All Questions
Tagged with cosmologydark-matter
274 questions
0votes
0answers
53views
Dark matter freeze-out in the Early Universe
Let us consider an Early Universe scenario in which I have dark matter particles (DM) $\chi_1$ and $\chi_2$, with a small mass splliting $\delta \ (m_2 = m_1 + \delta, \quad \delta \ll m_1, m_2)$, ...
- 81
0votes
0answers
94views
What is the Timescape Model of Cosmology?
I am seeing some articles about timescape and comparisons to ΛCDM. In particular there is an article in the Monthly Notices of the Royal Astronomical Society: Supernovae evidence for foundational ...
- 271
0votes
0answers
22views
Is there a model for the synthesis of light-sector heavy hadron formation during a first order phase transition?
I've recently been reading some research on theories of dark matter. So, I read about Fermi-balls (https://arxiv.org/abs/2008.04430), or non-topological solitons bound inside their own domain walls. ...
0votes
0answers
58views
In the beginning of time, regular and dark matter were strongly coupled?
It was mentioned during this lecture at this moment that in the early universe regular and dark matter were strongly coupled. This explains the existence of supermassive black holes in the beginning ...
0votes
0answers
42views
Calculation of freeze-out temperature
I'm struggling with an exercise that asks me to calculate the freeze-out temperature in term of $x_f = \frac{m_{\chi}}{T_f}$ of a Dark Matter fermion $\chi$ using the relation $ \left< \sigma v \...
1vote
1answer
73views
Does scalar field dark matter behave like dust in cosmology?
A uniform scalar field has pressure equal to its energy density (equation of state $w=1$) and so dilutes very rapidly as the universe expands, $\rho \approx a^{-6}$. However, some theories of dark ...
- 511
0votes
0answers
52views
Derive relic abandence of Dark Matter
I am reading Dodelson's Modern Cosmology and I have a question about how to derive equation 3.60 from equation 3.59. Equation 3.59 is $$\Omega_X = \left[\frac{4\pi^3 G g_*(m)}{45}\right]^{1/2} \frac{...
0votes
1answer
68views
Were we all intuitively misled into thinking that the universe has a 'speed' of expansion?
Universe has not even once had a speed of expansion but rather an acceleration. The thing is that since at small scales this acceleration is not noticiable it approaches a 'constant speed' given by ...
1vote
5answers
313views
Absolute invisibility in cosmos [closed]
I am a mathematician and not a physicist, so I have a lack of understanding subjects of physics. I would like to ask which physical objects are absolutely invisible by us -I mean which objects are ...
- 153
2votes
0answers
106views
Gravitational halos made of neutrinos...?
I have been recently interested in how halos made of standard model particles could be formed and behave. After asking some questions in this site, I was told about how neutrinos could form such halos....
- 3,018
3votes
1answer
103views
If dark matter is axion particles, how did such light particles slow down?
One candidate for dark matter is axions and there is tentative experimental evidence for their existence. Axions are very light, most models weigh them in at tiny fractions of an eV. It seems like ...
- 6,785
2votes
1answer
334views
What's the meaning of 'cold' in the CDM model?
On Wikipedia, it says In cosmology and physics, cold dark matter (CDM) is a hypothetical type of dark matter. According to the current standard model of cosmology, Lambda-CDM model, approximately 27% ...
0votes
2answers
96views
Test of the primordial black hole solution to dark matter
One of the ideas that might solve some of the dark matter problem are the existence of many small black holes. There is evidence, in principle, for the existence of these small black holes via the ...
- 1,430
1vote
1answer
176views
Why do people say that the $\Lambda$-CDM model has six independent parameters?
The Wikipedia article on the $\Lambda$-CDM model says that the model has six "independent parameters". It also says that the model has several "fixed" parameters and several "...
- 50.2k
3votes
2answers
194views
Does neglecting dark matter solve the Hubble tension?
If the total mass of the universe is smaller than estimated by neglecting the gravitational pull of dark matter, the estimated expansion rate should be greater. Does this consideration in the CMB ...
