arXiv subjects

Alper Hayreter

Publications and source records attributed to Alper Hayreter.

18 recordsLinked to original sources

arXiv2020

Color-octet scalar decays to a gluon and an electroweak gauge boson in the Manohar-Wise model

We 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 $γ$ 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 ($t\bar t$ and $t\bar b$); or for small Yukawa couplings in which case the colored scalars are fermiophobic. In the case of light scalars, ${\cal B}(S\to γg)$ can reach up to 10\% whereas ${\cal B}(S\to Z g)$ can reach a few percent. In the fermiophobic region of parameter space, ${\cal B}(S\to γg)$ and ${\cal B}(S\to Z g)$ can reach up to 72\% and 28\% respectively, whereas ${\cal B}(S\to g g)$ can be 100\%. For the charged scalar, the decay mode ${\cal B}(S^\pm \to W^\pm g)$ can become dominant in both scenarios.

hep-ph↗

arXiv2020

LHC constraints on $W^\prime,~Z^\prime$ that couple mainly to third generation fermions

We use the results of CMS and ATLAS searches for resonances that decay to $τν$ or $tb$ and $τ^+τ^-$ or $t\bar t$ final states to constrain the parameters of non-universal $W^\prime$ and $Z^\prime$ gauge bosons that couple preferentially to the third generation. For the former we consider production from $c\bar{b}$ annihilation and find very weak constraints on the strength of the interaction and only for the mass range between 800 and 1100 GeV from the $pp \to τ_h p_T^{\rm miss}$ channel. The constraints on the latter are much stronger and arise from both $t\bar t$ and $τ^+τ^-$ production. Treated separately, we find that the weak constraints on the $W^\prime$ still permit an explanation of the $R(D^{(\star)})$ anomalies with a light sterile neutrino whereas the stronger constraints on the $Z^\prime$ exclude significant light sterile neutrino contributions to the $K \to πν\barν$ rates. Within specific models the masses of $W^\prime$ and $Z^\prime$ are of course related and we briefly discuss the consequences.

hep-ph↗

arXiv2020

Deconvolution of the High Energy Particle Physics Data with Machine Learning

A method for correcting smearing effects using machine learning technique is presented. Compared to the standard deconvolution approaches in high energy particle physics, the method can use more than one reconstructed variable to predict the value of unsmeared quantity on an event-by-event basis. In this particular study, deconvolution is interpreted as a classification problem, and neural networks (NN) are trained to deconvolute the Z boson invariant mass spectrum generated with MadGraph and pythia8 Monte Carlo event generators in order to prove the principle. Results obtained from the machine learning method is presented and compared with the results obtained with traditional methods.

physics.data-an↗

arXiv2017

LHC constraints on color octet scalars

We extract constraints on the parameter space of the MW model by comparing the cross-sections for dijet, top-pair, dijet-pair, $t\bar t t \bar t$ and $b\bar b b \bar b$ productions at the LHC with the strongest available experimental limits from ATLAS or CMS at 8 or 13 TeV. Overall we find that masses below 1 TeV have not been excluded for color octet scalars as it is often claimed in the literature. The constraints that can be placed on coupling constants are typically weaker than those from existing theoretical considerations, with the exception of the parameter $η_D$.

hep-ph↗

arXiv2016

Yukawa sector for LFV in $h\to μτ$ and CP violation in $h\to ττ$

The 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 lepton flavor violating (LFV) signal $h\toμτ$, 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 $h\to ττ$. We study two types of models that single out the third generation and can induce large $h \to μτ$ rates with different consequences for CP violation in $h \to ττ$. 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.

hep-ph↗

arXiv2016

CP violation in $h\to ττ$ and LFV $h\to μτ$

The CMS collaboration has reported a possible lepton flavour violating (LFV) signal $h\toμτ$. 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 $h\to ττ$. 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.

hep-ph↗

arXiv2016

T-odd correlations from top-quark CEDM in lepton plus jets top-pair events

There exist several recent studies of the top-quark CEDM in the context of searching for CP 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 MadGraph, 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 $\bar{b}$ jets and propose a simple way to address this.

hep-ph↗

arXiv2015

Spin correlations and new physics in $τ$-lepton decays at the LHC

We 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.

hep-ph↗

arXiv2015

Higgs production constraints on anomalous fermion couplings

Certain 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.

hep-ph↗

arXiv2015

Constraining $τ$-lepton dipole moments and gluon couplings at the LHC

We study the constraints that can be placed on anomalous $τ$-lepton couplings at the LHC. We use an effective Lagrangian description for physics beyond the standard model which contains the $τ$-lepton anomalous magnetic moment, electric dipole moment and weak dipole moments in two operators of dimension six. We include in our study two additional operators of dimension eight that directly couple the $τ$-leptons to gluons and are therefore enhanced at the LHC. We consider the two main effects from these couplings: modifications to the Drell-Yan cross-section and to the $τ$-lepton pair production in association with a Higgs boson. We find that a measurement of the former at the 14% level can produce constraints comparable to existing ones for the anomalous dipole couplings; and that a bound on the latter at a sensitivity level of $500\ σ_{SM}$ or better would produce the best constraint on the $τ$-gluonic couplings.

hep-ph↗

arXiv2014

Top-quark forward-backward asymmetry from a color-octet t-channel resonance

We consider new physics contributions to the top-quark forward-backward asymmetry from a neutral $V^0_8$ 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 $Z^\prime$ and $W^\prime$. 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.

hep-ph↗

arXiv2013

Constraints on anomalous color dipole operators from Higgs boson production at the LHC

Physics beyond the standard model (SM) can be parameterized with an effective Lagrangian that respects the symmetries of the standard model and contains many operators of dimension six. We consider the subset of these operators that is responsible for flavor diagonal anomalous color magnetic (CMDM) and electric (CEDM) dipole couplings between quarks and gluons. Invariance of these operators under the SM implies that they contribute to Higgs boson production at the LHC and we study the corresponding constraints that can be placed on them. For the case of the top-quark we first review constraints from top-quark pair production and decay, and then compare them to what can be achieved by studying $t\bar{t}h$ production. We also constrain the corresponding couplings for $b$-quarks and light quarks by studying $pp \to b\bar{b}h$ and $pp \to hX$ respectively.

hep-ph↗

arXiv2011

Top Quark Pair Production and Asymmetry at the Tevatron and LHC in Left-Right Models

In light of the recent measurements of the top quark forward-backward asymmetry at the Fermilab Tevatron experiment, which in some regions of the parameter space shows a discrepancy of 3$σ$ compared to the SM prediction, we analyze top quark pair production and asymmetry in the context of left-right models both at the Tevatron and LHC. We use the minimal manifest left-right model and an asymmetric left-right model where gauge couplings and flavor mixing in the right-handed sector are allowed to differ from those in the left-handed sector. We explore the consequences of including effects from $W_R$ and $Z_R$ gauge bosons, consistent with phenomenological constraints from meson mixing and new bounds from ATLAS and CMS, for the $t \bar{t}$ cross section, invariant mass distribution and forward-backward asymmetry at the Tevatron, and predict their values at the LHC. We show that, choosing parameter benchmarks for the model while preserving agreement with collider, electroweak precision, and flavor violation data, the generic left-right model cannot account for the large deviations of the observed asymmetry at the Tevatron and also that it predicts very small charge asymmetries at the LHC.

hep-ph↗

arXiv2011

Production and Decays of $W_R$ bosons at the LHC

With the advent of the LHC, it is important to devise clear tests for Physics Beyond the Standard Model. Such physics could manifest itself in the form of new charged bosons, whose presence is most naturally occurring in left-right symmetric models (LRSM). We analyze the single $W_R$ boson production in an asymmetric left-right model, where the left and right quark mixing matrices are not constrained to be equal. We investigate the cross sections as well as branching ratios of $W_R$ bosons at the LHC, including constraints from low energy phenomenology. We then look for most likely signals in $pp \to W_R\ t \to t ~(dijet)$ production. Including the background, we find that LHC could show significant signals for the new charged bosons. We compare our results throughout with the manifest left-right symmetric model and comment on similarities and differences.

hep-ph↗

arXiv2010

B Decays in an Asymmetric Left-Right Model

Motivated by recently observed disagreements with the SM predictions in $B$ decays, we study $b \to d, s$ transitions in an asymmetric class of $SU(2)_L \times SU(2)_R \times U(1)_{B-L}$ models, with a simple one-parameter structure of the right handed mixing matrix for the quarks, which obeys the constraints from kaon physics. We use experimental constraints on the branching ratios of $b \to s γ$, $b \to c e {\bar ν}_e$, and $B_{d,s}^0 -\bar{B}^0_{d,s}$ mixing to restrict the parameters of the model: $\displaystyle {g_R}/{g_L}, M_{W_2}, M_{H^\pm}, \tan β$ as well as the elements of the right-handed quark mixing matrix $V^R_{CKM}$. We present a comparison with the more commonly used (manifest) left-right symmetric model. Our analysis exposes the parameters most sensitive to $b$ transitions and reveals a large parameter space where left- and right-handed quarks mix differently, opening the possibility of observing marked differences in behaviour between the standard model and the left-right model.

hep-ph↗

arXiv2009

Neutral Higgs Sector of the MSSM with Explicit CP violation and Non-Holomorphic Soft Breaking

Using the effective potential method, we computed one-loop corrections to the mass matrix of neutral Higgs bosons of the Non-Holomorphic Supersymmetric Standard Model (NHSSM) with explicit CP violation, where the radiative corrections due to the quarks and squarks of the third generation were taken into account. We observed that the non-holomorphic trilinear couplings can compete with the holomorphic ones in CP violating issues for the mass and mixing of the neutral Higgs bosons.

hep-ph↗

arXiv2008

Electric Dipole Moments in U(1)' Models

We study electric dipole moments (EDM) of electron and proton in E(6)--inspired supersymmetric models with an extra U(1) invariance. Compared to the Minimal Supersymmetric Standard Model (MSSM), in addition to offering a natural solution to the mu problem and predicting a larger mass for the lightest Higgs boson, these models are found to yield suppressed EDMs.

hep-ph↗

arXiv2007

Dilepton Signatures of Family Non-Universal U(1)'

The supersymmetric models extending the minimal supersymmetric standard model (MSSM) by an additional Abelian gauge factor U(1)' in order to solve the mu problem do generically suffer from anomalies disrupting the gauge coupling unification found in the MSSM. The anomalies are absent if the minimal matter content necessitated by the mu problem is augmented with exotic matter species having appropriate quantum numbers. Recently, it has been shown that anomaly cancellation can also be accomplished by introducing family non-universal U(1)' charges and non-holomoprhic soft-breaking terms. We discuss collider signatures of anomaly-free family non-universal U(1)' model by analyzing dilepton production in future colliders. We find that, both at LHC and NLC, one can establish existence/absence of such a Z' boson by simply comparing the number of dilepton production events for electron, muon and tau lepton. The signal is free of the SM background.

hep-ph↗