Heavy lepton quintuplet and TeV scale seesaw mechanism

doctoral thesis

• Title (croatian): Kvintuplet teških leptona i mehanizam njihalice na skali TeV-a
• Author: Branimir Radovčić
• Mentor: Ivica Picek (mentor)
• Committee member: Krešimir Kumerički (predsjednik povjerenstva)
• Committee member: Walter Grimus (član povjerenstva); strani drzavljanin: Nije dostupno
• Committee member: Vuko Brigljević (član povjerenstva)
• Committee member: Ivica Picek (član povjerenstva)
• Committee member: Mirko Planinić (član povjerenstva)
• Granter: University of Zagreb; Faculty of Science; (Department of Physics); Zagreb
• Defense date and country: 2013-03-10, Croatia
• Scientific / art field, discipline and subdiscipline: NATURAL SCIENCES; Physics
• Universal decimal classification (UDC): 53 - Physics

Abstract

Two novel seesaw models based on weak-isospin quintuplet leptons are presented. In the first one, the zero hypercharge Majorana quintuplet lepton is accompanied by a scalar weak-isospin quadruplet, and in the second one, a non-zero hypercharge Dirac quintuplet lepton is accompanied by two scalar weak-isospin quadruplets. In both models scalar quadruplets attain the induced vacuum expectation values. This leads to neutrino mass contribution ∼ v6H/M5 arising at the tree level from a dimension-nine operator. Additional neutrino mass contribution ∼ (1/16π2) ·v2H/M comes from a loop suppressed dimension-five operator. The empirical masses mν ∼ 0.1 eV can be achieved with the new states being within the reach of the Large Hadron Collider and the origin of the neutrino masses could be directly tested. The Drell-Yan production of the new fermions is abundant due to nontrivial electroweak gauge charges and their decays lead to interesting multilepton and same sign dilepton events. The charged components of new scalar multiplets contribute to loop-mediated Higgs decays h → γγ and h → Zγ. The neutral component of the Majorana quintuplet, previously identified as a minimal dark matter candidate, becomes unstable in the proposed seesaw setup. The stability can be restored by introducing a Z2 symmetry, in which case neutrinos get mass only from radiative contributions.

Abstract (croatian)

Prezentirana su dva nova mehanizma njihalice bazirana na kvintupletu leptona slabog izospina. U prvom je modelu Majoranin kvintuplet leptona isčezavajućeg hipernaboja u sprezi sa skalarnim kvadrupletom slabog izospina, a u drugom modelu je Diracov kvintuplet leptona neiščezavajućeg hipernaboja u sprezi s dva skalarna kvadrupleta slabog izospina. U oba modela skalarni kvadrupleti poprimaju induciranu vakuumsku očekivanu vrijednost. To vodi na doprinos masama neutrina ∼ v6H /M5 koji dolazi od operatora dimenzije devet na granastom nivou. Dodatni doprinos masama neutrina ∼ (1/16π2) · v2H /M dolazi od operatora dimenzije pet potisnutog na razini petlje. Eksperimentalne vrijednosti masa neutrina mν ∼ 0.1 eV se mogu ostvariti s novim stanjima u dosegu velikog hadronskog sudarivača i mogućnošću direktnog testiranja porijekla masa neutrina. Drell-Yanova produkcija novih fermiona je obilna zbog netrivijalnih elektroslabih naboja, a njihovi raspadi vode na interesantne dogadaje s više leptona u konačnom stanju i narušenjem leptonskog broja. Ispitana je uloga novih skalara u raspadima Higgsovog bozona na razini petlje, h → γγ i h → Zγ. Neutralna komponenta Majoraninog kvintupleta, prijašnji kandidat za minimalnu tamnu tvar, postaje nestabilna u predloženom modelu njihalice. Uvodenjem Z2 simetrije može se osigurati njezina stabilnost, a u tom slučaju neutrini dobivaju masu samo od doprinosa na razini petlje.

• Keywords: neutrino mass; beyond standard model; quintuplet leptons; exotic leptons; non-standard scalar fields; dark matter
• Keywords (croatian): mase neutrina; fizika izvan standardnog modela; kvintuplet leptona; egzotični leptoni; nestandardna skalarna polja; tamna tvar
• Language: english
• URN:NBN: urn:nbn:hr:217:416821
• Study programme: Title: Physics; Study programme type: university; Study level: postgraduate; Academic / professional title: doktor/doktorica znanosti, područje prirodnih znanosti, polje fizika (doktor/doktorica znanosti, područje prirodnih znanosti, polje fizika)
• Type of resource: Text
• Extent: XIV, 112 str.
• File origin: Born digital
• Access conditions: Open access
• Created on: 2017-08-23 10:05:23