Relativistic at freeze out? Definition of HDM

In summary, the statement about neutrinos being relativistic at freeze out in a HDM scenario may seem contradictory, but it is actually due to the fact that they decoupled from matter when the universe was still very hot. As the universe expands and cools, their temperature decreases and they are no longer relativistic.
  • #1
cohen990
7
0
Okay so in a HDM scenario, I have seen it described that the neutrinos were relativistic at freeze out. (If I could find it I would reference it.)

Is this a contradictory statement?

The condition for relativistic travel is E>>m but just before freezeout, the neutrino has energy equal to the thermal energy of the universe (as it is in thermal equilibrium). Since the particle freezes out when the energy of the universe [itex]\approx[/itex] the mass of the particle, then just before freeze out the particle is not relativistic! Correct?

Anyway, thanks for your time,

Dan
 
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  • #2
Since the particle freezes out when the energy of the universe ≈ the mass of the particle
Why? I don't think this is true.
 
  • #3
cohen990 said:
Okay so in a HDM scenario, I have seen it described that the neutrinos were relativistic at freeze out. (If I could find it I would reference it.)

Is this a contradictory statement?

The condition for relativistic travel is E>>m but just before freezeout, the neutrino has energy equal to the thermal energy of the universe (as it is in thermal equilibrium). Since the particle freezes out when the energy of the universe [itex]\approx[/itex] the mass of the particle, then just before freeze out the particle is not relativistic! Correct?

Anyway, thanks for your time,

Dan

I don't really know if this is what you asking, but if what you are talking about is something like the neutrino background of the universe (analogue to the CMB), then neutrinos 'decouple' (getting away from this thermal equilibrium soup) from matter when the universe was still incredibly hot. Therefore these neutrinos were relativistic when they escaped. But as of today, due to cosmological redshifts, their temperature is something around the CMB.
 

1. What is the definition of Relativistic at freeze out?

Relativistic at freeze out refers to the state of matter in the early universe, specifically during the period of freeze-out, where particles and radiation were highly energetic and moving at speeds close to the speed of light. This is a crucial concept in understanding the evolution of the universe and the formation of structures within it.

2. How does Relativistic at freeze out relate to the concept of Hot Dark Matter (HDM)?

Relativistic at freeze out is closely linked to the concept of Hot Dark Matter (HDM), which refers to a type of dark matter that was relativistic during the early stages of the universe. This type of dark matter is characterized by particles that move at high speeds and have a negligible rest mass. HDM is important in theories of structure formation and can help explain the large-scale structure of the universe.

3. What is the role of Relativistic at freeze out in the Big Bang theory?

Relativistic at freeze out plays a crucial role in the Big Bang theory, which is the prevailing model for the origin and evolution of the universe. During the early stages of the Big Bang, the universe was extremely hot and dense, and particles were in a relativistic state. Understanding this phase of the universe is crucial in validating the Big Bang theory and explaining the origin of the universe.

4. How is Relativistic at freeze out studied and measured?

Relativistic at freeze out is studied and measured through various methods, including cosmological observations, particle accelerator experiments, and theoretical models. Scientists use data from the cosmic microwave background, large-scale structure surveys, and other observations to study the early universe and determine the state of matter during the period of freeze-out.

5. What are the implications of Relativistic at freeze out in our understanding of the universe?

The study of Relativistic at freeze out has significant implications in our understanding of the universe. It helps us better understand the evolution of the universe, the formation of structures such as galaxies and galaxy clusters, and the nature of dark matter. It also provides insights into the fundamental laws of physics and can help test and refine theories of the early universe, such as inflation and the Big Bang theory.

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