State of the art POWHEG generators for top mass measurements at the LHC

We study the theoretical uncertainties in the determination of the top-quark mass using next-to-leading-order (NLO) generators, that describe the top-quark decay at different levels of accuracy, interfaced to parton showers (PS). Specifically we consider one generator that implements NLO corrections only in the production dynamics, one that also takes them into account in the top-quark decay in the narrow width approximation (NWA) and one that implements them exactly, including finite-width and interference effects. We aim at assessing the errors in top-mass determinations of purely theoretical origin. We do so by measuring relative peak position shifts of $Wb$-jet mass distributions. Besides the theoretical errors due to the use of less accurate NLO+PS generators, we also explore uncertainties related to shower and modelling of non-perturbative effects by comparing the results obtained by interfacing our generators to both Pythia and Herwig shower Monte Carlos (SMCs).Comment: Proceedings of the XXVI International Workshop on Deep-Inelastic Scattering and Related Subjects (DIS2018), 16-20 April 2018, Kobe, Japa

Hadroproduction of four top quarks in the POWHEG BOX

We present a new Monte Carlo event generator for the hadronic production of four top quarks in the POWHEG BOX framework. Besides the dominant next-to-leading order QCD corrections at $\mathcal{O}(\alpha_s^5)$ we also include all subleading electroweak productions channels at leading-order accuracy. We validate our theoretical predictions by comparing to parton-shower matched predictions obtained within the MC@NLO framework for stable top quarks. Furthermore, we investigate in detail the various sources of theoretical uncertainties. Finally, we investigate a single lepton plus jets signature to study for the first time the impact of the electroweak production modes as well as spin-correlation effects at the fiducial level.Comment: 14 pages, 8 figures, 1 table, matches published versio

Vliv krytých call opcí na výkonnost portfolia

This thesis aims to evaluate the performance of a covered call strategy writ- ten on Exchange-traded funds compared to a buy-and-hold strategy of the Exchange-traded fund on the US stock market. The strategy is constructed us- ing at-the-money, two-percent and five-percent out-of-the-money call options. The premium for the former is taken from historical market data and for the latter two calculated using the Black-Scholes-Merton formula adjusted for div- idends. The results further provide a two-period distinction to better account for di erent market periods, namely Covid-19 and the geopolitical conflict in Ukraine. The results fail to show evidence of a significant di erence between a covered call strategy and the buy-and-hold strategy. However, we provide possible applications of the strategy in certain market settings. The perfor- mance is evaluated on the basis of annualized returns and standard deviation, as ratios based on the mean-variance framework are omitted due to possible bias of negatively skewed distribution of returns of the covered call strategy. JEL Classification G10, G11, G12, G13, C02 Keywords Covered calls, ETF, Black-Scholes model, Op- tions pricing, Portfolio performance Title E ect of covered calls on portfolio performanceCie om tejto práce je zhodnoti v˝konnos stratégie kryt˝ch call opcií vypísan˝ch na fondy obchodované na burze v porovnaní so stratégiou nákupu a drûa- nia dan˝ch fondov na americkom akciovom trhu. Stratégia je zostavená s pouûitím kúpnych opcií at-the-money, dvojpercentn˝ch a pä percentn˝ch out- of-the-money. Prémia pre prvú z nich je prevzatá z historick˝ch trhov˝ch údajov a pre druhé dve je vypo ítaná pomocou Black-Scholesovho-Mertonovho vzorca upraveného o dividendy. V˝sledky alej poskytujú rozlíöenie na dve ob- dobia, aby sa lepöie zoh adnili fluktuácie na trhu, konkrétne Covid-19 a geopol- itick˝ konflikt na Ukrajine. V˝sledky nepreukazujú v˝znamn˝ rozdiel medzi stratégiou kryt˝ch kúpnych opcií a stratégiou nákupu a drûania. Uvádzame vöak, ûe stratégiu je moûné vyuûi v ur it˝ch trhov˝ch podmienkach. V˝kon- nos sa hodnotí na základe anualizovan˝ch v˝nosov a ötandardnej odch˝lky. Metriky zaloûené na rámci strednej odch˝lky sa vynechávajú z dôvodu moûného skreslenia kvôli tomu, ûe v˝nosy stratégie kryt˝ch call opcií majú negatívne zoöikmenie. Klasifikace JEL G10, G11, G12, G13, C02 Klí ová slova Kryté call opcie, ETF, Blackov-Scholesov model, Oce ovanie opcií, V˝konnos port- fólia Název práce Vliv kryt˝ch call opcí na v˝konnost portfo- liaInstitute of Economic StudiesInstitut ekonomických studiíFaculty of Social SciencesFakulta sociálních vě

Extracting the Top-Quark Width from Non-Resonant Production

In the context of the Standard Model (SM) of particle physics, the relationship between the top-quark mass and width ($\Gamma_t$) has been precisely calculated. However, the uncertainty from current direct measurements of the width is nearly 50%. A new approach for directly measuring the top-quark width using events away from the resonance peak is presented. By using an orthogonal dataset to traditional top-quark width extractions, this new method may enable significant improvements in the experimental sensitivity in a method combination. Recasting a recent ATLAS differential cross section measurement, we find $\Gamma_t$ = 1.28 $\pm$ 0.30 GeV (1.33 $\pm$ 0.29 GeV expected), providing the most precise direct measurement of the width.Comment: 7 pages, 2 figure

NLO+NLL limits on W′W' and Z′Z' gauge boson masses

QCD resummation predictions for the production of new charged ($W'$) and neutral ($Z'$) heavy gauge bosons decaying leptonically are presented. These results are obtained with our resummation code at next-to-leading order and next-to-leading logarithmic (NLO+NLL) accuracy. Our predictions are compared to PYTHIA at leading order (LO) supplemented with parton showers (PS) and FEWZ at NLO and next-to-next-to-leading order (NNLO) for the $p_T$-differential and total cross sections in the Sequential Standard Model (SSM) and general SU(2)$\times$SU(2)$\times$U(1) models. We show that the importance of resummation for total cross sections increases with the gauge boson mass. Finally, the latest ATLAS and CMS results are reinterpreted to derive new limits at NLO+NLL on $W'$ and $Z'$ boson masses in general extensions of the Standard Model.Comment: Proceeding of the XXIII International Workshop on Deep Inelastic Scattering and Related Subjects, April 27 - May 1, 2015, Southern Methodist University, Dallas, Texa

Resonance-aware NLOPS matching for off-shell ttˉ+tWt\bar t+tW production with semileptonic decays

The increasingly high accuracy of top-quark studies at the LHC calls for a theoretical description of $t\bar t$ production and decay in terms of exact matrix elements for the full $2\to 6$ process that includes the off-shell production and the chain decays of $t\bar t$ and $tW$ intermediate states, together with their quantum interference. Corresponding NLO QCD calculations matched to parton showers are available for the case of dileptonic channels and are implemented in the bb4l Monte Carlo generator, which is based on the resonance-aware POWHEG method. In this paper, we present the first NLOPS predictions of this kind for the case of semileptonic channels. In this context, the interplay of off-shell $t\bar t+tW$ production with various other QCD and electroweak subprocesses that yield the same semileptonic final state is discussed in detail. On the technical side, we improve the resonance-aware POWHEG procedure by means of new resonance histories based on matrix elements, which enable a realistic separation of $t\bar t$ and $tW$ contributions. Moreover, we introduce a general approach which makes it possible to avoid certain spurious terms that arise from the perturbative expansion of decay widths in any off-shell higher-order calculation, and which are large enough to jeopardise physical finite-width effects. These methods are implemented in a new version of the bb4l Monte Carlo generator, which is applicable to all dileptonic and semileptonic channels, and can be extended to fully hadronic channels. The presented results include a NLOPS comparison of off-shell against on-shell $t\bar t+tW$ production and decay, where we highlight various non-trivial aspects related to NLO and parton-shower radiation in leptonic and hadronic top decays.Comment: 78 pages, 20 figures, 6 table