In complex geometry, a part of mathematics, the term Inoue surface denotes several complex surfaces of Kodaira class VII. They are named after Masahisa Inoue, who gave the first non-trivial examples of Kodaira class VII surfaces in 1974.
The Inoue surfaces are not Kähler manifolds.
Inoue surfaces with b2 = 0
Inoue introduced three families of surfaces, S0, S+ and S−, which are compact quotients of (a product of a complex plane by a half-plane). These Inoue surfaces are solvmanifolds. They are obtained as quotients of by a solvable discrete group which acts holomorphically on .
The solvmanifold surfaces constructed by Inoue all have second Betti number . These surfaces are of Kodaira class VII, which means that they have and Kodaira dimension . It was proven by Bogomolov, Li-Yau  and Teleman that any surface of class VII with b2 = 0 is a Hopf surface or an Inoue-type solvmanifold.
These surfaces have no meromorphic functions and no curves.
The Inoue surfaces are constructed explicitly as follows.
Of type S0
Let φ be an integer 3 × 3 matrix, with two complex eigenvalues and a real eigenvalue c>1, with . Then φ is invertible over integers, and defines an action of the group of integers on . Let . This group is a lattice in solvable Lie group
acting on , with the -part acting by translations and the -part as .
We extend this action to by setting , where t is the parameter of the -part of , and acting trivially with the factor on . This action is clearly holomorphic, and the quotient is called Inoue surface of type S0.
The Inoue surface of type S0 is determined by the choice of an integer matrix φ, constrained as above. There is a countable number of such surfaces.
Of type S+
Let n be a positive integer, and be the group of upper triangular matrices
where x, y, z are integers. Consider an automorphism of , denoted as φ. The quotient of by its center C is . We assume that φ acts on as a matrix with two positive real eigenvalues a, b, and ab = 1.
Consider the solvable group , with acting on as φ. Identifying the group of upper triangular matrices with , we obtain an action of on . Define an action of on with acting trivially on the -part and the acting as . The same argument as for Inoue surfaces of type shows that this action is holomorphic. The quotient is called Inoue surface of type .
Of type S−
Inoue surfaces of type are defined in the same way as for S+, but two eigenvalues a, b of φ acting on have opposite sign and satisfy ab = −1. Since a square of such an endomorphism defines an Inoue surface of type S+, an Inoue surface of type S− has an unramified double cover of type S+.
Parabolic and hyperbolic Inoue surfaces
Parabolic and hyperbolic Inoue surfaces are Kodaira class VII surfaces defined by Iku Nakamura in 1984. They are not solvmanifolds. These surfaces have positive second Betti number. They have spherical shells, and can be deformed into a blown-up Hopf surface.
Parabolic Inoue surfaces contain a cycle of rational curves with 0 self- intersection and an elliptic curve. They are a particular case of Enoki surfaces which have a cycle of rational curves with zero self- intersection but without elliptic curve. Half-Inoue surfaces contain a cycle C of rational curves and are a quotient of a hyperbolic Inoue surface with two cycles of rational curves.
Hyperbolic Inoue surfaces are class VII0 surfaces with two cycles of rational curves.
- M. Inoue, On surfaces of class VII0, Inventiones math., 24 (1974), 269–310.
- Bogomolov, F.: Classification of surfaces of class VII0 with b2 = 0, Math. USSR Izv 10, 255–269 (1976)
- Li, J., Yau, S., T.: Hermitian Yang-Mills connections on non-Kahler manifolds, Math. aspects of string theory (San Diego, Calif., 1986), Adv. Ser. Math. Phys. 1, 560–573, World Scientific Publishing (1987)
- Teleman, A.: Projectively flat surfaces and Bogomolov's theorem on class VII0-surfaces, Int. J. Math., Vol. 5, No 2, 253–264 (1994)
- Keizo Hasegawa Complex and Kahler structures on Compact Solvmanifolds, J. Symplectic Geom. Volume 3, Number 4 (2005), 749–767.
- I. Nakamura, On surfaces of class VII0 with curves, Inv. Math. 78, 393–443 (1984).
- I. Nakamura: Survey on VII0 surfaces, Recent Developments in NonKaehler Geometry, Sapporo, 2008 March.