The prime goal of this thesis is to study anomalous gauge boson self couplings, triple gauge boson couplings in particular, with the help of spin polarization observables of the gauge bosons $Z$ and $W^\pm$ in the presence of beam polarizations where ever possible. The neutral triple gauge boson couplings, i.e., $ZZZ$, $ZZγ$, $Zγγ$, are studied in $ZZ/Zγ$ ($2lq\bar{q}/2lγ$) production at an $e^+e^-$ collider with and without beam polarization. Some of these anomalous couplings are also studied in $ZZ$ ($4l$) production at the LHC. In the charge sector the anomalous gauge boson couplings, i.e., $WWZ$, $WWγ$ have been studied at an $e^+e^-$ collider in $W^+W^-$ ($l^-\bar{ν_l}q^\prime\bar{q}$) production. The $WWZ$ anomalous couplings are also studied in $ZW^\pm$ production at LHC in $3l$ + missing $E_T$ channel. All the analyses at an $e^+$-$e^-$ collider have been performed for center-of-mass (CM) energy of $500$ GeV and integrated luminosity of $100$ fb$^{-1}$. The analyses at the LHC are performed at $13$ TeV CM energy of $pp$ collisions. The cross sections and polarization asymmetries, along with other asymmetries (forward-backward, azimuthal), are used to obtain simultaneous limits on the anomalous couplings using Markov-Chain--Monte-Carlo (MCMC) method in each process. The polarization asymmetries can distinguish between $CP$-even and $CP$-odd couplings and help to put tighter constraints on the couplings. The polarization of the initial $e^-$ and $e^+$ beam, in case of $e^+e^-$ collider, are used to increase the signal to background ratio, putting tighter constraints on the anomalous couplings. The polarization asymmetries are instrumental in the measurement of anomalous couplings should a deviation from the SM be observed.
Diboson production at the LHC is a process of great importance both in the context of tests of the SM and for direct searches for new physics. In this paper we present a phenomenological study of WW, WZ, and ZZ production considering event selections of interest for the anomalous triple-gauge-boson-coupling searches at the LHC: we provide theoretical predictions within the Standard Model at NLO QCD and NLO EW accuracy and study the effect of the anomalous triple-gauge-boson interactions at NLO QCD. For WW and ZZ production, the contribution of the gluon-initiated loop-induced processes is incl…
We study anomalous couplings among neutral gauge bosons in $ZZ$ production at the LHC for $\sqrt{s}=13$ TeV in $4$-lepton final state. We use the cross section and polarization asymmetries of the $Z$ boson to estimate simultaneous limits on anomalous coupling using Markov-Chain--Monte-Carlo (MCMC) method for luminosities $35.9$ fb$^{-1}$, $150$ fb$^{-1}$, $300$ fb$^{-1}$ and $1000$ fb$^{-1}$. The $CP$-even polarization asymmetry $A_{x^2-y^2}$ is sensitive mainly to the $CP$-odd couplings $f_4^{Z/γ}$ (quadratically) providing a probe to identify $CP$-odd nature of interaction at the LHC. We fin…
The anomalous trilinear gauge couplings of $Z$ and $γ$ are studied in $e^+e^-\to ZZ/Zγ$ with longitudinal beam polarizations using a complete set of polarization asymmetries for the $Z$ boson. We quantify the goodness of the beam polarization in terms of the likelihood and find the best-choice of $e^-$ and $e^+$ polarizations to be ($+0.16$, $-0.16$), ($+0.09$, $-0.10$) and ($+0.12$, $-0.12$) for $ZZ$, $Zγ$ and combined processes, respectively. Simultaneous limits on anomalous couplings are obtained for these choices of beam polarizations using Markov-Chain--Monte-Carlo (MCMC) for an $e^+e^-$ …
In these proceedings, we review results for several di-boson production processes beyond NLO QCD at high transverse momenta using the VBFNLO Monte-Carlo program together with the LOOPSIM method. Additionally, we show for the WZ production process how higher order QCD corrections can resemble anomalous coupling effects.
We study the anomalous trilinear gauge couplings of $Z$ and $γ$ using a complete set of polarization asymmetries for the $Z$ boson in $e^+e^-\to ZZ/Zγ$ processes with unpolarized initial beams. We use these polarization asymmetries, along with the cross section, to obtain a simultaneous limit on all the anomalous couplings using the Markov-Chain--Monte-Carlo (MCMC) method. For an $e^+e^-$ collider running at $500$ GeV center-of-mass energy and $100$ fb$^{-1}$ of integrated luminosity the simultaneous limits on the anomalous couplings are $1\sim3\times 10^{-3}$.
Four independent dimension-eight operators give rise to anomalous neutral triple gauge boson interactions, one CP-even and three CP-odd. Only the CP-even operator interferes with the Standard Model for the production of a pair of on-shell neutral bosons. However, the effects are found to be tiny due mainly to the mismatch of the Z boson polarization between the productions from the SM and the new operator.
One of the most-studied signals for physics beyond the standard model in the production of gauge bosons in electron-positron collisions is that due to the anomalous triple gauge boson couplings in the $Z γ$ final state. In this work, we study the implications of this at the ILC with polarized beams for signals that go beyond traditional anomalous triple neutral gauge boson couplings. Here we report a dimension-8 CP-conserving $Z γZ$ vertex that has not found mention in the literature. We carry out a systematic study of the anomalous couplings in general terms and arrive at a classification. We…
We consider the Higgs boson anomalous FCNC interactions with $u$, $c$, $d$, $s$ and $b$ quarks using the effective field theory framework. Constraints on anomalous couplings are derived from experimental results on Higgs boson production with subsequent decay into $b \bar{b}$ pair at LHC with $\sqrt{s} = 13 $~TeV. Upper limits on the branching fractions of $H \to b\bar{s}$ and $H \to b\bar{d}$ are set by performing a realistic detector simulation and accurately reproducing analysis selections of the CMS Higgs boson measurement in the four-lepton final state at $\sqrt{s} = 13$ TeV. The searches…
We study the anomalous $W^+W^-V$ ($V=γ,Z$) couplings in $e^+e^-\to W^+W^-$ using the complete set of polarization observables of $W$ boson with longitudinally polarized beams. We use most general Lorentz invariant form factors parametrization as well as $SU(2)\times U(1)$ invariant dimension $6$ effective operators for the effective $W^+W^-V$ couplings. We estimate simultaneous limits on the anomalous couplings in both the parametrizations using cross section, forward backward asymmetry and polarization observables of $W$ boson with different kinematical cuts using Markov-Chain--Monte-Carlo (M…
We study the anomalous $W^+W^-V$ ($V=γ,Z$) couplings in $e^+e^-\to W^+W^-$ using the complete set of polarization observables of $W$ boson with longitudinally polarized electron ($e^-$) and positron ($e^+$) beams. For the effective $W^+W^-V$ couplings, we use the most general Lorentz invariant form factor parametrization as well as $SU(2)\times U(1)$ invariant dimension-$6$ effective operators. We estimate simultaneous limits on the anomalous couplings using the Markov-Chain--Monte-Carlo (MCMC) method for an $e^+e^-$ collider running at center of mass energy of $\sqrt{s}=500$ GeV and the integ…
Searching for the Higgs boson is of first priority in LHC experiments. Once a Higgs candidate is found, we then need to know whether it is the standard model (SM) Higgs boson or a Higgs boson in new physics beyond the SM. So far we do not know what model of new physics will actually reflect the property of the nature. A model-independent way of measuring the anomalous couplings of the Higgs boson will provide a no-lose study, i.e., if we find nonvanishing anomalous couplings (deviation from the SM couplings), we can conclude that it is a new physics effect. In a previous paper \cite{QKLZ09}, w…
We study the LHC associated production of a Higgs boson and a W^+W^- vector-boson pair at 14 TeV, in the Standard Model and beyond. We consider different signatures corresponding to the cleanest H and W decay channels, and discuss the potential of the high-luminosity phase of the LHC. In particular, we investigate the sensitivity of the HWW production to possible anomalous Higgs couplings to vector bosons and fermions. Since the b-quark initiated partonic channel contributes significantly to this process, we find a moderate sensitivity to both the size and sign of an anomalous top-quark Yukawa…
We present a study of Higgs boson production in vector boson fusion and in association with a vector boson and its decay to two vector bosons, with a focus on the treatment of virtual loops and virtual photons. Our analysis is performed with the JHU generator framework. Comparisons are made to several other frameworks, and the results are expressed in terms of an effective field theory. New features of this study include a proposal on how to handle singularities involving Higgs boson decays to light fermions via photons, calculation of the partial Higgs boson width in the presence of anomalous…
We present a new program (iHixs) which computes the inclusive Higgs boson cross-section at hadron colliders. It incorporates QCD corrections through NNLO, real and virtual electroweak corrections, mixed QCD-electroweak corrections, quark-mass effects through NLO in QCD, and finite width effects for the Higgs boson and heavy quarks. iHixs can be used to obtain the most precise cross-section values in fixed order perturbation theory in the Standard Model. In addition, it allows for a consistent evaluation of the cross-section in modified Higgs boson sectors with anomalous Yukawa and electroweak …
We present predictions for the associated production of a Higgs boson at NLO+PS accuracy, including the effect of anomalous interactions between the Higgs and gauge bosons. We present our results in different frameworks, one in which the interaction vertex between the Higgs boson and Standard Model $W$ and $Z$ bosons is parameterized in terms of general Lorentz structures, and one in which Electroweak symmetry breaking is manifestly linear and the resulting operators arise through a six-dimensional effective field theory framework. We present analytic calculations of the Standard Model and Bey…
We revisit the isospin-breaking and electromagnetic corrections to the decay $τ^-\toπ^-π^0ν_τ$, which allow its use as input in the two-pion contribution to the (leading order) hadronic vacuum polarization part of the muon anomalous magnetic moment. We extend a previous resonance chiral Lagrangian analysis, which included those operators saturating the next-to-leading order chiral low energy constants, by including the contributions of the next subleading terms. As a result, we improve agreement between the two-pion tau decay and $e^+e^-$ data and reduce the discrepancy between experiment and …
The study of the anomalous non-resonant $HH$ production is presented from the point of view of effective field theory (EFT) parameterization. The searches for $pp \rightarrow HH \rightarrow γγWW$, $pp \rightarrow HH \rightarrow γγbb$ and $pp \rightarrow HH \rightarrow bbbb$ processes by ATLAS experiment at the Large Hadron Collider (LHC) are reproduced. The selection efficiencies and exclusion limits on the $HH$ production cross sections for different Beyond Standard Model (BSM) EFT benchmark models are obtained using the fast Monte-Carlo simulation of the ATLAS detector.
The process $p+p\to W^\pm W^+ W^-$ with lepton decays of $W$-bosons is shown to be promising for improving conditions for studies of parameter $λ$, which is the anomalous triple $W$-bosons interaction coupling constant.
Some short-distance properties of the fourth-rank hadronic vacuum polarization tensor are re-examined.Their consequences are critically discussed in the context of the hadronic light-by-light scattering contribution to the anomalous magnetic moment of the muon.
In this paper, we study the extent to which CP parity of a Higgs boson, and more generally its anomalous couplings to gauge bosons, can be measured at the LHC and a future electron-positron collider. We consider several processes, including Higgs boson production in gluon and weak boson fusion and production of a Higgs boson in association with an electroweak gauge boson. We consider decays of a Higgs boson including $ZZ, WW, γγ$, and $Z γ$. Matrix element approach to three production and decay topologies is developed and applied in the analysis. A complete Monte Carlo simulation of the above …
We propose to utilize the polarization information of the $Z$ bosons in $ZZ$ production, via the gluon-gluon fusion process $gg\to ZZ$, to probe the $Zt\bar{t}$ gauge coupling. The contribution of longitudinally polarized $Z$ bosons is sensitive to the axial-vector component ($a_t$) of the $Zt\bar{t}$ coupling. We demonstrate that the angular distribution of the charged lepton from $Z$ boson decays serves well for measuring the polarization of $Z$ bosons and the determination of $a_t$. We show that $ZZ$ production via the $gg\to ZZ$ process complement to $Zt\bar{t}$ and $tZj$ productions in me…
The production of Higgs bosons in weak boson fusion has the second largest cross section among Higgs-production processes at the LHC. As such, this process plays an important role in detailed studies of Higgs interactions with vector bosons. In this paper we extend the available description of Higgs boson production in weak boson fusion by considering anomalous $HVV$ interactions and NNLO QCD radiative corrections at the same time. We find that, while leading order QCD predictions are too uncertain to allow for detailed studies of the anomalous couplings, NLO QCD results are sufficiently preci…
We show how the $W$ boson polarization in the process of associated $W^{\pm}H$ production at the Large Hadron Collider (LHC) can be used to constrain anomalous $WWH$ couplings. We first calculate the spin density matrix for the $W$ to linear order in the anomalous couplings, which are assumed to be small. We then evaluate angular asymmetries in the decay distributions of leptons produced in the decay of the $W$ and show how they can be used to measure the individual elements of the polarization tensor. We estimate the limits that can be placed on the anomalous $WWH$ couplings at a future run o…
We estimate model-independent bounds that could be obtained on the anomalous $ZZH$ vertex using polarization parameters of the $Z$ boson produced in the Higgstrahlung process at the LHC. We calculate the eight independent polarization parameters from the spin density matrix elements of the $Z$, which can probe underlying new physics contributions to $ZH$ production. By using the approach that connects these polarization observables to the coefficients in the angular distribution of the decay products of the $Z$, we estimate the limits on the anomalous $ZZH$ coupling that can be obtained at the…
The anomalous magnetic moment of the muon is one of the most fundamental observables. It has been measured experimentally with a very high precision and on theory side the contributions from perturbative QED have been calculated up to five-loop level by numerical methods. Contributions to the muon anomalous magnetic moment from certain diagram classes are also accessible by alternative methods. In this paper we present the evaluation of contributions to the QED corrections due to insertions of the vacuum polarization function at five-loop level.
We consider the production of a single top quark in association with a $W$ boson at LHeC based $γp$ collider. We compute the cross section for the process $γp\rightarrow WtX$ with the anomalous $Wtb$ and $Wtbγ$ couplings. We find that the sensitivities to anomalous couplings of top quark are shown to be comparable, even better than the ones obtained from direct searches at hadron colliders.
We analyze allowed region of muon anomalous magnetic moment (muon $g-2$), satisfying lepton flavor violations, $Z$ boson decays, and collider physics, in a framework of multi-charged particles. Then we explore the typical size of the muon $g-2$, and discuss which modes dominantly affect muon $g-2$.
We study possible new physics interactions in the $ZZH$ vertex contributing to the Higgsstrahlung process $e^+ e^- \to ZH$ at proposed future $e^+e^-$ colliders using the polarization of the $Z$ as a probe. We calculate the spin density matrix of the $Z$ for the process and determine the eight independent polarization parameters of the $Z$ boson which have the potential to constrain the anomalous couplings. We study angular asymmetries using the decay leptons from the $Z$ boson which are simply related to the polarization observables. We also estimate the limits that can be placed on the anoma…
We study the anomalous $WWγ$ couplings at the Compact Linear Collider through the processes $e^{+}e^{-}\to W^+W^-$, $e^{-}e^{+} \to e^{-} γ^{*} e^{+} \to e^{+} ν_{e} W^-$ and $e^{-}e^{+}\to e^{-} γ^{*} γ^{*} e^{+} \to e^{-} W^+ W^- e^{+} $ $ (γ^{*}$ is the Weizsacker-Williams photon). We give the 95\% confidence level limits for unpolarized and polarized electron (positron) beam on the anomalous couplings for various values of the integrated luminosities and center-of-mass energies. We show that the obtained limits on the anomalous couplings through these processes can highly improve the curre…
