1,321 research outputs found
Q-instantons
We construct the half-supersymmetric instanton solutions that are
electric-magnetically dual to the recently discussed half-supersymmetric
Q7-branes. We call these instantons `Q-instantons'. Whereas the D-instanton is
most conveniently described using the RR axion \chi and the dilaton \phi, the
Q-instanton is most conveniently described using a different set of fields
\chi' and T, where \chi' is an axionic scalar. The real part of the Q-instanton
on-shell action is a function of T and the imaginary part is linear in \chi'.
Discrete shifts of the axion \chi' correspond to PSL(2,Z) transformations that
are of finite order. These are e.g. pure S-duality transformations relating
weak and strongly coupled regimes. We argue that near each orbifold point of
the quantum axion-dilaton moduli space PSL(2,Z)\PSL(2,R)/SO(2) the higher order
R^4 terms in the string effective action contain contributions from an infinite
sum of single multiply-charged instantons with the Q-instantons corresponding
to the orbifold points \tau=i,\rho where \tau is the complex axion-dilaton
field.Comment: 29 pages, 1 figur
Seven-branes and Supersymmetry
We re-investigate the construction of half-supersymmetric 7-brane solutions
of IIB supergravity. Our method is based on the requirement of having globally
well-defined Killing spinors and the inclusion of SL(2,Z)-invariant source
terms. In addition to the well-known solutions going back to Greene, Shapere,
Vafa and Yau we find new supersymmetric configurations, containing objects
whose monodromies are not related to the monodromy of a D7-brane by an SL(2,Z)
transformation.Comment: 31 pages, 3 figure
Non-extremal D-instantons
We construct the most general non-extremal deformation of the D-instanton
solution with maximal rotational symmetry. The general non-supersymmetric
solution carries electric charges of the SL(2,R) symmetry, which correspond to
each of the three conjugacy classes of SL(2,R). Our calculations naturally
generalise to arbitrary dimensions and arbitrary dilaton couplings.
We show that for specific values of the dilaton coupling parameter, the
non-extremal instanton solutions can be viewed as wormholes of non-extremal
Reissner-Nordstr\"om black holes in one higher dimension. We extend this result
by showing that for other values of the dilaton coupling parameter, the
non-extremal instanton solutions can be uplifted to non-extremal non-dilatonic
p-branes in p+1 dimensions higher.
Finally, we attempt to consider the solutions as instantons of (compactified)
type IIB superstring theory. In particular, we derive an elegant formula for
the instanton action. We conjecture that the non-extremal D-instantons can
contribute to the R^8-terms in the type IIB string effective action.Comment: 31 pages, 4 figures. v3: minor correction and reference adde
Non-propagating degrees of freedom in supergravity and very extended G_2
Recently a correspondence between non-propagating degrees of freedom in
maximal supergravity and the very extended algebra E_11 has been found. We
perform a similar analysis for a supergravity theory with eight supercharges
and very extended G_2. In particular, in the context of d=5 minimal
supergravity, we study whether supersymmetry can be realised on higher-rank
tensors with no propagating degrees of freedom. We find that in this case the
very extended algebra fails to capture these possibilities.Comment: 12 pages, 1 figure. v2: transformation properties of higher-rank
tensors under SU(2) R-symmetry analysed and refs added. v3: improved
discussion, published versio
Non-Abelian Born-Infeld theory without the square root
A non-Abelian Born-Infeld theory is presented. The square root structure that
characterizes the Dirac-Born-Infeld (DBI) action does not appear. The procedure
is based on an Abelian theory proposed by Erwin Schr\"{o}dinger that, as he
showed, is equivalent to Born-Infeld theory. We briefly mention other possible
similar proposals. Our results could be of interest in connection with string
theory and possible extensions of well known physical results in the usual
Born-Infeld Abelian case.Comment: 9 pages, no figures, revtex
Spectrum of Higher Derivative 6D Chiral Supergravity
Gauged off-shell Maxwell-Einstein supergravity in six dimensions with N=(1,0)
supersymmetry has a higher derivative extension afforded by a supersymmetrized
Riemann squared term. This theory admits a supersymmetric Minkowski x S^2
compactification with a U(1) monopole of unit charge on S^2. We determine the
full spectrum of the theory on this background. We also determine the spectrum
on a non-supersymmetric version of this compactification in which the monopole
charge is different from unity, and we find the peculiar feature that there are
massless gravitini in a representation of the S^2 isometry group determined by
the monopole charge.Comment: typos correcte
Counting supersymmetric branes
Maximal supergravity solutions are revisited and classified, with particular
emphasis on objects of co-dimension at most two. This class of solutions
includes branes whose tension scales with g_s^{-\sigma} for \sigma>2. We
present a group theory derivation of the counting of these objects based on the
corresponding tensor hierarchies derived from E11 and discrete T- and U-duality
transformations. This provides a rationale for the wrapping rules that were
recently discussed for \sigma<4 in the literature and extends them. Explicit
supergravity solutions that give rise to co-dimension two branes are
constructed and analysed.Comment: 1+33 pages. To the memory of Laurent Houart. v2: Published version
with added reference
Covariant Quantization of D-branes
We have found that kappa-symmetry allows a covariant quantization provided
the ground state of the theory is strictly massive. For D-p-branes a
Hamiltonian analysis is performed to explain the existence of a manifestly
supersymmetric and Lorentz covariant description of the BPS states of the
theory. The covariant quantization of the D-0-brane is presented as an example.Comment: 16 pages, no figure
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