arXiv subjects

Jeong Han Kim

Publications and source records attributed to Jeong Han Kim.

At least 19 recordsLinked to original sources

arXiv2026

Echoes of Self-Interacting Dark Matter from Binary Black Hole Mergers

Dark matter (DM) environments around black holes (BHs) can influence their mergers through dynamical friction, causing gravitational wave (GW) dephasing during the inspiral phase. While this effect is well studied for collisionless dark matter (CDM), it remains unexplored for self-interacting dark matter (SIDM) due to the typically low DM density in SIDM halo cores. In this work, by considering BH mergers within SIDM spikes, which can arise from models with a massive force mediator, we show that the GWs emitted are dephased in a distinct manner. To incorporate the feedback of the BH orbital motion that can significantly modify the DM profiles, we use $N$-body simulations to analyze GW dephasing in binary BH inspirals within CDM and SIDM spikes. By tracking the binary's motion in different DM environments, we show that the Laser Interferometer Space Antenna (LISA) can observe GW dephasing arising from SIDM spikes in particular scenarios. Our results indicate that these observations offer a possibility of distinguishing between binary-BH inspirals in different DM environments.

astro-ph.CO↗

arXiv2026

Boson Stars Hosting Black Holes

We study a self-gravitating ultralight dark matter condensate (a boson star) hosting a central black hole, in the nonrelativistic limit, which we refer to as a boson star black hole (BS-BH) system. We numerically solve the equations of hydrostatic equilibrium, consistently incorporating the gravitational potential of the black hole, to obtain all possible configurations of this BS-BH system for different boson star masses, interaction types, and black hole masses. We also propose an analytic expression for the density profile and compare it with the numerical results, finding good agreement for attractive interactions and for a finite range of mass ratios between the black hole and boson star. Finally, considering the inspiral of this BS-BH system with a second, smaller black hole, we study the dephasing of gravitational waves due to the presence of the dark matter environment. A Fisher matrix analysis reveals the regions of parameter space of the dark matter mass and self-coupling that future gravitational wave observatories such as LISA can probe.

gr-qc↗

arXiv2025

Gravitational Wave Duet by Resonating Binary Black Holes within Ultralight Dark Matter

Gravitational wave observations have significantly broadened our capacity to explore fundamental physics beyond the Standard Model, providing crucial insights into dark matter that are inaccessible through conventional methods. Here, we investigate the resonant interactions between binary black hole systems and solitons, self-gravitating configurations of ultralight bosonic dark matter, which induce metric perturbations and generate distinct oscillatory patterns in gravitational waves. Upcoming experiments such as the Laser Interferometer Space Antenna could detect the oscillatory patterns in gravitational waveforms, providing an evidence for solitons. Because the effect relies solely on gravity, it does not assume any coupling of the dark sector to Standard Model particles, highlighting the capability of future gravitational-wave surveys to probe dark matter.

astro-ph.CO↗

arXiv2025

Hunting and identifying coloured resonances in four top events with machine learning

We study prospects to search for pair or singly produced colour octet or colour sextet scalars which decay into two top quarks at the LHC. We focus on the same-sign lepton final state. We train a neural network comprising a simple multilayer perceptron combined with a convolutional neural network to optimize the separation of signal and background events. For LHC operated at 14 TeV and a luminosity of 3 ab$^{-1}$ we find an expected discovery reach of $m_8=1.8$ TeV and $m_6=1.92$ TeV for pair produced colour octets and sextets, respectively, and an expected exclusion reach of $m_8=2.02$ TeV and $m_6=2.14$ TeV. In a second step, we retrain the same network architecture to discriminate between signal processes. The network can clearly distinguish between the different colour representations. Moreover, we can also determine whether there is a significant contribution from single production to pair production for the same final state. The methodology can be applied to BSM candidates of different spin and colour representations.

hep-ph↗

arXiv2025

A new density limit for unanimity in majority dynamics on random graphs

Majority dynamics is a process on a simple, undirected graph $G$ with an initial Red/Blue color for every vertex of $G$. Each day, each vertex updates its color following the majority among its neighbors, using its previous color for tie-breaking. The dynamics achieves \textit{unanimity} if every vertex has the same color after finitely many days, and such color is said to \textit{win}. When $G$ is a $G(n,p)$ random graph, L. Tran and Vu (2019) found a codition in terms of $p$ and the initial difference $2Δ$ beteween the sizes of the Red and Blue camps, such that unanimity is achieved with probability arbitrarily close to 1. They showed that if $pΔ^2 \gg1 $, $pΔ\geq 100$, and $p\geq (1+\varepsilon) n^{-1}\log n$ for a positive constant $\varepsilon$, then unanimity occurs with probability $1 - o(1)$. If $p$ is not extremely small, namely $p > \log^{-1/16} n $, then Sah and Sawhney (2022) showed that the condition $pΔ^2 \gg 1$ is sufficient. If $n^{-1}\log^2 n \ll p \ll n^{-1/2}\log^{1/4} n$, we show that $p^{3/2}Δ\gg n^{-1/2}\log n$ is enough. Since this condition holds if $pΔ\geq 100$ for $p$ in this range, this is an improvement of Tran's and Vu's result. For the closely related problem of finding the optimal condition for $p$ to achieve unanimity when the initial coloring is chosen uniformly at random among all possible Red/Blue assignments, our result implies a new lower bound $p \gg n^{-2/3}\log^{2/3} n$, which improves upon the previous bound of $n^{-3/5}\log n$ by Chakraborti, Kim, Lee and T. Tran (2021).

math.CO↗

arXiv2024

Astrophysical and Cosmological Probes of Boosted Dark Matter

We present an in-depth study of two-component cold dark matter via extensive N-body simulations. We examine various cosmological observables including the temperature evolution, power spectrum, density perturbation, maximum circular velocity functions, and galactic density profiles. We find that a significant mass difference between the two components, coupled with the annihilation of the heavier into the lighter component, imparts warm dark matter (WDM)-like characteristics to the latter. This model benefits from the unique features of WDM, such as modifications to the matter power spectrum and density profiles, while avoiding stringent observational constraints on WDM mass. The two-component dark-matter model aligns with observational data and suggests new avenues for dark-matter detection in terrestrial experiments, particularly for light, sub-MeV DM candidates. Our findings provide a framework for understanding the small-scale structures and offer guidance for future particle physics and cosmological studies.

hep-ph↗

arXiv2024

Gravitational wave probes on self-interacting dark matter surrounding an intermediate mass black hole

The presence of dark matter overdensities surrounding a black hole can influence the evolution of a binary system. The gravitational wave signals emitted by a black hole binary offer a promising means to probe the dark matter environments near a black hole. The dense region of dark matter can lead to the dephasing of gravitational waveforms, which can be detected by upcoming experiments such as the Laser Interferometer Space Antenna (LISA). The dark matter density profile around the black hole can vary for different dark matter models. Our study specifically investigates the impact of the ultralight self-interacting scalar dark matter (SIDM) on the gravitational wave signals emitted by black hole binaries. A distinctive characteristic of SIDM surrounding a black hole, as opposed to collisionless dark matter, is the formation of a soliton core. We perform a Fisher matrix analysis to estimate the size of the soliton and the corresponding SIDM parameter space that future LISA-like gravitational wave experiments can explore.

hep-ph↗

arXiv2023

Warm Surprises from Cold Duets: N-Body Simulations with Two-Component Dark Matter

We explore extensive N-body simulations with two-component cold dark matter candidates. We delve into the temperature evolution, power spectrum, density perturbation, and maximum circular velocity functions. We find that the substantial mass difference between the two candidates and the annihilation of the heavier components to the lighter ones effectively endow the latter with warm dark matter-like behavior, taking advantage of all distinct features that warm dark matter candidates offer, without observational bounds on the warm dark matter mass. Moreover, we demonstrate that the two-component dark matter model aligns well with observational data, providing valuable insights into where and how to search for the elusive dark matter candidates in terrestrial experiments.

hep-ph↗

arXiv2023

Searching for Dark Photons with Maverick Top Partners

In this paper, we present a model in which an up-type vector-like quark (VLQ) is charged under a new $U(1)_d$ gauge force which kinetically mixes with the SM hypercharge. The gauge boson of the $U(1)_d$ is the dark photon, $γ_d$. Traditional searches for VLQs rely on decays into Standard Model electroweak bosons $W,Z$ or Higgs. However, since no evidence for VLQs has been found at the Large Hadron Collider (LHC), it is imperative to search for other novel signatures of VLQs beyond their traditional decays. As we will show, if the dark photon is much less massive than the Standard Model electroweak sector, $M_{γ_d}\ll M_Z$, for the large majority of the allowed parameter space the VLQ predominately decays into the dark photon and the dark Higgs that breaks the $U(1)_d$ . That is, this VLQ is a `maverick top partner' with nontraditional decays. One of the appeals of this scenario is that pair production of the VLQ at the LHC occurs through the strong force and the rate is determined by the gauge structure. Hence, the production of the dark photon at the LHC only depends on the strong force and is largely independent of the small kinetic mixing with hypercharge. This scenario provides a robust framework to search for a light dark sector via searches for heavy colored particles at the LHC.

hep-ph↗

arXiv2023

Uncovering doubly charged scalars with dominant three-body decays using machine learning

We propose a deep learning-based search strategy for pair production of doubly charged scalars undergoing three-body decays to $W^+ t\bar b$ in the same-sign lepton plus multi-jet final state. This process is motivated by composite Higgs models with an underlying fermionic UV theory. We demonstrate that for such busy final states, jet image classification with convolutional neural networks outperforms standard fully connected networks acting on reconstructed kinematic variables. We derive the expected discovery reach and exclusion limit at the high-luminosity LHC.

hep-ph↗

arXiv2023

Probing Cosmological Particle Production and Pairwise Hotspots with Deep Neural Networks

Particles with masses much larger than the inflationary Hubble scale, $H_I$, can be pair-produced non-adiabatically during inflation. Due to their large masses, the produced particles modify the curvature perturbation around their locations. These localized perturbations eventually give rise to localized signatures on the Cosmic Microwave Background (CMB), in particular, pairwise hotspots (PHS). In this work, we show that Convolutional Neural Networks (CNN) provide a powerful tool for identifying PHS on the CMB. While for a given hotspot profile a traditional Matched Filter Analysis is known to be optimal, a Neural Network learns to effectively detect the large variety of shapes that can arise in realistic models of particle production. Considering an idealized situation where the dominant background to the PHS signal comes from the standard CMB fluctuations, we show that a CNN can isolate the PHS with $\mathcal{O}(10)\%$ efficiency even if the hotspot temperature is $\mathcal{O}(10)$ times smaller than the average CMB fluctuations. Overall, the CNN search is sensitive to heavy particle masses $M_0/H_I=\mathcal{O}(200)$, and constitutes one of the unique probes of very high energy particle physics.

hep-ph↗

arXiv2022

Threshold functions for incidence properties in finite vector spaces

The main purpose of this paper is to provide threshold functions for the events that a random subset of the points of a finite vector space has certain properties related to point-flat incidences. Specifically, we consider the events that there is an $\ell$-rich $m$-flat with regard to a random set of points in $\mathbb{F}_q^n$, the event that a random set of points is an $m$-blocking set, and the event that there is an incidence between a random set of points and a random set of $m$-flats. One of our key ingredients is a stronger version of a recent result obtained by Chen and Greenhill (2021).

math.CO↗

arXiv2022

Probing the Top-Higgs Yukawa CP Structure in dileptonic $t \bar t h$ with $M_2$-Assisted Reconstruction

Constraining the Higgs boson properties is a cornerstone of the LHC program. We study the potential to directly probe the Higgs-top CP-structure via the $t\bar{t}h$ channel at the LHC with the Higgs boson decaying to a bottom pair and top-quarks in the dileptonic mode. We show that a combination of laboratory and $t\bar{t}$ rest frame observables display large CP-sensitivity, exploring the spin correlations in the top decays. To efficiently reconstruct our final state, we present a method based on simple mass minimization and prove its robustness to shower, hadronization and detector effects. In addition, the mass reconstruction works as an extra relevant handle for background suppression. Based on our results, we demonstrate that the Higgs-top CP-phase $(α)$ can be probed up to $\cosα< 0.7$ at the high luminosity LHC.

hep-ph↗

arXiv2022

Portraying Double Higgs at the Large Hadron Collider II

The Higgs potential is vital to understand the electroweak symmetry breaking mechanism, and probing the Higgs self-interaction is arguably one of the most important physics targets at current and upcoming collider experiments. In particular, the triple Higgs coupling may be accessible at the HL-LHC by combining results in multiple channels, which motivates to study all possible decay modes for the double Higgs production. In this paper, we revisit the double Higgs production at the HL-LHC in the final state with two $b$-tagged jets, two leptons and missing transverse momentum. We focus on the performance of various neural network architectures with different input features: low-level (four momenta), high-level (kinematic variables) and image-based. We find it possible to bring a modest increase in the signal sensitivity over existing results via careful optimization of machine learning algorithms making a full use of novel kinematic variables.

hep-ph↗

arXiv2022

Resolving Combinatorial Ambiguities in Dilepton $t \bar t$ Event Topologies with Neural Networks

We study the potential of deep learning to resolve the combinatorial problem in SUSY-like events with two invisible particles at the LHC. As a concrete example, we focus on dileptonic $t \bar t$ events, where the combinatorial problem becomes an issue of binary classification: pairing the correct lepton with each $b$ quark coming from the decays of the tops. We investigate the performance of a number of machine learning algorithms, including attention-based networks, which have been used for a similar problem in the fully-hadronic channel of $t\bar t$ production; and the Lorentz Boost Network, which is motivated by physics principles. We then consider the general case when the underlying mass spectrum is unknown, and hence no kinematic endpoint information is available. Compared against existing methods based on kinematic variables, we demonstrate that the efficiency for selecting the correct pairing is greatly improved by utilizing deep learning techniques.

hep-ph↗

arXiv2022

Mirror Twin Higgs Cosmology: Constraints and a Possible Resolution to the $H_0$ and $S_8$ Tensions

The mirror twin Higgs model (MTH) is a solution to the Higgs hierarchy problem that provides well-predicted cosmological signatures with only three extra parameters: the temperature of the twin sector, the abundance of twin baryons, and the vacuum expectation value (VEV) of twin electroweak symmetry breaking. These parameters specify the behavior of twin radiation and the acoustic oscillations of twin baryons, which lead to testable effects on the cosmic microwave background (CMB) and large-scale structure (LSS). While collider searches can only probe the twin VEV, through a fit to cosmological data we show that the existing CMB (Planck18 TTTEEE+lowE+lowT+lensing) and LSS (KV450) data already provide useful constraints on the remaining MTH parameters. Additionally, we show that the presence of twin radiation in this model can raise the Hubble constant $H_0$ while the scattering twin baryons can reduce the matter fluctuations $S_8$, which helps to relax the observed $H_0$ and $S_8$ tensions simultaneously. This scenario is different from the typical $Λ$CDM + $ΔN_{\rm eff}$ model, in which extra radiation helps with the Hubble tension but worsens the $S_8$ tension. For instance, when including the SH0ES and Planck SZ data in the fit, we find that a universe with $\gtrsim 20\%$ of the dark matter comprised of twin baryons is preferred over $Λ$CDM by $\sim4σ$. If the twin sector is indeed responsible for resolving the $H_0$ and $S_8$ tensions, future measurements from the Euclid satellite and CMB Stage 4 experiment will further measure the twin parameters to $O(1-10\%)$-level precision. Our study demonstrates how models with hidden naturalness can potentially be probed using precision cosmological data.

hep-ph↗

arXiv2022

Directly Probing the CP-structure of the Higgs-Top Yukawa at HL-LHC and Future Colliders

Constraining the Higgs boson properties is a cornerstone of the LHC program and future colliders. In this Snowmass contribution, we study the potential to directly probe the Higgs-top CP-structure via the $t\bar{t}h$ production at the HL-LHC, 100 TeV FCC and muon colliders. We find the limits on the CP phase ($α$) at 95% CL are $|α| \lesssim 36^\circ$ with dileptonic $t\bar t (h\to b\bar b) $ and $|α| \lesssim 25^\circ$ with combined $t\bar t (h\to γγ) $ at the HL-LHC. The 100 TeV FCC brings a significant improvement in sensitivity with $|α| \lesssim 3^\circ$ for the dileptonic $t\bar t (h\to b\bar b) $, due to the remarkable gain in the signal cross-section and the increased luminosity. At future muon colliders, we find that the bounds with semileptonic $t\bar t (h\to b\bar b) ν\barν$ are $|α| \lesssim 9^\circ$ for 10 TeV and $|α| \lesssim 3^\circ$ for 30 TeV, respectively.

hep-ph↗

arXiv2022

Matching in $pp \to t \bar{t} W/Z/h +$ jet SMEFT studies

In this paper, we explore the impact of extra radiation on predictions of $pp \to t\bar{t}X, X = h/W^{\pm}/Z$ processes within the dimension-6 SMEFT framework. While full next-to-leading order calculations are of course preferred, they are not always practical, and so it is useful to be able to capture the impacts of extra radiation using leading-order matrix elements matched to the parton shower. While a matched leading-order calculation for $t\bar{t}X$ is not expected to reproduce the next-to-leading order inclusive cross section precisely, we show that it does capture the relative impact of the EFT effects by considering the ratio of matched SMEFT inclusive cross sections to Standard Model values, $σ_{\rm SMEFT}(t\bar{t}Xj)/σ_{\rm SM}(t\bar{t}Xj) \equiv μ$. Furthermore, we compare leading order calculations with and without extra radiation and find several cases, such as the effect of the operator $(φ^{\dagger}i\!\overleftrightarrow{D}_{\!μ}φ) (\bar{t}γ^μt)$ on $t\bar{t}h$ and $t\bar{t}W$, for which the relative cross section prediction increases by more than $10\%$ -- significantly larger than the uncertainty derived by varying the input scales in the calculation, including the additional scales required for matching. Being leading order at heart, matching has the benefit that it can be applied to all operators and processes relevant to $pp \to t\bar{t}X, X = h/W^{\pm}/Z +$ jet, is computationally fast and not susceptible to negative weights. Therefore, it is a useful approach in $t\bar{t}X+$ jet studies where complete next-to-leading order results are currently unavailable or unwieldy.

hep-ph↗