arXiv subjects

Yuanchao Lou

Publications and source records attributed to Yuanchao Lou.

5 recordsLinked to original sources

arXiv2026

Fermionic Dark Matter Absorption and the High-Energy Event in LUX-ZEPLIN

The LUX-ZEPLIN (LZ) experiment has reported a single candidate event in the high-energy nuclear recoil window $248\pm32.5\ \mathrm{keV}_{\mathrm{nr}}$ with an exposure of $2.84\ \mathrm{ton}\cdot\mathrm{yr}$, while the low-energy spectrum remains consistent with background expectations. We demonstrate that this excess can be naturally explained by the neutral-current absorption of fermionic dark matter on xenon nuclei. For a dark matter mass $m_\chi \simeq 247\ \mathrm{MeV}$, the coherent absorption process produces a monoenergetic nuclear recoil at $E_R \simeq 248\ \mathrm{keV}_{\mathrm{nr}}$. At this momentum transfer, the absorption process enters the incoherent regime, where scattering off individual nucleons produces a broad recoil spectrum extending from $\sim 200\ \mathrm{keV}$ to $100.2\ \mathrm{MeV}$. We show that a single effective field theory coupling can simultaneously produce one event in the $248\pm32.5\ \mathrm{keV}_{\mathrm{nr}}$ window while remaining consistent with the non-observation of events in neighboring energy regions. The required single-nucleon absorption cross section is $\sigma_{\chi N}^{\mathrm{NC}} = 1.07\times10^{-46}\ \mathrm{cm}^2$, corresponding to an effective field theory scale $\Lambda \simeq 11.5\ \mathrm{TeV}$. However, a recasting analysis of KamLAND data on the neutron-emission channel $\chi+{}^{12}\mathrm{C} \to \nu + n + {}^{11}\mathrm{C}^*$ excludes this benchmark parameter space, establishing a significant tension between the LZ excess interpretation and existing constraints from large-volume scintillator detectors. We discuss the implications of this tension and prospects for resolving it with future dedicated high-energy analyses.

hep-ph↗

arXiv2026

Migdal Ionization as a Probe of Light Dark Matter from Nuclear Transition

Nuclear reactors serve as a key artificial source of light dark matter. Direct detection of reactor-produced dark matter faces substantial obstacles, since quenching effects suppress conventional elastic scattering signals below detector thresholds. We present a new search strategy utilizing the Migdal effect in germanium detectors to probe light dark matter produced via nuclear de-excitation from reactors. Using ON-OFF residual spectra from the TEXONO experiment, we set a new stringent limit on the dark matter and nucleus interaction over the mass range $0.01\,\text{MeV}\le m_\chi \lesssim 2.6\,\text{MeV}$, which provides a complementary bound to existing cosmological and astrophysical limits.

hep-ph↗

arXiv2026

Probing Dark Photons from Nuclear De-excitation in Reactor Neutrino Experiment

Reactor neutrino experiments serve as powerful probes of light new physics. We investigate MeV-scale visible dark photons ($A'$) produced in nuclear reactors through nuclear de-excitation following neutron capture $N^*\to N A'$. Compared with the conventional Compton-like production process $\gamma e^-\to A'e^-$, the nuclear de-excitation yields on-shell dark photons with masses up to the nuclear transition energy. Using data from the TEXONO CsI(Tl) detector, we derive the new constraints on the kinetic mixing parameter $\epsilon$ for dark photon masses in the range $0.1\,\mathrm{MeV} < m_{A'} < 6.9\,\mathrm{MeV}$. We find that nuclear de-excitation not only extends the mass reach of reactor searches to higher dark photon masses but also provides a stronger limit than the Compton-like production process.

hep-ph↗

arXiv2025

Are 2HDMs with a gauged $U(1)$ symmetry alive?

We investigate the phenomenology of 2 Higgs doublet models (2HDMs) with a new $U(1)$ gauge symmetry, $U(1)_X$, by which flavor changing neutral currents are forbidden at tree level. As an important consequence of the spontaneous breaking of both the $U(1)_X$ and electroweak symmetries by electroweak vacuum expectation values, upper limits appear on masses of an additional gauge boson $Z'$ and extra Higgs bosons which are less than the TeV scale. In addition, the standard model (SM) like Higgs boson $h$ and a heavier Higgs boson $H$ mainly decay into a pair of $Z'$ which induces four lepton final states. These new decay modes cannot be suppressed by taking no $Z$-$Z'$ mixing and/or the Higgs alignment limit. We find that the minimum setup of these 2HDMs has been excluded by current data for four lepton searches at LHC. Such severe constraints can, however, be avoided by introducing a pair of vector-like fermions $\chi$ which are singlet under the SM symmetry but charged under $U(1)_X$, and can be a candidate of dark matter. Thanks to the existence of $\chi$, $Z'$ can mainly decay into $\chi\bar{\chi}$ instead of SM leptons. As benchmark models, we consider the $U(1)_H$ and $U(1)_R$ models realized by fixing specific $U(1)_X$ charges, and find regions of parameter space allowed by theoretical and current experimental constraints. We clarify that $m_H \in [160, 220]$ GeV and $\tan \beta \in [3, 4.4]$ are allowed in the $U(1)_H$ model, while $m_H \in [160, 380]$ GeV and $\tan \beta \in [1.6, 4.4]$ are allowed in the $U(1)_R$ model. In both the models, the $Z'$ mass is constrained to be $100~\text{GeV} \lesssim m_{Z'} \lesssim 110$ GeV. Such a quite limited parameter space can further be explored at future collider experiments, e.g., High-Luminosity LHC and lepton colliders.

hep-ph↗

arXiv2024

Neutrino observables in gauged $U(1)_{L_\alpha-L_\beta}$ models with two Higgs doublet and one singlet scalars

We discuss neutrino sector in models with two Higgs doublet and one singlet scalar fields under local $U(1)_{L_\alpha- L_\beta}$ symmetry. A neutrino mass matrix is formulated for these models where the matrix is generated via type-I seesaw mechanism introducing right-handed neutrinos. The neutrino mass matrix has more degrees of freedom compared to minimal scenarios which have only one new scalar field, but its structure is still restricted by the symmetry. Then it is find that sum of neutrino mass can be lower than minimal scenarios and it is easier to satisfy observed constraints. In addition, we can fit neutrino data for $U(1)_{L_e - L_{\mu(\tau)}}$ cases which are disfavored in minimal models. Furthermore, some correlations among sum of neutrino mass and CP violating phases are still found although we have more free parameters.

hep-ph↗