Abstract
We characterize the subRiemannian cut locus of the origin in the free Carnot group of step two with three generators, giving a new, independent proof of a result by Myasnichenko (J Dyn Control Syst 8(4):573-597, 2002). We also calculate explicitly the cut time of any extremal path and the distance from the origin of all points of the cut locus. Furthermore, by using the Hamiltonian approach, we show that the cut time of strictly normal extremal paths is a smooth explicit function of the initial velocity covector. Finally, using our previous results, we show that at any cut point the distance has a corner-like singularity.
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Notes
After the submission of this paper, a precise conjecture for the cut locus on the free group in higher dimension has been formulated by Rizzi and Serres [27].
That is, the property \(F(r\alpha ,r\beta ,r\zeta ,\varphi )=\delta _r F(\alpha ,\beta ,\zeta , \varphi )\) for all \(r>0\), \(\alpha ,\beta ,\zeta \) admissible and \(\varphi >0\).
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Acknowledgements
We thank Luca Rizzi and Yuri Sachkov who kindly gave us several useful bibliographic information on the state of the art of the subject. We thank the anonymous referee for raising some useful questions, which led us to an improvement of the first draft of the paper. The authors are members of the Gruppo Nazionale per l’Analisi Matematica, la Probabilità e le loro Applicazioni (GNAMPA) of the Istituto Nazionale di Alta Matematica (INdAM)
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Montanari, A., Morbidelli, D. On the subRiemannian cut locus in a model of free two-step Carnot group. Calc. Var. 56, 36 (2017). https://doi.org/10.1007/s00526-017-1149-1
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DOI: https://doi.org/10.1007/s00526-017-1149-1