Large language models (LLMs) increasingly shape how consumers discover and evaluate brands. Brand portfolio theory predicts that revealing corporate ownership should produce perceptual interference via an awareness gate (Keller 1993; Aaker and Keller 1990). Yet LLMs encode portfolio relationships permanently in their parameters, raising the possibility of either maximal interference or complete immunity. We test these hypotheses in a preregistered experiment with 13 LLMs spanning seven training traditions (Western, Chinese, Russian, Indian, Japanese, European, Korean). Twenty brands from seven portfolio archetypes (LVMH, Unilever, P&G, Toyota, L'Oreal, Geely, Yandex) were rated under four prompt modalities – direct rating, naturalistic recommendation, multi-turn conversation with mid-dialogue portfolio reveal, and native-language framing – yielding 7,975 parsed observations. Portfolio framing produces near-zero change in Dimensional Concentration Index (mean |delta DCI| = .26). Equivalence testing confirms the null for 18/20 brands within +/-1.0 DCI points. Multi-turn revelation unlocks modest flattening for reverse-aspiration structures (Geely Auto d = -1.11, FDR-significant), but effects remain portfolio- and modality-specific rather than systematic. Native-language prompts activate model-specific discourse layers without directional amplification. These results generalize spectral immunity across model traditions and portfolio types, implying that house-of-brands shielding is automatic in AI-mediated markets while constructive interference is impossible. Brand managers cannot rely on portfolio architecture to reshape LLM perceptions except in extended conversational contexts. Theoretical implications for awareness-gate mechanisms and practical implications for "Share of Model" strategy are discussed. Includes paper.yaml (Paper Spec v0.1.0) – a machine-readable specification of the paper's claims, assumptions, and dependencies. See https://github.com/spectralbranding/paper-spec for the standard.
Dmitry Zharnikov (Tue,) studied this question.