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Irreducible components of module varieties: projective equations and rationality. (English) Zbl 1262.16011

Ara, P. (ed.) et al., New trends in noncommutative algebra. A conference in honor of Ken Goodearl’s 65th birthday, Washington, Seattle, WA, USA, August 9–14, 2010. Providence, RI: American Mathematical Society (AMS) (ISBN 978-0-8218-5297-2). Contemporary Mathematics 562, 141-167 (2012).
Summary: We expand the existing arsenal of methods for exploring the irreducible components of the varieties \(\text{Rep}(A,\mathbf d)\) which parametrize the representations with dimension vector \(\mathbf d\) of a finite dimensional algebra \(A\). To do so, we move back and forth between \(\text{Rep}(A,\mathbf d)\) and a projective variety, \(\text{GRASS}(A,\mathbf d)\), parametrizing the same set of isomorphism classes of modules. In particular, we show the irreducible components to be accessible in a highly compressed format within the projective setting. Our results include necessary and sufficient conditions for unirationality, smoothness, and normality, followed by applications. Moreover, they provide equational access to the irreducible components of \(\text{GRASS}(A,\mathbf d)\) and techniques for deriving qualitative information regarding both the affine and projective scenarios.
For the entire collection see [Zbl 1232.16001].

MSC:

16G10 Representations of associative Artinian rings
16G20 Representations of quivers and partially ordered sets
14M20 Rational and unirational varieties
14L30 Group actions on varieties or schemes (quotients)