36 citations · 36 across the 1 of their papers we have counts for
4 papers
Negative time delay of light by a gravitational concave lens
Koki Nakajima, Koji Izumi, Hideki Asada
Gravitational lens models, some of which might act as if a concave lens, have been recently investigated by using a static and spherically symmetric modified spacetime metric that…
Microlensed image centroid motions by an exotic lens object with negative convergence or negative mass
Takao Kitamura, Koji Izumi, Koki Nakajima +2
Gravitational lens models with negative convergence inspired by modified gravity theories, exotic matter and energy have been recently examined, in such a way that a static and sph…
Gravitational lensing shear by an exotic lens object with negative convergence or negative mass
Koji Izumi, Chisaki Hagiwara, Koki Nakajima +2
Gravitational lens models with negative convergence(surface mass density projected onto the lens plane) inspired by modified gravity theories, exotic matter and energy have been re…
Perturbation theory of multi-plane lens effects in terms of mass ratios: Approximate expressions of lensed-image positions for two lens planes
Koji Izumi, Hideki Asada
Continuing work initiated in an earlier publication (Asada, MNRAS. 394 (2009) 818), we make a systematic attempt to determine, as a function of lens and source parameters, the posi…