Abstract
During the past three decades fundamental progress has been made on constructing large torsion-free subgroups (i.e. subgroups of finite index) of the unit group \(\mathcal {U}(\mathbb {Z}G)\) of the integral group ring \(\mathbb {Z}G\) of a finite group G. These constructions rely on explicit constructions of units in \(\mathbb {Z}G\) and proofs of main results make use of the description of the Wedderburn components of the rational group algebra \(\mathbb {Q}G\). The latter relies on explicit constructions of primitive central idempotents and the rational representations of G. It turns out that the existence of reduced two degree representations play a crucial role. Although the unit group is far from being understood, some structure results on this group have been obtained. In this paper we give a survey of some of the fundamental results and the essential needed techniques.
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References
A. Bächle, Integral group rings of solvable groups with trivial central units, Forum Math. 30 (2018), no. 4, 845–855.
A. Bächle, G. Janssens, E. Jespers, A. Kiefer and D. Temmerman, Abelianization and fixed point properties of units in integral group rings, Math. Nachrichten (MANA2514), 47 pages, https://doi.org/10.1002/mana.202000514, (to appear) arXiv:1811.12184.
A. Bächle, G. Janssens, E. Jespers, A. Kiefer and D. Temmerman, A dichotomy for integral group rings via higher modular groups as amalgamated products, arXiv:1811.12226.
G. K. Bakshi and G. Kaur, A generalization of strongly monomial groups, J. Algebra 520 (2019), 419–439.
G. K. Bakshi and G. Kaur, Character triples and Shoda pairs, Journal of Algebra 491 (2017) 447–473.
G.K. Bakshi, R.S. Kulkarni, I.B.S. Passi, The rational group algebra of a finite group, J. Algebra Appl. 12 (3) (2013) 1250168, 17 pp.
G.K. Bakshi, S. Maheshwary, The rational group algebra of a normally monomial group, J. Pure Appl. Algebra 218 (9) (2014) 1583–1593.
G.K. Bakshi, S. Maheshwary, Extremely strong Shoda pairs with GAP, J. Symbolic Comput. 76 (5) (2016) 97–106.
G. Bakshi, S. Maheshwary and I. Passi, Integral group rings with all central units trivial, J. Pure Appl. Algebra 221 (2017), no. 8, 1955–1965.
H. Bass, The Dirichlet unit theorem, induced characters, and Whitehead groups of finite groups, Topology 4 (1966), 391–410.
B. Bekka, P. de la Harpe and A. Valette, Kazhdan?s property (T), Volume 11 of New Mathematical Monographs, Cambridge University Press, Cambridge, 2008.
A.A. Bovdi, Group Rings (Russian), A textbook, Užgorod. Gosudarstv. Univ., Uzhgorod, 1974. 118 pp.
D. Chillag and S. Dolfi, Semi-rational solvable groups, J. Group Theory 13 (2010), no. 4, 535–548.
F. Eisele, A. Kiefer and I. Van Gelder, Describing units of integral group rings up to com- mensurability, J. Pure Appl. Algebra 219 (2015), 2901–2916.
N. Gupta, Free group rings, Contemporary Mathematics 66, American Mathematical Society, Providence, RI, 1987. xii+129 pp.
M. Hertweck, A counterexample to the isomorphism problem for integral group rings, Ann. of Math. (2) 154 (2001), no. 1, 115–138.
G. Higman, Units in group rings, Ph.D. thesis, Oxford University Press, 1940.
E. Jespers and Á. del Río, Group ring groups, Vol. 1: Orders and generic constructions of units, De Gruyter Graduate, De Gruyter, Berlin, 2016. xii+447 pp. ISBN: 978-3-11-037278-6; 978-3-11-038617-2
E. Jespers and Á. del Río, Group ring groups, Vol. 2: structure theorems of unit groups, De Gruyter Graduate, De Gruyter, Berlin, 2016. xii+447 pp. ISBN: 978-3-11-041149-2; 978-3-11-041275-8.
G. Karpilovsky, Induced modules over group algebras. North-Holland Mathematics Studies 161, North-Holland Publishing Co., Amsterdam, 1990. xii+520 pp.
G. Karpilovsky, Unit groups of group rings, Pitman Monographs and Surveys in Pure and Applied Mathematics 47, Longman Scientific & Technical, Harlow; copublished in the United States with John Wiley & Sons, Inc., New York, 1989. xiv+393
G. Karpilovsky, Unit groups of classical rings, Oxford Science Publications, The Clarendon Press, Oxford University Press, New York, 1988. xiv+370 pp.
G. Karpilovsky, Structure of blocks of group algebras, Pitman Monographs and Surveys in Pure and Applied Mathematics 33, Longman Scientific & Technical, Harlow; John Wiley & Sons, Inc., New York, 1987. xviii+427 pp.
G. Karpilovsky, The Jacobson radical of group algebras, North–Holland Mathematics Studies 135, Notas de Matemática [Mathematical Notes], 115. North–Holland Publishing Co., Amsterdam, 1987. x+532 pp.
G. Karpilovsky, Commutative group algebras, Monographs and Textbooks in Pure and Applied Mathematics 78, Marcel Dekker, Inc., New York, 1983. x+223 pp.
E. Kleinert, Units of classical orders: a survey, Enseign. Math. 40 (1994), 205–248.
E. Kleinert, Units in skew fields (English summary) , Progress in Mathematics 186, Birkhäuser Verlag, Basel, 2000. viii+80 pp.
G. Lee, Group identities on units and symmetric units of group rings, Algebra and Applications, 12. Springer–Verlag London, Ltd., London, 2010. xii+194 pp.
I.B.N. Passi, Group rings and their augmentation ideals. Lecture Notes in Mathematics, 715. Springer, Berlin, 1979. vi+137 pp.
D.S. Passman, Infinite group rings, Pure and Applied Mathematics 6, Marcel Dekker, Inc., New York, 1971. viii+149 pp.
D.S. Passman, The algebraic structure of group rings, Reprint of the 1977 original, Robert E. Krieger Publishing Co., Inc., Melbourne, FL, 1985. xiv+734 pp.
D.S. Passman, Group rings, crossed products and Galois theory, CBMS Regional Conference Series in Mathematics 64, Published for the Conference Board of the Mathematical Sciences, Washington, DC; by the American Mathematical Society, Providence, RI, 1986. viii+71 pp.
W. Plesken, Group rings of finite groups over p–adic integers, Lecture Notes in Mathematics, 1026. Springer–Verlag, Berlin, 1983. ii+151 pp.
C. Polcino Milies, Units in group rings (Portuguese)m Monografías de Matemática [Mathematical Monographs] 58, Instituto de Matemática Pura e Aplicada (IMPA), Rio de Janeiro, 1998. 40 pp.
C. Polcino Milies, S.K. Sehgal, An introduction to group rings. Algebra and Applications 1, Kluwer Academic Publishers, Dordrecht, 2002. xii+371 pp.
I. Reiner, Class groups and Picard groups of group rings and orders, Conference Board of the Mathematical Sciences, Regional Conference Series in Mathematics, No. 26. American Mathematical Society, Providence, R. I., 1976. iv+44 pp.
KW. Roggenkamp, Integral representations and structure of finite group rings, Séminaire de Mathématiques Supérieures [Seminar on Higher Mathematics] 71, Presses de l’Université de Montréal, Montreal, Que., 1980.
K. W. Roggenkamp, M.J. Taylor, Group rings and class groups, DMV Seminar, 18. Birkhäuser Verlag, Basel, 1992. vi+210 pp.
A. Salwa, On free subgroups of units of rings, Proc. Amer. Math. Soc. 127 (1999), no. 9, 2569–2572.
S.K. Sehgal, Topics in group rings. Monographs and Textbooks in Pure and Applied Math. 50, Marcel Dekker, Inc., New York, 1978. vi+251 pp.
S.K. Sehgal, Units in integral group rings (With an appendix by Al Weiss), Pitman Monographs and Surveys in Pure and Applied Mathematics 69, Longman Scientific & Technical, Harlow, copublished in the United States with John Wiley & Sons, Inc., New York, 1993. xii+357 pp.
J.P. Serre, Trees, Springer Monographs in Mathematics, Translated from the French original by John Stillwell, Corrected 2nd printing of the 1980 English translation, Springer-Verlag, Berlin, 2003, x+142.
M. Taylor, Classgroups of group rings, London Mathematical Society Lecture Note Series 91, Cambridge University Press, Cambridge, 1984. xiii+119 pp.
A.E. Zalesskii, A.V. Mihalev, Group rings (Russian), Current problems in mathematics, Vol. 2 (Russian), pp. 5–118, (errata insert) Akad. Nauk SSSR Vsesojuz. Inst. Naučn. i Tehn. Informacii, Moscow, 1973.
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Communicated by Gadadhar Misra.
Dedicated to I.B.S. Passi on the occasion of his 80th birthday.
The author is supported in part by Onderzoeksraad of Vrije Universiteit Brussel, Fonds voor Wetenschappelijk Onderzoek (Belgium, grant G016117) and the International Centre for Theoretical Sciences (ICTS) during a visit for participating in the program- Group Algebras, Representations and Computation (Code: ICTS/Prog-garc2019/10)
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Jespers, E. Structure of group rings and the group of units of integral group rings: an invitation. Indian J Pure Appl Math 52, 687–708 (2021). https://doi.org/10.1007/s13226-021-00179-5
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DOI: https://doi.org/10.1007/s13226-021-00179-5