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John McKay

Publications and source records attributed to John McKay.

28 records · Page 2Linked to original sources
arXiv2014

Eta Products, BPS States and K3 Surfaces

Inspired by the multiplicative nature of the Ramanujan modular discriminant, Delta, we consider physical realizations of certain multiplicative products over the Dedekind eta-function in two parallel directions: the generating function of BPS states in certain heterotic orbifolds and elliptic K3 surfaces associated to congruence subgroups of the modular group. We show that they are, after string duality to type II, the same K3 surfaces admitting Nikulin automorphisms. In due course, we will present some identities arising from q-expansions as well as relations to the sporadic Mathieu group M24.

hep-th↗
arXiv2013

Almost Commutative Probability Theory

We solve two longstanding major problems in Free Probability. This is achieved by generalising the theory to one with values in arbitrary commutative algebras. We prove the existence of the multi-variable $S$-transform, and show that it is naturally realised as a faithful linear representation. Further, we prove that in dimension one, the analog of the classical relation between addition and multiplication of independent random variables holds for free random variables, if the co-domain is an algebra over the rationals. In this case the multiplicative problem can be reduced to the additive one, which is not true in dimensions greater than one. Finally, we classify the groups which arise as joint distributions of $n$-tuples of non-commutative random variables, endowed with the free convolution product, which is the binary operation that encodes the multiplication of free $n$-tuples.

math.PR↗
arXiv2013

Modular Subgroups, Dessins d'Enfants and Elliptic K3 Surfaces

We consider the 33 conjugacy classes of genus zero, torsion-free modular subgroups, computing ramification data and Grothendieck's dessins d'enfants. In the particular case of the index 36 subgroups, the corresponding Calabi-Yau threefolds are identified, in analogy with the index 24 cases being associated with K3 surfaces. In a parallel vein, we study the 112 semi-stable elliptic fibrations over P^1 as extremal K3 surfaces with six singular fibres. In each case, a representative of the corresponding class of subgroups is identified by specifying a generating set for that representative.

math.AG↗
arXiv2013

The $S$-transform in arbitrary dimensions

In this note we report the solution of the problem of defining the $S$-transform in Free Probability Theory in arbitrary dimensions. This is achieved by generalising the theory and embedding it into an algebraic-geometric framework. Finally, we classify the groups arising as distributions of s-tuples of non-commutative random variables.

math.RT↗
arXiv2012

N=2 Gauge Theories: Congruence Subgroups, Coset Graphs and Modular Surfaces

We establish a correspondence between generalized quiver gauge theories in four dimensions and congruence subgroups of the modular group, hinging upon the trivalent graphs which arise in both. The gauge theories and the graphs are enumerated and their numbers are compared. The correspondence is particularly striking for genus zero torsion-free congruence subgroups as exemplified by those which arise in Moonshine. We analyze in detail the case of index 24, where modular elliptic K3 surfaces emerge: here, the elliptic j-invariants can be recast as dessins d'enfant which dictate the Seiberg-Witten curves.

hep-th↗
arXiv2008

Aplicacion de la descomposicion racional univariada a monstrous moonshine (in Spanish)

This paper shows how to use Computational Algebra techniques, namely the decomposition of rational functions in one variable, to explore a certain set of modular functions, called replicable functions, that arise in Monstrous Moonshine. In particular, we have computed all the rational relations with coefficients in Z between pairs of replicable functions. ----- En este articulo mostramos como usar tecnicas de Algebra Computacional, concretamente la descomposcion de funciones racionales univariadas, para estudiar un cierto conjunto de funciones modulares, llamadas funciones replicables, que aparecen en Monstrous Moonshine. En concreto, hemos calculado todas las relaciones racionales con coeficientes en Z entre pares de funciones replicables.

math.NT↗
arXiv2008

Decomposing replicable functions

We describe an algorithm to decompose rational functions from which we determine the poset of groups fixing these functions.

math.NT↗
arXiv2003

Principal moduli and class fields

We study the values taken by Gamma_0(n) modular functions at elliptic points of order 2 for the Fricke extension that lie outside Gamma_0(n). In the case of a principal modulus (`Hauptmodul') for Gamma_0(n) or its Fricke extension, we determine the class fields generated by these values.

math.NT↗