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我们使用代数展开方法构造牛顿-胡克和卡洛尔(A)dS代数的有限维和无限维非相对论扩展,从D维的(反)de Sitter相对论代数开始。 这些代数还显示嵌入不同的仿射Kac-Moody代数中。 在三维情况下,我们构造了在这些对称下不变的Chern-Simons动作。 这导致了一系列非相对论引力理论,其中最简单的例子与扩展的牛顿-胡克和扩展的(后)牛顿引力以及它们的卡罗尔式对应物相对应。
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JHEP02(2020)009
Published for SISSA by Springer
Received: January 9, 2020
Accepted: January 15, 2020
Published: February 3, 2020
Newton-Hooke/Carrollian expansions of (A)dS and
Chern-Simons gravity
Joaquim Gomis,
a
Axel Kleinschmidt,
b,c
Jakob Palmkvist
d
and
Patricio Salgado-Rebolledo
e
a
Departament de F´ısica Qu`antica i Astrof´ısica and Institut de Ci`encies del Cosmos (ICCUB),
Universitat de Barcelona,
Mart´ı i Franqu`es, ES-08028 Barcelona, Spain
b
Max-Planck-Institut f¨ur Gravitationsphysik (Albert-Einstein-Institut),
Am M¨uhlenberg 1, DE-14476 Potsdam, Germany
c
International Solvay Institutes,
ULB-Campus Plaine CP231, BE-1050 Brussels, Belgium
d
Department of Mathematical Sciences,
Chalmers University of Technology and University of Gothenburg,
SE-412 96 G¨oteborg, Sweden
e
Instituto de F´ısica, Pontificia Universidad Cat´olica de Valpara´ıso,
Casilla 4059, Valparaiso, Chile
E-mail: joaquim.gomis@ub.edu, axel.kleinschmidt@aei.mpg.de,
jakob.palmkvist@chalmers.se, patricio.salgado@pucv.cl
Abstract: We construct finite- and infinite-dimensional non-relativistic extensions of the
Newton-Hooke and Carroll (A)dS algebras using the algebra expansion method, starting
from the (anti-)de Sitter relativistic algebra in D dimensions. These algebras are also
shown to be embedded in different affine Kac-Moody algebras. In the three-dimensional
case, we construct Chern-Simons actions invariant under these symmetries. This leads
to a sequence of non-relativistic gravity theories, where the simplest examples correspond
to extended Newton-Hooke and extended (post-)Newtonian gravity together with their
Carrollian counterparts.
Keywords: Classical Theories of Gravity, Space-Time Symmetries, Global Symmetries,
p-branes
ArXiv ePrint: 1912.07564
Open Access,
c
The Authors.
Article funded by SCOAP
3
.
https://doi.org/10.1007/JHEP02(2020)009
JHEP02(2020)009
Contents
1 Introduction 1
2 Expansions of the (A)dS algebra 3
2.1 Extended Newton-Hooke algebras 3
2.2 Extended Carroll (A)dS algebras 7
3 Newton-Hooke and Carrollian affine algebra 9
3.1 Newton-Hooke affine algebras 10
3.2 (A)dS Carrollian affine algebras 13
4 Chern-Simons non-relativistic gravities 14
4.1 Extended Newton-Hooke gravities 15
4.2 Extended Carrollian gravities 20
5 Conclusions and outlook 22
A Further generalisations 24
A.1 Non-relativistic expansions of the Maxwell algebra 25
A.2 Non-relativistic brane expansions of (A)dS 26
1 Introduction
Non-relativistic symmetries are usually obtained from relativistic ones by means of Lie
algebra contractions. The most well-known example is the Wigner-In¨on¨u contraction of
the Poincar´e algebra that leads to the Galilei algebra [1] by sending the speed of light to
infinity. Lie algebra contractions necessarily preserve the number of generators but can
alter the cohomology of the Lie algebra, thus allowing for different central extensions like
the Bargmann extension of the Galilei algebra [2], which is crucial when taking the limit
of the relativistic particle action to the non-relativistic one [3, 4].
In recent years, more general constructions of non-relativistic symmetry algebras from
relativistic ones have been explored. One example is given by the method of Lie algebra
expansions [5–7] applied to the Poincar´e algebra [8]. This method provides an infinite se-
quence of non-relativistic algebras extending the Galilei algebra with an increasing number
of generators, which have been used in [8–11] to construct various gravitational actions.
The Lie algebra expansion method can also be related to a sequence of post-Newtonian
limits as shown in [12], and has also been applied to derive diverse non-relativistic symme-
tries in the context of (super-)gravity [13–17]. Another method is based on a Galilean free
Lie algebra [18] that can be thought as the most general extension of the Galilei algebra
– 1 –
JHEP02(2020)009
and, upon taking quotients, has a connection to Lie algebra expansions and Kac-Moody
algebras. One interesting conceptual point made in [12] is that the sequence of Lie algebras
naturally comes with a generalisation of Minkowski space with more coordinates and an
extension of the Minkowski metric. Using this generalised Minkowski space it is possible to
define particle actions invariant under these extended algebras that naturally incorporate
post-Newtonian corrections in the non-relativistic limit.
In the present article, we study the non-relativistic symmetries obtained by Lie algebra
expansion of the AdS or dS algebra in D space-time dimensions, i.e. so(D−1, 2) or so(D, 1).
This generalises previous constructions to include a cosmological constant and generates
an infinite family of algebras of Newton-Hooke [19, 20] type. By taking the limit of the
cosmological constant to zero one recovers the non-relativistic algebras introduced in [10]
and further studied in [8, 12, 18].
Besides the non-relativistic limit related to Galilean symmetries (c → ∞) we also
consider the case of ultra-relativistic Carrollian limit (c → 0).
1
As is known from [24] the
Carroll algebra can be understood by very specific changes in the commutation relations
and associated changes in the starting point of the algebra expansion procedure. Applying
the expansion procedure then produces an infinite family of Lie algebras associated with
the Carrollian limit. We shall also show how our construction in both cases is related
to affine Kac-Moody algebras, where the role of the expansion parameter is taken by the
spectral (or loop) parameter of the affine algebra.
After the introduction of the infinite family of algebras we consider gravitational models
based on them by focussing on the case of 2+1 space-time dimensions. We construct Chern-
Simons theories based on these algebras since they admit non-degenerate bilinear forms. We
show that the family of algebras systematically generates non-relativistic gravity theories
extended by a cosmological constant, such as extended Newton-Hooke gravity [25, 26], that
reduces to extended Bargmann gravity for Λ → 0 [27, 28], and post-Newtonian gravity [11].
2
Our construction also connects to recent discussions of non-relativistic expansions of
the metric as described in [9, 10, 29–33]. This can be made very precise in the context of
the Chern-Simons formulation and we shall elaborate on this connection in the conclusions.
In an appendix, we generalise the expansion procedure to obtain an infinite family of
extensions of the non-relativistic Maxwell algebra. Moreover, we outline that our method
is not only applicable non-relativistic symmetries corresponding to point particle limits,
but also to extended objects where the D covariant dimensions are split into p + 1 and
D − p − 1 directions for a p-brane [34, 35]. Similar constructions in the case without a
cosmological constant have been considered previously in [8, 24, 36, 37].
Note added. While this manuscript was being finalised, the preprints [38, 39] appeared
on the arXiv that have some overlap with some of our results.
1
Work on Carroll symmetries in the context of electrodynamics and brane dynamics can be found for
instance in [21–23].
2
In [11] this was called ‘extended gravity’ but in the light of the results of [12] this is better understood
as a post-Newtonian correction.
– 2 –
JHEP02(2020)009
2 Expansions of the (A)dS algebra
In this section, we will construct an infinite family of non-relativistic algebras of the
Newton-Hooke and Carroll AdS type. The first members of this family will be given
by the Newton-Hooke algebra in the former case and the Carroll AdS algebra in the latter
(without extensions) [19, 20]. We also obtain an infinite-dimensional algebra that contains
these and other intermediate cases, generalises the one obtained in [8, 10, 18], as quotients.
All our algebras contain a cosmological constant as we start from the AdS algebra.
We will construct the series of non-relativistic algebras by means of Lie algebra ex-
pansions [5–7]. More precisely, we will use the semigroup expansion technique [7] with
semigroup S
(N)
E
, which will be defined below.
Our starting point is the (A)dS algebra in D dimensions:
[
˜
J
AB
,
˜
P
C
] = 2η
C[B
˜
P
A]
, (2.1a)
[
˜
J
AB
,
˜
J
CD
] = 4η
[A[C
˜
J
D]B]
, (2.1b)
[
˜
P
A
,
˜
P
B
] = −Λ
˜
J
AB
, (2.1c)
which denotes in a unified manner so(D −1, 2) (for Λ < 0) and so(D, 1) (for Λ > 0). Here,
˜
P
A
and
˜
J
AB
are the generators of spacetime translations and Lorentz transformations,
respectively. Capital indices run over A = 0, . . . , D −1 and the Minkowski metric has been
chosen to have mostly plus signature.
In order to perform a non-relativistic expansion of the (A)dS algebra, it is convenient
to decompose the relativistic indices in the time and space components, A = (0, a), where
a = 1, . . . , D − 1, and relabel the Lie algebra generators
3
as
˜
J
AB
→ {
˜
J
0a
≡
˜
G
a
,
˜
J
ab
},
˜
P
A
→ {
˜
P
0
≡
˜
H ,
˜
P
a
}. (2.2)
Then, the commutation relations (2.1) can be rewritten in the form
[
˜
G
a
,
˜
H] =
˜
P
a
, (2.3a)
[
˜
G
a
,
˜
P
b
] = δ
ab
˜
H , (2.3b)
[
˜
J
ab
,
˜
P
c
] = 2δ
c[b
˜
P
a]
, (2.3c)
[
˜
G
a
,
˜
G
b
] =
˜
J
ab
, (2.3d)
[
˜
J
ab
,
˜
G
c
] = 2δ
c[b
˜
G
a]
, (2.3e)
[
˜
J
ab
,
˜
J
cd
] = 4δ
[a[c
˜
J
d]b]
, (2.3f)
[
˜
P
a
,
˜
H] = Λ
˜
G
a
, (2.3g)
[
˜
P
a
,
˜
P
b
] = −Λ
˜
J
ab
. (2.3h)
We note that the decomposition (2.2) is adapted to point particles in the sense that one
direction — that can be thought of as the world-line direction of the particle — is singled
out. In appendix A.2, we also consider the case of extended objects.
2.1 Extended Newton-Hooke algebras
In order to perform expansions of (A)dS of Newton-Hooke type, we first note that (2.3)
allows for the following subspace decomposition V = V
0
⊕ V
1
[8]
V
0
= {
˜
H,
˜
J
ab
}, V
1
= {
˜
P
a
,
˜
G
a
}, (2.4)
3
Notice this convention is different from the one in [12] where
˜
J
a0
≡
˜
G
a
was used.
– 3 –
JHEP02(2020)009
which satisfies a Z
2
-graded structure, i.e.,
[V
0
, V
0
] ⊂ V
0
, [V
0
, V
1
] ⊂ V
1
, [V
1
, V
1
] ⊂ V
0
. (2.5)
This decomposition is similar to a symmetric space decomposition. The homogeneous coset
space in the case of AdS is SO(D −1, 2)/(SO(D − 1) × R) and SO(D, 1)/(SO(D −1) ×R)
in the dS case.
We will consider expansions with the semigroup S
(N)
E
= {λ
0
, . . . , λ
N+1
}, whose multi-
plication law is given by [7]
λ
i
· λ
j
=
(
λ
i+j
if i + j ≤ N ,
λ
N+1
if i + j > N ,
(2.6)
where λ
N+1
acts as the zero of the semigroup, as it satisfies λ
N+1
· λ
i
= λ
i
· λ
N+1
= λ
N+1
for all λ
i
. This semigroup admits the subset decomposition
S
(N)
0
= s
(N)
0
∪ {λ
N+1
} , s
(N)
0
=
λ
2m
| m = 0, . . . ,
N
2
,
S
(N)
1
= s
(N)
1
∪ {λ
N+1
} , s
(N)
1
=
λ
2m+1
| m = 0, . . . ,
N −1
2
,
(2.7)
which is compatible with (2.5) in the sense that
S
(N)
0
· S
(N)
0
⊂ S
(N)
0
, S
(N)
0
· S
(N)
1
⊂ S
(N)
1
, S
(N)
1
· S
(N)
1
⊂ S
(N)
0
, (2.8)
and therefore resonant with the choice of V
0
and V
1
in (2.4).
Thus, a reduced resonant expanded algebra can be defined as the direct sum
n
s
(N)
0
⊗ V
0
o
⊕
n
s
(N)
1
⊗ V
1
o
(2.9)
where the reduction condition in the algebra is implemented by the constraints
λ
N+1
⊗
˜
J
AB
= 0 , λ
N+1
⊗
˜
P
A
= 0 , (2.10)
which map the zero λ
N+1
of the semigroup to the zero element in the expanded algebra.
In the following we will show how, for different choices of the semigroup S
(N)
E
, the reduc-
tion (2.9) lead to a non-relativistic algebras that generalise the Newton-Hooke symmetry.
The simplest example in our construction corresponds to the expansion with the semi-
group S
(1)
E
, which as we will see is equivalent to a non-relativistic contraction of the (A)dS
algebra. In other words, this expansion gives the Newton-Hooke algebras. By setting
N = 1 in (2.6) and (2.9), the generators of the expanded algebra are given by
J
ab
= λ
0
⊗
˜
J
ab
, G
a
= λ
1
⊗
˜
G
a
,
H = λ
0
⊗
˜
H , P
a
= λ
1
⊗
˜
P
a
.
(2.11)
– 4 –
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