arXiv subjects
Publications and source records attributed to Changqian Li.
Let $G$ be a virtually compact special Gromov-hyperbolic group. We prove that the double $G *_H G$ along a quasiconvex subgroup $H$ is virtually compact special. More generally, we show that if a finite graph of groups has constant vertex groups, with each vertex group virtually compact special Gromov-hyperbolic and each edge group quasiconvex in its adjacent vertex groups, then its fundamental group is virtually compact special.
Given a compact cube complex $X$ that splits as a graph of virtually special cube complexes. Suppose that the fundamental groups of edge spaces are cyclonormal in the fundamental groups of adjacent vertex spaces. We show that $π_1X$ has finite stature with respect to vertex groups in the sense of Huang-Wise. In particular, when vertex groups are hyperbolic, this allows us to deduce virtual specialness of $X$.
The supernova (SN) core, characterized by its extreme temperature and density, serves as a unique laboratory for new-physics searches. Low-energy supernovae (LESNe) provide particularly powerful probes, as their low explosion energies place stringent limits on any additional energy deposition in the mantle by new particles. We present refined LESN constraints on lepton-flavor-violating (LFV) axions and axion-like particles (ALPs) with electron-muon couplings. We consider four production channels in the SN: muon decay, lepton bremsstrahlung, electron-muon coalescence, and semi-Compton scattering, the last of which is investigated here for the first time in the context of LFV-ALPs. We find that muon decay dominates in the low-mass regime, electron-muon coalescence in the high-mass regime, and semi-Compton scattering in the intermediate-mass range. To derive accurate limits, we compute both the energy transfer from the SN core to the mantle and the energy loss due to ALP production in the mantle, which can be substantial for both large and small couplings -- the latter case, to our knowledge, not previously noted in the literature. We find that LESNe provide the most stringent constraints on the parameter space for ALP masses above $\sim 110$ MeV. These refined results strengthen previous SN bounds and highlight the exceptional sensitivity of LESNe to LFV new physics.
The hot and dense conditions of the supernova core provide an ideal environment for the production of new feebly-interacting particles. Low-energy supernovae, characterized by low explosion energy, are particularly intriguing due to their stringent constraints on energy transfer from the core to the mantle by new particles. We investigate low-energy supernova constraints on millicharged particles by considering three production channels in the core: plasmon decay, proton bremsstrahlung, and electron-positron annihilation. We compute the energy deposition due to Coulomb scatterings of millicharged particles with protons in the mantle and find that low-energy supernovae impose the most stringent constraints on millicharged particles in the mass range of $\sim(12 - 170)$ MeV. Furthermore, we find that the electron-positron annihilation process, previously omitted in supernova studies on millicharged particles, is the dominant production channel in the high-mass region. This leads to new constraints from both supernova cooling calculations and low-energy supernova analyses. We also investigate MCP production via processes involving thermal pions and find that these processes could dominate over electron-positron annihilation, albeit with significant uncertainties.