Modules and binary quadratic forms

Division and Binary Quadratic Forms

has only three elements, written h(−23) = 3. There is an binary operation called composition that takes two primitive forms of the same discriminant to a third. Composition is commutative and associative, and makes the set of forms into a group, with identity 〈1, 0,−∆/4〉 for even discriminant and 〈1, 1, (1−∆)/4〉 for odd. From page 49 of Buell [1]: if a form 〈α, β, γ〉 represents a number r primi...

Clifford Modules and Invariants of Quadratic Forms

We construct new invariants of quadratic forms over commutative rings, using ideas from Topology. More precisely, we de…ne a hermitian analog of the Bott class with target algebraic K-theory, based on the classi…cation of Cli¤ord modules. These invariants of quadratic forms go beyond the classical invariants de…ned via the Cli¤ord algebra. An appendix by J.-P. Serre, of independent interest, de...

On Perfect Binary Quadratic Forms

A quadratic form f is said to be perfect if its values at points of the integer lattice form a semigroup under multiplication. A problem of V. Arnold is to describe all perfect binary integer quadratic forms. If there is an integer bilinear map s such that f(s(x, y)) = f(x)f(y) for all vectors x and y from the integer 2-dimensional lattice, then the form f is perfect. We give an explicit descri...

Composition of Binary Quadratic Forms

Cubic Residues and Binary Quadratic Forms

Let p > 3 be a prime, u, v, d ∈ Z, gcd(u, v) = 1, p u2 − dv2 and (−3d p ) = 1, where ( p ) is the Legendre symbol. In the paper we mainly determine the value of u−v √ d u+v √ d (p−( p3 ))/3 (mod p) by expressing p in terms of appropriate binary quadratic forms. As applications, for p ≡ 1 (mod 3) we obtain a general criterion for m(p−1)/3 (mod p) and a criterion for εd to be a cubic residue of p...