arXiv subjects

Ying-nan Mao

Publications and source records attributed to Ying-nan Mao.

At least 19 recordsLinked to original sources

arXiv2026

Model-independent probes of CP violation in the heavy scalar sector at muon colliders

We propose a model-independent test of CP violation in the scalar sector. We consider a heavy neutral scalar $h_2$ with tree-level couplings at the $h_2 V V$ and $h_2 h_1 Z$ vertices (with $V=W^{\pm},Z$), alongside the 125~GeV SM-like Higgs boson $h_1$. At future muon colliders (MuC), we exploit vector-boson-fusion (VBF) production of $h_2$ followed by the decay $h_2 \to Z h_1$. In our framework, observing the single process $V V \to h_2 \to Z h_1$ implies both relevant couplings are nonzero, which is sufficient to establish CP violation in the scalar sector. We simulate signal and backgrounds at $\sqrt{s}=3~(10)$~TeV with integrated luminosity $L=0.9~(10)~\mathrm{ab}^{-1}$. We then present the expected discovery sensitivities across the $(c_2,c_{12})$ parameter space (with the coupling parameters $c_{2}$ and $c_{12}$ defined in the text) for multiple $m_{h_2}$ hypotheses.

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arXiv2026

LAYCAST: LAYered CAvern Surface Tracker at future electron-positron colliders

We propose a detector concept, LAYered CAvern Surface Tracker (LAYCAST), to be installed on the ceiling and the wall of the cavern hosting the main experiment of future electron-positron colliders such as CEPC and FCC-ee. With detailed and realistic considerations of the design of such a new experiment, the proposed detector is dedicated to extending the sensitivity reach of the main detector to various theoretical scenarios of long-lived particles (LLPs). We study carefully four such scenarios involving a light scalar boson $X$, the heavy neutral lepton $N$, the lightest neutralino $\tildeχ^0_1$ in the R-parity-violating supersymmetry, and the axion-like particle $a$. Long-lived light scalar bosons are considered to be produced from the Standard-Model (SM) Higgs boson's decay ($h \to X X$) at the center-of-mass energy $\sqrt{s} =$ 240 GeV, while the other three types of LLPs are produced either from $Z$-boson decays (viz. $Z \to ν\, N, ~\tildeχ^0_1\, \tildeχ^0_1 $) or direct scattering process ($ e^- e^+ \to ~γ\, a$) at $\sqrt{s} =$ 91.2 GeV, where $γ$ and $ν$ denote the SM photon and neutrino, respectively. With Monte-Carlo simulations, we derive the sensitivities of the proposed experiment to these LLPs and the corresponding signal-event numbers. We also provide a dedicated estimate of a potentially important SM background from long-lived neutral kaons in hadronic $Z$ decays, and show that it is strongly suppressed by the combined requirements of the main detector and LAYCAST. Our findings show that LAYCAST can probe large new parameter space beyond both current bounds and the expected reach of the main experiments at CEPC and FCC-ee. Comparison with existing works in similar directions is also made.

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arXiv2026

Discovery prospects for photophobic axion-like particles at a 100 TeV proton--proton collider

We study heavy photophobic axion-like particles (ALPs) in the limit of an effectively vanishing diphoton coupling, $g_{aγγ}\simeq 0$, for which diphoton production and decay are suppressed and collider phenomenology is driven by electroweak interactions ($aWW$, $aZγ$, $aZZ$). We perform detector-level searches at a future $\sqrt{s}=$ 100 TeV $pp$ collider (SppC/FCC-hh), with an integrated luminosity of $\mathcal{L} =$ 20 ab$^{-1}$. We consider $a\to Zγ$ and $a\to W^+W^-$ decays. For $pp\to jj\,a$ we include both $s$-channel electroweak exchange and vector boson fusion (VBF)-like topologies, while the tri-$W$ signature arises from associated production $pp\to W^\pm a$ (via $s$-channel exchange) followed by $a\to W^+W^-$. We analyze three final states--$Zγjj$ with $Z\to\ell^+\ell^-$, tri-$W$ ($W^\pm W^\pm W^\mp$) with same-sign dimuons plus jets, and $W^+W^-jj$ with opposite-sign, different-flavor dilepton ($e^\pmμ^\mp$) plus jets. Among the two $WW$ final states, the VBF-assisted $jj\,a(\to W^+W^-)$ channel overtakes the purely $s$-channel tri-$W$ mode for $m_a \stackrel{>}{\sim}$ 1 TeV, reflecting 100~TeV signal/background kinematic shifts beyond naive energy/luminosity rescaling. A boosted-decision-tree (BDT) classifier built from kinematic observables provides the final signal--background separation, using detector-level simulations of signal and high-statistics SM backgrounds. At $\sqrt{s}=100$ TeV and $\mathcal{L} =$ 20 ab$^{-1}$, we present discovery sensitivities to the ALP--$W$ coupling $g_{aWW}$ over $m_a\in[100,\,7000]$ GeV. In parallel, we report model-independent discovery thresholds on $σ\times\mathrm{Br}$ for $pp\to jj\,a$ with $a\to Zγ$ and $a\to W^+W^-$, as well as for associated production $pp\to W^\pm a$ with $a\to W^+W^-$....

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arXiv2025

Discovery prospects for photophobic axion-like particles in the $WWjj$ final state at the High-Luminosity LHC

We evaluate discovery prospects for photophobic axion-like particles (ALPs) in the $WWjj$ final state at the High-Luminosity LHC (HL-LHC; $\sqrt{s}=14$ TeV, $L=3$ ab$^{-1}$). In the photophobic limit ($g_{aγγ}=0$), ALPs couple to electroweak gauge bosons and are produced in association with two jets ($pp\to jj a$) via both $s$-channel electroweak exchange and vector-boson-fusion (VBF)-like topologies, followed by $a\to W^+W^-$ decay. We target the different-flavour dilepton mode $W^+W^-\to e^\pmμ^\mpν\barν$ with two jets and moderate missing transverse momentum. The analysis employs a two-step strategy: an initial preselection that defines the signal-like final state, followed by a multivariate analysis (MVA) trained on dijet and dileptonic-$WW$ kinematics from both the $s$-channel and VBF-like production mechanisms to separate signal from background; the MVA threshold is optimized independently at each $m_a$. We present $2σ$ and $5σ$ discovery sensitivities for the ALP-$W$ coupling $g_{aWW}$ across the $170$--$4000$ GeV mass range. For $260$ GeV $\le m_a \le 1500$ GeV, the $2σ$ ($5σ$) sensitivity is approximately flat around 0.61 (0.76) TeV$^{-1}$. We also report model-independent discovery thresholds for the fiducial quantity $σ(pp\to jj a)\,\mathrm{Br}(a\to W^+W^-)$ over the same mass range to enable reinterpretation for other models. These results indicate that the $WWjj$ topology offers competitive and complementary sensitivity to heavy photophobic ALPs at the HL-LHC.

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arXiv2025

Sensitivities to New Resonance Couplings to $W$-Bosons at the LHC

We propose a search strategy at the HL-LHC for a new neutral particle $X$ that couples to $W$-bosons, using the process $p p \rightarrow W^{\pm} X (\rightarrow W^{+} W^{-})$ with a tri-$W$-boson final state. Focusing on events with two same-sign leptonic $W$-boson decays into muons and a hadronically decaying $W$-boson, our method leverages the enhanced signal-to-background discrimination achieved through a machine-learning-based multivariate analysis. Using the heavy photophobic axion-like particle (ALP) as a benchmark, we evaluate the discovery sensitivities on both production cross section times branching ratio $σ(p p \rightarrow W^{\pm} X) \times \textrm{Br}(X \rightarrow W^{+} W^{-})$ and the coupling $g_{aWW}$ for the particle mass over a wide range of 170-3000 GeV at the HL-LHC with center-of-mass energy $\sqrt{s} = 14$ TeV and integrated luminosity $\mathcal{L} = 3$ $\textrm{ab}^{-1}$. Our results show significant improvements in discovery sensitivity, particularly for masses above 300 GeV, compared to existing limits derived from CMS analyses of Standard Model (SM) tri-$W$-boson production at $\sqrt{s} = 13$ TeV. This study demonstrates the potential of advanced selection techniques in probing the coupling of new particles to $W$-bosons and highlights the HL-LHC's capability to explore the physics beyond the SM.

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arXiv2025

Testing CP-violation in a Heavy Higgs Sector at CLIC

We propose to probe CP-violation in the heavy (pseudo)scalar sector of an extended Higgs model, in which we make simultaneous use of the $HVV$ ($V=W^\pm, Z$) and $Ht\bar{t}$ interactions of a heavy Higgs state $H$. The CP-even component of $H$ can be probed through the tree level $HVV$ interaction while the CP-odd component of $H$ can be probed if the final $t\bar{t}$ pair can be tested to form a $^1S_0$ state. We can then confirm CP-violation if both CP-even and CP-odd components of $H$ are discovered. This is possible at the Compact Linear Collider (CLIC) by exploiting $H$ production from Vector-Boson Fusion (VBF) and decay to $t\bar{t}$ pairs. We analyze the distribution of the azimuthal angle between the leptons coming from top and antitop quarks, that would allow one to disentangle the CP nature of such a heavy Higgs state. We also show its implications for the 2-Higgs-Doublet Model (2HDM) with CP-violation.

hep-ph↗

arXiv2025

Search for the $γZ$ decay mode of heavy photophobic axion-like particles at the LHC

We assume the coupling of Axion-like particle (ALP) to diphoton $g_{aγγ} \sim 0$ and accomplish detailed analyses for the $γZ$ decay mode of such heavy photophobic ALPs at the high luminosity-Large Hadron Collider (HL-LHC). ALPs are produced with two jets via both the $s$-channel vector boson exchange and vector boson fusion processes, with the signal process $pp \to jj\, a (\to γ\, Z (\to \ell^+ \ell^-)\, ) $ for $\ell = e, μ$. Signal and background events are simulated at the detector-level. Preselection criteria target events with one photon, two oppositely charged electrons or muons, and two non-$b$-tagged jets. The ALP mass is reconstructed, and kinematic observables are input into a machine learning-based multivariate analysis for optimal background rejection. Discover sensitivities on the ALP's coupling to di-$W$ boson, $g_{aWW}$, are presented in the mass range from 100 to 4000 GeV at center-of-mass energy $\sqrt{s} = 14$ TeV and integrated luminosity $\mathcal{L}=$ 3 ab$^{-1}$ and 140 fb$^{-1}$. Sensitivities on the production cross section $σ(pp \to jj\, a)$ times the branching ratio Br$(a \to γZ)$ are also presented.

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arXiv2025

Limiting on ALP-photon Coupling through GRB221009A

This study investigates the constraints on ALPs parameters through the photon-ALP oscillation model, based on the high-energy photon propagation characteristics of the gamma-ray burst GRB 221009A. We briefly describe the Primakoff process and use it to derive the oscillation probability. Numerical simulations incorporate the GMF, IGMF, and EBL, utilizing the open-source code gammaALPs to simulate photon propagation from the source to Earth. By employing the chi2 statistical method and segmented spectral fitting of low-energy and high-energy observational data from HXMT-GECAM, the dependence of photon survival probability on ALP mass (ma) and coupling strength (ga) is analyzed. Results show that for the ALP mass range 10^-7 < ma < 10^2 neV, the upper limit on the coupling strength is ga < 0.27 * 10^-11 GeV^-1, improving constraints by one order of magnitude compared to the CAST experiment (6.6 * 10^-11 GeV^-1). Notably, high-energy data exhibit significantly stronger constraining power. This work provides a novel theoretical framework and observational basis for indirectly probing ALPs through extreme astrophysical phenomena.

astro-ph.HE↗

arXiv2025

The Standard Model quark/lepton masses and the Cabibbo-Kobayashi-Maskawa mixing in an ${\rm SU}(8)$ theory

The observed Standard Model (SM) quark/lepton mass hierarchies and the Cabibbo-Kobayashi-Maskawa (CKM) mixing pattern are described in an ${\rm SU}(8)$ theory through its realistic symmetry breaking pattern with three intermediate stages, which rely on a set of $d=5$ gravity-induced operators that break the emergent global symmetries in the chiral fermion sector, as well as the precise identifications of all non-trivially embedded SM flavors.

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arXiv2024

The gauge coupling evolutions of an ${\rm SU}(8)$ theory with the maximally symmetry breaking pattern

We study the renormalizable group equations (RGEs) of the extended strong and weak gauge couplings in an ${\rm SU}(8)$ theory, where three-generational SM fermions are non-trivially embedded. This framework was previously found to generate the observed SM quark/lepton mass hierarchies and the Cabibbo-Kobayashi-Maskawa mixing pattern through its maximally breaking pattern. The field theoretical two-loop RGEs can not achieve the gauge coupling unification with the minimal setup, unless additional adjoint Higgs fields as well as the gravity-induced $d=5$ term to the ${\rm SU}(8)$ field strength term are included.

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arXiv2024

The global $B-L$ symmetry in the flavor-unified ${\rm SU}(N)$ theories

We study the origin of the global $B-L$ symmetry in a class of flavor-unified theories with gauge groups of ${\rm SU}(N\geq 6)$. In particular, we focus on the ${\rm SU}(8)$ theory which can minimally embed three-generational SM fermions non-trivially. A reformulation of the third law for the flavor sector proposed by Georgi is useful to manifest the underlying global symmetries. The 't Hooft anomaly matching and the generalized neutrality conditions for Higgs fields play the key roles in defining the $B-L$ symmetry. Based on the global $B-L$ symmetry, we count the Higgs fields that can develop the VEVs and the massless sterile neutrinos in the ${\rm SU}(8)$ theory. We also prove that a global $B-L$ symmetry can always be defined in any ${\rm SU}(N\geq 6)$ theory when it is spontaneously broken to the SM gauge symmetry.

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arXiv2023

Search for heavy Majorana neutrinos in the $τ$ final state at proton-electron colliders

We utilize the lepton number violation signal process $p\, e^- \to τ^+ jjj$ to search for heavy Majorana neutrinos at future proton-electron colliders. The LHeC (FCC-eh) is considered to run with an electron beam energy of 60 GeV, a proton beam energy of 7 (50) TeV and an integrated luminosity of 1 (3) ab$^{-1}$, and the electron beam is considered to be unpolarized. We apply detector configurations and simulate signal and related standard model background events for both hadronic $τ_h$ and leptonic $τ_\ell$ final states, $\ell$ being a muon. After preselection, multivariate analyses are performed to reject the background. The strategy to reconstruct the heavy neutrino mass is developed and distributions of reconstructed mass are presented. Discovery sensitivities on parameter $|V_{τN}|^2 |V_{eN}|^2 / ( |V_{τN}|^2 + |V_{eN}|^2 )$ for the heavy neutrino mass between 10 and 3000 GeV are predicted. At the 2-$σ$ significance, the best discovery sensitivity is $\sim 1.2 \times10^{-5} \,\,(5.0 \times 10^{-6})$ at the LHeC (FCC-eh) when $m_N \sim 100$ GeV for the hadronic $τ_h$ final state. Sensitivities for the leptonic $τ_\ell$ final state are found to be similar to those for the hadronic $τ_h$ final state for most of the parameter space investigated. We also derive the limits on mixing parameters from electroweak precision data (EWPD) and DELPHI experiment. Assuming $|V_{τN}|^2 = |V_{eN}|^2 = |V_{\ell N}|^2$, sensitivity bounds from the LHeC and FCC-eh experiments are found to be stronger than those from EWPD when $m_N \lesssim 900$ GeV, and also stronger than those from DELPHI when $m_N \gtrsim 70$ GeV. Constraints are also interpreted and compared in the $|V_{τN}|^2$ vs. $|V_{e N}|^2$ plane.

hep-ph↗

arXiv2023

Probe the Mixing Parameter $|V_{τN}|^2$ for Heavy Neutrinos

Because of the difficulty in detecting final state taus, the mixing parameter $|V_{τN}|^2$ for heavy neutrino $N$ is not well studied at current experiments, compared with other mixing parameters $|V_{e N}|^2$ and $|V_{μN}|^2$. In this paper, we focus on a challenging scenario where $N$ mixes with active neutrino of tau flavour only, i.e. $ |V_{τN}|^2 \neq 0 $ and $|V_{e N}|^2 = |V_{μN}|^2 = 0$. We derive current constraints on $|V_{τN}|^2$ from the rare $Z$-boson decay and electroweak precision data (EWPD). To forecast the future limits, we also investigate the signal $p p \to τ^{\pm} τ^{\pm} j j $ via a Majorana heavy neutrino at future proton-proton colliders. To suppress the background, both taus are required to decay leptonically into muons, leading to the final state containing two same sign muons, at least two jets plus moderate missing energy. The signal and relevant background processes are simulated at the HL-LHC and SppC/FCC-hh with center-of-mass energy of 14 TeV and 100 TeV. The preselection and multivariate analyses based on machine-learning are performed to reduce background. Limits on $|V_{τN}|^2$ are shown for heavy neutrino mass in the range 10-1000 GeV based on measurements from the rare $Z$-boson decay and EWPD, and searches at the HL-LHC and SppC/FCC-hh with integrated luminosities of 3 and 20 ab$^{-1}$.

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arXiv2023

Can we discover lepton number violation with LHC far detectors?

Two classes of far detectors have been proposed or are under operation at the LHC. The first class is a series of neutrino detectors that are sensitive to light active neutrinos via either charged-current or neutral-current interactions; exemplary ideas are FASER$ν$, SND@LHC, and FLArE. Another type aims primarily at looking for displaced decays of long-lived particles (LLPs) into charged final-state particles, including ANUBIS and FASER. In this work, we propose searches for probing lepton number violation associated with a Majorana active/sterile neutrino, for the first time with these experiments, which, if discovered, would be a clear signature of new physics beyond the Standard Model. With Monte-Carlo simulation, we find that while the neutrino detectors, unfortunately, are estimated to have signal-event rates orders of magnitude below $\mathcal{O}(1)$, some LLP far detectors such as ANUBIS, if upgraded, would be most promising for discovering a Majorana sterile neutrino of mass $\mathcal{O}(\text{1})$ GeV in certain so-far unexcluded parameter space. In this exploratory work, we emphasize on the importance of leveraging the LHC far detectors for purposes beyond the planned ones, such as searching for lepton number violation.

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arXiv2023

A two-generational ${\rm SU}(7)$ model with extended weak sector: mass hierarchies, mixings, and the flavor non-universality

We study a possible gauge symmetry breaking pattern in an ${\rm SU}(7)$ grand unified theory, which describes the mass origins of all electrically charged SM fermions of the second and the third generations. Two intermediate gauge symmetries of ${\cal G}_{341}\equiv {\rm SU}(3)_c \otimes {\rm SU}(4)_W \otimes {\rm U}(1)_{X_0}$ and ${\cal G}_{331}\equiv {\rm SU}(3)_c \otimes {\rm SU}(3)_W \otimes {\rm U}(1)_{X_1}$ arise above the electroweak scale. SM fermion mass hierarchies between two generations can be obtained through a generalized seesaw mechanism. The mechanism can be achieved with suppressed symmetry breaking VEVs from multiple Higgs fields that are necessary to avoid tadpole terms in the Higgs potential. Some general features of the ${\rm SU}(7)$ fermion spectrum will be described, which include the existence of vectorlike fermions, the tree-level flavor changing weak currents between the SM fermions and heavy partner fermions, and the flavor non-universality between different SM generations from the extended weak sector.

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arXiv2023

Bottom quark and tau lepton masses in a toy ${\rm SU}(6)$

We study a toy ${\rm SU}(6)$ model with the symmetry breaking pattern of the extended $331$ symmetry of ${\rm SU}(3)_c \otimes {\rm SU}(3)_W \otimes {\rm U}(1)_X$. A "fermion-Higgs mismatching" symmetry breaking pattern is proposed for more realistic model building. Within such symmetry breaking pattern, only one Higgs doublet develops vacuum expectation value for the spontaneous electroweak symmetry breaking, and gives tree-level top quark mass. A natural VEV splittings in the $331$ breaking Higgs fields gives tree-level masses to both bottom quark and tau lepton. The $125\,{\rm GeV}$ SM-like Higgs boson discovered at the LHC can have Yukawa couplings to bottom quark and tau lepton as in the SM prediction, and this suggests the $331$ symmetry breaking scale to be $\sim {\cal O}(10)\,{\rm TeV}$.

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arXiv2021

Revisit to the $b\to cτν$ transition: in and beyond the SM

We perform an analysis of the $b\to cτν$ data, including $R(D^{(*)})$, $R(J/ψ)$, $P_τ(D^{*})$ and $F_L^{D^*}$, within and beyond the Standard Model (SM). We fit the $B\to D^{(*)}$ hadronic form factors in the HQET parametrization to the lattice and the light-cone sum rule (LCSR) results, applying the general strong unitarity bounds corresponding to $J^P=1^-$, $1^+$, $0^-$ and $0^+$. Using the obtained HQET relations between helicity amplitudes, we give the strong unitarity bounds on individual helicity amplitudes, which can be used in the BGL fits. Using the fitted form factors and taking into account the most recent Belle measurement of $R(D^{(*)})$ we investigate the model-independent and the leptoquark model explanations of the $b\to cτν$ anomalies. Specifically, we consider the one-operator, the two-operator new physics (NP) scenarios and the NP models with a single $R_2$, $S_1$ or $U_1$ leptoquark which is supposed to be able to address the $b\to cτν$ anomalies, and our results show that the $R_2$ leptoquark model is in tension with the limit $\mathcal B(B_c\to τν)<10\%$. Furthermore, we give predictions for the various observables in the SM and the NP scenarios/leptoquark models based on the present form factor study and the analysis of NP.

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arXiv2020

Two-Higgs-Doublet Model with Soft CP-violation Confronting Electric Dipole Moments and Colliders

We analyze CP-violating effects in both Electric Dipole Moment (EDM) measurements and future analyses at the Large Hadron Collider (LHC) assuming a Two-Higgs-Doublet Model (2HDM) with "soft" CP-violation. Our analysis of EDMs and current LHC constraints shows that, in the case of a 2HDM Type II and Type III, an $\mathcal{O}(0.1)$ CP-violating phase in the Yukawa interaction between $H_1$ (the $125~\textrm{GeV}$ Higgs boson) and fermions is still allowed. For these scenarios, we study CP-violating effects in the neutron EDM and $t\bar{t}H_1$ production at the LHC. Our analysis shows that such an $\mathcal{O}(0.1)$ CP-violating phase can be easily confirmed or excluded by future neutron EDM tests, with LHC data providing a complementary cross-check.

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