Measurement of the top-Yukawa coupling is important to understand the fermion mass generation mechanism and dynamics of electroweak symmetry breaking. We discuss the top quark anomalous couplings which can be described by higher dimensional operators. We investigate the process $e^-e^+ \to W^-W^+ν\barν\to t \bar t ν\barν$ to study the contribution of the anomalous top-Higgs coupling to the cross section. The effect of the dimension-six top-Higgs interaction on the cross section can be a few hundred percent greater than the SM prediction. Such a large effect can be measured at the International Linear Collider.
In order to establish supersymmetry (SUSY) at future colliders, the identity of gauge couplings and the corresponding Yukawa couplings between gauginos, sfermions and fermions needs to be verified. Here a first phenomenological study for determining the Yukawa coupling of the SUSY-QCD sector is presented, using a method which combines information from LHC and ILC.
We explore discrimination of two types of leptonic Yukawa interactions associated with Higgs triplet, $\bar L^c_L ΔL_L$, and with $SU(2)$ singlet doubly charged scalar, $\bar e_R^c k^{++} e_R$. These interactions can be distinguished by measuring the effects of doubly charged scalar boson exchange in the $e^+ e^- \to \ell^+ ell^-$ processes at polarized electron-positron colliders. We study a forward-backward asymmetry of scattering angular distribution to estimate the sensitivity for these effects at the ILC. In addition, we investigate prospects of upper bounds on the Yukawa couplings by com…
A precise measurement of the top quark Yukawa coupling is of great importance, since it may shed light on the mechanism of EWSB. We study the prospects of such measurement during the first phase of the ILC at sqrt(s)=500 GeV, focusing in particular on recent theoretical developments as well as the potential benefits of beam polarization. It is shown that both yield improvements that could possibly lead to a measurement competitive with the LHC.
In this talk, we discuss the SUSY-Yukawa sum rule, a relation among masses and mixing angles of the third-generation squarks which follows directly from the coupling relation responsible for canceling the quadratic divergence in the Higgs mass. Radiative corrections modify the sum rule, introducing dependence on a variety of SUSY parameters beyond the third-generation squark sector. If some of those parameters are measured experimentally, a sharp prediction for the sum rule is possible. We demonstrate this point with a quantitative study. We also discuss the prospects for measuring the ingredi…
Yukawa production of a light scalar can be explored at a linear collider. Light (pseudo)scalar can exist in extended Higgs models and an interesting example is the light pseudoscalar in Type-X two Higgs doublet model. The model can explain the anomalous magnetic moment of muon at large $\tan β$. We show that the available parameter space in this model can be examined by the Yukawa process at 5$σ$ at the ILC.
We discuss lepton flavor violation (LFV) associated with tau leptons in the general framework of the two Higgs doublet model, in which LFV couplings are introduced as a deviation from Model II Yukawa interaction. Parameters of the model are constrained from experimental results and also from requirements of theoretical consistencies such as vacuum stability and perturbative unitarity. Current data for LFV rare tau decays provide substantial upper limits on the LFV Yukawa couplings in the large $\tanβ$ region, which are comparable with predictions in fundamental theories. Here $\tanβ$ is the ra…
We report on the feasibility of the direct measurement of the top Yukawa coupling g_t at the International Linear Collider (ILC) during its first phase of operation with a center-of-mass energy of 500 GeV. The signal and background models incorporate the non-relativistic QCD corrections which enhance the production cross section near the t-tbar threshold. The e+e- -> t tbar H signal is reconstructed in the 6-jet + lepton and the 8-jet modes. The results from the two channels are combined. The background processes considered are e+e- -> t bbar W- / tbar b W+ (which includes e+e- -> t tbar), e+e…
Among the firm predictions of softly broken supersymmetry is the identity of gauge couplings and the corresponding Yukawa couplings between gauginos, sfermions and fermions. In the event that a SUSY-like spectrum of new particles is discovered at future colliders, a key follow-up will be to test these relations experimentally. In detailed studies it has been found that the SUSY-Yukawa couplings of the electroweak sector can be studied with great precision at the ILC, but a similar analysis for the Yukawa coupling of the SUSY-QCD sector is far more challenging. Here a first phenomenological stu…
A pattern of deviations in coupling constants of Standard Model (SM)-like Higgs boson from their SM predictions indicates characteristics of an extended Higgs sector. In particular, Yukawa coupling constants can deviate in different patterns in four types of Two Higgs Doublet Models (THDMs) with a softly-broken Z_2 symmetry. We can discriminate types of THDMs by measuring the pattern of these deviations. We calculate Yukawa coupling constants of the SM-like Higgs boson with radiative corrections in all types of Yukawa interactions in order to compare to future precision data at the Internation…
Recent progress in Higgs boson studies for the International e+e- Linear Collider (ILC) is reported. These studies include extended simulations of the measurement of the Higgs mass, measurements of the Higgs boson branching ratios at higher center-of-mass energies, and methods for extracting the Higgs boson self-coupling. Also, the interplay between the LHC and the ILC in the measurement of the top Yukawa coupling and in the extraction of the supersymmetric Higgs sector parameters is discussed.
We study the possibility of measuring neutrino Yukawa couplings in the Next-to-Minimal Supersymmetric Standard Model with right-handed neutrinos (NMSSMr) when the lightest Supersymmetric partner (a right-handed sneutrino) is the Dark Matter (DM) candidate, by exploiting a `dijet + dilepton + Missing Transverse Energy' (MET) signature. We show that, unlike the miminal realisation of Supersymmetry (SUSY), i.e., the MSSM, for which the DM candidate is a much heavier (fermionic) state (a neutralino), this non-minimal SUSY model offers one with a much lighter (bosonic) state (a sneutrino) as DM, wh…
We study the possibility of measuring neutrino Yukawa couplings in the Next-to-Minimal Supersymmetric Standard Model with right-handed neutrinos (NMSSMr) when the lightest right-handed sneutrino is the Dark Matter (DM) candidate, by exploiting a `dijet + dilepton + Missing Transverse Energy' signature. We show that, contrary to the miminal realisation of Supersymmetry (SUSY), the MSSM, wherein the DM candidate is typically a much heavier (fermionic) neutralino state, this extended model of SUSY offers one with a much lighter (bosonic) state as DM that can then be produced at the next generatio…
We consider the issue of the top quark Yukawa coupling measurement in a model in dependent and general case with the inclusion of CP-violation in the coupling. Arguably the best process to study this coupling is the associa ted production of Higgs boson along with a $t\bar t$ pair in a machine like the International Linear Collider (ILC). While detailed analyses of the sensitivity of the measurement assuming a Standard Model (SM) - like coupling are available in the context of ILC, conclude that th e coupling could be pinned down at about 10\% level with modest luminosity, our investigations s…
Physics at the ILC is reviewed focusing mostly on Higgs physics. It is emphasized that at the ILC it is possible to measure the $hZZ$ coupling totally model independently, which in turn allows model-independent normalization of various branching ratio measurements and consequently the absolute measurements of corresponding couplings. Combining them with the measurements of the top Yukawa coupling and the Higgs self-coupling at higher energies, the full ILC program is shown to allow a precision test of the mass-coupling relation.
We study the feasibility of the Type-X two Higgs doublet model (THDM-X) at collider experiments. In the THDM-X, new Higgs bosons mostly decay into tau leptons in the wide range of the parameter space. Such scalar bosons are less constrained by current experimental data, because of the suppressed quark Yukawa interactions. We discuss a search strategy of the THDM-X with multi-tau lepton final states at International linear collider and Large Hadron Collider. By using the collinear approximation, we show that a four tau lepton signature (e^+e^- -> HA -> 4τ) can be a clean signal.
The ILC physics working group is a mixture of experimentalists and theorists mainly working in Japan. It has its origin in the previous LC physics study group and has been reformed with the initiative of a JSPS Creative Scientific Research project: "Research and Development of a Novel Detector System for the International Linear Collider". The working group is, however, formally independent of the JSPS project and is open to everybody who is interested in ILC physics. The primary task of the working group is to reexamine the ILC physics in the context of the expected LHC outcome and to further…
The discovery at the LHC of a scalar particle with properties that are so far consistent with the SM Higgs boson is one of the most important advances in the history of particle physics. The challenge of future collider experiments is to determine whether its couplings will show deviations from the SM Higgs, as this would indicate new physics at the TeV scale, and also to probe the flavor structure of the Yukawa couplings. As a benchmark alternative to the SM Higgs, we consider a generic two Higgs doublet model (2HDM) and analyze the precision to which the LHC14, an ILC250, 500, 1000 GeV and a…
With the prospect of improved Higgs measurements at the LHC and at proposed future colliders such as ILC, CLIC and TLEP we study the non-custodial Randall-Sundrum model with bulk SM fields and compare brane and bulk Higgs scenarios. We compute the electroweak precision observables and argue that incalculable contributions to these, in the form of higher dimensional operators, could have a non-negligable impact. This could potentially reduce the bound on the lowest Kaluza-Klein gauge boson masses to the 5 TeV range, making these states detectable at the LHC. In a second part, we compute the mis…
With high luminosity and energy at the ILC and clean SM backgrounds, the top-charm production at the ILC should have powerful potential to probe new physics. The littlest Higgs model with discrete symmetry named "T-parity"(LHT) is one of the most promising new physics models. In this paper, we study the FC processes $e^+e^-(γγ)\to t\bar{c}$ at the ILC in the LHT model. Our study shows that the LHT model can make a significant contribution to these processes. When the masses of mirror quarks become large, these two processes are accessible at the ILC. So the top-charm production at the ILC prov…
We study the effects of gluon radiation in top pair production and their decays for e+e- annihilation at the ILC. To achieve this we apply the POWHEG method and interface our results to the Monte Carlo event generator Herwig++. We consider a center-of-mass energy of 500GeV and compare decay correlations and bottom quark distributions before hadronization.
The International Linear e+e- Collider (ILC) could go into operation in the second half of the upcoming decade. Experimental analyses and theory calculations for the physics at the ILC are currently performed. We review recent progress, as presented at the LCWS06 in Bangalore, India, in the fields of Higgs boson physics and top/QCD. Also the area of loop calculations, necessary to achieve the required theory precision, is included.
A scan of the top quark pair production threshold at a future electron-positron collider provides the possibility for high-precision measurements of the top quark mass, and, when using two dimensional fits of the measured cross sections, also of other properties such as the width and the Yukawa coupling. The energy range of the scan and the distribution of the integrated luminosity can be optimized depending on the main goals of the threshold program. This contribution examines the possibility to determine the top quark mass in fast exploratory measurements with an adequate precision to enable…
The CMS collaboration reported an intriguing \sim 3 sigma (local) excess at 96 GeV in the light Higgs-boson search in the diphoton decay mode. This mass coincides with a \sim 2 sigma (local) excess in the bb final state at LEP. We present the interpretation of this possible signal as the lightest Higgs boson in the 2 Higgs Doublet Model with an additional real Higgs singlet (N2HDM). It is shown that the type II and type IV (flipped) of the N2HDM can perfectly accommodate both excesses simultaneously, while being in agreement with all experimental and theoretical constraints. The excesses are m…
We study the possible reach of the proposed International Linear Collider (ILC) in exploring the lepton flavor violating (LFV) Higgs boson decay $h\toμτ$. Two generic types of models are investigated, both involving an extended scalar sector. For the first type, the rest of the scalars are heavy and beyond the reach of ILC but the LFV decay occurs through a tiny admixture of the Standard Model (SM) doublet with the heavy degrees of freedom. In the second class, which is more constrained from the existing data, the SM Higgs boson does not have any LFV decay but there are other scalars degenerat…
Single top quark production at the ILC can be used to obtain a high precision measurements of the the Vtb CKM matrix element as well as the effective tbW coupling. We have calculated the QCD correction for the cross section in the context of an effective vector boson approximation. Our results show a 10% increase due to the strong interaction.
A pattern of deviations in the Standard Model (SM) like Higgs boson ($h$) couplings from their SM predictions depends on the structure of the Higgs sector and the Yukawa interaction. In particular, in Two Higgs Doublet Models (THDMs) with a softly-broken $Z_2$ symmetry, different characteristic patterns of deviation in Yukawa coupling constants ($hf\bar{f}$) can be allowed depending on four types of Yukawa interactions. We calculate $hf\bar{f}$ coupling constants at the one-loop level in all the types of THDMs. Even if there is no deviation in the $hf\bar{f}$ couplings at the tree level, they …
The physics case for studying top-quark physics at the International Linear Collider is well established. This summary places in context the top-quark physics goals, examines the current state-of-the art in understanding of the top-quark mass, and identifies some areas in which the study of the top-quark mass enhances our understanding of new techniques.
We study the effects of gluon radiation in top pair production and their decays for e+e- annihilation at the ILC. To achieve this we apply the POWHEG method and interface our results to the Monte Carlo event generator Herwig++. We consider a center-of-mass energy of \sqrt{s}=500 GeV and compare decay correlations and bottom quark and anti-quark distributions before hadronization.
I will briefly review the status of higher-order calculations for top-quark observables, comment on the need for improvements, discuss some of the recent theoretical advances, and present a few examples to highlight the role of top-quark observables in searches for signals of physics beyond the Standard Model.
We study the effects of unparticle physics in the pair productions of top quarks at the LHC and ILC. By considering vector, tensor and scalar unparticle operators, as appropriate, we compute the total cross sections for pair production processes depending on scale dimension $d_{\U}$. We find that the existence of unparticles would lead to measurable enhancements on the SM predictions at the LHC. In the case of ILC this may become two orders of magnitude larger than that of SM, for smaller values of $d_\U$, a very striking signal for unparticles.
We investigate the weak electric and magnetic dipole moments of top quark-Z boson interactions at the Large Hadron Collider (LHC) and the International Linear Collider (ILC). Their vanishingly small magnitude in the Standard Model makes these couplings ideal for probing New Physics interactions and for exploring the role of top quarks in electroweak symmetry breaking. In our analysis, we consider the production of two top quarks in association with a Z boson at the LHC, and top quark pairs mediated by neutral gauge bosons at the ILC. These processes yield direct sensitivity to top quark-Z boso…
In the littlest Higgs model with T-parity, we studied the contributions of the new particles to the top-quark pair production via $e^{+}e^{-}$ collision at the International Linear Collider. We calculated the top-quark pair production cross section and found this process can generate significantly relative correction. The result may be a sensitive probe of the littlest Higgs model with T-parity.
The process of top quark pair production at the ILC with subsequent decays of one of the top quarks to a charged Higgs boson and b-quark is considered. The charged Higgs decays to tau leptons whose polarization is the opposite to those coming from W bosons. This difference is reflected in the energy distributions of the tau decay products in the top quark rest frame, which can be reconstructed at the ILC using the recoil mass technique. We present an analysis including spin correlations, backgrounds, ISR/FSR and beamstrahlung, and show that a fit of the shape of the pion energy spectrum yields…
We calculate the electroweak and QCD corrections to W-W+ -> tt and ZZ -> tt. We also consider the interplay of these corrections with the effect of anomalous interactions that affect the massive weak bosons and the top. The results at the VV level fusion are convoluted with the help of the effective vector boson approximation to give predictions for a high energy e+e- collider.
The top-color assisted technicolor (TC2) mode predicts the existence of a pair of charged top-pions $π^{\pm}_t$. In this paper, we study the production of the charged top-pions pair $π^{\pm}_t$ at next generation $γγ$ colliders. The results show that the production rates can reach the level of $10^2$ fb with reasonable parameter space. With a large number of events and the clean background, the charged top-pion should be observable at the $γγ$ colliders. Therefore, our studies can help us to search for charged top-pion, and furthermore, to test the TC2 model.
We consider a possibility to naturally explain tiny neutrino masses without the lepton number violation. We study a simple model with SU(2)_L singlet charged scalars (s_1^+, s_2^+) as well as singlet right-handed neutrino (nu_R). Yukawa interactions for Dirac neutrinos, which are forbidden at the tree level by a softly-broken Z_2 symmetry, are induced at the one-loop level via the soft-breaking term in the scalar potential. Consequently neutrinos obtain small Dirac masses after the electroweak symmetry breaking. It is found that constrains from neutrino oscillation measurements and lepton flav…
In this paper we study the effect of new physics contributions to the top quark pair production ($t\bar{t}$) in a possible future linear collider, such as the International Linear Collider (ILC). The use of a dimension-six gauge invariant effective operator approach allows to compare the prospected results at the ILC with the current ones obtained at the Large Hadron Collider (LHC), both in neutral and charged current processes. We also prove that the use of specific observables, together with a combination of measurements in different polarized beam scenarios and with different center-of-mass…
We investigated top quark effects on virtual photon structure functions by pQCD. We include the top quark mass effects on the virtual photon structure function with the quark parton model and with the operator product expansion up to the next-to-leading order in QCD. We also consider the threshold effect on the running coupling constant in the calculation to the effective photon structure function with a matching condition. The numerical calculations are investigated in the kinematical region expected at the future international linear collider.
We explore the prospect of Yukawa production of a light boson which can exist in an extended Higgs sector. A particularly interesting case is the light pseudoscalar in Type-X two Higgs doublet model which can explain the anomalous magnetic moment of muon at large $\tanβ$. Considering ILC $Higgs$ $factory$ with $\sqrt{s}=250$ GeV, we show that the available parameter space can be fully examined by the (tau) Yukawa process at $5σ$. We also demonstrate the mass reconstruction of such a light particle which helps to sizably minimize the background events.
In topcolor-assisted technicolor models (TC2) the hitherto unconstrained lepton flavor mixing induced by the new gauge boson $Z'$ will lead to the lepton flavor violating productions of $τ\bar μ$, $τ\bar e$ and $μ\bar e$ in photon-photon collision at the proposed International Linear Collider (ILC). Through a comparative analysis of these processes, we find that the better channels to probe the TC2 is the production of $τ\bar μ$ or $τ\bar e$ which occurs at a much higher rate than $μ\bar e$ production due to the large mixing angle and the large flavor changing coupling, and may reach the detec…
We study the top-quark pair production via polarized and unpolarized photon collisions at the International Linear Collider in the context of the littlest Higgs model with T-parity. We calculate the production cross section of the process $γγ\rightarrow t\bar{t}$ and find the effects can be more significant in the $- -$ polarized photon collision mode than in other collision modes, and the relative correction can be expected to reach about -1% in the favorable parameter space.
The littlest Higgs model with T-parity (LHT) has new flavor-changing (FC) couplings with the Standard Model (SM) quarks, which do not suffer strong constraints from electroweak precision data. So these FC interactions may enhance the cross sections of some flavor-changing neutral-current (FCNC) processes. In this work, we study the FC top-charm associated productions via $e^{-}γ$ collision at the ILC. We find that the cross sections are sensitive to the mirror quark masses. With reasonable values of the parameters, the cross sections may reach the detectable level and provide useful informatio…
We have studied the associated production processes of a neutral top-Higgs in the topcolor assisted technicolor model with a pair of heavy quarks in γγcollisions at the International Linear Collider (ILC). We find that the cross section for t\bar{t}h_t in γγcollisions is at the level of a few fb with the c.m. energy \sqrt{s}=1000 GeV, which is consistent with the results of the cross section of t\bar{t}H in the standard model and the cross section of t\bar{t}h in the minimal supersymmetric standard modeland the little Higgs models. It should be distinct that hundreds of to thousands of h_t per…
Top quark decays are of particular interest as a mean to test the standard model (SM) predictions, both for the dominant ($t\to b+W$) and rare decays ($t\to q+W, cV, cVV,cϕ^0,bWZ$). As the latter are highly suppressed, they become an excellent window to probe the predictions of theories beyond the SM. In particular, in this paper, we evaluate the corrections from new physics to the CKM-suppressed SM top quark decay $t\to q+W$ ($q=d,s$), both within the effective lagrangian approach and the MSSM and we discuss the perspectives to probe those predictions at the ILC.
The large top quark mass suggests that the top plays a pivotal role in Electroweak symmetry-breaking dynamics and, as a result, may have modified couplings to Electroweak bosons. Hadron colliders can provide measurements of these couplings at the ~10% level, and one of the early expected triumphs of the International Linear Collider is to reduce these uncertainties to the per cent level. In this article, we propose the first direct measurement of the Standard Model W-t-b coupling at the ILC, from measurements of t tbar-like signals below the t tbar production threshold. We estimate that the IL…
We discuss complementarity of discovery reaches of heavier neutral Higgs bosons and charged Higgs bosons at the LHC and the International Linear Collider (ILC) in two Higgs doublet models (2HDMs). We perform a comprehensive analysis on their production and decay processes for all types of Yukawa interaction under the softly-broken discrete symmetry which is introduced to avoid flavour changing neutral currents, and we investigate parameter spaces of discovering additional Higgs bosons at the ILC beyond the LHC reach. We find that the 500 GeV run of the ILC with the integrated luminosity of 500…
I discuss the calculation of cross sections for processes with six and eight fermions in the final state, contributing to single-top production and associated top-Higgs production at a linear collider. I describe the schemes for the treatment of finite decay widths implemented in the matrix element generator O'Mega and give a numerical comparison for single-top production. In the case of single top production, after reducing vector boson fusion backgrounds by appropriate cuts, the effect of including the full six fermion final state amounts to 2-5%. In associated top-Higgs production, non-reso…
We study pair production of scalar top quarks in polarized photon-photon collisions with the subsequent decay of the top squarks into b-quarks and charginos. We simulate this process by using PYTHIA6.4 for an electron beam energy 2E_beam =1000 GeV. A set of criteria for physical variables is proposed which leads to a good separation of stop signal events from top quark pair production being the main background. These criteria allow us to reconstruct the mass of the top squark provided that the neutralino mass is known.
We assume that the 125 GeV Higgs discovered at the LHC is the heavy CP-even Higgs of the two-Higgs-doublet models, and examine the parameter space in the Type-I, Type-II, Lepton-specific and Flipped models allowed by the latest Higgs signal data, the relevant experimental and theoretical constraints. Further, we show the projected limits on $\tanβ$, $\sin(β-α)$, $Hf\bar{f}$ and $HVV$ couplings from the future measurements of the 125 GeV Higgs at the LHC and ILC, including the LHC with integrated luminosity of 300 fb$^{-1}$ (LHC-300 fb$^{-1}$) and 3000 fb$^{-1}$ (LHC-3000 fb$^{-1}$) as well as …
The ILC Higgs White Paper is a review of Higgs Boson theory and experiment at the International Linear Collider (ILC). Theory topics include the Standard Model Higgs, the two-Higgs doublet model, alternative approaches to electroweak symmetry breaking, and precision goals for Higgs boson experiments. Experimental topics include the measurement of the Higgs cross section times branching ratio for various Higgs decay modes at ILC center of mass energies of 250, 500, and 1000 GeV, and the extraction of Higgs couplings and the total Higgs width from these measurements. Luminosity scenarios based o…
We study pair production of scalar top quarks in e+e- collisions with the subsequent decay of the top squarks into b-quarks and charginos. We simulate this process by using PYTHIA6.4 for the beam energy 2Ebeam = 350, 400, 500, 800, 1000 GeV. A set of criteria for physical variables is proposed, which provides good separation of stop signal events from top quark pair production being the main background. These criteria allow us to reconstruct the mass of the top squark with an integrared luminosity of 1000 1/fb provided that the neutralino mass is known.
In the present work the $Z^\prime tc$ coupling is bounded by using the current experimental data on the $D^{0}-\bar{D^{0}}$ meson-mixing system. It is found that the strength associated to this coupling is less than $5.75\times 10^{-2}$. The single top production through the $e^+e^-\to Z^\prime\to tc$ process at the $Z^\prime$ boson resonance is studied and we found that around $10^7$ $tc$ events will be expected at the International Linear Collider. For the $Z^\prime\to tc$ decay, we predict a branching ratio of $10^{-2}$.
Full one-loop electroweak-corrections for an $e^-e^+\rightarrow t \bar{t}$ process associated with sequential $t\rightarrow b μν_μ$ decay are discussed. At the one-loop level, the spin-polarization effects of the initial electron and positron beams are included in the total and differential cross sections. A narrow-width approximation is used to treat the top-quark production and decay while including full spin correlations between them. We observed that the radiative corrections due to the weak interaction have a large polarization dependence on both the total and differential cross sections.…
Prospects to search for a new massless neutral gauge boson, the paraphoton, in e+ e- collisions at center-of-mass energies of 0.5 and 1 TeV are studied. The paraphoton naturally appears in models with abelian kinetic mixing. A possible realistic model independent lowest order effective Lagrangian contains magnetic interactions of the paraphoton with the Standard Model fermion fields. These interactions are proportional to the fermion mass and grow with energy, with however very weak paraphoton couplings to ordinary matter. At the ILC, a potentially interesting process to search for the parapho…
With the prospect of improved Higgs measurements at the LHC and at proposed future colliders such as ILC, CLIC and TLEP we study the non-custodial Randall-Sundrum model with bulk SM fields and compare brane and bulk Higgs scenarios. The latter bear resemblance to the well studied type III two-Higgs-doublet models. We compute the electroweak precision observables and argue that incalculable contributions to these, in the form of higher dimensional operators, could have an impact on the T-parameter. This could potentially reduce the bound on the lowest Kaluza-Klein gauge boson masses to the 5 Te…
Some aspects of electroweak physics at the International Linear Collider (ILC) are reviewed. The importance of precision measurements in the Higgs sector and in top-quark physics is emphasized, and the physics potential of the GigaZ option of the ILC is discussed. It is shown in particular that even in a scenario where the states of new physics are so heavy that they would be outside of the reach of the LHC and the first phase of the ILC, the GigaZ precision on the effective weak mixing angle may nevertheless allow the detection of quantum effects of new physics.
The assumption of a new symmetry provides a nice explanation of the existence of dark matter and an elegant way to avoid the electroweak constraints. This symmetry often requires the pair production of new particles at colliders and it guarantees that cascade decays down to the lightest particle give rise to missing energy plus jets and leptons. For a long time, supersymmetry with the conserved R-parity was the only candidate for such signals. However, any new physics with this type of new symmetry may show up with similar signals and the discrimination between different models at the LHC is q…
In the Standard Model (SM) the couplings of the Higgs boson to SM particles and itself (self-couplings) are uniquely specified once the masses of the particles in question as well as the Higgs boson mass are given. Precision measurements of these couplings in the future collider experiments are the key to either verifying the mechanism of the electroweak symmetry breaking in the SM or uncovering physics beyond the SM. This article gives an overview of how various Higgs couplings will be measured at the ILC. Emphasis is put on the ILC's capability of performing fully model independent determina…
We report on a study of top pair production at the International Linear Collider (ILC) around center of mass energy (E$_{\rm CM}$) = 350 GeV using an ILD detector simulator based on the Detailed Baseline Design (DBD) configuration. Here we will report on a result of 6-Jet final state, $t\ bar{t} \rightarrow bWbW \rightarrow bqqbqq$. A result for the 4-Jet final state, $t\ bar{t} \rightarrow bWbW \rightarrow bqqblν$, which has almost the same statics as that of the 6-Jet final state will be included in the future. For an energy scan of 11 center of mass energy points (340 - 350GeV) and two beam…
Run-I results from the CMS collaboration show an excess of events in the decay $h \to μτ_e$ with a local significances of 2.4$σ$. This could be the first hint of flavour violation in the Higgs sector. We summarise the bounds on the flavour violating Yukawa couplings from direct searches, low energy measurements and projected future experiments. We discuss the sensitivity of upcoming HL-LHC runs and future lepton colliders in measuring lepton-flavour violating couplings using an effective field theory framework. For the HL-LHC we find limits on BR($h\to μτ$) and BR$(h\to e τ) \lesssim \mathcal{…
