bio  website  math.umass.edu/~jeh 

location  U. Massachusetts, Amherst  
age  75  
visits  member for  5 years, 5 months 
seen  6 hours ago  
stats  profile views  16,234 
Moreorless retired professor at UMass Amherst.
Basically an algebraist with interests in Lie theory,
specifically representation theory and related
algebraic geometry.
1d

comment 
How to associate a proper parabolic subgroup of a real s.s Lie group $G$ to a nontrivial unipotent element in a non uniform lattice in $G$?
Since the 1972 BorelTits paper is referred to here and in the link just posted by grghxy, maybe it's a good idea to add a link to it (though it's in French): gdz.sub.unigoettingen.de/dms/load/img/?PPN=GDZPPN002088894 
1d

comment 
How to associate a proper parabolic subgroup of a real s.s Lie group $G$ to a nontrivial unipotent element in a non uniform lattice in $G$?
This is a useful approach, but it's a good idea to add an explicit reference/link to the BorelTits result. (The question asked could also use more background.) Note too that the "unipotent" concept here requires identification of the complex Lie group with an algebraic group where the Jordan decomposition makes sense. Then the real group is the group of real points, etc. 
1d

revised 
How to associate a proper parabolic subgroup of a real s.s Lie group $G$ to a nontrivial unipotent element in a non uniform lattice in $G$?
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2d

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Does anyone have an electronic copy of Waldspurger's “Sur les coefﬁcients de Fourier des formes modulaires de poids demientier”?
@David: It might have helped matters to include the page numbering, since the article is over 100 pages long (and has been very often cited, indicating its influence). So far Elsevier's Science Direct have not reached back nearly so far in their archive to create searchable PDF files, though they now permit free access to older papers which have PDF versions. 
Jul 27 
revised 
1dimensional representations of the affine Hecke algebra for $SL_2$
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Jul 26 
comment 
Characterizations of JacobsonMorozov parabolics associated to a nilpotent
@hic: Concerning your question, the answer is certainly yes (see Carter's extensive discussion in his Chapter 5, in particular Prop. 5.7.3 where $P$ denotes the JM parabolic. Your example is a good one to illustrate what is going on. 
Jul 26 
answered  1dimensional representations of the affine Hecke algebra for $SL_2$ 
Jul 25 
comment 
Characterizations of JacobsonMorozov parabolics associated to a nilpotent
P.S. I've tried to make my answer more precise, but the details here are rather complicated to spell out. 
Jul 25 
revised 
Characterizations of JacobsonMorozov parabolics associated to a nilpotent
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Jul 25 
comment 
Characterizations of JacobsonMorozov parabolics associated to a nilpotent
@hic: Concerning Richardson orbits, it's a good idea to look at a textbook like the one by CollingwoodMcGovern (or Carter's 1985 book). Basically, to each parabolic subalgebra corresponds a nilpotent orbit determined by the dense orbit in its nilradical, and in type $A_n$ all nilpotent orbits occur this way (but not in general). Concerning $SL_3$, I'll doublecheck the details; but what you say doesn't sound correct. 
Jul 25 
revised 
Characterizations of JacobsonMorozov parabolics associated to a nilpotent
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Jul 25 
answered  Characterizations of JacobsonMorozov parabolics associated to a nilpotent 
Jul 25 
revised 
Characterizations of JacobsonMorozov parabolics associated to a nilpotent
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Jul 25 
comment 
1dimensional representations of the affine Hecke algebra for $SL_2$
It's essential to distinguish carefully between the "affine Weyl group" (or Hecke algebra) and the "extended" version, both of which enter into the work of KazhdanLusztig and others influenced by them. (In this direction, it would also be very helpful to indicate which sources you are primarily relying on.) 
Jul 24 
revised 
What are the “tensorclosed” object of the BGG category $\mathcal{O}$ of a semisimple Lie algebra $\mathfrak{g}$?
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Jul 24 
answered  Invariants of the maximal unipotent subgroup of GL(n) acting on the space of n by n matrices 
Jul 24 
revised 
highest weight the halfsum of positive roots
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Jul 23 
revised 
highest weight the halfsum of positive roots
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Jul 23 
answered  highest weight the halfsum of positive roots 
Jul 22 
answered  Linear Algebra classic books 