Journal of High Energy Physics

, 2018:94 | Cite as

Tensor bounds on the hidden universe

  • Adrián del Rio
  • Ruth Durrer
  • Subodh P. PatilEmail author
Open Access
Regular Article - Theoretical Physics


During single clock inflation, hidden fields (i.e. fields coupled to the inflaton only gravitationally) in their adiabatic vacua can ordinarily only affect observables through virtual effects. After renormalizing background quantities (fixed by observations at some pivot scale), all that remains are logarithmic runnings in correlation functions that are both Planck and slow roll suppressed. In this paper we show how a large number of hidden fields can partially compensate this suppression and generate a potentially observable running in the tensor two point function, consistently inferable courtesy of a large N resummation. We detour to address certain subtleties regarding loop corrections during inflation, extending the analysis of [1]. Our main result is that one can extract bounds on the hidden field content of the universe from bounds on violations of the consistency relation between the tensor spectral index and the tensor to scalar ratio, were primordial tensors ever detected. Such bounds are more competitive than the naive bound inferred from requiring inflation to occur below the strong coupling scale of gravity if deviations from the consistency relation can be bounded to within the sub-percent level. We discuss how one can meaningfully constrain the parameter space of various phenomenological scenarios and constructions that address naturalness with a large number of species (such as ‘N-naturalness’) with CMB observations up to cosmic variance limits, and possibly future 21cm and gravitational wave observations.


Cosmology of Theories beyond the SM Renormalization Regularization and Renormalons 


Open Access

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Copyright information

© The Author(s) 2018

Authors and Affiliations

  • Adrián del Rio
    • 1
  • Ruth Durrer
    • 2
  • Subodh P. Patil
    • 3
    Email author
  1. 1.Departamento de Fisica Teorica, IFIC. Centro Mixto Universidad de Valencia-CSIC, Facultad de FisicaUniversidad de ValenciaValenciaSpain
  2. 2.Dept. of Theoretical PhysicsUniversity of GenevaGeneva-4Switzerland
  3. 3.Niels Bohr International Academy and Discovery Center, Niels Bohr InstituteCopenhagenDenmark

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