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Local Coefficients and Gamma Factors for Principal Series of Covering Groups

About this Title

Fan Gao, Freydoon Shahidi and Dani Szpruch

Publication: Memoirs of the American Mathematical Society
Publication Year: 2023; Volume 283, Number 1399
ISBNs: 978-1-4704-5681-8 (print); 978-1-4704-7400-3 (online)
DOI: https://doi.org/10.1090/memo/1399
Published electronically: January 19, 2023
Keywords: Covering groups, Whittaker functionals, local coefficients matrix, scattering matrix, gamma factor, Plancherel measure

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Table of Contents

Chapters

  • 1. Introduction
  • 2. Covering groups
  • 3. Local coefficients matrix and scattering matrix
  • 4. Plancherel measure and gamma factor
  • 5. Exceptional point and the Casselman–Shalika formula
  • 6. The fundamental group $\pi _1(\overline {G}_{Q,n}^\vee )$ and periodicity of $b_{W,n}$
  • 7. Two Poincaré series
  • 8. Principal series of $\overline {GL}_2$ and $\overline {SL}_2$
  • 9. Local coefficients matrix for $\overline {SL}_2$
  • 10. Local coefficients matrices for $\overline {GL}_2$ and invariants via restrictions

Abstract

We consider an $n$-fold Brylinski–Deligne cover of a reductive group over a $p$-adic field. Since the space of Whittaker functionals of an irreducible genuine representation of such a cover is not one-dimensional, one can consider a local coefficients matrix arising from an intertwining operator, which is the natural analogue of the local coefficients in the linear case. In this paper, we concentrate on genuine principal series representations and establish some fundamental properties of such a local coefficients matrix, including the investigation of its arithmetic invariants. As a consequence, we prove a form of the Casselman–Shalika formula which could be viewed as a natural analogue for linear algebraic groups. We also investigate in some depth the behaviour of the local coefficients matrix with respect to the restriction of genuine principal series from covers of $GL_2$ to $SL_2$. In particular, some further relations are unveiled between local coefficients matrices and gamma factors or metaplectic-gamma factors.

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References

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