Optical angular momentum transfer to trapped absorbing particles

Particle rotation resulting from the absorption of light carrying angular momentum has been measured. When absorbing CuO particles (1-5μm) were trapped in a focused ‘‘donut’’ laser beam, they rotated, due to the helical phase structure of the beam. Changing the polarization of the light from plane to circular caused the rotation frequency to increase or decrease, depending on the sense of the polarization with respect to the helicity of the beam. Rotation frequencies were obtained by Fourier analysis of amplitude fluctuations in the backscattered light from the particles. © 1996 The American Physical Society

BPS branes in discrete torsion orbifolds

We investigate D-branes in a Z_3xZ_3 orbifold with discrete torsion. For this class of orbifolds the only known objects which couple to twisted RR potentials have been non-BPS branes. By using more general gluing conditions we construct here a D-brane which is BPS and couples to RR potentials in the twisted and in the untwisted sectors.Comment: 20 pages, LaTe

Fractional two-branes, toric orbifolds and the quantum McKay correspondence

We systematically study and obtain the large-volume analogues of fractional two-branes on resolutions of orbifolds C^3/Z_n. We study a generalisation of the McKay correspondence proposed in hep-th/0504164 called the quantum McKay correspondence by constructing duals to the fractional two-branes. Details are explicitly worked out for two examples -- the crepant resolutions of C^3/Z_3 and C^3/Z_5.Comment: 34 pages, 2 figures, LaTeX (JHEP3 style); (v2) typos corrected; (v3) sec 3 reorganise

Matrix Factorizations and Homological Mirror Symmetry on the Torus

We consider matrix factorizations and homological mirror symmetry on the torus T^2 using a Landau-Ginzburg description. We identify the basic matrix factorizations of the Landau-Ginzburg superpotential and compute the full spectrum, taking into account the explicit dependence on bulk and boundary moduli. We verify homological mirror symmetry by comparing three-point functions in the A-model and the B-model.Comment: 41 pages, 9 figures, v2: reference added, minor corrections and clarifications, version published in JHE

Defect Perturbations in Landau-Ginzburg Models

Perturbations of B-type defects in Landau-Ginzburg models are considered. In particular, the effect of perturbations of defects on their fusion is analyzed in the framework of matrix factorizations. As an application, it is discussed how fusion with perturbed defects induces perturbations on boundary conditions. It is shown that in some classes of models all boundary perturbations can be obtained in this way. Moreover, a universal class of perturbed defects is constructed, whose fusion under certain conditions obey braid relations. The functors obtained by fusing these defects with boundary conditions are twist functors as introduced in the work of Seidel and Thomas.Comment: 46 page

Rigidity and defect actions in Landau-Ginzburg models

Studying two-dimensional field theories in the presence of defect lines naturally gives rise to monoidal categories: their objects are the different (topological) defect conditions, their morphisms are junction fields, and their tensor product describes the fusion of defects. These categories should be equipped with a duality operation corresponding to reversing the orientation of the defect line, providing a rigid and pivotal structure. We make this structure explicit in topological Landau-Ginzburg models with potential x^d, where defects are described by matrix factorisations of x^d-y^d. The duality allows to compute an action of defects on bulk fields, which we compare to the corresponding N=2 conformal field theories. We find that the two actions differ by phases.Comment: 53 pages; v2: clarified exposition of pivotal structures, corrected proof of theorem 2.13, added remark 3.9; version to appear in CM

Gauge theories from wrapped and fractional branes

We compare two applications of the gauge/gravity correspondence to a non conformal gauge theory, based respectively on the study of D-branes wrapped on supersymmetric cycles and of fractional D-branes on orbifolds. We study two brane systems whose geometry is dual to N=4, D=2+1 super Yang-Mills theory, the first one describing D4-branes wrapped on a two-sphere inside a Calabi-Yau two-fold and the second one corresponding to a system of fractional D2/D6-branes on the orbifold R^4/Z_2. By probing both geometries we recover the exact perturbative running coupling constant and metric on the moduli space of the gauge theory. We also find a general expression for the running coupling constant of the gauge theory in terms of the "stringy volume" of the two-cycle which is involved in both types of brane systems.Comment: AMS-LaTeX, 35 pages, no figures. Minor typos corrected, version to appear in NP

Pseudorapidity distributions of charged particles from Au+Au collisions at the maximum RHIC energy, Sqrt(s_NN) = 200 GeV

We present charged particle densities as a function of pseudorapidity and collision centrality for the 197Au+197Au reaction at Sqrt{s_NN}=200 GeV. For the 5% most central events we obtain dN_ch/deta(eta=0) = 625 +/- 55 and N_ch(-4.7<= eta <= 4.7) = 4630+-370, i.e. 14% and 21% increases, respectively, relative to Sqrt{s_NN}=130 GeV collisions. Charged-particle production per pair of participant nucleons is found to increase from peripheral to central collisions around mid-rapidity. These results constrain current models of particle production at the highest RHIC energy.Comment: 4 pages, 5 figures; fixed fig. 5 caption; revised text and figures to show corrected calculation of and ; final version accepted for publicatio

Quark Gluon Plasma an Color Glass Condensate at RHIC? The perspective from the BRAHMS experiment

We review the main results obtained by the BRAHMS collaboration on the properties of hot and dense hadronic and partonic matter produced in ultrarelativistic heavy ion collisions at RHIC. A particular focus of this paper is to discuss to what extent the results collected so far by BRAHMS, and by the other three experiments at RHIC, can be taken as evidence for the formation of a state of deconfined partonic matter, the so called quark-gluon-plasma (QGP). We also discuss evidence for a possible precursor state to the QGP, i.e. the proposed Color Glass Condensate.Comment: 32 pages, 18 figure

Recent Results from the BRAHMS Experiment

We present recent results obtained by the BRAHMS experiment at the Relativistic Heavy Ion Collider (RHIC) for the systems of Au + Au and Cu + Cu at \rootsnn{200} and at 62.4 GeV, and p + p at \rootsnn{200}. Nuclear modification factors for Au + Au and Cu + Cu collisions are presented. Analysis of anti-particle to particle ratios as a function of rapidity and collision energy reveal that particle populations at the chemical freeze-out stage for heavy-ion reactions at and above SPS energies are controlled by the baryon chemical potential. From the particle spectra we deduce significant radial expansion ($\beta \approx$ 0.75), as expected for systems created with a large initial energy density. We also measure the elliptic flow parameter $v_2$ versus rapidity and \ptn. We present rapidity dependent $p/\pi$ ratios within $0 < y < 3$ for Au + Au and Cu + Cu at \rootsnn{200}. \Raa is found to increase with decreasing collision energy, decreasing system size, and when going towards more peripheral collisions. However, \Raa shows only a very weak dependence on rapidity (for $0 < y < 3.2$), both for pions and protons.Comment: 16 pages and 14 figures, proceedings for plenary talk at Quark Matter 2005, Budapest, Hungar