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Testing chirality of primordial gravitational waves with Planck and future CMB data: no hope from angular power spectra
Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
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Number of Authors: 5
2016 (English)In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, no 7, 044Article in journal (Refereed) Published
Abstract [en]

We use the 2015 Planck likelihood in combination with the Bicep2/Keck likelihood (BKP and BK14) to constrain the chirality, chi, of primordial gravitational waves in a scale invariant scenario. In this framework, the parameter chi enters theory always coupled to the tensor -to -scalar ratio, r, e.g. in combination of the form chi . r. Thus, the capability to detect chi critically depends on the value of r. We find that with present data sets chi is de facto unconstrained. We also provide forecasts for chi from future CMB experiments, including COrE+, exploring several fiducial values of r. We find that the current limit on r is tight enough to disfavor a neat detection of chi. For example, in the unlikely case in which r similar to 0.1(0.05), the maximal chirality case, i.e. chi = +/- 1, could be detected with a significance of similar to 2.5(1.5)sigma at best. We conclude that the two-point statistics at the basis of CMB likelihood functions is currently unable to constrain chirality and may only provide weak limits on chi in the most optimistic scenarios. Hence, it is crucial to investigate the use of other observables, e.g. provided by higher order statistics, to constrain these kinds of parity violating theories with the CMB.

Place, publisher, year, edition, pages
2016. no 7, 044
Keyword [en]
cosmological parameters from CMBR, gravitational waves and CMBR polarization, physics of the early universe
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:su:diva-134169DOI: 10.1088/1475-7516/2016/07/044ISI: 000381830000045OAI: oai:DiVA.org:su-134169DiVA: diva2:1040749
Available from: 2016-10-28 Created: 2016-10-03 Last updated: 2016-10-28Bibliographically approved

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Gerbino, Martina
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The Oskar Klein Centre for Cosmo Particle Physics (OKC)Department of PhysicsNordic Institute for Theoretical Physics (Nordita)
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