Questions tagged [bao]
Baryon Acoustic Oscillations (BAO) are periodic density fluctuations in the density of matter in the universe. BAO is observed in the large-scale structure of the universe (e.g. distribution of clusters and quasars) in addition to the power spectrum of fluctuations in the Cosmic Microwave Background (CMB).
29 questions
1
vote
1
answer
37
views
Why quantum fluctuation during inflation contributes to structure formation and how it sets the initial condition?
I'm trying to understand the role of the inflaton condensate and quantum fluctuations during inflation and how they evolve into the large-scale structure we observe today. Here's where I’m getting ...
- 378
0
votes
0
answers
31
views
Standing barionic waves in CMB require that the geometry - i.e. the spatial perimeter condition - does not change for a sufficiently long time
Standing barionic waves in CMB require that the geometry - i.e. the spatial perimeter condition - does not change for a sufficiently long time. How long should the standing wave of a byryon ...
1
vote
1
answer
133
views
Sound speed of Baryonic Acoustic Oscillations
I've read in scientific papers, that at the time of decoupling the baryonic sound speed was 5 km/s. Can anyone tell me how this is deduced or point to textbook/papers that do a derivation? I want to ...
- 39
0
votes
0
answers
52
views
$\Lambda$CDM's observations and the universe's matter content
It's known that the current value of the universe's total density parameter $\Omega_0=1$.
According to the $\Lambda$CDM model, the current density parameter of baryonic matter $\Omega_P \sim 0.04$, ...
- 405
3
votes
1
answer
144
views
Multipole ${\it l}$ value for the second acoustic peak in the CMB power spectrum
So according to the Planck paper https://arxiv.org/pdf/1502.01582.pdf page 20, the first peak is ${\it l}$=220, but the second peak is ${\it l}$=537. Not quite the double of the first peak, why? If ...
- 191
1
vote
1
answer
163
views
Issues with baryon acoustic oscillations
I have a difficulty understanding the various explanations of baryon acoustic oscillations that I've been reading. Even on this site, I haven't been able to find answers that directly address the ...
- 115
4
votes
1
answer
222
views
How do BAOs provide evidence for dark matter?
So far my understanding of BAOs is that they are a relic of the old universe formed by the freezing of acoustic density waves in baryonic matter as the universe entered the recombination epoch. These ...
- 51
1
vote
1
answer
112
views
The Difference between angular and anisotropic BAO
I was reading an article and saw these 2 different BAO definitions.
anisotropic BAO;
$$\alpha_{\perp} \equiv \frac{d_A(z)}{r_d}\frac{r^{fid}_d}{d_A(z)^{fid}}$$
angular BAO;
$$\theta(z) = \frac{r_d}{...
- 3,160
1
vote
1
answer
116
views
Proof of an accelerated expansion of the universe [duplicate]
Are there any more "proofs" of an accelerated expansion of the universe other than:
$1:$ that galaxies that are farther away from us are also more redshifted.
$2:$ using "Baryon ...
- 11
0
votes
1
answer
352
views
How is Hubble constant measured by the method of observing BAO?
How is Hubble constant measured by the method of observing BAO?By just reading some articles it seems to me a more complex method than the astronomic scale.Can this method be explained in few words to ...
- 1,835
0
votes
0
answers
55
views
How do cosmologists measure cosmological distances and the expansion history of the universe?
Cosmologists from the BOSS and eBoss surveys construct 3-D maps of correlated galaxy positions, measure their redshifts and use the comoving BAO feature as a standard ruler. With these data, how do ...
- 986
2
votes
0
answers
119
views
Formula to get scales of the two components (radial and perpendicular) of Baryonic Acoustic Oscillations (BAO)
In an astrophysics context about BAO (Baryonic Acoustic Oscillation), it is written on the following paper BAO paper :
"BAO are much smaller in amplitude than the CMB acoustic peaks, and are ...
user87745
0
votes
0
answers
66
views
The formula for the CMB Damping Tail makes no sense
The formula for the Damping Tail in the CMB BAO analysis generally has the form:
$$\mathcal{D}(k)=\int_{0}^{\eta_0}\dot\tau \exp\left\{-\left[\frac {k}{k_D(\eta)} \right]^2\right\}\mathrm d\eta $$I ...
user32023
1
vote
0
answers
201
views
How to relate CMB acoustic peak to BAO in galaxy surveys to better than a factor 2?
Question for a friendly cosmologist.
Let's define the sound horizon as $s = \int_0^{t_{ls}} c_s (1+z) dt$ where $c_s$ is speed of sound in primordial plasma (roughly $c/\sqrt{3}$ but you can include ...
- 61.8k
3
votes
1
answer
318
views
How does the CMB constrain the baryon asymmetry?
The CMB contains information about baryon acoustic oscillations in which baryons (I assume protons and electrons) and photons form a plasma exhibiting sound waves. How is information about the baryon ...
- 861
5
votes
2
answers
220
views
Are neutrinos just different states of a single particle, in essence?
When Neutrino oscillation phenomenon is analysed quantum mechanically, it is said that,
\begin{align}
|\nu_e \rangle &= \cos(\theta) | \nu_1 \rangle + \sin(\theta) |\nu_2 \rangle,\\
|\nu_\mu \...
- 2,313
0
votes
1
answer
1k
views
What is the present day photon density, $\rho_{\gamma, 0}$?
I'm attempting to perform the integration that will yield the sound horizon at recombination:
$$
c_s^2 = \frac{c^2}{3}\left[\frac{3}{4}\frac{\rho_{b,0}(1+z)^3}{\rho_{\gamma,0}(1+z)^4}
+ 1\right]^{-1}...
user32023
0
votes
1
answer
231
views
BAO : Relation between redshift, Hubble constant and radial
From this link https://en.wikipedia.org/wiki/Baryon_acoustic_oscillations#Measured_observables_of_dark_energy , I can't get this relation :
$$c\Delta z = H(z)\Delta \chi\quad\quad(1)$$
with $z$ ...
user87745
3
votes
1
answer
220
views
What causes structure formation: Baryon acoustic oscillations or inflation?
Formation of structures such as galaxies and galaxy clusters require anisotropies in the cosmic plasma which (as I understand) were due to the anisotropies or density inhomogeneities created by Baryon ...
- 27.2k
2
votes
1
answer
248
views
Is the baryonic acoustic oscillation a sound wave?
I was told by a friend that a baryon acoustic oscillations are sound waves with a wavelength so large that they can travel through a vacuum. Is there any truth to this? I read what Wikipedia has to ...
- 1,359
3
votes
2
answers
526
views
Different cold dark matter density parameters from early- and late-Universe observations
Edit: @John Rennie, thank you for your good and concise review of how the parameters of the $\Lambda$CDM model evolve with time. However, the answer I was looking for was a different one (sorry for ...
- 1,803
0
votes
1
answer
206
views
Is BAO a standing or moving wave?
The sound horizon is the distance that a wave of plasma can move from the end of Inflation to Recombination (roughly 300,000 years). In several papers and talks, this is described as a moving wave (...
user32023
1
vote
0
answers
39
views
Are there any public program that can calculate baryon acoustic oscillations (BAO) acoustic peak from the data Lyman alpha spectra of BOSS?
Are there any public program that can calculate baryon acoustic oscillations (BAO) acoustic peak from the data Lyman alpha spectra of Baryon Oscillation Spectroscopic Survey (BOSS)? I am confused in ...
1
vote
1
answer
116
views
Baryon Acoustic oscillations - simple confusion about length scales
I am confused about length scales and baryon acoustic oscillations. I am clearly missing something very simple.
The length scale found in the $SDSS$ and $2dF$ data is quoted as being $150Mpc$. ...
- 11
2
votes
1
answer
140
views
What determines the size of features on the CMB?
I have been learning about baryon acoustic oscillations. I am however confused about the size of the features as seen on the CMB.
It is claimed that the largest structures have a size given by the ...
- 861
1
vote
1
answer
453
views
baryon acoustic oscillation
I have one question about baryon acoustic oscillation.
I understand why we should have the baryon-photon fluid sound wave before recombination: Suppose we have a spherical overdense region. This ...
- 327
1
vote
1
answer
386
views
Galaxy bias and baryon acoustic oscillations (BAO)
I have a doubt with the concept of galaxy bias and how it affects baryon acoustic oscillations, it is supposed to mean that by measuring the distribution of galaxies we are not measuring the actual ...
- 31
1
vote
1
answer
3k
views
Why is the Baryon Acoustic Oscillations (BAO) calculated like this?
In the Wikipedia, it says that, when calculating the Baryon Acoustic Oscillations (sound horizon), we measure $150\text{ Mpc}$, saying that the sound horizon is the "Physical Length of sound horizon ...
- 1,443
7
votes
1
answer
2k
views
Connection between BAO und CMB Spectrum
I have a problem understanding the connection between the accoustic peaks in the CMB spectrum and the baryon oscillation picture. On the one hand it is stated, that the odd accoustic peaks (1,3,5..) ...
- 10.3k