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New York Journal of Mathematics
Volume 32 (2026), 676-690

  

Noe Barcenas and Mario Velasquez

Positive scalar curvature and crystallographic fundamental groups

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Published: May 3, 2026.
Keywords: Gromov-Lawson-Rosenberg Conjecture, Group homology, (connective) topological K-theory, extensions of Zn by Z/m.
Subject [2020]: 46L80, 53C27.

Abstract
We examine positive and negative results for the Gromov-Lawson-Rosenberg Conjecture within the class of crystallographic groups. We give necessary conditions within the class of split extensions of free abelian by cyclic groups to satisfy the unstable Gromov-Lawson-Rosenberg Conjecture. We also give necessary conditions within the same class of groups which are counterexamples for the conjecture.

Acknowledgements

The first named author aknowledges support of DGAPA-PAPIIT Grant IN101423. Both authors thank the exchange program CIC-UNAM.


Author information

Noe Barcenas
Centro de Ciencias Matematicas
UNAM \\Ap.Postal 61-3 Xangari
Morelia, Michoacan 58089, MEXICO

barcenas@matmor.unam.mx

Mario Velasquez
Universidad Nacional de Colombia Sede Bogota
Departamento de Matematicas
Facultad de Ciencias
Cra. 30 cll 45 - Ciudad Universitaria, Bogota, Colombia

mavelasquezme@unal.edu.co