8,766 research outputs found
(N,p,q) Harmonic Superspace
A family of harmonic superspaces associated with four-dimensional spacetime
is described. Some applications to supersymmetric field theories, including
supergravity, are given.Comment: 25 pages, latex file, improved. Minor text errors correcte
Patching DFT, T-duality and Gerbes
We clarify the role of the dual coordinates as described from the
perspectives of the Buscher T-duality rules and Double Field Theory. We show
that the T-duality angular dual coordinates cannot be identified with Double
Field Theory dual coordinates in any of the proposals that have been made in
the literature for patching the doubled spaces. In particular, we show with
explicit examples that the T-duality angular dual coordinates can have
non-trivial transition functions over a spacetime and that their identification
with the Double Field Theory dual coordinates is in conflict with proposals in
which the latter remain inert under the patching of the B-field. We then
demonstrate that the Double Field Theory coordinates can be identified with
some C-space coordinates and that the T-dual spaces of a spacetime are
subspaces of the gerbe in C-space. The construction provides a description of
both the local symmetry and the T-dual spaces of spacetime.Comment: minor changes, references adde
Anomalies and divergences in N=4 supergravity
The invariants in D=4, N=4 supergravity are discussed up to the three-loop
order (where one expects a general R^4 structure). Because there is an anomaly
in the rigid SL(2,R) symmetry of this theory, the analysis of possible
restrictions on three-loop divergences due to duality needs careful treatment.
We show that this anomalous symmetry is still strong enough at the three-loop
order to require duality invariance of candidate counterterms. Provided one
makes the additional assumption that there exists a full 16-supercharge
off-shell formulation of the theory, counterterms at L \ge 2 loops would also
have to be writable as full-superspace integrals. At the three-loop order such
a duality-invariant full-superspace integral candidate counterterm exists, but
its duality invariance is marginal in the sense that the full-superspace
counter-Lagrangian is not itself duality invariant. We show that, subject to
the assumption that a full off-shell quantisation formalism exists, such
marginal invariants are not allowable as counterterms.Comment: 15 pages, version published in Phys. Lett.
Invariants and divergences in half-maximal supergravity theories
The invariants in half-maximal supergravity theories in D=4,5 are discussed
in detail up to dimension eight (e.g. R^4). In D=4, owing to the anomaly in the
rigid SL(2,R) duality symmetry, the restrictions on divergences need careful
treatment. In pure N=4 supergravity, this anomalous symmetry still implies
duality invariance of candidate counterterms at three loops. Provided one makes
the additional assumption that there exists a full 16-supercharge off-shell
formulation of the theory, counterterms at L>1 loops would also have to be
writable as full-superspace integrals. At the three-loop order such a
duality-invariant full-superspace integral candidate counterterm exists, but
its duality invariance is marginal in the sense that the full-superspace
counter-Lagrangian is not itself duality-invariant. We show that such marginal
invariants are not allowable as counterterms in a 16-supercharge off-shell
formalism. It is not possible to draw the same conclusion when vector
multiplets are present because of the appearance of F^4 terms in the SL(2,R)
anomaly. In D=5 there is no one-loop anomaly in the shift invariance of the
dilaton, and we argue that this implies finiteness at two loops, again subject
to the assumption that 16 supercharges can be preserved off-shell.Comment: 81 page
Twistor Spaces for QKT Manifolds
We find that the target space of two-dimensional (4,0) supersymmetric sigma
models with torsion coupled to (4,0) supergravity is a QKT manifold, that is, a
quaternionic K\"ahler manifold with torsion. We give four examples of
geodesically complete QKT manifolds one of which is a generalisation of the
LeBrun geometry. We then construct the twistor space associated with a QKT
manifold and show that under certain conditions it is a K\"ahler manifold with
a complex contact structure. We also show that, for every 4k-dimensional QKT
manifold, there is an associated 4(k+1)-dimensional hyper-K\"ahler one.Comment: 25 pages, phyzz
AdS/SCFT in Superspace
A discussion of the AdS/CFT correspondence in IIB is given in a superspace
context. The main emphasis is on the properties of SCFT correlators on the
boundary which are studied using harmonic superspace techniques. These
techniques provide the easiest way of implementing the superconformal Ward
identities. The Ward identities, together with analyticity, can be used to give
a compelling argument in support of the non-renormalisation theorems for two-
and three-point functions, and to establish the triviality of extremal and
next-to-extremal correlation functions. The OPE in is also briefly discussed.Comment: 10 pages; talk given by PSH at 2nd Gursey Memorial Conference, June
200
BPS Solitons in M5-Brane Worldvolume Theory with Constant Three-Form Field
We study BPS solutions for a self-dual string and a neutral string in
M5-brane worldvolume theory with constant three-form field. We further
generalize such solitons to superpose with a calibrated surface. We also study
a traveling wave on a calibrated surface in the constant three-form field
background.Comment: 12 pages, LaTeX, minor correction, added referenc
On duality symmetries of supergravity invariants
The role of duality symmetries in the construction of counterterms for
maximal supergravity theories is discussed in a field-theoretic context from
different points of view. These are: dimensional reduction, the question of
whether appropriate superspace measures exist and information about non-linear
invariants that can be gleaned from linearised ones. The former allows us to
prove that F-term counterterms cannot be E7(7)-invariant in D=4, N=8
supergravity or E6(6)-invariant in D=5 maximal supergravity. This is confirmed
by the two other methods which can also be applied to D=4 theories with fewer
supersymmetries and allow us to prove that N=6 supergravity is finite at three
and four loops and that N=5 supergravity is three-loop finite.Comment: Clarification of arguments and their consistency with higher
dimensional divergences added, e.g. we prove the 5D 4L non-renormalisation
theorem. The 4L N=6 divergence is also ruled out. References adde
Dynamics of the DBI Spike Soliton
We compare oscillations of a fundamental string ending on a D3-brane in two
different settings: (1) a test-string radially threading the horizon of an
extremal black D3-brane and (2) the spike soliton of the DBI effective action
for a D3-brane. Previous work has shown that overall transverse modes of the
test-string appear as l=0 modes of the transverse scalar fields of the DBI
system. We identify DBI world-volume degrees of freedom that have dynamics
matching those of the test-string relative transverse modes. We show that there
is a map, resembling T-duality, between relative and overall transverse modes
for the test-string that interchanges Neumann and Dirichlet boundary conditions
and implies equality of the absorption coefficients for both modes. We give
general solutions to the overall and relative transverse parts of the DBI
coupled gauge and scalar system and calculate absorption coefficients for the
higher angular momentum modes in the low frequency limit. We find that there is
a nonzero amplitude for l>0 modes to travel out to infinity along the spike,
demonstrating that the spike remains effectively 3+1-dimensional.Comment: 15 pages, 1 figur
Performance of the Birmingham Solar-Oscillations Network (BiSON)
The Birmingham Solar-Oscillations Network (BiSON) has been operating with a
full complement of six stations since 1992. Over 20 years later, we look back
on the network history. The meta-data from the sites have been analysed to
assess performance in terms of site insolation, with a brief look at the
challenges that have been encountered over the years. We explain how the
international community can gain easy access to the ever-growing dataset
produced by the network, and finally look to the future of the network and the
potential impact of nearly 25 years of technology miniaturisation.Comment: 31 pages, 19 figures. Accepted by Solar Physics: 2015 October 20.
First online: 2015 December 7. Open Acces
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