CFTs blueshift tensor fluctuations universally

Matthew Baumgart, Jonathan J. Heckman, Logan Thomas

Research output: Contribution to journalArticlepeer-review

2 Scopus citations


The strong constraints of conformal symmetry cause any nearly-conformal sector to blueshift tensor fluctuations in cosmology. Hidden sectors with approximate conformal symmetry, which may be quite large, are a well-motivated extension of physics beyond the Standard Models of particle physics and cosmology. They can therefore lead to a detectable shift in the tensor tilt for next-generation CMB and gravitational wave experiments. We compute the leading-order contribution to the in-in graviton two-point function from virtual loops in such sectors to demonstrate this universal effect. In units where a single conformally-coupled scalar is 1, limits from Stage-IV CMB experiments could bound the size of this extra sector to be smaller than ∼1015, under a plausible calculational assumption backed by a simple power counting argument. This would be sufficient to rule out N-Naturalness as a complete resolution of the hierarchy problem.

Original languageEnglish (US)
Article number034
JournalJournal of Cosmology and Astroparticle Physics
Issue number7
StatePublished - Jul 1 2022


  • Inflation and CMBR theory
  • gravitational waves and CMBR polarization
  • power spectrum
  • primordial gravitational waves (theory)

ASJC Scopus subject areas

  • Astronomy and Astrophysics


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