CFTs blueshift tensor fluctuations universally

• Published in: Journal of cosmology and astroparticle physics Vol. 2022; no. 7; pp. 34 - 58
• Main Authors: Baumgart, Matthew, Heckman, Jonathan J., Thomas, Logan
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 01.07.2022; Institute of Physics (IOP)
• Subjects: Astronomical models; Cosmology; Fluctuations; Gravitational waves; gravitational waves and CMBR polarization; Gravitons; Inflation and CMBR theory; Mathematical analysis; Particle physics; PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; power spectrum; primordial gravitational waves (theory); Symmetry; Tensors
• ISSN: 1475-7516; 1475-7516
• DOI: 10.1088/1475-7516/2022/07/034

Abstract 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 ∼10 15 , 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.