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).

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Definition of the sound horizon

I have been looking at the sound horizon $r_s$ as used for CMB and BAO analysis. In the literature this is defined as $$ r_s(z,\mathbf{x}) = \int_0^z \frac{c_s dz^\prime}{H(z',\mathbf{x})} \quad (1), $...
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Connection between BAO & CMB power spectrum

During the entire pre-recombination phase, the plasma is the site of acoustic oscillations. These have left their mark both in the CMB power spectrum and in the matter power spectrum. The first peak ...
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94 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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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117 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 ...
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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 \...
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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}...
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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 $z$ ...
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117 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 ...
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125 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 ...
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444 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 ...
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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 (...
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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 ...
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71 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 $150Mpc$. ...
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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 ...
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324 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 ...
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373 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 ...
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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 ...
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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..) ...