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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).

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).

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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..) are compressions peaks, i.e. peaks which have just…
jak
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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 oscillations can be used as a "standard ruler"…
user333276
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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 \rangle &= -\sin(\theta )| \nu_1 \rangle + \cos(\theta) |…
Our
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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 the fundamental wave vs harmonics analogy were to…
ABC
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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 asymmetry of the universe contain in this? Why do…
Kris
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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 Acoustic Oscillations (BAO). Here is a very nice…
SRS
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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 the incorrect and inaccurate formulation of my…
Thomas
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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 stuck and would love some clarity. First off, the…
Chandra Prakash
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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 washed out on small scales. BAO in the observed galaxy…
user87745
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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 say about BAOs but I couldn't really understand the…
Kantura
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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 distance sound waves could have traveled through…
Kris
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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 try to understand it from first principles
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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 following issues: My image of these oscillations goes…
Physics2718
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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; $$\theta(z) = \frac{r_d}{d_A(1+z)}\frac{180}{\pi}$$ Of course there's…
camarman
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Proof of an accelerated expansion of the universe

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 acoustic oscillations" to compare the sound horizon today with the…
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