International School for Advanced Studies

About: International School for Advanced Studies is a education organization based out in Trieste, Friuli-Venezia Giulia, Italy. It is known for research contribution in the topics: Galaxy & Dark matter. The organization has 3751 authors who have published 13433 publications receiving 588454 citations. The organization is also known as: SISSA & Scuola Internazionale Superiore di Studi Avanzati.

Non-Lagrangian theories from brane junctions

Abstract: In this article we use 5-brane junctions to study the 5D T N SCFTs corresponding to the 5D N = 1 uplift of the 4D N = 2 strongly coupled gauge theories, which are obtained by compactifying N M5 branes on a sphere with three full punctures. Even though these theories have no Lagrangian description, by using the 5-brane junctions proposed by Benini, Benvenuti and Tachikawa, we are able to derive their Seiberg-Witten curves and Nekrasov partition functions. We cross-check our results with the 5D super-conformal index proposed by Kim, Kim and Lee. Through the AGTW correspondence, we discuss the relations between 5D superconformal indices and n -point functions of the q -deformed W N Toda theories.

Nearby early-type galaxies with ionized gas - III. Analysis of line-strength indices with new stellar population models

Abstract: Aims. The paper is devoted to the study of the underlying stellar population of a sample of 65 nearby early-type galaxies, predominantly located in low density environments, a large fraction of which show emission lines. Methods. Ages, metallicities, and [ α /Fe] ratios have been derived through the comparison of Lick indices measured at different galacto-centric distances (7 apertures and 4 gradients) with new simple stellar population (SSP) models that account for the presence of α /Fe-enhancement. The SSPs cover a wide range of ages ($10^{9}{-}16$ $\times$ 10 9 yr), metallicities (0.0004 ≤ Z ≤ 0.05), and [ α /Fe] ratios (0–0.8). To derive the stellar population parameters, we use an algorithm that provides, together with the most likely solution in the (age, Z , [ α /Fe] ) space, the probability density function along the age-metallicity degeneracy. Results. We derive a large spread in age, with SSP-equivalent ages ranging from a few to 15 Gyr. Age does not show any significant trend with central velocity dispersion $\sigma_{\rm c}$, but E galaxies appear on average older than lenticulars. On the contrary, a significant increasing trend of metallicity and [ α /Fe] with $\sigma_{\rm c}$ is observed, testifying that the chemical enrichment was more efficient and the duration of the star formation shorter in more massive galaxies. These latter two relations do not depend on galaxy morphological type. We have also sought possible correlations with the local galaxy density $\rho_{xyz}$, but neither metallicity nor α -enhancement show clear trends. However, we find that while low density environments (LDE) ($\rho_{xyz} \le 0.4$) contain very young objects (from 1 Gyr to 4 Gyr), none of the galaxies in the higher density environments (HDE) (40% of galaxies with a measured density) is younger than 5 Gyr. Considering the lack of environmental effect on the [ α /Fe] ratio and the high value of [ α /Fe] in some young massive objects, we argue that young galaxies in LDE are more likely due to recent rejuvenation episodes. By comparing the number of “rejuvenated” objects with the total number of galaxies in our sample, and by means of simple two-SSP component models, we estimate that, on average, the rejuvenation episodes do not involve more than 25% of the total galaxy mass. The good quality of the data also allow us to analyze the gradients of stellar populations. An average negative metallicity gradient $\Delta \log Z/\Delta \log (r/r_{\rm e}) \sim -0.21$ is firmly detected, while the age and α -enhancement spatial distributions within r e /2 appear quite flat. These observations suggest that, in a given galaxy, the star formation proceeded on similar timescales all across the central r e /2 region, but with an increasing efficiency toward the center.

Weight Shifting Operators and Conformal Blocks

Abstract: We introduce a large class of conformally-covariant differential operators and a crossing equation that they obey. Together, these tools dramatically simplify calculations involving operators with spin in conformal field theories. As an application, we derive a formula for a general conformal block (with arbitrary internal and external representations) in terms of derivatives of blocks for external scalars. In particular, our formula gives new expressions for “seed conformal blocks” in 3d and 4d CFTs. We also find simple derivations of identities between external-scalar blocks with different dimensions and internal spins. We comment on additional applications, including deriving recursion relations for general conformal blocks, reducing inversion formulae for spinning operators to inversion formulae for scalars, and deriving identities between general 6j symbols (Racah-Wigner coefficients/“crossing kernels”) of the conformal group.

Time-dependent mean field theory for quench dynamics in correlated electron systems.

Abstract: A simple and very flexible variational approach to the out-of-equilibrium quantum dynamics in strongly correlated electron systems is introduced through a time-dependent Gutzwiller wave function. As an application, we study the simple case of a sudden change of the interaction in the fermionic Hubbard model and find at the mean-field level an extremely rich behavior. In particular, a dynamical transition between small and large quantum quench regimes is found to occur at half-filling, in accordance with the analysis of Eckstein et al., Phys. Rev. Lett. 103, 056403 (2009), obtained by dynamical mean-field theory, that turns into a crossover at any finite doping.