arXiv subjects

XinXin Qi

Publications and source records attributed to XinXin Qi.

12 recordsLinked to original sources

arXiv2026

Nonthermal Solar Stalling of an Inelastic Scalar Signal in Xenon

The LUX-ZEPLIN experiment has reported one nuclear-recoil candidate at $248\kev$ in an extended-energy search. We construct an anomaly-free $U(1)_{B-3L_τ}$ model in which an $840\gev$ complex scalar undergoes an endothermic transition with splitting $320\kev$. A $160\mev$ vector with dark charge $Q_χ=1$ gives $0.958$ accepted events in a public LZ-response reconstruction while scalar annihilation yields $Ωh^2=0.1200$. The physical nucleon ratio $f_n/f_p=-0.86985$ suppresses solar iron capture, leaving $C_\odot=1.09\times10^{19}\,{\rm s}^{-1}$. We then evolve captured particles in energy, angular momentum, and internal state, including finite collision rates, thermal nuclear velocities, and the excited-state decay. The distribution stalls at an equivalent radius $r_{\rm eff}=0.194$--$0.198\rsun$, for which $Γ_{\rm ann}=(1.33$--$1.38)\times10^{15}\,{\rm s}^{-1}$, below a model-specific IceCube public-data proxy by more than three orders of magnitude. The benchmark also lies below the dedicated NA64 $B-L$ limit. Thus solar-neutrino bounds on electroweak inelastic dark matter do not transfer model-independently to light-mediator scalar realizations.

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arXiv2026

Heavy fermionic dark matter in a secluded $Z_4$ framework

We investigate heavy Majorana dark matter $χ$ in a secluded scalar sector with a spontaneously broken $Z_4$ symmetry. The symmetry forbids a bare Majorana mass, providing a dynamical origin for the dark matter mass, while a residual $Z_2$ symmetry ensures its stability. We find that the thermal relic abundance can be predominantly determined by the secluded annihilation process $χχ\to h_2h_2$ , where $h_2$ is the new heavy Higgs boson. The dominant annihilation process is p-wave suppressed at low velocities, leading to a strong suppression of the present-day annihilation rate relative to that at freeze-out. Consequently, the model can accommodate a heavy thermal dark matter candidate with highly suppressed indirect-detection signals while retaining potentially testable signatures in direct-detection experiments.

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arXiv2026

FIMPs in a two-component dark matter model with $Z_2 \times Z_4$ symmetry

We investigate the FIMP-FIMP regime in a two-component dark matter model with a $Z_2\times Z_4$ symmetry, where a singlet scalar $S$ and a Majorana fermion $χ$ serve as the dark matter candidates. A singlet scalar $S_0$ with vacuum expectation value $v_0$ generates the fermion mass through the relation $m_χ=y_{sf}v_0$. We show that the tiny Yukawa coupling $y_{sf}$ needed to reproduce the observed relic abundance naturally leads to a large symmetry-breaking scale $v_0$, which induces an ultra-feeble portal coupling $λ_{ds}$ responsible for the production of $S$. We find that $λ_{ds}$ can reach values of $10^{-25}\lesssimλ_{ds}\lesssim10^{-13}$, while gravitational freeze-in provides an irreducible contribution at extremely small couplings. Our results demonstrate that the relic abundance constraint, combined with symmetry breaking and freeze-in dynamics, naturally drives the portal interaction responsible for scalar dark matter production into the ultra-feeble regime.

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arXiv2025

Mixed WIMP-FIMP scenario in a two-component dark matter model

We consider the mixed WIMP-FIMP scenario in a two-component dark matter model with $Z_2 \times Z_4$ symmetry, where a singlet scalar $S$ and a Majarano fermion $χ$ are introduced as dark matter candidates. We also introduce another singlet scalar $S_0$ with a non-zero vacuum expectation value to the SM so that the fermion dark matter can obtain mass after spontaneous symmetry breaking. Either $S$ or $χ$ relic density can be generated via the "Freeze-out" mechanism. In contrast, the other DM candidate relic density is obtained by the "Freeze-in" mechanism, and we therefore have two different cases. In the case of $χ$ as WIMP and $S$ as FIMP, we perform random scans to estimate the allowed parameter space consistent with the dark matter constraint. The results show that this case is viable over a wide range of dark matter masses with the Yukawa coupling of $S_0$ and $χ$ should be larger than 1. Instead, for the case of $S$ as WIMP and $χ$ as FIMP, the viable parameter space is more constrained by the direct detection experiements, and we have two regions with $m_S \approx 62.5$ GeV and $m_S>400$ GeV under the constraints, which is consistent with the singlet scalar DM result but the scalar DM mass can be as low as a few hundred GeV for the heavy mass region in the model.

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arXiv2025

A two-component dark matter model with $Z_2 \times Z_4$ symmetry

We consider a two-component dark matter model with $Z_2 \times Z_4$ symmetry, where a singlet scalar $S$ and a Majorana fermion $χ$ are introduced as dark matter candidates. We also introduce another singlet scalar $S_0$ with a non-zero vacuum expectation value to the SM so that the fermion dark matter can obtain mass after spontaneous symmetry breaking. We have a new Higgs boson in the model and in the case of the decoupling limit, the fermion dark matter production is only determined by $S$ and the new Higgs boson. The mass hierarchy of these new particles can make a difference in the reaction rate of dark matter annihilation processes, contributing to different viable parameter spaces for different mass orderings. We randomly scanned the parameter space with six various cases under relic density constraint and found that when $χ$ is the lightest among the dark sector, $χ$ production is generated via the so-called forbidden channels. Moreover, we consider the combined limits arising from Higgs invisible decay, dark matter relic density and direct detection constraints. Within the chosen parameter space, direct detection results put the most stringent constraint, and we have a more flexible value for the scalar dark matter mass when the mass of $χ$ is not smaller than the new Higgs boson mass.

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arXiv2024

Z_5 two-component dark matter in the Type-II seesaw mechanism

We consider the Z5 two-component dark matter model within the framework of the Type-II seesaw mechanism. Due to the new annihilation processes related to triplets, the light component cannot necessarily be dominant in the dark matter relic density, which is different from the Z5 two-component dark matter model in the SM. The model is considered to explain the excess of electron-positron flux measured by the AMS-02 Collaborations in this work, which is encouraged by the decay of the triplets arising from dark matter annihilations in the Galactic halo. We discuss the cases of the light and heavy components determining dark matter density within a viable parameter space satisfying relic density and direct detection constraints, and by fitting the antiproton spectrum observed in the PAMELA and AMS experiments, we find that the parameter space is flexible and the electron-positron flux excess can be obtained in both cases with the mass of two dark matter particles being larger than that of the triplets'.

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arXiv2024

Dark matter, leptogenesis and Z' in the B-L model

We discuss the interplay between dark matter, leptogenesis and a new gauge boson $Z^\prime$ in the $B-L$ model. A fermion dark matter $χ$ carrying $U(1)_{B-L}$ charge is introduced to the model but not coupling with other particles. We consider the freeze-out and freeze-in mechanisms, and obtain the correct relic density respectively. We have scanned the feasible parameter space and found that the dark matter direct detection experiments imposed the most stringent constraints on the parameter space. The constraint on the parameter space places a limit on the mass of dark matter with $m_χ \approx 1/2 M_{Z'}$ within a narrow region in the case of freeze-out scenario, and we can obtain the right baryon asymmetry result in the case of $m_χ\subset[654$ GeV, 664 GeV]. For the freeze-in scenario, we have a much broader parameter space for $m_χ$ and $M_{Z^\prime}$ but $g_{BL}$ is restricted at $10^{-5}$ level for $Q=0.1$. In both scenarios, $g_{BL}-M_{Z^\prime}$ is limited within a narrow region by the dark matter relic density, direct detection and baryon asymmetry constraints.

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arXiv2023

Non-thermal dark matter production and leptogenesis in a $L_μ-L_τ$ model

We discuss the possibility of light scalar dark matter generated by right-handed neutrino in a $L_μ-L_τ$ model, in which the dark matter $ϕ_{dm}$ carries $U(1)_{L_μ-L_τ}$ charge but it is a singlet in the Standard Model. We discuss the case that dark matter production mainly comes from scattering associated with a pair of right-handed neutrinos non-thermally while other related processes are highly suppressed. A feasible parameter space is considered and we found the correct dark matter relic density can be obtained without influencing the result of leptogenesis result. The heavier right-handed neutrino will induce colder dark matter production and the allowed dark matter mass region is $[\rm 10^{-5}\ GeV,0.1\ GeV]$.

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arXiv2023

Inflation and Dark Matter in the $Z_5$ Model

We discuss the possibility of unifying dark matter physics and inflation in the $Z_5$ model of the two-component dark matter. Inflation driven by the two-component dark matter fields can be divided into two cases, singlet dark matter inflation and mixed dark matter inflation, where both two-component play the role of inflaton in the latter case. For dark matter, we focus on the mixed dark matter inflation case. We show a viable parameter space that satisfies the theoretical and dark matter relic density constraint in the case of successful inflation. It turns out that the dark matter density is dominated by the light component, which is consistent with the feature of the $Z_5$ model of the two-component dark matter.

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arXiv2023

Interplay between dark matter and leptogenesis in a common framework

We consider the interplay between dark matter and leptogenesis in a common framework, where three right-handed neutrinos, one fermionic dark matter and two singlet scalars are introduced into the Standard Model. The mixing of the two singlet scalars not only determine the dark matter relic density but also connect right-handed neutrino with dark matter. We consider that the baryon asymmetry is generated via the resonant leptogenesis and the right-handed neutrino masses are at TeV level. We present a viable parameter space satisfying relic density constraint, and the parameter space is more flexible in the case of a larger mixing angle. We found that the existence of dark matter in the model can not only dilute the baryon asymmetry but can also generate a larger baryon asymmetry due to the process of dark matter annihilation into a pair of right-handed neutrinos even though dark matter mass is lighter than right-handed neutrino mass. The enhanced effect depends on the dark matter mass $m_χ$ as well as right-handed neutrino mass $m_N$, and one still can find a baryon asymmetry enhanced in the case of $m_N=800$ GeV.

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arXiv2022

Scalar dark matter with $Z_3$ symmetry in Type-II Seesaw

We study a simple complex scalar singlet dark matter (DM) model with $Z_3$ symmetry in the framework of type-II seesaw mechanism. We use the model to explain the excess of electron-positron flux measured by AMS-02, DAMPE and Fermi-LAT collaborations, which is encouraged by the decay of the triplets produced from dark matter annihilations in the Galactic halo. We focus on the non-degenerate case in which the mass of DM is larger than that of the triplets' and deliberately alleviate the leptophilic properties of the DM, so that the semi-annihilation effects are enhanced. With the guarantee of $Z_3$ symmetry, by fitting the antiproton spectrum observed in PAMELA and AMS experiments, we find that the DM cubic terms and the couplings between DM and Higgs are strongly constrained, leading to the semi-annihilation cross section fraction less than $3\%$ when DM mass is given at 3 TeV.

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arXiv2021

Scalar dark matter and Muon $g-2$ in a $U(1)_{L_μ-L_τ}$ model

We consider a simple scalar dark matter model within the frame of gauged $L_μ-L_τ$ symmetry. A gauge boson $Z'$ as well as two scalar fields $S$ and $Φ$ are introduced to the Standard Model (SM). $S$ and $Φ$ are SM singlet but both with $U(1)_{L_μ-L_τ}$ charge. The real component and imaginary component of $S$ can acquire different masses after spontaneously symmetry breaking, and the lighter one can play the role of dark matter which is stabilized by the residual $Z_2$ symmetry. A viable parameter space is considered to discuss the possibility of light dark matter as well as co-annihilation case, and we present current $(g-2)_μ$ anomaly, Higgs invisible decay, dark matter relic density as well as direct detection constriants on the parameter space.

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