Ila Varma, University of Toronto
Counting Number Fields by P^1 height
When do two irreducible polynomials with integer coefficients define the same number field? One can define an action of GL_2 × GL_1 on the space of polynomials of degree n so that for any two polynomials f and g in the same orbit, the roots of f may be expressed as rational linear transformations of the roots of g; thus, they generate the same field. In this article, we show that almost all polynomials of degree n with size at most X can only define the same number field as another polynomial of degree n with size at most X if they lie in the same orbit for this group action. (Here we measure the size of polynomials by the greatest absolute value of their coefficients.)
This improves on work of Bhargava, Shankar, and Wang, who proved a similar statement for a positive proportion of polynomials. Using this result, we prove that the number of degree n fields such that the smallest polynomial defining the field has size at most X is asymptotic to a constant times X^{n+1} as long as n \ge 3. For n = 2, we obtain a precise asymptotic of the form 27/(pi^2) * X^2
This is joint work with Arango-Pineros, Gundlach, Lemke Oliver, McGown, Sawin, Serrano Lopez, and Shankar.
MC 5479