arXiv subjects

Ting-Kuo Chen

Publications and source records attributed to Ting-Kuo Chen.

15 recordsLinked to original sources

arXiv2026

Baryoid Dark Matter from $\mathbb{Z}_N$ Domain Walls: The $(N-1):1$ origin of the dark matter-baryon coincidence

We propose an explanation for the dark matter-baryon coincidence based on collapsing $\mathbb{Z}_N$ domain walls, which form a novel compact baryonic state: the baryoid. A baryoid has an asteroid-scale mass and up-to-nuclear-scale energy density, and can serve as a dark matter candidate. Starting from equal baryon numbers in the domains formed in the early universe, the collapse of the domain walls after the QCD phase transition leads to a baryon-number ratio of $(N-1):1$ between the false- and true-vacuum domains. Since baryons are slightly lighter in the false-vacuum domains than in the true-vacuum domain, the resulting dark matter-to-baryon energy-density ratio is naturally close to, but slightly smaller than, $(N-1):1$, or $6:1$ for $N=7$. We calculate the domain-wall dynamics and the efficiency of baryon-number trapping, derive the resulting baryoid properties, and discuss a broad set of phenomenological probes.

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arXiv2025

Interpretation of LHC excesses at 95 GeV and 152 GeV in an extended Georgi-Machacek model

We analyze the excesses at 95 GeV in the light Higgs-boson searches in the di-photon decay channel reported by CMS and ATLAS, which combined are at the level of three standard deviations and are compatible with the excess in the $b\bar{b}$ final state observed at LEP, together with an excess in the di-photon channel at around 152 GeV reported based on a sideband analysis. We demonstrate that these excesses can be well described in a minimally extended Georgi-Machacek (meGM) model. This is enabled by four key features of the meGM model: (1) a natural prediction for scalar boson masses of $\lesssim$200 GeV arising from the condition to describe both the Higgs boson signal at 125 GeV and the excesses at 95 GeV, (2) the prediction for a doubly charged Higgs boson that can potentially enhance the di-photon decay rates, (3) asymmetric $WW$ and $ZZ$ couplings to neutral scalar bosons that are induced by mild custodial symmetry breaking, and (4) the approximate preservation of the electroweak $\rho$ parameter to be 1 at tree level. We show in our numerical analysis that the meGM model naturally improves the fit to the LHC data around 152 GeV when describing the excesses at 95 GeV. At the same time, the model also predicts additional light CP-odd and charged scalar bosons that can be potentially probed in future experiments, which motivates dedicated searches in the upcoming LHC runs. We also present the results of sensitivity studies for the 95 and 125 GeV Higgs-boson couplings at the HL-LHC and future $e^+e^-$ colliders, which demonstrate very interesting prospects for probing the meGM model at future colliders.

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arXiv2025

Toponia at the HL-LHC and FCC-ee

The hint of a pseudoscalar toponium state at the Large Hadron Collider (LHC) opens a new avenue for studying a novel class of QCD (quasi-)bound states with comparable formation and decay times. Compared with charmonium and bottomonium, toponium is a quasi-bound state, resembling a hydrogen atom of the strong interaction, although it appears as a broader resonance. We compute the masses and annihilation decay widths of the lowest $S$-wave ($\eta_t$, $\psi_t$) and $P$-wave ($\chi_{t0}$, $\chi_{t1}$) toponium states, and assess their discovery prospects at the High-Luminosity LHC (HL-LHC) and future lepton colliders, such as the $e^+e^-$ stage of the Future Circular Collider (FCC-ee). Detecting the vector $\psi_t$ state at the HL-LHC is hindered by the Landau-Yang theorem and the gluon-dominated production environment of the collider, whereas lepton colliders offer promising sensitivity through both constituent and two-body decays. A more precise measurement of the $\eta_t$ mass, approximately equal to that of $\psi_t$, at the LHC could help determine the optimal $t\bar{t}$ threshold center-of-mass energy for FCC-ee. The $P$-wave states remain challenging to observe at both the HL-LHC and future lepton colliders. We also discuss how toponium measurements can be used to probe top-quark properties and to conduct indirect searches for new physics, including light scalars that couple to the top quark.

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arXiv2025

Wess-Zumino-Witten Interactions of Axions: Three-Flavor

We present a complete Lagrangian describing axion interactions with pseudoscalar and (axial-)vector mesons within the three light-flavor quark framework. This formulation incorporates both the standard chiral Lagrangian and the full Wess-Zumino-Witten (WZW) term. By including instanton effects associated with the anomalous $U(1)_A$ symmetry, we demonstrate that physical observables remain invariant under arbitrary chiral phase rotations of the quark fields. This comprehensive Lagrangian provides a robust and consistent framework for exploring axion phenomenology through its interactions with mesons and gauge bosons. As a demonstration, we compute the decay widths of GeV-scale axions into various mesonic final states for several benchmark axion models.

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arXiv2025

Flow-based Nonperturbative Simulation of First-order Phase Transitions

We present a flow-based method for simulating and calculating nucleation rates of first-order phase transitions in scalar field theory on a lattice. Motivated by recent advancements in machine learning tools, particularly normalizing flows for lattice field theory, we propose the ``partitioning flow-based Markov chain Monte Carlo (PFMCMC) sampling" method to address two challenges encountered in normalizing flow applications for lattice field theory: the ``mode-collapse" and ``rare-event sampling" problems. Using a (2+1)-dimensional real scalar model as an example, we demonstrate the effectiveness of our PFMCMC method in modeling highly hierarchical order parameter probability distributions and simulating critical bubble configurations. These simulations are then used to facilitate the calculation of nucleation rates. We anticipate the application of this method to (3+1)-dimensional theories for studying realistic cosmological phase transitions.

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arXiv2025

QCD-Collapsed Domain Walls: QCD Phase Transition and Gravitational Wave Spectroscopy

For a discrete symmetry that is anomalous under QCD, the domain walls produced in the early universe from its spontaneous breaking can naturally annihilate due to QCD instanton effects. The gravitational waves generated from wall annihilation have their amplitude and frequency determined by both the discrete symmetry breaking scale and the QCD scale. The evidence of stochastic gravitational waves at nanohertz observed by pulsar timing array experiments suggests that the discrete-symmetry-breaking scale is around 100 TeV, assuming the domain-wall explanation. The annihilation temperature is about 100 MeV, which could naturally be below the QCD phase transition temperature. We point out that the QCD phase transition within some domains with an effective large QCD $θ$ angle could be a first-order one. To derive the phase diagram in $θ$ and temperature, we adopt a phenomenological linear sigma model with three quark flavors. The domain-wall explanation for the NANOGrav, EPTA, PPTA and CPTA results hints at a first-order QCD phase transition, which predicts additional gravitational waves at higher frequencies. If the initial formation of domain walls is also a first-order process, this class of domain-wall models predicts an interesting gravitational wave spectroscopy with frequencies spanning more than ten orders of magnitude, from nanohertz to 100 Hz.

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arXiv2025

QCD Vacuum Energy and Its Implication for Quark Nugget Stability

In this work, we employ both theoretical and data-driven methods to derive the QCD vacuum energy, utilizing the GMOR relation, the low-energy theorem, and the equation of state from Lattice QCD. The QCD vacuum energy is determined to be between around $(163\,\mbox{MeV})^4$ and $(190\,\mbox{MeV})^4$. With the assumptions of complete deconfinement, vanishing gluon condensate, full chiral-symmetry restoration, and the validity of perturbative QCD at baryon chemical potentials of order of the proton mass, a very specific kind of quark nugget is found to be less stable than ordinary nuclei.

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arXiv2024

Approaching Stable Quark Matter

The determination of whether the ground state of baryon matter in Quantum Chromodynamics (QCD) is the ordinary nucleus or a quark matter state remains a long-standing question in physics. A critical parameter in this investigation is the bag parameter $B$, which quantifies the QCD vacuum energy and can be computed using nonperturbative methods such as Lattice QCD (LQCD). By combining the equation of state derived from perturbative QCD (pQCD) with the bag parameter to fit the LQCD-simulated data for isospin-dense matter, we address the stability of quark matter within the LQCD+pQCD framework. Our findings suggest that the current data imposes an upper bound on $B^{1/4} \lesssim 160$ MeV, approaching a conclusive statement on quark matter stability. Given the lower bound on $B$ from the quark condensate contribution to the vacuum energy, the stable 2-flavor quark matter remains possible, whereas the stable 2+1-flavor quark matter is excluded, assuming complete deconfinement and chiral-symmetry restoration and the reliability of pQCD at baryon chemical potentials around the proton mass. Additionally, we derive more general thermodynamic bounds on the quark matter energy-per-baryon and $B$, which, while weaker, provide complementary insights.

hep-ph↗

arXiv2024

Wess-Zumino-Witten Interactions of Axions

We present a consistent derivation of the complete Wess-Zumino-Witten interactions of axions, including the counter-term necessary to guarantee the gauge invariance of the Standard Model. By treating the derivative of the axion field as a background gauge field and incorporating auxiliary chiral rotation phases, we ensure consistency in the axion-interaction Lagrangian. This approach allows us to derive basis-independent physical interactions of axions with gauge bosons and vector mesons. As an example, we explore the interaction of $a$-$\omega$-$\gamma$ to illustrate the potential for searching for axion-like particles at colliders.

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arXiv2024

A 95 GeV Higgs Boson in the Georgi-Machacek Model

CMS and ATLAS have reported small excesses in the search for low-mass Higgs bosons in the di-photon decay channel at exactly the same mass, $95.4~$GeV. These searches rely on improved analysis techniques, enhancing in particular the discrimination against the $Z \to e^+e^-$ background. In models beyond the Standard Model (SM) that extend the Higgs sector with triplets, doubly-charged Higgs bosons are predicted which can contribute substantially to the di-photon decay rate of a light Higgs boson. The Georgi-Machacek (GM) Model is of particular interest in this context, since despite containing Higgs triplets it preserves the electroweak $ρ$-parameter to be$~$1 at the tree level. We show that within the GM model, a Higgs boson with a mass of $\sim 95~$GeV with a di-photon decay rate as observed by CMS and ATLAS can be well described. We discuss the di-photon excess in conjunction with an excess in the $b \bar b$ final state observed at LEP and an excess observed by CMS in the di-tau final state, which have been found at comparable masses with local significances of about $2σ$ and $3σ$, respectively. The presence of a Higgs boson at about $95~$GeV within the GM model would imply good prospects of the searches for additional light Higgs bosons. In particular, the observed excess in the di-photon channel would be expected to be correlated in the GM model with a light doubly-charged Higgs boson in the mass range between $100~$GeV and $200~$GeV, which motivates dedicated searches in upcoming LHC Runs.

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arXiv2023

CP Violation in a Model with Higgs Triplets

We discuss CP-violation in a model with a real and a complex isospin triplet Higgs fields without introducing any symmetries except for the electroweak gauge symmetry. This corresponds to the minimal extension of the Higgs sector with the following properties: (i) providing new source of CP violation, (ii) absence of quark flavor changing neutral currents at tree level, and (iii) enabling the electroweak rho parameter to be unity at tree level in the scenario without imposing any new symmetries. Our model can be regarded as the generalized version of the Georgi-Machacek model, in which the global $SU(2)_L\times SU(2)_R$ symmetry is explicitly broken due to CP-violating terms in the potential. We present analytic formulas for theoretical constraints from perturbative unitarity and vacuum stability as well as contributions to the electron electric dipole moment (EDM) and the neutron EDM from all the Barr-Zee type diagrams. We then examine the parameter space allowed by the constraints mentioned above and also those from the uniqueness of the vacuum, measurements at Tevatron and LHC by using \texttt{HEPfit} to perform a global parameter fit. We find that the decays of the two lightest extra neutral (singly-charged) scalars, $H_1$ and $H_2$ ($H_1^\pm$), into $hZ$ ($WZ$) can be significant at the same time under the constraints, which can serve as direct evidence of CP violation in our model, but not from models with multi-doublet extensions.

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arXiv2022

Explanation of the $W$ mass shift at CDF II in the Georgi-Machacek Model

The CDF II experiment has recently determined the mass of the $W$ boson to be $m_W(\text{CDF II}) = 80.4335 \pm 0.0094~$GeV, which deviates from the standard model prediction at $7σ$ level. Although this new result is in tension with other experiments such as those at LHC and LEP, it is worth discussing possible implications on new physics by this anomaly. We show that this large discrepancy can be explained by non-aligned vacuum expectation values of isospin triplet scalar fields in the Georgi-Machacek model extended with custodial symmetry breaking terms in the potential. The latter is required to avoid an undesirable Nambu-Goldstone boson as well as to be consistent treatment of radiative corrections. With $m_W(\text{CDF II})$ as one of the renormalization inputs at the 1-loop level, we derive the required difference in the triplet vacuum expectation values, followed by a discussion of phenomenological consequences in the scenario.

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arXiv2022

Updated constraints on Georgi-Machacek model, and its electroweak phase transition and associated gravitational waves

With theoretical constraints such as perturbative unitarity and vacuum stability conditions and updated experimental data of Higgs measurements and direct searches for exotic scalars at the LHC, we perform an updated scan of the allowed parameter space of the Georgi-Machacek (GM) model. With the refined global fit, we examine the allowed parameter space for inducing strong first-order electroweak phase transitions (EWPTs) and find only the one-step phase transition is phenomenologically viable. Based upon the result, we study the associated gravitational wave (GW) signals and find most of which can be detected by several proposed experiments. We also make predictions on processes that may serve as promising probes to the GM model in the near future at the LHC, including the di-Higgs productions and several exotic scalar production channels.

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arXiv2022

A Simple Model of Dark Matter and CP Violation

We propose a simple model of dark matter and CP violation and consider the associated triple and quadruple productions of 125 GeV Higgs bosons at the Large Hadron Collider (LHC). In the model, the dark matter is a vector-like dark fermion $(\barχ, χ)$ interacting with the Standard Model only through a complex messenger scalar $S$ which is an electroweak singlet. New sources of CP violation reside in the most general scalar potential involving the doublet $H$ and the singlet $S$, as well as in the dark Yukawa coupling between $S$ and $(\barχ, χ)$. We study current experimental constraints from Higgs measurements, searches for new scalars at the LHC, precision electroweak measurements, EDM measurements, dark matter relic density, as well as direct and indirect detections of dark matter. A smoking-gun signature of CP violation could come from the Higgs-to-Higgs decays, $h_3\to h_2h_1$, where $h_3/h_2/h_1$ are the heaviest scalar, second heaviest scalar and the SM-like 125-GeV Higgs, respectively. Taking into account other Higgs-to-Higgs decays, such as $h_3\to 2h_2$ and $h_3/h_2\to 2h_1$, then gives rise to novel $3h_1$ and $4h_1$ final states, which have yet to be searched for experimentally. We present four benchmarks and show the event rates for $3h_1$ and $4h_1$ final states could be as large as ${\cal O}(10)\ {\rm fb}$ and ${\cal O}(1)\ {\rm fb}$, respectively, at the 14-TeV LHC. This work opens up a new frontier of searching for triple and quadruple Higgs bosons at a high energy collider.

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arXiv2021

Distinguishing $W'$ Signals at Hadron Colliders Using Neural Networks

We investigate a neural network-based hypothesis test to distinguish different $W'$ and charged scalar resonances through the $\ell+\require{cancel}\cancel{E}_T$ channel at hadron colliders. This is traditionally challenging due to a four-fold ambiguity at proton-proton colliders, such as the Large Hadron Collider. Of the neural network approaches we studied, we find a multi-class classifier based on a fully-connected neural network trained upon 2D histograms made from kinematic variables of the final state $\ell$ to be the most powerful. Furthermore, by considering the 1-jet processes, we demonstrate that one can generalize to multiple $2D$ histograms to represent different variable pairs. Finally, as a comparison to traditional approaches, we compare our method with Bayesian hypothesis testing and discuss the pros and cons of each approach. The neural network scheme presented in this paper is a powerful tool that can help probe the properties of charged resonances.

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