Pseudospherical surfaces on time scales: a geometric definition and the spectral approach

We define and discuss the notion of pseudospherical surfaces in asymptotic coordinates on time scales. Thus we extend well known notions of discrete pseudospherical surfaces and smooth pseudosperical surfaces on more exotic domains (e.g, the Cantor set). In particular, we present a new expression for the discrete Gaussian curvature which turns out to be valid for asymptotic nets on any time scale. We show that asymptotic Chebyshev nets on an arbitrary time scale have constant negative Gaussian curvature. We present also the quaternion-valued spectral problem (the Lax pair) and the DarbouxBäcklund transformation for pseudospherical surfaces (in asymptotic coordinates) on arbitrary time scales. Mathematics Subject Classification 2000: 53A05, 39A12, 37K35, 52C07. PACS Numbers: 02.40.Hw, 02.40.Dr, 02.30.Ik, 02.60.Jh