arXiv subjects

Soojin Lee

Publications and source records attributed to Soojin Lee.

At least 19 recordsLinked to original sources

arXiv2026

Measuring the trilinear Higgs self-coupling in Higgs boson pair production at multi-TeV muon colliders

The trilinear Higgs self-coupling determines the shape of the Higgs potential, and its measurement is a central goal of future colliders. We assess the sensitivity of multi-TeV muon colliders to the coupling modifier $\kappa_3$ in Higgs boson pair production via vector boson fusion, using the $b\bar{b}b\bar{b}$ final state at $\sqrt{s}=3$ TeV with $1$ ab$^{-1}$ and at $10$ TeV with $10$ ab$^{-1}$. Events are analyzed in two complementary regions, a resolved region with four jets and a boosted region with two large-radius jets. To extract the signal from backgrounds a few orders of magnitude larger, we combine a supervised jet-to-Higgs pairing network based on the SPANet approach, topological data analysis of the event energy flow, and two dedicated classifiers, $D_{\rm HH}$ for the signal-to-background separation and $D_{\kappa_3}$ for the $\kappa_3$ shape information. The coupling is extracted from a two-dimensional likelihood fit to the distribution of the two classifier outputs. Combining the two regions, we obtain $0.80<\kappa_3<1.29$ at $3$ TeV and $0.96<\kappa_3<1.05$ at $10$ TeV at $68\%$ confidence level. The $10$ TeV determination reaches the few-percent level in this statistics-limited projection, which surpasses by a large amount the precision projected for the HL-LHC.

hep-ph↗

arXiv2026

Strong First-Order Electroweak Phase Transitions and Gravitational Waves in the Normal Two-Higgs-Doublet Model: A Comparative Study of the Four Yukawa Types and Thermal Resummation Schemes

We present a comprehensive global analysis of strong first-order electroweak phase transitions (SFOEWPTs) and their associated stochastic gravitational-wave (GW) backgrounds within the Normal Scenario of the $CP$-conserving Two-Higgs-Doublet Model (2HDM) with softly broken $Z_2$ symmetry, where the lighter $CP$-even scalar is identified as the observed $125~\text{GeV}$ Higgs boson. Across all four Yukawa structures (Type-I, II, X, and Y), we track the finite-temperature vacuum evolution, transition dynamics, and GW signatures. To quantify the theoretical uncertainty associated with thermal resummation, we perform a detailed comparison between the Parwani and Arnold--Espinosa prescriptions. While both schemes find that single-step paths overwhelmingly dominate successful transitions and consistently favor the Higgs alignment limit, the resulting SFOEWPT parameter space exhibits a pronounced scheme dependence. The Arnold-Espinosa prescription severely restricts the viable parameter space (with upper bounds on the heavy-scalar masses below approximately 800 GeV) and introduces an extreme parametric sensitivity that produces fragmented distributions and irregular voids in the heavy-scalar mass planes. In contrast, the more stable Parwani prescription allows heavy-scalar masses below $\sim 1.6~\text{TeV}$. We further identify highly restricted GW parameter regions capable of yielding a four-year LISA signal-to-noise ratio above 10, while demonstrating that the acoustic GW source is generically short-lived, leading to a substantial suppression of the predicted signal amplitude. Our results highlight the strong complementarity between future space-based GW observations and high-energy collider searches in probing the cosmological viability of the 2HDM.

hep-ph↗

arXiv2026

Intrinsic Properties of Large CP Violation in the Complex Two-Higgs-Doublet Model

We investigate the parameter space supporting large CP violation (CPV) in the complex two-Higgs-doublet model with softly broken $Z_{2}$ symmetry, where the 125~GeV Higgs boson is identified as the lightest neutral Higgs boson $H_1$. Through a comprehensive global scan of Type-I and Type-II models under theoretical, collider, and eEDM constraints, we identify distinct structures that facilitate large CPV. In Type-I, gauge-sector CPV is maximized when the 125~GeV Higgs boson is nearly degenerate with a second neutral scalar. For the ensemble of physically viable points, the predicted eEDM values typically exceed $10^{-31}\,e\cdot\mathrm{cm}$, placing the model largely within the sensitivity of next-generation experiments. Conversely, Type-II models strongly suppress gauge-sector CPV while allowing for nearly maximal CPV in the Yukawa sector. Destructive interference among various contributions allows for $|d_e|$ values as low as $O(10^{-35})\,e\cdot\mathrm{cm}$, resulting in no phenomenologically relevant lower bound. Finally, we uncover the phenomenon of ``hidden CPV'' in the near-alignment limit, characterized by CP-violating mixing between the heavy neutral Higgs bosons governed by the angle $α_3$. We demonstrate that this hidden CPV can be experimentally probed at future colliders via CP-violating Yukawa interactions of $H_2$ and $H_3$, as well as the robust $H_2$-$H_3$-$Z$ coupling.

hep-ph↗

arXiv2026

Can a pseudoscalar with a mass of 365 GeV in the 2HDM explain the CMS $t\bar{t}$ excess?

We analyze the CMS-reported t tbar excess within conventional Two-Higgs-Doublet Models of Types I, II, X, and Y, using the best-fit pseudoscalar parameters MA = 365 GeV, GammaA over MA = 2 percent, and tan beta = 1.28. Applying theoretical and experimental constraints, including stability, unitarity, perturbativity, flavor constraints, and collider bounds, we find that perturbativity limits the charged and heavy neutral Higgs masses to below about 723 GeV. Flavor constraints exclude Types II and Y, while the remaining parameter space in Types I and X is ruled out by recent t tbar Z measurements from ATLAS and CMS. We conclude that conventional Two-Higgs-Doublet Models cannot explain the observed t tbar excess, although toponium effects in the background modeling may modify this conclusion. This contribution is based on the proceedings of the 18th International Workshop on Top Quark Physics (TOP2025).

hep-ph↗

arXiv2025

An Artificial Intelligence Framework for Measuring Human Spine Aging Using MRI

The human spine is a complex structure composed of 33 vertebrae. It holds the body and is important for leading a healthy life. The spine is vulnerable to age-related degenerations that can be identified through magnetic resonance imaging (MRI). In this paper we propose a novel computer-vison-based deep learning method to estimate spine age using images from over 18,000 MRI series. Data are restricted to subjects with only age-related spine degeneration. Eligibility criteria are created by identifying common age-based clusters of degenerative spine conditions using uniform manifold approximation and projection (UMAP) and hierarchical density-based spatial clustering of applications with noise (HDBSCAN). Model selection is determined using a detailed ablation study on data size, loss, and the effect of different spine regions. We evaluate the clinical utility of our model by calculating the difference between actual spine age and model-predicted age, the spine age gap (SAG), and examining the association between these differences and spine degenerative conditions and lifestyle factors. We find that SAG is associated with conditions including disc bulges, disc osteophytes, spinal stenosis, and fractures, as well as lifestyle factors like smoking and physically demanding work, and thus may be a useful biomarker for measuring overall spine health.

cs.CV↗

arXiv2025

Multi-step Strong First-Order Electroweak Phase Transitions in the Inverted Type-I 2HDM: Parameter Space, Gravitational Waves, and Collider Phenomenology

We investigate the electroweak phase transition (EWPT) within the inverted Type-I two-Higgs-doublet model, where the observed $125\,\text{GeV}$ Higgs boson is identified as the heavier \textit{CP}-even scalar $H$. Through a comprehensive parameter-space scan consistent with current theoretical and experimental constraints, we identify regions supporting strong first-order EWPTs (SFOEWPTs), including multi-step transitions. We find that two-step SFOEWPTs occur as frequently as one-step transitions, while three-step transitions can occur, albeit rarely. Crucially, the parameter spaces inducing one-step and two-step transitions are partially yet significantly separated: one-step transitions restrict the charged Higgs mass and $\tanβ$ to $m_{H^\pm}\in[295,441]\,\text{GeV}$ and $\tanβ\in[4.2,8.8]$, whereas two-step transitions allow $m_{H^\pm}\in[100,350]\,\text{GeV}$ and $\tanβ\in[2.5,45.4]$. Notably, negative values of $\sin(β-α)$ arise almost exclusively in one-step scenarios. We present the calculation of gravitational wave (GW) signal-to-noise ratios (SNRs) at LISA for multi-step EWPTs, finding that detectable GW signals ($\text{SNR}>10$) predominantly emerge from two-step transitions. Furthermore, we demonstrate that the correlation between the vacuum uplifting measure $ΔF_0$ and $ξ_c$ persists in one-step transitions and breaks down in multi-step cases. Finally, we perform a dedicated collider analysis for representative SFOEWPT parameter points at the $1.5\,\text{TeV}$ CLIC, identifying $e^+ e^- \to H^+ H^- \to W^+ W^- hh$ as a promising discovery channel. Enhanced $h\toγγ$ branching ratios for negative $\sin(β-α)$ motivate two complementary golden final states, $W^+ W^- b\bar{b} τ^+ τ^-$ and $W^+ W^- b\bar{b}γγ$, which demonstrate high discovery potential due to negligible Standard Model backgrounds.

hep-ph↗

arXiv2025

Discovery Prospects for the Light Charged Higgs Boson Decay to an Off-Shell Top Quark and a Bottom Quark at Future High-Energy Colliders

The charged Higgs boson ($H^\pm$) with a mass below the top quark mass remains a viable possibility within the Type-I two-Higgs-doublet model under current constraints. While previous LHC searches have primarily focused on the $H^\pm\toτ^\pmν$ decay mode, the decay channel into an off-shell top quark and a bottom quark, $H^\pm \rightarrow t^*b$, is leading or subleading for $H^\pm$ masses between 130 and 170 GeV. This study investigates the discovery potential of future colliders for this off-shell decay mode through pair-produced charged Higgs bosons decaying via $H^+H^-\rightarrow t^*bτν\rightarrow bbjjτν$. We perform signal-to-background analyses at the HL-LHC and a prospective 100 TeV proton-proton collider, employing cut-flow strategies and the Boosted Decision Tree method. However, due to the softness of the $b$ jets, signal significances fall below detection thresholds at these facilities. Extending our study to a multi-TeV muon collider (MuC), we demonstrate that a 3 TeV MuC achieves high signal significance, surpassing the $5σ$ threshold with an integrated luminosity of 1 ab$^{-1}$ and a 10\% background uncertainty. Specifically, for $M_{H^\pm} = 130$, 150, and 170 GeV, the significances are 13.7, 13.5, and 6.06, respectively. In contrast, a 10 TeV MuC requires 10 ab$^{-1}$ to achieve similar results. Our findings highlight the critical role of the MuC in probing the new signal channel $H^\pm\rightarrow t^*b$, offering a promising avenue for future charged Higgs boson searches involving off-shell top quarks.

hep-ph↗

arXiv2025

Emerging Photon Jets in the Hadronic Calorimeter: A Novel Signature of Neutral Long-Lived Particles at the LHC

We propose a novel collider signature for neutral long-lived particles (LLPs): the emerging photon jet in the hadronic calorimeter (HCAL). This signature arises when a neutral LLP decays into photons within the HCAL, producing an electromagnetic shower without associated charged tracks or energy deposits in the electromagnetic calorimeter (ECAL). To demonstrate the viability of this approach, we consider the fermiophobic Higgs boson $h_{\rm f}$ in the Type-I two-Higgs-doublet model as a representative scenario. In the ultralight regime ($m_{h_{\rm f}} < 1$ GeV), $h_{\rm f}$ decays exclusively into a photon pair via loop-induced processes, resulting in a suppressed width and consequently a long lifetime. Focusing on the golden channel $pp \to H^\pm h_{\rm f} \to W^\pm h_{\rm f} h_{\rm f}$, we analyze the exotic final state in which one $h_{\rm f}$ decays in the ECAL and appears as a highly collimated photon jet (reconstructed as a single photon), while the other decays within the HCAL, producing an emerging photon jet. Through a detailed signal-to-background analysis incorporating realistic detector effects via fast simulation, we demonstrate that this signature achieves discovery-level sensitivity at the HL-LHC across a broad region of parameter space consistent with theoretical and experimental constraints. While our study focuses on the fermiophobic Higgs, the emerging photon jet in the HCAL constitutes a broadly applicable and previously unexplored strategy for detecting neutral LLPs decaying into photons, opening a new avenue in LLP searches at colliders.

hep-ph↗

arXiv2025

Probing a Heavy Dark $Z$ Boson at Multi-TeV Muon Colliders: Leveraging the Optimized Recoil Mass Technique

We investigate the discovery potential of multi-TeV muon colliders for a heavy dark $Z$ boson ($Z_{\rm D}$) with a mass above 1 TeV through the associated production channel $μ^+μ^- \to Z_{\rm D}γ$. This process enables precise $M_{Z_{\rm D}}$ reconstruction using the photon recoil mass ($m_{\rm recoil}$). Focusing on the $Z_{\rm D} \to jjX$ and $Z_{\rm D} \to e^+e^-$ decay modes, we present strategies for achieving high sensitivity to the kinetic mixing parameter $\varepsilon$ at 3, 6, and 10 TeV muon colliders with integrated luminosities of 1, 4, and 10 ab$^{-1}$ respectively, assuming $Z_{\rm D}$ decays exclusively into Standard Model particles. A key innovation is our optimized implementation of $M_{Z_{\rm D}}$-dependent cuts on $m_{\rm recoil}$, which accounts for the energy-dependent detector response. For heavier $Z_{\rm D}$, the associated photon becomes less energetic, leading to better photon energy resolution and thus enabling more stringent $m_{\rm recoil}$ cuts. This approach enhances $\varepsilon$ sensitivity for heavier $Z_{\rm D}$. Conversely, for lighter $Z_{\rm D}$, the lower-energy electron pair from $Z_{\rm D} \to e^+e^-$ enables tighter cuts on the invariant mass of the electron pair ($m_{ee}$), providing better sensitivity in the lighter mass regime. Combining these complementary $m_{\rm recoil}$- and $m_{ee}$-based selections with both $jjX$ and $e^+e^-$ channels, we achieve $\varepsilon$ sensitivity down to $O\left(10^{-3}\right)$ as $M_{Z_{\rm D}}$ approaches $\sqrt{s}$, substantially surpassing the reach of a 100 TeV proton-proton collider. Even if $Z_{\rm D}$ decays into dark-sector particles, the recoil mass method remains effective, establishing muon colliders as powerful facilities for exploring heavy dark sectors.

hep-ph↗

arXiv2024

Can a pseudoscalar with a mass of 365 GeV in two-Higgs-doublet models explain the CMS $t\bar{t}$ excess?

We investigate the recently reported $t\bar{t}$ excess by the CMS Collaboration within the framework of conventional Two-Higgs-Doublet Models (2HDMs). Considering all four types (I, II, X, and Y), we perform a comprehensive parameter space scan using the best-fit values for a pseudoscalar boson $A$: $M_A = 365$ GeV, $Γ_A/M_A = 2\%$, and $\tanβ= 1.28$. Theoretical requirements and experimental constraints are systematically applied, including conditions from a bounded-below scalar potential, vacuum stability, unitarity, perturbativity, Flavor-Changing Neutral Currents (FCNCs), and direct searches at high-energy colliders. Our analysis shows that perturbativity imposes upper bounds of around 723 GeV on $M_{H^\pm}$ and $M_H$. FCNC constraints exclude all viable parameter space in Types II and Y, while a small region persists in Types I and X, but this region is ultimately ruled out by recent $t\bar{t} Z$ measurements by the ATLAS and CMS Collaborations at the LHC. We conclude that conventional 2HDMs alone cannot accommodate a pseudoscalar boson that explains the observed $t\bar{t}$ excess within viable parameter space. However, incorporating toponium effects in the background fit could potentially alter this conclusion.

hep-ph↗

arXiv2024

A Panoramic Study of $K$-Factors for 111 Processes at the 14 TeV LHC

In this comprehensive study, we investigate $K$-factors ($K=σ_{\text{NLO}}/σ_{\text{LO}}\equiv 1+δK$) for a broad array of Standard Model processes at the 14 TeV LHC, which are pivotal for background assessments in Beyond the Standard Model (BSM) searches. Using MadGraph5_aMC@NLO, we calculate the leading-order and next-to-leading order (NLO) cross-sections and compute the corresponding $K$-factors for 111 processes. Our analysis reveals $K$-factors ranging from 1.005 for $pp \to jjj$ to 4.221 for $pp\to W^\pm γγγ$. Key findings include: (i) processes involving photons display significantly high $K$-factors, attributed to gluon-initiated processes at NLO; (ii) processes with multiple particle productions, particularly those involving vector bosons, exhibit elevated $K$-factors due to multiple real emission processes; (iii) there exists an inverse correlation between the number of jets and $δK$, indicating that the addition of jets generally leads to a decrease in $δK$. Additionally, our investigation into differential $K$-factors relative to transverse momentum and invariant mass shows notable increases with higher $p_T$, but minimal changes with invariant mass. This study highlights the indispensable role of precise $K$-factor evaluations for accurate interpretations of BSM search outcomes.

hep-ph↗

arXiv2023

Probing Light Fermiophobic Higgs Boson via diphoton jets at the HL-LHC

In this study, we explore the phenomenological signatures associated with a light fermiophobic Higgs boson, $h_{\rm f}$, within the type-I two-Higgs-doublet model at the HL-LHC. Our meticulous parameter scan illuminates an intriguing mass range for $m_{h_{\rm f}}$, spanning $[1,10]{\;{\rm GeV}}$. This mass range owes its viability to substantial parameter points, largely due to the inherent challenges of detecting the soft decay products of $h_{\rm f}$ at contemporary high-energy colliders. Given that this light $h_{\rm f}$ ensures $Br(h_{\rm f}\toγγ)\simeq 1$, $Br(H^\pm \to h_{\rm f} W^\pm)\simeq 1$, and $M_{H^\pm}\lesssim 330{\;{\rm GeV}}$, we propose a golden discovery channel: $pp\to h_{\rm f}H^\pm\to γγγγ\,l^\pmν$, where $l^\pm$ includes $e^\pm$ and $μ^\pm$. However, a significant obstacle arises as the two photons from the $h_{\rm f}$ decay mostly merge into a single jet due to their proximity within $ΔR<0.4$. This results in a final state characterized by two jets, rather than four isolated photons, thus intensifying the QCD backgrounds. To tackle this, we devise a strategy within \textsc{Delphes} to identify jets with two leading subparticles as photons, termed diphoton jets. Our thorough detector-level simulations across 18 benchmark points predominantly show signal significances exceeding the $5σ$ threshold at an integrated luminosity of $3{\;{\rm ab}^{-1}}$. Furthermore, our approach facilitates accurate mass reconstructions for both $m_{h_{\rm f}}$ and $M_{H^\pm}$. Notably, in the intricate scenarios with heavy charged Higgs bosons, our application of machine learning techniques provides a significant boost in significance.

hep-ph↗

arXiv2023

Exploring lepton flavor violation phenomena of the $Z$ and Higgs bosons at electron-proton colliders

We comprehensively study the potential for discovering lepton flavor violation (LFV) phenomena associated with the $Z$ and Higgs bosons at the LHeC and FCC-he. Our meticulous investigation reveals the remarkable suitability of electron-proton colliders for probing these rare new physics signals. This is due to the distinct advantages they offer, including negligible pileups, minimal QCD backgrounds, electron-beam polarization $P_e$, and the capability of distinguishing the charged-current from neutral-current processes. In our pursuit of LFV of the $Z$ boson, we employ an innovative indirect probe, utilizing the $t$-channel mediation of the $Z$ boson in the process $p e^- \to j τ^-$. For LFV in the Higgs sector, we scrutinize direct observations of the on-shell decays of $H\to e^+τ^-$ and $H\to μ^\pmτ^\mp$ through the charged-current production of $H$. Focusing on $H\to e^+τ^-$ proves highly efficient due to the absence of positron-related backgrounds in the charged-current modes at electron-proton colliders. Through a dedicated signal-to-background analysis with the boosted decision tree algorithm, we demonstrate that the LHeC with the total integrated luminosity of $1{\,{\rm ab}^{-1}}$ can put significantly lower $2σ$ bounds than the HL-LHC with $3{\,{\rm ab}^{-1}}$. Specifically, we find ${\rm{Br}}(Z\to eτ)< 2.2 \times 10^{-7}$, ${\rm{Br}}(H\to eτ) <1.7 \times 10^{-4} $, and ${\rm{Br}}(H\to μτ) < 1.0 \times 10^{-4}$. Furthermore, our study uncovers the exceptional precision of the FCC-he in measuring the LFV signatures of the $Z$ and Higgs bosons, which indicates the potential for future discoveries in this captivating field.

hep-ph↗

arXiv2023

Community-Aware Transformer for Autism Prediction in fMRI Connectome

Autism spectrum disorder(ASD) is a lifelong neurodevelopmental condition that affects social communication and behavior. Investigating functional magnetic resonance imaging (fMRI)-based brain functional connectome can aid in the understanding and diagnosis of ASD, leading to more effective treatments. The brain is modeled as a network of brain Regions of Interest (ROIs), and ROIs form communities and knowledge of these communities is crucial for ASD diagnosis. On the one hand, Transformer-based models have proven to be highly effective across several tasks, including fMRI connectome analysis to learn useful representations of ROIs. On the other hand, existing transformer-based models treat all ROIs equally and overlook the impact of community-specific associations when learning node embeddings. To fill this gap, we propose a novel method, Com-BrainTF, a hierarchical local-global transformer architecture that learns intra and inter-community aware node embeddings for ASD prediction task. Furthermore, we avoid over-parameterization by sharing the local transformer parameters for different communities but optimize unique learnable prompt tokens for each community. Our model outperforms state-of-the-art (SOTA) architecture on ABIDE dataset and has high interpretability, evident from the attention module. Our code is available at https://github.com/ubc-tea/Com-BrainTF.

q-bio.NC↗

arXiv2023

$τ^\pm νγγ$ and $\ell^\pm \ell^\pm γγ{\rlap{\,/}{E}_T} X$ to probe the fermiophobic Higgs boson with high cutoff scales

The light fermiophobic Higgs boson $h_{\rm f}$ in the type-I two-Higgs-doublet model can evade the current search programs at the LHC since its production through the quark-antiquark annihilation and gluon fusion is not feasible. The particle can be more elusive if the model retains stability up to the Planck scale because the efficient discovery channels are missing from the existing search chart. Through the comprehensive scanning, we show that all the viable parameter points with the Planck cutoff scale require $ m_{h_{\rm f}} \in[80,\, 120]{\;{\rm GeV}}$ and $M_{A/H^\pm} \in [90,\,150]{\;{\rm GeV}}$. Since $h_{\rm f}h_{\rm f}\to γγW^+ W^-$ and $H^\pm \to τ^\pm ν/h_{\rm f}W^\pm$ are dominant in this case, two final states are more efficient to probe $h_{\rm f}$ than the conventional search mode of $4γ+W^\pm/Z$. One is $τ^\pmνγγ$ from $pp \to H^\pm(\toτ^\pmν) h_{\rm f}(\to γγ)$ and the other is $\ell^\pm \ell^\pm γγ{\rlap{\,/}{E}_T} X$ ($\ell^\pm=e^\pm,μ^\pm$) from $pp \to H^\pm(\to h_{\rm f}W^\pm) h_{\rm f} \to γγW^+ W^-W^\pm $, $pp \to H^\pm(\to h_{\rm f} W^\pm) A(\to h_{\rm f} Z) \to γγW^+ W^- W^\pm Z $, and $pp \to H^+(\to h_{\rm f} W^+)H^-(\to h_{\rm f} W^-)\to γγW^+ W^- W^+ W^-$. The inclusive $\ell^\pm \ell^\pm γγ{\rlap{\,/}{E}_T} X$ consists of a same-sign dilepton, two prompt photons, and missing transverse energy. We perform the signal-background analysis at the detector level. With the total integrated luminosity of $300\;{\rm fb}^{-1}$ and the 5\% background uncertainty, two proposed channels at the 14 TeV LHC yield signal significances above five in the entire viable parameter space of the fermiophobic type-I with a high cutoff scale.

hep-ph↗

arXiv2023

Predicting Development of Chronic Obstructive Pulmonary Disease and its Risk Factor Analysis

Chronic Obstructive Pulmonary Disease (COPD) is an irreversible airway obstruction with a high societal burden. Although smoking is known to be the biggest risk factor, additional components need to be considered. In this study, we aim to identify COPD risk factors by applying machine learning models that integrate sociodemographic, clinical, and genetic data to predict COPD development.

q-bio.QM↗

arXiv2023

Disentangling the high and low cutoff scales via the trilinear Higgs couplings in the type-I two-Higgs-doublet model

The type-I two-Higgs-doublet model in the inverted Higgs scenario can retain the theoretical stability all the way up to the Planck scale. The Planck-cutoff scale, $Λ_{\rm cut}^{\rm Planck}$, directly impacts the mass spectra such that all the extra Higgs boson masses should be light below about 160 GeV. However, the observation of the light masses of new Higgs bosons does not indicate the high cutoff scale because a low cutoff scale can also accommodate the light masses. Over the viable parameter points that satisfy the theoretical requirements and the experimental constraints, we show that the trilinear Higgs couplings for low $Λ_{\rm cut}$ are entirely different from those for the Planck-cutoff scale. The most sensitive coupling to the cutoff scale is from the $h$-$h$-$h$ vertex, where $h$ is the lighter CP-even Higgs boson at a mass below 125 GeV. Among the multi-Higgs productions mediated by Higgs bosons, the gluon fusion processes of $gg \to h h $ and $gg \to AA$ are insensitive to the cutoff scale, yielding a small variation of $\mathcal{O}(1)\,{\rm fb}$ according to $Λ_{\rm cut}$. The smoking-gun signature is from the triple Higgs production of $q\bar{q}' \to W^* \to H^\pm hh$, which solely depends on the $h$-$h$-$h$ vertex. The cross section for $Λ_{\rm cut}=1\,{\rm TeV}$ is about $10^3$ times larger than that for the Planck-cutoff scale. Since the decay modes of $H^\pm \to W^* h/W^* A$ and $h/A \to bb$ are dominant, the process yields the $6b+\ellν$ final state, which enjoys an almost background-free environment. Consequently, the precision measurement of $pp \to H^\pm hh$ can probe the cutoff scale of the model.

hep-ph↗

arXiv2022

Status of the two-Higgs-doublet model in light of the CDF $m_W$ measurement

The most recent $W$-boson mass measurement by the CDF collaboration with a substantially reduced uncertainty indicates a significant deviation from the standard model prediction, as large as $7σ$ if taken literally. Then the Peskin-Takeuchi parameters of $S$ and $T$ shift to larger values, which has profound consequences in searching for physics beyond the SM. In the framework of two-Higgs-doublet models, we study the effect of the new $W$-boson mass measurement on the parameter space. Combined with other constraints including theoretical requirements, flavor-changing neutral currents in $B$ physics, the cutoff scale above 1 TeV, Higgs precision data, and direct collider search limits from the LEP, Tevatron, and LHC experiments, we find upper bounds on the masses of the heavy Higgs bosons: $M_{H, A, H^\pm} \lesssim 1.1$ TeV in type I, II, X, and Y for the normal Higgs scenario; $M_{H^\pm} \lesssim 450 $ GeV and $M_{A} \lesssim 420 $ GeV in type I and X for the inverted scenario where the heavier $CP$-even Higgs boson is the observed one. Another important finding is that type II and type Y in the inverted scenario are completely excluded. Such unprecedented findings imply that the upcoming LHC run can readily close out a large portion of the still-available parameter space.

hep-ph↗