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.

Symmetric obstruction theories and Hilbert schemes of points on threefolds

Abstract: We introduce the notion of symmetric obstruction theory and study symmetric obstruction theories which are compatible with C*-actions. We prove that the contribution of an isolated fixed point under a C*-action to equivariant Donaldson-Thomas type invariants is +/- 1. As an application, we compute weighted Euler characteristics of all Hilbert schemes of points on any 3-fold. Moreover, we calculate the zero-dimensional Donaldson-Thomas invariants of any projective Calabi-Yau 3-fold. This proves a conjecture of Maulik-Nekrasov-Okounkov-Pandharipande.

Early-Type Galaxies in the Hubble Deep Field: The Star Formation History*

Abstract: We have investigated the properties of a complete K-band selected sample of 35 elliptical and S0 galaxies brighter than K = 20.15 mag in the Hubble deep field, as representative of the field galaxy population. This sample has been derived from deep K-band image by the KPNO-IRIM camera, by applying a rigorous morphological classification scheme based on quantitative analyses of the surface brightness profiles. The completeness of the sample is proved by a careful evaluation of all biasing effects inherent in the automated selection procedure. Fifteen objects have spectroscopic redshifts, while for the remaining 20 a photometric redshift is estimated from a seven-color broadband spectrum (including four HST and three near-IR bands). This data set, based on public archives from HST and from deep observations at Kitt Peak and Hawaii, is unique for its morphological information and for its photometric and spectroscopic coverage. The broadband spectra of the sample galaxies, together with a few basic assumptions about the IMF and the stellar evolutionary paths, allow us to date their dominant stellar populations. The majority of bright early-type galaxies in this field are found at redshifts z 1.3 to display colors indicative of a fairly wide range of ages (typically 1.5 to 3 Gyr). Because of the different cosmological timescales, the star formation history depends to some extent on the assumed value for the cosmological deceleration parameter: we find that the major episodes of star formation (SF) building up typical M galaxies have taken place during a wide redshift interval 1 1.3, which should be detectable during the luminous star formation phase expected to happen at these redshifts. Obvious solutions are (1) that the merging events triggering the SF imply strongly perturbed morphologies that prevent selecting them by our morphological classification filter, or (2) that a dust-polluted interstellar medium (ISM) obscures the (either continuous or episodic) events of star formation, after which gas consumption (or a galactic wind) cleans up the galaxy. We conclude that the likely solution is a combination thereof, i.e., a set of dust-enshrouded merging-driven starbursts occurring during the first few gigayears of the galaxy's lifetime. While our main conclusions are moderately dependent on the assumed value of q0, an open universe is favored in our analysis by the match of the K-band local luminosity functions with the observed numbers of faint distant galaxies. Two sources of uncertainty in our analysis, i.e., the possible presence of a background cluster or group at z ~ 1 in the HDF (possibly contaminating the z distribution) and the lack of a complete spectroscopic identification, are shown unlikely to affect our main results. In any case, they will be reduced soon by new observations in the southern HDF and by deep spectroscopic surveys with large telescopes.

Search for invisible decays of a Higgs boson using vector-boson fusion in pp collisions at √s=8 TeV with the ATLAS detector

Abstract: A search for a Higgs boson produced via vector-boson fusion and decaying into invisible particles is presented, using 20.3 fb−1 of proton-proton collision data at a centre-of-mass energy of 8 TeV recorded by the ATLAS detector at the LHC. For a Higgs boson with a mass of 125 GeV, assuming the Standard Model production cross section, an upper bound of 0.28 is set on the branching fraction of H → invisible at 95% confidence level, where the expected upper limit is 0.31. The results are interpreted in models of Higgs-portal dark matter where the branching fraction limit is converted into upper bounds on the dark-matter-nucleon scattering cross section as a function of the dark-matter particle mass, and compared to results from the direct dark-matter detection experiments.

Measurements of W ± Z production cross sections in pp collisions at √s = 8 TeV with the ATLAS detector and limits on anomalous gauge boson self-couplings

Abstract: This paper presents measurements of W(+/-)Z production in pp collisions at a center-of-mass energy of 8 TeV. The gauge bosons are reconstructed using their leptonic decay modes into electrons and m ...

Quantum quenches, thermalization, and many-body localization

Abstract: We conjecture that thermalization following a quantum quench in a strongly correlated quantum system is closely connected to many-body delocalization in the space of quasi-particles. This scenario is tested in the anisotropic Heisenberg spin chain with different types of integrability-breaking terms. We first quantify the deviations from integrability by analyzing the level spacing statistics and the inverse participation ratio of the system's eigenstates. We then focus on thermalization, by studying the dynamics after a sudden quench of the anisotropy parameter. Our numerical simulations clearly support the conjecture, as long as the integrability-breaking term acts homogeneously on the quasiparticle space, in such a way as to induce ergodicity over all the relevant Hilbert space.