arXiv subjects

Xia Wan

Publications and source records attributed to Xia Wan.

16 recordsLinked to original sources

arXiv2026

A HEFT Perspective on the Type-II Seesaw Model and the Complete Basis of Lepton-Number-Violating Operators

We perform the complete tree-level matching of the type-II seesaw model onto the Higgs effective field theory (HEFT) through $\mathcal{O}(p^4)$ in the chiral expansion. Employing a nonlinear field representation and the primary-HEFT power-counting scheme, we retain the dependence on the independent heavy-scalar masses, the neutral-scalar mixing angle, and the triplet vacuum expectation value without introducing additional expansions in these parameters. To systematically describe lepton-number violation, we construct a complete and nonredundant basis of LNV HEFT operators through $\mathcal{O}(p^4)$, including their full flavor multiplicities, using a complex dressed spurion that encodes the $B-L$ charge and custodial orientation of the LNV insertion. The basis is independently validated by Hilbert-series counting. We then compare our matching results with those for the corresponding real-triplet extension and with a previously proposed broken-phase effective field theory. These comparisons identify the effects of the additional CP-odd and doubly charged scalar states and show that the overlapping broken-phase results are recovered after the appropriate parameter expansion, while HEFT retains the unexpanded nonlinear electroweak structure. We further discuss representative implications for Higgs and electroweak precision observables, vector-boson scattering, multi-Higgs production, anomalous gauge couplings, top-quark processes, neutrinoless double-beta decay, charged-lepton flavor violation, and same-sign dilepton production.

hep-ph↗

arXiv2026

Revealing the Two-Fold Ambiguity: Tau Momentum Reconstruction and Its Impact on Entanglement Observables

The neutrinos produced in $\tau$ decays cannot be directly detected, making the reconstruction of $\tau$ kinematics challenging and affecting measurements of quantum correlations such as spin entanglement. For the process $e^+e^- \to \tau^+\tau^- \to \pi^+ \bar{\nu}_\tau\pi^-\nu_\tau$, the kinematic constraints allow the $\tau$ momenta to be reconstructed up to a well-known two-fold ambiguity, regardless of the presence of an intermediate resonance state. In this paper, we present a geometric interpretation of this ambiguity and propose a numerical reconstruction method based on singular value decomposition (SVD). Using only the information from visible final-state particles and decay kinematics, the method reconstructs the two possible solutions for the $\tau^+\tau^-$ pair. The reconstruction performance is validated with Monte Carlo simulations in typical collider environments. We further investigate the impact of the spurious solution on spin-entanglement measurements and show that reliable entanglement signals can still be extracted even when the true and spurious solutions cannot be experimentally distinguished. This work provides a practical approach for $\tau$-lepton kinematic reconstruction and spin-entanglement measurements in $e^+e^-$ collider experiments.

hep-ph↗

arXiv2026

Establishing the Primary HEFT as a Precision Benchmark for UV-HEFT Matching

We match the real Higgs triplet model (RHTM) onto HEFT under different parameter choices and power-counting schemes, thereby obtaining several representative HEFT formulations and clarifying their relations. We establish the primary HEFT (pHEFT) as a benchmark framework, demonstrating that alternative HEFT constructions can be systematically derived from it. A key advantage of the pHEFT construction is its parameter choice, which maintains linear relations between the UV Lagrangian parameters and squared heavy masses. By strictly employing the inverse squared heavy masses as the expansion parameters without imposing additional constraints, pHEFT preserves maximal ultraviolet (UV) information and ensures higher perturbative accuracy by avoiding the additional truncations inherent in more complex, non-linear formulations or extra constraints. Through the analysis of the $Z_2$-symmetric real singlet model and the 2HDM, we illustrate the criteria for identifying viable primary HEFT constructions in UV models with scalar extensions. Furthermore, for the first time, we derive the HEFT operators of the RHTM involving fermions.

hep-ph↗

arXiv2025

Matching the real Higgs triplet extension of Standard Model to HEFT

We make a first matching of the real Higgs triplet extension (RHTE) of the standard model to the Higgs effective field theory (HEFT), which is also known as electroweak chiral Lagrangian (EWChL). In the RHTE, the ratio $\xi$ of two VEVs separately from triplet and doublet is a tiny quantity, due to the constrained custodial symmetry violation. Based on the nonlinear representation~\cite{Song:2024kos} of RHTE and functional method, we get the HEFT in the power counting of $\xi$. By comparing its phenomenological results of $hh\to hh$, $W W \to h h$, $Z Z \to hh $ to SMEFT's, we show its convergence property is as good as SMEFT's. Besides we explicitly show that the HEFT is available in the phase transition region where SMEFT fails.

hep-ph↗

arXiv2024

A Non-linear Representation of General Scalar Extensions of the Standard Model for HEFT Matching

We introduce a non-linear representation of ultraviolet~(UV) complete model, $U$ representation, under which matching HEFT to general scalar extensions of the standard model is straightforward. The main idea is to express a scalar multiplet in its linear form rotated by $U$ matrices, where $U$ matrix is exponential form of Goldstones based on Pauli matrices and meanwhile is a special $SU(2)_L$ rotation. All together the doublet is expressed in $U$ matrix multiplying a doublet column or bidoublet matrix, which is composed of physical Higgs. We show a complete matching between HEFT and real triplet extension. Meanwhile, under tensor notation, we give $U$ representation for general scalar extensions.

hep-ph↗

arXiv2022

Fractional quantum fields with Le'vy paths

We develop a path integral approach to quantum field theory that is defined over the paths of the Le'vy flights possessing a fractal dimension $1<d_f<2$. In standard quantum field theory, the fractality of the Brownian trajectories lead to a dispersion relation of quadric form. While the Le'vy paths lead fractional quantum field theory to a fractional dispersion relation. By considering Le'vy paths in time, we calculate density of states for a massless scalar field with box boundary condition. The density of states show behaviors dual to lower dimensional system, and the corresponding black body radiation has an energy spectrum dual to that in lower dimensional black body radiation. We derive the fractional equations of motion for scalar field, vector field and spinor field in zero temperature. Their propagators have been calculated. Based on above derivation, we calculate the one-loop self-energy of electron in Lev'y paths to show how this scheme works equally in renormalization as dimensional regularization does. Nevertheless, We found that gauge symmetry prevent Dirac spinor field from Le'vy paths and demonstrate that these paths in Dirac spinor field leds to unstable electrons, thus Le'vy paths are overcame by ordinary Brownian paths. While Le'vy paths are permitted in electromagnetic field by gauge symmetry. It led to a non-local phase and interaction with electron where electron charge is a composite quantity rather than a fundamental constant which maybe physically observable.

hep-th↗

arXiv2022

Custodial Symmetry Violation in Scalar Extensions of the Standard Model

The new measurement of the W boson mass from the CDF collaboration shows a significant tension with the Standard Model prediction, which evidences violation of custodial symmetry in the scalar sector. We study the scalar extensions of the Standard Model, which can be categorized into two classes, scalar sector with custodial symmetry (Georgi-Machacek model and its generalizations) and scalar sector without custodial symmetry, and explore how these extensions fit to the electroweak precision data and the CDF new $m_W$ . The favored oblique parameters are coming from either the large mass splitting in the multiplet via the loop contribution or the large vacuum expectation value which breaks custodial symmetry at the tree level. In particular, we find that $\mathcal{O}(100)$ GeV new particles are allowed in the scalar extension scenarios.

hep-ph↗

arXiv2021

Exploring $HVV$ amplitudes with $CP$ violation by decomposition and on-shell scattering amplitude methods

$CP$ violation may play an important role in Baryogenesis in early universe, and should be examined at colliders comprehensively. We study $CP$ properties of $HVV$ vertexes between Higgs and gauge boson pairs with defining a $CP$ violation phase angle $\xi$, which indicates the mixture of $CP$-even and $CP$-odd Higgs states in $HVV$ in new physics. A series of $HVV$ amplitudes $H\to\gamma\gamma, H\to\gamma V\to \gamma \ell\ell$, and $H\to VV\to 4\ell$ with $CP$ phase angle are studied systematically, which explains explicitly why $CP$ violation could only be probed in $4\ell$ process independently. We get a novel amplitude decomposition relation which illustrates if two preconditions (multilinear momentum dependent vertexes and current $J_\mu$ of $V\to \ell^+ \ell^-$ is formally proportional to a photon's polarization vector) are satisfied, an high-point amplitude can be decomposed into a summation of a series of low-point amplitudes. As a practical example, the amplitude of $H\to\gamma V\to \gamma \ell\ell$, and $H\to VV\to 4\ell$ processes can be decomposed into summation of many $H\to\gamma\gamma$ amplitudes. Meanwhile, we calculate these amplitudes in the framework of on-shell scattering amplitude method, with considering both massless and massive vector gauge bosons with $CP$ violation phase angle. The above two approaches provides consistent results and exhibit clearly the $CP$ violation $\xi$ dependence in the amplitudes.

hep-ph↗

arXiv2021

Probe CP violation in $H\to γZ$ through forward-backward asymmetry

We suggest that the forward-backward asymmetry $(A_{FB})$ of the charged leptons in $gg\to H\toγZ\toγ\ell^-\ell^+$ process could be used to probe the CP violating $HγZ$ coupling when the interference from $gg\toγZ\toγ\ell^-\ell^+$ process is included. With CP violation in $HγZ$ coupling, the interference effect leads to a non-vanishing $A_{FB}$, which is also sensitive to the strong phase differences. The resonant and non-resonant strong phases together make $A_{FB}(\hat{s})$ change sign around Higgs mass $M_H$. For phenomenology study, we suggest the integral over one-side mass region below $M_H$ to magnify the $A_{FB}$ strength.

hep-ph↗

arXiv2020

Anomalous $H\to ZZ \to 4\ell$ decay and its interference effects at the LHC

We calculate the spinor helicity amplitudes of anomalous $H\to ZZ \to 4\ell$ decay. After embedding these analytic formulas into the $\texttt{MCFM}$ package, we study the interference effects between the anomalous $gg\to H\to ZZ \to 4\ell$ process and the SM processes, which are indispensable in the Higgs off-shell region. Subsequently, the constraints on the anomalous couplings are estimated using LHC experimental data.

hep-ph↗

arXiv2019

Probe $CP$-violating $Hγγ$ coupling through interferometry

The diphoton invariant mass distribution of interference between $gg\to H \to γγ$ and $gg\to γγ$ is almost antisymmetric around the Higgs mass $M_H$. We propose a new observable $A_{\text{int}}$ to quantify this effect, which is a ratio of a sign-reversed integral around $M_H$ ( e.g. $\int^{M_H}_{M_H-5~\mbox{GeV}} -\int_{M_H}^{M_H+5~\mbox{GeV}}$) and the cross section of the Higgs signal. We study $A_{\text{int}}$ both in Standard Model (SM) and new physics with various $CP$-violating $Hγγ$ couplings. The $A_{\text{int}}$ in SM could reach a value of $10\%$, while for $CP$-violating $Hγγ$ couplings $A_{\text{int}}$ could range from $10\%$ to $-10\%$, which is probable to be detected in HL-LHC experiment. The $A_{\text{int}}$ with both $CP$-violating $Hγγ$ and $Hgg$ couplings are also studied and its value range is further extended.

hep-ph↗

arXiv2017

An optimal scheme for top quark mass measurement near $t\bar{t}$ threshold at future $e^{+}e^{-}$ colliders

A simulation of top quark mass measurement scheme near the $t\bar{t}$ production threshold in future $e^{+}e^{-}$ colliders, e.g. the Circular Electron Positron Collider(CEPC), is performed. $χ^2$ fitting method is adopted to determine the number of energy points to be taken and their locations. Our result shows that the optimal energy point is located near the largest slope of the cross section to beam energy and the most efficient scheme is to concentrate all luminosity on this single energy point in one parameter top mass fitting case. This suggests that the so called data driven method can be a best choice for the future real experimental measurement. Conveniently, the top mass statistical uncertainty can also be calculated directly by the error matrix even without any sampling and fitting. Agreement of the above two optimization methods has been checked. Our conclusion is that by taking 50~$fb^{-1}$ total effective integrated luminosity data, the statistical uncertainty of the top potential subtracted mass can be suppressed to about 7~MeV and the total uncertainty is about 30~MeV. This precision will help to identify the stability of the electroweak vacuum at the Planck scale.

hep-ph↗

arXiv2017

Probe CP violation in $H\to γZ$ through forward-backward asymmetry

We suggest that the forward-backward asymmetry $(A_{FB})$ of the charged lepton in $gg\to H\toγZ\toγ\ell^-\ell^+$ process could be used to probe the CP violating $HγZ$ coupling when the interference from $gg\toγZ\toγ\ell^-\ell^+$ process is included. With CP violation in $HγZ$ coupling, the interference effect leads to a non-vanishing $A_{FB}$, which is also sensitive to the strong phase differences. The resonant and non-resonant strong phases together make $A_{FB}(\hat{s})$ change sign around Higgs mass $M_H$. For phenomenology study, we suggest the integral over one-side mass region below $M_H$ to magnify the $A_{FB}$ strength.

hep-ph↗

arXiv2013

Searching for Charged Higgs Boson in Polarized Top Quark

The charged Higgs boson is quite common in many new physics models. In this study we examine the potential of observing a heavy charged Higgs boson in its decay mode of top-quark and bottom-quark in the Type-II Two-Higgs-Doublet-Model. In this model, the chirality structure of the coupling of charged Higgs boson to the top- and bottom-quark is very sensitive to the value of $\tanβ$. As the polarization of the top-quark can be measured experimentally from the top-quark decay products, one could make use of the top-quark polarization to determine the value of $\tanβ$. We preform a detailed analysis of measuring top-quark polarization in the production channels $gb\to tH^-$ and $g\bar{b}\to \bar{t}H^+$. We calculate the helicity amplitudes of the charged Higgs boson production and decay.Our calculation shows that the top-quark from the charged Higgs boson decay provides a good probe for measuring $\tanβ$, especially for the intermediate $\tanβ$ region. On the contrary, the top-quark produced in association with the charged Higgs boson cannot be used to measure $\tanβ$ because its polarization is highly contaminated by the $t$-channel kinematics.

hep-ph↗

arXiv2012

Constraints on the Universal Varying Yukawa Couplings: from SM-like to Fermiophobic

Varying the Standard Model (SM) fermion Yukawa couplings universally by a generic positive scale factor ($F_{Yu}$), we study the phenomenological fit to the current available experimental results for the Higgs boson search at hadron colliders. We point out that the Higgs production cross section and its decay branching ratio to $γγ$ can be varied oppositely by $F_{Yu}$ to make their product almost invariant. Thus, our scenario and the SM Higgs are indistinguishable in the inclusive $H\to γγ$ channel. The current measurements on direct Yukawa coupling strength in the $H\to b\bar{b}/ττ$ channel are not precise enough to fix the scale factor $F_{Yu}$. The most promising is the vector-boson-fusion channel in which the CMS has already observed possible suppression effect on the Yukawa couplings. Further more, the global $χ^2$ fit of the experimental data can get the optimal value by introducing a suppression factor $F_{Yu}\sim1/2$ on the SM Yukawa couplings.

hep-ph↗

arXiv2012

Toward the Natural and Realistic NMSSM with and without R-Parity

From the current ATLAS and CMS results on Higgs boson mass and decay rates, the NMSSM is obviously better than the MSSM. To explain the fine-tuning problems such as gauge hiearchy problem and strong CP problem in the SM, we point out that supersymmetry does not need to provide a dark matter candidate, i.e., R-parity can be violated. Thus, we consider three kinds of the NMSSM scenarios: in Scenarios I and II R-parity is conserved and the lightest neutralino relic density is respectively around and smaller than the observed value, while in Scenario III R-parity is violated. To fit all the experimental data, we consider the χ^2 analyses, and find that the Higgs boson mass and decay rates can be explained very well in these Scenarios. Considering the small χ^2 values and fine-tuning around 2-3.7% (or 1-2%), we obtain the viable parameter space with light (or relatively heavy) supersymmetric particle spectra only in Scenario III (or in Scenarios I and II). Because the singlino, Higgsinos, and light stop are relatively light in general, we can relax the LHC supersymmetry search constraints but the XENON100 experiment gives a strong constraint in Scenarios I and II. In all the viable parameter space, the anomalous magnetic moment of the muon (g_μ - 2)/2 are generically small. With R-parity violation, we can increase (g_μ - 2)/2, and avoid the contraints from the LHC supersymmetry searches and XENON100 experiment. Therefore, Scenario III with R-parity violation is more natural and realistic than Scenarios I and II.

hep-ph↗