Register to reply

Relativistic at freeze out? Definition of HDM

by cohen990
Tags: definition, freeze, relativistic
Share this thread:
cohen990
#1
Nov19-12, 01:33 PM
P: 7
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
Phys.Org News Partner Astronomy news on Phys.org
Smallest known galaxy with a supermassive black hole found
Mystery of rare five-hour space explosion explained
Glowing galaxies in telescopic timelapse
mfb
#2
Nov20-12, 07:39 AM
Mentor
P: 12,081
Since the particle freezes out when the energy of the universe ≈ the mass of the particle
Why? I don't think this is true.
Astrofan
#3
Jan7-13, 08:09 AM
P: 21
Quote Quote by cohen990 View Post
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.


Register to reply

Related Discussions
A simple definition to Non-Relativistic Quantum mechanics? Quantum Physics 4
The big freeze Biology, Chemistry & Other Homework 1
Freeze Ray Chemistry 11
Can Anti-freeze freeze? Biology, Chemistry & Other Homework 2
Relativistic momentum definition Special & General Relativity 14