ScalingStacks

6.3 Other examples of solutions to ( 32 ) and ( 33 ) [03LS]

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6.3 Other examples of solutions to (32) and (33)

The functions u,vu,v of Propositions 6.7 and 6.8 provide examples of explicit solutions of equations (32) and (33). Here are some more examples of solutions to (32) and (33). The author constructed them by choosing a particular form for u,vu,v involving arbitrary functions of only one variable, and solving the resulting o.d.e.s.

Example 6.9 Let α,b,c∈ℝ\alpha,b,c\in\mathbin{\mathbb{R}} and define u⁡(x,y)=α​y+bu(x,y)=\alpha y+b and v⁡(x,y)=α​x+cv(x,y)=\alpha x+c. Then u,vu,v satisfy (33) for any value of aa. The corresponding special Lagrangian 3-folds are the result of applying a diagonal SU(3)\mathop{\rm SU}(3) matrix to one of the fibres of the fibration of Corollary 4.2.

The next example uses the idea that if u⁡(x)=12​y2​g​(x)−(2​g​(x))−1u(x)={\textstyle\frac{1}{2}}y^{2}g(x)-(2g(x))^{-1} for some function g>0g>0, then (u2+y2)1/2=12​y2​g​(x)+(2​g​(x))−1(u^{2}+y^{2})^{1/2}={\textstyle\frac{1}{2}}y^{2}g(x)+(2g(x))^{-1}. This simplifies (32).

Example 6.10 Define u⁡(x,y)=12​y2​sech2x−12​cosh2⁡xu(x,y)={\textstyle\frac{1}{2}}y^{2}{\textstyle\mathop{\rm sech}}^{2}x-{\textstyle\frac{1}{2}}\cosh^{2}x and v⁡(x,y)=y​tanh⁡xv(x,y)=y\tanh x. Then uu and vv satisfy (32). Equation (31) with a=0a=0 defines an explicit nonsingular special Lagrangian 3-fold NN in ℂ3\mathbin{\mathbb{C}}^{3}. It can be shown that NN is ruled, and arises from Harvey and Lawson’s ‘austere submanifold’ construction [9, §III.3.C] of SL mm-folds in ℂm\mathbin{\mathbb{C}}^{m}, as the normal bundle of a catenoid in ℝ3\mathbin{\mathbb{R}}^{3}.

The following example assumes that u⁡(x,y)=y​g​(x)u(x,y)=y\,g(x) for some nonzero gg.

Example 6.11 Define u⁡(x,y)=−y​sinh⁡2​xu(x,y)=-y\sinh 2x and v=y−12​cosh⁡2​xv=y-{\textstyle\frac{1}{2}}\cosh 2x on the half-plane y⩾0y\geqslant 0 in ℝ2\mathbin{\mathbb{R}}^{2}. Then u,vu,v satisfy (32). So equation (31), with the additional condition that y=Im(z1​z2)⩾0y=\mathop{\rm Im}(z_{1}z_{2})\geqslant 0, defines an explicit special Lagrangian 3-fold NN in ℂ3\mathbin{\mathbb{C}}^{3}. It turns out (surprisingly) that NN is nonsingular, and is equivalent to one of the SL 3-folds constructed in [12, Ex. 7.4] by evolving paraboloids in ℂ3\mathbin{\mathbb{C}}^{3}.

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