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One open question of particle physics is whether or not neutrinos and anti-neutrinos are the same particle , in which case it would be a Majorana fermion , or whether they are different particles , in which case they would be Dirac fermions .
 Majorana, Dirac
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Majorana, Dirac