killing–Yano tensor. This tensor determines basic properties of such black
holes while also underlying the separability of the Hamilton–Jacobi, Klein–Gordon, and (torsion-modified)
Dirac field equations in their background. As a specific example, we consider the Chong–Cveti
ˇ
c–Lü–
Pope
black hole of D = 5 minimal gauged supergravity and show that the torsion-modified vector
field equations can also be separated, with the principal tensor playing a key role in the separability
ansatz. For comparison, separability of the Proca field in higher-dimensional Kerr–NUT–AdS spacetimes
(including new explicit formulae in odd dimensions) is also presented.
© 2019 The Author(s). 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
Hidden symmetries of dynamics play a crucial role for the study
of diverse physical systems that can be relativistic or not, with
or without gravity, classical or quantum [1]. Particularly useful for
black hole physics is the hidden symmetry of the principal Killing–
Yano
tensor [2]. Such a tensor not only generates other explicit and
hidden symmetries, it also determines the algebraic type of the
solution, and allows for a separation of variables when studying
physical field equations in black hole spacetimes.
The
Golden Era of field equation separability in Kerr geome-
try
spanned the late 60s and 70s. During this period, separable
solutions were found for particles following geodesic motion, test
scalar and spinor fields, as well as massless vector (spin 1) and
tensor (spin 2) fields [3–8]. Much later, after the generalization
of Kerr geometry to higher dimensions by Myers and Perry [9], a
flurry of papers extended the results for geodesic motion [10], and
test scalar [11] and spinor [12]fields to arbitrary dimensions—all
thanks to the principal tensor. However, the appropriate separa-
*
Corresponding author.
E-mail
addresses: rcayuso@perimeterinstitute.ca (R. Cayuso),
fgray@perimeterinstitute.ca (F. Gray), dkubiznak@perimeterinstitute.ca
(D. Kubiz
ˇ
nák),
amargalit@perimeterinstitute.ca (A. Margalit),
rsouza@perimeterinstitute.ca (R.G. Souza), lthiele@perimeterinstitute.ca (L. Thiele).
tion scheme for vector and tensor in dimensions D > 4 remained
elusive.
A
breakthrough on this front came in 2017 when Lunin [13]
demonstrated
the separability of Maxwell’s equations in Myers–
Perry-(A)dS
geometry [14]. Lunin’s approach was novel in that it
provided a separable ansatz for the vector potential rather than the
field strength, a method that had previously seen success in D = 4
dimensions
[7,8]. In 2018, Frolov, Krtous, and Kubiznak showed
that Lunin’s ansatz can be written in a covariant form, in terms of
the principal tensor [15,16], allowing them to extend Lunin’s result
to general (possibly off-shell) Kerr–NUT–AdS spacetimes [17]. The
separation of massive vector (Proca) field perturbations in these
spacetimes (an achievement previously absent even for the four-
dimensional
Kerr geometry) followed shortly after that [18], see
also [19–21].
The
separability of the vector field hinges on the existence of
the principal tensor. Such a tensor: i) determines the canonical
(preferred) coordinates in which the separation occurs, ii) gener-
ates
the towers of explicit and hidden symmetries linked to the
‘symmetry operators’ of the separated vector equation, and iii) ex-
plicitly
enters the separation ansatz for the vector potential P .
Namely, this ansatz can be written in the following covariant form:
P
a
= B
ab
∇
b
Z , (1)
https://doi.org/10.1016/j.physletb.2019.07.007
0370-2693/
© 2019 The Author(s). 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
.