
arXiv: 1810.02700
In this paper, we construct Hölder maps to Carnot groups equipped with a Carnot metric, especially the first Heisenberg group H \mathbb {H} . Pansu and Gromov [Carnot-Carathéodory spaces seen from within, Birkhäuser, Basel, 1996] observed that any surface embedded in H \mathbb {H} has Hausdorff dimension at least 3 3 , so there is no α \alpha -Hölder embedding of a surface into H \mathbb {H} when α > 2 3 \alpha >\frac {2}{3} . Züst [Anal. Geom. Metr. Spaces 3 (2015), pp. 73–92] improved this result to show that when α > 2 3 \alpha >\frac {2}{3} , any α \alpha -Hölder map from a simply-connected Riemannian manifold to H \mathbb {H} factors through a metric tree. In the present paper, we show that Züst’s result is sharp by constructing ( 2 3 − ϵ ) (\frac {2}{3}-\epsilon ) -Hölder maps from D 2 D^2 and D 3 D^3 to H \mathbb {H} that do not factor through a tree. We use these to show that if 0 > α > 2 3 0>\alpha > \frac {2}{3} , then the set of α \alpha -Hölder maps from a compact metric space to H \mathbb {H} is dense in the set of continuous maps and to construct proper degree-1 maps from R 3 \mathbb {R}^3 to H \mathbb {H} with Hölder exponents arbitrarily close to 2 3 \frac {2}{3} .
Mathematics - Metric Geometry, 53C17, 22E25, Carnot groups, Nilpotent and solvable Lie groups, FOS: Mathematics, Hölder maps, Metric Geometry (math.MG), Group Theory (math.GR), Mathematics - Group Theory, Sub-Riemannian geometry
Mathematics - Metric Geometry, 53C17, 22E25, Carnot groups, Nilpotent and solvable Lie groups, FOS: Mathematics, Hölder maps, Metric Geometry (math.MG), Group Theory (math.GR), Mathematics - Group Theory, Sub-Riemannian geometry
| selected citations These citations are derived from selected sources. This is an alternative to the "Influence" indicator, which also reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically). | 1 | |
| popularity This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network. | Average | |
| influence This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically). | Average | |
| impulse This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network. | Average |
