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Steepest descent on real flag manifolds  [PDF]
J. -H. Eschenburg,A. -L. Mare
Mathematics , 2002,
Abstract: Real flag manifolds are the isotropy orbits of noncompact symmetric spaces $G/K$. Any such manifold $M$ enjoys two very peculiar geometric properties: It carries a transitive action of the (noncompact) Lie group $G$, and it is embedded in euclidean space as a taut submanifold. The aim of the paper is to link these two properties by showing that the gradient flow of any height function is a one-parameter subgroup of $G$, where the gradient is defined with respect to a suitable homogeneous metric $s$ on $M$; this generalizes the Kaehler metric on adjoint orbits (the so-called complex flag manifolds).
Real group orbits on flag manifolds  [PDF]
Dmitri Akhiezer
Mathematics , 2011,
Abstract: In this survey, we gather together various results on the action of a real form of a complex semisimple Lie group on its flag manifolds. We start with the finiteness theorem of J.Wolf implying that at least one of the orbits is open. We give a new proof of the converse statement for real forms of inner type, essentially due to F.M.Malyshev. Namely, if a real semisimple Lie group of inner type has an open orbit on an algebraic homogeneous space of the complexified group then the homogeneous space is a flag manifold. To prove this, we recall, partly with proofs, some results of A.L.Onishchik on the factorizations of reductive groups. Finally, we discuss the cycle spaces of open orbits and define the crown of a symmetric space of non-compact type. With some exceptions, the cycle space agrees with the crown. We sketch a complex analytic proof of this result, due to G.Fels, A.Huckleberry and J.Wolf.
Orientability of vector bundles over real flag manifolds  [PDF]
Mauro Patr?o,Luiz A. B. San Martin,Laércio J. dos Santos,Lucas Seco
Mathematics , 2010,
Abstract: We investigate the orientability of a class of vector bundles over flag manifolds of real semi-simple Lie groups, which include the tangent bundle and also stable bundles of certain gradient flows. Closed formulas, in terms of roots, are provided.
Experimentation and conjectures in the real Schubert calculus for flag manifolds  [PDF]
James Ruffo,Yuval Sivan,Evgenia Soprunova,Frank Sottile
Mathematics , 2005,
Abstract: The Shapiro conjecture in the real Schubert calculus, while likely true for Grassmannians, fails to hold for flag manifolds, but in a very interesting way. We give a refinement of the Shapiro conjecture for the flag manifold and present massive (15.76 gigahertz-years) computational experimentation in support of this refined conjecture. We also prove the conjecture in some special cases using discriminants and establish relationships between different cases of the conjecture.
Orbits of real forms in complex flag manifolds  [PDF]
Andrea Altomani,Costantino Medori,Mauro Nacinovich
Mathematics , 2006,
Abstract: We study, from the point of view of CR geometry, the orbits M of a real form G of a complex semisimple Lie group G in a complex flag manifold G/Q. In particular we characterize those that are of finite type and satisfy some Levi nondegeneracy conditions. These properties are also graphically described by attaching to them some cross-marked diagrams that generalize those for minimal orbits that we introduced in a previous paper. By constructing canonical fibrations over real flag manifolds, with simply connected complex fibers, we are also able to compute their fundamental group.
Some real and unreal enumerative geometry for flag manifolds  [PDF]
Frank Sottile
Mathematics , 2000,
Abstract: We present a general method for constructing real solutions to some problems in enumerative geometry which gives lower bounds on the maximum number of real solutions. We apply this method to show that two new classes of enumerative geometric problems on flag manifolds may have all their solutions be real and modify this method to show that another class may have no real solutions, which is a new phenomenon. This method originated in a numerical homotopy continuation algorithm adapted to the special Schubert calculus on Grassmannians and in principle gives optimal numerical homotopy algorithms for finding explicit solutions to these other enumerative problems.
Equivariant cohomology of real flag manifolds  [PDF]
Augustin-Liviu Mare
Mathematics , 2004,
Abstract: Let $P=G/K$ be a semisimple non-compact Riemannian symmetric space, where $G=I_0(P)$ and $K=G_p$ is the stabilizer of $p\in P$. Let $X$ be an orbit of the (isotropy) representation of $K$ on $T_p(P)$ ($X$ is called a real flag manifold). Let $K_0\subset K$ be the stabilizer of a maximal flat, totally geodesic submanifold of $P$ which contains $p$. We show that if all the simple root multiplicities of $G/K$ are at least 2 then $K_0$ is connected and the action of $K_0$ on $X$ is equivariantly formal. In the case when the multiplicities are equal and at least 2, we will give a purely geometric proof of a formula of Hsiang, Palais and Terng concerning $H^*(X)$. In particular, this gives a conceptually new proof of Borel's formula for the cohomology ring of an adjoint orbit of a compact Lie group.
Geodesics and Normal Sections on Real Flag Manifolds
Sánchez,Cristián U.; Giunta,Ana M.; Tala,José E.;
Revista de la Uni?3n Matem??tica Argentina , 2007,
Abstract: in the present paper we study riemannian and canonical geodesics in a real flag manifold m, considered as curves in the ambient euclidean space of the natural embedding of m.
Experimentation and conjectures in the real Schubert calculus for flag manifolds (extended abstract)  [PDF]
James Ruffo,Yuval Sivan,Evgenia Soprunova,Frank Sottile
Mathematics , 2005,
Abstract: The Shapiro conjecture in the real Schubert calculus fails to hold for flag manifolds, but in a very interesting way. In this extended abstract, we give a refinement of that conjecture for the flag manifold and present massive experimentation (over 12 GigaHertz-Years) that supports our refined conjecture. We also establish relationships between different cases of the conjecture and describe some new phenomena uncovered in this experimentation.
Orbits of real forms in complex flag manifolds  [PDF]
Andrea Altomani,Costantino Medori,Mauro Nacinovich
Mathematics , 2007,
Abstract: We investigate the $CR$ geometry of the orbits $M$ of a real form $G_0$ of a complex simple group $G$ in a complex flag manifold $X=G/Q$. We are mainly concerned with finite type, Levi non-degeneracy conditions, canonical $G_0$-equivariant and Mostow fibrations, and topological properties of the orbits.
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