We apply the inverse Gertsenshtein effect, i.e., the graviton-photon conversion in the presence of a magnetic field, to constrain high-frequency gravitational waves (HFGWs). Using existing astrophysical measurements, we compute upper limits on the GW energy densities Ω_GW at 16 different frequency bands. Given the observed magnetisation of galaxy clusters with field strength B ∼ μG correlated on 𝒪(10) kpc scales, we estimate HFGW constraints in the 𝒪(10²) GHz regime to be Ω_GW ≲ 10¹⁶ with the temperature measurements of the Atacama Cosmology Telescope (ACT). Similarly, we conservatively obtain Ω_GW ≲ 10¹³ (10¹¹) in the 𝒪(10²) MHz (𝒪(10) GHz) regime by assuming uniform magnetic field with strength B ∼ 0.1 nG and saturating the excess signal over the Cosmic Microwave Background (CMB) reported by radio telescopes such as the Experiment to Detect the Global EoR Signature (EDGES), LOw Frequency ARray (LOFAR), and Murchison Widefield Array (MWA), and the balloon-borne second generation Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission (ARCADE2) with graviton-induced photons. The upcoming Square Kilometer Array (SKA) can tighten these constraints by roughly 10 orders of magnitude, which will be a step closer to reaching the critical value of Ω_GW = 1 or the Big Bang Nucleosynthesis (BBN) bound of Ω_GW ≃ 1.2 × 10^-6. We point to future improvement of the SKA forecast and estimate that proposed CMB measurement at the level of 𝒪(10^0-2) nK, such as Primordial Inflation Explorer (PIXIE) and Voyage 2050, are needed to viably detect stochastic backgrounds of HFGWs.

中文翻译：

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逆格特森斯坦效应作为高频引力波的探针

我们应用逆格特森斯坦效应，即磁场存在下的引力子-光子转换，来约束高频引力波（HFGW）。利用现有的天体物理测量，我们计算了16 个不同频段的GW 能量密度 Ω _GW的上限。考虑到观测到的星系团磁化强度和场强乙 ～ μG 与 𝒪(10) kpc 尺度相关，我们利用阿塔卡马宇宙学望远镜 (ACT) 的温度测量估计 𝒪(10 ² ) GHz 范围内的 HFGW 约束为 Ω _GW  ≲ 10 ¹⁶ 。类似地，我们通过假设强度均匀的磁场，在 𝒪(10 ² ) MHz (𝒪(10) GHz) 范围内保守地获得 Ω _GW  ≲ 10 ¹³ (10 ^{11 )}乙 ∼ 0.1 nG 并使射电望远镜报告的宇宙微波背景 (CMB) 上的多余信号饱和，例如探测全球 EoR 特征实验 (EDGES)、低频阵列 (LOFAR) 和默奇森宽场阵列 (MWA)，以及用于宇宙学、天体物理学和漫发射的气球载第二代绝对辐射计 (ARCADE2)，具有引力子诱导光子。即将推出的平方公里阵列 (SKA) 可以将这些约束收紧大约 10 个数量级，这将更接近达到 Ω _{GW = 1 的临界值或 Ω GW}  ≃ 1.2 × 的大爆炸核合成 (BBN) 界限10 ^-6。我们指出 SKA 预测的未来改进，并估计需要在 𝒪(10 ^0-2 ) nK水平上进行拟议的 CMB 测量，例如 Primordial Inflation Explorer (PIXIE) 和 Voyage 2050，以切实检测 HFGW 的随机背景。