Physics Letters B 765 (2017) 377–381
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Physics Letters B
www.elsevier.com/locate/physletb
Protected couplings and BPS dyons in half-maximal supersymmetric
string vacua
Guillaume Bossard
a,∗
, Charles Cosnier-Horeau
a,b
, Boris Pioline
c,b
a
Centre de Physique Théorique, Ecole Polytechnique, Université Paris-Saclay, 91128 Palaiseau Cedex, France
b
Sorbonne Universités, Laboratoire de Physique Théorique et Hautes Energies, CNRS UMR 7589, Université Pierre et Marie Curie,
4
place Jussieu, 75252 Paris Cedex 05, France
c
CERN, Theoretical Physics Department, 1211 Geneva 23, Switzerland
a r t i c l e i n f oa b s t r a c t
Article history:
Received
11 November 2016
Accepted
12 December 2016
Available
online 15 December 2016
Editor:
N. Lambert
We analyze four- and six-derivative couplings in the low energy effective action of D =3string vacua
with half-maximal supersymmetry. In analogy with an earlier proposal for the (∇)
4
coupling, we
propose that the ∇
2
(∇)
4
coupling is given exactly by a manifestly U-duality invariant genus-two
modular integral. In the limit where a circle in the internal torus decompactifies, the ∇
2
(∇)
4
coupling
reduces to the ∇
2
F
4
and R
2
F
2
couplings in D = 4, along with an infinite series of corrections of
order e
−R
, from four-dimensional 1/4-BPS dyons whose worldline winds around the circle. Each of these
contributions is weighted by a Fourier coefficient of a meromorphic Siegel modular form, explaining and
extending standard results for the BPS index of 1/4-BPS dyons.
© 2016 Published by Elsevier B.V. This is an open access article under the CC BY license
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.
String vacua with half-maximal supersymmetry offer an inter-
esting
window into the non-perturbative regime of string theory
and the quantum physics of black holes, unobstructed by intri-
cacies
present in vacua with less supersymmetry. In particular,
the low-energy effective action at two-derivative order does not
receive any quantum corrections, and all higher-derivative interac-
tions
are expected to be invariant under the action of an arithmetic
group G(Z), known as the U-duality group, on the moduli space
G/K of massless scalars [1–4]. This infinite discrete symmetry also
constrains the spectrum of BPS states, and allows to determine,
for any values of the electromagnetic charges, the number of BPS
black hole micro-states (counted with signs) in terms of Fourier
coefficients of certain modular forms [5–7]. This property has been
used to confirm the validity of the microscopic stringy description
of BPS black holes at an exquisite level of precision, both for small
black holes (preserving half of the supersymmetries of the back-
ground)
[8,9] and for large black holes (preserving a quarter of the
same) [10–18].
In
this letter, we shall exploit U-duality invariance and super-
symmetry
Ward identities to determine certain higher-derivative
*
Corresponding author.
E-mail
addresses: guillaume.bossard@polytechnique.edu (G. Bossard),
charles.cosnier-horeau@polytechnique.edu (C. Cosnier-Horeau),
boris.pioline@cern.ch (B. Pioline).
couplings in the low-energy effective action of three-dimensional
string vacua with 16 supercharges, for all values of the moduli.
These protected couplings are analogues of the R
4
and ∇
6
R
4
couplings in toroidal compactifications of type II strings, which
have been determined exactly in [19,20] and in many subsequent
works. Our motivation for studying these protected couplings in
D = 3is that they are expected to encode the infinite spectrum
of BPS black holes in D = 4, in a way consistent with the U-
duality
group G
3
(Z). The latter contains the four-dimensional U-
duality
group G
4
(Z), but is potentially far more constraining. Thus,
these protected couplings provide analogues of ‘black hole parti-
tion
functions’, which do not suffer from the usual difficulties in
defining thermodynamical partition functions in theories of quan-
tum
gravity, and are manifestly automorphic [21].
The
fact that solitons in D = 4may induce instanton cor-
rections
to the quantum effective potential in dimension D = 3
is
well known in the context of gauge theories with compact
U (1) [22]. In the context of quantum field theories with 8 rigid
supersymmetries, BPS dyons in four dimensions similarly cor-
rect
the moduli space metric after reduction on a circle [23,
24].
In string vacua with 16 local supersymmetries, one similarly
expects that 1/2-BPS dyons in D = 4will contribute to four-
derivative
scalar couplings of the form F
abcd
() ∇
a
∇
b
∇
c
∇
d
in D = 3, while both 1/2-BPS and 1/4-BPS dyons in D = 4
will
contribute to six-derivative scalar couplings of the form
http://dx.doi.org/10.1016/j.physletb.2016.12.035
0370-2693/
© 2016 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
.