Observing Left-Right Symmetry in the Cosmic Microwave Background

Abstract

We consider the possibility of probing left-right symmetric model (LRSM) via cosmic microwave background (CMB). We adopt the minimal LRSM with Higgs doublets, also known as the doublet left-right model (DLRM), where all fermions including the neutrinos acquire masses only via their couplings to the Higgs bidoublet. Due to the Dirac nature of light neutrinos, there exist additional relativistic degrees of freedom which can thermalise in the early universe by virtue of their gauge interactions corresponding to the right sector. We constrain the model from Planck 2018 bound on the effective relativistic degrees of freedom and also estimate the prospects for planned CMB Stage IV experiments to constrain the model further. We find that $W_R$ boson mass below 4.06 TeV can be ruled out from Planck 2018 bound at $2\sigma$ CL in the exact left-right symmetric limit which is equally competitive as the LHC bounds from dijet resonance searches. On the other hand Planck 2018 bound at $1\sigma$ CL can rule out a much larger parameter space out of reach of present direct search experiments, even in the presence of additional relativistic degrees of freedom around the TeV corner. We also study the consequence of these constraints on dark matter in DLRM by considering a right handed real fermion quintuplet to be the dominant dark matter component in the universe.

29 pages, 8 figures, matches version accepted for publication in Phys. Rev. D

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• Unraveling the Dirac Neutrino with Cosmological and Terrestrial Detectors
• Naturally Light Dirac and Pseudo-Dirac Neutrinos from Left-Right Symmetry
• Dark matter produced from right-handed neutrinos
• Low scale Dirac leptogenesis and dark matter with observable $\Delta N_{\mathrm{eff}}$
• Freeze-in Dark Matter via Light Dirac Neutrino Portal
• Survey of Texture Zeros with Light Dirac Neutrinos
• Concealing Dirac neutrinos from cosmic microwave background
• Probing Left-Right Symmetry via Gravitational Waves from Domain Walls
• Affleck-Dine Cogenesis of Baryon and Dark Matter
• Collider and CMB complementarity of leptophilic dark matter with light Dirac neutrinos