Shimmering gravitons in the gamma-ray sky

Abstract

What is the highest energy at which gravitons can be observed? We address this question by studying graviton-to-photon conversion — the inverse-Gertsenshtein effect — in the magnetic field of the Milky Way. We find that above ∼ 1 PeV the effective photon mass grows large enough to quench the conversion rate. For sub-PeV energies, the induced photon flux is comparable to the sensitivity of LHAASO to a diffuse γ-ray background, but only for graviton abundances of order Ωgw h 2 0 ∼ 1. In the future, owing to a better understanding of γ-ray backgrounds, larger effective areas and longer observation times, sub-PeV shimmering gravitons with a realistic abundance of Ωgw h 2 0 ∼ 0.01 could be detected. We show how such a large abundance is achieved in a cosmologically-motivated scenario of post-recombination superheavy dark matter decay. Therefore, the sub-PeV range might be the ultimate energy frontier at which gravitons can be observed.

Macroscopic quantum response to gravitational waves

“…In the lower frequency range of approximately 10 −18 to 10 −16 Hz, there is a viable method for observing gravitational waves, namely, through the cosmic microwave background observations [4][5][6]. On the flip side, the detection of gravitational waves at frequencies higher than kHz is still in the process of being developed, and it even calls for novel ideas [7][8][9][10][11][12][13][14][15][16][17][18][19][20]. This is the case even though high frequency gravitational waves hold theoretical interest for investigating new areas of physics [10].…”

Inverse Gertsenshtein effect as a probe of high-frequency gravitational waves

“…(i) Astrophysical and cosmological magnetic fields: magnetic fields are ubiquitous as they are observed across many scales in the Universe, from planets and stars [39][40][41] to galaxy and cluster scales [42,43]. Correspondingly, graviton-photon conversion is studied in the presence of planetary magnetospheres [44], highly magnetised objects such as neutron stars, pulsars, magnetars, and BHs [45][46][47][48][49], Milky Way magnetic fields [50] and largescale magnetic fields originating in the early Universe, i.e., primordial (cosmological) magnetic fields (PMFs) [33,51,52].…”

Quantum decay of scalar and vector boson stars and oscillons into gravitons

“…In both cases, the predicted typical frequency of the stochastic gravitational wave is very high. Recently there are many proposals to detect such high frequency gravitational waves [156][157][158][159][160][161][162][163][164][165][166], although it is still challenging to detect it.…”