We examine the CP-conserving (CPC) and CP-violating (CPV) effects of a general HZZ coupling through a study of the process H -> ZZ* -> 4 leptons at the LHC. We construct asymmetries that directly probe these couplings. Further, we present complete analytical formulae for the angular distributions of the decay leptons and for some of the asymmetries. Using these we have been able to identify new observables which can provide enhanced sensitivity to the CPV $H ZZ$ coupling. We also explore probing CP violation through shapes of distributions in different kinematic variables, which can be used for Higgs bosons with mH < 2 mZ.
In this article, the prospects for studying the tensor structure of the HZZ vertex with the LHC experiments are presented. The structure of tensor couplings in Higgs di-boson decays is investigated by measuring the asymmetries and by studing the shapes of the final state angular distributions. The expected background contributions, detector resolution, and trigger and selection efficiencies are taken into account. The potential of the LHC experiments to discover sizeable non-Standard Model contributions to the HZZ vertex with $300\;{\rm fb}^{-1}$ and $3000\;{\rm fb}^{-1}$ is demonstrated.
New physics models predict the possibility of extra neutral gauge bosons ($Z'$) associated with an extra $U(1)'$ gauge symmetry. We study the couplings of the Higgs boson to the $Z$ boson and $Z'$ boson predicted by the new physics models. The couplings of the $Z'$ boson to quarks can also be investigated through the $Z'q\bar{q}$ interactions. The accessible ranges of the parameter space have been searched for processes $pp\rightarrow HZX$ and $pp\rightarrow HHZX$ at the LHC with $\sqrt{s}=14$ TeV.
The weak boson fusion process for neutral Higgs boson production is investigated with particular attention to the accuracy with which the Higgs boson couplings to weak bosons can be determined in final states that contain a Higgs boson plus at least two jets at CERN Large Hadron Collider energies. We determine that an accuracy of δg/g ~ 10% on the effective coupling g may be possible after the accumulation of ~ 200 inverse fb of integrated luminosity.
For a generic Higgs boson, measuring the relative sign and magnitude of its couplings with the $W$ and $Z$ bosons is essential in determining its origin. Such a test is also indispensable for the 125-GeV Higgs boson. We propose that the ratio of the $HWW$ and $HZZ$ couplings $λ_{WZ}$ can be directly determined through the $W^+W^-H$ production, where $H$ denotes a generic Higgs boson, owing to the tree-level interference effect. While this is impractical at the LHC due to the limited sensitivity, it can be done at future $e^+e^-$ colliders, such as a 500-GeV ILC with the beam polarization $P(e^…
Being one of the golden channels for precise measurement of Higgs properties, the process $gg \to H\to ZZ \rightarrow 4l$ provides an opportunity to detect the anomalous $HZZ$ couplings in searching of new physics beyond the Standard Model. In this paper, we adopt the method of spinor helicity amplitudes to calculate the amplitudes of process $gg \to H \to ZZ \rightarrow 2e2μ$ at the LHC in the frame of the effective dimension-6 operators. Signal processes of CP-even and CP-odd anomalous $HVV$ couplings in Higgs on/off-shell region and their interference are simulated by using the package MCFM…
We study the sensitivity of constraining the model independent Higgs-Z-Z coupling under effective theory up to dimension-6 operators at the future Higgs factory. Utilizing the current conceptual design parameters of the Circular Electron Positron Collider, we give the experimental limits for the model independent operators by the total Higgsstrahlung cross section and angular distribution of Z boson decay in the Higgs factory. Especially, we give very small sensitivity limit for the CP violation parameter $\tilde g$, which will be a clear window to test the Standard Model and look for New Phys…
The electroweak symmetry breaking (EWSB) mechanism is still an undecided question in particle physics. We propose to utilize the single top quark and Higgs associated production ($th$), $Zh$ production via gluon fusion at the LHC to probe the couplings between the Higgs and the gauge bosons and further to test the EWSB. We demonstrate that the $th$ and $gg\to Zh$ productions are sensitive to the relative sign of couplings ($ht\bar{t}$, $hWW$) and ($ht\bar{t}$, $hZZ$), respectively. We find that the relative sign between $hWW$ and $hZZ$ couplings could be fully determined after combining the pr…
We examine the effect of a general HZZ coupling through a study of the Higgs decay to leptons via Z bosons at the LHC. We discuss various methods for placing limits on additional couplings, including measurement of the partial width, threshold scans, and asymmetries constructed from angular observables. We find that only the asymmetries provide a definitive test of additional couplings. We further estimate the significances they provide.
We investigate the implication of the recent discovery of a Higgs-like particle in the first phase of the LHC Run 1 on the Inert Higgs Doublet Model (IHDM). The determination of the Higgs couplings to SM particles and its intrinsic properties will get improved during the new LHC Run 2 starting this year. The new LHC Run 2 would also shade some light on the triple Higgs coupling. Such measurement is very important in order to establish the details of the electroweak symmetry breaking mechanism. Given the importance of the Higgs couplings both at the LHC and $e^+e^-$ Linear Collider machines, ac…
Electroweak precision measurements established that custodial symmetry is preserved to a good accuracy in the gauge sector after electroweak symmetry breaking. However, recent LHC results might be interpreted as pointing towards Higgs couplings that do not respect such symmetry. Motivated by this possibility, we reconsider the presence of an explicitly custodial breaking coupling in a generic Higgs parameterization. After briefly commenting on the large UV sensitivity of the T parameter to such a coupling, we perform a fit to results of Higgs searches at LHC and Tevatron, and find that the app…
We show that in supersymmetric models with explicit flavor lepton number violation due to soft supersymmetry breaking mass terms there could be detectable flavor lepton number violation in slepton decays. We estimate LHC discovery potential of the lepton flavor number violation in slepton decays.
Models of minimal lepton flavor violation where the seesaw scale is higher than the relevant flavor scale predict that all lepton flavor violation is proportional to the charged lepton Yukawa matrix. If extra vector-like leptons are within the reach of the LHC, it will be possible to test the resulting predictions in ATLAS/CMS.
A new process with the lepton flavor violation (LFV) is presented in the setup for LHC. The LFV is induced by the one-loop effect through Higgs bosons in the framework of the type-III two Higgs doublet model. It is demonstrated that the vast of parameter space in the Yukawa sector could be accessed by current and future LHC experiments.
We review and clarify some cases of geometrical CP violation, the framework of spontaneous CP violation through complex phases with values that are independent of parameters of the potential. We present a flavour model based on Delta(27) featuring spontaneous CP violation, that can reproduce all quark masses and mixing data. The scalar sector of the model has exotic properties that can be tested at the LHC.
Recent results from Super Kamiokande suggest $ν_μ-ν_τ$ mixing and hence lepton flavor violation. In supersymmetric models, this flavor violation may have implications for the pattern of slepton masses and mixings. Possible signals for this mixing in the decays of sleptons produced at the LHC are discussed. The sensitivity expected is compared to that of rare decays such as $τ\to μγ$.
We discuss a few new characteristic features of the loop-induced MSSM Higgs-sector CP violation at the LHC based on two scenarios: (i) CPX and (ii) Trimixing.
In a generic supersymmetric extension of the Standard Model, there will be lepton flavor violation at a neutral gaugino vertex due to misalignment between the lepton Yukawa couplings and the slepton soft masses. Sleptons produced at the LHC through the cascade decays of squarks and gluinos can give a sizable number of events with 4 leptons. This channel could give a clean signature of supersymmetric lepton flavor violation under conditions which are identified.
In supersymmetric scenarios, the seesaw mechanism involving heavy right-handed neutrinos implies sizable lepton flavor violation (LFV) in the slepton sector. We discuss the potential of detecting LFV processes at the LHC in mSUGRA+seesaw scenarios and for general mixing in either the left- or right-handed slepton sector. The results are compared with the sensitivity of rare LFV mu -> e gamma decay experiments.
We construct for the first time a flavor model, based on the smallest discrete symmetry Delta(27) that implements spontaneous CP violation with a complex phase of geometric origin, which can actually reproduce all quark masses and mixing data. We show that its scalar sector has exotic properties that can be tested at the LHC.
This paper investigates a signature of Lorentz invariance violation with the $t\bar{t}$ production at the LHC and future hadron colliders. Possible deviations from the Lorentz symmetry remain poorly constrained in the top quark sector. With a dedicated analysis of $t\bar{t}$ events produced at the LHC, bounds in the top sector can be improved by up to three orders of magnitude relative to Tevatron, the only measurement existing so far. The sensitivity will be even further enhanced at the HL-LHC and future colliders.
We observe that the flavour symmetries of the Standard Model gauge sector, broken as they are in the Standard Model Yukawa Lagrangian, naturally suppress baryon and lepton number violation at low energies and, simultaneously, make it accessible at the LHC through resonant processes involving at least six fermions from all three generations. We establish a model independent classification of such transitions and identify two classes that give rise to particularly clean LHC signatures, namely $\bar t μ^+ e^+$ and $\bar t \bar t$ + jets.
Hints of flavor violation at both charged and neutral current decays of mesons have been observed in experiments such as LHCb, Belle, and BaBar. The anomalies in the result can be addressed in the effective field theory (EFT) framework. The effective operators predict different beyond standard model (BSM) signatures and the four point interaction vertices can be probed at Large Hadron Collider (LHC). In this context, the discovery projection of two opposite sign leptons and a $b$-jet signature is studied in this paper at 13 TeV LHC.
We study the conditions required for $χ_2 \to χ+ τ^\pm μ^\mp$ decays to yield observable tau flavour violation at the LHC, for cosmologically interesting values of the neutralino relic density. These condition can be achieved in the framework of a SU(5) model with a see-saw mechanism that allows a possible coexistence of a LHC signal a low prediction for radiative LFV decays.
We discuss several manifestations of charged lepton flavour violation at high energies. Focusing on a supersymmetric type I seesaw, considering constrained and semi-constrained supersymmetry breaking scenarios, we analyse different observables, both at the LHC and at a future Linear Collider. We further discuss how the synergy between low- and high-energy observables can shed some light on the underlying mechanism of lepton flavour violation.
We explore the CP violation in the charged Higgs production associated with a top quark at the LHC in the MSSM. The supersymmetric phases of gaugino masses and trilinear $A$ terms lead to a CP violating asymmetry of the cross section in the $ p p \to g b \to t H^\pm$ process through loop corrections to the $tbH^\pm$ vertex. We find that a CP violation more than 10 % is possible if the charged Higgs boson is heavy enough.
We briefly review flavour violation in the lepton sector: starting from neutrino oscillations and their implications, we consider several charged lepton flavour violating observables at high and low energies. We present new physics models and discuss the rôle of the latter in disentangling them. In particular, we show how the interplay of different observables allows to derive important information on the underlying mechanism of lepton flavour violation. As an example, we discuss the impact of a type-I SUSY seesaw concerning lepton flavour violation at low energies and at colliders (LHC and a …
We discuss the potential to observe effects of CP violation in squark decay chains at the LHC. As the CP-violating observable we use the asymmetry composed by triple products of final state momenta. Extending methods for momentum reconstruction we show that there are good prospects for observation of these effects at the LHC. Finally, we include the main experimental factors and discuss the expected sensitivity.
We discuss the potential of observing effects of CP-violation phases in squark decay chains at the LHC. As the CP-odd observable, we use the asymmetry composed by triple products of final state momenta. There are good prospects of observing these effects using the method of kinematic reconstruction for the final and intermediate state particles. We also discuss the main experimental factors and the expected sensitivity.
We present an extensive analysis of gauge-mediated supersymmetry breaking models with minimal and non-minimal flavour violation. We first demonstrate that low-energy, precision electroweak, and cosmological constraints exclude large "collider-friendly" regions of the minimal parameter space. We then discuss various possibilities how flavour violation, although naturally suppressed, may still occur in gauge-mediation models. The introduction of non-minimal flavour violation at the electroweak scale is shown to relax the stringent experimental constraints, so that benchmark points, that are also…
A possibility to measure CP-violation in B0-decays by ATLAS experiment was investigated. With one year of running at luminosity 10^33 cm-2s-1 with a muon pt-trigger threshold of 20GeV and rapidity coverage eta<2.5 of the tracking detector the rate of 1490 events B0->J/psi->mumupipi can be reached.
We discuss CP violation in top-antitop production at the LHC, induced by gluon fusion and final-state Higgs exchange. Results by Bernreuther and Brandenburg are confirmed and further reduced. The lepton energy asymmetry is studied in detail in explicit Two-Higgs-Doublet Models with near-maximal mixing in the neutral Higgs sector. Unless there is only one light Higgs particle, and unless (in Model II) tanbeta \lsim 1, the CP-violating effects are very small, possibly too small to be seen at the LHC.
We investigate the potential of the LHC to probe the R parity violating couplings involving the third generation by considering single top production. This study is based on particle level event generation for both signal and background, interfaced to a simplified simulation of the ATLAS detector.
Majorana neutrino mass models with a scale of lepton number violation (LNV) of order TeV potentially lead to signals at the LHC. Here, we consider an extension of the standard model with a coloured octet fermion and a scalar leptoquark. This model generates neutrino masses at 2-loop order. We make a detailed MonteCarlo study of the LNV signal at the LHC in this model, including a simulation of standard model backgrounds. Our forecast predicts that the LHC with 300/fb should be able to probe this model up to colour octet fermion masses in the range of (2.6-2.7) TeV, depending on the lepton flav…
Spontaneous CP violation motivates the introduction of two Higgs doublets in the electroweak theory, such a simple extension of the standard model has five physical Higgs bosons and rich CP-violating sources. Exploration on more than one Higgs boson is a direct evidence for new physics beyond the standard model. The neutral Higgs production at LHC is investigated in such a general two Higgs doublet model with spontaneous CP violation, it is shown that the production cross section and decays of the neutral Higgs boson can significantly be different from the predictions from the standard model.
The tiny neutrino masses can be explained naturally by extending the standard model with right-handed Majorana neutrinos in low-scale seesaw mechanism, and the CP violation effect induced by Majorana phase is interesting and worth studying at colliders. In this paper, we investigate the prospects for measuring CP violation in top quark pair production and rare decay via Majorana neutrinos at the LHC. The CP asymmetry stems from the significant interference of contributions from two different Majorana neutrinos and can be appreciable when the two neutrino masses are nearly-degenerate. It is fou…
We review the SM extensions with scalar multiplets including doubly-charged components eventually observable as di-leptonic resonances at the LHC. Special emphasis is payed to the limits on LNV implied by doubly-charged scalar searches at the LHC, and to the characterization of the multiplet doubly-charged scalars belong to if they are observed to decay into same-sign charged lepton pairs.
The mixing between third and second (or first) generation squarks is very small in supersymmetric models with minimal flavor violation such as gauge-, anomaly- or gaugino-mediation. An opportunity to measure this mixing will arise if the lightest stop is close enough in mass to the lightest neutralino, so that the decays into third generation quarks are kinematically forbidden. We analyze under which circumstances it might become possible to measure at the Large Hadron Collider (LHC) the rate of the flavor changing stop decays.
Hadron colliders are providing a unique opportunity for testing Lorentz invariance and CPT symmetry at high energy and in a laboratory. A first measurement in the top-quark sector was performed at the Tevatron. We present here prospective studies for testing Lorentz invariance in top-quark pair production at the LHC and future colliders. The b-quark sector was investigated recently at LHCb. Eventually, new bounds on photon parameters can be extracted from the observation of TeV photons at the LHC. We will conclude by highlighting other opportunities provided by hadron colliders.
Signals for Lorentz and CPT violation can appear in a wide range of experiments including hadron colliders like the LHC. We present a calculation of the Lorentz-violating cross section for top-quark pair production via gluon fusion. This process dominates at the LHC, and analysis of LHC data should permit sharpening the constraints on top-quark Lorentz violation obtained recently by the D0 Collaboration. We also present a separate calculation of single-top production, which is sensitive to CPT violation. Data from the LHC can be used to measure coefficients for CPT violation in the top-quark s…
In this talk I discuss possibilities of probing the CP violation (CPV) in the Minimal Supersymmetric Standard Model (MSSM), at the LHC as well as its effects on the LHC SUSY phenomenology. In the latter case I mainly discuss its effect on the Higgs-sector and hence on Higgs Phenomenology at the LHC. After outlining the possibilities that a study of the $\ch_1 \nt_2$ production at the LHC might offer, I will summarise the effects of the CPV in MSSM on the Higgs searches at the LHC. Further, I will discuss how a study of the process $H^\pm \to W^+ ϕ_1$ may be able to plug a 'hole" in the $\tan β…
In Two-Higgs-Doublet models, the conditions for CP violation can be expressed in terms of invariants under U(2) rotations among the two SU(2) Higgs doublet fields. In order to design a strategy for measuring the invariants we express them in terms of observables, i.e., masses and couplings of scalar bosons. We find amplitudes directly sensitive to the invariants. Observation of the Standard-Model-like Higgs boson at the LHC severely constrains the models. In particular, in the model with Z_2 symmetry imposed on dimension-4 terms (in order to eliminate tree-level flavour-changing neutral curren…
The experimental success of the predictions of the Standard Model in the flavour sector suggests that New Physics should possess a highly non-generic flavour structure. Different approaches to this idea of Minimal Flavour Violation have been proposed and studied during the last years. At last, the LHC provides the possibility to test these patterns from different points of view, i.e. through the direct search of New Physics at the high energy frontier, and through the indirect constraints at the intensity frontier of precision measurements.
We review Lepton Flavour Violation (LFV) in the supersymmetric version of the seesaw mechanism (type I, II, III) and in Left-Right models. The LFV needed to explain neutrino masses and mixings is the only source of LFV and has experimental implications both in low-energy experiments where we search for the radiative decays of leptons, and at the LHC where we look at its imprint on the LFV decays of the sparticles and on slepton mass splittings. We discuss how this confrontation between high- and low-energy LFV observables may provide information about the underlying mechanism of LFV.
A striking manifestation of CP violation in the electroweak symmetry breaking sector would be the existence of neutral Higgs boson(s) with undefined CP parity. We analyse signatures of such a boson, with a mass of about 300 GeV or larger, produced in high energy proton-proton collisions at LHC energies in its top-quark antitop-quark decay channel. The large irreducible $t\bar t$ background is taken into account. We propose, both for the dilepton and the lepton + jets decay channels of $t\bar t$, several correlations and asymmetries with which (Higgs sector) CP violation can be traced. We show …
We investigate a model in which tiny neutrino masses are generated at the two-loop level by using scalar leptoquark and diquark multiplets. The diquark can be singly produced at the LHC, and it can decay into a pair of leptoquarks through the lepton number violating interaction. Subsequent decays of the two leptoquarks can provide a clear signature of the lepton number violation, namely two QCD jets and a pair of same-signed charged leptons without missing energy. We show that the signal process is not suppressed while neutrino masses are appropriately suppressed.
We study a possibility to detect charged sleptons and flavour lepton number violation at LHC (CMS). We investigate the production and decays of right- and left-handed sleptons separately. We have found that for luminosity L = 10**5 1/pb it would be possible to detect right-handed sleptons with a mass up to 325 GeV and left-handed ones with a mass up to 350 GeV. We also investigate a possibility to look for flavour lepton number violation in slepton decays due to the mixing of different slepton generations. We find that for the maximal (smu_R - se_R) mixing it is possible to detect such effect …
Extra dimension is one of the most attractive candidates beyond the Standard Model. In warped extra dimensional space-time, not only gauge hierarchy problem but also quark-lepton mass hierarchy can be naturally explained. In this setup, a sizable parity violation through Kaluza-Klein gluon exchange appears in QCD process such as helicity dependent top pair production. We investigate this QCD parity violating process by use of $SO(5) \times U(1)$ gauge-Higgs unification model. We evaluate LHC observable quantities, i.e., a charge asymmetry and a forward-backward asymmetry of the top pair produc…
We study the potential to observe CP-violating effects in SUSY cascade decay chains at the LHC. Asymmetries composed by triple products of momenta of the final state particles are sensitive to CP-violating effects. Due to large boosts that dilute the asymmetries, these can be difficult to observe. Extending the methods of momentum reconstruction we show that the original size of these asymmetries may be measurable. A study is done at the hadronic level with backgrounds to estimate the expected sensitivity at the LHC.
We analyze the constraints on a CP-violating, flavor conserving, two Higgs doublet model from the measurements of Higgs properties and from the search for heavy Higgs bosons at LHC, and show that the stronger limits typically come from the heavy Higgs search channels. The limits on CP violation arising from the Higgs sector measurements are complementary to those from EDM measurements. Combining all current constraints from low energy to colliders, we set generic upper bounds on the CP violating angle which parametrizes the CP odd component in the 126 GeV Higgs boson.
A simple formalism to describe flavor and CP violation in a model independent way is provided. Our method is particularly useful to derive robust bounds on models with arbitrary mechanisms of alignment. Known constraints on flavor violation in the K and D systems are reproduced in a straightforward and covariant manner. Assumptions-free limits, based on top flavor violation at the LHC, are then obtained. In the absence of signal, with 100 fb^{-1} of data, the LHC will exclude weakly coupled (strongly coupled) new physics up to a scale of 0.6 TeV (7.6 TeV), while at present no general constrain…
We study CP asymmetries in two-body decays of top squarks into neutralinos and sleptons at the LHC. These asymmetries are used to probe the CP phases possibly present in the stop and neutralino sector of the Minimal Supersymmetric Standard Model. Taking into account bounds from experimental electric dipole moment searches, we identify areas in the mSUGRA parameter space where CP asymmetries can be sizeable and discuss the feasibility of their observation at the LHC. As a result, potentially detectable CP asymmetries in stop decays at the LHC are found, motivating further detailed experimental …
We study a possibility to detect sleptons and flavour lepton number violation at LHC (CMS). We investigate the production and decays of right- and left-handed sleptons separately. We have found that for L = 10**5 1/pb it would be possible to discover right-handed sleptons with a mass up to 350 GeV and left-handed ones with a mass up to 350 GeV. We also investigate a possibility to look for flavour lepton number violation in slepton decays due to the mixing of different generations sleptons. We find that for the maximal (smu_R - se_R) mixing it is possible to detect such effect for sleptons wit…
