The variational method is a powerful approach to solve many-body quantum problems nonperturbatively. However, in the context of relativistic field theory, it needs meet three seemingly incompatible requirements outlined by Feynman: extensivity, computability, and lack UV sensitivity. In practice, methods break one three, which translates into need have an IR or cutoff. this letter, I introduce ...

It was recently conjectured that the ratio of the shear viscosity to entropy density eta/s for any fluid always exceeds [formula: see text]. A theoretical counterexample to this bound can be constructed from a nonrelativistic gas by increasing the number of species in the fluid while keeping the dynamics essentially independent of the species type. The question of whether the underlying structu...

A central problem in quantum condensed matter physics is the critical theory governing the zero-temperature quantum phase transition between strongly renormalized Fermi liquids as found in heavy fermion intermetallics and possibly in high-critical temperature superconductors. We found that the mathematics of string theory is capable of describing such fermionic quantum critical states. Using th...

We provide a brief overview of the basic tools and concepts of quantum field theoretical scattering theory. This article is commissioned by the Encyclopedia of Mathematical Physics, edited by J.-P. Françoise, G. Naber and T.S. Tsun, to be published by the Elsevier publishing house. 1 Physical Motivation and Mathematical Setting The primary connection of relativistic quantum field theory to expe...

This is the first of a two-part introduction to some interpretive questions that arise in connection with quantum field theories (QFTs). Some of these questions are continuous with those familiar from the discussion of ordinary non-relativistic quantum mechanics (QM). For example, questions about locality can be rigorously posed and fruitfully pursued within the framework of QFT. A stark disana...

1.1. It embodies deep and beautiful principles. These are, first of all, the general principles of quantum mechanics, special relativity, and locality, that lead one to relativistic quantum field theory [1]. In addition, we require invariance under the nonabelian gauge symmetry SU(3), the specific matter content of quarks – six spin 1/2 Dirac fermions which are color triplets – and renormalizab...

1.1. It embodies deep and beautiful principles. These are, first of all, the general principles of quantum mechanics, special relativity, and locality, that lead one to relativistic quantum field theory [1]. In addition, we require invariance under the nonabelian gauge symmetry SU(3), the specific matter content of quarks – six spin 1/2 Dirac fermions which are color triplets – and renormalizab...