Construction of Nodal Bubbling Solutions for the Weighted Sinh-Poisson Equation
Abstract
We consider the weighted sinh-Poisson equation Δu + 2ε2|x|2αsinh u = 0 in B1(0), u = 0 on ∂B1(0), where ε > 0 is a small parameter, α ∈ (−1, +∞)∖{0}, and B1(0) is a unit ball in ℝ2. By a constructive way, we prove that for any positive integer m, there exists a nodal bubbling solution uε which concentrates at the origin and the other m-points , l = 2, …, m + 1, such that as ε → 0, , where λ ∈ (0,1) and m is an odd integer with (1 + α)(m + 2) − 1 > 0, or m is an even integer. The same techniques lead also to a more general result on general domains.
1. Introduction
Theorem 1. For any positive integer m, there exists a nodal solution uε to problem (5) which concentrates at the origin and the other m-points , l = 2, …, m + 1, such that as ε → 0,
Definition 2 (see [41].)We say that q* is a C0-stable critical point of in Λk,m if for any sequence of functions ψj such that uniformly on the compact subsets of Λk,m, ψj has a critical point ξj such that .
In particular, if q* is a strict local maximum or minimum point of , q* is a C0-stable critical point of .
Theorem 3. Assume that {n, k, m} ⊂ ℕ ∪ {0} and is a C0-stable critical point of in Λk,m with k + m ≥ 1. Then, for any sufficiently small ε > 0, there exists different points qε,l ∈ Ω′∖Γ, l ∈ J2 ∪ J3, away from ∂Ω ∪ Γ, so that problem (11), for ql = qε,l, l ∈ J2, has a nodal solution uε such that as ε → 0,
Besides, uε remains uniformly bounded on for any δ > 0, and for any points ql, l ∈ J1, and , as ε → 0,
Note that for the case n = 1 and k = 0 (or n = k = 0), Theorem 3 was partly proved in [12] (or [25]) only when c(x) = 1 and αl ∈ (0, +∞)∖ℕ, l ∈ J1. In contrast with the results of [12, 25], this theorem provides a more complex concentration phenomenon involving the existence of changing-sign solutions for problem (11) with both positive and negative bubbles near the singular sources ql, l ∈ J1 ∪ J2, and some other discrete points. Unlike the concentration set in [12] only contains singular sources ql with αl ∈ (0, +∞)∖ℕ and l ∈ J1, and no singular source points in the domain, our concentration set also contains some singular sources ql with αl ∈ (−1,0) and l ∈ J1, except for singular sources ql, l ∈ J2, where concentration points and singular sources coincide at the limit. As for the latter exception, which till now is a similar but very simple concentration phenomenon it appears only in [38] for the study of the Liouville equation with a singular source of integer multiplicity.
In order to obtain multiple sign-changing blow up solutions of problem (11), we use a Lyapunov-Schmidt finite-dimensional reduction scheme and convert the problem into a finite-dimensional one, for a suitable asymptotic reduced energy, related to in (12). Thus, a stable critical point of leads to the existence of multiple sign-changing blow up solutions to (11). However, in view of different signs of Green’s functions in (12), it seems very difficult to find out a stable critical point of for a general bounded domain Ω. A simple approach can help us to overcome this difficulty by imposing the very strong symmetry condition on the domain of the problem, namely, we use the symmetry of the unit ball B1(0) to reduce the problem of finding solutions of (5) to that of finding an absolute minimum point of f(λ) defined in (8), and so we get the existence of nodal bubbling solutions for (5) in Theorem 1. On the other hand, motivated by the obtained results in [23], we believe that Theorem 1 should be valid for a general domain than a unit ball. More precisely, we suspect that, if 0 ∈ Ω and Ω is symmetric with respect to the origin, it is possible to construct a family of sign-changing blow up solutions whose maxima and minima are located alternately at the origin and the vertices of a regular polygon, and so Theorem 1 will be a consequence of this general result.
2. Construction of the Approximate Solution
3. The Linearized Problem and the Nonlinear Problem
Our main interest in this problem is its bounded solvability for any h ∈ 𝒞*, uniform in small ε and points q ∈ Λk,m(δ), as the following result states.
Proposition 4. There exist positive numbers ε0 and C such that for any h ∈ 𝒞*, there is a unique solution ϕ ∈ L∞(Ωε), scalars cij ∈ ℝ, i ∈ J2 ∪ J3, j = 1,2, to problem (38) for all ε < ε0 and points q ∈ Λk,m(δ), which satisfies
Moreover, the map q′ ↦ ϕ is C1, precisely for l ∈ J2 ∪ J3, s = 1,2,
We begin by stating a priori estimate for solutions of (38) satisfying orthogonality conditions with respect to Zi0, i ∈ J1, and Zij, i ∈ J2 ∪ J3, j = 0,1, 2.
Lemma 5. There exist positive numbers ε0 and C such that for any points q ∈ Λk,m(δ), h ∈ 𝒞* and any solution ϕ to the following equation:
Proof. We have the following steps.
Step 1. We first construct a suitable barrier. To realize it, we claim that for ε > 0 small enough, there exist Rd > 0 and
Thus, we have 1/2 ≤ g1i(y) ≤ 1, and
By (32),
So, if d is taken small and fixed, by (47)-(48), it follows that for |zi | ≥ Rd,
Let be a positive, bounded solution of in Ω and on ∂Ω. Set . Then, g2 is a positive, uniformly bounded function in Ωε such that
Consider
Step 2. Consider the following “inner norm”:
Let us claim that there exists a constant C3 > 0, such that
Let us take
From the maximum principle, it follows that on , which provides the estimate (53).
Step 3. We prove the priori estimate (43) by contradiction. Let us assume the existence of a sequence εj → 0, and points , functions hj with , solutions ϕj with , such that (41)-(42) hold. From the estimate (53), for some κ > 0, namely, for some i. To simplify the notation, let us denote ε = εj and . Set and . By (32), satisfies
We will give next a priori estimate for the solutions of (41) satisfying orthogonality conditions with respect to Zij, i ∈ J2 ∪ J3, j = 1,2.
Lemma 6. There exist positive numbers ε0 and C such that for any points q ∈ Λk,m(δ), h ∈ 𝒞* and any solution ϕ to (41) with the following orthogonality conditions:
Proof. Consider the radial solution , for the following equation:
Let η1 and η2 be radial smooth cut-off functions on ℝ2 so that
Set
Besides, let us define
Thus,
Multiplying (69) by , and integrating by parts, it follows that
Let us claim that for , there exists some constant C > 0 independent of ε, such that
Once these estimates (73)-(74) are proven, it easily follows that
This, together with (65), (70), and (73), easily gives the estimate (60) of ϕ.
Proofs of (73) and (74). Let us first define that
For ri : = |zi | ≤ R, by (32),
For R < ri ≤ R + 1, , 1 − ψi = O(1/|log ε|), and |∇ψi | = O(1/|log ε|). Then,
Furthermore,
Integrating by parts the first term of I2, it follows that
Integrating by parts the first term again, it also follows that
Then,
For R + 1 < ri ≤ δ(4viρi) −1, . Then,
Note that , |∇ψi| ≤ C/(|zi|log (1/ε)), and . Then,
Besides,
Some simple computations show that
Then, there exists some constant C > 0 independent of ε and R such that
For δ(4viρi) −1 < ri ≤ δ(viρi) −1, . Then,
Note that ψi = O(1/|log ε|), |∇ψi| = O(ρi/|log ε|), and . Then,
Furthermore,
As a result, the estimates (73)-(74) can be easily derived from (77)–(91).
Proof of Proposition 4. We first establish the a priori estimate (39). Testing (38) against η2iZij, i ∈ J2 ∪ J3, j = 1,2, and integrating by parts, it follows that
Observe that
Then,
Note that 〈h, η2iZij〉 = O(∥h∥*). This, together with (92)–(94), implies that
By (60),
Combining this with (95), we find that the a priori estimate (39) holds. Furthermore,
Next, we prove the solvability of problem (38). Consider the following Hilbert space:
By Fredholm’s alternative, this is equivalent to the uniqueness of solutions to this problem, which is guaranteed by (39). As a consequence, there exists a unique solution ϕ = T(h), scalars cij, i ∈ J2 ∪ J3, j = 1,2, for problem (38) with h ∈ 𝒞*, where T : 𝒞* ↦ L∞(Ωε) is a continuous linear map satisfying ∥T(h)∥∞ ≤ C(log (1/ε))∥h∥*.
Finally, we give the a priori estimate (40). Let us Differentiate (38) with respect to the parameters , l ∈ J2 ∪ J3, s = 1,2. Formally, should satisfy
We consider the constants bij, i ∈ J2 ∪ J3, j = 1,2, defined as
By (31), it follows that uniformly holds on Λk,m(δ), which implies that for i ∈ J2 ∪ J3, j = 1,2,
Define
We then have
Thus, can be uniquely expressed as
Furthermore, elliptic regularity theory implies that ϕ = T(h) is differentiable with respect to , l ∈ J2 ∪ J3, s = 1,2. Note that , , , and for i ≠ l. This, together with (39) and (97)–(106), implies that
The following result can be proved through arguments similar to these of [39].
Proposition 7. There exist positive numbers ε0 and C such that for any ε < ε0 and points q ∈ Λk,m(δ), there is a unique solution ϕ ∈ L∞(Ωε), scalars cij ∈ ℝ, i ∈ J2 ∪ J3, j = 1,2, of problem (108), which satisfies
Moreover, the map q′ ↦ ϕ is C1, precisely for l ∈ J2 ∪ J3, s = 1,2,
4. Variational Reduction
Lemma 8. For any points q ∈ Λk,m(δ), the functional Fε(q) is of class C1. Moreover, for ε > 0 small enough, if DqFε(q) = 0, then points q ∈ Λk,m(δ) satisfy (112).
Proof. Observe that for l ∈ J2 ∪ J3, s = 1,2,
Then, if DqFε(q) = 0, we have
Set
A simple computation shows that
This, together with the estimate (110) of , implies that
Set
Thus, (116) can be rewritten as: for any l ∈ J2 ∪ J3, s = 1,2,
This is a diagonal dominant system and we thus get cij = 0 for all i, j.
Next, we give a precise asymptotic expansion of Fε(q) defined in (113).
Lemma 9. The following precise asymptotic expansion holds
Proof. Let us first give a priori estimate of θε(q), where θε(q) = Fε(q) − Jε(Vq). Using DJε(Vq + ϕ)[ϕ] = 0, a Taylor expansion and an integration by parts, it follows that
Note that , , and = O(∥ϕ∥∞). These, together with (109), imply that θε(q) = O(ρ2 | log ε|), and so Fε(q) = Jε(Vq) + O(ρ2 | log ε|).
Next, we only need to give an asymptotic expansion of Jε(Vq). Observe that
By (22),
Note that
Then, for any i ≠ j, by (128)–(130),
By (128),
Making the complex changes of variables with , we get
On the other hand, by (128)-(129), we have
Besides, by (32),
Using the choice for μi’s by (31), together with (125), (135), and (136), it follows that
This, together with (12), easily gives the asymptotic expansion (123) of Fε(q).
5. Proofs of Theorems
Proof of Theorem 3. According to Lemma 8, we only need to find a critical point of the function, consider
By (123), uniformly holds on Λk,m(δ). By Definition 2, there exists a critical point qε of Fε such that . Moreover, up to a subsequence, there exists points such that as ε → 0, and . Thus, is a family of solutions of problem (25) (or (27)). Set for any x ∈ Ω. As a result, uε is a family of solutions of problem (11) with the qualitative properties predicted by the theorem, as it can be easily shown.
Proof of Theorem 1. Set q1 = (0,0), c(x) = 1, and al = (−1) l−1 for l = 1, …, m + 1. If α ∈ ℕ,
We will seek a nodal solution for problem (5) with the concentration points 0 and , l = 2, …, m + 1. Note that
By Theorem 3, we can reduce the problem of finding solutions of (5) to that of finding a C0-stable critical point of the function f(λ):(0,1) → ℝ defined in (8). Obviously, lim λ→0+f(λ) = lim λ→1−f(λ) = +∞, which implies that f(λ) has an absolute minimum point λ0 in (0,1). Then, λ0 is a C0-stable critical point of f(λ).
Conflict of Interests
The authors declare that there is no conflict of interests regarding the publication of this paper.
Acknowledgments
We would like to thank the anonymous referees for their helpful comments which improved this paper. This research is supported by the National Natural Science Foundation of China (Grant no. 11171214) and the foundation of Nanjing Agricultural University (Grant no. LXYQ201300106).
Appendix
Proofs of (32) and (33). For |zi | ≤ δ(viρi) −1, by (22)-(23),
Furthermore, for |zi | ≤ δ(viρi) −1, a direct computation shows that
Similarly, for |zi | ≤ δ(viρi) −1,
On the other hand, if |zi | ≥ δ(viρi) −1, for any , it is easy to check that
This, together with (A.3), implies (32).
Next, by our definitions,
So, if |zi | ≥ δ(viρi) −1, for all i,
As a result, combining (A.4)-(A.5) with (A.7)-(A.8), we get (33).