Abstract
Let χ be an irreducible character of a finite groupG. Letp=∞ or a prime. Letm p (χ) denote the Schur index of χ overQ p , the completion ofQ atp. It is shown that ifx is ap′-element ofG such that\(X_u \left( x \right) \in Q_p \left( X \right)\) for all irreducible charactersX u ofG thenm p (χ)/vbχ(x). This result provides an effective tool in computing Schur indices of characters ofG from a knowledge of the character table ofG. For instance, one can read off Benard’s Theorem which states that every irreducible character of the Weyl groupsW(E n), n=6,7,8 is afforded by a rational representation. Several other applications are given including a complete list of all local Schur indices of all irreducible characters of all sporadic simple groups and their covering groups (there is still an open question concerning one character of the double cover of Suz).
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References
M. Benard,On the Schur indices of characters of the exceptional Weyl groups, Ann. of Math.94 (1971), 89–107.
M. Benard,The Schur subgroup I, J. Algebra22 (1972), 374–377.
M. Benard,Schur indices and cyclic defect groups, Ann. of Math.103 (1976), 283–304.
M. Benard,Schur indexes of sporadic simple groups, J. Algebra58 (1979), 508–522.
M. Benard and M. M. Schacher,The Schur subgroup II, J. Algebra22 (1972), 378–385.
R. Brauer,On the algebraic structure of group rings, J. Math. Soc. Japan3 (1951), 237–251.
W. Feit,Characters of Finite Groups, Benjamin, New York, Amsterdam, 1967.
W. Feit,The Representation Theory of Finite Groups, North-Holland, Amsterdam, London, 1982.
D. Fendel,A characterization of Conway’s group. 3, J. Algebra24 (1973), 159–196.
R. L. Griess, Jr.,Schur multipliers of finite simple groups (Proc. Sympos. Pure Math., Vol. 37, Santa Cruz, 1979), Am. Math. Soc., Providence, RI, 1980, pp. 279–282.
K. Harada,On the simple group F of order 214.36.56.7.11.19, Proc. Conf. on Finite Groups, Academic Press, New York, San Francisco, London, 1976, pp. 119–276.
D. C. Hunt,Character tables of certain finite simple groups, Bull. Austral. Math. Soc.5 (1971), 1–42.
G. D. James,The modular characters of the Mathieu groups, J. Algebra27 (1973), 57–111.
Z. Janko,Some new simple groups of finite order I, Ist. Naz. Alita. Math. Symposia Mathematics, Vol. 1, Odensi Gubbio, 1968, pp. 25–64.
G. J. Janusz,Simple components of Q[SL(2,q)], Commun. Algebra1 (1974), 1–22.
W. Jonsson and J. McKay,More about the Mathieu group M 22 Can. J. Math.28 (1976), 929–937.
J. H. Lindsey II,On a six dimensional projective representation of the Hall-Janko group, Pacific J. Math.35 (1970), 175–186.
R. Lyons,Evidence for a new finite simple group, J. Algebra20 (1972), 540–569.
J. McKay,The nonabelian simple groups G, |G|<10 6—character tables, Commun. Algebra7 (1979), 1407–1445.
J. McKay and D. B. Wales,The multipliers of the simple groups of order 604, 800 and 50, 232, 960, J. Algebra17 (1971), 262–272.
M. O’Nan,Some evidence for the existence of a new simple group, Proc. London Math. Soc. (3)32 (1976), 421–479.
A. Rudvalis,Characters of the covering group of the Higman-Sims group, J. Algebra33 (1975), 135–143.
E. Witt,Die algebraische Struktur des Gruppenringes einer endlichen Gruppe über einem Zahlenkorper, J. fur Math.190 (1952), 231–245.
D. Wright,The irreducible characters of the simple group of M. Suzuki of order 448, 345, 497, 600, J. Algebra29 (1974), 303–323.
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This work was partly supported by NSF Grant MCS-8201333.
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Feit, W. The computations of some Schur indices. Israel J. Math. 46, 274–300 (1983). https://doi.org/10.1007/BF02762888
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DOI: https://doi.org/10.1007/BF02762888