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Probing the thermal character of analogue Hawking radiation for shallow water waves?

by Prof. Renaud Parentani (Laboratoire de Physique Theorique d'Orsay)

May 13, 2014 from 03:00 PM to 04:30 PM

Where Aula Teorici - Via Irnerio 46

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In 2011, S. Weinfurtner et al. observed in the Vancouver experiment the blocking of shallow water waves by a stationary counter flow, and found that the spectrum obeys the thermal law. In this work, we numerically compute the coefficients governing this scattering. When the flow is transcritical, they closely follow Hawking's prediction according to which black holes should emit a thermal spectrum. We then study how the spectrum deviates from thermality when reducing the maximal flow velocity, with a particular attention to subcritical flows since these have been recently used to test Hawking's prediction. For low frequencies, we show, first, that the scattering coefficients are dominated by elastic hydrodynamical channels and, second, that the Planckianity of the spectrum is completely lost. Our numerical results reproduce rather well the observations made in Vancouver. Nevertheless, we propose a new interpretation of what has been observed, as well as new experimental tests.