## CAMB: High ell CMB residuals not stable

Use of Cobaya. camb, CLASS, cosmomc, compilers, etc.
Luke Hart
Posts: 70
Joined: July 13 2015
Affiliation: University of Manchester

### CAMB: High ell CMB residuals not stable

I have a model that varies the CMB in the thermal history only and when I plot the CMB residuals (i.e., ) the high- contributions to the CMB spectra blow well out of proportion. I show the residuals here and you can see the response just shoots up where actually its quite a simple variation (take my word for it!)
Any ideas on why this would be happening in CAMB and how we can change it?
testdummy.png (294.81 KiB) Viewed 221 times

Antony Lewis
Posts: 1719
Joined: September 23 2004
Affiliation: University of Sussex
Contact:

### Re: CAMB: High ell CMB residuals not stable

I don't know what spectra you are plotting, or whether this is stable to changes in accuracy parameters?

Luke Hart
Posts: 70
Joined: July 13 2015
Affiliation: University of Manchester

### Re: CAMB: High ell CMB residuals not stable

So this is the TT power spectra (i.e., ) and using an . The particular model variations are difficult to explain without a) discussing a paper in preparation too much or b) taking up lots of time – main point is that it is a variation that exclusively affects the ionisation history. I tried changing

Code: Select all

accuracy_boost = 3
but that didn't fix anything either.

Antony Lewis
Posts: 1719
Joined: September 23 2004
Affiliation: University of Sussex
Contact:

### Re: CAMB: High ell CMB residuals not stable

lensed or unlensed? The silk tail is presumably quite sensitive to the timing of reionziation since falling so steeply.

Luke Hart
Posts: 70
Joined: July 13 2015
Affiliation: University of Manchester

### Re: CAMB: High ell CMB residuals not stable

Thanks Antony. This is specifically lensed, however the impact between the two is fairly similar. The model variations used in this case were also centred around the recombination epoch with no knock on to reionisation. I'm just trying to ascertain whether the CMB should be so erratic at higher (obviously since this is a residual, there is every chance that this is just blown up by how small the CMB spectra is).