SU(2) WZW D-branes and quantized worldvolume U(1) flux on S^2

We discuss possible D-brane configurations on SU(2) group manifolds in the sigma model approach. When we turn the boundary conditions of the spacetime fields into the boundary gluing conditions of chiral currents, we find that for all D-branes except the spherical D2-branes, the gluing matrices R^a_{b} depend on the fields, so the chiral Kac-Moody symmetry is broken, but conformal symmetry is maintained. Matching the spherical D2-branes derived from the sigma model with those from the boundary state approach we obtain a U(1) field strength that is consistent with flux quantization.Comment: 10 pages, Latex, several corrections (the previous version was not approved by the first two authors

Steady-State Ab Initio Laser Theory for N-level Lasers

We show that Steady-state Ab initio Laser Theory (SALT) can be applied to find the stationary multimode lasing properties of an N-level laser. This is achieved by mapping the N-level rate equations to an effective two-level model of the type solved by the SALT algorithm. This mapping yields excellent agreement with more computationally demanding N-level time domain solutions for the steady state

The Power of Poincar\'e: Elucidating the Hidden Symmetries in Focal Conic Domains

Focal conic domains are typically the "smoking gun" by which smectic liquid crystalline phases are identified. The geometry of the equally-spaced smectic layers is highly generic but, at the same time, difficult to work with. In this Letter we develop an approach to the study of focal sets in smectics which exploits a hidden Poincar\'e symmetry revealed only by viewing the smectic layers as projections from one-higher dimension. We use this perspective to shed light upon several classic focal conic textures, including the concentric cyclides of Dupin, polygonal textures and tilt-grain boundaries.Comment: 4 pages, 3 included figure

Multispectral Bioluminescence Tomography: Methodology and Simulation

Bioluminescent imaging has proven to be a valuable tool for monitoring physiological and pathological activities at cellular and molecular levels in living small animals. Using biological techniques, target cells can be tagged with reporters encoding several kinds of luciferase enzymes, which generate characteristic photons in a wide spectrum covering the infrared range. Part of the diffused light can reach the body surface of the small animal, be separated into several spectral bands using appropriate filters, and collected by a sensitive CCD camera. Here we present a bioluminescence tomography (BLT) method for a bioluminescent source reconstruction from multispectral data measured on the external surface, and demonstrate the advantages of multispectral BLT in a numerical study using a heterogeneous mouse chest phantom. The results show that the multispectral approach significantly improves the accuracy and stability of the BLT reconstruction even if the data are highly noisy

Vertical Integration and Competitive Balance in Professional Sports: Evidence from Minor League Baseball

Major League Baseball (MLB) teams regularly call up players from their Minor League Baseball (MiLB) affliates to fulfill roster needs. This paper utilizes a manually collected panel of player call-ups between 1946 and 2019 and studies their impact on competitive balance in the minor leagues. Our results indicate an overall positive relationship between call-ups and competitive balance in the MiLB, with the pro-competitive effect primarily driven by the AA leagues and not AAA leagues. We also  find suggestive evidence of the effect being likely explained by the promotion of MiLB players to MLB, rather than the demotion of MLB players to MiLB. Our findings provide important policy implications regarding vertical relationships and human capital development in professional sports

Stock Market Reactions to Presidential Statements: Evidence from Company-Specific Tweets

When the President of the United States tweets, do investors respond? We analyze the impact of tweets from President Trump\u27s official Twitter accounts from November 9, 2016 to July 31, 2017 that include the name of a publicly traded company. We find that these tweets move company stock prices and increase trading volume, volatility and institutional investor attention, with a stronger impact before the presidential inauguration. The initial impact of the presidential tweets on stock prices appears to dissipate over the next few trading days. Overall, the results show that investors pay attention to presidential company-specific statements even when such statements have no lasting effect on shareholder value