High-frequency gravitational waves are the subject of rapidly growing interest in the theoretical and experimental community. In this work we calculate the resonant conversion of gravitational waves into photons in the magnetospheres of neutron stars via the inverse Gertsenshtein mechanism. The resonance occurs in regions where the vacuum birefringence effects cancel the classical plasma contribution to the photon dispersion relation, leading to a massless photon in the medium which becomes kinematically matched to the graviton. We set limits on the amplitude of a possible stochastic background of gravitational waves using X-ray and IR flux measurements of neutron stars. Using Chandra (2–8 keV) and NuSTAR (3–79 keV) observations of RX J1856.6-3754, we set strain limits ℎlim𝑐≃10−26–10−24 in the frequency range 5×1017  Hz≲𝑓≲2×1019  Hz. Our limits are many orders of magnitude stronger than existing constraints from individual neutron stars at the same frequencies. We also use recent JWST observations of the Magnetar 4U 0142+61 in the range 2.7×1013  Hz≲𝑓≲5.9×1013  Hz, setting a limit ℎlimc≃5×10−19. These constraints are in complementary frequency ranges to laboratory searches with CAST, OSQAR and ALPS II. We expect these limits to be improved both in reach and breadth with a more exhaustive use of telescope data across the full spectrum of frequencies and targets.

中文翻译：

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中子星磁层中引力波的共振转换


高频引力波是理论和实验界迅速增长的兴趣主题。在这项工作中，我们通过逆 Gertsenshtein 机制计算了引力波在中子星磁层中向光子的共振转换。共振发生在真空双折射效应抵消了经典等离子体对光子色散关系的贡献的区域，导致介质中的无质量光子在运动学上与引力子匹配。我们使用中子星的 X 射线和红外通量测量对引力波可能的随机背景的振幅设置了限制。使用 RX J1856.6-3754 的 Chandra （2-8 keV） 和 NuSTAR （3-79 keV） 观测，我们在 5×1017 Hz≲f≲2×1019 Hz 的频率范围内设置应变限值 hlimc≃10-26-10-24。我们的极限比相同频率下单个中子星的现有约束强许多个数量级。我们还使用了最近在 2.7×1013 Hz≲f≲5.9×1013 Hz 范围内对 Magnetar 4U 0142+61 的 JWST 观测，并设定了极限 hlimc≃5×10−19。这些限制与使用 CAST、OSQAR 和 ALPS II 进行实验室搜索的频率范围相辅相成。我们预计，随着望远镜数据在整个频率和目标频谱上得到更详尽的使用，这些限制将在范围和广度上得到改善。