bio  website  front.math.ucdavis.edu/… 

location  Cornell  
age  45  
visits  member for  5 years, 5 months 
seen  2 hours ago  
stats  profile views  10,727 
Math professor at Cornell,
PhD 1996
1h

comment 
Picard group of Schubert varieties
Indeed; one way to think about it is that we know the map $c_1:Pic\to H^2$ is an isomorphism for $G/B$, and this restriction fact says that the same is true for $X_w$. Since $X_w$ is a union of $G/B$'s cells it's easy to compute the map $H^2(G/B) \to H^2(X_w)$ and it has the kernel you describe. 
13h

revised 
Root in positive Weyl chamber
added 68 characters in body 
15h

answered  Root in positive Weyl chamber 
2d

answered  Are there any Algebraic Geometry Theorems that were proved using Combinatorics? 
Mar 26 
answered  Moduli space of flat connections over a torus 
Mar 25 
answered  Continuity of Intersection Multiplicities 
Mar 24 
comment 
On QCartier Divisors
I think the basic issue is that the notion of Cartier divisor is a schemetheoretic one, and the notion of Weil divisor isn't, really. For example, consider the two pure codim 1 subschemes of $\{(x,y):xy=0\}$ defined by $x=y^2=0$ vs. $x^2=y=0$. Do you want those to be equal as Weil divisors (2x the origin)? I would say yes. 
Mar 21 
comment 
Derivation of Blattner's conjecture in the BeilinsonBernstein picture
It's definitely got some of the ingredients, and in particular, draws attention to the importance of Korbits with smooth closure. It doesn't reference Blattner directly though. Thanks! 
Mar 21 
comment 
Grobner basis and subsets
I agree; if $A$ is given as a finite list it's clear, otherwise it depends strongly on how $A$ is specified. 
Mar 19 
comment 
Geometric proof of BorelWeil theorem
You might like Bott's short survey "On induced representations" in The mathematical heritage of Hermann Weyl (Durham, NC, 1987), 1–13, Proc. Sympos. Pure Math., 48, Amer. Math. Soc., Providence, RI, 1988. Personally, I find it a lot easier to use complex algebraic geometry to think about BorelWeil (much less BorelWeilBott!) but to each his own. 
Mar 19 
comment 
Richardson varieties over finite fields
Indeed it doesn't make a big difference: for each open Richardson in $X^\circ_w \cap X^v_\circ \subseteq G/P$, the open Richardson $X^\circ_w \cap X^v_\circ \subseteq G/B$ maps to it isomorphically, if $w,v \in W^P$ i.e. are minimal coset representatives in $W/W_P$. 
Mar 19 
revised 
Explicit equations for Schubert varieties
added 61 characters in body 
Mar 19 
asked  Is the upper boundary of a Schubert variety Cartier? 
Mar 11 
revised 
The action of the center on the extended Dynkin diagram
added 85 characters in body 
Mar 10 
answered  The action of the center on the extended Dynkin diagram 
Mar 10 
comment 
Deforming a basis of a polynomial ring
I think $a=0$ is triangular one way, $b=0$ triangular the other way. The onebox rule is here: mathoverflow.net/questions/88569/… 
Mar 10 
awarded  Nice Question 
Mar 10 
revised 
Deforming a basis of a polynomial ring
added 5 characters in body 
Mar 10 
asked  Deforming a basis of a polynomial ring 
Mar 9 
awarded  Nice Answer 