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Invariant differential operator
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Invariant differential operator : ウィキペディア英語版
Invariant differential operator
In mathematics and theoretical physics, an invariant differential operator is a kind of mathematical map from some objects to an object of similar type. These objects are typically functions on \mathbb^n, functions on a manifold, vector valued functions, vector fields, or, more generally, sections of a vector bundle.
In an invariant differential operator D, the term ''differential operator'' indicates that the value Df of the map depends only on f(x) and the derivatives of f in x. The word ''invariant'' indicates that the operator contains some symmetry. This means that there is a group G with a group action on the functions (or other objects in question) and this action is preserved by the operator:
:D(g\cdot f)=g\cdot (Df).
Usually, the action of the group has the meaning of a change of coordinates (change of observer) and the invariance means that the operator has the same expression in all admissible coordinates.
==Invariance on homogeneous spaces==
Let ''M'' = ''G''/''H'' be a homogeneous space for a Lie group G and a Lie subgroup H. Every representation \rho:H\rightarrow\mathrm(\mathbb) gives rise to a vector bundle
:V=G\times_\mathbb\;\text\;(gh,v)\sim(g,\rho(h)v)\;\forall\;g\in G,\;h\in H\;\text\;v\in\mathbb.
Sections \varphi\in\Gamma(V) can be identified with
:\Gamma(V)=\)\varphi(g)\;\forall\;g\in G,\; h\in H\}.
In this form the group ''G'' acts on sections via
:(\ell_g \varphi)(g')=\varphi(g^g').
Now let ''V'' and ''W'' be two vector bundles over ''M''. Then a differential operator
:d:\Gamma(V)\rightarrow\Gamma(W)
that maps sections of ''V'' to sections of ''W'' is called invariant if
:d(\ell_g \varphi) = \ell_g (d\varphi).
for all sections \varphi in \Gamma(V) and elements ''g'' in ''G''. All linear invariant differential operators on homogeneous parabolic geometries, i.e. when ''G'' is semi-simple and ''H'' is a parabolic subgroup, are given dually by homomorphisms of generalized Verma modules.

抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)
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