Math 2.0

Several complex variables and analytic spaces Definition

Strongly pseudoconvex domain

Builds on Levi formLevi pseudoconvex domain

Definition

Let Ω⊆ℂn\Omega \subseteq \C^n be a domain with C2C^2 boundary, and let ρ\rho be a defining function of Ω\Omega. For p∈∂Ωp \in \partial\Omega, let HpH_p be the complex tangent space of ∂Ω\partial\Omega at pp. The domain Ω\Omega is strongly pseudoconvex if the Levi form of ∂Ω\partial\Omega is positive definite at every boundary point: ∑j,k=1n∂2ρ∂zj∂zˉk(p) wjwˉk>0for all p∈∂Ω and all w∈Hp∖{0}.\sum_{j,k=1}^{n} \frac{\partial^2 \rho}{\partial z_j \partial \bar z_k}(p)\, w_j \bar w_k > 0 \quad \text{for all } p \in \partial\Omega \text{ and all } w \in H_p \setminus \set{0}. A boundary point where this holds is a strongly pseudoconvex point.

Remarks

A strongly pseudoconvex domain is Levi pseudoconvex. Many authors also ask Ω\Omega to be bounded. Example: the unit ball, with ρ(z)=∣z∣2−1\rho(z) = \abs{z}^2 - 1, has Levi form ∣w∣2\abs{w}^2, which is positive for w≠0w \ne 0. Non-example: the domain {z∈ℂ2:∣z1∣2+∣z2∣4<1}\set{z \in \C^2 : \abs{z_1}^2 + \abs{z_2}^4 < 1} is Levi pseudoconvex but not strongly pseudoconvex. At p=(1,0)p = (1, 0), with ρ(z)=∣z1∣2+∣z2∣4−1\rho(z) = \abs{z_1}^2 + \abs{z_2}^4 - 1, the space HpH_p is {w:w1=0}\set{w : w_1 = 0} and Lρ(p;(0,w2))=4∣p2∣2∣w2∣2=0L_\rho(p; (0, w_2)) = 4 \abs{p_2}^2 \abs{w_2}^2 = 0. A bounded domain Ω\Omega with C2C^2 boundary is strongly pseudoconvex if and only if it has a defining function that is strictly plurisubharmonic near ∂Ω\partial\Omega. This means that Lρ(p;⋅)L_\rho(p; \cdot) is positive definite on all of ℂn\C^n, not only on HpH_p.

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  1. Levi form concept
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Further reading

  1. Web https://en.wikipedia.org/wiki/Pseudoconvexity
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MSC32T15, 32T05
DefinesStrongly pseudoconvex domain
UsesLevi form, Levi pseudoconvex domain

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