arXiv subjects

Seong-Sik Kim

Publications and source records attributed to Seong-Sik Kim.

10 recordsLinked to original sources

arXiv2026

Self-resonant dark matter with $Z_4$ gauged symmetry

We present a new model for two-component scalar dark matter (DM), consisting of two complex scalar fields. In this model, both the DM components are stable due to the remaining $Z_4$ gauge symmetry, which is the remnant of the $U(1)^\prime$ local symmetry. When the resonance condition for DM masses is fulfilled, we show that the elastic co-scattering processes between two components of dark matter ($u$-channel processes) are enhanced due to the Yukawa potential with a small effective mass for the lighter DM mediator, so we can use such co-scattering processes for dark matter to explain the small-scale problems at galaxies. Moreover, there are also semi-annihilation processes that two components of dark matter annihilate into one dark matter particle and a dark photon/Higgs, which are enhanced by the $u$-channel Sommerfeld factor. Focusing on some benchmark models for two-component dark matter satisfying the observed relic density, we obtain the bounds for the dark photon portal couplings from the direct detection for boosted dark matter, which is produced from the semi-annihilation processes at the galactic center.

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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

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 Proton Lifetime in SUSY SU(5) GUTs with Split Superpartners

We consider the interplay of the muon $g-2$ anomaly and the proton decay in the SUSY SU(5) GUTs with generation-independent scalar soft masses. In these scenarios, we introduce a number of $\bf 5+{\bar 5}$ messenger fields with doublet-triplet splitting in general gauge mediation to transmit SUSY breaking to the visible sector by gauge loops. As a result, squarks and sleptons receive generation-independent soft SUSY breaking masses, which are split already at the messenger scale. Taking into account the perturbative unification of gauge couplings as well as the bounds from electroweak precision and vacuum stability bounds, we showed the parameter space in general gauge mediation to explain the muon $g-2$ anomaly with smuon and sneutrino loops while evading the strong bounds on squarks and gluinos from the Large Hadron Collider. We also obtained the dominant Higgsino contributions to the proton decay mode, $p\to K^+{\barν}$, with general generation-independent sparticle masses for squarks and sleptons. Even for split scalar soft masses in our model, however, we found that the bounds from the proton decay are satisfied only if the effective Yukawa couplings of the colored Higgsinos are suppressed further by a factor of order $10^{-4}-10^{-3}$. We illustrated how such a suppression factor is realized in orbifold GUTs in the extra dimension where the colored Higgsinos in the bulk are not coupled to the matter fields localized at the orbifold fixed points at the leading order.

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arXiv2023

Positivity Bounds on Higgs-Portal Freeze-in Dark Matter

We consider the relic density and positivity bounds for freeze-in scalar dark matter with general Higgs-portal interactions up to dimension-8 operators. When dimension-4 and dimension-6 Higgs-portal interactions are proportional to mass squares for Higgs or scalar dark matter in certain microscopic models such as massive graviton, radion or general metric couplings with conformal and disformal modes, we can take the dimension-8 derivative Higgs-portal interactions to be dominant for determining the relic density via the 2-to-2 thermal scattering of the Higgs fields after reheating. We discuss the implications of positivity bounds for microscopic models. First, massive graviton or radion mediates attractive forces between Higgs and scalar dark matter and the resultant dimension-8 operators respect the positivity bounds. Second, the disformal couplings in the general metric allow for the subluminal propagation of graviton but violate the positivity bounds. We show that there is a wide parameter space for explaining the correct relic density from the freeze-in mechanism and the positivity bounds can curb out the dimension-8 derivative Higgs-portal interactions nontrivially in the presence of the similar dimension-8 self-interactions for Higgs and dark matter.

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arXiv2023

Positivity Bounds on Higgs-Portal Dark Matter

We consider the positivity bounds for WIMP scalar dark matter with effective Higgs-portal couplings up to dimension-8 operators. Taking the superposed states for Standard Model Higgs and scalar dark matter, we show that the part of the parameter space for the effective couplings, otherwise unconstrained by phenomenological bounds, is ruled out by the positivity bounds on the dimension-8 derivative operators. We find that dark matter relic density, direct and indirect detection and LHC constraints are complementary to the positivity bounds in constraining the effective Higgs-portal couplings. In the effective theory obtained from massive graviton or radion, there appears a correlation between dimension-8 operators and other effective Higgs-portal couplings for which the strong constraint from direct detection can be evaded. Nailing down the parameter space mainly by relic density, direct detection and positivity bounds, we find that there are observable cosmic ray signals coming from the dark matter annihilations into a pair of Higgs bosons, $WW$ or $ZZ$.

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arXiv2022

The $SU(2)_D$ lepton portals for muon $g-2$, $W$ boson mass and dark matter

We propose a novel model which extends the Standard Model (SM) by introducing a $SU(2)_D$ gauge symmetry. In this model, a dark $SU(2)_D$ Higgs doublet and a Higgs bi-doublet can contribute to the muon $g-2$ anomaly and the $W$ boson mass, remaining in tune with the recent experimental results. At the same time, the isospin charged gauge boson of $SU(2)_D$ becomes a plausible candidate for Dark Matter(DM). We find that the resulting parameter space can fit the muon $g-2$, the $W$ boson mass and the DM constraints simultaneously.

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arXiv2022

The $SU(2)_D$ lepton portals for muon $g-2$, $W$ boson mass and dark matter

We propose a novel model for lepton flavor and dark matter based on the $SU(2)_D$ gauge symmetry and vector-like leptons in its fundamental representations. We introduce a dark $SU(2)_D$ Higgs doublet and a Higgs bi-doublet for the mass mixing between the vector-like lepton and the lepton. As a result, the seesaw lepton masses are generated and there are sizable one-loop contributions to the muon $g-2$ via the $SU(2)_D$ gauge bosons and the relatively heavy vector-like lepton, as indicated in Fermilab E989. The tree-level mass mixing between the $Z$ boson and the isospin neutral gauge boson of $SU(2)_D$ in our model accounts for the shift in the $W$ boson mass, being consistent with Tevatron CDFII. Finally, we show that the isospin charged gauge boson of $SU(2)_D$ becomes a plausible candidate for dark matter with a small mass splitting tied up to the modified $W$ boson mass, and there is a viable parameter space where the favored corrections to the muon $g-2$ and the $W$ boson mass and the dark matter constraints are simultaneously fulfilled.

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arXiv2022

Models for Self-resonant Dark Matter

We consider a new mechanism for enhancing the self-scattering and annihilation cross sections for dark matter with multiple components but without a light mediator. The lighter dark matter component plays a role of the $u$-channel pole in the elastic co-scattering for dark matter, leading to a large self-scattering cross section and a Sommerfeld enhancement for semi-annihilation processes. Taking the effective theory approach for self-resonant dark matter, we present various combinations of multiple dark matter components with spins and parities, showing a $u$-channel pole in the co-scattering processes. Adopting dark photon and dark Higgs portals for self-resonant dark matter, we impose the relic density condition as well as indirect detection bounds on semi-annihilation channels with a Sommerfeld enhancement and discuss potential signals for direct detection experiments.

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arXiv2021

Self-resonant Dark Matter

We present a novel mechanism for Sommerfeld enhancement for dark matter interactions without the need for light mediators. Considering a model for two-component dark matter with a triple coupling, we find that one of dark matter particles leads to an $u$-channel resonance in dark matter elastic scattering. From the sum of the $u$-channel ladder diagrams, we obtain a Bethe-Salpeter equation with a delay term and identify the Sommerfeld factor from the elastic scattering of two dark matter components for the first time. We discuss the implications of our results for enhancing dark matter self-scattering and annihilation.

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