We express two CR invariant surface area elements in terms of quantities in pseudohermitian geometry. We deduce the Euler-Lagrange equations of the associated energy functionals. Many solutions are given and discussed. In relation to the singular CR Yamabe problem, we show that one of the energy functionals appears as the coefficient (up to a constant multiple) of the log term in the associated volume renormalization.So they are minimizers for E 1 with zero energy. See Example 2 in Subsection 4.1.Conjecture 1 The shifted Heisenberg spheres are the only closed minimizers for E 1 (with zero energy) in H 1 .On the other hand, usual distance spheres (or Heisenberg spheres) defined by r 4 + 4t 2 = ρ 4 0 (ρ 0 > 0) are critical points of higher energy level for E 1 . See the remark in the end of Example 3 of Subsection 4.1. Another interesting example is the Clifford torus in S 3 . It is a critical point of E 1 with positive energy.Conjecture 2 The Clifford torus is the unique minimizer among all surfaces of torus type for E 1 up to CR automorphisms of S 3 .Critical points of E 2 include vertical planes in H 1 , the surface defined by t = √ 3 2 r 2 in H 1 and surfaces foliated by a linear combination ofe 1 ande 2 (e 1 := ∂ x +y∂ t , e 2 := ∂ y − x∂ t ). We show that E 2 is unbounded from below and above in general. See the remark in the end of Example 3 of Subsection 4.2. 2115-M-001-013-and the National Center for Theoretical Sciences for the constant support. P. Yang would like to thank the NSF of the U.S. for the support of the grant: DMS 1509505. Y. Zhang would like to thank Proessor Alice Chang for her invitation and the Department of Mathematics of Princeton University for its hospitality. He is supported by CSC scholarship 201606345025 and the Fundamental Research Funds for the Central Universities. P. Yang thanks Sean Curry for posing this question.
Two CR invariant surface area elementsIn [1], the first author constructed two CR invariant area elements on a nonsingular (noncharacteristic) surface Σ in a strictly pseudoconvex CR 3-manifold (M, ξ, J). Here ξ denotes a contact bundle and J : ξ → ξ is an endomorphism such that J 2 = −Id. We recall ([3]) that a point p ∈ Σ is called singular if its tangent plane T p Σ coincides with the contact plane ξ p at p. We call a surface nonsingular if