{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"a9afde8df441e9adfa5adb7da0911488cc114f1ad037b0b33a65ef1e3694031b","created":"2026-10-03T07:18:08Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"df22a31bc2a97030628f2cac8b8005a03d740e804e4c126ffbcc56a85f7478a8","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"identification","assisted_by":[],"external_id":"qft.cft-rg.lambda-point-alpha","kind":"phenomenon","literature_status":"contested","n":"1","parents":[],"plain":"The heat capacity of liquid helium near its superfluid transition was measured in orbit with high precision. Its critical exponent disagrees with the theoretical value by many error bars.","posed_since":"","precise":"The He-4 superfluid transition is in the 3D $O(2)$ universality class, with $\\alpha = 2 - 3\\nu$. The Space Shuttle measurement gives $\\alpha = -0.0127(3)$ (Lipa et al. 2003), while the conformal bootstrap gives $\\nu = 0.67175(10)$, i.e. $\\alpha = -0.01526(30)$ (Chester et al. 2020), in agreement with Monte Carlo; the tension is about 8 standard deviations. Determine whether the discrepancy comes from the experimental analysis (corrections to scaling, finite size, residual gravity), from the identification with the $O(2)$ fixed point, or from an error in theory.","problem_ref":null,"references":"","settled_by":"A new He-4 specific-heat measurement with independent systematics, or the identification of a specific error in the 2003 analysis or in the theoretical value.","status_note":"No new measurement as of 2025; resummation claims of agreement with experiment have not displaced the bootstrap and Monte Carlo value.","title":"Helium $\\lambda$-point heat-capacity exponent disagrees with 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