All Questions
Tagged with cosmology statistical-mechanics
18
questions with no upvoted or accepted answers
8
votes
0
answers
245
views
Does quark color contribute to "spin degeneracy" for QGP calculations?
Like the title say, does quark color matter in counting contributions in a early universe plasma (QGP), as when adding up the total plasma energy density, or is it just spin? The book I have (Pathria) ...
- 397
8
votes
0
answers
145
views
Does the Standard Model plasma develop a spontaneous magnetisation at finite temperature?
Reference: arXiv:1204.3604v1 [hep-ph] Long-range magnetic fields in the ground state of the Standard Model plasma.
Alexey Boyarsky, Oleg Ruchayskiy, Mikhail Shaposhnikov.
The authors of this paper ...
- 16.6k
4
votes
0
answers
97
views
What kind of matter's energy density scales as the inverse of the scale factor
We know that radiation energy density scales as $a^{-4}$ with EoS parameter ($w=\frac{1}{3}$), matter as $a^{-3}$ with ($w=0$), curvature as $a^{-2}$ with ($w=-\frac{1}{3}$).
Then which kind of matter ...
- 682
3
votes
0
answers
126
views
Evolution of black holes ensemble
Background:
I’ve read many times that arrow of time can be explained from extremely low entropy of the Universe at the Big Bang (http://preposterousuniverse.com/eternitytohere/faq.html). The argument ...
- 69
2
votes
0
answers
65
views
Bose-Einstein statistics in de Sitter spacetime
The metric in de Sitter spacetime with $(+,-,-,-)$ as metric signature is, in cartesian coordinates:
\begin{equation}
ds^2=dt^2-a^2(t)(dx^2+dy^2+dz^2).
\end{equation}
Where $a(t)=e^{Ht}$. How do I ...
- 2,613
2
votes
0
answers
87
views
How is the entropy of the universe defined?
My understanding is that to define the entropy of a system what you have to do is as follows:
Define the boundaries of your system.
Define a set of "microstates" of the system.
Define a partition of ...
- 225
2
votes
0
answers
158
views
How could the universe's expansion "remove the mean gravitational potential"?
I'm citing W. C. Saslaw's The Distribution of the Galaxies: Gravitational Clustering in Cosmology, chapter 25, where he adresses (what seems to be a Newtonian approximation of) the thermodynamic ...
- 2,463
2
votes
1
answer
91
views
No Temperature in an Expanding Universe?
The statistical definition of temperature as $\bigg(\dfrac{\partial \ln \Omega}{\partial E}\bigg)^{-1}$ inherently assumes the existence of a well-defined energy. To my understanding, a well-defined ...
user87745
1
vote
1
answer
94
views
The content of early universe and max limit on the number of particles
When the size of the observable universe was small as a proton what was the physical content of it?
Was there a limit of particles in such a tiny volume with enormous high density and energy?
Can we ...
- 489
1
vote
0
answers
36
views
Why are two assumptions for the approximation from the BE, FD to MB distribution and $T$ invariance in the Boltzmann equation reasonable?
As the title says, I can not understand whether the assumptions
are reasonable.
If an interaction $1+2\leftrightarrow 3+4$ is taken into account, the number variance in time is proportional to
$$|\...
1
vote
0
answers
41
views
Internal degrees of freedom of a Weyl spinor
In statistical mechanics, we have formulas like
$$
n
=
\frac{g}{2\pi^2}
\int_m^\infty
\frac{E(E^2 - m^2)^{1/2}}{e^{(E - \mu)/T} \pm 1}\ dE
.
$$
where $g$ is the internal degrees of freedom. What is ...
- 574
1
vote
0
answers
37
views
Axions approaching thermal distribution
I am reading Sikivie's paper on Axion Cosmology. I have the equation:
$$\frac{\mathrm{d}}{\mathrm{dt}}[R^3(n_a^{th}-n_a^{eq})] = -\Gamma R^3(n_a^{th}-n_a^{eq}) \tag{1}$$
where $R(t)$ is the ...
- 1,222
1
vote
0
answers
322
views
Fermi-Dirac vs. Maxwell-Boltzmann distribution in the early universe plasma
From my studies, I remember that the quantum effects relative to the bosonic or fermonic nature of the particles play a role only in the conditions of degenerate gas: when the plasma is very dense and ...
1
vote
0
answers
192
views
Energy density of particle species in thermal equilibrium
I am reading the book Kolb and Turner "The Early Universe". In the thermodynamics section they mention that the total energy density of different species in equilibrium is
$$\rho=T^4\sum_{\...
user255856
1
vote
0
answers
32
views
What might be the equillibrium Distribution Function of Dark Matter?
Can we assign a thermal distribution function to Dark Matter(not necessarily known ones)?
Is it possible that they won't even follow thermal distribution function and maybe a function of something ...
- 624