Lattice study of two-dimensional N=(2,2) super Yang-Mills at large-N

We study two-dimensional N=(2,2) SU(N) super Yang-Mills theory on Euclidean two-torus using Sugino's lattice regularization. We perform the Monte-Carlo simulation for N=2,3,4,5 and then extrapolate the result to N = infinity. With the periodic boundary conditions for the fermions along both circles, we establish the existence of a bound state in which scalar fields clump around the origin, in spite of the existence of a classical flat direction. In this phase the global (Z_N)^2 symmetry turns out to be broken. We provide a simple explanation for this fact and discuss its physical implications.Comment: 24 pages, 13 figure

The Interplay of Spin and Charge Channels in Zero Dimensional Systems

We present a full fledged quantum mechanical treatment of the interplay between the charge and the spin zero-mode interactions in quantum dots. Quantum fluctuations of the spin-mode suppress the Coulomb blockade and give rise to non-monotonic behavior near this point. They also greatly enhance the dynamic spin susceptibility. Transverse fluctuations become important as one approaches the Stoner instability. The non-perturbative effects of zero-mode interaction are described in terms of charge (U(1)) and spin (SU(2)) gauge bosons.Comment: 4.5 pages, 2 figure

Absence of sign problem in two-dimensional N=(2,2) super Yang-Mills on lattice

We show that N=(2,2) SU(N) super Yang-Mills theory on lattice does not have sign problem in the continuum limit, that is, under the phase-quenched simulation phase of the determinant localizes to 1 and hence the phase-quench approximation becomes exact. Among several formulations, we study models by Cohen-Kaplan-Katz-Unsal (CKKU) and by Sugino. We confirm that the sign problem is absent in both models and that they converge to the identical continuum limit without fine tuning. We provide a simple explanation why previous works by other authors, which claim an existence of the sign problem, do not capture the continuum physics.Comment: 27 pages, 24 figures; v2: comments and references added; v3: figures on U(1) mass independence and references added, to appear in JHE

Real-time testing of the on-site warning algorithm in southern California and its performance during the July 29 2008 M_w5.4 Chino Hills earthquake

The real-time performance of the τ_c -P_d on-site early warning algorithm currently is being tested within the California Integrated Seismic Network (CISN). Since January 2007, the algorithm has detected 58 local earthquakes in southern California and Baja with moment magnitudes of 3.0 ≤ M_w ≤ 5.4. Combined with newly derived station corrections the algorithm allowed for rapid determination of moment magnitudes and Modified Mercalli Intensity (MMI) with uncertainties of ±0.5 and ±0.7 units, respectively. The majority of reporting delays ranged from 9 to 16 s. The largest event, the July 29 2008 M_w5.4 Chino Hills earthquake, triggered a total of 60 CISN stations in epicentral distances of up to 250 km. Magnitude predictions at these stations ranged from M_w4.4 to M_w6.5 with a median of M_w5.6. The closest station would have provided up to 6 s warning at Los Angeles City Hall, located 50 km to the west-northwest of Chino Hills

Variational cluster approach to correlated electron systems in low dimensions

A self-energy-functional approach is applied to construct cluster approximations for correlated lattice models. It turns out that the cluster-perturbation theory (Senechal et al, PRL 84, 522 (2000)) and the cellular dynamical mean-field theory (Kotliar et al, PRL 87, 186401 (2001)) are limiting cases of a more general cluster method. Results for the one-dimensional Hubbard model are discussed with regard to boundary conditions, bath degrees of freedom and cluster size.Comment: 4 pages, final version with minor change

Searching and fixating: scale-invariance vs. characteristic timescales in attentional processes

In an experiment involving semantic search, the visual movements of sample populations subjected to visual and aural input were tracked in a taskless paradigm. The probability distributions of saccades and fixations were obtained and analyzed. Scale-invariance was observed in the saccadic distributions, while the fixation distributions revealed the presence of a characteristic (attentional) time scale for literate subjects. A detailed analysis of our results suggests that saccadic eye motions are an example of Levy, rather than Brownian, dynamics.Comment: Accepted to Europhysics Letters (2011

Formulation of Supersymmetry on a Lattice as a Representation of a Deformed Superalgebra

The lattice superalgebra of the link approach is shown to satisfy a Hopf algebraic supersymmetry where the difference operator is introduced as a momentum operator. The breakdown of the Leibniz rule for the lattice difference operator is accommodated as a coproduct operation of (quasi)triangular Hopf algebra and the associated field theory is consistently defined as a braided quantum field theory. Algebraic formulation of path integral is perturbatively defined and Ward-Takahashi identity can be derived on the lattice. The claimed inconsistency of the link approach leading to the ordering ambiguity for a product of fields is solved by introducing an almost trivial braiding structure corresponding to the triangular structure of the Hopf algebraic superalgebra. This could be seen as a generalization of spin and statistics relation on the lattice. From the consistency of this braiding structure of fields a grading nature for the momentum operator is required.Comment: 45 page

Coordination Dependence of Hyperfine Fields of 5sp Impurities on Ni Surfaces

We present first-principles calculations of the magnetic hyperfine fields H of 5sp impurities on the (001), (111), and (110) surfaces of Ni. We examine the dependence of H on the coordination number by placing the impurity in the surfaces, on top of them at the adatom positions, and in the bulk. We find a strong coordination dependence of H, different and characteristic for each impurity. The behavior is explained in terms of the on-site s-p hybridization as the symmetry is reduced at the surface. Our results are in agreement with recent experimental findings.Comment: 4 pages, 3 figure