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.

Variational description of Mott insulators.

Abstract: The Gutzwiller wave function for a strongly correlated model can, if supplemented with a long-range Jastrow factor, provide a proper variational description of Mott insulators, so far unavailable. We demonstrate this concept in the prototypical one-dimensional $t\ensuremath{-}{t}^{\ensuremath{'}}$ Hubbard model, where at half-filling we reproduce all known phases, namely, the ordinary Mott undimerized insulator with power-law spin correlations at small ${t}^{\ensuremath{'}}/t$, the spin-gapped metal above a critical ${t}^{\ensuremath{'}}/t$ and small $U$, and the dimerized Mott insulator at large repulsion.

Higgs at last

Abstract: We update the experimental constraints on the parameters of the Higgs effective Lagrangian. We combine the most recent LHC Higgs data in all available search channels with electroweak precision observables from SLC, LEP-1, LEP-2, and the Tevatron. Overall, the data are perfectly consistent with the 126 GeV particle being the Standard Model Higgs boson. The Higgs coupling to W and Z bosons relative to the Standard Model one is constrained in the range [0.98, 1.08] at 95% confidence level, independently of the values of other Higgs couplings. Higher-order Higgs couplings to electroweak gauge bosons are also well constrained by a combination of LHC Higgs data and electroweak precision tests.

Direct evidence for a gapless Z 2 spin liquid by frustrating Néel antiferromagnetism

Abstract: By direct calculations of the spin gap in the frustrated Heisenberg model on the square lattice, with nearest- (${J}_{1}$) and next-nearest-neighbor (${J}_{2}$) super-exchange couplings, we provide a solid evidence that the spin-liquid phase in the frustrated regime $0.45\ensuremath{\lesssim}{J}_{2}/{J}_{1}\ensuremath{\lesssim}0.6$ is gapless. Our numerical method is based on a variational wave function that is systematically improved by the application of few Lanczos steps and allows us to obtain reliable extrapolations in the thermodynamic limit. The peculiar nature of the nonmagnetic state is unveiled by the existence of $S=1$ gapless excitations at $k=(\ensuremath{\pi},0)$ and $(0,\ensuremath{\pi})$. The magnetic transition can be described and interpreted by a variational state that is built from Abrikosov fermions having a ${Z}_{2}$ gauge structure and four Dirac points in the spinon spectrum.

Reconstructing the density of states by history-dependent metadynamics.

Abstract: We present a novel method for the calculation of the energy density of states $D(E)$ for systems described by classical statistical mechanics. The method builds on an extension of a recently proposed strategy that allows the free-energy profile of a canonical system to be recovered within a preassigned accuracy [A. Laio and M. Parrinello, Proc. Natl. Acad. Sci. U.S.A. 99, 12562 (2002)]. The method allows a good control over the error on the recovered system entropy. This fact is exploited to obtain $D(E)$ more efficiently by combining measurements at different temperatures. The accuracy and efficiency of the method are tested for the two-dimensional Ising model (up to size $50\ifmmode\times\else\texttimes\fi{}50$) by comparison with both exact results and previous studies. This method is a general one and should be applicable to more realistic model systems.