# Cheng-Wei ChiangNational Taiwan University | NTU · Department of Physics

Cheng-Wei Chiang

PhD in Physics

## About

195

Publications

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## Publications

Publications (195)

The CDF II experiment has recently determined the mass of the W boson to be mW(CDF II)=80.4335±0.0094 GeV, which deviates from the standard model prediction at 7σ level. Although this new result is in tension with other experiments such as those at LHC and LEP, it is worth discussing possible implications on new physics by this anomaly. We show tha...

With theoretical constraints such as perturbative unitarity and vacuum stability conditions and updated experimental data of Higgs measurements and direct searches for exotic scalars at the LHC, we perform an updated scan of the allowed parameter space of the Georgi-Machacek (GM) model. With the refined global fit, we examine the allowed parameter...

We study the benefits of jet- and event-level deep learning methods in distinguishing vector boson fusion (VBF) from gluon-gluon fusion (GGF) Higgs production at the LHC. We show that a variety of classifiers (CNNs, attention-based networks) trained on the complete low-level inputs of the full event achieve significant performance gains over shallo...

A bstract
We construct a scotogenic Majorana neutrino mass model in a gauged U(1) X extension of the standard model, where the mass of the gauge boson and the unbroken gauge symmetry, which leads to a stable dark matter (DM), can be achieved through the Stueckelberg mechanism. It is found that the simplest version of the extended model consists of...

Although searches for dark matter have lasted for decades, no convincing signal has been found without ambiguity in underground detections, cosmic ray observations, and collider experiments. We show by example that gravitational wave (GW) observations can be a supplement to dark matter detections if the production of dark matter follows a strong fi...

Although searches for dark matter have lasted for decades, no convincing signal has been found without ambiguity in underground detections, cosmic ray observations, and collider experiments. We show by example that gravitational wave (GW) observations can be a supplement to dark matter detections if the production of dark matter follows a strong fi...

With theoretical constraints such as perturbative unitarity and vacuum stability conditions and updated experimental data of Higgs measurements and direct searches for exotic scalars at the LHC, we perform an updated scan of the allowed parameter space of the Georgi-Machacek (GM) model. With the refined global fit, we examine the allowed parameter...

The CDF II experiment has recently determined the mass of the $W$ boson to be $m_W(\text{CDF II}) = 80.4335 \pm 0.0094~$GeV, which deviates from the standard model prediction at $7\sigma$ level. Although this new result is in tension with other experiments such as those at LHC and LEP, it is worth discussing possible implications on new physics by...

We study the quasi-two-body $D\to TP$ decays and the three-body $D$ decays proceeding through intermediate tensor resonances, where $T$ and $P$ denote tensor and pseudoscalar mesons, respectively. We employ $D\to T$ transition form factors based upon light-cone sum rules and the covariant light-front quark model to evaluate the decay rates, with th...

We discuss a model with a dark sector, in which smallness of mass for charged leptons and neutrinos can naturally be explained by one-loop effects mediated by particles in the dark sector. These new particles, including dark matter candidates, also contribute to the anomalous magnetic dipole moment, denoted by $(g-2)$, for charged leptons. We show...

A unique characteristic of exponentially growing scattering amplitude arises in an anomalous Abelian effective field theory when an extremely light Dirac neutrino mass is introduced to break the symmetry. We show that the low energy effective Lagrangian can be made explicitly gauge invariant with the help of a nonlinear representation of the Goldst...

We construct a scotogenic Majorana neutrino mass model in a gauged $U(1)_X$ extension of the standard model, where the mass of the gauge boson and the unbroken gauge symmetry, which leads to a stable dark matter (DM), can be achieved through the Stueckelberg mechanism. It is found that the simplest version of the extended model consists of the two...

We study the quasi-two-body $D\to SP$ decays and the three-body $D$ decays proceeding through intermediate scalar resonances, where $S$ and $P$ denote scalar and pseudoscalar mesons, respectively. Our main results are: (i) Certain external and internal $W$-emission diagrams with the emitted meson being a scalar meson are na{\"i}vely expected to van...

Direct CP violation in two-body $D\to PP$ and $D\to V\!P$ decays is studied within the framework of the topological amplitude approach for tree amplitudes and the QCD factorization approach for penguin amplitudes. It is the interference between tree and long-distance penguin and penguin-exchange amplitudes that pushes CP asymmetry difference betwee...

A unique characteristic of exponentially growing scattering amplitude arises in an anomalous Abelian effective field theory when an extremely light Dirac neutrino mass is introduced to break the symmetry. We show that the low energy effective Lagrangian can be made explicitly gauge invariant with the help of a nonlinear representation of the Goldst...

We reexamine direct CP violation in the quasi-two-body D→VP decays and study CP asymmetries in three-body D decays proceeding through intermediate vector resonances within the framework of the topological amplitude approach for tree amplitudes and the QCD factorization approach for penguin amplitudes. Using the same mechanism of incorporating long-...

We study the two-Higgs-doublet model with a type-II seesaw mechanism. In view of constraints from the Higgs data, we consider the aligned two-Higgs-doublet scheme and its effects on muon anomalous magnetic dipole moment, aμ, including both one-loop and two-loop Barr-Zee type diagrams. Thanks to a sizable trilinear scalar coupling, the Barr-Zee type...

When the Standard Model Higgs sector is extended with a complex singlet that breaks global lepton number symmetry spontaneously, a massless Goldstone boson called the Majoron J arises. In addition to increasing Higgs invisible decay through mixing, the Majoron can generally have flavor-changing interactions with fermions. We find that Type-III sees...

We discuss a mechanism where charged lepton masses are derived from one-loop diagrams mediated by particles in a dark sector including a dark matter candidate. We focus on a scenario where the muon and electron masses are generated at one loop with new O(1) Yukawa couplings. The measured muon anomalous magnetic dipole moment, (g−2)μ, can be explain...

We re-examine direct CP violation in the quasi-two-body $D\to V\!P$ decays and study CP asymmetries in three-body $D$ decays proceeding through intermediate vector resonances within the framework of the topological amplitude approach for tree amplitudes and the QCD factorization approach for penguin amplitudes. As pointed out by us in 2012, the lon...

We study the two-Higgs-doublet model with type-II seesaw mechanism. In view of constraints from the Higgs data, we consider the aligned two-Higgs-doublet scheme and its effects on muon anomalous magnetic dipole moment, $a_{\mu}$, including both one-loop and two-loop Barr-Zee type diagrams. Thanks to a sizable trilinear scalar coupling, the Barr-Zee...

We discuss a mechanism where charged lepton masses are derived from one-loop diagrams mediated by particles in a dark sector including a dark matter candidate. We focus on a scenario where the muon and electron masses are generated at one loop with new ${\cal O}(1)$ Yukawa couplings. The measured muon anomalous magnetic dipole moment, $(g-2)_\mu$,...

It is customary to apply the so-called narrow width approximation Γ(B→RP3→P1P2P3)=Γ(B→RP3)B(R→P1P2) to extract the branching fraction of the quasi-two-body decay B→RP3, with R and P3 being an intermediate resonant state and a pseudoscalar meson, respectively. However, the above factorization is valid only in the zero width limit. We consider a corr...

A bstract
We study discovery prospects for a real triplet extension of the Standard Model scalar sector at the Large Hadron Collider (LHC) and a possible future 100 TeV pp collider. We focus on the scenario in which the neutral triplet scalar is stable and contributes to the dark matter relic density. When produced in pp collisions, the charged tri...

For three-body hadron decays mediated by intermediate resonances with large widths, we show how to properly extract the quasi-two-body decay rates for a meaningful comparison with the corresponding theoretical estimates, using several B decays as explicit examples. We compute the correction factor from finite width effects in the QCD factorization...

It is customary to apply the so-called narrow width approximation $\Gamma(B\to RP_3\to P_1P_2P_3)=\Gamma(B\to RP_3)\B(R\to P_1P_2)$ to extract the branching fraction of the quasi-two-body decay $B\to RP_3$, with $R$ and $P_3$ being an intermediate resonant state and a pseudoscalar meson, respectively. However, the above factorization is valid only...

For three-body $B$ decays mediated by intermediate resonances, we show how to properly extract the quasi-two-body decay rates for a meaningful comparison with the corresponding theoretical estimates. We compute the correction factor from finite width effects in the QCD factorization approach, and make a comparison with that using the experimental p...

A bstract
We propose simple models with a flavor-dependent global U(1) ℓ and a discrete ℤ 2 symmetries to explain the anomalies in the measured anomalous magnetic dipole moments of muon and electron, ( g − 2) μ,e , while simultaneously accommodating a dark matter candidate. These new symmetries are introduced not only to avoid the dangerous lepton...

We study discovery prospects for a real triplet extension of the Standard Model scalar sector at the Large Hadron Collider (LHC) and a possible future 100 TeV $pp$ collider. We focus on the scenario in which the neutral triplet scalar is stable and contributes to the dark matter relic density. When produced in $pp$ collisions, the charged triplet s...

We demonstrate that the classification of boosted, hadronically decaying, weak gauge bosons can be significantly improved over traditional cut-based and boosted decision tree-based methods using deep learning and the jet charge variable. We construct binary taggers for W+ vs W− and Z vs W discrimination, as well as an overall ternary classifier for...

A bstract
We study the LHC sensitivity to probe a long-lived heavy neutrino N in the context of Z′ models. We focus on displaced vertex signatures of N when pair produced via a Z′ , decaying to leptons and jets inside the inner trackers of the LHC experiments. We explore the LHC reach with current long-lived particle search strategies for either on...

Direct CP violation in the hadronic charm decays provides a good testing ground for the Kobayashi-Maskawa mechanism in the Standard Model. Any significant deviations from the expectation would be indirect evidence of physics beyond the Standard Model. In view of improved measurements from LHCb and BESIII experiments, we reanalyze the Cabibbo-favore...

Direct CP violation in the hadronic charm decays provides a good testing ground for the Kobayashi-Maskawa mechanism in the Standard Model. Any significant deviations from the expectation would be indirect evidence of physics beyond the Standard Model. In view of improved measurements from LHCb and BESIII experiments, we re-analyze the Cabibbo-favor...

We study the LHC sensitivity to probe a long-lived heavy neutrino $N$ in the context of $Z'$ models. We focus on displaced vertex signatures of $N$ when pair produced via a $Z'$, decaying to leptons and jets inside the inner trackers of the LHC experiments. We explore the LHC reach with current long-lived particle search strategies for either one o...

We demonstrate that the classification of boosted, hadronically-decaying weak gauge bosons can be significantly improved over traditional cut-based and BDT-based methods using deep learning and the jet charge variable. We construct binary taggers for $W^+$ vs. $W^-$ and $Z$ vs. $W$ discrimination, as well as an overall ternary classifier for $W^+$/...

In this work we perform a complete one-loop calculation of the flavor-changing top quark decays \(t\rightarrow cg\) and \(t\rightarrow cZ\) in the universal extra-dimensional models. We find that the branching ratios of these decays in the minimal scenario remain unaltered from the Standard Model expectations for currently allowed values of the inv...

We consider a two-Higgs doublet model extended with a broken Abelian gauge symmetry under which all Standard Model (SM) quarks, fourth generation fermions and a new SM-singlet scalar boson are charged. Such a setup is shown to be able to accommodate the muon anomalous magnetic dipole moment while being consistent with existing constraints of flavor...

We consider a two-Higgs doublet model extended with a broken Abelian gauge symmetry under which all Standard Model (SM) quarks, fourth generation fermions and a new SM-singlet scalar boson are charged. Such a setup is shown to be able to accommodate the muon anomalous magnetic dipole moment while being consistent with existing constraints of flavor...

Off the beaten track of scalar singlet and doublet extensions of the Standard Model, triplets combine an interesting LHC phenomenology with an explanation for neutrino masses. The Georgi-Machacek model falls into this category, but it has never been fully explored in a global fit. We use the HEPfit package to combine recent experimental Higgs data...

We revisit the electroweak phase transition in the standard model with a real scalar, utilizing several calculation methods to investigate scheme dependences. We quantify the numerical impacts of Nambu–Goldstone resummation, required in one of the schemes, on the strength of the first-order electroweak phase transition. We also employ a gauge-indep...

A bstract
The present work introduces two possible extensions of the Standard Model Higgs sector. In the first case, the Zee-Babu type model for the generation of neutrino mass is augmented with a scalar triplet and additional singly charged scalar singlets. The second scenario, on the other hand, generalizes the Type-II seesaw model by replicating...

The invisible variant axion models (VAMs) offer a very attractive solution for the strong CP problem without the domain wall problem. We consider the up-type specific variant axion models and examine their compatibility with the muon g−2 anomaly and the constraints from lepton flavor universality, several flavor observables, and top-quark measureme...

In order for scale factors κV(V=W,Z) of the 125-GeV Higgs boson couplings to have the possibilities of being greater than unity and κW≠κZ while keeping the electroweak ρ parameter unity at tree level, the Higgs sector must be extended with at least two exotic SU(2)L multiplets in addition to the doublet Higgs field in the Standard Model. By the req...

In order for scale factors $\kappa_{V}^{}~(V=W,Z)$ of the 125-GeV Higgs boson couplings to have the possibilities of being greater than unity and $\kappa_{W}^{} \neq \kappa_{Z}^{}$ while keeping the electroweak $\rho$ parameter unity at tree level, the Higgs sector must be extended with at least two exotic $SU(2)_L$ multiplets in addition to the do...

We present the physics program of the Belle II experiment, located on the intensity frontier SuperKEKB e+e- collider. Belle II collected its first collisions in 2018, and is expected to operate for the next decade. It is anticipated to collect 50/ab of collision data over its lifetime. This book is the outcome of a joint effort of Belle II collabor...

We revisit the electroweak phase transition in the standard model with a real scalar, utilizing several calculation methods to investigate scheme dependences. We quantify the numerical impacts of Nambu-Goldstone resummation, required in one of the schemes, on the strength of the first-order electroweak phase transition. We also employ a gauge-indep...

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 HW W and HZZ couplings λW Z can be directly determined through the W ⁺W ⁻H production, where H denotes a...

Off the beaten track of scalar singlet and doublet extensions of the Standard Model, triplets combine an interesting LHC phenomenology with an explanation for neutrino masses. The Georgi-Machacek model falls into this category, but it has never been fully explored in a global fit. We use the {\texttt{HEPfit}} package to combine recent experimental...

The present work introduces two possible extensions of the Standard Model Higgs sector. In the first case, the Zee-Babu type model for the generation of neutrino mass is augmented with a scalar triplet and additional singly charged scalar singlets. The second scenario, on the other hand, generalizes the Type-II seesaw model by replicating the numbe...

In this work we perform a complete one-loop calculation of the flavor-changing top quark decays $t\to cg$ and $t\to cZ$ in the universal extra dimensional models. We find that the branching ratios of these decays in the minimal scenario remain unaltered from the Standard Model expectations for currently allowed values of the inverse compactificatio...

The invisible variant axion models (VAM's) offer a very attractive solution for the strong CP problem without the domain wall problem. We consider the up-type specific variant axion models and examine their compatibility with the muon $g-2$ anomaly and the constraints from lepton flavor universality, several flavor observables, and top quark measur...

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 $\lambda_{WZ}$ can be directly determined through the $W^+W^-H$ production...

We compute renormalized vertices of the 125 GeV Higgs boson $h$ with the weak gauge bosons ($hVV$), fermions ($hf\bar{f}$) and itself ($hhh$) in the Georgi-Machacek model at one-loop level. The renormalization is performed based on the on-shell scheme with the use of the minimal subtraction scheme only for the $hhh$ vertex. We explicitly show the g...

We explain the $e^+ e^-$ excess observed by the DAMPE Collaboration using a dark matter model based upon the Higgs triplet model and an additional hidden $SU(2)_X$ gauge symmetry. Two of the $SU(2)_X$ gauge bosons are stable due to a residual discrete symmetry and serve as the dark matter candidate. We search the parameter space for regions that ca...

We propose a model having a gauged $SU(2)$ symmetry associated with the second and third generations of leptons, dubbed $SU(2)_{\mu\tau}$, of which $U(1)_{L_\mu-L_\tau}$ is an Abelian subgroup. In addition to the Standard Model fields, we introduce two types of scalar fields. One exotic scalar field is an $SU(2)_{\mu\tau}$ doublet and SM singlet th...

We propose a model to explain several muon-related experimental anomalies and the abundance of dark matter. For each SM lepton family, we introduce vector-like exotic leptons that form an iso-doublet and a right-handed Majorana fermion as an iso-singlet. A real/complex scalar field is added as a dark matter candidate. We impose a global $U(1)_\mu$...

The invisible variant axion model is very attractive as it is free from the domain wall problem. This model requires at least two Higgs doublets at the electroweak scale, with one Higgs doublet carrying a nonzero Peccei-Quinn (PQ) charge and the other being neutral under the PQ $\text U(1)$ symmetry. We consider a scenario where only the right-hand...

A bstract
Of all $$ B\to D\overline{D} $$ B → D D ¯ decays, the $$ {B}^0\to {D}^0\overline{D^0} $$ B 0 → D 0 D 0 ¯ decay has the smallest observed branching ratio as it takes place primarily via the suppressed W -exchange diagram. The CP asymmetry for this mode is yet to be measured experimentally. By exploiting the relationship among the decay amp...

We analyze the theoretical and phenomenological considerations for the electroweak phase transition and dark matter in an extension of the Standard Model with a complex scalar singlet (cxSM). In contrast with earlier studies, we use a renormalization group improved scalar potential and treat its thermal history in a gauge invariant manner. We find...

We study gauge dependence of gravitational waves produced from a first-order phase transition in classical scale-invariant $U(1)'$ models. Accidental gauge independence of the one-loop effective potential in this class of models is spoiled by including thermal resummation. The gauge artifact in the resummed effective potential propagates to the gra...

We calculate 1-loop radiative corrections to the $hZZ$ and $hWW$ couplings in models with next--to--simplest Higgs sectors satisfying the electroweak $\rho$ parameter equal to 1 at tree level: the Higgs singlet model, the two-Higgs doublet models, and the Georgi-Machacek model. Under theoretical and current experimental constraints, the three model...

A recent LHCb measurement of the ratio $R_{K^*}$ of $B\to K^*\mu\bar\mu$ to $B\to K^*e\bar e$ branching fractions has shown evidence of deviation from the standard model (SM) expectation. This adds to the known anomalies also induced by the $b\to s\ell\bar\ell$ transitions, resulting in a confidence level now as high as 4$\sigma$. We analyze whethe...

Possible spin-parity quantum numbers for excited charmed baryon resonances are discussed in this work. Our main results are: (i) Among the five newly observed $\Omega_c$ states, we have identified $\Omega_c(3090)$ and $\Omega_c(3119)$ with radially excited $\frac12^+(2S)$ and $\frac32^+(2S)$ states, respectively, and $\Omega_c(3000)$ with $\frac12^...

We study a simple one-loop induced neutrino mass model that contains both bosonic and fermionic dark matter candidates and has the capacity to explain the muon anomalous magnetic moment anomaly. We perform a comprehensive analysis by taking into account the relevant constraints of charged lepton flavor violation, electric dipole moments, and neutri...

We study constraints and implications of the recent LHCb measurement of ${\cal B}(B_s \to \mu^+\mu^-)$ for tree-level Higgs-mediated flavor-changing neutral current (FCNC) interactions. Combined with experimental data on $B_s$ mass difference $\Delta m_s$, the $h \to \mu \tau$, and the $h \to \tau^+\tau^-$ decay branching ratios from the LHC, we fi...

Higgs bosons pair production is well known for its sensitivity to probing the sign and size of Higgs boson self coupling, providing a way to determine whether there is an extended Higgs sector. The Georgi-Machacek (GM) model extends the Standard Model (SM) with an $SU(2)_L$ triplet scalar field that has one real and one complex components. The Higg...

Rare leptonic kaon and pion decays $K^+(\pi^+) \to \mu^+\, \nu_{\mu}\, e^+ e^-$ can be used to probe a dark photon of mass ${\cal O}(10)$~MeV, with the background coming from the mediation of a virtual photon. This is most relevant for the 16.7-MeV dark photon proposed to explain a 6.8$\sigma$ anomaly recently observed in $^8$Be transitions by the...

We investigate feasibility of electroweak baryogenesis with lepton flavor violation in a two-Higgs doublet model. By scrutinizing heavy Higgs boson mass spectra, regions satisfying both strong first-order electroweak phase transition and the muon $g-2$ anomaly are identified. We also estimate the baryon number density by exploiting extra Yukawa cou...

We consider a class of models with extra complex scalars that are charged under both the Standard Model and a hidden strongly coupled $SU(N)_H$ gauge sector, and discuss the scenarios where the new scalars are identified as the messenger fields that mediate the spontaneously broken supersymmetries from the hidden sector to the visible sector. The n...

Two-body charmed meson decays $D\to VP$ are studied within the framework of the diagrammatic approach. Under flavor SU(3) symmetry, all the flavor amplitude sizes and their associated strong phases are extracted by performing a $\chi^2$ fit. Thanks to the recent measurement of $D_s^+\to\pi^+\rho^0$, the magnitudes and the strong phases of the $W$-a...

We study the implications of flavor-changing neutral currents (FCNC’s) in a model with the SU(2)l×SU(2)h×U(1)Y electroweak gauge symmetry for several anomalies appearing in b→sℓℓ¯ induced B decays in LHCb data. In this model, SU(2)l and SU(2)h govern the left-handed fermions in the first two generations and the third generation, respectively. The p...

In this paper, we revisit a visible heavy QCD axion model in light of the recent reports on the $750$ GeV diphoton resonance by the ATLAS and CMS experiments. In this model, the axion is made heavy with the help of the mirror copied sector of the Standard Model while the successful Peccei-Quinn mechanism is kept intact. We identify the $750$ GeV re...

The observation of diphoton excess around the mass of 750 GeV in LHC Run-II motivates us to consider whether the singlet Higgs boson in the custodial Higgs triplet model can serve as a good candidate because an earlier study of comprehensive parameter scan shows that it can have the right mass in the viable mass spectra. By assuming the singlet Hig...