Thursday, March 31, 2011
For those interested in a cryptographical challenge, the Feds are asking for help on the cracking of a code written by Ricky McCormick, 41, three days before he was found dead on June 30th, 1999 in a St. Louis field.
"We are really good at what we do," said Dan Olson, the chief of the FBI's Cryptanalysis and Racketeering Records Unit. "But we could use some help with this one."
Read more on the challenge at MSNBC.
Tuesday, March 08, 2011
Persson posted a nice paper recently, exploring the relationships between Calabi-Yau threefolds, U-duality groups and automorphic instanton partition functions. The paper discusses recent attempts at describing the moduli space in type IIA/B string theory on X×S^1, or the hypermultiplet moduli space in type IIB/A on X. It is well known that in certain classes of N=2 supergravities (e.g. magic supergravities) one can use automorphic techniques to constrain quantum corrections. Given a D=3 U-duality group G_3(Z), BPS-degeneracies are recovered from the Fourier coefficients of its related automorphic forms. From this stems the conjecture that the instanton partition function in N=2 supergravity on R^3×S^1 should correspond to an automorphic representation in the quaternionic discrete series of G_3.
Abstract: We survey recent results on quantum corrections to the hypermultiplet moduli space M in type IIA/B string theory on a compact Calabi-Yau threefold X, or, equivalently, the vector multiplet moduli space in type IIB/A on X x S^1. Our main focus lies on the problem of resumming the infinite series of D-brane and NS5-brane instantons, using the mathematical machinery of automorphic forms. We review the proposal that whenever the low-energy theory in D=3 exhibits an arithmetic "U-duality" symmetry G(Z) the total instanton partition function arises from a certain unitary automorphic representation of G, whose Fourier coefficients reproduce the BPS-degeneracies. For D=4, N=2 theories on R^3 x S^1 we argue that the relevant automorphic representation falls in the quaternionic discrete series of G, and that the partition function can be realized as a holomorphic section on the twistor space Z over M. We also offer some comments on the close relation with N=2 wall crossing formulae.