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.

Rapid variability in the synchrotron self Compton model for blazars

Abstract: ABSTRA C T Blazars are characterized by large amplitude and rapid variability, indicating that the electron distribution is changing rapidly, often on time-scales shorter than the light-crossing time. The emitting region is sufficiently compact to let radiative losses dominate the cooling of highenergy electrons. We study the time-dependent behaviour of the electron distribution after episodic electron injection phases, and calculate the observed synchrotron and self-Compton radiation spectra. Since photons produced in different parts of the source have different travel times, the observed spectrum is produced by the electron distribution at different stages of evolution. Even a homogeneous source then resembles an inhomogeneous one. Time delays between the light curves of fluxes at different frequencies are possible, as illustrated for the specific case of the BL Lac object Mrk 421.

Local integrals of motion in many‐body localized systems

Abstract: We review the current (as of Fall 2016) status of the studies on the emergent integrability in many-body localized models. We start by explaining how the phenomenology of fully many-body localized systems can be recovered if one assumes the existence of a complete set of (quasi)local operators which commute with the Hamiltonian (local integrals of motions, or LIOMs). We describe the evolution of this idea from the initial conjecture, to the perturbative constructions, to the mathematical proof given for a disordered spin chain. We discuss the proposed numerical algorithms for the construction of LIOMs and the status of the debate on the existence and nature of such operators in systems with a many-body mobility edge, and in dimensions larger than one.

A first top partner hunter’s guide

Abstract: We provide a systematic effective lagrangian description of the phenomenology of the lightest top-partners in composite Higgs models. Our construction is based on symmetry, on selection rules and on plausible dynamical assumptions. The structure of the resulting simplified models depends on the quantum numbers of the lightest top partner and of the operators involved in the generation of the top Yukawa. In all cases the phenomenology is conveniently described by a small number of parameters, and the results of experimental searches are readily interpreted as a test of naturalness. We recast presently available experimental bounds on heavy fermions into bounds on top partners: LHC has already stepped well inside the natural region of parameter space.

The Properties of the X-Ray Holes in the Intracluster Medium of the Perseus Cluster

Abstract: : High-resolution X-ray and low-frequency radio imaging now allow us to examine in detail the interaction and physical properties of the radio source 3C 84 and the surrounding thermal gas. The radiative and dynamical properties of the inner X-ray holes, which coincide with the radio lobes, indicate that the ratio of the energy factor k to the filling factor f is in the range 180 < k/f < 500. We define k to be the ratio of the total particle energy to that of the electrons radiating above a fiducial frequency of 10 MHz. The relativistic plasma and magnetic field are not in equipartition, since the field must be a factor of 4 or more lower than required for pressure balance. Unexpected steep-spectrum spurs in the low-frequency radio maps point to outer X-ray holes, which are plausibly buoyant old radio lobes. The evidence that the inner lobes are currently expanding subsonically, yet have not detached due to buoyancy, and the requirement that the synchrotron cooling time must exceed the age of the hole enable us to constrain the jet power of the nucleus to between 10(exp 44) and 10(exp 45) erg s (exp-1), depending on the filling factor of the relativistic plasma.

Fate of gravitational collapse in semiclassical gravity

Abstract: While the outcome of gravitational collapse in classical general relativity is unquestionably a black hole, up to now no full and complete semiclassical description of black hole formation has been thoroughly investigated. Here we revisit the standard scenario for this process. By analyzing how semiclassical collapse proceeds we show that the very formation of a trapping horizon can be seriously questioned for a large set of, possibly realistic, scenarios. We emphasize that in principle the theoretical framework of semiclassical gravity certainly allows the formation of trapping horizons. What we are questioning here is the more subtle point of whether or not the standard black hole picture is appropriate for describing the end point of realistic collapse. Indeed if semiclassical physics were in some cases to prevent formation of the trapping horizon, then this suggests the possibility of new collapsed objects which can be much less problematic, making it unnecessary to confront the information paradox or the runaway end point problem.