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5-step lesson. Step 1: 'The problem: Loop integrals in QFT diverge. Example: electron self-energy Σ(p) = ∫d⁴k [propagator × vertex × propagator] → ∫dk/k → ln(Λ) → ∞ as cutoff Λ→∞. Similarly: vacuum polarization, vertex correction. These shift the mass, charge, and field normalization by infinite amo

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