Colored scalars as flavor messengers in grand unified theories

We critically review the proton decay due to the scalar leptoquark exchanges within SU(5) and flipped SU(5) frameworks to address the issue of the model dependence of the relevant tree level operators. We quantify if, and when, it is necessary to have the leptoquark mass close to a grand unification scale. We summarize novel results regarding a possibility to have a collider accessible leptoquark without a rapid proton decay. The relevant state could be observed indirectly through its influence on physical processes such as the forward-backward asymmetry in t¯t production due to an antisymmetric set of couplings to a pair of up-quarks. The same leptoquark could affect the muon anomalous magnetic moment through the interaction of a lepton-quark nature. We accordingly investigate whether both sets of couplings can be simultaneously sizable without any conflict with matter stability

Unification versus proton decay in SU(5)

We investigate unification constraints in the simplest renormalizable non-supersymmetric SU(5) framework. We show that in the scenario where the Higgs sector is composed of the 5, 24, and 45 dimensional representations the proton could be practically stable. We accordingly demonstrate that of all the SU(5) scenarios only the non-renormalizable one with the 5, 24, and 15 dimensional Higgs multiplets can be verify if low-energy supersymmetry is not realized in Nature.Comment: 10 pages, minor correction

Leptoquark toolbox for precision collider studies

We implement scalar and vector leptoquark (LQ) models in the universal FeynRules output (UFO) format assuming the Standard Model fermion content and conservation of baryon and lepton numbers. Scalar LQ implementations include next-to-leading order (NLO) QCD corrections. We report the NLO QCD inclusive cross sections in proton-proton collisions at 13 TeV, 14 TeV, and 27 TeV for all on-shell LQ production processes. These comprise (i) LQ pair production ($p p \to \Phi \Phi$) and (ii) single LQ + lepton production ($p p \to \Phi \ell$) for all initial quark flavours ($u$, $d$, $s$, $c$, and $b$). Vector LQ implementation includes adjustable non-minimal QCD coupling. We discuss several aspects of LQ searches at a hadron collider, emphasising the implications of $SU(2)$ gauge invariance, electroweak and flavour constraints, on the possible signatures. Finally, we outline the high-$p_T$ search strategy for LQs recently proposed in the literature to resolve experimental anomalies in $B$-meson decays. In this context, we stress the importance of complementarity of the three LQ related processes, namely, $p p \to \Phi \Phi$, $p p \to \Phi \ell$, and $p p \to \ell \ell$.Comment: 18 pages, 5 figures, 3 tables. Version published in JHE

Novel Leptoquark Pair Production at LHC

We introduce a novel mechanism for the leptoquark pair production at LHC that is of a $t$-channel topology and is quark-quark initiated. This mechanism operates under fairly general conditions. One of them is that the two leptoquarks in question couple to the same lepton and the other one is that the fermion numbers of these two leptoquarks differ by two. The strength of the proposed mechanism provides an alternative way to the conventional processes to efficiently constrain the parameter space of the two leptoquark scenarios at LHC whenever the aforementioned conditions are met. We accordingly present one case study to outline the physics potential of this novel production mechanism.Comment: 14 pages, 5 figure

Light colored scalars from grand unification and the forward-backward asymmetry in top quark pair production

The experimental results on the t bar t production cross section at the Tevatron are well described by the QCD contributions within the standard model, while the recent measurement of the forward-backward asymmetry cannot be accounted for within this framework. We consider light colored scalars appearing in a particular SU(5) GUT model within the 45-dimensional Higgs representation. A virtue of the model is that it connects the presence of a light colored SU(2) singlet (Delta_6) and a color octet weak doublet (Delta_1) with bounds on the proton lifetime, which constrain the parameter space of both scalars. We find that both the t bar t production cross section and the forward-backward asymmetry can be accommodated simultaneously within this model. The experimental results prefer a region for the mass of Delta_6 around 400 GeV, while Delta_1 is then constrained to have a mass around the TeV scale as well. We analyze possible experimental signatures and find that Delta_6 associated top production could be probed in the t bar t + jets final states at Tevatron and the LHC.Comment: 12 pages, 13 figures, version as publishe

Limits on scalar leptoquark interactions and consequences for GUTs

A colored weak singlet scalar state with hypercharge 4/3 is one of the possible candidates for the explanation of the unexpectedly large forward-backward asymmetry in t tbar production as measured by the CDF and D0 experiments. We investigate the role of this state in a plethora of flavor changing neutral current processes and precision observables of down-quarks and charged leptons. Our analysis includes tree- and loop-level mediated observables in the K and B systems, the charged lepton sector, as well as the Z to b bbar decay width. We perform a global fit of the relevant scalar couplings. This approach can explain the (g-2)_mu anomaly while tensions among the CP violating observables in the quark sector, most notably the nonstandard CP phase (and width difference) in the Bs system cannot be fully relaxed. The results are interpreted in a class of grand unified models which allow for a light colored scalar with a mass below 1TeV. We find that the renormalizable SU(5) scenario is not compatible with our global fit, while in the SO(10) case the viability requires the presence of both the 126- and 120-dimensional representations.Comment: 26 pages, 7 figures; version as publishe

Fully Testable Axion Dark Matter within a Minimal SU(5)SU(5) GUT

We present a minimal Grand Unified Theory model, based on $SU(5)$ gauge symmetry and a global $U(1)$ Peccei-Quinn symmetry, that predicts the existence of an ultralight axion dark matter within a narrow mass range of $m_a\in[0.1,\,4.7]\,$neV. This mass window is determined through an interplay between gauge coupling unification constraints, partial proton decay lifetime limits, and the need to reproduce the experimentally observed fermion mass spectrum. The entire parameter space of the proposed model will be probed through a synergy between several low-energy experiments that look for proton decay (Hyper-Kamiokande), axion dark matter through axion-photon coupling (ABRACADABRA and DMRadio-GUT) and nucleon electric dipole moments (CASPEr Electric).Comment: 28 pages + references, 9 figures, version accepted in PR

Hibridna traheotomija u vrijeme hibridnih automobila i hibridnih kongresa - ima li mjesto u COVID-19 jedinicama intenzivnog liječenja?

Pandemija COVID-19 postavila je velike izazove pred liječnike u cijelom svijetu. Riziku infekcije osobito su izloženi otorinolaringolozi, a traheotomija predstavlja jednu od najrizičnijih operacija. U radu se opisuje tehnika hibridne traheotomije koju su autori uočili čitajući literaturu o traheotomijama, te prednosti i nedostaci iste