Bruce Kleiner

{{short description|American mathematician}}

{{Infobox scientist

| name = Bruce Kleiner

| image = Bruce Kleiner.jpeg

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| caption = Bruce Kleiner in Oberwolfach, 2004

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| nationality = American

| fields = Mathematics

| workplaces = New York University

| alma_mater = University of California, Berkeley

| doctoral_advisor = Wu-Yi Hsiang

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| awards = NAS Award for Scientific Reviewing (2013){{cite web|title=Courant's Kleiner wins National Academy of Sciences Award|url=http://www.nyu.edu/about/news-publications/news/2013/02/05/courants-kleiner-wins-national-academy-of-sciences-award.html|website=New York University|access-date=10 January 2016}}
Simons Fellow in Mathematics (2014){{cite web|title=2014 Simons Fellows Awardees: Mathematics|url=https://www.simonsfoundation.org/funding/funding-opportunities/mathematics-physical-sciences/simons-fellow-program/simons-fellows-awardees-mathematics/2014-simons-fellows-awardees-mathematics/|website=Simons Foundation|access-date=10 January 2016|archive-url=https://web.archive.org/web/20150324141519/https://www.simonsfoundation.org/funding/funding-opportunities/mathematics-physical-sciences/simons-fellow-program/simons-fellows-awardees-mathematics/2014-simons-fellows-awardees-mathematics/|archive-date=24 March 2015|url-status=dead}}

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Bruce Alan Kleiner is an American mathematician, working in differential geometry and topology and geometric group theory.

He received his Ph.D. in 1990 from the University of California, Berkeley. His advisor was Wu-Yi Hsiang. Kleiner is a professor of mathematics at New York University.

Kleiner has written expository papers on the Ricci flow. Together with John Lott of the University of Michigan, he filled in details of Grigori Perelman's proof of the Geometrization conjecture (from which the Poincaré conjecture follows) in the years 2003–2006. Theirs was the first publication acknowledging Perelman's accomplishment (in May, 2006), which was shortly followed by similar papers by Huai-Dong Cao and Xi-Ping Zhu (in June) and John Morgan and Gang Tian (in July).

Kleiner found a relatively simple proof of Gromov's theorem on groups of polynomial growth. He also proved the Cartan–Hadamard conjecture in dimension 3.{{cite journal|last=Kleiner|first=Bruce|date=1992|title=An isoperimetric comparison theorem|journal=Inventiones Mathematicae|volume=108|issue=1|pages=37–47|doi=10.1007/bf02100598|issn=0020-9910|bibcode=1992InMat.108...37K|s2cid=16836013}}