6,477 research outputs found
A Geometry for Non-Geometric String Backgrounds
A geometric string solution has background fields in overlapping coordinate
patches related by diffeomorphisms and gauge transformations, while for a
non-geometric background this is generalised to allow transition functions
involving duality transformations. Non-geometric string backgrounds arise from
T-duals and mirrors of flux compactifications, from reductions with duality
twists and from asymmetric orbifolds. Strings in ` T-fold' backgrounds with a
local -torus fibration and T-duality transition functions in are
formulated in an enlarged space with a fibration which is geometric,
with spacetime emerging locally from a choice of a submanifold of each
fibre, so that it is a subspace or brane embedded in the enlarged
space. T-duality acts by changing to a different subspace of .
For a geometric background, the local choices of fit together to give a
spacetime which is a bundle, while for non-geometric string backgrounds
they do not fit together to form a manifold. In such cases spacetime geometry
only makes sense locally, and the global structure involves the doubled
geometry. For open strings, generalised D-branes wrap a subspace of each
fibre and the physical D-brane is the part of the part of the physical
space lying in the generalised D-brane subspace.Comment: 28 Pages. Minor change
Background independent action for double field theory
Double field theory describes a massless subsector of closed string theory
with both momentum and winding excitations. The gauge algebra is governed by
the Courant bracket in certain subsectors of this double field theory. We
construct the associated nonlinear background-independent action that is
T-duality invariant and realizes the Courant gauge algebra. The action is the
sum of a standard action for gravity, antisymmetric tensor, and dilaton fields
written with ordinary derivatives, a similar action for dual fields with dual
derivatives, and a mixed term that is needed for gauge invariance.Comment: 45 pages, v2: minor corrections, refs. added, to appear in JHE
On the construction of variant supergravities in D=11, D=10
We construct with a geometric procedure the supersymmetry transformation laws
and Lagrangian for all the ``variant'' D=11 and D=10 Type IIA supergravities.
We identify into our classification the D=11 and D=10 Type IIA ``variant''
theories first introduced by Hull performing T-duality transformation on both
spacelike and timelike circles. We find in addition a set of D=10 Type IIA
``variant'' supergravities that can not be obtained trivially from eleven
dimensions compactifying on a circle.Comment: 21 pages, Late
Untangling the Conceptual Isssues Raised in Reydon and Scholz’s Critique of Organizational Ecology and Darwinian Populations
Reydon and Scholz raise doubts about the Darwinian status of organizational ecology by arguing that Darwinian principles are not applicable to organizational populations. Although their critique of organizational ecology’s typological essentialism is correct, they go on to reject the Darwinian status of organizational populations. This paper claims that the distinction between replicators and interactors, raised in modern philosophy of biology but not discussed by Reydon and Scholz, points the way forward for organizational ecologists. It is possible to conceptualise evolving Darwinian populations providing the inheritance mechanism is appropriately specified. By this approach, adaptation and selection are no longer dichotomised, and the evolutionary significance of knowledge transmission is highlightedPeer reviewe
Symmetries in M-theory: Monsters, Inc
We will review the algebras which have been conjectured as symmetries in
M-theory. The Borcherds algebras, which are the most general Lie algebras under
control, seem natural candidates.Comment: 6 pages, talk given by PHL at Cargese 200
U-duality as General Coordinate Transformations, and Spacetime Geometry
We show that the full global symmetry groups of all the D-dimensional maximal
supergravities can be described in terms of the closure of the internal general
coordinate transformations of the toroidal compactifications of D=11
supergravity and of type IIB supergravity, with type IIA/IIB T-duality
providing an intertwining between the two pictures. At the quantum level, the
part of the U-duality group that corresponds to the surviving discretised
internal general coordinate transformations in a given picture leaves the
internal torus invariant, while the part that is not described by internal
general coordinate transformations can have the effect of altering the size or
shape of the internal torus. For example, M-theory compactified on a large
torus T^n can be related by duality to a compactification on a small torus, if
and only if n\ge 3. We also discuss related issues in the toroidal
compactification of the self-dual string to D=4. An appendix includes the
complete results for the toroidal reduction of the bosonic sector of type IIB
supergravity to arbitrary dimensions D\ge3.Comment: Latex, 28 page
Spiral cracks in drying precipitates
We investigate the formation of spiral crack patterns during the desiccation
of thin layers of precipitates in contact with a substrate. This
symmetry-breaking fracturing mode is found to arise naturally not from torsion
forces, but from a propagating stress front induced by the fold-up of the
fragments. We model their formation mechanism using a coarse-grain model for
fragmentation and successfully reproduce the spiral cracks. Fittings of
experimental and simulation data show that the spirals are logarithmic,
corresponding to constant deviation from a circular crack path. Theoretical
aspects of the logarithmic spirals are discussed. In particular we show that
this occurs generally when the crack speed is proportional to the propagating
speed of stress front.Comment: 4 pages, 5 figures, RevTe
T-duality in the weakly curved background
We consider the closed string propagating in the weakly curved background
which consists of constant metric and Kalb-Ramond field with infinitesimally
small coordinate dependent part. We propose the procedure for constructing the
T-dual theory, performing T-duality transformations along coordinates on which
the Kalb-Ramond field depends. The obtained theory is defined in the
non-geometric double space, described by the Lagrange multiplier and
its -dual . We apply the proposed T-duality procedure to the
T-dual theory and obtain the initial one. We discuss the standard relations
between T-dual theories that the equations of motion and momenta modes of one
theory are the Bianchi identities and the winding modes of the other
Intersection rules, dynamics and symmetries
We consider theories containing gravity, at most one dilaton and form field
strengths. We show that the existence of particular BPS solutions of
intersecting extremal closed branes select the theories, which upon dimensional
reduction to three dimensions possess a simple simply laced Lie group symmetry
G. Furthermore these theories can be fully reconstructed from the dynamics of
such branes and of their openings. Amongst such theories are the effective
actions of the bosonic sector of M-theory and of the bosonic string. The BPS
intersecting brane solutions form representations of a subgroup of the group of
Weyl reflections and outer automorphisms of the triple Kac-Moody extension G+++
of the G algebra, which cannot be embedded in the overextended Kac-Moody
subalgebra G++ characterising the cosmological Kasner solutions.Comment: Latex 30 pages, 3 figure
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