Speaker
Description
We study stimulated emission and absorption of gravitons in a squeezed vacuum
state immersed in a thermal radiation bath. Employing one-loop
interaction-picture perturbation theory, we track the time evolution of the
graviton number operator and its expectation value in the squeezed vacuum,
which characterizes the inflationary graviton state. In a Minkowski background
with a thermal bath as a toy example, we demonstrate that the net graviton
emission or absorption rate depends sensitively on the initial squeezing
parameters. As a thought experiment, we consider LIGO/Virgo-like detectors
operating in radiation at temperatures of order 0.1 GeV and find that graviton
occupation numbers at frequencies of order 100 Hz can be significantly
enhanced, suggesting a novel mechanism for amplifying gravitational-wave
signals. Although these conditions exceed current experimental capabilities,
they point toward potential future advances in detection. Extending our
analysis to an expanding, radiation-dominated universe, we show that subhorizon
gravitons undergo stimulated absorption, while superhorizon modes exhibit
secular logarithmic growth, indicating the breakdown of perturbative methods
and motivating further investigation. These findings open a new direction for
exploring graviton coherence effects in realistic cosmological and laboratory
settings.
