20.07.2013 Views

NEAR OPTIMAL BOUNDS IN FREIMAN'S THEOREM

NEAR OPTIMAL BOUNDS IN FREIMAN'S THEOREM

NEAR OPTIMAL BOUNDS IN FREIMAN'S THEOREM

SHOW MORE
SHOW LESS

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

158 MARGULIS and MOHAMMADI<br />

PROPOSITION B.2<br />

Let Q0(x,y,z) = 2xz − y 2 be the standard quadratic form of signature (2, 1) on<br />

R 3 . Let = gZ 3 ,whereg ∈ GL3(Q). Let T > 0 be a large parameter, and let τ<br />

be a sufficiently small parameter. Assume that the entries of g are rational numbers<br />

whose nominator and denominators are bounded by a fixed power of T τ , and also<br />

suppose that |det g| ≤T τ . Further assume that the length of the shortest vector in <br />

is c = O(1). Then if T is large enough, we have<br />

# w ∈ P () : Q0(w) = 0 and w ≤T 0. Note that C is dilation-invariant. Let λ = disc() 1/3 , and define<br />

1 = 1/λ. The lattice 1 is unimodular, and the length of the shortest vector in<br />

1 is at least c/λ. Let¯g ∈ PGL3(Q) denote the image of g. Indeed, 1 = ¯gZ 3 . The<br />

counting problem in (98) follows if we show that<br />

<br />

# w ∈ P (1) : Q0(w) = 0 and w ≤ T<br />

<br />

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!