Primordial gravitational wave constraints from Planck 2015

In summary, the recent study by Luca Pagano, Laura Salvati, and Alessandro Melchiorri has used the latest Planck data to constrain primordial gravitational waves from the universe exiting inflation. Combining CMB, BAO, lensing, and primordial deuterium observations, they have obtained a tighter constraint of \Omega_{gw} h^2 < 1.7 \times 10^{-6} at 95% c.l., which improves previous cosmological bounds by a factor of 5 and recent direct measurements by 50%. However, the results are still rather elusive, with Planck + BAO + lensing giving a slightly higher upper bound of \Omega_{gw} h^2 <
  • #1
Garth
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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 [itex]\Omega_{gw} h^2 < 1.7 .10 ^{-6} [/itex] 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
 
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  • #2
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.
 
  • #3
Well, they used deuterium to get lowest upper bound - their Table 1 shows the upper bounds without deuterium as well.

upload_2015-8-12_10-42-25.png


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

Garth
 
  • #4
How does deuterium relate to any of this?
 
  • #5
bcrowell said:
How does deuterium relate to any of this?
To constrain [itex]\Omega_b[/itex]?

Only a guess, but they claim to get a lower upper bound on [itex]\Omega_{gw}h^2[/itex] 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
 

FAQ: Primordial gravitational wave constraints from Planck 2015

What are primordial gravitational waves?

Primordial gravitational waves are ripples in the fabric of spacetime that are thought to have originated in the early universe, shortly after the Big Bang. They are considered to be a key piece of evidence for the theory of cosmic inflation.

What is the significance of the Planck 2015 data in regards to primordial gravitational waves?

The Planck 2015 data is significant because it provides the most precise measurements to date of the cosmic microwave background (CMB) radiation, which is the remnant radiation from the Big Bang. This data allows scientists to better study and constrain the properties of primordial gravitational waves.

How are primordial gravitational waves detected?

Primordial gravitational waves are detected through their imprint on the CMB radiation. They cause a specific pattern of polarization in the CMB, which can be measured by instruments such as the Planck satellite.

What do the constraints from Planck 2015 tell us about the properties of primordial gravitational waves?

The constraints from Planck 2015 suggest that primordial gravitational waves have a relatively small amplitude, with a power spectrum that is consistent with the predictions of cosmic inflation. This supports the idea that inflation occurred in the early universe.

How does the study of primordial gravitational waves contribute to our understanding of the universe?

The study of primordial gravitational waves is important because it can provide insights into the earliest moments of the universe and the physics that governed it. It also helps to test and refine theories such as cosmic inflation and provides a better understanding of the overall structure and evolution of the universe.

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