arXiv subjects

Sin Kyu Kang

Publications and source records attributed to Sin Kyu Kang.

At least 19 recordsLinked to original sources

arXiv2026

The $ν$EYE Neutrino Telescope: Conceptual Design Report

The $\bfνEYE$ neutrino project leverages the existing large pit at Yemilab located in South Korea, to reveal the existence of sterile neutrino, the up-turn of the neutrinos from the Sun, and the first minimum of the neutrino oscillation over distances on the order of tens of kilometers for the first time. This initiative is expected to facilitate a wide range of significant scientific and technological advancements within both South Korean and international communities engaged in neutrino science and technology. The $\bfνEYE$ aims to investigate the largely unexplored sector of almost-massless lepton in the elementary particle physics in detail. The emphasis will be placed on the study of real time nuclear processes and reactions involving possible sterile neutrinos on timescales down to nanoseconds in ultra-high intense or radioactive neutrino beams for the first time in the world; the $\bfνEYE$ looks at to-be universal oscillation (``up-turn'' in the electron neutrino survival probability) of neutrinos predicted by the three neutrino oscillation paradigm. This will confirm or deny our current understanding on the particle interactions of the lepton sector; and measurement of the first oscillation minimum between the first and second neutrinos in mass.

hep-ex↗

arXiv2026

From LUX-ZEPLIN to Colliders: Probing Higgsino Dark Matter

The high-energy nuclear recoil event with recoil energy $E_R \approx 248\text{ keV}$ observed by the LZ collaboration provides an exciting hint toward a model with a $1.1\text{ TeV}$ Higgsino inelastic dark matter. Such a recoil energy requires a mass splitting of order ($δ\approx 350\text{ keV}$) between the two nearly-degenerate neutral states. We show that within the framework of the MSSM, the model predicts a nearly-degenerate charged Higgsino state, chargino, whose mass splitting from the neutral states is of order $\mathcal{O}(350)$~MeV. The subsequent decays of such charginos once produced at colliders would lead to a sub-centimeter charged track or tracklet (with lifetime $τ\approx 0.025\text{ ns}$) at the detector. We show that such a scenario is not constrained by the current LHC bounds, and could be tested at future high-energy colliders, including HL-LHC, 100 TeV $pp$ colliders, and muon colliders. The most critical requirement is how short a track or tracklet can be reconstructed.

hep-ph↗

arXiv2026

Searching for Dark Photon Tridents Through Primordial Black Hole Signatures

The detection of gamma-ray signals from primordial black holes (PBHs) could provide compelling evidence for their role as a dark matter candidate, particularly through the observation of their Hawking radiation. Future gamma-ray observatories, such as e-ASTROGAM, and the next-generation telescopes, are poised to explore this possibility by measuring both Standard Model (SM) and beyond-the-SM particle emissions. A particularly promising avenue involves production of dark photons by PBHs, which is a hypothetical particle that decays into photons. In this work, we investigate the trident decay of dark photons with mass $m_{A'}\leq 1$ MeV focusing on their primary emission from asteroid-mass PBHs. We assume that the dark photons produced via Hawking radiation decay into photons well before reaching Earth, thereby enhancing the detectable gamma-ray flux. The energy spectrum of the photons decaying from the dark photons is distinct from that of direct Hawking-radiated photons due to higher degree of freedom, leading to observable modifications in the gamma-ray signal. Using the asteroid-mass PBHs as a case study, we demonstrate that future gamma-ray missions could detect dark-photon signatures and distinguish them from conventional Hawking radiation. This approach enables the exploration of previously inaccessible parameter spaces in dark photon mass $m_{A'}\leq 1$ MeV and their coupling to photons, offering a viable avenue to uncover the properties of dark sectors and the nature of asteroid-mass PBHs.

hep-ph↗

arXiv2026

Majoron Dark Energy via Freezing Induced by Quantum Coherence

We propose a nonequilibrium mechanism for Majoron dark energy in which the late-time freezing of a physical Majoron is induced by quantum coherence in a hidden pseudo-Dirac sterile fermion reservoir. The evolving Majoron background derivatively couples to the hidden pseudo-Dirac number current and drives a lagged reservoir response with a finite memory time. In the short-memory regime, the causal response kernel reduces to $\dot X+Γ_{\rm PD}X=β\ddotϕ$. The leading linear-response matching $Q=αX$ then yields an effective scalar equation containing the exchange structure $q_{\rm exch}\ddotϕ/\dotϕ$. We show that this term can dynamically suppress the Majoron velocity and sustain a response-dominated freezing branch even when the intrinsic Majoron mass is larger than the present Hubble scale. The microscopic origin of the lag variable is identified with the phase-lagged off-diagonal coherence of the hidden pseudo-Dirac ensemble, while the response strength is controlled by a response-weighted hidden density rather than by an independent gravitating component. The resulting state is a metastable nonequilibrium frozen phase with $w_ϕ\simeq -1$, rather than an exactly static cosmological constant.

hep-ph↗

arXiv2026

Global analysis of a minimally extended scotogenic model

We perform a global analysis of a minimally extended scotogenic model motivated by observed non-zero neutrino masses, viable dark matter (DM) candidates, and the instability of the Standard Model (SM) vacuum at high-energies. We examine the bounded-from-below conditions, vacuum stability, and RG-driven perturbativity bounds arising from the extended scalar sector, alongside a comprehensive set of flavor and electroweak (EW) precision observables - including the muon anomalous magnetic moment $Δa_μ$, the radiative decays $\ell_α \rightarrow \ell_β γ$ and $\ell_α \rightarrow 3\ell_β$, and the $μ\rightarrow e$ conversion rate, the oblique parameters, and leptonic decays of $Z$ and $H$ bosons. A numerical scan reveals four notable features: the DESI BAO bound would rule out the inverted hierarchy if confirmed by other experiments; the oblique parameters are projected to be within the reach of future precision measurements; the viable fermionic DM candidate mass lies in the range $120-350 \operatorname{GeV}$, while the CP-odd scalar is constrained to $350-600 \operatorname{GeV}$; and our result on $Z \rightarrow \operatorname{Invisible}$ is compatible with the world average at the $3σ$ level and is favored by the recent ATLAS measurement at the $3σ$ level.

hep-ph↗

arXiv2026

The Simplest Dirac Scoto-Seesaw Realization

We present a simple Dirac scoto-seesaw framework based on the anomaly-free $U(1)_{B-L}$ charge assignment $(-4,-4,5)$ for $ν_R$. This chiral charge assignment naturally accounts for the observed neutrino mass-squared differences, with $Δm^2_{\rm atm}$ generated at tree level and $Δm^2_{\rm sol}$ arising radiatively. After the spontaneous breaking of gauged $U(1)_{B-L}$, a residual $Z_6$ symmetry stabilizes the dark matter candidate. We investigate two minimal realizations of the framework, finding that both normal and inverted orderings are viable in one case, whereas only normal ordering survives in the other, with distinctive features for neutrino observables. Moreover, the chiral nature of the $U(1)_{B-L}$ charges suppresses the dilepton branching fraction of $Z'$, resulting in weaker ATLAS mass bounds than in the conventional vector $B-L$ scenario, thereby easing constraints on the dark sector. We explore the dark matter phenomenology of the singlet scalar and fermionic dark matter candidates. While singlet scalar DM is often severely constrained, the presence of the $Z'$ portal together with annihilation and co-annihilation channels substantially broadens the allowed parameter space. Thus, the framework offers a predictive scenario for neutrino and dark matter phenomenology that can be probed in future experiments.

hep-ph↗

arXiv2026

Radiative Dirac Neutrino Masses from Modular $S_3$ Symmetry in an Axion Model

We present a unified axion model framework that simultaneously addresses the origin of neutrino masses, leptonic flavor structure, the strong CP problem, and dark matter. The model is based on a global $U(1)_{\rm PQ}$ symmetry combined with a modular $S_3$ symmetry and is realized within a novel class of KSVZ-type axion model. Exotic colored fermions and scalars mediate radiative neutrino mass generation at the one loop-level. The PQ charge assignment forbids tree-level neutrino masses and leaves a residual $Z_3$ symmetry that ensures the Dirac nature of neutrinos. In the minimal realization, the neutrino mass matrix is of rank two, predicting one massless neutrino. Consequently, the sum of neutrino masses is constrained for both the normal and inverted hierarchies. We analyze the implications for charged lepton flavor violation and the lepton $g-2$. The axion emerging from this framework dynamically resolves the strong CP problem and accounts for the observed dark matter abundance. Notably, the predicted axion-photon coupling is within reach of upcoming experiments and consistent with existing astrophysical and cosmological bounds.

hep-ph↗

arXiv2025

Neutrino Dipole Portal

The neutrino dipole portal (NDP) is a minimal and predictive extension of the Standard Model, in which a transition magnetic moment operator couples an active neutrino to a heavy neutral lepton via the electromagnetic field. This higher-dimensional interaction gives rise to distinctive processes such as neutrino up-scattering, radiative decays, meson transitions, and modifications of recoil spectra, offering multiple avenues for discovery. In this review, we discuss the theoretical foundations of the NDP, its ultraviolet completions, and the associated production and decay mechanisms across laboratory, astrophysical, and cosmological settings. Current constraints arise from accelerator searches, recoil-based detectors, collider studies, and high energy neutrino observatories, complemented by robust bounds from Big Bang Nucleosynthesis, the Cosmic Microwave Background, and supernova cooling. Future experimental and observational efforts, including next-generation neutrino experiments, multi-ton dark matter detectors, and improved cosmological and astrophysical probes, are anticipated to test the remaining allowed regions. The NDP thus provides a simple, well-motivated, and broadly testable framework at the intersection of particle physics, astrophysics, and cosmology.

hep-ph↗

arXiv2025

A two scalar triplets model as common origin for dark matter, neutrino masses, baryon asymmetry and inflation

We propose an extension of the standard model (SM) by two SU(2) triplet scalars and an inert SU(2) doublet. We demonstrate that this setup can simultaneously produce an inflaton and baryon asymmetry in the early universe, provide a dark matter candidate and explain the smallness of neutrino masses. The two triplets are particularly important as they become mediators for the production of dark matter and the generation of lepton asymmetry, as well as contribute an inflaton. The inert doublet results in a dark matter candidate. The required CP-violation for lepton asymmetry is obtained by interference between the triplet mediators that communicate the dark sector to the SM sector. More precisely, the complex Breit-Wigner propagators of the triplets and their mixing, result in an asymmetric production of leptons and antileptons that is boosted before dark matter freeze-out. In this case, simultaneously achieving enough dark matter relic abundance and proper matter-antimatter asymmetry limits the available parameter space of the model. Moreover, the scalar triplets are coupled non-minimally to gravity and give rise to the inflaton. We calculate the inflationary parameters and check that we can obtain predictions consistent with Planck constraints from 2018. We also perform an analysis of the reheating for the inflaton decays/annihilations to relativistic SM particles.

hep-ph↗

arXiv2025

Neutrino Masses and Mixing in an Axion Model

We propose a novel framework that simultaneously addresses three critical issues: tiny neutrino masses and their mixing patterns, dark matter, and the strong CP problem. Our model extends the Peccei-Quinn (PQ) symmetry by incorporating modular $S_3$ symmetry, which plays a central role in explaining the observed neutrino mixing structure. The field content includes two vector-like colored fermions and three colored scalars as $S_3$ singlets, an isospin doublet inert scalar and a singlet PQ scalar, each assigned appropriate modular weights. We show that such an extension, together with a suitable assignment of modular weights to the fields, can lead to holomorphic modular forms of Yukawa interactions, which can be derived from a superpotential. Furthermore, we explore an extension of the model to include non-holomorphic Yukawa interactions in the non-supersymmetric framework and show that the results are distinct from the holomorphic case. Tiny neutrino masses are generated radiatively through colored mediators, while the KSVZ-type axion appears to dynamically resolve the strong CP problem. We investigate the phenomenology of lepton flavor violation and the muon $g-2$ anomaly within this framework. Additionally, we explore the axion's properties and its role as dark matter.

hep-ph↗

arXiv2025

Probing Double-Peaked Gamma-Ray Spectra from Primordial Black Holes with Next-Generation Gamma-Ray Experiments

Primordial black holes (PBHs), hypothesized to form in the early universe from gravitational collapse of density fluctuations, represent a well-motivated dark matter (DM) candidate. Their potential detection through gamma-ray signatures arising from Hawking radiation would provide definitive evidence for their existence and constrain their contribution to the DM abundance. Unlike conventional DM candidates, PBHs emit a unique, thermal-like spectrum of particles as they evaporate, including photons, neutrinos, and possible beyond-the-Standard Model particles. Future high-sensitivity gamma-ray observatories, such as e-ASTROGAM and other next-generation telescopes, will play a pivotal role in this search. With improved energy resolution and sensitivity, these missions can disentangle PBH-originating photons from astrophysical backgrounds, probe subtle spectral features such as multi-peak structures, and test exotic evaporation models. Such observations could either confirm PBHs as a viable DM component or place stringent limits on their abundance across critical mass windows. In this work, we explore the distinguishing features of a double-peaked gamma-ray spectrum produced by PBHs, focusing on the asteroid-mass window ($10^{15}$ g to $10^{17}$ g), where Hawking radiation peaks in the MeV to GeV range. Using a likelihood-based analysis, we demonstrate how future missions could discriminate between single- and double-peaked PBH scenarios, the latter arising in cosmological models predicting multi-modal PBH mass distributions. Our results highlight the diagnostic power of spectral shape analysis in identifying PBH populations and constrain the parameter space for which a double-peaked signal could be detectable above background.

hep-ph↗

arXiv2025

Unveiling the Invisible: ALPs and Sterile Neutrinos at the LHC and HL-LHC

We investigate the potential of using the signature of mono-Higgs plus large missing energies to constrain on two new physics models, namely the model of an axion-like particle (ALP) and the model of sterile neutrinos. We focus on the Higgs-ALP interactions starting at dimension-six and the Higgs-sterile neutrino interactions starting at dimension-five, via the processes $pp \to h a a$ for ALP production and $pp \to h N N$ for sterile neutrinos at the LHC and High Luminosity LHC (HL-LHC), followed by the Higgs decay $h \to b \bar{b}$. We establish bounds on the ALP-Higgs coupling $\frac{C_{aH}}{Λ^2}$ and sterile neutrino-Higgs coupling $\frac{λ_3}{M_*}$, respectively, for ALP and sterile-neutrino mass ranging from 1 to 60 GeV, using the recent ATLAS data on mono-Higgs plus missing energies at the LHC $(\sqrt{s} = 13\;{\rm TeV}\; {\rm and}\; \mathcal{L} = 139\; {\rm fb}^{-1})$. The most stringent constraint occurs in the missing transverse energy $M_{ET}$ range $200 < M_{ET} \leq 350$ GeV. We also estimate the sensitivities that we can achieve at the HL-LHC ($\sqrt{s} = 14$ TeV and $\mathcal{L} = 3000$ fb$^{-1}$). We obtain improved sensitivities across various missing energy regions. The ALP model exhibits better sensitivities, particularly at lower mass range, compared to the sterile neutrino model, which shows weaker sensitivities across similar mass and energy ranges. Our results underscore the potential of the mono-Higgs signature as a robust probe for physics beyond the Standard Model.

hep-ph↗

arXiv2024

Pathways to proton's stability via naturally small neutrino masses

In the present work, the connection between the smallness of the neutrino masses and the stability of the proton is studied. We analyze this connection from different perspectives: the smallness of neutrino mass and the proton stability originate from the same source, small neutrino masses lead to a long lived proton, and the smallness of the proton decay width as a cause of the naturally small neutrino masses. All the schemes are studied in detail and UV realizations are given. We discuss advantages of each scheme and outline further investigation directions.

hep-ph↗

arXiv2023

Simple Modular invariant model for Quark, Lepton, and flavored-QCD axion

We propose a minimal extension of the Standard Model by incorporating sterile neutrinos and a QCD axion to account for the mass and mixing hierarchies of quarks and leptons and to solve the strong CP problem, and by introducing $G_{\rm SM}\times Γ_N\times U(1)_X$ symmetry. We demonstrate that the K{ä}hler transformation corrects the weight of modular forms in the superpotential and show that the model is consistent with the modular and $U(1)_X$ anomaly-free conditions. This enables a simple construction of a modular-independent superpotential for scalar potential. Using minimal supermultiplets, we demonstrate a level 3 modular form-induced superpotential. Sterile neutrinos explain small active neutrino masses via the seesaw mechanism and provide a well-motivated $U(1)_X$ breaking scale, whereas gauge singlet scalar fields play crucial roles in generating the QCD axion, heavy neutrino mass, and fermion mass hierarchy. The model predicts a range for the $U(1)_X$ breaking scale from $10^{13}$ GeV to $10^{15}$ GeV for $1\,\mbox{TeV}< m_{3/2}<10^6\,\mbox{TeV}$. In the supersymmetric limit, all Yukawa coefficients in the superpotential are given by complex numbers with an absolute value of unity, implying a democratic distribution. Performing numerical analysis, we study how model parameters are constrained by current experimental results. In particular, the model predicts that the value of the quark Dirac CP phase falls between $38^\circ$ to $87^\circ$, which is consistent with experimental data, and the favored value of the neutrino Dirac CP phase is around $250^\circ$. Furthermore, the model can be tested by ongoing and future experiments on axion searches, neutrino oscillations, and $0νββ$-decay.

hep-ph↗

arXiv2023

Common origin of dark matter, baryon asymmetry and neutrino masses in the standard model with extended scalars

We propose a model that simultaneously addresses the existence of a dark matter candidate, baryon asymmetry and tiny neutrino masses and mixing by introducing two SU(2) triplet scalars and an inert SU(2) doublet scalar on top of the standard model. The two triplet scalars serve as mediators in generation of lepton asymmetry and determination of relic density of dark matter. They also play an essential role in generation of tiny neutrino masses and inducing CP violation. The inert scalar is regarded as a dark matter candidate. The interference due to complex Breit-Wigner propagators for the triplets will result in CP-asymmetry that depends on the difference between their masses and a relative complex phase between their couplings to standard model leptons. Moreover, the production of lepton asymmetry will be closely tied to the evolution of dark matter, limiting the parameter space where the correct relic abundance and matter-antimatter asymmetry can be simultaneously accomplished.

hep-ph↗

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

Implications of the new CDF-II $W$-boson mass on two-Higgs-doublet models

We present the implications of the recent measurement of $W$ boson at CDF II on the two-Higgs-doublet model (2HDM). In the analysis, we impose theoretical bounds such as vacuum stability and perturbative unitarity, and several experimental constraints. In addition, we take into account the measurement of $\sin^2θ_W(m_Z)_{\rm \bar{MS}}$ on top of the CDF $W$-boson mass to investigate how the $S$ and $T$ parameters are determined. We explore two possible scenarios depending on whether the Higgs boson observed at the LHC is the lighter or heavier of $CP$-even neutral Higgs bosons for 2HDM type I and II. Using the results, we show how the parameter space is constrained, and compare it with the one based on the PDG average of $m_W$. Furthermore, we explore phenomenological consequences of electroweak precision observables that can be affected by $m_W$ within the predictions of the 2HDM, and the reduction in parameter space expected from future measurements at the Future Circular Lepton Collider.

hep-ph↗

arXiv2022

Confronting the prediction of leptonic Dirac CP-violating phase with experiments

We update and improve past efforts to predict the leptonic Dirac CP-violating phase with models that predict perturbatively modified tribimaximal or bimaximal mixing. Simple perturbations are applied to both mixing patterns in the form of rotations between two sectors. By translating these perturbed mixing matrices to the standard parameterization for the neutrino mixing matrix we derive relations between the Dirac CP-phase and the oscillation angles. We use these relations together with current experimental results to constrain the allowed range for the CP-phase and determine its probability density. Furthermore, we elaborate on the prospects for future experiments probing on the perturbations considered in this work. We present a model with $A_4$ modular symmetry that is consistent with one of the described perturbed scenarios and successfully predicts current oscillation parameter data.

hep-ph↗