1,168 research outputs found
Massive Type II in Double Field Theory
We provide an extension of the recently constructed double field theory
formulation of the low-energy limits of type II strings, in which the RR fields
can depend simultaneously on the 10-dimensional space-time coordinates and
linearly on the dual winding coordinates. For the special case that only the RR
one-form of type IIA carries such a dependence, we obtain the massive
deformation of type IIA supergravity due to Romans. For T-dual configurations
we obtain a `massive' but non-covariant formulation of type IIB, in which the
10-dimensional diffeomorphism symmetry is deformed by the mass parameter.Comment: 21 page
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
Microstructure-dependent DC set switching behaviors of Ge-Sb-Te-based phase-change random access memory devices accessed by in situ TEM
Phase-change random access memory (PCRAM) is one of the most promising nonvolatile memory devices. However, inability to secure consistent and reliable switching operations in nanometer-scale programing volumes limits its practical use for highdensity applications. Here, we report in situ transmission electron microscopy investigation of the DC set switching of Ge-Sb-Te (GST)-based vertical PCRAM cells. We demonstrate that the microstructure of GST, particularly the passive component surrounding the dome-shaped active switching volume, plays a critical role in determining the local temperature distribution and is therefore responsible for inconsistent cell-to-cell switching behaviors. As demonstrated by a PCRAM cell with a highly crystallized GST matrix, the excessive Joule heat can cause melting and evaporation of the switching volume, resulting in device failure. The failure occurred via two-step void formation due to accelerated phase separation in the molten GST by the polaritydependent atomic migration of constituent elements. The presented real-time observations contribute to the understanding of inconsistent switching and premature failure of GST-based PCRAM cells and can guide future design of reliable PCRAM.1176Ysciescopu
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
Double Field Theory Formulation of Heterotic Strings
We extend the recently constructed double field theory formulation of the
low-energy theory of the closed bosonic string to the heterotic string. The
action can be written in terms of a generalized metric that is a covariant
tensor under O(D,D+n), where n denotes the number of gauge vectors, and n
additional coordinates are introduced together with a covariant constraint that
locally removes these new coordinates. For the abelian subsector, the action
takes the same structural form as for the bosonic string, but based on the
enlarged generalized metric, thereby featuring a global O(D,D+n) symmetry.
After turning on non-abelian gauge couplings, this global symmetry is broken,
but the action can still be written in a fully O(D,D+n) covariant fashion, in
analogy to similar constructions in gauged supergravities.Comment: 28 pages, v2: minor changes, version published in JHE
Differential geometry with a projection: Application to double field theory
In recent development of double field theory, as for the description of the
massless sector of closed strings, the spacetime dimension is formally doubled,
i.e. from D to D+D, and the T-duality is realized manifestly as a global O(D,D)
rotation. In this paper, we conceive a differential geometry characterized by a
O(D,D) symmetric projection, as the underlying mathematical structure of double
field theory. We introduce a differential operator compatible with the
projection, which, contracted with the projection, can be covariantized and may
replace the ordinary derivatives in the generalized Lie derivative that
generates the gauge symmetry of double field theory. We construct various gauge
covariant tensors which include a scalar and a tensor carrying two O(D,D)
vector indices.Comment: 1+22 pages, No figure; a previous result on 4-index tensor removed,
presentation improve
N=1 Supersymmetric Double Field Theory
We construct the N=1 supersymmetric extension of double field theory for
D=10, including the coupling to an arbitrary number n of abelian vector
multiplets. This theory features a local O(1,9+n) x O(1,9) tangent space
symmetry under which the fermions transform. It is shown that the supersymmetry
transformations close into the generalized diffeomorphisms of double field
theory.Comment: 22 pages, v2: minor corrections, ref. added, to appear in JHE
Incorporation of fermions into double field theory
Based on the stringy differential geometry we proposed earlier, we
incorporate fermions such as gravitino and dilatino into double field theory in
a manifestly covariant manner with regard to O(D,D) T-duality, diffeomorphism,
one-form gauge symmetry for B-field and a pair of local Lorentz symmetries. We
note that there are two kinds of fermions in double field theory: O(D,D)
singlet and non-singlet which may be identified, respectively as the common and
the non-common fermionic sectors in type IIA and IIB supergravities. For each
kind, we construct corresponding covariant Dirac operators. Further, we derive
a simple criterion for an O(D,D) rotation to flip the chirality of the O(D,D)
non-singlet chiral fermions, which implies the exchange of type IIA and IIB
supergravities.Comment: (v1) 1+21 pages, no figure; (v2) Refs. added, to appear in JHEP; (v3)
minor change, a comment in the last section removed and Eq.(3.22) correcte
Odderon in baryon-baryon scattering from the AdS/CFT correspondence
Based on the AdS/CFT correspondence, we present a holographic description of
various C-odd exchanges in high energy baryon-baryon and baryon-antibaryon
scattering, and calculate their respective contributions to the difference in
the total cross sections. We predict that, due to the warp factor of AdS_5, the
total cross section in pp collisions is larger than in p\bar{p} collisions at
asymptotically high energies.Comment: 23 pages, v2: minor changes, to be published in JHE
- …