Supercuspidal characters of reductive *p*
-adic groups
(with Loren Spice),
2007,
available at `arXiv:0707.3313`.

Abstract: We compute the characters of many supercuspidal representations of reductive *p*-adic groups. Specifically, we deal with representations that arise via Yu's construction from data satisfying a certain compactness condition. Each character is expressed in terms of a depth-zero character of a smaller group, the (linear) characters appearing in Yu's construction, and Fourier transforms of orbital integrals, in addition to certain explicitly computed signs and cardinalities.

Good product expansions for tame elements of *p*
-adic groups
(with Loren Spice),
2007,
available at `arXiv:math.RT/0611554`.

Abstract: We show that, under fairly general conditions, many elements of a *p*-adic group can be well approximated by a product whose factors have properties that are helpful in performing explicit character computations.

The local character expansion near a tame, semisimple element (with Jonathan Korman), Amer. J. Math., 129 (2007), no. 2, 381-403.

Abstract: Consider the character of an irreducible admissible representation of a *p*-adic reductive group. The Harish-Chandra-Howe local expansion expresses this character near a semisimple element as a linear combination of Fourier transforms of nilpotent orbital integrals. Under mild hypotheses (we assume neither that the group is connected, nor that the underlying field has characteristic zero), we describe an explicit region on which the local character expansion is valid.

On certain multiplicity one theorems (with Dipendra Prasad), Israel J. Math, 153 (2006), 221-245.

Abstract: We prove several multiplicity one theorems. For *k*a local field not of characteristic two, and*V*a symplectic space over*k*, any irreducible admissible representation of the symplectic similitude group*GSp*(*V*) decomposes with multiplicity one when restricted to the symplectic group*Sp*(*V*) . We prove the analogous result for*GO*(*V*) and*O*(*V*) , where*V*is an orthogonal space over*k*. When*k*is non-archimedean, we prove the uniqueness of Fourier-Jacobi models for representations of*GSp*(4) , and the existence of such models for supercuspidal representations of*GSp*(4) .

Depth-zero base change for unramified *U*(2, 1)
, (with Joshua Lansky),
J. Number Theory
114 (2005),
no. 2,
pp. 324-360.
Printer's error corrected in vol. 121 (2006), no. 1, 186.

Abstract: We give an explicit description of *L*-packets and quadratic base change for depth-zero representations of unramified unitary groups in two and three variables. We show that this base change is compatible with unrefined minimal*K*-types.

Discrete series representations
of unipotent *p*
-adic groups,
(with Alan Roche),
J. Lie Theory
15
(2005), 261-267.

Abstract: For a certain class of locally profinite groups, we show that an irreducible smooth discrete series representation is necessarily supercuspidal and, more strongly, can be obtained by induction from a linear character of a suitable open and compact modulo center subgroup. If *F*is a non-Archimedean local field, then our class of groups includes the groups of*F*-points of unipotent algebraic groups defined over*F*. We therefore recover earlier results of van Dijk and Corwin.

Injectivity, projectivity, and supercuspidal representations, (with Alan Roche), J. London Math. Soc. (2) 70 (2004), no. 2, 356-368.

Abstract: Let *G*be a reductive*p*-adic group. Consider the category of smooth (complex) representations of*G*in which a (fixed) closed cocompact subgroup of the centre acts by a (fixed) character. It is well known that the supercuspidal representations in this category are both injective and projective. We show that conversely an admissible injective or projective object is necessarily supercuspidal.

Murnaghan-Kirillov theory for supercuspidal
representations of tame general linear groups, (with S. DeBacker),
J. Reine Angew. Math.
**575**
(2004), 1-35.

Abstract: This paper exploits the formalism of Moy and Prasad to sharpen and extend a result of Murnaghan. Let *F*be a nonarchimedean local field of residual characteristic*p*>*n*. We show that the character of a supercuspidal representation of**GL**_{n}(*F*) can be expressed on a large set as its formal degree times the Fourier transform of an elliptic orbital integral. We prove a similar result for tame, very supercuspidal representations of more general reductive groups. Finally, we examine a consequence for local character expansions.

Discrete series characters of division algebras
and
*GL*_{n}
over a *p*
-adic field
(with L. Corwin and P. J. Sally, Jr.),
in
Contributions to Automorphic Forms, Geometry, and Number Theory
,
pp. 57-64.
Edited by H. Hida, D. Ramakrishnan, and F. Shahidi.
Johns Hopkins University Press, 2004.

Abstract: Let *D*be a central division algebra over a nonarchimedean local field*F*. Assume that the degree of*D*is prime to the residual characteristic of*F*. Then we present explicit formulas for all irreducible characters of the multiplicative group of*D*. Proofs will appear elsewhere.

A generalization of a result of Kazhdan and Lusztig,
(with S. DeBacker),
Proc. Amer. Math. Soc.,
**132** (2004),
no. 6,
1861-1868.

Abstract: Kazhdan and Lusztig show that every topologically nilpotent, regular semisimple orbit in the Lie algebra of a simple, split group over the field (( *t*)) is, in some sense, close to a regular nilpotent orbit. We generalize this result to a setting that includes most quasisplit*p*-adic groups.

Some applications of Bruhat-Tits theory to harmonic
analysis on the Lie algebra of a reductive *p*
-adic group
(with S. DeBacker),
Mich. J. Math. 50 (2002), No. 2, 263-286.
(An early version of this work was distributed under the title
``Moy-Prasad filtrations and harmonic analysis''.)
MR:2003g:22016.

Abstract: Let *F*denote a complete nonarchimedean local field with perfect residue field. Let**G**be a connected reductive group defined over*F*. This paper exploits the formalism of Moy and Prasad to sharpen and extend familiar harmonic analysis results for the Lie algebra of*G*. We show that the*G*-orbits of the Moy-Prasad filtration lattices are asymptotic to the set of nilpotent elements. In the Lie algebra, we define*G*-domains in terms of the filtration lattices and explore their properties. We then show that the domain where the local expansion for*G*-invariant distributions is valid behaves well with respect to parabolic induction.

A construction of types,
Analyse harmonique sur le groupe
*Sp*_{4}
,
(CIRM,
Luminy, June, 1998), Paul Sally, ed.
University of Chicago Lecture Notes in Representation Theory,
1999.

An intertwining result for *p*
-adic groups, (with Alan Roche).
Canad. J. Math.,
52 (2000),
no. 3,
449-467.

Abstract: For a reductive *p*-adic group*G*, we compute the supports of the Hecke algebras for the*K*-types for*G*lying in a certain frequently-occurring class. When*G*is classical, we compute the intertwining between any two such*K*-types.

Refined anisotropic *K*
-types and supercuspidal representations,
Pacific J. Math.,
**185** (1998),
no. 1,
1-32.
MR:2000f:22019.
Zbl
924.22015.

Abstract: Let *F*be a nonarchimedean local field, and*G*a connected reductive group defined over*F*. We classify the representations of*G*(*F*) that contain any anisotropic unrefined minimal*K*-type satisfying a certain tameness condition. We show that these representations are induced from compact (mod center) subgroups, and we construct corresponding refined minimal*K*-types.

Self-contragredient supercuspidal representations of
*GL*_{n}
,
Proc. Amer. Math. Soc.,
**125** (1997),
No. 8,
2471-2479. MR:97j:22038.
Zbl
886.22011.

Abstract: Let *F*be a non-archimedean local field of residual characteristic*p*. Then*GL*_{n}(*F*) has tamely ramified self-contragredient supercuspidal representations if and only if*n*or*p*is even. When such representations exist, they do so in abundance.

Reading encrypted diplomatic correspondence: An undergraduate research project, (with Ryan Fuoss, Michael Levin, and Amanda Youell), to appear in Cryptologia.

Abstract: We describe the cryptanalysis of a collection of sixteenth-century Spanish diplomatic correspondence, performed by undergraduates who do not know Spanish.

Undergraduate research in mathematics at the University of Akron, Proceeding of the Conference on Promoting Undergraduate Research in Mathematics (Chicago, 2006), Joseph A. Gallian, ed., American Mathematical Society, pp. 145-148.

Abstract: The University of Akron has been active in undergraduate research in mathematics for several years. We describe the history of this activity, particularly during the last two summers.

Groups of order *p*^{4}
made less difficult
(with Michael Garlow and Ethel R. Wheland), preprint.

Abstract: Using only elementary methods, we classify the groups of order *p*^{4}, for*p*an odd prime.

The Neighborhood Covering Heuristic (NCH) Approach for the General Mixed Integer Programming Problem, (with A. A. Sterns, Douglas Kline, and Scott Collins), Final Report completed for the Navy Personnel Research, Science, and Technology Division, Contract N00014-03-M-0254, Office of Naval Research, 2004.

Abstract: We present a new approach to the mixed integer programming problem. We compare this approach to the traditional branch and bound method on thousands of randomly generated problems.