52 research outputs found
On Yangian and Long Representations of the Centrally Extended su(2|2) Superalgebra
The centrally extended su(2|2) superalgebra is an asymptotic symmetry of the
light-cone string sigma model on AdS5 x S5. We consider an evaluation
representation of the conventional Yangian built over a particular
16-dimensional long representation of the centrally extended su(2|2).
Interestingly, we find that S-matrices compatible with this evaluation
representation do not exist. On the other hand, by requiring centrally extended
su(2|2) invariance and explicitly solving the Yang-Baxter equation, we find a
scattering matrix for long-short representations of the Lie superalgebra. We
notice that this S-matrix is invariant under a different representation of
non-evaluation type, induced from the tensor product of short representations.
Our findings concern the conventional Yangian only, and are not applied to
possible algebraic extensions of the latter.Comment: Version accepted for publication in JHE
The Bound State S-matrix of the Deformed Hubbard Chain
In this work we use the q-oscillator formalism to construct the atypical
(short) supersymmetric representations of the centrally extended Uq (su(2|2))
algebra. We then determine the S-matrix describing the scattering of arbitrary
bound states. The crucial ingredient in this derivation is the affine extension
of the aforementioned algebra.Comment: 44 pages, 3 figures. v2: minor correction
Secret Symmetries in AdS/CFT
We discuss special quantum group (secret) symmetries of the integrable system
associated to the AdS/CFT correspondence. These symmetries have by now been
observed in a variety of forms, including the spectral problem, the boundary
scattering problem, n-point amplitudes, the pure-spinor formulation and quantum
affine deformations.Comment: 20 pages, pdfLaTeX; Submitted to the Proceedings of the Nordita
program `Exact Results in Gauge-String Dualities'; Based on the talk
presented by A.T., Nordita, 15 February 201
An Exceptional Algebraic Origin of the AdS/CFT Yangian Symmetry
In the su(2|2) spin chain motivated by the AdS/CFT correspondence, a novel
symmetry extending the superalgebra su(2|2) into u(2|2) was found. We pursue
the origin of this symmetry in the exceptional superalgebra d(2,1;epsilon),
which recovers su(2|2) when the parameter epsilon is taken to zero. Especially,
we rederive the Yangian symmetries of the AdS/CFT spin chain using the
exceptional superalgebra and find that the epsilon-correction corresponds to
the novel symmetry. Also, we reproduce the non-canonical classical r-matrix of
the AdS/CFT spin chain expressed with this symmetry from the canonical one of
the exceptional algebra.Comment: 20 pages, 3 figures, v3: minor changes and references adde
Quantum Symmetries and Marginal Deformations
We study the symmetries of the N=1 exactly marginal deformations of N=4 Super
Yang-Mills theory. For generic values of the parameters, these deformations are
known to break the SU(3) part of the R-symmetry group down to a discrete
subgroup. However, a closer look from the perspective of quantum groups reveals
that the Lagrangian is in fact invariant under a certain Hopf algebra which is
a non-standard quantum deformation of the algebra of functions on SU(3). Our
discussion is motivated by the desire to better understand why these theories
have significant differences from N=4 SYM regarding the planar integrability
(or rather lack thereof) of the spin chains encoding their spectrum. However,
our construction works at the level of the classical Lagrangian, without
relying on the language of spin chains. Our approach might eventually provide a
better understanding of the finiteness properties of these theories as well as
help in the construction of their AdS/CFT duals.Comment: 1+40 pages. v2: minor clarifications and references added. v3: Added
an appendix, fixed minor typo
Integrable boundaries in AdS/CFT: revisiting the Z=0 giant graviton and D7-brane
We consider the worldsheet boundary scattering and the corresponding boundary
algebras for the Z=0 giant graviton and the Z=0 D7-brane in the AdS/CFT
correspondence. We consider two approaches to the boundary scattering, the
usual one governed by the (generalized) twisted Yangians and the q-deformed
model of these boundaries governed by the quantum affine coideal subalgebras.
We show that the q-deformed approach leads to boundary algebras that are of a
more compact form than the corresponding twisted Yangians, and thus are
favourable to use for explicit calculations. We obtain the q-deformed
reflection matrices for both boundaries which in the q->1 limit specialize to
the ones obtained using twisted Yangians.Comment: 36 pages. v2: minor typos corrected, references updated; v3:
published versio
Two-loop test of the N=6 Chern-Simons theory S-matrix
Starting from the integrable two-loop spin-chain Hamiltonian describing the
anomalous dimensions of scalar operators in the planar N=6 superconformal
Chern-Simons theory of ABJM, we perform a direct coordinate Bethe ansatz
computation of the corresponding two-loop S-matrix. The result matches with the
weak-coupling limit of the scalar sector of the all-loop S-matrix which we have
recently proposed. In particular, we confirm that the scattering of A and B
particles is reflectionless. As a warm up, we first review the analogous
computation of the one-loop S-matrix from the one-loop dilatation operator for
the scalar sector of planar N=4 superconformal Yang-Mills theory, and compare
the result with the all-loop SU(2|2)^{2} S-matrix.Comment: 21 pages, no figure; references adde
Increasing vegetable intakes: rationale and systematic review of published interventions
Purpose
While the health benefits of a high fruit and vegetable consumption are well known and considerable work has attempted to improve intakes, increasing evidence also recognises a distinction between fruit and vegetables, both in their impacts on health and in consumption patterns. Increasing work suggests health benefits from a high consumption specifically of vegetables, yet intakes remain low, and barriers to increasing intakes are prevalent making intervention difficult. A systematic review was undertaken to identify from the published literature all studies reporting an intervention to increase intakes of vegetables as a distinct food group.
Methods
Databases—PubMed, PsychInfo and Medline—were searched over all years of records until April 2015 using pre-specified terms.
Results
Our searches identified 77 studies, detailing 140 interventions, of which 133 (81 %) interventions were conducted in children. Interventions aimed to use or change hedonic factors, such as taste, liking and familiarity (n = 72), use or change environmental factors (n = 39), use or change cognitive factors (n = 19), or a combination of strategies (n = 10). Increased vegetable acceptance, selection and/or consumption were reported to some degree in 116 (83 %) interventions, but the majority of effects seem small and inconsistent.
Conclusions
Greater percent success is currently found from environmental, educational and multi-component interventions, but publication bias is likely, and long-term effects and cost-effectiveness are rarely considered. A focus on long-term benefits and sustained behaviour change is required. Certain population groups are also noticeably absent from the current list of tried interventions
Engineered Models of Metastasis with Application to Study Cancer Biomechanics
Three-dimensional complex biomechanical interactions occur from the initial steps of tumor formation to the later phases of cancer metastasis. Conventional monolayer cultures cannot recapitulate the complex microenvironment and chemical and mechanical cues that tumor cells experience during their metastatic journey, nor the complexity of their interactions with other, noncancerous cells. As alternative approaches, various engineered models have been developed to recapitulate specific features of each step of metastasis with tunable microenvironments to test a variety of mechanistic hypotheses. Here the main recent advances in the technologies that provide deeper insight into the process of cancer dissemination are discussed, with an emphasis on three-dimensional and mechanical factors as well as interactions between multiple cell types
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