CosmoCoffee

[Syksy Rasanen]

The authors compare how much information there in the BAO peak compared to the overall shape of the large-scale structure power spectrum. They basically conclude that at present, the information in the LSS data (when combined with the CMB) is dominated by the BAO scale.

For me, the model-independent extraction of the BAO scale via spectral analysis was particularly interesting.

There is one statement which I did not understand. On page 6 the authors explain the positive correlation between the dark energy equation of state ω and the primordial spectral index by saying that as ω becomes closer to zero (i.e. grows), the late ISW becomes larger. I would have thought that as ω goes to zero, the late ISW effect would vanish.

[Ben Gold]

They're using CAMB, which if I remember correctly defaults to always using a sound speed of 1 for dark energy, regardless of what w is set to. So I don't think dark energy quite behaves like CDM as w→0, which seems to be what you're thinking of.

But I think what's more important for late ISW is that as long as w < 0, a larger w (closer to zero) means dark energy remains dominant back to higher redshift than for a more negative w, and this longer duration of dark energy dominance leads to more ISW. To put it another way: if w→ − ∞, then you get zero late ISW, because Ω_de was zero up until a fraction of a second ago.

[Syksy Rasanen]

I see, that makes sense.

[Beth Reid]

[Syksy Rasanen]

Right, I should have specified that for extended models, there is extra information in the overall shape. The authors point this out for the example of a variable number of neutrino species together with a variable dark energy equation of state. In this case, the neutrino masses, equations of state and the spectral index all benefit from the shape information.

How important do you think is the H₀ prior?