Variation of local systems and parabolic cohomology
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چکیده
Given a family of local systems on the punctured Riemann sphere, its parabolic cohomology is a local system on the base space. We derive exact formulas for the monodromy of this local system. Using the comparison theorem between singular and étale cohomology, we can also (under some conditions) bound its field of moduli. As an application, we prove that the simple groups PSL2(p ) admit regular realizations over the field Q(t) for primes p 6≡ 1, 4, 16 mod 21.
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تاریخ انتشار 2003