Search

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, $\Gamma_A/M_A = 2\%$, and $\tan\beta = 1.28$. 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., Comment: 16 pages with 4 figures

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 $H^\pm\to\tau\nu$ 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 $H^+H^-\rightarrow t^*b\tau\nu\rightarrow bbjj\tau\nu$. 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 $5\sigma$ threshold with an integrated luminosity of 1 ab$^{-1}$, assuming 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., Comment: 31 pages with 8 figures and 4 tables

In this comprehensive study, we investigate $K$-factors ($K=\sigma_{\text{NLO}}/\sigma_{\text{LO}}\equiv 1+\delta K$) 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 $pp\to W^\pm \gamma\gamma\gamma$. 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 $\delta K$, indicating that the addition of jets generally leads to a decrease in $\delta K$. 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., Comment: References are added

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 $Br(h_{\rm f}\to\gamma\gamma)\simeq 1$, $Br(H^\pm \to h_{\rm f} W^\pm)\simeq 1$, and $M_{H^\pm}\lesssim 330{\;{\rm GeV}}$, we propose a golden discovery channel: $pp\to h_{\rm f}H^\pm\to \gamma\gamma\gamma\gamma \,l^\pm\nu$, where $l^\pm$ includes $e^\pm$ and $\mu^\pm$. 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 $\Delta R<0.4$. 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 $5\sigma$ 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., Comment: 36 pages with 12 figures

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., Comment: Accepted by 26th International Conference on Medical Image Computing and Computer Assisted Intervention (MICCAI 2023)

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 $p e^- \to j \tau^-$. For LFV in the Higgs sector, we scrutinize direct observations of the on-shell decays of $H\to e^+\tau^-$ and $H\to \mu^\pm\tau^\mp$ through the charged-current production of $H$. Focusing on $H\to e^+\tau^-$ 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 $2\sigma$ bounds than the HL-LHC with $3{\,{\rm ab}^{-1}}$. Specifically, we find ${\rm{Br}}(Z\to e\tau)< 2.2 \times 10^{-7}$, ${\rm{Br}}(H\to e\tau) <1.7 \times 10^{-4} $, and ${\rm{Br}}(H\to \mu\tau) < 1.0 \times 10^{-4}$. 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., Comment: Extensive updates including the BDT analysis for the LFV Z, the distinction between the LFV Z and LHV Z', and the signal significance when the number of backgrounds approach 0

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 $h_{\rm f}h_{\rm f}\to \gamma\gamma W^+ W^-$ and $H^\pm \to \tau^\pm \nu/h_{\rm f}W^\pm$ are dominant in this case, two final states are more efficient to probe $h_{\rm f}$ than the conventional search mode of $4\gamma+W^\pm/Z$. One is $\tau^\pm\nu \gamma\gamma$ from $pp \to H^\pm(\to\tau^\pm\nu) h_{\rm f}(\to \gamma\gamma)$ and the other is $\ell^\pm \ell^\pm \gamma\gamma {\rlap{\,/}{E}_T} X$ ($\ell^\pm=e^\pm,\mu^\pm$) from $pp \to H^\pm(\to h_{\rm f}W^\pm) h_{\rm f} \to \gamma\gamma W^+ W^-W^\pm $, $pp \to H^\pm(\to h_{\rm f} W^\pm) A(\to h_{\rm f} Z) \to \gamma\gamma W^+ W^- W^\pm Z $, and $pp \to H^+(\to h_{\rm f} W^+)H^-(\to h_{\rm f} W^-)\to \gamma\gamma W^+ W^- W^+ W^-$. The inclusive $\ell^\pm \ell^\pm \gamma\gamma {\rlap{\,/}{E}_T} X$ 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., Comment: Final version to appear in JHEP

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., Comment: submitted to EMBC 2023

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, $\Lambda_{\rm cut}^{\rm Planck}$, 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 $\Lambda_{\rm cut}$ 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 $\Lambda_{\rm cut}$. 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 $\Lambda_{\rm cut}=1\,{\rm TeV}$ 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 $6b+\ell\nu$ 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., Comment: Final version to appear in PRD

The null results in the new physics searches at the LHC do not exclude an intermediate-mass new particle if it is fermiophobic. Type-I in the two-Higgs-doublet model accommodates a fermiophobic light Higgs boson $h_{\rm f}$ if $\alpha=\pi/2$. The heavier $CP$-even Higgs boson explains the observed Higgs boson at a mass of 125 GeV. We first obtain the still-valid parameter space satisfying the theoretical requirements, flavor-changing neutral currents in $B$ physics, the cutoff scale above 1 TeV, Higgs precision data, and the direct collider search bounds at high energy colliders. We also study the high energy scale behavior via the analysis of the renormalization group equations. An important result is that the fermiophobic type-I can maintain the stability of the scalar potential all the way up to the Planck scale if $m_{h_{\rm f}}$ is larger than half the observed Higgs boson mass. Since the parameter space is severely curtailed, especially for the high cutoff scale, the signal rates in the multi-photon states of new Higgs bosons at the LHC are well predicted. We suggest the processes of $4\gamma+VV'$ ($V^{(\prime)}=Z, W^\pm$) as the golden discovery channels for the model since they enjoy an almost background-free environment and substantial selection efficiencies for four photons., Comment: 20 pages with 4 figures

The recent measurement of the $W$ boson mass by the CDF collaboration adds an anomaly to the long-standing discrepancy in the muon anomalous magnetic moment, $\Delta a_\mu$. Although type-X in the two-Higgs-doublet model provides an attractive solution to $\Delta a_\mu$ through a light pseudoscalar $A$, the model confronts the exotic Higgs decays of $h\to AA$ and the lepton flavor universality data in the $\tau$ and $Z$ decays. To save the model, we propose that the light pseudoscalar be Higgs-phobic. Through the random scanning over the entire parameter space, we perform a comparative study of the Higgs-phobic type-X with and without the CDF $m_W$ measurement, called the CDF and PDG cases respectively. Both cases can explain the two anomalies as well as all the other constraints but have significant differences in the finally allowed parameter space. For example, a small region with almost degenerate masses of new Higgs bosons around 100 GeV is allowed only in the PDG case. The cutoff scale of the model is also studied via the analysis of renormalization group equations, which reaches up to $10^5~{\rm GeV}$ ($10^7~{\rm GeV}$) in the CDF (PDG) case. Since the dominant decay modes are $A\to \tau\tau$, $H \to Z A$, and $H^\pm\to W^\pm A$ in most of the viable parameter space, we propose the $4\tau+VV'$ states as the golden discovery channel at the LHC., Comment: Final version to appear in PRD

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 $7\sigma$ 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., Comment: Discussions on the "survival probability" are corrected