arXiv subjects

Jongkuk Kim

Publications and source records attributed to Jongkuk Kim.

At least 19 recordsLinked to original sources

arXiv2026

Pseudo-scalar dark matter from a broken gauged symmetry

We propose a novel model for pseudo-scalar dark matter (PSDM) by extending the Standard Model (SM) with a dark gauged $U(1)_X$ symmetry, but without dark charged fermions. We impose a $Z_2$ symmetry to ensure the stability of pseudo-scalar dark matter and regard the $U(1)_X$ symmetry as being broken dominantly by a large VEV of the singlet scalar field. The would-be Goldstone associated with the $U(1)_X$ gauge boson is almost orthogonal to the direction of PSDM. As a result, we show that PSDM appears as a stable pseudo-Nambu-Goldstone boson receiving the mass from the $U(1)_X$ invariant mixing potential and the corresponding cross section for direct detection gets suppressed even for the weak-scale mass of PSDM. We also show that the correct relic density can be explained by the PSDM annihilations into the SM particles or into a pair of light Higgs-like scalars, being compatible with the bounds from Higgs invisible decay, Higgs data and indirect detection.

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arXiv2026

A Unified Dark Matter Explanation for $\boldsymbol{B^+ \!\to K^+ν\barν}$ and the Super-Kamiokande Antineutrino Excess

Recent results from Super-Kamiokande and Belle II have revealed intriguing excesses over Standard Model expectations. Super-Kamiokande observes a mild excess of $\barν_e^{}$-like events near $20\,\,\mathrm{MeV}$, while Belle II reports a branching fraction for $B^+ \!\to K^+ν\barν$ that exceeds the Standard Model prediction by approximately $2.7σ$. In this work, we study the simplest UV-complete complex scalar dark matter model with a gauged $\text{U}(1)_{\textsf{L}_μ- \textsf{L}_τ}^{}$ symmetry. We demonstrate that a light dark sector can simultaneously reproduce the observed dark matter relic density and accommodate both excesses within a unified framework.

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arXiv2026

Decaying vector dark matter with low reheating temperature for KM3NeT signal and its impact on gravitational waves

We propose a new model to explain the KM3NeT neutrino event through a low reheating scenario with a suppression in the GW spectrum originating from cosmic string networks. To achieve this, we extend the SM gauge sector by an abelian gauge symmetry and a singlet scalar. Once the abelian gauge symmetry spontaneously breaks, the extra gauge boson acquires mass and becomes a suitable Dark Matter (DM) candidate. Due to the kinetic mixing with the hypercharge gauge group, DM can decay into SM particles. To explain the KM3NeT signal, we need $\mathcal{O}(100)$ PeV DM, which can be produced in the correct order of DM density in a low reheating scenario. In this scenario, the overabundance issue of heavy DM can be tackled by diluting its abundance through the continuous injection of entropy when the matter-like inflaton decays into the SM bath. Using the low reheating scenario, we can obtain the correct value of DM density both for freeze-out and freeze-in mechanisms for super-heavy DM. Moreover, we have studied the Gravitational Waves (GWs) produced from cosmic strings, which fall within the detectable range of future proposed GW experiments. Additionally, the dominance of a quadratic inflaton potential before the reheating temperature changes the temperature-scale factor relation, which suppresses the GW spectrum at higher frequencies. Choosing an arbitrarily low reheating temperature provides only a tiny fraction of the DM density due to dilution from entropy injection. This fraction of the vector DM suggests that only the extragalactic contribution is relevant in the KM3NeT event because DM lifetime is shorter than the age of the Universe.

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arXiv2025

$B^+\to K^+ ν\barν$ Excess and DM semi-annihilation

In 2023, Belle II collaboration announced the observarion of the $B^+ \to K^+ ν\barν$ decay channel for the first time. This decay channel provides a clean signal with high precision in theoretical calculation. However, we encounter $2.8σ$ deviation from the Standard Model (SM) prediction. To resolve this excess, we study scalar dark matter (DM) model with local discrete $Z_3$ symmetry. Assuming dark $U(1)_X \equiv U(1)_{L_μ- L_τ}$ symmetry, this $U(1)_{L_μ- L_τ}$ symmetry is spontaneously broken into local discrete $Z_3$ by non-zero vacuum expectation value of dark Higgs boson. Considering dark Higgs mass is $2$GeV, we can explain the recent ${\rm Br} (B^+ \to K^+ ν\barν)$ excess reported from Belle II collaboration and relic abundance at the same time.

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arXiv2025

Linking the KM3-230213A Neutrino Event to Dark Matter Decay and Gravitational Wave signals

The KM3NeT collaboration recently reported the detection of an ultra-high-energy (UHE) neutrino event, dubbed KM3-230213A. This is the first observed neutrino event with energy of the order of $\mathcal{O}(100) {\rm PeV}$, the origin of which remains unclear. In this paper, we interpret this high energy neutrino event in terms of the Dirac fermion dark matter (DM) $χ$ decays via the right-handed (RH) neutrino portal assuming the Type-I seesaw mechanism for neutrino masses and mixings. Furthermore, the Dirac fermion dark matter $χ$ is assumed to be charged under $U(1)_X$ dark gauge symmetry, which is spontaneously broken by the vacuum expectation value (VEV) of the dark Higgs $Φ$. In this scenario, DM can decay into a pair of Standard Model (SM) particles, such as neutrinos, leptons, and gauge bosons via the RH neutrino portals for $v_Φ\gg m_χ$. Then we can reply on the HDMSpectra package to generate the neutrino and $γ$-ray spectra from heavy DM decays. If the DM mass is around $440\ {\rm PeV}$ with a lifetime $5\times 10^{29}$ sec, it can account for the KM3-230213A event. However, such heavy DM cannot be produced through the thermal freeze-out mechanism due to overproduction and violation of unitarity bounds. We focus on the UV freeze-in production of DM through a dimension-5 operator, which helps in producing the DM dominantly in the early Universe. Finally, the large value of the dark Higgs field VEV opens up the intriguing possibility of generating gravitational waves (GWs) spectra from cosmic strings. We have found a reasonable set of parameter values that can address the KM3NeT signal, yield the correct value of the DM relic density through freeze-in mechanism, and allow for the possible detection of GW signal at the future detectors.

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arXiv2025

Neutrino masses and mixed dark matter from doublet and singlet scalars

We consider the extension of the Standard Model with an inert scalar doublet, three right-handed neutrinos, and singlet scalar fields, $φ$ and $S$. In this model, neutrino masses are zero in the limit of the unbroken $Z_4$ discrete symmetry. We show that when the singlet scalar field $φ$ gets a VEV, the $Z_4$ symmetry is broken to $Z_2$, and neutrino masses are generated at one-loops due to the mixings between the neutral components of the inert scalar doublet and the singlet scalar field $S$. There is a dark matter candidate from the lightest neutral scalar field, which is a mixture of the inert scalar doublet and the singlet scalar field $S$, in general. The $Z_4$ breaking mass terms are constrained by electroweak precision data and direct detection (DD) bounds for dark matter, favoring small mixings or almost degenerate masses for the DM scalars. As a result, we discuss the implications of the results for small neutrino masses and DD-safe dark matter.

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arXiv2025

Higgs portal vector dark matter at a low reheating temperature

In this study, we explore vector dark matter (DM) production in the early Universe focusing on a scenario with a low reheating temperature. One can achieve low reheat temperature in many ways, for example, by considering a longer lifetime of the inflaton field. We analyze the impact of various model parameters on DM production, including gauge coupling and reheat temperature, while incorporating all relevant constraints from DM relic density, collider bounds, and DM direct and indirect detection experiments. Our results reveal a strong correlation between DM mass and reheat temperature, with viable parameter space requiring $T_R/M_{W_D} \sim 0.1$. While DM production from decays is generally subdominant, we identify a regime where freeze-in production from decay is dominant due to the phase space suppression. For DM masses below 100 GeV, production is primarily driven by SM fermions, whereas higher masses come due to the Higgses annihilation. The enhanced coupling strength in our framework enables potential detection in direct and indirect detection and collider experiments. The direct detection experiments have already explored some parts of the region and future DARWIN will explore the further region whereas for indirect detection, the detection prospects for the present case are futile. We found that a very narrow region of the parameter space has been explored by the DM direct detection contrary to the WIMP DM case where most of the parameter space has been ruled out.

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arXiv2025

Multi-component dark matter and Galactic 511 keV $γ$-ray emission

We study multi-component dark matter scenarios and the Galactic 511 keV $γ$-ray emission line signal in the framework of a local, dark $U(1)_D$ extension of the Standard Model. A light vector dark matter particle associated with the dark $U(1)_D$ may decay and annihilate to electron-positron pairs. The produced positrons may in turn form positroniums that subsequently annihilate to two photons, accounting for the observed line signal of the Galactic 511 keV $γ$-ray emission. Three scenarios are investigated. First, we consider the minimal $U(1)_D$ extension where a dark gauge boson and a dark Higgs boson are newly introduced to the particle content. As a second scenario, we consider WIMP-type dark matter with the introduction of an extra dark fermion which, in addition to the dark gauge boson, may contribute to the dark matter relic abundance. It is thus a multi-component dark matter scenario with a UV-complete dark $U(1)_D$ symmetry. In particular, the vector dark matter may account for a small fraction of the total dark matter relic abundance. Finally, we consider the scenario where the dark matter particles are of the FIMP-type. In this case, both the light vector and fermion dark matter particles may be produced via the freeze-in and super-WIMP mechanisms. Considering theoretical and observational constraints, we explore the allowed parameter space where the Galactic 511 keV $γ$-ray line signal and the dark matter relic can both be explained. We also discuss possible observational signatures.

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arXiv2025

Recent $B^+ \!\to K^+ν\barν$ excess and muon $g-2$ illuminating light dark sector with Higgs portal

The Belle II collaboration recently announced that they observed the $B^+ \!\to K^+ν\barν$ decay process for the first time. This dineutrino mode of $B^+ \!\to K^+ν\barν$ has been theoretically identified as a very clean channel. However, their result encounters a $2.7{}^{}σ$ deviation from the Standard Model (SM) calculation. On the other hand, last year, Fermilab released new data on muon $g-2$ away from the SM expectation with $5{}^{}σ$. In this letter, we study the simplest UV-complete $\text{U}(1)_{\textsf{L}_μ- \textsf{L}_τ}^{}$-charged complex scalar Dark Matter (DM) model. Thanks to the existence of light dark Higgs boson and light dark photon, we can explain the observed relic density of DM and resolve the results reported by both Belle II and Fermilab experiments simultaneously. As a byproduct, the Hubble tension is alleviated by taking $ΔN_\textsf{eff}^{} \simeq 0.3$ induced by the light dark photon.

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arXiv2025

Small Neutrino Masses from a Decoupled Singlet Scalar Field

We propose a unified solution with $Z_4$ discrete symmetry for small neutrino masses and stability of dark matter. The Standard Model is extended with an inert doublet scalar, a dark singlet scalar, a spurion scalar and right-handed neutrinos, which all transform nontrivially under $Z_4$. After the $Z_4$ symmetry is broken to $Z_2$ by the VEV of the spurion, much below the mass scale of the dark singlet scalar, a small lepton number violating coupling for the inert doublet is generated at tree level, so small neutrino masses are obtained at one-loops for relatively light new fields. We discuss the important roles of the $Z_4$ symmetry for neutrino masses, dark matter physics and thermal leptogenesis.

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arXiv2024

Muon $(g-2)$ and Thermal WIMP DM in ${\rm U(1)}_{L_μ-L_τ} $ Models

The ${\rm U(1)}_{L_μ- L_τ}$ model is anomaly-free with the Standard Model (SM) fermion content, and can make substantial contributions to the muon $(g-2)$ at the level of $Δa_μ\sim O(10) \times 10^{-10}$ for $M_{Z'} \sim O(10-100)$ MeV and $g_X \sim (4 - 8) \times 10^{-4}$. In this light $Z'$ region, it was claimed that the model can also incorporate thermal WIMP dark matter (DM) if $M_{\rm DM} \sim M_{Z'}/2$. This setup relies on DM particles annihilating into SM particles through a $Z'$-mediated $s$-channel. In this work, we show that this tight relationship between $M_{Z'}$ and $M_{\rm DM}$ can be evaded or nullified both for scalar and spin-1/2 DM by considering the contributions from the dark Higgs boson ($H_1$). The dark Higgs boson plays an important role, not only because it gives mass to the dark photon but also because it introduces additional DM annihilation channels, including new final states such as $H_1 H_1$, $Z' Z'$, and $Z' H_1$. As a result, the model does not require a close mass correlation between the $Z'$ boson and dark matter $M_{\rm DM} \sim M_{Z'}/2$ any longer, allowing for a broader range of mass possibilities for both scalar and fermionic dark matter types. We explore in great details various scenarios where the $U(1)$ symmetry is either fully broken or partially remains as discrete symmetries, $Z_2$ or $Z_3$. This approach broadens the model's capacity to accommodate various WIMP dark matter phenomena in the light $Z'$ region where the muon $(g-2)_μ$ makes a sensitive probe of the model.

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arXiv2024

Axion-Mediated Inelastic Dark Matter

We consider the axion-mediated scattering processes between dark matter (DM) and nucleus. Substantial contributions are made via the CP-odd gluonic current which induces the spin-dependent process. Since the QCD axion is too feebly coupled to the visible particles, non-QCD axions are necessary for the current DM experiments to accomplish the ample sensitivity. In the case of multi-component DM models, the inelastic scattering processes also make sizable contributions to the direct detection. The supersymmetry (SUSY) and clockwork (CW) mechanism provide a realistic model for the QCD and non-QCD axions and the axion-mediated DM scattering processes. In the SUSY CW axion model, the lightest axino is the DM particle and the axions mediate the elastic and inelastic scattering processes. We show that the current and future XENONnT can produce relevant constraints for some parameter space of the model.

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arXiv2024

Non-thermal WIMPy Baryogenesis with Primordial Black Hole

We consider the possibility that the weakly interacting massive particles produced from the evaporation of primordial black hole can explain both the relic density of dark matter and the baryon asymmetry of the Universe, through their annihilation which violate B and CP-symmetry. We find that the primordial black hole with mass less than $10^7 {\rm g}$ is a good candidate as an source of TeV dark matter with the total annihilation cross section $\left\langleσ_a \upsilon\right\rangle \lesssim 10^{-7} \ {\rm GeV}^{-2}$ and the B-violating scattering cross section $\left\langleσ_B \upsilon\right\rangle \lesssim 2\times 10^{-9} \ {\rm GeV^{-2}}$. This large annihilation cross section of dark matter in this model would make it available to search them in the indirect search for dark matter such as gamma-ray or neutrino observations.

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arXiv2024

Muon $g-2$, dark matter, and neutrino mass explanations in a modular $A_4$ symmetry

We study a successful model to explain the muon anomalous magnetic moment originating from Yukawa-type interactions {in a supersymmetric theory}. Thanks to a modular $A_4$ flavor symmetry, any lepton flavor violations that spoil the model are forbidden. We also investigate a predictive radiative seesaw model including a dark matter (DM) candidate. At first, we construct the minimum model to satisfy the neutrino oscillation data and obtain several predictions such as Dirac CP and Majorana phases, the neutrino masses through $χ^2$ analysis. However, the minimum model would not provide our promising DM candidate. Thus, we minimally extend the model and find a good DM candidate. In the extended framework, we show the allowed regions to satisfy the muon anomalous magnetic moment and the observed relic density of dark matter in addition to predictions of the lepton sector.

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arXiv2024

Pseudo Nambu-Goldstone Boson DM with Linear Symmetry Breaking: Revisited

In this work, we revisit pseudo Nambu Goldstone boson (pNGB) DM model where global $U(1)$ dark symmetry is spontaneously broken as well as explicitly with broken by with linear symmetry breaking, focusing on the dark matter mass range in $500 {\rm GeV} \lesssim m_{\rm DM} \lesssim O(10)$ TeV. This model is interesting not only in its own in the context of pNGB DM, but also in the context of cosmological collider signatures from heavy particle mass regime without Boltzmann suppressions, $H \lesssim m_{\rm heavy} \lesssim 60 H$, through the chemical potential type interaction. After imposing perturbative unitarity, perturbativity, correct thermal relic density and constraints from colliders and (in)direct detection experiments, we find that pNGB DM mass is allowed up to $\sim 1 (10)$ TeV for the dark Higgs mass $m_{H_2} = 1 (100)$ TeV for the Higgs-dark Higgs mixing $\sin θ= 0.1$. We also consider the case where global $U(1)$ dark symmetry is not spontaneously broken, where DM is no longer pNGB. In this case, DM and dark Higgs masses are nearly degenerate in the range of a few TeV $\lesssim m_{{\rm DM}, H_2} \lesssim \sim 70$ TeV. Low mass region for pNGB DM and $H_2$ could be directly probed in colliders or indirect DM detections, whereas the heavy mass regime could be probed through the non-Gaussianity at the level of $f_{\rm NL} \sim O(0.01-10)$ if $H$ is as low as $O(1-10)$ TeV.

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arXiv2023

Supernova Axion Emissivity with $Δ(1232)$ Resonance in Heavy Baryon Chiral Perturbation Theory

In this paper, we evaluate the energy loss rate of supernovae induced by the axion emission process $π^- + p \to n + a$ with the $Δ(1232)$ resonance in the heavy baryon chiral perturbation theory for the first time. Given the axion-nucleon-$Δ$ interactions, we include the previously ignored $Δ$-mediated graphs to the $π^- + p \to n + a$ process. In particular, the $Δ^0$-mediated diagram can give a resonance contribution to the supernova axion emission rate when the center-of-mass energy of the pion and proton approaches the $Δ(1232)$ mass. With these new contributions, we find that for the typical supernova temperatures, compared with the earlier work with the axion-nucleon (and axion-pion-nucleon contact) interactions, the supernova axion emissivity can be enhanced by a factor of $\sim$4(2) in the Kim-Shifman-Vainshtein-Zakharov model and up to a factor of $\sim$5(2) in the Dine-Fischler-Srednicki-Zhitnitsky model with small $\tanβ$ values. Remarkably, we notice that the $Δ(1232)$ resonance gives a destructive contribution to the supernova axion emission rate at high supernova temperatures, which is a nontrivial result in this study.

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arXiv2023

Fermi-LAT GeV excess and muon $g-2$ in a modular $A_4$ symmetry

The recent measurement of muon anomalous magnetic dipole moment (muon $g-2$) suggests that there might exist new physics that dominantly interacts with muons. The observed gamma-ray excess from Fermi-LAT indicates that dark matter annihilates into a specific charged fermions. We propose a successful model simultaneously to explain the Fermi-LAT GeV gamma-ray excess and sizable muon $g-2$ with a modular $A_4$ symmetry. Due to nature of this symmetry, our DM only interacts with pairs of muon and we explain sizable muon $g-2$ without suffering from constraints of any lepton flavor violations. We numerically show our allowed spaces on each measurements of Fermi-LAT, relic density of DM and muon $g-2$, randomly scanning our input parameters.

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arXiv2022

Natural mass hierarchy among three heavy Majorana neutrinos for resonant leptogenesis under modular $A_4$ symmetry

It is clear that matter is dominant in the Universe compared to antimatter. We call this problem baryon asymmetry. The baryon asymmetry is experimentally determined by both cosmic microwave background and big bang nucleosynthesis measurements. To resolve the baryon number asymmetry of the Universe as well as neutrino oscillations, we study a radiative seesaw model in a modular $A_4$ symmetry. Degenerate heavy Majorana neutrino masses can be naturally realized in an appropriate assignments under modular $A_4$ with large imaginary part of modulus $τ$, and it can induce measured baryon number via resonant leptogenesis that is valid in around TeV scale energy theory. We also find that the dominant contribution to the CP asymmetry arises from Re[$τ$] through our numerical analysis satisfying the neutrino oscillation data.

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