Majoranovi fermioni in gugalnični mehanizem

Nevtrini so osnovni delci, za katere je dolgo veljalo, da so brezmasni. Takšne napove tudi Standardni model, trenutno splošno sprejeti teoretični okvir, ki opisuje osnovne delce in interakcije med njimi. Eksperimenti so potrdili, da nevtrini v resnici imajo maso, zaradi česar se je pojavila potreba po novih teorijah, ki bi lahko to maso razložile. V članku je predstavljena ena od možnih razširitev Standardnega modela, gugalnični mehanizem tipa I. Najprej so predstavljeni osnovni koncepti, potrebni za razumevanje Standardnega modela in njegovih razširitev. Sledi predstavitev Higgsovega mehanizma, ki razloži maso ostalih leptonov, na koncu pa je predstavljen gugalnični mehanizem, ki razloži maso nevtrinov. Spoznamo, da so lahko mase nevtrinov Diracovega ali Majoranovega tipa, slednja pri ostalih leptonih ni dovoljena. Če imajo nevtrini maso Majoranovega tipa, obstajajo procesi, ki bi kršili ohranitev leptonskega števila, kar se v moderni eksperimentalni fiziki osnovnih delcev aktivno išče.

Majorana fermions and the seesaw mechanism

Neutrinos are elementary particles that were long believed to be massless. This is also what the Standard Model — the widely accepted theoretical framework describing elementary particles and their interactions — predicts. However, experimental evidence has shown that neutrinos do, in fact, have nonzero mass. This discovery has led to the need for new theories capable of explaining the origin of that mass. This article focuses on the Type I seesaw mechanism, a proposed extension of the Standard Model that accounts for neutrino masses. First, some of the fundamental concepts necessary to understand the Standard Model and its possible extensions are introduced. This is followed by an explanation of the Higgs mechanism, which accounts for the masses of other fermions. Finally, the seesaw mechanism itself is presented. Neutrino masses can be either of the Dirac or Majorana type, with the latter being forbidden for other leptons. If neutrinos are Majorana particles, processes that violate lepton number conservation become possible — one of the key focuses of current experimental searches in particle physics.