arXiv subjects

Wei-Shu Hou

Publications and source records attributed to Wei-Shu Hou.

At least 19 recordsLinked to original sources

arXiv2025

Enhanced Charged Higgs Signal at the LHC

We investigate the discovery prospects of a charged Higgs boson ($H^\pm$) at the Large Hadron Collider (LHC) via the process $cg\to bH^\pm \to bc\bar{b}$ within the framework of a general two Higgs doublet model (G2HDM). In most two Higgs doublet models, the $H^+ cb$ coupling ($g_{H^+cb}$) is usually suppressed by the CKM matrix element $V_{cb}$. In G2HDM, there are additional Yukawa couplings, the process $cg\to bH^\pm \to bc\bar{b}$ is enhanced by the coupling $g_{H^+cb} \simeq \rtc V_{tb}$ in both the production and decay of the charged Higgs boson. We study possible physics backgrounds and evaluate the discovery potential with realistic acceptance cuts and tagging efficiencies at collider energies of $\sqrt{s}=$13 and 14 TeV. We apply $b$-tagging and $c$-tagging and show that $m_{H^+}$ can be extracted by pairing the tagged $b$ and $c$-jets. Our analysis leads to promising results for the current LHC and expected high-luminosity LHC.

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arXiv2025

Probing an extra Higgs boson at future linear $e^+ e^-$ colliders

We investigate the possibility of probing an extra Higgs boson at future linear $e^+ e^-$ colliders. We consider the production process $e^+e^- \to Hν\barν$, followed by the decay $H \to W^+W^-$, where $H$ is the extra $\textit{CP}$-even Higgs boson of the general two Higgs doublet model (G2HDM). This process is governed by the $\textit{CP}$-even Higgs mixing angle, $\cosγ$, offering direct access to this parameter. We discuss constraints on $\cosγ$ using existing LHC data and test the viability of the G2HDM top-quark-driven scenario for electroweak baryogenesis. We perform a full Monte Carlo simulation of the signal and background, and show that an extra Higgs boson in the mass range $200 \leq m_H \leq 400$ GeV could be probed at high energy linear $e^+ e^-$ colliders. Promising results are found for CLIC running at 1.5 and 3 TeV collision energies.

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arXiv2025

Lattice investigation of custodial two-Higgs-doublet model at weak quartic couplings

The $SU(2){-}$gauged custodial two-Higgs-doublet model, which shares the same global-symmetry properties with the standard model, is studied non-perturbatively on the lattice. The additional Higgs doublet enlarges the scalar spectrum and opens the possibility for spontaneous breaking of the global symmetry. In this work we start by showing the occurrence of spontaneous breaking of the custodial symmetry in a region of the parameter space of the model. Following this, both the spectrum and the running of the gauge coupling are examined at weak quartic couplings in the presence of the custodial symmetry. The calculations are performed with energy cutoffs ranging from 300 to 600 GeV on a line of constant standard model physics, obtained by tuning bare couplings to fix the ratio between the masses of the Higgs and the $W$ bosons, as well as the value of the renormalized gauge coupling at the scale of the $W$ boson mass. The realizable masses for the additional scalar states are explored. For the choice of bare quartic couplings in this work, the estimated lower bound of these masses is found to be well below the $W$ boson mass, and independent of the cutoff. We also study the finite temperature electroweak transition along this line of constant standard model physics, revealing properties of a smooth crossover behavior.

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arXiv2025

Probing the general 2HDM with flavor violation through $A \to ZH$

We investigate the LHC discovery prospects for a second Higgs doublet through $A \to ZH$ weak decay. The latter is identified as the $\textit{smoking gun signature}$ of two Higgs doublet models (2HDMs) with first-order electroweak (EW) phase transition, a necessary condition for EW baryogenesis. In the general 2HDM (G2HDM) that has flavor-changing neutral Higgs couplings, $H$ may decay dominantly via $t\bar c + \bar tc$ final states, giving rise to trilepton signals. By a phenomenological analysis, we show that $A \to ZH$ in $\ell^+ \ell^- t\bar c$ or $\ell^+ \ell^- \bar t c$ final states could be a promising probe of G2HDM at the LHC with flavor violation.

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arXiv2025

Searching for resonant flavor-changing charged Higgs production at the LHC

We suggest a resonant $c \bar b \to H^+$ production search, followed by bosonic $H^+ \to W^+ H$ weak decay at the Large Hadron Collider (LHC). In the general two-Higgs-doublet model (G2HDM) that has flavor-changing neutral Higgs couplings, $H^+$ is resonantly produced via the top-charm $ρ_{tc} V_{tb}$ coupling at tree level, while $H^+ \to W^+ H$ weak decay occurs within the exotic second doublet, leading eventually to same-sign dilepton signals. We perform a signal-to-background analysis at the 14 TeV LHC and show that discovery seems possible with LHC Run 2 data already at hand.

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arXiv2024

Lattice study of SU(2) gauge theory coupled to four adjoint Higgs fields

Gauge theories with matter fields in various representations play an important role in different branches of physics. Recently, it was proposed that several aspects of the interesting pseudogap phase of cuprate superconductors near optimal doping may be explained by an emergent $SU(2)$ gauge symmetry. Around the transition with positive hole-doping, one can construct a $(2+1)-$dimensional $SU(2)$ gauge theory coupled to four adjoint scalar fields which gives rise to a rich phase diagram with a myriad of phases having different broken symmetries. We study the phase diagram of this model on the Euclidean lattice using the Hybrid Monte Carlo algorithm. We find the existence of multiple broken phases as predicted by previous mean field studies. Depending on the quartic couplings, the $SU(2)$ gauge symmetry is broken down either to $U(1)$ or $\mathbb{Z}_2$ in the perturbative description of the model. We further study the confinement-deconfinement transition in this theory, and find that both the broken phases are deconfining in the range of volumes that we studied. However, there exists a marked difference in the behavior of the Polyakov loop between the two phases.

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arXiv2024

Reconstructing the general 2HDM charged Higgs boson at the LHC

We study the discovery prospects for a charged Higgs boson via the $b g\to c H^- \to c \bar t b$ process at the Large Hadron Collider (LHC). Focusing on the general Two Higgs Doublet Model (G2HDM) that possesses extra Yukawa couplings, the process is controlled by extra top couplings $ρ_{tc}$ and $ρ_{tt}$, which can drive electroweak baryogenesis (EWBG) to account for the baryon asymmetry of the Universe (BAU). We propose benchmark points (BPs) and demonstrate that evidence could emerge at 14 TeV LHC and luminosity of 300 fb$^{-1}$, with discovery potential at 600 fb$^{-1}$.

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arXiv2023

Probing Baryogenesis with Radiative Beauty Decay and Electron EDM

With the Large Hadron Collider (LHC) running, we should probe electroweak baryogenesis (EWBG) while probing $CP$ violation (CPV) with electron electric dipole moment (eEDM). Rooted in the flavor structure of the Standard Model (SM), the general two Higgs doublet model (g2HDM) with a second set of Yukawa couplings can deliver EWBG while surviving eEDM. We point out a chiral-enhanced top-bottom interference effect that makes $b \to sγ$ decay an exquisite window on EWBG and eEDM, and illustrate the importance of the $ΔA_{CP}$ observable at Belle II.

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arXiv2023

Discovery Prospects for Electron and Neutron Electric Dipole Moments in the General Two Higgs Doublet Model

Baryon asymmetry of the Universe offers one of the strongest hints for physics Beyond the Standard Model (BSM). Remarkably, in the general two Higgs Doublet Model (g2HDM) that possesses a second set of Yukawa matrices, one can have electroweak baryogenesis (EWBG) while the electron electric dipole moment (eEDM) is evaded by a natural flavor tuning that echoes SM. We show that eEDM may first emerge around $10^{-30}\,e$ cm or so, followed by neutron EDM (nEDM) down to $10^{-27}\,e$ cm. We illustrate a cancellation mechanism for nEDM itself, which in turn can be probed when a facility capable of pushing down to $10^{-28}\,e$ cm becomes available.

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arXiv2023

Enhanced $B_q \to \ell\ell^\prime$ and $B \to (K, π) \ell\ell^\prime$ in light of $(g-2)_μ$

We study lepton flavor violating (LFV) $B$ decays in a general two Higgs doublet model with sub-TeV exotic scalars. Two different parameter spaces are explored: one dominated by extra top Yukawa coupling $ρ_{tt}$, the other by LFV couplings relevant for the muon $g-2$ anomaly. In the first case, flavor constraints such as $\ell \to \ell^\primeγ$, $h \to \ell\ell^\prime$ imply LFV $B$ decays are far below experimental sensitivities. The second case needs to be close to the alignment limit, but $B_q \to τμ$ and $B \to (K, π) τμ$ rates can lie within the sensitivities of Belle II and LHCb Upgrade II. Neutral $B$ meson mixings and $B,\, K,\, π\to \ell ν$ decays provide important flavor constraints on parameter space. $B$ decays involving $e$-$τ$ violation are constrained by $μ\to e$ processes.

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arXiv2022

Strange processes in general two Higgs doublet model

In the general two Higgs doublet model (g2HDM) that has extra Yukawa couplings, we analyze their New Physics (NP) contributions to kaon mixing parameter $\varepsilon_K$, direct CP violation parameter $\varepsilon^\prime/\varepsilon$, and rare $K^+ \to π^+ν\barν$, $K_L \to π^0ν\barν$, and $K_{L, S} \to μ^+ μ^-$ decays. We study correlations between these observables, and call special attention to a unique complementarity of kaon mixing and rare $K\to πν\barν$ decays in probing the exotic Higgs mass spectrum of g2HDM. The importance of kaon physics in probing NP vis-à-vis B physics is stressed. One unexpected feature we uncover is the special sensitivity of $K^+ \to π^+ν\barν$ to TeV scale charged Higgs boson.

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arXiv2022

Searching for Charged Higgs Bosons via $e^+ e^- \to H^+ H^- \to c\bar{b} \bar{c}b $ at Linear Colliders

We study a search for the charged Higgs boson via $e^+e^- \to H^+H^- \to c\bar{b}\bar{c}b$ at the 500 GeV ILC. In a general two Higgs doublet model without $Z_2$ symmetry, extra Yukawa couplings $ρ_{tt}$ and $ρ_{tc}$ can drive baryogenesis, but searches at the HL-LHC may still go empty-handed if the couplings are relatively weak. Taking $m_{H^+ } \simeq m_H \simeq m_A \simeq 200$ GeV, with $ρ_{tt}$, $ρ_{tc}\sim 0.1$ and no $h(125)$-$H$ mixing, $H^+ \to c\bar b$ decay is dominant, and the $c\bar{b}\bar{c}b$ final state is likely overwhelmed by QCD background at the LHC. We show that the electroweak production of $H^+ H^-$ at the ILC is discoverable with integrated luminosity of 1 ab$^{-1}$. Furthermore, we show that $m_{H^+}$ can be extracted by requiring the two pairs of $b$ and light jets be roughly equal in mass, without assuming the mass value. Thus, ILC can probe low mass Higgs bosons in multijet final states to complement HL-LHC in the future

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arXiv2022

Charged Lepton EDM with Extra Yukawa Couplings

In a two Higgs doublet model with extra Yukawa couplings, we assess the new physics contributions to charged lepton electric dipole moment. We focus especially on muon (and tau) EDM where in the coming decade several experiments $-$ Muon g-2, J-PARC and PSI (and Belle II) $-$ will push sensitivities down by several orders of magnitude. With the working assumption that extra Yukawa couplings are analogous to SM ones in strength and taking exotic scalar masses in sub-TeV range, we find that $μ$ and $τ$ EDM can be enhanced to values larger than new physics scenarios that scale with lepton mass. The main effect comes from the flavor-conserving extra top coupling $ρ_{tt}$ via well-known two-loop diagrams. Deviating from our working assumption, if the muon $g-2$ anomaly arises from the one-loop diagram, driven by singly enhanced lepton flavor violating $ρ_{τμ}$ coupling, it can also induce rather large muon EDM, accessible at upcoming experiments.

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arXiv2022

Charged lepton flavor violation in light of Muon $g-2$

The recent confirmation of the muon $g-2$ anomaly by the Fermilab g-2 experiment may harbinger a new era in $μ$ and $τ$ physics. In the context of general two Higgs doublet model, the discrepancy can be explained via one-loop exchange of sub-TeV exotic scalar and pseudoscalars, namely $H$ and $A$, that have flavor changing neutral couplings $ρ_{τμ}$ and $ρ_{μτ}$ at $\sim 20$ times the usual tau Yukawa coupling, $λ_τ$. Taking $ρ_{\ell\ell^\prime}\sim λ_{ \rm min(\ell, \ell^\prime)}$, we show that the above solution to muon $g-2$ then predicts enhanced rates of various charged lepton flavor violating processes, which should be accessible at upcoming experiments. We cover muon related processes such as $μ\to e γ$, $μ\to eee$ and $μN \to e N$, and $τ$ decays $τ\to μγ$ and $τ\to μμμ$. A similar one-loop diagram with $ρ_{eτ}= ρ_{τe} = {\cal O}(λ_e)$ induces $μ\to eγ$, bringing the rate right into the sensitivity of the MEG~II experiment. The $μeγ$ dipole can be probed further by $μ\to 3e$ and $μN \to e N$. With its promised sensitivity range and ability to use different nuclei, the $μN \to eN$ conversion experiments can not only make discovery, but access the extra diagonal quark Yukawa couplings $ρ_{qq}$. For the $τ$ lepton, we find that $τ\to μγ$ would probe $ρ_{ττ}$ down to $λ_τ$ or lower, while $τ\to 3μ$ would probe $ρ_{μμ}$ to ${\cal O}(λ_μ)$.

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arXiv2021

Collider Prospects for Muon $g-2$ in General Two Higgs Doublet Model

Recent progress on muon $g-2$ measurement prompts one to take it even more seriously. In the general two Higgs doublet model that allows extra Yukawa couplings, we take a simplified approach of single enhanced coupling. We fix the charged lepton flavor violating coupling, $ρ_{τμ} = ρ_{μτ}$, via the one-loop mechanism, for illustrative masses of the heavy scalar $H$ and pseudoscalar $A$, where we assume $m_A = m_{H^+}$. Since extra top Yukawa couplings are plausibly the largest, we turn on $ρ_{tt}$ and find that LHC search for $gg \to H,\,A \to τμ$ gives more stringent bound than from $τ\to μγ$ with two-loop mechanism. Turning on a second extra top Yukawa coupling, $ρ_{tc}$, can loosen the bound on $ρ_{tt}$, but LHC constraints can again be more stringent than from $B \to Dμν$ vs $Deν$ universality. This means that evidence for $H,\,A \to τμ$ may yet emerge with full LHC Run 2 data, while direct search for $τ^\pmμ^\mp bW^+$ or $t\bar cbW^+$ (plus conjugate) may also bear fruit.

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arXiv2021

Decadal Mission for the New Physics Higgs/Flavor Era

The LHC has not discovered any New Physics beyond the anticipated $h(125)$ boson, and new ideas abound for out-of-the-box searches, or Effective Field Theories with multi-TeV cutoff. But, have we exhausted dimension-4 operators involving sub-TeV particles that are {\it not} exotic (non-XLP)? We advocate the existence of an extra Higgs doublet that carry extra Weinberg couplings, where {\it emergent} mass-mixing hierarchies {\it and} alignment have hidden their effects very well so far. ${\cal O}(1)$ Higgs quartics can induce first order electroweak phase transition and imply sub-TeV $H, A, H^\pm$ spectrum. The extra Weinberg couplings, led by $ρ_{tt}$ and $ρ_{tc}$ at ${\cal O}(1)$, can drive electroweak baryogenesis, while $|ρ_{ee}/ρ_{tt}| \propto λ_e/λ_t$, the ratio of usual electron and top Weinberg couplings, can tame electron EDM. Finding these extra Higgs bosons via $cg \to tH/A \to tt\bar c$, $tt\bar t$ and $cg \to bH^+ \to bt\bar b$ processes (and those allowed by Higgs boson splittings) at the LHC, and pushing the flavor frontier to break the flavor code, would usher in a new Higgs/flavor era. A new scale at 10--20 TeV, possibly related to the Landau pole of the scalar sector, may emerge.

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arXiv2021

A Final Word on FCNC-Baryogenesis from Two Higgs Doublets

Electroweak baryogenesis in a two-Higgs doublet model is a well-motivated and testable scenario for physics beyond the Standard Model. An attractive way of providing $CP$ violation is through flavor-changing Higgs couplings, where the top-charm coupling is hardly constrained. This minimal scenario can be tested by searching for heavy charged and neutral Higgs bosons at the LHC. While the charged Higgs signature requires a dedicated analysis, the neutral Higgs signature will be covered by a general search for same-sign top pairs. Together, they provide a conclusive test of this kind of baryogenesis.

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arXiv2021

Prospect and implications of $cg\to bH^+\to b A W^+$ production at the LHC

We study the prospect for discovering the $cg\to bH^+\to b A W^+$ process at the LHC. Induced by the top-flavor changing neutral Higgs coupling $ρ_{tc}$, the process may emerge if $m_{H^+} > m_A + m_{W^+}$, where $H^+$ and $A$ are charged and $CP$-odd Higgs bosons in the general two Higgs Doublet Model (g2HDM). We show that the $cg\to bH^+\to b A W^+$ process can be discovered at LHC Run 3, while the full Run 2 data at hand can constrain the parameter space significantly by searching for the same-sign dilepton final state. The process has unique implications on the hint of $gg\to A \to t \bar t$ excess at $m_A\approx 400$ GeV reported by CMS. When combined with other existing constraints, the $cg\to bH^+\to b A W^+$ process can essentially rule out the g2HDM explanation of such an excess.

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