Detectability of axion-like dark matter for different time-delay interferometry combinations in space-based gravitational wave detectors

TL;DR

This work investigates detecting axion-like dark matter via axion-induced birefringence in space-based laser interferometers, focusing on waveplate-enabled polarization responses and three first-generation TDI combinations (Monitor, Beacon, Relay) for the ASTROD-GW mission. By deriving the single-link and multi-link responses and translating them into one-sided PSDs, the authors quantify the axion-photon coupling sensitivity $g_{a\gamma}$ across frequency bands, comparing against Sagnac and other detectors. They find Monitor-E and Relay-U provide superior high-frequency sensitivity around $g_{a\gamma} \sim 10^{-13}\ \mathrm{GeV}^{-1}$, while Sagnac dominates at low frequencies, with ASTROD-GW capable of probing axion masses down to $m \sim 10^{-20}\ \mathrm{eV}$ in the $[10^{-7},10^{-3}]$ Hz band. The results highlight the complementary role of different TDI combinations and guide future exploration of advanced TDI configurations to expand the axion-like dark matter search reach in space-based GW detectors.

Abstract

In the space-based gravitational wave detections, the axion-like dark matter would alter the polarization state of the laser link between spacecrafts due to the birefringence effect. However, current designs of space-based laser interferometer are insensitive to variations in the polarization angle. Thus, the additional wave plates are employed to enable the response of the axion-induced birefringence effect. We calculate and compare the sensitivities of different space-based detectors, accounting for three time-delay interferometry combinations, including Monitor, Beacon, and Relay. We find that the Monitor and Beacon combinations have better sensitivity in the high-frequency range, and the optimal sensitivity reaches $g_{aγ}\sim 10^{-13}\text{GeV}^{-1}$, while the Sagnac combination is superior in the low-frequency range. We also find that ASTROD-GW can cover the detection range of axion-like dark matter mass down to $10^{-20}\text{eV}$.

Figures (12)

• Figure 1: Schematic diagram of the configuration of the three spacecrafts in the interferometer. Each spacecraft is equipped with two optical platforms, labeled $j$ and $j'$, where $j\in \{a,b,c\}$ and $j'\in \{a',b',c'\}$. By convention, labels corresponding to light traveling in the clockwise direction are denoted with a prime symbol, for instance, $a'$.
• Figure 2: Schematic diagram of the modification to the single laser link. By adding waveplates to each optical path, the emitted and received light is converted into circularly polarized light. The optical path undergoes an alteration such that the light propagating along the clockwise directed optical path(blue line) exhibits left-handed circular polarization, while the light propagating along the counter-clockwise directed optical path(red line) exhibits right-handed circular polarization.
• Figure 3: The space-time diagram of Monitor-E combination. The red solid line and the blue dashed line represent two groups of laser links. The horizontal axis indicates the spacecraft's serial number, and the vertical axis represents the time direction.
• Figure 4: The space-time diagram of the Beacon-P combination. The solid and dashed lines constitute two groups of laser links, with different colors distinguishing the laser links emitted at different times.
• Figure 5: The space-time diagram of the Relay-U combination, where solid and dashed lines represent two groups of laser links. Compared with the Monitor-E and Beacon-P combinations, the Relay-U combination exhibits a longer delay time and a more symmetrical synthesized virtual laser link.