A search for pair production of doubly charged Higgs bosons ((H^{pm pm})), each decaying into a pair of prompt, isolated, and highly energetic leptons with the same electric charge, is presented. The search uses a proton-proton collision data sample at a centre-of-mass energy of 13 TeV corresponding to an integrated luminosity of 139 fb(^{-1}) recorded by the ATLAS detector during Run 2 of the Large Hadron Collider (LHC). This analysis focuses on same-charge leptonic decays, (H^{pm pm} rightarrow ell^{pm} ell^{prime pm}), where (ell, ell^{prime} = e, mu, tau), in two-, three- and four-lepton channels but only considers final states, which include electrons or muons. No evidence of a signal is observed. Assuming that the branching ratios to each possible leptonic final state are equal, (mathcal{B}(H^{pm pm} rightarrow e^{pm} e^{pm} / e^{pm} mu^{pm} / mu^{pm} mu^{pm} / e^{pm} tau^{pm} / mu^{pm} tau^{pm} / tau^{pm} tau^{pm}) = 1/6), the corresponding upper limits on the pair production cross-section of doubly charged Higgs bosons are derived as a function of its mass, (m_{H^{pm pm}}), at a 95% confidence level. The limits, which are the strongest produced by the ATLAS Collaboration to date, are obtained for the left-right symmetric type-II seesaw model. Additionally, this work provides the first direct test of the Zee-Babu neutrino mass model at the LHC.V doktorskem delu je predstavljeno iskanje nastanka para dvojno nabitih Higgsovih bozonov ((H^{pm pm})), izmed katerih vsak razpade na par neposrednih, izoliranih in visokoenergijskih leptonov z enakim električnim nabojem. V analizi so uporabljeni podatki, zabeleženi z detektorjem ATLAS med drugim obratovalnim ciklom (Run 2) velikega hadronskega trkalnika (LHC), kar ustreza integrirani luminoznosti 139 fb(^{-1}). Zajeti so bili med trki protonov pri težiščni energiji 13 TeV. Analiza se osredotoča na razpade delca ((H^{pm pm})) v par leptonov z enakim nabojem, (H^{pm pm} rightarrow ell^{pm} ell^{prime pm}), pri čemer je (ell, ell^{prime} = e, mu, tau). Posebej so obravnavana končna stanja z dvema, tremi in štirimi leptoni, vendar so upoštevana le ta, ki vključujejo elektrone ali mione. Statistična obdelava podatkov ne kaže znatnih odstopanj od napovedi Standardnega modela. Ob predpostavki, da so razvejitvena razmerja v vsa možna leptonska končna stanja enaka, (mathcal{B}(H^{pm pm} rightarrow e^{pm} e^{pm} / e^{pm} mu^{pm} / mu^{pm} mu^{pm} / e^{pm} tau^{pm} / mu^{pm} tau^{pm} / tau^{pm} tau^{pm}) = 1/6), so izpeljane ustrezne zgornje meje produkcijskih sipalnih presekov dvojno nabitih Higgsovih bozonov kot funkcija njihove mase (m_{H^{pm pm}}), pri stopnji zaupanja 95 %. Meje, ki so najstrožje, kar jih je doslej objavila kolaboracija ATLAS, so določene za gugalnični mehanizem tipa II znotraj levo-desno simetričnega modela. Poleg tega je to delo prvi neposredni preizkus modela Zee-Babu na LHC
