Higgs-Dilaton cosmology: Are there extra relativistic species?

Abstract

Recent analyses of cosmological data suggest the presence of an extra relativistic component beyond the Standard Model content. The Higgs-Dilaton cosmological model predicts the existence of a massless particle -the dilaton- associated with the spontaneous symmetry breaking of scale invariance and undetectable by any accelerator experiment. Its ultrarelativistic character makes it a suitable candidate for contributing to the effective number of light degrees of freedom in the Universe. In this Letter we analyze the dilaton production at the (p)reheating stage right after inflation and conclude that no extra relativistic degrees of freedom beyond those already present in the Standard Model are expected within the simplest Higgs-Dilaton scenario. The elusive dilaton remains thus essentially undetectable by any particle physics experiment or cosmological observation.

7 pages, 1 figure, corrected typos; added references

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• Scale and Weyl Invariance in Einstein-Cartan Gravity
• Preheating in Einstein-Cartan Higgs Inflation: Oscillon formation
• Higgs inflation and its extensions and the further refining dS swampland conjecture
• Fifth forces and broken scale symmetries in the Jordan frame
• Higgs inflation and scalar weak gravity conjecture
• FeynMG: a FeynRules extension for scalar-tensor theories of gravity
• A particle's perspective on screening mechanisms
• Dark Horse, Dark Matter: Revisiting the SO(16)x SO(16)' Nonsupersymmetric Model in the LHC and Dark Energy Era
• No-scale Brans-Dicke Gravity -- ultralight scalar boson & heavy inflaton
• Higgs-dilaton model revisited: can dilaton act as QCD axion?
• Fifth forces and frame invariance
• Ephemeral Oscillons in Scalar-Tensor Theories: The Higgs-like case
• Higgs-Dilaton Inflation in Einstein-Cartan gravity
• Testing the Starobinsky model of inflation with resonant cavities