245 research outputs found
Kleinian Geometry and the N=2 Superstring
This paper is devoted to the exploration of some of the geometrical issues
raised by the superstring. We begin by reviewing the reasons that
-functions for the superstring require it to live in a
four-dimensional self-dual spacetime of signature , together with some
of the arguments as to why the only degree of freedom in the theory is that
described by the gravitational field. We then move on to describe at length the
geometry of flat space, and how a real version of twistor theory is relevant to
it. We then describe some of the more complicated spacetimes that satisfy the
-function equations. Finally we speculate on the deeper significance of
some of these spacetimes.Comment: 30 pages, AMS-Te
Sigma-model soliton intersections from exceptional calibrations
A first-order `BPS' equation is obtained for 1/8 supersymmetric intersections
of soliton-membranes (lumps) of supersymmetric (4+1)-dimensional massless sigma
models, and a special non-singular solution is found that preserves 1/4
supersymmetry. For 4-dimensional hyper-K\"ahler target spaces () the BPS
equation is shown to be the low-energy limit of the equation for a
Cayley-calibrated 4-surface in \bE^4\times HK_4. Similar first-order
equations are found for stationary intersections of Q-lump-membranes of the
massive sigma model, but now generic solutions preserve either 1/8
supersymmetry or no supersymmetry, depending on the time orientation.Comment: 21 pages. Version 3: Minor corrections and one further reference:
version published in JHE
Magnetic bubble refraction and quasibreathers in inhomogeneous antiferromagnets
The dynamics of magnetic bubble solitons in a two-dimensional isotropic
antiferromagnetic spin lattice is studied, in the case where the exchange
integral J(x,y) is position dependent. In the near continuum regime, this
system is described by the relativistic O(3) sigma model on a spacetime with a
spatially inhomogeneous metric, determined by J. The geodesic approximation is
used to describe low energy soliton dynamics in this system: n-soliton motion
is approximated by geodesic motion in the moduli space of static n-solitons,
equipped with the L^2 metric. Explicit formulae for this metric for various
natural choices of J(x,y) are obtained. From these it is shown that single
soliton trajectories experience refraction, with 1/J analogous to the
refractive index, and that this refraction effect allows the construction of
simple bubble lenses and bubble guides. The case where J has a disk
inhomogeneity (taking the value J_1 outside a disk, and J_2<J_1 inside) is
considered in detail. It is argued that, for sufficiently large J_1/J_2 this
type of antiferromagnet supports approximate quasibreathers: two or more
coincident bubbles confined within the disk which spin internally while their
shape undergoes periodic oscillations with a generically incommensurate period.Comment: Conference proceedings paper for talk given at Nonlinear Physics
Theory and Experiment IV, Gallipoli, Italy, June 200
The geodesic approximation for lump dynamics and coercivity of the Hessian for harmonic maps
The most fruitful approach to studying low energy soliton dynamics in field
theories of Bogomol'nyi type is the geodesic approximation of Manton. In the
case of vortices and monopoles, Stuart has obtained rigorous estimates of the
errors in this approximation, and hence proved that it is valid in the low
speed regime. His method employs energy estimates which rely on a key
coercivity property of the Hessian of the energy functional of the theory under
consideration. In this paper we prove an analogous coercivity property for the
Hessian of the energy functional of a general sigma model with compact K\"ahler
domain and target. We go on to prove a continuity property for our result, and
show that, for the CP^1 model on S^2, the Hessian fails to be globally coercive
in the degree 1 sector. We present numerical evidence which suggests that the
Hessian is globally coercive in a certain equivariance class of the degree n
sector for n>1. We also prove that, within the geodesic approximation, a single
CP^1 lump moving on S^2 does not generically travel on a great circle.Comment: 29 pages, 1 figure; typos corrected, references added, expanded
discussion of the main function spac
Instanton Moduli and Topological Soliton Dynamics
It has been proposed by Atiyah and Manton that the dynamics of Skyrmions may
be approximated by motion on a finite dimensional manifold obtained from the
moduli space of SU(2) Yang-Mills instantons. Motivated by this work we describe
how similar results exist for other soliton and instanton systems. We describe
in detail two examples for the approximation of the infinite dimensional
dynamics of sine-Gordon solitons by finite dimensional dynamics on a manifold
obtained from instanton moduli. In the first example we use the moduli space of
CP1 instantons and in the second example we use the moduli space of SU(2)
Yang-Mills instantons. The metric and potential functions on these manifolds
are constructed and the resulting dynamics is compared with the explicit exact
soliton solutions of the sine-Gordon theory.Comment: uuencoded tex file, 27 pages including 4 figures, requires phyzzx
macro. DAMTP 94-5
Nahm Transform and Moduli Spaces of CPn Models on the Torus
There is a Nahm transform for two-dimensional gauge fields which establishes
a one-to-one correspondence between the orbit space of U(N) gauge fields with
topological charge k defined on a torus and that of U(k) gauge fields with
charge N on the dual torus. The main result of this paper is to show that a
similar duality transform cannot exist for CPn instantons. This fact
establishes a significative difference between 4-D gauge theories and CPn
models. The result follows from the global analysis of the moduli space of
instantons based on a complete and explicit parametrization of all self-dual
solutions on the two-dimensional torus. The boundary of the space of regular
instantons is shown to coincide with the space of singular instantons. This
identification provides a new approach to analyzing the role of overlapping
instantons in the infrared sector of CPn sigma models.Comment: 28 pages, 5 eps-figure
Uniqueness Theorem of Static Degenerate and Non-degenerate Charged Black Holes in Higher Dimensions
We prove the uniqueness theorem for static higher dimensional charged black
holes spacetime containing an asymptotically flat spacelike hypersurface with
compact interior and with both degenerate and non-degenerate components of the
event horizon.Comment: 9 pages, RevTex, to be published in Phys.Rev.D1
Scattering of Macroscopic Heterotic Strings
We show that macroscopic heterotic strings, formulated as strings which wind
around a compact direction of finite but macroscopic extent, exhibit
non-trivial scattering at low energies. This occurs at order velocity squared
and may thus be described as geodesic motion on a moduli space with a
non-trivial metric which we construct. Our result is in agreement with a direct
calculation of the string scattering amplitude.Comment: 14 pp (harvmac l
More on scattering of Chern-Simons vortices
I derive a general formalism for finding kinetic terms of the effective
Lagrangian for slowly moving Chern-Simons vortices. Deformations of fields
linear in velocities are taken into account. From the equations they must
satisfy I extract the kinetic term in the limit of coincident vortices. For
vortices passing one over the other there is locally the right-angle
scattering. The method is based on analysis of field equations instead of
action functional so it may be useful also for nonvariational equations in
nonrelativistic models of Condensed Matter Physics.Comment: discussion around Eq.(45) is generalised, one more condition for the
local right-angle scattering is adde
Estratégias utilizadas pela equipe de enfermagem aos clientes submetidos à antineoplásicos
Durante o tratamento com antineoplásicos, os pacientes além de defrontar-se com os efeitos adversos, possuem também dúvidas, ansiedade e medo, para isso a enfermagem deve realizar uma abordagem não somente técnica, mas também humanizada. Objetivamos em compreender como a equipe de enfermagem assiste os pacientes submetidos ao tratamento antineoplásico. Desenvolvemos um estudo bibliográfico com abordagem quanti-qualitativa, onde as produções científicas foram consultadas através da base de dados do SCIELO, LILACS e BDENF. Realizou-se uma análise explicativa dos textos em relação à assistência de enfermagem concomitante aos profissionais de saúde e pacientes em tratamento com antineoplásicos. Utilizando os seguintes descritores: antineoplásicos, assistência de enfermagem e reações adversas. Identificamos 26 produções relacionadas ao tema, sendo 72% encontradas no LILACS, 21% no BDENF e 7% no SCIELO. As temáticas que tiveram maior relevância foram extravasamento de antineoplásicos e caquexia, ambas correspondendo a 37,5% das publicações científicas abordadas. Concluímos com essa pesquisa que se faz necessário a compreensão da equipe de enfermagem acerca da temática abordada, e a capacitação dos mesmos a fim de diminuir os problemas ocasionados durante o tratamento
- …