Negative-Energy Spinors and the Fock Space of Lattice Fermions at Finite Chemical Potential

Recently it was suggested that the problem of species doubling with Kogut-Susskind lattice fermions entails, at finite chemical potential, a confusion of particles with antiparticles. What happens instead is that the familiar correspondence of positive-energy spinors to particles, and of negative-energy spinors to antiparticles, ceases to hold for the Kogut-Susskind time derivative. To show this we highlight the role of the spinorial ``energy'' in the Osterwalder-Schrader reconstruction of the Fock space of non-interacting lattice fermions at zero temperature and nonzero chemical potential. We consider Kogut-Susskind fermions and, for comparison, fermions with an asymmetric one-step time derivative.Comment: 14p

Instantons of M(atrix) Theory in PP-Wave Background

M(atrix) theory in PP-wave background possesses a discrete set of classical vacua, all of which preserves 16 supersymmetry and interpretable as collection of giant gravitons. We find Euclidean instanton solutions that interpolate between them, and analyze their properties. Supersymmetry prevents direct mixing between different vacua but still allows effect of instanton to show up in higher order effective interactions, such as analog of v^4 interaction of flat space effective theory. An explicit construction of zero modes is performed, and Goldstone zero modes, bosonic and fermionic, are identified. We further generalize this to massive M(atrix) theory that includes fundamental hypermultiplets, corresponding to insertion of longitudinal fivebranes in the background. After a brief comparison to their counterpart in AdS\times S, we close with a summary.Comment: 25 pages, LaTeX, references added, section 5 update

Euclidean Fermi fields with a hermitean Feynman-Kac-Nelson formula. I

We construct free, Euclidean, spin one-half, quantum fields with the following properties: (i) CAR; (ii) Symanzik positivity; (iii) Osterwalder-Schrader positivity; (iv) no doubling of particle or spin states. They admit the recovery of the relativistic Dirac field by the Osterwalder-Schrader technique. We then formally parametrize interacting theories by a natural class of Hermitean, Euclidean actions, and obtain a simple, Hermitean, Feynman-Kac-Nelson formula. The interacting theory formally obeys all the properties (i)–(iv), and admits the reconstruction of a physical Hilbert space, including a Hermitean, contraction semigroup for the Wick rotated time evolution. We propose a system of axioms for the interacting theory.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46510/1/220_2005_Article_BF01651549.pd

Trust and privacy in distributed work groups

Proceedings of the 2nd International Workshop on Social Computing, Behavioral Modeling and PredictionTrust plays an important role in both group cooperation and economic exchange. As new technologies emerge for communication and exchange, established mechanisms of trust are disrupted or distorted, which can lead to the breakdown of cooperation or to increasing fraud in exchange. This paper examines whether and how personal privacy information about members of distributed work groups influences individuals' cooperation and privacy behavior in the group. Specifically, we examine whether people use others' privacy settings as signals of trustworthiness that affect group cooperation. In addition, we examine how individual privacy preferences relate to trustworthy behavior. Understanding how people interact with others in online settings, in particular when they have limited information, has important implications for geographically distributed groups enabled through new information technologies. In addition, understanding how people might use information gleaned from technology usage, such as personal privacy settings, particularly in the absence of other information, has implications for understanding many potential situations that arise in pervasively networked environments.Preprin

Criticality in the 2+1-dimensional compact Higgs model and fractionalized insulators

We use a novel method of computing the third moment M_3 of the action of the 2+1-dimensional compact Higgs model in the adjoint representation with q=2 to extract correlation length and specific heat exponents nu and alpha, without invoking hyperscaling. Finite-size scaling analysis of M_3 yields the ratio (1+alpha)/nu and 1/nu separately. We find that alpha and nu vary along the critical line of the theory, which however exhibits a remarkable resilience of Z_2 criticality. We propose this novel universality class to be that of the quantum phase transition from a Mott-Hubbard insulator to a charge-fractionalized insulator in two spatial dimensions.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Let

Theory for Dynamical Short Range Order and Fermi Surface Volume in Strongly Correlated Systems

Using the fluctuation exchange approximation of the one band Hubbard model, we discuss the origin of the changing Fermi surface volume in underdoped cuprate systems due to the transfer of occupied states from the Fermi surface to its shadow, resulting from the strong dynamical antiferromagnetic short range correlations. The momentum and temperature dependence of the quasi particle scattering rate shows unusual deviations from the conventional Fermi liquid like behavior. Their consequences for the changing Fermi surface volume are discussed. Here, we investigate in detail which scattering processes might be responsible for a violation of the Luttinger theorem. Finally, we discuss the formation of hole pockets near half filling.Comment: 5 pages, Revtex, 4 postscript figure

Traveling wave deceleration of heavy polar molecules in low-field seeking states

We demonstrate the deceleration of heavy polar molecules in low-field seeking states by combining a cryogenic source and a travelling-wave Stark decelerator. The cryogenic source provides a high intensity beam with low speed and temperature, and the travelling-wave decelerator provides large deceleration forces and high phase-space acceptance. We prove these techniques using YbF molecules and find the experimental data to be in excellent agreement with numerical simulations. These methods extend the scope of Stark deceleration to a very wide range of molecules.Comment: 5 pages, 4 figure

The Geometry of Quantum Mechanics

A recent notion in theoretical physics is that not all quantum theories arise from quantising a classical system. Also, a given quantum model may possess more than just one classical limit. These facts find strong evidence in string duality and M-theory, and it has been suggested that they should also have a counterpart in quantum mechanics. In view of these developments we propose "dequantisation", a mechanism to render a quantum theory classical. Specifically, we present a geometric procedure to "dequantise" a given quantum mechanics (regardless of its classical origin, if any) to possibly different classical limits, whose quantisation gives back the original quantum theory. The standard classical limit $\hbar\to 0$ arises as a particular case of our approach.Comment: 15 pages, LaTe

Topological susceptibility in Yang-Mills theory in the vacuum correlator method

We calculate the topological susceptibility of the Yang-Mills vacuum using the field correlator method. Our estimate for the SU(3) gauge group, \chi^{1/4} = 196(7) MeV, is in a very good agreement with the results of recent numerical simulations of the Yang-Mills theory on the lattice.Comment: 5 pages (JETP Letters style