Thursday, May 22nd - h.
Aula Seminari (A34)
Texas Tech. University
According to the Big Bang model, the Universe is ﬁlled
with (anti-)neutrinos. When the Universe was about one second old,these
particles decoupled.Since that moment, their wavelengths have been expanding
in proportion to the size of the Universe. Their present spectrum is believed
to be a momentum-redshifted relativistic Fermi –Dirac distribution, characterized
by a temperature of 1.95 K.
The present density o these Big Bang relics is estimated at ∼100 cm −3,
for each neutrino ﬂavor.That is nine orders of magnitude larger than the density
o baryons in the Universe. In spite of this enormous density,relic neutrinos
have until now escaped direct detection. The single most important reason
for that is their extremely small kinetic energy, which makes it very diﬃcult
to ﬁnd a process through which they might reveal themselves. The only indirect
indication for their existence is the “missing mass ” phenomenon, i.e.the
apparent discrepancy between the gravitational mass and the luminous mass
in our own andother galaxies.
In this talk, I will propose a process through which relic neutrinos might
and I will present experimental evidence for the occurrence of this process.
I will show
that a variety o characteristic features of the high-energy hadronic cosmic
in particular the abrupt changes in the spectral index that occur around3
PeV and 300
PeV, as well as the corresponding changes in elemental composition that
from kinks in the X max distribution, can be explained in great detail
with relic Big Bang antineutrinos, provided that the latter have a mass
of ∼0 .5 eV/c 2 .