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Standardni model ima dve naključni globalni simetriji $U(1)_{B}$ barionsko in $U(1)_{e} times U(1)_{mu} times U(1)_{tau}$ in leptonsko, ki velja za vsako družino posebej. Barionsko število je definirano tako, da imajo barioni (n,p) barionsko število $B = 1$, antibarioni $(overline{n}, overline{p})$ barionsko število $B = -1$. Leptonsko število pa je definirano za leptone $L_{e,mu,tau} = 1$, za antileptone $overline{L}_{e,mu,tau} = -1$. Obe simetriji sta ohranjeni znotraj standardnega modela in zato preprečujeta oscilacije barionov in razpad protona. Teorija velikega poenotenja ($GUT$) razširi standardni model z uvedbno novih hipotetičnih delcev leptokvarkev (LQ). Ti pa so novi prenosniki interakcije, ki omogočijo kršitev barionskega števila za $Delta B = 1$ eno enoto in s tem možni razpad protona. Pri kršitvi barionskega števila za $Delta B = 2$ pa imamo oscilacije med barioni $n - overline{n}$. Kršitev leptonskega števila za $Delta L = 2$ dve enoti, ki se eksperimentalno išče pri beta razpadu, bi določila naravo nevtrina, ki bi bil Majorana nevtrino. V tem magistrskem delu obravnavamo oscilacije med barioni s poudarkom na nevtronu. Opišemo razpad nevtrona v Majorana fermion $n rightarrow chi$ na drevesnem nivoju in nato še na nivoju ene zanke. Na drevesnem nivoju je prenosnik interakcije leptokvarek $S_{1}$, na nivoju ene zanke pa $overline{S}_{1}$. Eksperimentalno potrjena oscilacija med nevtronom in antinevtronom bi imela velik pomen pri razlagi neravnovesja med snovjo in antisnovjo v našem vesolju. Veliko eksperimentov si prizadeva izmeriti mešalni čas med nevtronom in antinevtronom, s čimer bi potrdili oscilacijo med nevtronom in antinevtronom. Standard Model has two accidental global symmetries $U(1)_{B}$ baryon number and $U(1)_{e} times U(1)_{mu} times U(1)_{tau}$ lepton number, which holds for each family. We define baryon number $B = 1$ for baryons $(n,p)$ and $B = -1$ for antibaryons $(overline{n}, overline{p})$. For lepton number we define $L_{e,mu,tau} = 1$ for leptons and $overline{L}_{e,mu,tau} = -1$ for antileptons. Both symmetries are conserved in Standard Model for which oscillations between baryons and proton decay are forbidden in Standard Model. Grand Unified Theory (GUT) introduces new hypothetical particles Leptoquarks (LQ) for which we get theory Beyond Standard Model (BSM). LQ are new interaction mediators that allow us to violate the baryon number for one or two units. Violation for one unit gives us proton decay and violation for two units gives us neutron antineutron oscillations. There is also an experimental search for double beta dacay, which would violate a lepton number for $Delta L = 2$ two units and give us proof that the neutrino is a Majorana fermion. In this thesis we consider oscillations between baryons with emphasis on the neutron. We calculate decay amplitude for the transition of a neutron into Majorana fermion $n rightarrow chi$ on tree-level and one-loop level. At the tree level, LQ $S_{1}$ is interaction mediator, and $overline{S}_{1}$ is the interaction mediator for one loop. Experimental observations of the neutron antineutron oscillation would greatly impact the asymmetry between matter and antimatter. Many experiments are trying to measure oscillation time between neutron and antineutron, which would prove the existence of neutron antineutron oscillation. |
