Browsing by Author "Hayreter, Alper"
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ArticlePublication Open Access Color-octet scalar decays to a gluon and an electroweak gauge boson in the Manohar-Wise model(American Physical Society, 2020-12-28) Hayreter, Alper; Valencia, G.; Natural and Mathematical Sciences; HAYRETER, AlperWe present one loop results for the amplitudes giving rise to couplings between a color octet scalar, a gluon, and an electroweak gauge boson. These amplitudes could signal new physics in( )gamma jet, Z jet and W jet production at the LHC. We compute the relevant branching ratios and identify regions of parameter space where these decay modes become important. This can happen for scalar masses below the threshold for decay into heavy quark pairs ((tt) over bar and t (b) over bar) or for small Yukawa couplings in which case the colored scalars are fermiophobic. In the ease of light scalars, 8(S -> gamma g) can reach up to 10% whereas B(S -> Zg) can reach a few percent. In the fermiophobic region of parameter space, B(S -> gamma g) and B(S -> Zg) can reach up to 72% and 28% respectively, whereas B(S -> gg) can be 100%. For the charged scalar, the decay mode 8(S-+/- -> W(+/-)g) can become dominant in both scenarios.
ArticlePublication Metadata only CP violation in h → ττ and LFV h → μτ(Elsevier, 2016-09-10) Hayreter, Alper; He, H.-G.; Valencia, G.; Natural and Mathematical Sciences; HAYRETER, AlperThe CMS Collaboration has reported a possible lepton flavor violating (LFV) signal h→μτ. Whereas this does not happen in the standard model (SM), we point out that new physics responsible for this type of decay would, in general, also produce charge-parity (CP) violation in h→ττ. We estimate the size of this effect in a model independent manner and find that a large asymmetry, of order 25%, is allowed by current constraints.Conference ObjectPublication Metadata only Higgs production constraints on anomalous fermion couplings(Elsevier, 2016) Hayreter, Alper; Valencia, G.; Natural and Mathematical Sciences; HAYRETER, AlperCertain anomalous fermion-gauge boson couplings, such as the flavor diagonal anomalous color magnetic (CMDM) and color electric (CEDM) dipole moments of quarks are not fully gauge invariant under the SM. Restoring gauge invariance with an elementary Higgs doublet implies that they also contribute to Higgs boson production at the LHC and we study the corresponding constraints that can be placed on them. In a similar manner we study the constraints that can be placed on the τ-lepton anomalous magnetic moment, electric dipole moment, weak dipole moments, and dimension eight gluonic couplings at the LHC.ArticlePublication Open Access Investigating the violation of charge-parity symmetry through top-quark chromoelectric dipole moments by using machine learning techniques(Jagiellonian University, 2023) Işıldak, B.; Hudaverdi, M.; Ilgın, F.; Hayreter, Alper; Salva, S.; Şimşek, E.; Guyer, S.; Law; HEPER, Mehmet AltanThere are a number of studies in the literature on the search for Charge- Parity (CP) violating signals in top-quark productions at the LHC. In most of these studies, ChromoMagnetic Dipole Moments (CMDM) and ChromoElectric Dipole Moments (CEDM) of top quarks are bounded either by deviations from the Standard Model (SM) cross sections or by T-odd asymmetries in di-muon channels. However, the required precision on these cross section values is far beyond from that ATLAS or CMS experiments can reach. In this letter, the investigation of CEDM-based asymmetries in the semileptonic top-pair decays is presented as T-odd asymmetries in the CMS experiment. Expected asymmetry values are determined at the detector level using MadGraph5, Pythia 8, and Delphes softwares along with the discrimination of the signal and the background with Deep Neural Networks (DNN).ArticlePublication Metadata only LHC constraints on color octet scalars(American Physical Society, 2017-08-09) Hayreter, Alper; Valencia, G.; Natural and Mathematical Sciences; HAYRETER, AlperWe extract constraints on the parameter space of the Manohar and Wise model by comparing the cross sections for dijet, top-pair, dijet-pair,t (t) over bart (t) over bar and b (b) over barb (b) over bar productions at the LHC with the strongest available experimental limits from ATLAS or CMS at 8 or 13 TeV. Overall we find mass limits around 1 TeV in the most sensitive regions of parameter space, and lower elsewhere. This is at odds with generic limits for color octet scalars often quoted in the literature where much larger production cross sections are assumed. The constraints that can be placed on coupling constants are typically weaker than those from existing theoretical considerations, with the exception of the parameter eta(D).ArticlePublication Open Access LHC constraints on W′, Z′ that couple mainly to third generation fermions(Springer Nature, 2020-11-03) Hayreter, Alper; He, X. G.; Valencia, G.; Natural and Mathematical Sciences; HAYRETER, AlperWe use the results of CMS and ATLAS searches for resonances that decay to tau nu or tb and tau(+)tau(-) or t (t) over bar final states to constrain the parameters of non-universal W' and Z' gauge bosons that couple preferentially to the third generation. For the former we consider production from c (b) over bar annihilation and find very weak constraints on the strength of the interaction and only for themass range between 800 and 1100 GeV from the pp -> tau(h)p(T)(miss) channel. The constraints on the latter are much stronger and arise from both t (t) over bar and tau(+)tau(-) production. Treated separately, we find that the weak constraints on the W' still permit an explanation of the R(D-(star)) anomalies with a light sterile neutrino whereas the stronger constraints on the Z' exclude significant light sterile neutrino contributions to the K -> pi nu(nu) over bar rates. Within specific models the masses of W' and Z' are of course related and we briefly discuss the consequences.ArticlePublication Metadata only Spin correlations and new physics in τ -lepton decays at the LHC(Springer International Publishing, 2015-07) Hayreter, Alper; Valencia, G.; Natural and Mathematical Sciences; HAYRETER, AlperWe use spin correlations to constrain anomalous τ -lepton couplings at the LHC including its anomalous magnetic moment, electric dipole moment and weak dipole moments. Single spin correlations are ideal to probe interference terms between the SM and new dipole-type couplings as they are not suppressed by the τ -lepton mass. Double spin asymmetries give rise to T -odd correlations useful to probe CP violation purely within the new physics amplitudes, as their appearance from interference with the SM is suppressed by m τ . We compare our constraints to those obtained earlier on the basis of deviations from the Drell-Yan cross-section.ArticlePublication Metadata only T-odd correlations from the top-quark chromoelectric dipole moment in lepton plus jets top-pair events(American Physical Society, 2016-01-01) Hayreter, Alper; Valencia, G.; Natural and Mathematical Sciences; HAYRETER, AlperThere exist several recent studies of the top-quark chromoelectric dipole moment (CEDM) in the context of searching for charge parity violating signals in top-quark pair production at the LHC. Most of these studies constrain the CEDM either from deviations in the top-pair cross section from its standard model value, or from T-odd asymmetries in the dimuon channel. Motivated by ATLAS and CMS interest, we extend the study of T-odd asymmetries to the lepton plus jets channel. At the parton level, using madgraph5, we identify the most promising signals and their statistical sensitivity. We find that the signals with larger sensitivity to the CEDM require distinguishing between b and b¯ jets and propose a simple way to address this.ArticlePublication Open Access Top-quark forward-backward asymmetry from a color-octet t-channel resonance(American Physical Society, 2014-05-09) Cheng, L.; Hayreter, Alper; Valencia, G.; Natural and Mathematical Sciences; HAYRETER, AlperWe consider new physics contributions to the top-quark forward-backward asymmetry from a neutral V-8(0) or charged V-8(+) color-octet vector exchanged in the t channel. We study the phenomenological constraints on these particles arising from the Tevatron and LHC7 measurements and compare them with those on their color-singlet counterparts Z' and W'. We find that the color octets fare better than the singlets in that they generate a lower A(C), a lower high-invariant mass cross section at LHC7 and a lower same sign top-pair cross section. However, they also generate a lower A(FB) than their color-singlet counterparts.ArticlePublication Metadata only Yukawa sector for lepton flavor violating in h -> mu tau and CP violation in h -> tau tau(American Physical Society, 2016-10-01) Hayreter, Alper; He, X.-G.; Valencia, G.; Natural and Mathematical Sciences; HAYRETER, AlperThe Higgs boson discovered at the LHC opened a new chapter for particle physics. Its properties need to be studied in detail to distinguish a purely standard model (SM) Higgs boson from one of many scalars in an enlarged Higgs sector. The CMS Collaboration has reported a possible signal for lepton flavor violation in h→μτ, which if confirmed, implies that the Higgs sector is larger than in the SM. New physics responsible for this type of decay may, in general, also introduce other observable effects such as charge-parity (CP) violation in h→ττ. We study two types of models that single out the third generation and can induce large h→μτ rates with different consequences for CP violation in h→ττ. Predictions for the size of the CP violating couplings require knowledge of the lepton Yukawa matrices and we discuss this in the context of two different textures considering all existing constraints.