arXiv subjects

Lin-Yun He

Publications and source records attributed to Lin-Yun He.

4 recordsLinked to original sources

arXiv2026

Graviton energy spectra arising from the KSVZ axion model

Axion, the goldstone boson arising from the spontaneous breaking of a global $U(1)$ Peccei-Quinn symmetry, provides a dynamical solution to the strong CP problem and is an excellent dark matter candidate. Various experiments are designed to search for the axion, however no confirmative signal has been observed. On the other hand, there are also hypothetical heavy particles in axion models, such as the heavy scalar $s$, which is the CP-even component of the complex scalar that carries $U(1)_{PQ}$ charge, and the vector-like heavy quark (VLQ) in the Kim-Shifman-Vainshtein-Zakharov~(KSVZ) axion model. Studying signals induced by them are helpful for axion searches. In this paper, we calculate the graviton bremsstrahlung energy spectrum arising from the decay of the heavy scalar or VLQ in the KSVZ model. The result shows that these heavy particles can emit ultrahigh-frequency gravitational waves (GWs), with the peak frequency depending on the model's parameter inputs. In addition, the graviton spectrum is distinguished from the thermal GW background at high frequencies if there is an early matter-dominated era induced by these heavy particles. Future measurements of ultrahigh-frequency GWs may provide indirect evidence for the KSVZ axion.

hep-ph↗

arXiv2025

Mono-lepton Signature of a Neutrino-philic Dark Fermion at Hadron Colliders

Searching for dark matter at high-energy colliders and direct detection experiments can effectively cover nearly the entire mass range from the MeV to the TeV scale. In this paper, we focus on four-fermion contact interactions formulated within the framework of Effective Field Theory. Specifically, we present a detailed analysis of mono-lepton production at the LHC. Our results demonstrate that tensor operators exhibit superior sensitivity in the mono-lepton channel, constraining energy scales up to 3\,TeV for a nearly massless dark fermion using current LHC data. Moreover, these operators mediate both spin-independent and spin-dependent absorption processes in nuclear targets. A systematic comparison of constraints between direct detection experiments and collider measurements reveals the LHC's distinct advantage in exploring sub-GeV dark matter candidates while maintaining competitive sensitivity at the TeV scale. Notably, direct detection experiments such as Super-Kamiokande and Borexino achieve complementary constraints in the 10-100\,TeV mass range through their unique capabilities: utilization of light nuclei targets, large exposure volumes, and distinctive features of the recoil energy spectra.

hep-ph↗

arXiv2024

Constraining Gluonic Contact Interaction of a Neutrino-philic Dark Fermion at Hadron Colliders and Direct Detection Experiments

Weakly interacting fermions with the Standard Model particles are promising candidates for the dark matter. In this paper, we study signatures of the gluonic interactions of a dark fermion and a neutrino at hadron colliders and direct detection experiments. The lowest order interactions are described by contact operators in dimension 7. At hadron colliders, the mono-jet production is the most sensitive channel. And these operators can also induce both spin-independent and spin-dependent absorption of the dark fermion at nuclear targets. We show that for a nearly massless dark fermion, the energy scales are constrained to be higher than 500 GeV and 1.2 TeV by the current LHC and HE-LHC searches, respectively. Furthermore, we also find that almost all the parameter space accessible by the spin-independent absorption has been excluded by the current LHC constraints. In contrast, for spin-dependent absorption at light nuclear targets there is still some parameter space which cannot be reached by current and upcoming LHC searches.

hep-ph↗

arXiv2024

Complementary Search of Fermionic Absorption Operators at Hadron Collider and Direct Detection Experiments

Instead of the energy recoil signal at direct detection experiments, dark fermion appears as missing energy at hadron colliders. For a fermionc dark sector particle that coupled with quarks and neutrino via absorption operators, its production at collider is accompanied by an invisible neutrino. We study in details the mono-$X$ (photon, jet, and $Z$) productions at the Large Hadron Collider (LHC). We start from the quark-level absorption operators to make easy comparison between the collider and direct detection experiments. In other words, we study the model-independent constraints on a dark fermion with absorption operator. In addition, the interplay and comparison with the possible detection at the neutrino experiments, especially Borexino, is also briefly discussed. We find that light nuclear target can provide the stronger constraints on both spin-dependent and spin-independent absorption operators.

hep-ph↗