6,549 research outputs found
Light-like noncommutativity and duality from open strings/branes
In this paper we perform some non-trivial tests for the recently obtained
open membrane/D-brane metrics and `generalized' noncommutativity parameters
using Dp/NS5/M5-branes which have been deformed by light-like fields. The
results obtained give further evidence that these open membrane/D-brane metrics
and `generalized' noncommutativity parameters are correct. Further, we use the
open brane data and supergravity duals to obtain more information about
non-gravitational theories with light-like noncommutativity, or `generalized'
light-like noncommutativity. In particular, we investigate various duality
relations (strong coupling limits). In the light-like case we also comment on
the relation between open membrane data (open membrane metric etc.) in six
dimensions and open string data in five dimensions. Finally, we investigate the
strong coupling limit (high energy limit) of five dimensional NCYM with
\Theta^{12}=\Theta^{34}. In particular, we find that this NCYM theory can be UV
completed by a DLCQ compactification of M-theory.Comment: 24 pages, Latex. v2:Comments and references added. v3:Version
published in JHE
A New and Elementary CP^n Dyonic Magnon
We show that the dressing transformation method produces a new type of dyonic
CP^n magnon in terms of which all the other known solutions are either
composites or arise as special limits. In particular, this includes the
embedding of Dorey's dyonic magnon via an RP^3 subspace of CP^n. We also show
how to generate Dorey's dyonic magnon directly in the S^n sigma model via the
dressing method without resorting to the isomorphism with the SU(2) principle
chiral model when n=3. The new dyon is shown to be either a charged dyon or
topological kink of the related symmetric-space sine-Gordon theories associated
to CP^n and in this sense is a direct generalization of the soliton of the
complex sine-Gordon theory.Comment: 21 pages, JHEP3, typos correcte
Dissipative quantum mechanics and Kondo-like impurities on noncommutative two-tori
In a recent paper, by exploiting the notion of Morita equivalence for field
theories on noncommutative tori and choosing rational values of the
noncommutativity parameter (in appropriate units), a general
one-to-one correspondence between the -reduced conformal field theory (CFT)
describing a quantum Hall fluid (QHF) at paired states fillings and an Abelian noncommutative field theory (NCFT) has been
established . That allowed us to add new evidence to the relationship between
noncommutativity and quantum Hall fluids\cite% {ncmanybody}. On the other hand,
the -reduced CFT is equivalent to a system of two massless scalar bosons
with a magnetic boundary interaction as introduced by Callan et al., at the so
called ``magic''\ points. We are then able to describe, within such a
framework, the dissipative quantum mechanics of a particle confined to a plane
and subject to an external magnetic field normal to it. Here we develop such a
point of view by focusing on the case which corresponds to a quantum Hall
bilayer. The key role of a localized impurity which couples the two layers is
emphasized and the effect of noncommutativity in terms of generalized magnetic
translations (GMT) is fully exploited. As a result, general GMT operators are
introduced, in the form of a tensor product, which act on the QHF and defect
space respectively, and a comprehensive study of their rich structure is
performed.Comment: 18 pages, 1 figure, accepted for publication in International Journal
of Modern Physics
The Spectrum of Strings on Warped AdS_3 x S^3
String theory on NS-NS AdS_3 x S^3 admits an exactly marginal deformation
which breaks the SL(2,R)_R x SL(2,R)_L isometry of AdS_3 down to SL(2,R)_R x
U(1)_L. The holographic dual is an exotic and only partially understood type of
two-dimensional CFT with a reduced unbroken global conformal symmetry group. In
this paper we study the deformed theory on the string worldsheet. It is found
to be related by a spectral flow which is nonlocal in spacetime to the
undeformed worldsheet theory. An exact formula for the spectrum of massive
strings is presented.Comment: 26 pages, no figure
Holographic Lovelock Gravities and Black Holes
We study holographic implications of Lovelock gravities in AdS spacetimes.
For a generic Lovelock gravity in arbitrary spacetime dimensions we formulate
the existence condition for asymptotically AdS black holes. We consider small
fluctuations around these black holes and determine the constraint on Lovelock
parameters by demanding causality of the boundary theory. For the case of cubic
Lovelock gravity in seven spacetime dimensions we compute the holographic Weyl
anomaly and determine the three point functions of the stress energy tensor in
the boundary CFT. Remarkably, these correlators happen to satisfy the same
relation as the one imposed by supersymmetry. We then compute the energy flux;
requiring it to be positive is shown to be completely equivalent to requiring
causality of the finite temperature CFT dual to the black hole. These
constraints are not stringent enough to place any positive lower bound on the
value of viscosity. Finally, we conjecture an expression for the energy flux
valid for any Lovelock theory in arbitrary dimensions.Comment: 31 pages, 1 figure, harvmac, references added, calculation of
viscosity/entropy ratio include
Reflecting magnons from D7 and D5 branes
We obtain the reflection matrices for the scattering of elementary magnons
from certain open boundaries, corresponding to open strings ending on D7 and D5
branes in . In each case we consider two possible orientations
for the vacuum state. We show that symmetry arguments are sufficient to
determine the reflection matrices up to at most two unknown functions. The D7
reflection matrices obey the boundary Yang Baxter-Equation. This is automatic
for one vacuum orientation, and requires a natural choice of ratio between two
unknowns for the other. In contrast, the D5 reflection matrices do not obey the
boundary Yang Baxter-Equation. In both cases we show consistency with the
existent weak and strong coupling results.Comment: 32 pages, 1 figure; v2: added references and minor changes; v3: error
in boundary Yang-Baxter equation for D5 reflection matrix note
In search of a UV completion of the standard model \u2014 378,000 models that don\u2019t work
Asymptotically safe extensions of the Standard Model have been searched for by adding vector-like fermions charged under the Standard Model gauge group and having Yukawa-like interactions with new scalar fields. Here we study the corresponding renormalization group \u3b2-functions to next and next-to-next to leading order in the perturbative expansion, varying the number of extra fermions and the representations they carry. We test the fixed points of the \u3b2-functions against various criteria of perturbativity to single out those that are potentially viable. We show that all the candidate ultraviolet fixed points are unphysical for these models: either they are unstable under radiative corrections, or they cannot be matched to the Standard Model at low energies
S-matrix for magnons in the D1-D5 system
We show that integrability and symmetries of the near horizon geometry of the
D1-D5 system determine the S-matrix for the scattering of magnons with
polarizations in AdS3 S3 completely up to a phase. Using
semi-classical methods we evaluate the phase to the leading and to the one-loop
approximation in the strong coupling expansion. We then show that the phase
obeys the unitarity constraint implied by the crossing relations to the
one-loop order. We also verify that the dispersion relation obeyed by these
magnons is one-loop exact at strong coupling which is consistent with their BPS
nature.Comment: 40 pages, Latex, Role of Virasoro constraints clarified, version
matches with published versio
Causality in AdS/CFT and Lovelock theory
We explore the constraints imposed on higher curvature corrections of the
Lovelock type due to causality restrictions in the boundary of asymptotically
AdS space-time. In the framework of AdS/CFT, this is related to positivity of
the energy constraints that arise in conformal collider physics. We present
explicit analytic results that fully address these issues for cubic Lovelock
gravity in arbitrary dimensions and give the formal analytic results that
comprehend general Lovelock theory. The computations can be performed in two
ways, both by considering a thermal setup in a black hole background and by
studying the scattering of gravitons with a shock wave in AdS. We show that
both computations coincide in Lovelock theory. The different helicities, as
expected, provide the boundaries defining the region of allowed couplings. We
generalize these results to arbitrary higher dimensions and discuss their
consequences on the shear viscosity to energy density ratio of CFT plasmas, the
possible existence of Boulware-Deser instabilities in Lovelock theory and the
extent to which the AdS/CFT correspondence might be valid for arbitrary
dimensions.Comment: 35 pages, 20 figures; v2: minor amendments and clarifications
include
String Multiplets from an Invariant 2-Brane
We study a three-dimensional gauge theory obtained from the dimensional
reduction of a D4-brane worldvolume theory in the background of space-time
moduli. An SL(3) symmetry in this theory, which acts on fields as well as
coupling constants, is identified. By comparing the energies with the string
tensions, we show that certain 1/2 supersymmetric classical solutions of this
theory can be identified as SL(3,Z) multiplets of type II strings in eight
dimensions. Results are then generalized to the non-linear Born-Infeld action.
We also discuss the possibility of 1/8 BPS states in this theory and their
representations in terms of string networks.Comment: 17 pages, Latex, minor correction
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