39 research outputs found
Supersymmetric moduli of the SU(2) x R linear dilaton background and NS5-branes
We study several classes of marginal deformations of the conformal field
theory SU(2) x R. This theory describes the near-horizon region of a stack of
parallel and coincident NS5-branes and is related holographically to little
string theory. We investigate the supersymmetry properties of these
deformations and we elucidate their role in the context of holography. The
conformal field theory moduli space contains "non-holographic" operators that
do not seem to have a simple interpretation in little string theory.
Subsequently, we analyze several NS5-brane configurations in terms of SU(2) x R
deformations. We discuss in detail interesting phenomena, like the excision of
the strong coupling region associated with the linear dilaton and the
manifestation of the symmetries of an NS5-brane setup in the deforming
operators. Finally, we present a class of conformally hyperkaehler geometries
that arise as "non-holographic" deformations of SU(2) x R.Comment: 38 pages, 1 figure, 1 table; version to appear in JHE
Pomerons and BCFW recursion relations for strings on D-branes
We derive pomeron vertex operators for bosonic strings and superstrings in
the presence of D-branes. We demonstrate how they can be used in order to
compute the Regge behavior of string amplitudes on D-branes and the amplitude
of ultrarelativistic D-brane scattering. After a lightning review of the BCFW
method, we proceed in a classification of the various BCFW shifts possible in a
field/string theory in the presence of defects/D-branes. The BCFW shifts
present several novel features, such as the possibility of performing single
particle momentum shifts, due to the breaking of momentum conservation in the
directions normal to the defect. Using the pomeron vertices we show that
superstring amplitudes on the disc involving both open and closed strings
should obey BCFW recursion relations. As a particular example, we analyze
explicitly the case of 1 -> 1 scattering of level one closed string states off
a D-brane. Finally, we investigate whether the eikonal Regge regime conjecture
holds in the presence of D-branes.Comment: 49 pages; v2 corrected references and minor typos; v3 minor typos
corrected, version to appear in NP
Worldsheet theories for non-geometric string backgrounds
We show that twisted doubled tori can be used to construct a general class of
worldsheet models describing non-geometric string backgrounds. By employing a
first order formulation of interacting chiral bosons, we first refine the
analysis on the general conditions of worldsheet Lorentz invariance and then
prove that twisted doubled tori provide good duality symmetric backgrounds.
Subsequently we apply our general analysis to several examples which enable us
to gain new insight on the difference between geometric, locally geometric and
genuine non-geometric backgrounds.Comment: Latex, 25 pages; v2 Fixed typos; v3 Sections 2 and 3 expanded; v4
Published versio
Discrete Torsion, Covering Groups and Quiver Diagrams
Without recourse to the sophisticated machinery of twisted group algebras,
projective character tables and explicit values of 2-cocycles, we here present
a simple algorithm to study the gauge theory data of D-brane probes on a
generic orbifold G with discrete torsion turned on. We show in particular that
the gauge theory can be obtained with the knowledge of no more than the
ordinary character tables of G and its covering group G*. Subsequently we
present the quiver diagrams of certain illustrative examples of SU(3)-orbifolds
which have non-trivial Schur Multipliers. The paper serves as a companion to
our earlier work (arXiv:hep-th/0010023) and aims to initiate a systematic and
computationally convenient study of discrete torsion.Comment: 26 pages, 8 figures, some errors correcte
Discrete Torsion, Non-Abelian Orbifolds and the Schur Multiplier
Armed with the explicit computation of Schur Multipliers, we offer a
classification of SU(n) orbifolds for n = 2,3,4 which permit the turning on of
discrete torsion. This is in response to the host of activity lately in vogue
on the application of discrete torsion to D-brane orbifold theories. As a
by-product, we find a hitherto unknown class of N = 1 orbifolds with non-cyclic
discrete torsion group. Furthermore, we supplement the status quo ante by
investigating a first example of a non-Abelian orbifold admitting discrete
torsion, namely the ordinary dihedral group as a subgroup of SU(3). A
comparison of the quiver theory thereof with that of its covering group, the
binary dihedral group, without discrete torsion, is also performed.Comment: 23 pages, 2 figures, references added and some typos correcte
Stepwise Projection: Toward Brane Setups for Generic Orbifold Singularities
The construction of brane setups for the exceptional series E6,E7,E8 of SU(2)
orbifolds remains an ever-haunting conundrum. Motivated by techniques in some
works by Muto on non-Abelian SU(3) orbifolds, we here provide an algorithmic
outlook, a method which we call stepwise projection, that may shed some light
on this puzzle. We exemplify this method, consisting of transformation rules
for obtaining complex quivers and brane setups from more elementary ones, to
the cases of the D-series and E6 finite subgroups of SU(2). Furthermore, we
demonstrate the generality of the stepwise procedure by appealing to Frobenius'
theory of Induced Representations. Our algorithm suggests the existence of
generalisations of the orientifold plane in string theory.Comment: 22 pages, 3 figure
Scherk-Schwarz reduction of M-theory on G2-manifolds with fluxes
We analyse the 4-dimensional effective supergravity theories obtained from
the Scherk--Schwarz reduction of M-theory on twisted 7-tori in the presence of
4-form fluxes. We implement the appropriate orbifold projection that preserves
a G2-structure on the internal 7-manifold and truncates the effective field
theory to an N=1, D=4 supergravity. We provide a detailed account of the
effective supergravity with explicit expressions for the Kaehler potential and
the superpotential in terms of the fluxes and of the geometrical data of the
internal manifold. Subsequently, we explore the landscape of vacua of M-theory
compactifications on twisted tori, where we emphasize the role of geometric
fluxes and discuss the validity of the bottom-up approach. Finally, by reducing
along isometries of the internal 7-manifold, we obtain superpotentials for the
corresponding type IIA backgrounds.Comment: 43 pages, Latex; v3 typos corrected, one reference added, JHEP
versio
The Partition Function of the Two-Dimensional Black Hole Conformal Field Theory
We compute the partition function of the conformal field theory on the
two-dimensional euclidean black hole background using path-integral techniques.
We show that the resulting spectrum is consistent with the algebraic
expectations for the SL(2,R)/U(1) coset conformal field theory construction. In
particular, we find confirmation for the bound on the spin of the discrete
representations and we determine the density of the continuous representations.
We point out the relevance of the partition function to all string theory
backgrounds that include an SL(2,R)/U(1) coset factor.Comment: 17 pages, references added and typos correcte
Conformal chiral boson models on twisted doubled tori and non-geometric string vacua
We derive and analyze the conditions for quantum conformal and Lorentz
invariance of the duality symmetric interacting chiral boson sigma-models,
which are conjectured to describe non-geometric string theory backgrounds. The
one-loop Weyl and Lorentz anomalies are computed for the general case using the
background field method. Subsequently, our results are applied to a class of
(on-shell) Lorentz invariant chiral boson models which are based on twisted
doubled tori. Our findings are in agreement with those expected from the
effective supergravity approach, thereby firmly establishing that the chiral
boson models under consideration provide the string worldsheet description of
N=4 gauged supergravities with electric gaugings. Furthermore, they demonstrate
that twisted doubled tori are indeed the doubled internal geometries underlying
a large class of non-geometric string compactifications. For compact gaugings
the associated chiral boson models are automatically conformal, a fact that is
explained by showing that they are actually chiral WZW models in disguise.Comment: 37 pages; v2: minor improvements, version to appear in Nucl. Phys.