arXiv subjects

Dongjoo Kim

Publications and source records attributed to Dongjoo Kim.

10 recordsLinked to original sources

arXiv2026

Cutoff Scales in the Type-I 2HDM with Strongly First-Order Electroweak Phase Transitions: One-Step versus Multistep

We investigate the UV viability of strongly first-order electroweak phase transitions (SFOEWPTs) in the Type-I two-Higgs-doublet model (2HDM), considering both the Normal and Inverted Scenarios (NS and IS). For each scenario, we scan $5\times10^6$ physical parameter points and determine the cutoff scale $\Lambda_{\rm c}$ through a two-loop renormalization-group analysis, where $\Lambda_{\rm c}$ is set by the first violation of perturbativity, tree-level unitarity, or vacuum stability. For one-step transitions, the SFOEWPT strength and high-scale UV validity exhibit a pronounced tension: the maximal transition strength $\xi_p$ decreases with increasing $\Lambda_{\rm c}$. Requiring $\Lambda_{\rm c}>10~\text{TeV}$ limits the transition strength to $\xi_p\lesssim2.7$ in the NS and $\xi_p\lesssim1.8$ in the IS, while requiring $\xi_p>1$ restricts the cutoff scale to $\Lambda_{\rm c}\lesssim O(10^6)~\text{GeV}$ in both scenarios. Multistep transitions exhibit qualitatively different behavior. Two-step SFOEWPTs, found in appreciable numbers only in the IS, can remain theoretically consistent up to $\Lambda_{\rm c}\sim O(10^{15})~\text{GeV}$ while reaching $\xi_p\simeq7$, without exhibiting the pronounced $\xi_p$-$\Lambda_{\rm c}$ anticorrelation characteristic of one-step transitions. Imposing UV validity also sharpens the phenomenologically viable parameter space. In particular, increasing the minimum allowed cutoff scale for two-step SFOEWPTs in the IS favors a light scalar spectrum and moderate $\tan\beta$, providing a promising target for current and future collider searches.

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

Flexibility-Aware Framework for Efficient Planner-Initiated Siting of Data Center

Explosive growth in energy-intensive AI data centers is outstripping the pace of power grid interconnection and transmission expansion. While operational flexibility has been proposed to mitigate this stress, existing processes are often reactive and evaluate projects only after they enter a multi-year interconnection queue. To address this, we introduce a planner-initiated siting framework that integrates (i) reliability-gated screening, (ii) system-wide market-impact assessment under standardized flexibility envelopes (firm, pause, and shift), and (iii) entropy-weighted multi-criteria scoring to produce ranked, pre-certified catalogues of interconnection-ready locations. Applied to a synthetic 2,000-bus Texas power system, the framework demonstrates that operational flexibility expands the siting frontier by 9-17% at 1 GW and 19-21% at 2 GW compared to firm operation. Median all-hour average prices remain essentially unchanged (USD 24.32/MWh for the 2 GW cases), and the shift envelope attenuates peak-hour price dispersion by approximately 3.4% with minimal side effects during off-peak hours. Utilizing pre-certified envelopes to bypass major transmission reinforcements, this workflow enables first energization in 12-18 months, a conservative reduction of 3.5-4 years versus the conventional 5-8 year project-led process. This technology-agnostic framework provides a proactive decision-making tool for system operators and regulators to fast-track large flexible loads while preserving grid reliability and market stability.

eess.SY↗

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

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 $\alpha_3$. 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↗

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 $\tan\beta$ to $m_{H^\pm}\in[295,441]\,\text{GeV}$ and $\tan\beta\in[4.2,8.8]$, whereas two-step transitions allow $m_{H^\pm}\in[100,350]\,\text{GeV}$ and $\tan\beta\in[2.5,45.4]$. Notably, negative values of $\sin(\beta-\alpha)$ 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 $\Delta F_0$ and $\xi_c$ 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 $h\to\gamma\gamma$ branching ratios for negative $\sin(\beta-\alpha)$ motivate two complementary golden final states, $W^+ W^- b\bar{b} \tau^+ \tau^-$ and $W^+ W^- b\bar{b}\gamma\gamma$, which demonstrate high discovery potential due to negligible Standard Model backgrounds.

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

3GPP Network Architecture Enhancement for Ambient IoT Service

Ambient internet of things (A-IoT) paradigm is under study in 3GPP with the intention to provide a sustainable solution for the IoT market without any need to replace the batteries and operate in harsh environments where it is difficult to replenish batteries. This article provides insight on 3rd Generation Partnership Project (3GPP) discussions in Release 18 and 19 with the focus on network architecture aspects. 3GPP has recently decided to start normative work in its Radio Access Network (RAN) Working Group (WG) and discussions are ongoing to start a work item in other WGs with more focus on architecture aspects. We explore and analyze various aspects of system design related to architecture requirements to support A-IoT service, different architecture options to consider, security and authentication mechanisms for A-IoT devices as well as key challenges for standardization of A-IoT service.

cs.NI↗

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, $\Gamma_A/M_A = 2\%$, 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.

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↗