arXiv subjects

Levent Selbuz

Publications and source records attributed to Levent Selbuz.

9 recordsLinked to original sources

arXiv2023

Mono-Photon Events with Light Higgs bosons in Secluded UMSSM

We explore the Higgs boson implications of a class of supersymmetric models, which extends the MSSM gauge group by a $U(1)^{\prime}$ symmetry, which is broken at low energy scales by VEVs of four MSSM singlet fields. These singlets also form a secluded sector, and one of them is allowed to interact with the MSSM Higgs fields directly. After the $U(1)^{\prime}$ and electroweak symmetry breaking, the low scale spectra include six CP-even and 4 CP-odd Higgs bosons, whose masses can lie from 80 GeV to 2-3 TeV. We find that the heavy CP-even Higgs bosons can be probed through their decays into a pair of SM gauge bosons currently up to about $m_{h_{i}} \simeq 1.5$ TeV, while their probe can be extended to about $m_{h_{i}} \simeq 2.5$ TeV in near future. The most interesting feature of the low scale spectra in the class of Secluded $U(1)^{\prime}$ models is to include two light CP-odd Higgs bosons whose masses are bounded at about 250 GeV by the current collider and DM experiments, when the LSP neutralino is mostly formed by the MSSM singlets. These light CP-odd Higgs bosons should be formed by the MSSM singlet scalars to be consistent with the current constraints. Despite their singlet nature, they can be traced through their associated production with photons. In our work, we consider their productions at the collider experiments together with photons, and we realize that these light Higgs bosons can potentially be probed during Run-3 experiments of LHC when they are lighter than about 100 GeV. We also show that Run-4 and HL-LHC experiments will be able to probe these light scalars up to about 250 GeV.

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arXiv2022

Model Characterization and Dark Matter in the Secluded $U(1)^\prime$ Model

We consider a class of $U(1)^\prime$-extended MSSM in which the $U(1)^{\prime}$ symmetry is broken by vacuum expectation values (VEVs) of four MSSM singlet fields. While one MSSM singlet field interacts with the MSSM Higgs fields, three of them interact only with each other in forming a secluded sector. Assigning universal $U(1)^{\prime}$ charges for three families, the anomaly cancellation condition requires exotic fields which are assumed to be heavy and decoupled. We discuss a variety of $U(1)^{\prime}$ charge assignments and anomaly cancellation, $Z^{\prime}/Z$ hierarchy, neutralinos, charginos and the Higgs sector. We find that the typical spectra involve two CP-odd Higgs bosons lighter than about 200 GeV and 600 GeV respectively, which are mostly formed by the MSSM singlet fields. If the relic density of dark matter is saturated only by a neutralino, compatible solutions predict LSP neutralinos formed by the MSSM singlet fields in the mass scales below about 600 GeV, while it is possible to realize MSSM neutralino LSP above these mass scales. One can classify the implications in three scenarios. Scenario I involves NLSP charginos, while Scenario II involves charginos which do not participate coannihilation processes with the LSP neutralino. These two scenarios predict MSSM singlet LSP neutralinos, while Scenario I leads to larger scattering cross-sections of dark matter. Scenario III has the solutions in which the MSSM neutralinos are considerably involved in LSP decomposition which yields very large scattering cross-section excluded by the direct detection experiments.

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arXiv2018

Charged Higgs in MSSM and Beyond

We conduct a numerical study over the constrained MSSM (CMSSM), Next-to-MSSM (NMSSM) and $U(1)$ extended MSSM (UMSSM) to probe the allowed mass ranges of the charged Higgs boson and its dominant decay patterns, which might come into prominence in near future collider experiments. {We present results obtained from a limited scan for CMSSM} as a basis and compare its predictions with the extended models. We observe within our data that a wide mass range is allowed as $0.5(1) \lesssim m_{H^{\pm}} \lesssim 17$ TeV in UMSSM (NMSSM). We find that the dominant decay channel is mostly $H^{\pm}\rightarrow tb$ such that ${\rm BR}(H^{\pm}\rightarrow tb) \sim 80\%$. While this mode remains dominant over the whole allowed parameter space of CMSSM, we realize some special domains in the NMSSM and UMSSM, in which ${\rm BR}(H^{\pm}\rightarrow tb) \lesssim 10\%$. In this context, the decay patterns of the charged Higgs can play a significant role to distinguish among the SUSY models. In addition to the $tb$ decay mode, we find that the narrow mass scale in CMSSM allows only the decay modes for the charged Higgs boson to $τν$ ($\sim 16\%$), and their supersymmetric partners $\tildeτ\tildeν$ ($\sim 13\%$). On the other hand, it is possible to realize the mode in NMSSM and UMSSM in which the charged Higgs boson decays into a chargino and neutralino pair up to about $25\%$. {This decay mode requires non-universal boundary conditions within the MSSM framework to be available, since CMSSM yields ${\rm BR} (H^{\pm}\rightarrow \tildeχ_{1}^{0}\tildeχ_{1}^{\pm}) \lesssim 1\%$.} It can also be probed in near future collider experiments through the missing energy and CP-violation measurements...

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arXiv2013

Neutralino and Chargino Production in U(1)' at the LHC

We examine the production and the decay modes of neutralinos and charginos in a softly-broken supersymmetric model with an extra Abelian symmetry U(1)'. We perform the study in a U(1)' model with a secluded sector, where the tension between the electroweak scale and developing a large enough mass for Z' is resolved by incorporating three additional SU(2) singlet fields into the model. Although the chargino sector is the same as in the MSSM, the neutralino sector of the model is very rich: five new fermion fields are added to the neutral sector bring the total neutralino states to nine. We implement the model into standard packages and perform a detailed and systematic analysis of production and decay modes at the LHC, for three different scenarios, and concentrating on final signals (1) 1 lepton+jets +MET, (2) 2 leptons+jets +MET and (3) 3 lepton+0jets +MET, and comment on the case with 0 lepton+jets +MET. We discuss backgrounds and indicate how these signals can be observed, and how the model can be distinguished from other supersymmetric model scenarios.

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arXiv2013

Sterile neutrinos in U(1)' with R-parity Violation

Motivated by results from short-baseline neutrino oscillation data, we study neutrino masses and mixing in U(1)' supersymmetric models with R-parity breaking. Whether R-parity is broken spontaneous or through (effective) bilinear terms in the Lagrangian, the breaking terms induce mixing between the neutralinos and neutrinos, creating a scenario in which some neutralinos can be heavy, and some light. Both the right-handed neutrino and the singlino (fermionic partner of the additional singlet Higgs field) can be light, and act as sterile neutrinos, which reconcile some of the anomalies observed in solar baseline and reactor experiments. We show that, scanning a large range of the parameter space satisfying solar and atmospheric neutrino constraints, the mass and mixing parameters of the sterile neutrinos are very restrictive, leading to some predictive features for the U(1)' scenarios.

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arXiv2013

Higgs Bosons in supersymmetric U(1)' models with CP Violation

We study the Higgs sector of the U(1)'-extended MSSM with CP violation. This is an extension of the MSSM Higgs sector by one singlet field, introduced to generate the μterm dynamically. We are particularly interested in non-standard decays of Higgs particles, especially of the lightest one, in the presence of CP violating phases for μ_{eff} and the soft parameters. We present analytical expressions for neutral and charged Higgs bosons masses at tree and one-loop levels, including contributions from top and bottom scalar quark sectors. We then study the production and decay channels of the neutral Higgs for a set of benchmark points consistent with low energy data and relic density constraints. Numerical simulations show that a Higgs boson lighter than 2m_W can decay in a quite distinctive manner, including invisible modes into two neutralinos (h->χ^0χ^0) up to 50% of the time, when kinematically allowed. The branching ratio into h->bb, the dominant decay in the SM, is reduced in some U(1)' models and enhanced in others, while the branching ratios for the decays h -> τ+ τ-, h -> WW^* and h -> Z Z^*-> 4l are always reduced with respect to their SM expectations. This possibility has important implications for testing the U(1)' model both at the LHC and later at the ILC.

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arXiv2010

Scalar Neutrinos at the LHC

We study a softly-broken supersymmetric model whose gauge symmetry is that of the standard model (SM) gauge group times an extra Abelian symmetry U(1)'. We call this gauge-extended model U(1)' model, and we study a U(1)' model with a secluded sector such that neutrinos acquire Dirac masses via higher-dimensional terms allowed by the U(1)' invariance. In this model the mu term of the minimal supersymmetric model (MSSM) is dynamically induced by the vacuum expectation value of a singlet scalar. In addition, the model contains exotic particles necessary for anomaly cancellation, and extra singlet bosons for achieving correct Z'/Z mass hierarchy. The neutrinos are charged under U(1)', and thus, their production and decay channels differ from those in the MSSM in strength and topology. We implement the model into standard packages and perform a detailed analysis of sneutrino production and decay at the Large Hadron Collider, for various mass scenarios, concentrating on three types of signals: (1) 0lep+ MET,(2) 2lep+MET, and (3) 4lep + MET. We compare the results with those of the MSSM whenever possible, and analyze the SM background for each signal. The sneutrino production and decays provide clear signatures enabling distinction of the U(1)' model from the MSSM at the LHC.

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arXiv2010

Sneutrino Dark Matter: Symmetry Protection and Cosmic Ray Anomalies

We present an R-parity conserving model of sneutrino dark matter within a Higgs-philic U(1)' extension of the minimal supersymmetric standard model. In this theory, the mu parameter and light Dirac neutrino masses are generated naturally upon the breaking of the U(1)' gauge symmetry. The leptonic and hadronic decays of sneutrinos in this model, taken to be the lightest and next-to-lightest superpartners, allow for a natural fit to the recent results reported by the PAMELA experiment.

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arXiv2008

Trilinear Higgs couplings in the two Higgs doublet model with CP violation

We carry out a detailed analysis of the general two Higgs doublet model with CP violation. We describe two different parametrizations of this model, and then study the Higgs boson masses and the trilinear Higgs couplings for these two parametrizations. Within a rather general model, we find that the trilinear Higgs couplings have a significant dependence on the details of the model, even when the lightest Higgs boson mass is taken to be a fixed parameter. We include radiative corrections in the one-loop effective potential approximation in our analysis of the Higgs boson masses and the Higgs trilinear couplings. The one-loop corrections to the trilinear couplings of the two Higgs doublet model also depend significantly on the details of the model, and can be rather large. We study quantitatively the trilinear Higgs couplings, and show that these couplings are typically several times larger than the corresponding Standard Model trilinear Higgs coupling in some regions of the parameter space. We also briefly discuss the decoupling limit of the two Higgs doublet model.

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