312 research outputs found
Geometric Second Order Field Equations for General Tensor Gauge Fields
Higher spin tensor gauge fields have natural gauge-invariant field equations
written in terms of generalised curvatures, but these are typically of higher
than second order in derivatives. We construct geometric second order field
equations and actions for general higher spin boson fields, and first order
ones for fermions, which are non-local but which become local on gauge-fixing,
or on introducing auxiliary fields. This generalises the results of Francia and
Sagnotti to all representations of the Lorentz group.Comment: 34 pages, LaTeX. Reference adde
On Dual Formulation for Higher Spin Gauge Fields in
We obtain dual actions for spin massless fields in by
solving different algebraic constraints in the same first-order theory. Flat
space dual higher spin actions obtained by Boulanger, Cnockaert and Henneaux
\cite{BH} by solving differential constraints are shown to result from our
formulation in a sort of quasi-classical approximation for the flat limit. The
case of is considered in detail.Comment: LaTeX, 13 pages, no figure
Higher-Spin Gauge Interactions for Matter Fields in Two Dimensions
We formulate a new model which describes higher-spin gauge interactions for
matter fields in two dimensions. This model is a higher-spin generalization of
d2 gravity and turns out to be integrable. No vanishing higher-spin current
conditions are imposed on the matter fields.Comment: LaTex, 10 pages, no figures, to be published in Phys. Lett.
High Spin Gauge Fields and Two-Time Physics
All possible interactions of a point particle with background
electromagnetic, gravitational and higher-spin fields is considered in the
two-time physics worldline formalism in (d,2) dimensions. This system has a
counterpart in a recent formulation of two-time physics in non-commutative
field theory with local Sp(2) symmetry. In either the worldline or field theory
formulation, a general Sp(2) algebraic constraint governs the interactions, and
determines equations that the background fields of any spin must obey. The
constraints are solved in the classical worldline formalism (h-bar=0 limit) as
well as in the field theory formalism (all powers of h-bar). The solution in
both cases coincide for a certain 2T to 1T holographic image which describes a
relativistic particle interacting with background fields of any spin in (d-1,1)
dimensions. Two disconnected branches of solutions exist, which seem to have a
correspondence as massless states in string theory, one containing low spins in
the zero Regge slope limit, and the other containing high spins in the infinite
Regge slope limit.Comment: LaTeX 22 pages. Typos corrected in version
Non-geometric backgrounds, doubled geometry and generalised T-duality
String backgrounds with a local torus fibration such as T-folds are naturally
formulated in a doubled formalism in which the torus fibres are doubled to
include dual coordinates conjugate to winding number. Here we formulate and
explore a generalisation of this construction in which all coordinates are
doubled, so that the doubled space is a twisted torus, i.e. a compact space
constructed from identifying a group manifold under a discrete subgroup. This
incorporates reductions with duality twists, T-folds and a class of flux
compactifications, together with the non-geometric backgrounds expected to
arise from these through T-duality. It also incorporates backgrounds that are
not even locally geometric, and suggests a generalisation of T-duality to a
more general context. We discuss the effective field theory arising from such
an internal sector, give a world-sheet sigma model formulation of string theory
on such backgrounds and illustrate our discussion with detailed examples.Comment: 81 page
Dynamics of Higher Spin Fields and Tensorial Space
The structure and the dynamics of massless higher spin fields in various
dimensions are reviewed with an emphasis on conformally invariant higher spin
fields. We show that in D=3,4,6 and 10 dimensional space-time the conformal
higher spin fields constitute the quantum spectrum of a twistor-like particle
propagating in tensorial spaces of corresponding dimensions. We give a detailed
analysis of the field equations of the model and establish their relation with
known formulations of free higher spin field theory.Comment: JHEP3 style, 40 pages; v2 typos corrected, comments and references
added; v3 published versio
Bone marrow-derived cells are implicated as a source of lymphatic endothelial progenitors in human breast cancer.
Bone marrow-derived endothelial progenitor cells (EPCs) infiltrate into sites of neovascularization in adult tissues and mature into functional blood endothelial cells (BECs) during a process called vasculogenesis. Human marrow-derived EPCs have recently been reported to display a mixed myeloid and lymphatic endothelial cell (LEC) phenotype during inflammation-induced angiogenesis; however, their role in cancer remains poorly understood. We report the in vitro differentiation of human cord blood CD133(+)CD34(+) progenitors into podoplanin(+) cells expressing both myeloid markers (CD11b, CD14) and the canonical LEC markers vascular endothelium growth factor receptor 3 (VEGFR-3), lymphatic vessel endothelial hyaluronan receptor 1 (LYVE-1), and prospero homeobox 1 (PROX-1). These podoplanin(+) cells displayed sprouting behavior comparable to that of LECs in vitro and a dual hemangiogenic and lymphangiogenic activity in vivo in an endothelial cell sprouting assay and corneal vascularization assay, respectively. Furthermore, these cells expressed vascular endothelium growth factor (VEGF) family members A, -C, and -D. Thus, bone-marrow derived EPCs stimulate hemangiogenesis and lymphangiogenesis through their ability to differentiate into LECs and to produce angiogenic factors. Importantly, plasma from patients with breast cancer induced differentiation of CD34(+) cord blood progenitors into hemangiogenic and lymphangiogenic CD11b(+) myeloid cells, whereas plasma from healthy women did not have this effect. Consistent with these findings, circulating CD11b(+) cells from breast cancer patients, but not from healthy women, displayed a similar dual angiogenic activity. Taken together, our results show that marrow-derived EPCs become hemangiogenic and lymphangiogenic upon exposure to cancer plasma. These newly identified functions of bone-marrow derived EPCs are expected to influence the diagnosis and treatment of breast cancer
Topological A-Type Models with Flux
We study deformations of the A-model in the presence of fluxes, by which we
mean rank-three tensors with antisymmetrized upper/lower indices, using the
AKSZ construction. Generically these are topological membrane models, and we
show that the fluxes are related to deformations of the Courant bracket which
generalize the twist by a closed 3-from , in the sense that satisfying the
AKSZ master equation implies the integrability conditions for an almost
generalized complex structure with respect to the deformed Courant bracket. In
addition, the master equation imposes conditions on the fluxes that generalize
. The membrane model can be defined on a large class of - and -structure manifolds, including geometries inspired by
supersymmetric -models with additional supersymmetries due to almost
complex (but not necessarily complex) structures in the target space.
Furthermore, we show that the model can be defined on three particular
half-flat manifolds related to the Iwasawa manifold.
When only -flux is turned on it is possible to obtain a topological string
model, which we do for the case of a Calabi-Yau with a closed 3-form turned on.
The simplest deformation from the A-model is due to the
component of a non-trivial -field. The model is generically no longer
evaluated on holomorphic maps and defines new topological invariants.
Deformations due to -flux can be more radical, completely preventing
auxiliary fields from being integrated out.Comment: 30 pages. v2: Improved Version. References added. v3: Minor changes,
published in JHE
BPS preons and the AdS-M-algebra
We present here the AdS generalization of BPS preons, which were introduced
as the hypothetical constituents of M-theory preserving all but one
supersymmetries. Our construction, suggested by the relation of `lower
dimensional preons' with higher spin theories, can be considered as a
deformation of the M-algebraic description of the single supersymmetry broken
by a preon, and provides another reason to identify the AdS generalization of
the M-algebra, which we call the AdS-M-algebra, with osp(1|32).Comment: Plain latex, no figures, 19 pages minor corrections, one ref. added,
as published in JHEP 04 (2008) 06
An epitaxial model for heterogeneous nucleation on potent substrates
© The Minerals, Metals & Materials Society and ASM International 2012In this article, we present an epitaxial model for heterogeneous nucleation on potent substrates. It is proposed that heterogeneous nucleation of the solid phase (S) on a potent substrate (N) occurs by epitaxial growth of a pseudomorphic solid (PS) layer on the substrate surface under a critical undercooling (ΔT ). The PS layer with a coherent PS/N interface mimics the atomic arrangement of the substrate, giving rise to a linear increase of misfit strain energy with layer thickness. At a critical thickness (h ), elastic strain energy reaches a critical level, at which point, misfit dislocations are created to release the elastic strain energy in the PS layer. This converts the strained PS layer to a strainless solid (S), and changes the initial coherent PS/N interface into a semicoherent S/N interface. Beyond this critical thickness, further growth will be strainless, and solidification enters the growth stage. It is shown analytically that the lattice misfit (f) between the solid and the substrate has a strong influence on both h and ΔT ; h decreases; and ΔT increases with increasing lattice misfit. This epitaxial nucleation model will be used to explain qualitatively the generally accepted experimental findings on grain refinement in the literature and to analyze the general approaches to effective grain refinement.EPSRC Centre for Innovative Manufacturing in Liquid Metal Engineerin
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