arXiv subjects

Jin-Han Liang

Publications and source records attributed to Jin-Han Liang.

10 recordsLinked to original sources

arXiv2026

LZ Nuclear-Recoil Excess from Boosted Light Magnetic Dipole-dipole Dark Matter

The LZ collaboration has reported a nuclear-recoil excess near 248 keV with a global significance of $2.6\sigma$. Although halo dark matter with a magnetic dipole-dipole interaction and a TeV-scale mass provides the best fit to the excess among the interactions considered by LZ, it predicts a considerable number of events at lower recoil energies, where no excess is observed. We show that a boosted velocity distribution can alleviate this tension and provide a better fit to the LZ recoil spectrum. Moreover, the boost opens up the possibility of explaining the excess with much lighter dark matter, with masses down to the GeV scale. We demonstrate these features first in a model-independent analysis and then realize them in a concrete dark matter model, in which halo dark matter annihilates into on-shell mediators that subsequently decay into boosted dark-sector particles. Our results demonstrate that boosted dark sector particles provide a viable interpretation of the LZ excess.

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arXiv2026

Baryon-number-violating nucleon decays into a dark photon particle

Baryon-number-violating (BNV) nucleon decays into a light new particle represent an exciting yet experimentally unexplored frontier. In this work, we systematically study nucleon decays into a dark photon using a low-energy effective field theory extended with a dark photon $X$, referred to as $X$LEFT. We first construct a complete set of leading-order BNV $X$LEFT operators and then perform a systematic matching onto the chiral perturbation theory for operators involving light $u,d,s$ quarks that dominantly contribute to nucleon decays. Within the chiral framework, we derive general expressions for the decay widths of both two- and three-body nucleon decays and analyze the momentum distributions in the latter. Finally, we thoroughly reinterpret the existing experimental data on conventional two-body modes (into a lepton and a meson) to set lower bounds on partial lifetimes of the corresponding three-body modes involving an additional dark photon. These bounds allow us to further set stringent constraints on the $X$LEFT operators and other correlated decay modes. Our results provide a toolkit for future experimental and theoretical studies of these exotic nucleon decays.

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arXiv2026

Systematic study of lepton-flavor-violating dark matter interactions via indirect detection in effective field theories

Lepton-flavor-violating (LFV) interactions involving dark matter (DM) particles remain a largely unexplored area. In this study, we systematically investigate LFV DM interactions within the framework of effective field theories by analyzing astrophysical photons and positrons produced from DM annihilation. Employing the astrophysical photon and positron data collected by Fermi-LAT, INTEGRAL, XMM-Newton, and AMS-02, we place meaningful constraints on all leading-order effective operators involving a DM pair and a flavor-violating charged lepton pair. Our analysis covers the three well-known DM candidates: a scalar, a fermion, and a vector particle. For the photon flux, we consider contributions from final-state radiation, radiative decay, and inverse Compton scattering and examine their respective sensitivity regions across different DM masses and photon energies. We find that, for DM masses below $\mathcal{O}(20\,\rm GeV)$, INTEGRAL provides the most stringent constraints on annihilation cross sections and effective operators in all three LFV channels, whereas AMS-02 offers the strongest constraints above $\mathcal{O}(20~\rm GeV)$.

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arXiv2025

A New Probe for Long-Lived Particles at Higgs Factories: Displaced Photons in the Hadronic Calorimeter

The search for dark matter and other photon-portal long-lived particles (LLPs) at electron-positron colliders often relies on the mono-photon signature. At future Higgs factories operating at the $Z$-pole, this approach faces a critical challenge: the irreducible background from $e^+e^- \to ν\barνγ$ becomes overwhelming. We propose a novel strategy that overcomes this limitation by searching for displaced photons from LLP decays within the barrel of the hadronic calorimeter. This signature exploits the architectural shielding of the detector to create a nearly background-free environment. Our analysis demonstrates exceptional sensitivity to LLPs with decay lengths from $\sim$1 to $10^6$ meters, improving upon conventional searches by up to one order of magnitude for benchmark photon-portal models.

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arXiv2025

Probing lepton flavor violating dark matter scenarios via astrophysical photons and positrons

In this Letter we explore, for the first time, the constraints on lepton flavor violating (LFV) dark matter (DM) scenarios via the astrophysical photons and positrons, including both the annihilation and decay modes, ${\tt DM(+DM)}\to e^\pm \mu^\mp, e^\pm \tau^\mp, \mu^\pm \tau^\mp$. Given the presence of LFV interactions in various DM models and the challenge of probing such interactions at terrestrial facilities, such as DM direct detection and collider experiments, indirect detection offers a unique approach to investigating them. We utilize the currently available photon datasets from the XMM-Newton, INTEGRAL, and Fermi-LAT telescopes, along with the positron datasets from the AMS-02 satellite, to establish stringent bounds on the relevant annihilation cross sections or decay widths. In particular, we include contributions to the photon spectrum from final state radiation, radiative decays, and inverse Compton scattering. We find that the INTEGRAL (AMS-02) provides the most stringent bound on the annihilation cross sections and decay widths for DM mass below (above) approximately 20 GeV, which are comparable to those of their lepton flavor conserving counterparts.

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arXiv2025

A systematic investigation on vector dark matter-nucleus scattering in effective field theories

In this paper, we systematically investigate the general spin-one dark matter-nucleus interactions within the framework of effective field theories (EFT). We consider both the nonrelativistic (NR) and the relativistic EFT descriptions of the DM interactions with nucleons and quarks. In the NREFT framework, we present a complete list of NR operators for spin-one DM coupling to nucleons and compute their contributions to the DM response functions. Next, we consider all possible leading-order relativistic EFT operators between DM and light quarks and the photon, and perform NR reductions to match them onto the NREFT. We then derive the nuclear scattering rate from these interactions, and employ recent DM direct detection data (from both the nuclear recoil and the Migdal effect) to constrain all these EFT operators and DM electromagnetic properties. We find the elastic nuclear recoil data (from PandaX-4T, XENONnT, LZ, and DarkSide-50) set stringent bounds on the EFT coefficients for a DM mass above a few GeV while the Migdal effect datasets (from PandaX-4T, XENONnT, and DarkSide-50) can probe the DM mass region as small as 20 MeV. Lastly, we construct a UV complete model that can provide a complex spin-one DM candidate, and at the same time generate DM-quark/photon operators discussed in this work.

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arXiv2024

Revisiting general dark matter-bound-electron interactions

In this Letter we revisit general dark matter (DM)-bound-electron interactions studied previously in the influential work [R. Catena {\it et al.,} Atomic responses to general dark matter-electron interactions, Phys. Rev. Res. 2, 033195 (2020)] For the most general DM-electron nonrelativistic or relativistic interactions for DM with spin up to 1, we find the average ionization matrix element squared can be organized into three terms, each of which is a product of a DM response function ($a_{0,1,2}$) and a linear combination ($\widetilde W_{0,1,2}$) of the four atomic response functions ($W_{1,2,3,4}$) given in that work, $ \widetilde W_0 = W_1, \, \widetilde W_1 = |\pmb{v}_0^\perp|^2 W_1 - 2 {m_e\, \pmb{q}\cdot \pmb{v}_0^\perp \over \pmb{q}^2} W_2 + W_3,\, \widetilde W_2 = { (\pmb{q}\cdot \pmb{v}_0^\perp)^2 \over \pmb{q}^2} W_1 - 2 {m_e\, \pmb{q}\cdot \pmb{v}_0^\perp \over \pmb{q}^2} W_2 + {m_e^2 \over \pmb{q}^2}W_4$. Furthermore, we find a crucial minus sign was missed for the calculation of $W_2$ in that work, which has significant phenomenological consequences when explaining experimental bounds on specific DM scenarios. Due to the corrected sign, there can be significant cancellations between the $W_2$ and $W_{3,4}$ terms, so that $\widetilde W_{1,2}$ are dominated by the usual response function $W_1$ in some cases. Many DM scenarios involving DM or electron axial-vector current can yield $W_2$ and thus are potentially affected by the sign. As an example, we show that the recent XENON1T constraint on the fermionic DM anapole moment is weakened by a factor of 2 or so. We also present a complete list of NR operators for spin-1 DM and compute their contributions to the DM response functions.

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arXiv2024

Comprehensive constraints on fermionic dark matter-quark tensor interactions in direct detection experiments

Effective field theory (EFT) provides a model-independent framework for interpreting the results of dark matter (DM) direct detection experiments. In this study, we demonstrate that the two fermionic DM-quark tensor operators, $(\barχ iσ^{μν} γ^5 χ) (\bar{q} σ_{μν}q)$ and $(\barχ σ^{μν} χ) (\bar{q} σ_{μν} q)$, can contribute to the DM electric and magnetic dipole moments via nonperturbative QCD effects, in addition to the well-studied contact DM-nucleon operators. We then investigate the constraints on these two operators by considering both the contact and the dipole contributions using the XENON1T nuclear recoil and Migdal effect data. We also recast other existing bounds on the DM dipole operators, derived from electron and nuclear recoil measurements in various direct detection experiments, as constraints on the two tensor operators. For $m_χ\lesssim 1\,\rm GeV$, our results significantly extend the reach of constraints on the DM-quark tensor operators to masses as low as $5\,\rm MeV$, with the bound exceeding that obtained by the Migdal effect with only contact interactions by an order of magnitude or so. In particular, for the operator $(\barχ σ^{μν}iγ_5 χ) (\bar{q} σ_{μν}q)$ with DM mass $m_χ\gtrsim 10\,\rm GeV$, the latest PandaX constraint on the DM electric dipole moment puts more stringent bounds than the previous direct detection limit.

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arXiv2024

A systematic investigation on dark matter-electron scattering in effective field theories

In this paper, we systematically investigate the general dark matter-electron interactions within the framework of effective field theories (EFT). We consider both the non-relativistic (NR) EFT and the relativistic EFT descriptions of the interactions with the spin of dark matter (DM) up to one, i.e., the scalar ($ϕ$), fermion ($χ$), and vector $(X)$ DM scenarios. We first collect the leading-order NR EFT operators describing the DM-electron interactions, and construct especially the NR operators for the vector DM case. Next, we consider all possible leading-order relativistic EFT operators including those with a photon field and perform the NR reduction to match them onto the NR EFT. Then we rederive the DM-bound-electron scattering rate within the NR EFT framework and find that the matrix element squared, which is the key input that encodes the DM and atomic information, can be compactly decomposed into three terms. Each term is a product of a DM response function $(a_{0,1,2})$, which is essentially a factor of Wilson coefficients squared, and its corresponding generalized atomic response function ($\widetilde W_{0,1,2}$). Lastly, we employ the electron recoil data from the DM direct detection experiments (including XENON10, XENON1T, and PandaX-4T) to constrain all the non-relativistic and relativistic operators in all three DM scenarios. We set strong bounds on the DM-electron interactions in the sub-GeV region. Particularly, we find that the latest PandaX-4T S2-only data provide stringent constraints on dark matter with a mass greater than approximately 20 MeV, surpassing those from the previous XENON10 and XENON1T experiments.

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arXiv2023

Dark Sector Effective Field Theory

We introduce the effective field theory of two different light dark particles interacting with the standard model (SM) light states in a single vertex, termed dark sector effective field theory (DSEFT). We focus on the new light particles with spin up to 1 and being real in essence, namely, new real scalars $ϕ$ and $S$, Majorana fermions $χ$ and $ψ$, and real vectors $X_μ$ and $V_μ$. In the framework of low energy effective field theory with QED and QCD symmetry, the DSEFT can be classified into six categories, including the scalar-scalar-SM ($ϕS$-SM), fermion-fermion-SM ($χψ$-SM), vector-vector-SM ($X V$-SM), scalar-fermion-SM ($ϕχ$-SM), scalar-vector-SM ($ϕX$-SM), and fermion-vector-SM ($χX$-SM) cases. For each case, we construct the effective operator basis up to canonical dimension 7, which will cover most interesting phenomenology at low energy. As a phenomenological example, we investigate the longstanding neutron lifetime anomaly through the neutron dark decay modes $n \to χϕ\text{ or } χX$ from the effective interactions in the fermion-scalar-SM or fermion-vector-SM case. When treating the light fermion as a dark matter candidate, we also explore the constraints from DM-neutron annihilation signal at Super-Kamiokande. We find the neutron dark decay in each scenario can accommodate the anomaly, at the same time, without contradicting with the Super-Kamiokande limit.

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