Preprint 12/2002

Connections on naturally reductive spaces, their Dirac operator and homogeneous models in string theory

Ilka Agricola

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Submission date: 12. Feb. 2002
Pages: 27
published in: Communications in mathematical physics, 232 (2003) 3, p. 535-563 
DOI number (of the published article): 10.1007/s00220-002-0743-y
MSC-Numbers: 53C27, 53C30
Keywords and phrases: kostant's dirac operator, naturally reductive space, invariant connection
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Given a reductive homogeneous space M=G/H endowed with a naturally reductive metric, we study the one-parameter family of connections formula11 joining the canonical and the Levi-Civita connection (t=0, 1/2). We show that the Dirac operator formula15 corresponding to t=1/3 is the so-called ``cubic' Dirac operator recently introduced by B. Kostant, and derive the formula for its square for any t, thus generalizing the classical Parthasarathy formula on symmetric spaces. Applications include the existence of a new G-invariant first order differential operator formula23 on spinors and an eigenvalue estimate for the first eigenvalue of formula25. This geometric situation can be used for constructing Riemannian manifolds which are Ricci flat and admit a parallel spinor with respect to some metric connection formula27 whose torsion formula29 is a 3-form, the geometric model for the common sector of string theories. We present some results about solutions to the string equations and give a detailed discussion of some 5-dimensional example.

03.07.2017, 01:40