Graduate Thermality & Nonthermality of Radiation in Curved Spacetimes

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The discussion focuses on the thermal and non-thermal characteristics of Hawking-Unruh radiation in curved spacetimes, particularly in non-inertial frames. Some researchers categorize radiation as non-thermal or approximately thermal if it deviates from a Planckian distribution, complicating the association of a characteristic temperature. Conversely, others argue that thermality can still be present even without Planckian features, as demonstrated by the asymptotic behavior of Unruh-DeWitt detectors reaching a Gibbs thermal state. This divergence in definitions leads to confusion regarding the distinction between thermality and non-thermality in the context of acceleration and Hawking radiation. Clarifying these concepts is essential for understanding the nature of radiation in curved spacetimes.
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I have been reading some material related to the thermal and non-thermal features of Hawking-Unruh radiation. It seems some authors label any radiation that emanates within curved spacetimes (including non-inertial frames) either as non-thermal or approximately thermal if it doesn't follow a typical Planckian character, which in other words means it is hard to associate a characteristic temperature with the radiation. https://doi.org/10.1103/PhysRevD.96.025023, https://doi.org/10.1007/JHEP07(2015)009. On the other hand, some associate thermality with the radiation even if it doesn't display Planckian feautures. In one of the papers, e.g., https://arxiv.org/abs/2101.11933 , authors say the thermality is when an Unruh-DeWitt detector asymptotically reaches a Gibbs thermal state (with connections to Kubo-Martin-Schwinger condition) without having anything to do with Planckian distribution. I am totally confused how to draw the line between thermality and non-thermality of acceleration/Hawking radiation.
 
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In this video I can see a person walking around lines of curvature on a sphere with an arrow strapped to his waist. His task is to keep the arrow pointed in the same direction How does he do this ? Does he use a reference point like the stars? (that only move very slowly) If that is how he keeps the arrow pointing in the same direction, is that equivalent to saying that he orients the arrow wrt the 3d space that the sphere is embedded in? So ,although one refers to intrinsic curvature...

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