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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 $chi cdot r$. Thus, the capability to detect $chi$ critically depends on the value of $r$. We find that with present data set $chi$ is textit{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 $rsim0.1(0.05)$, the maximal chirality case, i.e. $chi = pm1$, could be detected with a significance of $sim2.5(1.5)sigma$ 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 kind of parity violating theories with the CMB.
The cosmic expansion is computed for various dynamical vacuum models $Lambda(H)$ and confronted to the Cosmic Microwave Background (CMB) power spectrum from Planck. We also combined CMB in a joint analysis with other probes in order to place constrai
We show that the new precise measurements of Cosmic Microwave Background (CMB) temperature and polarization anisotropies made by the Planck satellite significantly improves previous constraints on the cosmic gravitational waves background (CGWB) at f
We discuss whether an unaccounted contribution to the Cosmic Microwave Background polarization $B$-mode by primordial magnetic fields (PMFs) can bias future constraints on inflationary gravitational waves. As a case-study, we consider a scale-invaria
We demonstrate how to obtain optimal constraints on a primordial gravitational wave component in lensed Cosmic Microwave Background (CMB) data under ideal conditions. We first derive an estimator of the tensor-to-scalar ratio, $r$, by using an error-
We present the Planck likelihood, a complete statistical description of the two-point correlation function of the CMB temperature fluctuations. We use this likelihood to derive the Planck CMB power spectrum over three decades in l, covering 2 <= l <=