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R. N. Mohapatra
in the hot environment of the early universe, the process is expected to be
quite rapid. This so-called sphaleron process which is effective in the early
universe helps to convert the lepton asymmetry produced in the decay of
right-handed neutrino to baryon asymmetry in an instant [70]. This provides
a different way of using Sakharov conditions to understand the matter–antimatter asymmetry of the universe, and the route goes via the neutrino seesaw.
This particular scenario is of special interest for neutrinos, since the same
seesaw mechanism that is supposed to explain the small neutrino masses is
also responsible for understanding matter–anti-matter asymmetry. It provides
a single unified approach to two different problems—small neutrino mass and
asymmetry between matter and anti-matter. In fact, if the seesaw scenario is
confirmed, neutrinos might have pulled another miracle in the universe: they
create matter, in addition to making matter grow to nuclei, and produce life
in the end. What a role for a tiny particle that no one can see and that passes
through us in huge numbers every second, without us ever noticing anything.
Can we ever test this hypothesis? This scenario known as leptogenesis could
happen at a very early moment of the universe e.g. when the universe was
only 10
−28 s old [26] or when it was somewhat older at 10
−12 s old [84].
The latter scenario raises the possibility that the idea of leptogenesis can be
tested in the colliders which can attain higher energies than the Large Hadron
Collider. There are also scenarios where leptogenesis is connected to the CP
violating phase in the neutrino oscillations [25], which can be tested in current
experiments.
If there is CP violation in the neutrino sector, the neutrinos would oscillate
at a different rate than neutrinos. This is what the experimentalists at T2K and
NoVA are trying to find out. Both these experiments send muon neutrino and
muon anti-neutrino beams over long distances to see if there is difference in
the oscillation rate between them. There are some indications that there may
be, although the jury is still out on this question. The Fermilab experiment
DUNE, already mentioned, will also search for this asymmetry.
There are of course several other ways to understand baryon asymmetry.
Nobody yet knows which mechanism was operating in the early universe.
For instance, it is also possible to understand the origin of matter with Dirac
neutrinos [37], although it is little less straightforward than the case of seesaw
models for Majorana neutrinos. It is interesting that particle physics ideas
associated with the neutrino have the potential to solve such a major cosmic
mystery. Detailed discussion of leptogenesis within the seesaw picture, see [25].
R. N. Mohapatra
in the hot environment of the early universe, the process is expected to be
quite rapid. This so-called sphaleron process which is effective in the early
universe helps to convert the lepton asymmetry produced in the decay of
right-handed neutrino to baryon asymmetry in an instant [70]. This provides
a different way of using Sakharov conditions to understand the matter–antimatter asymmetry of the universe, and the route goes via the neutrino seesaw.
This particular scenario is of special interest for neutrinos, since the same
seesaw mechanism that is supposed to explain the small neutrino masses is
also responsible for understanding matter–anti-matter asymmetry. It provides
a single unified approach to two different problems—small neutrino mass and
asymmetry between matter and anti-matter. In fact, if the seesaw scenario is
confirmed, neutrinos might have pulled another miracle in the universe: they
create matter, in addition to making matter grow to nuclei, and produce life
in the end. What a role for a tiny particle that no one can see and that passes
through us in huge numbers every second, without us ever noticing anything.
Can we ever test this hypothesis? This scenario known as leptogenesis could
happen at a very early moment of the universe e.g. when the universe was
only 10
−28 s old [26] or when it was somewhat older at 10
−12 s old [84].
The latter scenario raises the possibility that the idea of leptogenesis can be
tested in the colliders which can attain higher energies than the Large Hadron
Collider. There are also scenarios where leptogenesis is connected to the CP
violating phase in the neutrino oscillations [25], which can be tested in current
experiments.
If there is CP violation in the neutrino sector, the neutrinos would oscillate
at a different rate than neutrinos. This is what the experimentalists at T2K and
NoVA are trying to find out. Both these experiments send muon neutrino and
muon anti-neutrino beams over long distances to see if there is difference in
the oscillation rate between them. There are some indications that there may
be, although the jury is still out on this question. The Fermilab experiment
DUNE, already mentioned, will also search for this asymmetry.
There are of course several other ways to understand baryon asymmetry.
Nobody yet knows which mechanism was operating in the early universe.
For instance, it is also possible to understand the origin of matter with Dirac
neutrinos [37], although it is little less straightforward than the case of seesaw
models for Majorana neutrinos. It is interesting that particle physics ideas
associated with the neutrino have the potential to solve such a major cosmic
mystery. Detailed discussion of leptogenesis within the seesaw picture, see [25].