1,721,012 research outputs found
Z' phenomenology in tt¯ and its asymmetries at the LHC
No full textThis thesis presents a collection of studies considering Z' physics in the tt¯ final state at the Large Hadron Collider (LHC), focusing largely on its charge and spin asymmetry observables. The analyses employ parton level simulations in the presence of the tree-level backgrounds and realistic reconstruction efficiency estimates. A number of extra U (1) models are studied, including various common benchmark models currently considered at the LHC as well as models more suited to tt¯ searches from composite Higgs scenarios and extra dimensions. The studies address the ability of tt¯, with its asymmetries, to distinguish models from the Standard Model background and one another, both on its own and as a complementary channel to other, more traditional final states with the view to a complete characterisation of the Z' couplings. Scenarios with two quasi-degenerate resonances are also considered where tt¯ asymmetries can identify their presence when cross section observables cannot resolve the two peaks
Axions and axion-like particles: collider searches
No full textWe give an overview of collider searches for Axion-like particles (ALPs). The intention of this review is to give a pedagogical introduction to collider phenomenology of ALPs, and provide a starting point for newcomers, including suitable references to deepen their knowledge. We motivate how ALPs arise from the breaking of approximate global symmetries and describe their interactions across different scales in an effective field theory framework. We further review the dominant production and decay channels for ALPs at high-energy hadron and lepton colliders as well as indirect ways to probe their interactions via precision measurements of Standard Model processes
Non-thermal production of heavy vector dark matter from relativistic bubble walls
No full textHeavy vector boson dark matter at the TeV scale or higher may be produced non-thermally in a first-order phase transition taking place at a lower energy scale. While the production of vector dark matter has previously been studied for bubble wall collisions, here we calculate production by bubble wall expansion in a plasma, which can be the dominant production mechanism. We compute the results numerically and provide an analytical fit for the vector dark matter density. The numerical fit is also validated for scalar dark matter production, obtaining results in agreement with past literature. We find that vector pair production leads to bubble wall friction with a novel boost factor scaling behaviour compared to transition radiation emission of a single vector. We conclude that TeV-scale WIMP vector dark matter can be efficiently produced non-thermally by first-order phase transitions in a wide region of parameter space where thermal freeze-out is inefficient. In this scenario, the phase transition scale is predicted to be in the sub-GeV to O(10) TeV range and could therefore be accessible to future gravitational wave detectors
Triboson production in the SMEFT
No full textWe study the production of three electroweak gauge bosons at the LHC, in the effective field theory of the standard model, at dimension six and next-to-leading order in QCD. We present results for inclusive cross-sections and differential distributions, finding that these QCD corrections are large, often vary across the phase-space and notably differ from those observed in the standard model. We then explore the potential of the recently observed triboson production processes for improving the sensitivity brought by electroweak precision observables and diboson data. The additional sensitivity we observe is dominated by resonant Higgs boson contributions, with decays to photon pairs in particular. A global analysis including Higgs boson data is therefore needed for a fair assessment of the future reach of triboson measurements on heavy new physics
Electroweak corrections in the SMEFT: four-fermion operators at high energies
No full textIn the Standard Model (SM), electroweak (EW) corrections become significant at high energies, particularly at the tera-electronvolt scale and beyond, due to the presence of Sudakov logarithms. At these energy scales, the Standard Model Effective Field Theory (SMEFT) framework provides an enhanced sensitivity to potential new physics effects. This motivates the inclusion of EW corrections not only for SM predictions but also for analyses within SMEFT. In this work, we compute EW corrections in the high-energy limit for a selected set of dimension-six operators, specifically the class of four-fermion contact interactions, in key hard-scattering processes relevant to both current and future colliders: top-quark pair production at the Large Hadron Collider (LHC) and in a muon collider scenario, as well as the Drell-Yan process at the LHC. We first discuss the technical details and challenges associated with evaluating EW Sudakov logarithms in SMEFT, contrasting them with the SM case. We then present phenomenological results for the aforementioned processes, highlighting the non-trivial effects introduced by EW corrections arising from the insertion of dimension-six, four-fermion operators. Importantly, the resulting K-factors exhibit significant deviations from their SM counterparts, with dependencies not only on the process but also on the specific operators considered. Finally, we explore the potential to lift flat directions in the SMEFT parameter space by incorporating higher-order corrections, using Fisher information techniques
Automated one-loop computations in the SMEFT
Get PDFWe present the automation of one-loop computations in the standard-model effective field theory at dimension 6. Our general implementation, dubbed smeft@nlo, covers all types of operators: bosonic and two- and four-fermion ones. Included ultraviolet and rational counterterms presently allow for fully differential predictions, possibly matched to the parton shower, up to the one-loop level in the strong coupling or in four-quark operator coefficients. Exact flavor symmetries are imposed among light quark generations, and an initial focus is set on top-quark interactions in the fermionic sector. We illustrate the potential of this implementation with novel loop-induced and next-to-leading-order computations relevant for top-quark, electroweak, and Higgs-boson phenomenology at the LHC and future colliders.We present the automation of one-loop computations in the standard-model effective field theory at dimension six. Our general implementation, dubbed SMEFT@NLO, covers all types of operators: bosonic, two- and four-fermion ones. Included ultraviolet and rational counterterms presently allow for fully differential predictions, possibly matched to parton shower, up to the one-loop level in the strong coupling or in four-quark operator coefficients. Exact flavor symmetries are imposed among light quark generations and an initial focus is set on top-quark interactions in the fermionic sector. We illustrate the potential of this implementation with novel loop-induced and next-to-leading-order computations relevant for top-quark, electroweak, and Higgs-boson phenomenology at the LHC and future colliders
Top-philic ALP phenomenology at the LHC: the elusive mass-window
No full textWe study the LHC phenomenology of an Axion Like Particle (ALP) that couples only derivatively with the top quark at tree level. We inspect the radiatively induced couplings with the SM fermions and (gauge) bosons and the associated production and decay mechanisms of the ALP. We focus on the most challenging mass window that remains open for a top-philic ALP, i.e., the range between tens and hundreds of GeV. Not only ALP production processes but also virtual ALP contributions to final states with top quarks are considered in detail. We show how searches through resonant production, such as ALP production in association with a pair, are complementary to precision measurements of and final states, the latter being competitive or even more powerful for a top-philic ALP in this mass window. Finally, we explore the scenario where the top-philic ALP acts as a mediator to a dark-matter sector, resulting in missing energy signatures at the LHC. We find that the LHC constraints from , and ALP + jet production, together with those from + ALP production, can already exclude a large fraction of the parameter space leading to the correct relic abundance
Complementarity of forward-backward asymmetry for discovery of Z' bosons at the Large Hadron Collider
No full textThe Forward-Backward Asymmetry (AFB) in Z' physics is commonly only thought of as an observable which possibly allows one to profiling a Z' signal by distinguishing different models embedding such (heavy) spin-1 bosons. In this brief review, we examine the potential of AFB in setting bounds on or even discovering a Z' at the Large Hadron Collider (LHC) and proof that it might be a powerful tool for this purpose. We analyse two different scenarios: Z's with a narrow and wide width, respectively. We find that, in both cases, AFB can complement the conventional searches in accessing Z' signals traditionally based on cross section measurements only
Forward-backward asymmetry as a discovery tool for Z' bosons at the LHC
Get PDFThe Forward-Backward Asymmetry (AFB) in Z? physics is commonly only perceived as the observable which possibly allows one to interpret a Z? signal appearing in the Drell-Yan channel by distinguishing different models of such (heavy) spin-1 bosons. In this paper, we revisit this issue, showing that the absence of any di-lepton rapidity cut, which is commonly used in the literature, can enhance the potential of the observable at the LHC. We moreover examine the ability of AFB in setting bounds on or even discovering a Z? at the Large Hadron Collider (LHC) concluding that it may be a powerful tool for this purpose. We analyse two different scenarios: Z?-bosons with a narrow and wide width, respectively. We find that, in the first case, the significance of the AFB search can be comparable with that of the ‘bump’ search usually adopted by the experimental collaborations; however, in being a ratio of (differential) cross sections, the AFB has the advantage of reducing experimental systematics as well as theoretical errors due to PDF uncertainties. In the second case, the AFB search can outperform the bump search in terms of differential shape, meaning the AFB distribution may be better suited for new broad resonances than the event counting strategy usually adopted in such cases
Single-top associated production with a or boson at the LHC: the SMEFT interpretation
Get PDFAt the LHC, top quarks can be produced singly with a sizeable rate via electroweak interactions. This process probes a limited set of top-quark electroweak couplings, i.e., the same entering the top-quark decay, yet at higher scales and with a different sensitivity. Requiring the production of a Z or H boson in association with single-top significantly extends the sensitivity of this process to new physics, opening up the unique possibility of testing top-Higgs, top-gauge, triple gauge, gauge-Higgs interactions without being dominated by QCD interactions. We consider tZj and tHj production at the LHC, providing predictions at next-to-leading accuracy in QCD in the framework of the standard model effective field theory, including all relevant operators up to dimension six. We perform the first complete study of the sensitivity to new interactions of these processes, highlighting the interplay and complementarity among tj, tZj and tHj in simultaneously constraining top-quark, triple gauge, and gauge-Higgs interactions in the current and future runs at the LHC.At the LHC, top quarks can be produced singly with a sizeable rate via electroweak interactions. This process probes a limited set of top-quark electroweak couplings, i.e. , the same entering the top-quark decay, yet at higher scales and with a different sensitivity. Requiring the production of a or boson in association with single-top significantly extends the sensitivity of this process to new physics, opening up the unique possibility of testing top-Higgs, top-gauge, triple gauge, gauge-Higgs interactions without being dominated by QCD interactions. We consider and production at the LHC, providing predictions at next-to-leading accuracy in QCD in the framework of the standard model effective field theory, including all relevant operators up to dimension six. We perform the first complete study of the sensitivity to new interactions of these processes, highlighting the interplay and complementarity among , and in simultaneously constraining top-quark, triple gauge, and gauge-Higgs interactions in the current and future runs at the LHC
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