Multiple positive solutions with prescribed masses for a coupled Schr\"odinger system: mass mixed and Sobolev critical coupled case
Pith reviewed 2026-05-08 01:57 UTC · model grok-4.3
The pith
For small positive coupling ν the Sobolev-critical coupled Schrödinger system admits two distinct positive solutions with fixed L2 masses, one a local minimizer and one a mountain-pass solution.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
The system admits two positive solutions (u, v, λ1, λ2) in H^1(R^N, R^2) × R^2 for all N ≥ 3 when ν is small enough. One solution is realized as a local minimizer on the constraint set and the other as a mountain-pass critical point. The new interaction estimates control the cross terms sufficiently to produce the required geometry and to guarantee strict positivity without any auxiliary conditions on p, q or N.
What carries the argument
New technical lemmas on interaction estimates between the components that bound the critical cross term and permit verification of mountain-pass geometry together with positivity.
Load-bearing premise
The new interaction estimates between the two components are valid and sufficient to produce the mountain-pass geometry and positivity without extra restrictions on the exponents or dimension.
What would settle it
A concrete choice of p, q, α, β satisfying the mass-mixed and critical-coupling conditions for which the mountain-pass critical value fails to produce a second positive solution when ν is taken arbitrarily small.
read the original abstract
The aim of this paper is to establish multiple positive normalized solutions $(u,v,\lambda_1,\lambda_2)\in H^1(\mathbb{R}^N,\mathbb{R}^2)\times \mathbb{R}^2$ to the following coupled Schr\"odinger system involving Sobolev critical exponent: $$ \begin{cases} -\Delta u+\lambda_1 u=\mu_1|u|^{p-2}u+\nu\alpha|u|^{\alpha-2}u|v|^\beta, x\in \mathbb{R}^N,\\ -\Delta v+\lambda_2 v=\mu_2|v|^{q-2}v+\nu\beta|v|^{\beta-2}v|u|^\alpha, x\in \mathbb{R}^N,\\ \int_{\mathbb{R}^N}|u|^2\mathrm{d}x=a, \int_{\mathbb{R}^N}|v|^2\mathrm{d}x=b, \end{cases} N\geq 3, $$ where $\mu_1,\mu_2, \nu, a, b>0$. We are particularly interested in the mass mixed case that $2<p, q<2+\frac{4}{N}, \alpha>1, \beta>1$, and $\alpha+\beta=2^*:=\frac{2N}{N-2}$. For sufficiently small $\nu>0$, we demonstrate that the above system admits two positive solutions, one of which serves as a local minimizer, and the other as a mountain pass solution. By developing some new technical lemmas on the interaction estimates, we are managed to resolves Soave's open problem [{\it J. Funct. Anal.}, 2020, Remark 1.1] within the context of the system case. Notably, our existence result holds true for all dimensions $N\geq 3$. Our results also significantly extend the result of Gou and Jeanjean [{\it Nonlinearity}, 2018, Theorem 1.1] to the Sobolev critical coupled case and removing the hypothesis ``either $p,q\leq \alpha+\beta-\frac{2}{N}$ or $|p-q|\leq \frac{2}{N}$" for $N\geq 5$. Additionally, we also establish a sequence of properties for the local minimizer, including local uniqueness, continuity with respect to the small parameter $\nu$, and the limiting profiles for $\nu\rightarrow 0^+$.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript proves existence of two positive normalized solutions (u,v) to a coupled Schrödinger system with Sobolev-critical coupling term ν|u|^{α-2}u|v|^β (and symmetric) under L²-mass constraints ∫|u|²=a, ∫|v|²=b. For all N≥3 and sufficiently small ν>0 in the mass-mixed regime 2<p,q<2+4/N with α+β=2*, one solution is obtained as a local minimizer and the second via mountain-pass geometry. The argument relies on new interaction estimates to control the cross term, establish the mountain-pass level below the compactness threshold, and guarantee positivity. Additional properties of the local minimizer (local uniqueness, continuity in ν, and limiting profiles as ν→0) are derived. The results resolve Soave’s open problem in the system setting and remove the exponent restrictions of Gou–Jeanjean for N≥5.
Significance. If the new interaction estimates hold uniformly, the result is significant: it supplies the first complete existence theory for the critical coupled case without auxiliary restrictions on p,q, supplies the missing system analogue of Soave’s scalar result, and includes a detailed asymptotic analysis as ν→0. The variational construction with explicit control of the cross term is a technical advance that could apply to other critical systems.
major comments (1)
- [New technical lemmas on interaction estimates (referenced in the abstract and used throughout §§3–5)] The mountain-pass geometry and positivity rest entirely on the new interaction estimates for ∫|u|^α|v|^β under the L² constraints (used to keep the mountain-pass value strictly below the compactness threshold and to prevent sign-changing solutions). These estimates must be shown to remain uniform when p or q approaches the upper mass-subcritical bound 2+4/N or when the supports of the limiting profiles become separated; loss of uniformity would allow the critical value to reach or exceed the threshold, destroying both existence and the positivity claim. The manuscript should supply the precise statement of these lemmas together with the key estimates that guarantee uniformity in the critical case.
minor comments (2)
- [Introduction] The abstract states that the result holds for all N≥3; the introduction should explicitly recall the precise statement of Soave’s open problem (Remark 1.1) and the exact hypothesis removed from Gou–Jeanjean (Theorem 1.1) so that the improvement is immediately visible.
- [Section on properties of the local minimizer] Notation for the limiting profiles as ν→0 should be introduced once and used consistently when stating the local-uniqueness and continuity properties of the local minimizer.
Simulated Author's Rebuttal
We thank the referee for the careful reading and constructive feedback on our manuscript. We address the major comment below and will revise the paper to enhance the presentation of the technical results.
read point-by-point responses
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Referee: [New technical lemmas on interaction estimates (referenced in the abstract and used throughout §§3–5)] The mountain-pass geometry and positivity rest entirely on the new interaction estimates for ∫|u|^α|v|^β under the L² constraints (used to keep the mountain-pass value strictly below the compactness threshold and to prevent sign-changing solutions). These estimates must be shown to remain uniform when p or q approaches the upper mass-subcritical bound 2+4/N or when the supports of the limiting profiles become separated; loss of uniformity would allow the critical value to reach or exceed the threshold, destroying both existence and the positivity claim. The manuscript should supply the precise statement of these lemmas together with the key estimates that guarantee uniformity in the critical case.
Authors: We agree that the interaction estimates are fundamental to establishing the mountain-pass geometry, the strict inequality below the compactness threshold, and the positivity of solutions. These estimates are derived in Section 3 using the mass-subcritical assumption on p and q together with the critical coupling α + β = 2*. In the revised manuscript we will state the relevant lemmas (currently embedded in the proofs of Propositions 3.3 and 4.1) explicitly as standalone results, including the precise uniformity statements: the constants remain independent of p, q ∈ (2, 2 + 4/N) and of the separation distance between the supports of the limiting profiles. The uniformity follows from the strict subcriticality of the mass terms (which controls the L^{2+4/N} norms) combined with a careful cut-off argument that prevents the cross term from reaching the critical threshold. We will also add a short remark explaining why the estimates do not degenerate at the boundary of the parameter range. These additions will make the dependence on the new lemmas fully transparent. revision: yes
Circularity Check
Derivation self-contained via new interaction estimates and variational methods
full rationale
The paper establishes existence of two positive normalized solutions for small ν>0 by constructing a local minimizer and a mountain-pass critical point in the constrained variational setting. The key new ingredient consists of technical lemmas providing interaction estimates for the cross term ∫|u|^α|v|^β under L²-mass constraints; these lemmas are developed independently to control the mountain-pass level below the compactness threshold and to ensure positivity, without reducing the existence statement to a quantity defined by the same construction. No parameters are fitted to data, no ansatz is smuggled via self-citation, and the cited prior results (Soave, Gou-Jeanjean) serve as external benchmarks rather than load-bearing self-referential steps. The argument therefore remains non-circular.
Axiom & Free-Parameter Ledger
axioms (2)
- standard math Sobolev embeddings and the definition of the critical exponent 2*
- standard math Existence of local minimizers and mountain-pass critical points on the constraint manifold
Reference graph
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