Can Self-Ordering Scalar Fields explain the BICEP2 B-mode signal?

Abstract

We show that self-ordering scalar fields (SOSF), i.e. non-topological cosmic defects arising after a global phase transition, cannot explain the B-mode signal recently announced by BICEP2. We compute the full $C_{\ell }^B$ angular power spectrum of B-modes due to the vector and tensor perturbations of SOSF, modeled in the large-N limit of a spontaneous broken global O(N) symmetry. We conclude that the low-$\ell$ multipoles detected by BICEP2 cannot be due mainly to SOSF, since they have the wrong spectrum at low multipoles. As a byproduct we derive the first cosmological constraints on this model, showing that the BICEP2 B-mode polarization data admits at most a 2-3% contribution from SOSF in the temperature anisotropies, similar to (but somewhat tighter than) the recently studied case of cosmic strings.

14 pages, 5 figures

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• Gravitational Waves and Scalar Perturbations from Spectator Fields
• BICEP2 implications for single-field slow-roll inflation revisited
• Constraining topological defects with temperature and polarization anisotropies
• Inflation without quantum gravity
• Gravitational waves as a probe of SUSY scale
• Probing early-universe phase transitions with CMB spectral distortions
• Primordial magnetic fields from self-ordering scalar fields
• Constraining primordial vector mode from B-mode polarization