Cosmic neutrino primer

[Martin]

this is a good general introduction to the CNB (cosmic neutrino background)

by a couple of people at Dartmouth

 

http://arxiv.org/abs/astro-ph/0608303

Anisotropy of the Cosmic Neutrino Background

Ryan J. Michney, Robert R. Caldwell

5 pages, 2 figures

 

"The cosmic neutrino background (CNB) consists of low-energy relic neutrinos which decoupled from the cosmological fluid at a redshift z ~ 10^{10}. Despite being the second-most abundant particles in the universe, direct observation remains a distant challenge. Based on the measured neutrino mass differences, one species of neutrinos may still be relativistic with a thermal distribution characterized by the temperature T ~ 1.9K. We show that the temperature distribution on the sky is anisotropic, much like the photon background, experiencing Sachs-Wolfe and integrated Sachs-Wolfe effects."

 

these neutrinos are the second most abundant particle in the world

(the most abundant of all are the CMB photons) and this article says they have traveled over 45 billion LY to reach us

and they have slowed down in the process so they have much lower energy than neutrinos we get from the sun or from supernovas.

So the CNB will be very difficult to observe. they give a cross-section indicated how difficult to detect

and ANISOTROPY in the CNB will be even more difficult to detect

but the authors do a good job of discussing all this, and it is probably a good idea to be aware of the CNB since it is the "other" cosmic background and the CMB has become so important.

 

lots I dont understand about the CNB, if anyone wants to do some explaining of the basics, or elucidate any points in the article, they would be welcome.

=============

Robert Caldwell is the senior author, he as 43 papers on arxiv going back to 1993 and has co-authored individually with people like Cooray, DeDeo, Dodelson, Doran, Langlois, Linder, Steinhardt. He has spent time at good places. I think it is a reliable mainstream paper, more authorative than the run of the mill.

[CanadaAotS]

er... I have questions as well

 

how did they get here from 45 billion ly if the universe is supposedly 15 billion ly old app. ?

[Martin]

er... I have questions as well

 

how did they get here from 45 billion ly if the universe is supposedly 15 billion ly old app. ?

 

45 billion LY is a normal figure for the "particle horizon"

after the photon or other particle has traveled a ways the space behind it EXPANDS so it has come from farther away than you thought

 

 

check out Ned Wright's calculator

put in z =1100 the redshift of the CMB and see how far away

the MATTER IS NOW WHICH RELEASED THE PHOTONS THAT WE DETECT NOW.

http://www.astro.ucla.edu/~wright/cosmolog.htm

 

http://www.astro.ucla.edu/~wright/CosmoCalc.html

 

when I type in z = 1100

and press "general"

45.655 billion LY

what about you, do you get that also?

 

IOW the most distant matter that we now see (which emitted photons that are now reaching us) is NOW about 45 billion LY from here.

or 46 billion---something around that far.

[insane_alien]

oh man i had just about got my head round a universe with a radius of 15 thousand million lightyears now your saying its more than double that?

[CanadaAotS]

The comoving radial distance, which goes into Hubble's law, is 13997.6 Mpc or 45.655 Gly.

 

yes I see... I get what you are saying as well about it being 45 bil ly away

[Martin]

oh man i had just about got my head round a universe with a radius of 15 thousand million lightyears now your saying its more than double that?

 

more like three times

heh heh

try practicing with a cosmology calculator, there are several out there

[Martin]

The comoving radial distance' date=' which goes into Hubble's law, is 13997.6 Mpc or 45.655 Gly.

 

yes I see... I get what you are saying as well about it being 45 bil ly away[/quote']

 

Good! check out some of the rest of Ned Wright's site, if you havent already

 

he has FAQ and a cosmology tutorial with lots of pictures

and news items etc.

 

there is also some great articles by Charles Lineweaver online if you want

 

notice that ned wright puts in values for dark energy (0.73) and matter density including dark matter (0.27) and the Hubble parameter (71)

 

if you change the cosmological parameters you get different answers for the age of the universe and for distances to various redshifts etc.

 

 

another excellent cosm. calculator is Siobhan Morgan's

she is a prof in Iowa somewhere.

http://www.earth.uni.edu/~morgan/ajjar/Cosmology/cosmos.html

 

she makes you work a little, you have to type in 0.27 for matter, 0.73 for cosmological constant, and 71 for Hubble

 

then you get close to same answers as you do with ned wright's calculator

 

she also gives you some output information that his does not----good to try both