513 research outputs found
Manifestly Supersymmetric RG Flows
Renormalisation group (RG) equations in two-dimensional N=1 supersymmetric
field theories with boundary are studied. It is explained how a manifestly N=1
supersymmetric scheme can be chosen, and within this scheme the RG equations
are determined to next-to-leading order. We also use these results to revisit
the question of how brane obstructions and lines of marginal stability appear
from a world-sheet perspective.Comment: 22 pages; references added, minor change
A Safety Transport Model for Validation of UK Coach Operators for School Journeys
Coaches are considered to be one of the safest modes of transport for children in the UK. In the last 10 years alone, 1191 children were injured in 371 coach crashes. Though the government has strict regulations to maintain road worthiness of the coaches, operator non-compliance was the major reason for these accidents. In last year alone, 137 coach operator licenses have been revoked due to operator non-compliance in the UK. Currently, there is no process to reliably mitigate the safety risks of children travelling by coaches. This has created a requirement to validate all the coach operators before using their coaches for school trips. This paper proposes a novel safety model for validation of coach operators prior to commencement of coach journeys
Supersymmetric non-linear sigma-models with boundaries revisited
We study two-dimensional supersymmetric non-linear sigma-models with
boundaries. We derive the most general family of boundary conditions in the
non-supersymmetric case. Next we show that no further conditions arise when
passing to the N=1 model. We present a manifest N=1 off-shell formulation. The
analysis is greatly simplified compared to previous studies and there is no
need to introduce non-local superspaces nor to go (partially) on-shell. Whether
or not torsion is present does not modify the discussion. Subsequently, we
determine under which conditions a second supersymmetry exists. As for the case
without boundaries, two covariantly constant complex structures are needed.
However, because of the presence of the boundary, one gets expressed in terms
of the other one and the remainder of the geometric data. Finally we recast
some of our results in N=2 superspace and discuss applications.Comment: LaTeX, 23 page
The local symmetries of M-theory and their formulation in generalised geometry
In the doubled field theory approach to string theory, the T-duality group is
promoted to a manifest symmetry at the expense of replacing ordinary Riemannian
geometry with generalised geometry on a doubled space. The local symmetries are
then given by a generalised Lie derivative and its associated algebra. This
paper constructs an analogous structure for M-theory. A crucial by-product of
this is the derivation of the physical section condition for M-theory
formulated in an extended space.Comment: 20 pages, v2: Author Name corrected, v3: typos correcte
A Multi-Wavelength High Resolution Study of the S255 Star Forming Region. General structure and kinematics
We present observational data for two main components (S255IR and S255N) of
the S255 high mass star forming region in continuum and molecular lines
obtained at 1.3 mm and 1.1 mm with the SMA, at 1.3 cm with the VLA and at 23
and 50 cm with the GMRT. The angular resolution was from ~ 2" to ~ 5" for all
instruments. With the SMA we detected a total of about 50 spectral lines of 20
different molecules (including isotopologues). About half of the lines and half
of the species (in particular N2H+, SiO, C34S, DCN, DNC, DCO+, HC3N, H2CO,
H2CS, SO2) have not been previously reported in S255IR and partly in S255N at
high angular resolution. Our data reveal several new clumps in the S255IR and
S255N areas by their millimeter wave continuum emission. Masses of these clumps
are estimated at a few solar masses. The line widths greatly exceed expected
thermal widths. These clumps have practically no association with NIR or radio
continuum sources, implying a very early stage of evolution. At the same time,
our SiO data indicate the presence of high-velocity outflows related to some of
these clumps. In some cases, strong molecular emission at velocities of the
quiescent gas has no detectable counterpart in the continuum. We discuss the
main features of the distribution of NH3, N2H+, and deuterated molecules. We
estimate properties of decimeter wave radio continuum sources and their
relationship with the molecular material.Comment: 21 pages, 26 figures, accepted for publication in Astrophysical
Journa
On the Riemann Tensor in Double Field Theory
Double field theory provides T-duality covariant generalized tensors that are
natural extensions of the scalar and Ricci curvatures of Riemannian geometry.
We search for a similar extension of the Riemann curvature tensor by developing
a geometry based on the generalized metric and the dilaton. We find a duality
covariant Riemann tensor whose contractions give the Ricci and scalar
curvatures, but that is not fully determined in terms of the physical fields.
This suggests that \alpha' corrections to the effective action require \alpha'
corrections to T-duality transformations and/or generalized diffeomorphisms.
Further evidence to this effect is found by an additional computation that
shows that there is no T-duality invariant four-derivative object built from
the generalized metric and the dilaton that reduces to the square of the
Riemann tensor.Comment: 36 pages, v2: minor changes, ref. added, v3: appendix on frame
formalism added, version to appear in JHE
A Double Sigma Model for Double Field Theory
We define a sigma model with doubled target space and calculate its
background field equations. These coincide with generalised metric equation of
motion of double field theory, thus the double field theory is the effective
field theory for the sigma model.Comment: 26 pages, v1: 37 pages, v2: references added, v3: updated to match
published version - background and detail of calculations substantially
condensed, motivation expanded, refs added, results unchange
Ramond-Ramond Cohomology and O(D,D) T-duality
In the name of supersymmetric double field theory, superstring effective
actions can be reformulated into simple forms. They feature a pair of vielbeins
corresponding to the same spacetime metric, and hence enjoy double local
Lorentz symmetries. In a manifestly covariant manner --with regard to O(D,D)
T-duality, diffeomorphism, B-field gauge symmetry and the pair of local Lorentz
symmetries-- we incorporate R-R potentials into double field theory. We take
them as a single object which is in a bi-fundamental spinorial representation
of the double Lorentz groups. We identify cohomological structure relevant to
the field strength. A priori, the R-R sector as well as all the fermions are
O(D,D) singlet. Yet, gauge fixing the two vielbeins equal to each other
modifies the O(D,D) transformation rule to call for a compensating local
Lorentz rotation, such that the R-R potential may turn into an O(D,D) spinor
and T-duality can flip the chirality exchanging type IIA and IIB
supergravities.Comment: 1+37 pages, no figure; Structure reorganized, References added, To
appear in JHEP. cf. Gong Show of Strings 2012
(http://wwwth.mpp.mpg.de/members/strings/strings2012/strings_files/program/Talks/Thursday/Gongshow/Lee.pdf
Permeable conformal walls and holography
We study conformal field theories in two dimensions separated by domain
walls, which preserve at least one Virasoro algebra. We develop tools to study
such domain walls, extending and clarifying the concept of `folding' discussed
in the condensed-matter literature. We analyze the conditions for unbroken
supersymmetry, and discuss the holographic duals in AdS3 when they exist. One
of the interesting observables is the Casimir energy between a wall and an
anti-wall. When these separate free scalar field theories with different
target-space radii, the Casimir energy is given by the dilogarithm function of
the reflection probability. The walls with holographic duals in AdS3 separate
two sigma models, whose target spaces are moduli spaces of Yang-Mills
instantons on T4 or K3. In the supergravity limit, the Casimir energy is
computable as classical energy of a brane that connects the walls through AdS3.
We compare this result with expectations from the sigma-model point of view.Comment: Latex file, 34 pages, 8 figures, uses JHEP3.cls. Typos corrected and
references adde
D-Brane Wess-Zumino Terms and U-Duality
We construct gauge-invariant and U-duality covariant expressions for
Wess-Zumino terms corresponding to general Dp-branes (for any p<D) in arbitrary
2<D<11 dimensions. A distinguishing feature of these Wess-Zumino terms is that
they contain twice as many scalars as the 10-D compactified dimensions, in line
with doubled geometry. We find that for D<10 the charges of the
higher-dimensional branes can all be expressed as products of the 0-brane
charges, which include the D0-brane and the NS-NS 0-brane charges. We give the
general expressions for these charges and show how they determine the
non-trivial conjugacy class to which some of the higher-dimensional D-branes
belong.Comment: 42 pages. Typos corrected, an error in table 6 corrected, comments in
the conclusions adde
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