Primordial gravitational wave constraints from Planck 2015

[Garth]

In today's Physics ArXiv: New constraints on primordial gravitational waves from Planck 2015.

Authors Luca Pagano, Laura Salvati, and Alessandro Melchiorri of the Physics Department and INFN, Universita di Roma.

CONCLUSIONS
We have used the latest Planck data to constrain a possible cosmological gravitational wave background at frequencies greater than 10^-15 Hz.
Our tighter constraint is \Omega_{gw} h^2 < 1.7 .10 ^{-6} at 95% c.l., obtained combining CMB with BAO, Lensing and primordial Deuterium observations. This result improves previous cosmological bounds by a factor 5 and the recent LIGO-VIRGO direct measurements by 50%.

Primordial gravitational waves from the universe exiting Inflation get more and more elusive.

Garth

 

[Chronos]

We already know our deuterium counts don't match predictions, so I find it unsurprising to get peculiar results when they are wedged into the mix.

 

[Garth]

Well, they used deuterium to get lowest upper bound - their Table 1 shows the upper bounds without deuterium as well.

Planck + BAO + lensing gives \Omega_{gw} h^2 < 1.9 \times 10^{-6}, still rather elusive!

Garth

 

[bcrowell]

How does deuterium relate to any of this?

 

[Garth]

How does deuterium relate to any of this?

To constrain \Omega_b?

Only a guess, but they claim to get a lower upper bound on \Omega_{gw}h^2 from 1.9 to 1.7 x 10^-6.

As I said that is pretty immaterial as the 1.9 x 10^-6 upper limit still leaves any such gws pretty insignificant.

Garth