How can majorana neutrinos still be CP violating?

In summary: CP violation can still occur if neutrinos are considered to be their own antiparticles, however this is done by introducing phase angles into the CKM matrix.
  • #1
lizzie96
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This question is probably very over-simplistic, however: if neutrinos are majorana particles, which are their own antiparticles, how could they still be CP violating?

I don't understand precisely how this would work, but physicists I have spoken to said that neutrinos being majorana could still be consistent with CP violation.

Thank you for any help!
 
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  • #2
you can always have CP violation if you introduce phase angles in the CKM matrix... how is that connected to the nature of neutrinos?
 
  • #3
There is a mixing matrix, the PMNS matrix, which (Wikipedia) "contains information on the mismatch of quantum states of leptons when they propagate freely and when they take part in the weak interactions". Like the corresponding CKM matrix for quarks, it is a 3x3 unitary matrix. CP-violation results from complex phases of the matrix elements.

The number of independent parameters in the PMNS matrix can be reduced by rephasing the lepton fields

j → exp(iφj) ℓj

with arbitrary φj's, which leaves the charged lepton mass terms invariant. However, due to the Majorana nature of the neutrinos, the rephasing

νj → exp(iψj) νj

is not allowed, since it would not keep the Majorana mass terms invariant.

Consequently, if neutrinos are Majorana, the PMNS matrix can contain more CP-violating phases than the CKM matrix. In general there will be three mixing angles and three phases.

(Remarks largely lifted from this paper.)
 
  • #4
This question is probably very over-simplistic, however: if neutrinos are majorana particles, which are their own antiparticles, how could they still be CP violating?

It seems that you are thinking intuitivley, if there is no distinct neutrino and anti neutrino , how could there be asymmetry bewteen the two?

Well, for examples , a CP eigenstate ( a state that is its own anti particle) has an eigenvalue. It can be 1 ( cp even) or -1 (cp odd). If this isn't conserved, you have CP violation.
 
  • #5
Thank you, that makes much more sense now! I was thinking about it in the way that ofirg said, without really understanding the reasoning/maths. The paper explains it all very well.
 

FAQ: How can majorana neutrinos still be CP violating?

1. How are majorana neutrinos different from other types of neutrinos?

Majorana neutrinos are different from other types of neutrinos because they are their own antiparticles. This means that they have the same mass and spin as their antiparticles, whereas other types of neutrinos have different masses and spins from their antiparticles.

2. How can majorana neutrinos be CP violating?

Majorana neutrinos can be CP violating because they can oscillate between their matter and antimatter states, which is known as neutrino oscillation. This oscillation can violate the symmetry between matter and antimatter, known as CP symmetry, and result in CP violation.

3. What evidence supports the theory of majorana neutrinos being CP violating?

There is currently no direct evidence for majorana neutrinos being CP violating. However, there have been experiments that have observed neutrino oscillations, which indirectly support the theory. Additionally, the Standard Model of particle physics predicts that CP violation should occur in neutrino oscillations.

4. How does CP violation in majorana neutrinos affect the universe?

If majorana neutrinos are CP violating, it could help explain the matter-antimatter asymmetry in the universe. The Big Bang theory predicts that equal amounts of matter and antimatter should have been created in the early universe, but there is a significant imbalance with more matter than antimatter. CP violation in majorana neutrinos could be one possible explanation for this asymmetry.

5. What further research is being done to understand CP violation in majorana neutrinos?

Scientists are conducting experiments, such as the DUNE experiment in the United States and the T2K experiment in Japan, to study neutrino oscillations and search for CP violation. They are also working on developing new theories and models to better understand the phenomenon. Additionally, advancements in technology and particle accelerators may allow for more precise measurements and potentially provide new insights into CP violation in majorana neutrinos.

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