Re: Lepton predictions and cosmological limits on neutrino mass

From: Francis Bursa (francis_at_strcprstskrzkrk.co.uk)
Date: 02/18/05 

Date: Fri, 18 Feb 2005 17:43:48 +0000 (UTC)

Phillip Helbig---remove CLOTHES to reply wrote:
> In article <bUeQd.12973$vK5.8471@twister.nyroc.rr.com>, "Jay R. Yablon"
> <jyablon@nycap.rr.com> writes:
>
>
>>Here we have a bunch of experimental particle physicists saying they are
>>confident that the tau mass is less than 18 MeV, and will not make any
>>claims beyond that. Then, you have the cosmologists telling the particle
>>folks that they are almost TEN MILLION times more confident of their ceiling
>>at about 2eV. And, these are cosmologists talking to particle folks about
>>the mass of a particle. I didn't even think much about it much before, but
>>this whole situation seems preposterous, which is why I didn't think about
>>it.
>
>
> No, it's not at all preposterous. If I recall correctly, the strongest
> cosmological (better: astrophysical) comes from the time-of-flight
> measurement from neutrinos from a supernova in one of the Magellanic
> clouds. The interpretation is rather straightforward. The
> particle-physics limit is an UPPER LIMIT; no-one says that it can't be
> much lower.

The supernova measurment gives a limit for the electron neutrino mass.
More recently there's a cosmological limit on the *sum* of the neutrino
masses - the best limit is that the sum is less than 0.71eV. It may be
possible to stretch this to a few eV, but not to anywhere near 18MeV.

Also, there's the neutrino oscillation results. These give differences
between the mass-squares of the three flavours of neutrinos. The
differences are around 10^-4 to 10^-3 eV^2. Combining these with the
direct electron-neutrino mass limit, around 2eV, shows again that none
of the neutrinos can be above a few eV. This is completely independent
of the cosmological limit.

>
>>Somebody is way off base here.
>
>
> There is no conflict, it's just that one limit is better than the other.
>
>
>>If the cosmological folks are right, then
>>the particle people can improve the accuracy of their experiments for the
>>next hundred years and they'll never come up with anything. Yet, if
>>the particle people are continuing to push their ceilings down, they must
>>figure that they are going to come up with a mass before they devise an
>>experiment that is ten million times more sensitive. Or, they have a
>>phenomenal research grant and nobody to answer to.
>
>
> Or, they get paid to do other things, and the limits on the neutrino
> mass are obtained "for free".
>
Or maybe they've stopped looking? The 18MeV limit was published in 1998,
around the time the neutrino oscillation data was starting to appear. I
suspect people may have given up on the direct searches once it became
apparent that the tau neutrino mass must be much much lower.

Francis Bursa 

-- 
Francis Bursa,
Merton College,
Oxford

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