Gadha Lekshmi P
Author directory2026
Geometric Separation Without Functional Specialization: Auditing Subspace Disentanglement in Dual-Encoder LLM Paraphrase Detection
Govind Arun | Ashish Abraham | Gadha Lekshmi P
Proceedings of the Seventh Workshop on Insights from Negative Results in NLP
Govind Arun | Ashish Abraham | Gadha Lekshmi P
Proceedings of the Seventh Workshop on Insights from Negative Results in NLP
Explicit subspace disentanglement, enforcing orthogonality and simplex constraints on learned projections, is an increasingly common recipe for paraphrase models claimed to separate lexical, syntactic, and semantic information. A dual-encoder hierarchical model trained with these constraints on the DiPPer corpus of LLM-generated paraphrases produces near-perfect geometric separation, a pairwise Centered Kernel Alignment (CKA) of roughly 0.0007, yet that separation is not evidence of functional linguistic specialization. Three results establish this. First, near-zero CKA is largely preordained by an explicit orthogonality penalty, which converges to 4×10-6. Second, each of the three subspaces, including the nominally syntactic one for which we identify no functional probe, classifies paraphrase in isolation at F1 above 0.986, so the subspaces are not functionally distinct. Third, removing disentanglement at matched capacity costs only 0.013 F1, leaving most of the reported gain attributable to dual-encoder capacity rather than disentanglement. Capacity-matched ablations and controlled functional probes, not CKA alone, are required to substantiate disentanglement claims; orthogonality penalties otherwise manufacture the very metric used to certify them.