Partially Quenched Chiral Condensates from the Replica Method

A large-N_f expansion is used to compute the partially quenched chiral condensate of QCD in the microscopic finite-volume scaling region.Comment: LaTeX, 7 page

Wilson chiral perturbation theory, Wilson-Dirac operator eigenvalues and clover improvement

Chiral perturbation theory for eigenvalue distributions, and equivalently random matrix theory, has recently been extended to include lattice effects for Wilson fermions. We test the predictions by comparison to eigenvalue distributions of the Hermitian Wilson-Dirac operator from pure gauge (quenched) ensembles. We show that the lattice effects are diminished when using clover improvement for the Dirac operator. We demonstrate that the leading Wilson low-energy constants associated with Wilson (clover) fermions can be determined using spectral information of the respective Dirac operator at finite volume.Comment: Presented at "Xth Quark Confinement and the Hadron Spectrum," October 2012, Garching, Germany. To appear as PoS (Confinement X) 07

New Factorization Relations for Yang Mills Amplitudes

A double-cover extension of the scattering equation formalism of Cachazo, He and Yuan (CHY) leads us to conjecture covariant factorization formulas of n-particle scattering amplitudes in Yang-Mills theories. Evidence is given that these factorization relations are related to Berends-Giele recursions through repeated use of partial fraction identities involving linearized propagators.Comment: 7 pages, 3 figures, version to appear in PR

Constraints on New Physics from Baryogenesis and Large Hadron Collider Data

We demonstrate the power of constraining theories of new physics by insisting that they lead to electroweak baryogenesis, while agreeing with current data from the Large Hadron Collider. The general approach is illustrated with a singlet scalar extension of the Standard Model. Stringent bounds can already be obtained, which reduce the viable parameter space to a small island.Comment: 4 pages, 2 figures. References added, figures updated. Version to appear in PR

N=4 Supersymmetry on a Space-Time Lattice

Maximally supersymmetric Yang--Mills theory in four dimensions can be formulated on a space-time lattice while exactly preserving a single supersymmetry. Here we explore in detail this lattice theory, paying particular attention to its strongly coupled regime. Targeting a theory with gauge group SU(N), the lattice formulation is naturally described in terms of gauge group U(N). Although the U(1) degrees of freedom decouple in the continuum limit we show that these degrees of freedom lead to unwanted lattice artifacts at strong coupling. We demonstrate that these lattice artifacts can be removed, leaving behind a lattice formulation based on the SU(N) gauge group with the expected apparently conformal behavior at both weak and strong coupling

Phase Structure of Lattice N=4 Super Yang-Mills

We make a first study of the phase diagram of four-dimensional N=4 super Yang-Mills theory regulated on a space-time lattice. The lattice formulation we employ is both gauge invariant and retains at all lattice spacings one exactly preserved supersymmetry charge. Our numerical results are consistent with the existence of a single deconfined phase at all observed values of the bare coupling.Comment: 29 pages, 11 figures. References added, minor edits to tex

Unusual identities for QCD at tree-level

We discuss a set of recently discovered quadratic relations between gauge theory amplitudes. Such relations give additional structural simplifications for amplitudes in QCD. Remarkably, their origin lie in an analogous set of relations that involve also gravitons. When certain gluon helicities are flipped we obtain relations that do not involve gravitons, but which refer only to QCD.Comment: Talk given at XIV Mexican School on Particles and Fields, Morelia, Nov. 201

Monodromy and Jacobi-like Relations for Color-Ordered Amplitudes

We discuss monodromy relations between different color-ordered amplitudes in gauge theories. We show that Jacobi-like relations of Bern, Carrasco and Johansson can be introduced in a manner that is compatible with these monodromy relations. The Jacobi-like relations are not the most general set of equations that satisfy this criterion. Applications to supergravity amplitudes follow straightforwardly through the KLT-relations. We explicitly show how the tree-level relations give rise to non-trivial identities at loop level.Comment: 28 pages, 8 figures, JHEP