arXiv subjects

Kohei Eguchi

Publications and source records attributed to Kohei Eguchi.

4 recordsLinked to original sources

arXiv2026

Terahertz Synthetic FM Triplet for Distortion-Free Stabilization and Lamb-Dip Spectroscopy

We demonstrate a distortion-free terahertz frequency stabilization technique using a "synthetic FM triplet" to overcome modulation sideband interference associated with high-density spectral lines in molecular clocks. By applying this method to the rotational transitions of acetonitrile (CH$_3$CN), we successfully generated clean derivative waveforms free from inter-line interference, achieving a fractional frequency instability of $1 \times 10^{-9}$ at an averaging time of $1~\mathrm{s}$. Furthermore, we report the observation of Lamb-dips using this high-fidelity approach. Our results establish acetonitrile as a promising candidate for high-agility molecular clocks and provide a robust solution for precision spectroscopy of molecules with complex hyperfine structures.

physics.optics↗

arXiv2025

Lamb-dip spectroscopy of rotational levels with UTC-PD terahertz emitter

Pump-probe saturation spectroscopy in the sub-terahertz region was performed in the rotational transition (J, K) = (16, 0) <- (15, 0) for gas-phase acetonitrile molecules in the counter-propagating configuration. We observed Lamb-dips at much lower excitation powers than previously reported. The linewidth in the zero-pressure limit was 10 kHz, which was estimated from the intensity and pressure dependence. This corresponds to the transit-time broadening.

physics.optics↗

arXiv2018

Gauge anomaly with vector and axial-vector fields in six dimensional curved space

Imposing the conservation equation of the vector current for a fermion of spin $\frac{1}{2}$ at the quantum level, a gauge anomaly for the fermion coupling with non-Abelian vector and axial--vector fields in six--dimensional curved space is expressed in tensorial form. The anomaly consists of terms that resemble the chiral U(1) anomaly and the commutator terms that disappear if the axial--vector field is Abelian.

hep-th↗

arXiv2008

Mechanism of robust circadian oscillation of KaiC phosphorylation in vitro

By incubating the mixture of three cyanobacterial proteins, KaiA, KaiB, and KaiC, with ATP in vitro, Kondo and his colleagues reconstituted the robust circadian rhythm of the phosphorylation level of KaiC (Science, 308; 414-415 (2005)). This finding indicates that protein-protein interactions and the associated hydrolysis of ATP suffice to generate the circadian rhythm. Several theoretical models have been proposed to explain the rhythm generated in this "protein-only" system, but the clear criterion to discern different possible mechanisms was not known. In this paper, we discuss a model based on the two basic assumptions: The assumption of the allosteric transition of a KaiC hexamer and the assumption of the monomer exchange between KaiC hexamers. The model shows a stable rhythmic oscillation of the phosphorylation level of KaiC, which is robust against changes in concentration of Kai proteins. We show that this robustness gives a clue to distinguish different possible mechanisms. We also discuss the robustness of oscillation against the change in the system size. Behaviors of the system with the cellular or subcellular size should shed light on the role of the protein-protein interactions in in vivo circadian oscillation.

q-bio.MN↗