Sonoluminescence: Photon production in time-dependent analog systems

Sonoluminescence is a well-known laboratory phenomenon where an oscillating gas bubble in the appropriate environment periodically emits a flash of light in the visible frequency range. In this work, we study the system in the framework of analog gravity. We model the oscillating bubble in terms of analog geometry and propose a nonminimal coupling prescription of the electromagnetic field with the geometry. The geometry behaves as an analogous oscillating time-dependent background in which repeated flux of photons are produced in a wide frequency range through parametric resonance from quantum vacuum. Due to our numerical limitation, we could reach the frequency up to <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mrow><a:mo>∼</a:mo><a:msup><a:mrow><a:mn>10</a:mn></a:mrow><a:mrow><a:mn>5</a:mn></a:mrow></a:msup><a:mtext> </a:mtext><a:mtext> </a:mtext><a:msup><a:mrow><a:mi mathvariant="normal">m</a:mi></a:mrow><a:mrow><a:mo>−</a:mo><a:mn>1</a:mn></a:mrow></a:msup></a:mrow></a:math>. However, we numerically fit the spectrum in a polynomial form including the observed frequency range around <d:math xmlns:d="http://www.w3.org/1998/Math/MathML" display="inline"><d:mrow><d:mo>∼</d:mo><d:msup><d:mrow><d:mn>10</d:mn></d:mrow><d:mrow><d:mn>7</d:mn></d:mrow></d:msup><d:mtext> </d:mtext><d:mtext> </d:mtext><d:msup><d:mrow><d:mi mathvariant="normal">m</d:mi></d:mrow><d:mrow><d:mo>−</d:mo><d:mn>1</d:mn></d:mrow></d:msup></d:mrow></d:math>. Our current analysis seems to suggest that parametric resonance in analog background may play a fundamental role in explaining such phenomena in the quantum field theory framework.