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.

Generalized Gibbs ensembles for quantum field theories

Abstract: We consider the non-equilibrium dynamics in isolated systems, described by quantum field theories (QFTs) After being prepared in a density matrix that is not an eigenstate of the Hamiltonian, such systems are expected to relax locally to a stationary state In a presence of local conservation laws, these stationary states are believed to be described by appropriate generalized Gibbs ensembles Here we demonstrate that in order to obtain a correct description of the stationary state, it is necessary to take into account conservation laws that are not (ultra-)local in the usual sense of QFT, but fulfil a significantly weaker form of locality We discuss implications of our results for integrable QFTs in one spatial dimension

GABA-mediated giant depolarizing potentials as coincidence detectors for enhancing synaptic efficacy in the developing hippocampus

Abstract: Spontaneously occurring neuronal oscillations constitute a hallmark of developmental networks. They have been observed in the retina, neocortex, hippocampus, thalamus, and spinal cord. In the immature hippocampus, the so-called “giant depolarizing potentials” (GDPs) are network-driven synaptic events generated by γ-aminobutyric acid (GABA), which at this stage is depolarizing and excitatory. We have tested the hypothesis that during the first postnatal week, GDP-associated calcium signals may alter the properties of synaptic transmission at poorly developed mossy fiber (MF)-CA3 connections. We found that “pairing” GDPs with MF stimulation induced a persistent increase in synaptic efficacy at MF-CA3 synapses. When the interval between GDPs and MF stimulation was increased, the potentiating effect progressively declined and disappeared. The potentiation depended on activation of voltage-dependent calcium channels and calcium flux. This activity may contribute to the refinement of neuronal connectivity before the establishment of the adult neuronal circuit.

Gamma-ray bursts in the comoving frame

Abstract: We estimate the bulk Lorentz factor Γ0 of 31 gamma-ray bursts (GRBs) using the measured peak time of their afterglow light curves. We consider two possible scenarios for the estimate of Γ0: the case of a homogeneous circumburst medium or a wind density profile. The values of Γ0 are broadly distributed between few tens and several hundreds with average values ∼138 and ∼66 for the homogeneous and wind density profile, respectively. We find that the isotropic energy and luminosity correlate in a similar way with Γ0, i.e. and , while the peak energy Epeak∝Γ0. These correlations are less scattered in the wind density profile than in the homogeneous case. We then study the energetics, luminosities and spectral properties of our bursts in their comoving frame. The distribution of is very narrow with a dispersion of less than a decade in the wind case, clustering around erg s−1. Peak photon energies cluster around ∼ 6 keV. The newly found correlations involving Γ0 offer a general interpretation scheme for the spectral energy correlation of GRBs. The Epeak–Eiso and Epeak–Liso correlations are due to the different Γ0 factors and the collimation-corrected correlation, Epeak–Eγ (obtained by correcting the isotropic quantities for the jet opening angle θj), can be explained if = constant. Assuming the Epeak–Eγ correlation as valid, we find a typical value of θjΓ0∼ 6–20, in agreement with the predictions of magnetically accelerated jet models.

Density-gradient-vorticity relation in perfect-fluid Robertson-Walker perturbations.

Abstract: In a previous paper, a second-order propagation equation was derived for covariant and gauge-invariant {ital vector} {ital fields} characterizing density inhomogeneities in an almost-Friedmann-Lemaitre-Robertson-Walker (-FLRW) perfect-fluid universe. However, an error there led to omission of a term representing an effect of vorticity on {ital spatial} {ital density} {ital gradients} at linear level. Here we determine this interaction (leading to an extra term in the second-order propagation equation for the spatial density gradient), and examine its geometrical and physical meaning. We define a new local decomposition of the observed density gradient and we show that the scalar variable defined in the decomposition naturally describes density clumping, and satisfies the standard Bardeen second-order equation. The physical meaning of the other variables defined in the decomposition is discussed, and their propagation equations are presented. Finally, the vorticity-induced time growth of the density gradient is derived in the long-wavelength limit.

Simplified Models for Dark Matter and Missing Energy Searches at the LHC

Abstract: The study of collision events with missing energy as searches for the dark matter (DM) component of the Universe are an essential part of the extensive program looking for new physics at the LHC. Given the unknown nature of DM, the interpretation of such searches should be made broad and inclusive. This report reviews the usage of simplified models in the interpretation of missing energy searches. We begin with a brief discussion of the utility and limitation of the effective field theory approach to this problem. The bulk of the report is then devoted to several different simplified models and their signatures, including s-channel and t-channel processes. A common feature of simplified models for DM is the presence of additional particles that mediate the interactions between the Standard Model and the particle that makes up DM. We consider these in detail and emphasize the importance of their inclusion as final states in any coherent interpretation. We also review some of the experimental progress in the field, new signatures, and other aspects of the searches themselves. We conclude with comments and recommendations regarding the use of simplified models in Run-II of the LHC.