Revisiting Large Neutrino Magnetic Moments

Current experimental sensitivity on neutrino magnetic moments is many orders of magnitude above the Standard Model prediction. A potential measurement of next-generation experiments would therefore strongly request new physics beyond the Standard Model. However, large neutrino magnetic moments generically tend to induce large corrections to the neutrino masses and lead to fine-tuning. We show that in a model where neutrino masses are proportional to neutrino magnetic moments. We revisit, discuss and propose mechanisms that still provide theoretical consistent explanations for a potential measurement of large neutrino magnetic moments. We find only two viable mechanisms to realize large transition magnetic moments for Majorana neutrinos only.Comment: 12 pages, 7 figure

Electroweak Absolute, Meta-, and Thermal Stability in Neutrino Mass Models

We analyze the stability of the electroweak vacuum in neutrino mass models containing right handed neutrinos or fermionic isotriplets. In addition to considering absolute stability, we place limits on the Yukawa couplings of new fermions based on metastability and thermal stability in the early Universe. Our results reveal that the upper limits on the neutrino Yukawa couplings can change significantly when the top quark mass is allowed to vary within the experimental range of uncertainty in its determination.Comment: 7 pages, 4 figures, match published versio

Electroweak breaking and Dark Matter from the common scale

We propose a classically scale invariant extension of the Standard Model where the electroweak symmetry breaking and the mass of the Dark Matter particle come from the common scale. We introduce U(1)X gauge symmetry and X-charged scalar Φ and Majorana fermion N. Scale invariance is broken via Coleman–Weinberg mechanism providing the vacuum expectation value of the scalar Φ. Stability of the dark matter candidate N is guaranteed by a remnant Z2 symmetry. The Higgs boson mass and the mass of the Dark Matter particle have a common origin, the vacuum expectation value of Φ. Dark matter relic abundance is determined by annihilation NN→ΦΦ. We scan the parameter space of the model and find the mass of the dark matter particle in the range from 500 GeV to a few TeV

Kvintuplet teških leptona i mehanizam njihalice na skali TeV-a

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.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

Radiative neutrino mass with scotogenic scalar triplet

AbstractWe present a radiative one-loop neutrino mass model with hypercharge zero scalar triplet in conjunction with another charged singlet scalar and an additional vectorlike lepton doublet. We study three variants of this mass model: the first one without additional beyond-SM symmetry, the second with imposed DM-stabilizing discrete Z2 symmetry, and the third in which this Z2 symmetry is promoted to the gauge symmetry U(1)D. The two latter cases are scotogenic, with a neutral component of the scalar triplet as a dark matter candidate. In first scotogenic model the Z2-odd dark matter candidate is at the multi-TeV mass scale, so that all new degrees of freedom are beyond the direct reach of the LHC. In second scotogenic setup, with broken U(1)D symmetry the model may have LHC signatures or be relevant to astrophysical observations, depending on the scale of U(1)D breaking

TeV-scale Seesaw with Quintuplet Fermions

We propose a new seesaw model based on fermionic hypercharge zero weak quintuplet in conjunction with additional scalar quadruplet which attains an induced vev. The model provides both tree-level seesaw ~ v^6/M^5 and a loop-suppressed radiative ~ (1 / 16 \pi^2) v^2/M contributions to active neutrino masses. The empirical masses m_\nu ~ 10^{-1} eV can be achieved with M ~ TeV new states, accessible at the LHC. For 5 fb^{-1} of accumulated integrated luminosity at the LHC, there could be ~ 500 doubly-charged \Sigma^{++} or \bar{\Sigma^{++}} fermions with mass M_\Sigma = 400 GeV, leading to interesting multi-lepton signatures. The neutral component of the fermion quintuplet, previously identified as minimal dark matter candidate, becomes unstable in the proposed seesaw setup. The stability can be restored by introducing a Z_2 symmetry, in which case neutrinos get mass only from radiative contributions.Comment: 19 pages, 9 figures, corresponds to published versio

Exotic Seesaw-Motivated Heavy Leptons at the LHC

We study the LHC potential for discovering TeV-scale SU(2)_L 5-plet fermions introduced recently to explain small neutrino masses. We show that the Drell-Yan production and the decays of new exotic Sigma leptons are testable at the LHC. Their production is abundant due to nontrivial electroweak gauge charges. For 1 fb^-1 of integrated luminosity at the present LHC sqrt{s}=7 TeV, there can be 270 Sigma-Sigmabar pairs produced for M_Sigma = 400 GeV. Besides producing same-sign dilepton events, they could lead, due to a chosen small mixing between heavy and light leptons, to ~10 golden decays Sigma^{+++}(Sigma^{+++}-bar) --> W^\pm W^\pm l^\pm with a specific decay signature.Comment: 31 pages, 10 figures, corresponds to the PRD versio

Supkutani ksantom u nimfe (Nymphicus hollandicus) - prikaz slučaja.

Subcutaneous tumor in a 17-year-old female cockatiel is described. The yellowish, elliptic tumor measuring 4×3 cm was noticed by the owner of this bird, on the right side of the cloaca. The skin was damaged and the wound was bleeding. After the clinical examination, surgical removal of the tumor was suggested. Histopathological examination revealed the presence of a xanthoma. In a period of one year, neither the reoccurrence of the skin xanthoma nor any health problems were observed.U radu je opisan potkožni tumor u nimfe stare 17 godina. S lijeve strane kloake vlasnik je uočio žućkastu, eliptičnu tvorevinu veličine 4×3 cm. Iznad otekline koža je bila oštećena te je krvarila. Nakon kliničkog pregleda predloženo je kirurško odstranjenje tumora. Histopatološki je ustanovljen ksantom. U razdoblju od jedne godine ksantom se nije ponovo pojavio, a nisu zabilježene ni druge zdravstvene poteškoće

Novel TeV-scale seesaw mechanism with Dirac mediators

We propose novel tree level seesaw mechanism with TeV-scale vectorlike Dirac mediators that produce Majorana masses of the known neutrinos. The gauge quantum number assignment to the Dirac mediators allows them to belong to a weak triplet and a five-plet of nonzero hypercharge. The latter leads to new seesaw formula m_\nu ~ v^6/M^5, so that the empirical masses m_\nu ~ 10^{-1} eV can be achieved by M ~ TeV new states. There is a limited range of the parameter space with M < a few 100 GeV where the tree level contribution dominates over the respective loop contributions and the proposed mechanism is testable at the LHC. We discuss specific signatures for Dirac type heavy leptons produced by Drell-Yan fusion at the LHC.Comment: 10 pages, 1 figure, version corresponding to PL