Abstract:
Upgrades to improve the sensitivity of gravitationa wave detectors are critical for enriching our understandings of the sources and for more precise tests of gravity theories and more precise astronomical observations. Unlike other state-of-the-art detectors such as Advanced LIGO and Advanced Virgo, KAGRA requires different approach for the upgrade since it is the only detector which employs cryogenic cooling of the test mass mirrors. Here, we present possible KAGRA upgrade plans which can be realized by reducing or increasing the input laser power, increasing the mirror mass and injecting frequency dependent squeezed vacuum. We show that each upgrade is effective for different frequency bands and gives different impact on gravitational wave science. We then discuss an effective progression of upgrades based on technical feasibility and science cases.