JHEP01(2019)140
pergravity have appeared in [1, 2, 27]. In the present article we will give a proof of the
conjecture at the level of supergr avity action and field equations. This will enable us to
highlight the relevant dual field t he ory for this problem, the β-supergr avity. The use of su-
pergravity language will help us pos e certain unsolved problems that cannot be addressed
in the string sigma-model formalism: the generalised version of β-supergravity, and d = 11
generalization of t he whole Yang-Baxter deformation narrative.
Proof of the conjecture at the supergravity level can be achieved, in prin ci p l e, by
making the fiel d redefinition (
1.1) directly in the supergravity field equat i ons for the trans-
formed fields g
mn
, b
mn
, φ. One can then expand th e equations in power s of β
mn
, use the
Killing bi-vector ansatz (
1.2), and see if the structure of the CYBE emerges. Such per-
turbative approach to proving the conjecture was undertaken recently in [
2], where it was
shown that up to the third order in powers of β the supergravity field equations reduce to
the CYBE. The complete non- perturbative p roof for an arbitrary initial metric G
mn
was
still lacking.
It turns out, however, that the field redefiniti on (1.1) can be performed consistently in
the full type II supergravity ac ti on. This has been done explicitly in [
28] and the resulting
theory whose dynamical fields are the metric G
mn
, t he bi-vector field β
mn
, and the dilaton
Φ is called β-supergravity. Initially the interest in rewriting of the theory in such a way
stemmed from the goal of finding a supergravity description for non-geometric backgrounds
characterised by the Q-flux [29, 30] . In the framework of β-supergravity the Q-fl ux is simply
given by Q
m
pq
= ∇
m
β
pq
, and in general can be related to the torsion of the Weitzenb¨ock
connection in Dou bl e Field Theory [
31, 32].
Double Field Theory (DFT) provides the most transparent understanding of the struc-
ture of β-supergravity. DFT is a field theory on the doubled spacetime that incorporates
the usual supergravity and is explicitly covariant under the O( d, d) symmetry group com-
ing from the string theory T-duality [33, 34] (see [35, 36] for review; earlier applications of
DFT to Yang-Baxter deformations include [
18–20, 37]). Dynamical fields of t he theory are
the T-duality invariant dilaton d and the so-called generalised metric
H ∈
O(10, 10)
O(1, 9) × O(1, 9)
. (1.5)
Such coset element can be parametrised by the metric g
mn
and the Kalb-Ramond field
b
mn
, which gives the usual field content of the NS-NS sector of supergravity. Alternatively,
the same element can be parametrised by the fields G
mn
and β
mn
, in which case DFT
reduces to β-supergravity. At the level of fiel d s this reparametrization of the coset element
is precisely the open-closed string map (
1.1).
This allows t o make a formal transition from the standard description of typ e II su-
pergravity with dynami c al fields g
mn
, b
mn
, φ, which in this context is referre d to as the
b-frame of DFT, to the description in terms of the fields G
mn
, β
mn
, Φ in the β-frame. The
dynamical equations in the β-frame can be used to derive the CYBE under the assumption
of the ansatz (
1.2), as we show below.
This paper is organised as follows. In se c ti on
2 a short r ev iew of β-supergravity is
given, followed by the proof of the conjecture. In section
3 we discuss possible applications
and consequences of the technique.
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