314 research outputs found
D-branes and the Noncommutative Torus
We show that in certain superstring compactifications, gauge theories on
noncommutative tori will naturally appear as D-brane world-volume theories.
This gives strong evidence that they are well-defined quantum theories. It also
gives a physical derivation of the identification proposed by Connes, Douglas
and Schwarz of Matrix theory compactification on the noncommutative torus with
M theory compactification with constant background three-form tensor field.Comment: harvmac, 5 pp. Minor error fixe
The gauge algebra of double field theory and Courant brackets
We investigate the symmetry algebra of the recently proposed field theory on
a doubled torus that describes closed string modes on a torus with both
momentum and winding. The gauge parameters are constrained fields on the
doubled space and transform as vectors under T-duality. The gauge algebra
defines a T-duality covariant bracket. For the case in which the parameters and
fields are T-dual to ones that have momentum but no winding, we find the gauge
transformations to all orders and show that the gauge algebra reduces to one
obtained by Siegel. We show that the bracket for such restricted parameters is
the Courant bracket. We explain how these algebras are realised as symmetries
despite the failure of the Jacobi identity.Comment: 25 pages, LaTe
Stringy AdS3 from the Worldsheet
We investigate the behaviour of the bosonic string on AdS3 with H-flux at
stringy scales, looking in particular for a `tensionless' limit in which there
are massless higher spin gauge fields. We do this by revisiting the physical
spectrum of the sl(2,R) WZW model and considering the limit in which k
becomes small. At k=3 we find that there is an infinite stringy tower of
massless higher spin fields which are part of a continuum of light states. This
can be viewed as a novel tensionless limit, which appears to be distinct from
that inferred from the symmetric orbifold description of superstring AdS3
vacua.Comment: 13 page
Worldvolume Theories, Holography, Duality and Time
Duality transformations involving compactifications on timelike as well as
spacelike circles link M-theory, the 10+1-dimensional strong coupling limit of
IIA string theory, to other 11-dimensional theories in signatures 9+2 and 6+5
and to type II string theories in all 10-dimensional signatures. These theories
have BPS branes of various world-volume signatures, and here we construct the
world-volume theories for these branes, which in each case have 16
supersymmetries. For the generalised D-branes of the various type II string
theories, these are always supersymmetric Yang-Mills theories with 16
supersymmetries, and we show that these all arise from compactifications of the
supersymmetric Yang-Mills theories in 9+1 or 5+5 dimensions. We discuss the
geometry of the brane solutions and, for the cases in which the world-volume
theories are superconformally invariant, we propose holographically dual string
or M theories in constant curvature backgrounds. For product space solutions
, there is in general a conformal field theory associated with the
boundary of and another with the boundary of .Comment: 35 pages, harvma
The first use of Fulton's K for assessing and comparing the conditions of inter-tidal fish populations
Fulton's K condition factor was applied, for the first time, to inter-tidal specimens of the shanny (Lipophrys pholis) and long-spined scorpion fish (Taurulus bubalis) from two English rocky shore and two Welsh rocky shore sites during summer 2010 and winter 2011. As both species contribute to the diet of commercial species such as cod (Gadus morhua) and near-threatened species such as the European otter (Lutra lutra), their condition may affect that of these predators. Fulton's K found that inter-tidal Welsh fish maintained a âgoodâ condition between seasons, whereas the inter-tidal English fish were in a poorer condition during winter. Although condition also changed amongst the sites on each coast, further studies are needed into fish morphologies, environmental parameters, prey availabilities and abundances, and fish specimen sex and maturities
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