On September 14, 2015 at 09:50:45 UTC the two detectors of the Laser Interferometer Gravitational-Wave Observatory simultaneously observed a transient gravitational-wave signal. The signal sweeps upwards in frequency from 35 to 250 Hz with a peak gravitational-wave strain of 1.0×10(-21). It matches the waveform predicted by general relativity for the inspiral and merger of a pair of black holes and the ringdown of the resulting single black hole. The signal was observed with a matched-filter signal-to-noise ratio of 24 and a false alarm rate estimated to be less than 1 event per 203,000 years, equivalent to a significance greater than 5.1σ. The source lies at a luminosity distance of 410(-180)(+160)  Mpc corresponding to a redshift z=0.09(-0.04)(+0.03). In the source frame, the initial black hole masses are 36(-4)(+5)M⊙ and 29(-4)(+4)M⊙, and the final black hole mass is 62(-4)(+4)M⊙, with 3.0(-0.5)(+0.5)M⊙c(2) radiated in gravitational waves. All uncertainties define 90% credible intervals. These observations demonstrate the existence of binary stellar-mass black hole systems. This is the first direct detection of gravitational waves and the first observation of a binary black hole merger.

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The Observation of Gravitational Waves from a Binary Black Hole Merger

Rise of silicene: A competitive 2D material

Graphene is a two-dimensional carbon material with a honeycomb lattice and Dirac-like low-energy excitations. When Zeeman and spin-orbit interactions are neglected, its Landau levels are fourfold degenerate, explaining the 4e2/h separation between quantized Hall conductivity values seen in recent experiments. In this Letter we derive a criterion for the occurrence of interaction-driven quantum Hall effects near intermediate integer values of e2/h due to charge gaps in broken symmetry states.

Quantum Hall Ferromagnetism in Graphene

Theorists have discovered topological insulators that are insulating in their interior and on their surfaces but have conducting channels at corners or along edges.

(d - 2)-dimensional edge states of rotation symmetry protected topological states

Z. Jiang, 2, ∗ Y. Zhang, H. L. Stormer, 3, 4 and P. Kim Department of Physics, Columbia University, New York, New York 10027, USA National High Magnetic Field Laboratory, Tallahassee, Florida 32310, USA Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027, USA Bell Laboratories, Alcatel-Lucent, Murray Hill, New Jersey 07974, USA (Dated: February 1, 2008)

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The Nature of Quantum Hall States near the Charge Neutral Dirac Point in Graphene

We report here a study on the effect of hydrogenation on a new one-atom thick material made of silicon and carbon atoms (silicene/graphene (SG) hybrid) within density functional theory. The structural, electronic and magnetic properties are investigated for non-, semi- and fully hydrogenated SG hybrids in a chair configuration and are compared with their parent materials. Calculations reveal that pure SG is a non-zero band gap semi-conductor with stable planar honeycomb structure. So mixing C and Si in an alternating manner gives another way to generate a finite band gap in one-atom thick materials. Fully hydrogenation makes the gap larger; however half chemical modification with H reduces the gap in favor of ferromagnetism order. The findings of this work open a wide spectrum of possibilities for designing SG-based nanodevices with controlled and tuned properties.

https://iopscience.iop.org/article/10.1088/0953-8984/24/48/485502/pdf

DFT investigations of the hydrogenation effect on silicene/graphene hybrids

We study mirror symmetry of supermanifolds constructed as fermionic extensions of compact toric varieties. We mainly discuss the case where the linear sigma A-model contains as many fermionic fields as there are U(1) factors in the gauge group. In the mirror super-Landau-Ginzburg B-model, focus is on the bosonic structure obtained after integrating out all the fermions. Our key observation is that there is a relation between the super-Calabi-Yau conditions of the A-model and quasi-homogeneity of the B-model, and that the degree of the associated superpotential in the B-model is given in terms of the determinant of the fermion charge matrix of the A-model.

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Toric Calabi–Yau supermanifolds and mirror symmetry

We develop the non-commutative Chern-Simons gauge model analysis modeling the description of the hierarchical states of fractional quantum Hall fluids. For a generic level n of the hierarchy, we show that the order parameter matrix Kab is given by θ−2Tr (τaτb), where {τa,1 ≤ a ≤ n} define a specific set of n × n matrices depending on the parameter θ and the levels la of the CS effective field theory. Our analysis predicts the existence of a third order tensor of order parameters Cabc induced by the external magnetic field. It is shown that the Cabc's are not new order parameters and are given by θdabc, where dabc are numbers depending on the la's. We also give the generalized quantum Hall soliton extending that obtained in the case of the Laughlin state.

NC Branes and Hierarchies in Quantum Hall Fluids

We study the BPS and non BPS black attractors in 7D N=2 supergravity embedded in 11D M-theory compactified on K3. Combining Kahler and complex moduli in terms of SO(3) representations, we build the Dalbeault like (DL) basis for the second cohomology of K3 and set up the fundamental relations of the special "hyperKahler" geometry of the underlying moduli space of the 7D theory. We study the attractor eqs of the 7D black branes by using the method of the criticality of the effective potential and also by using the extension of the so called 4D new attractor approach to 7D N=2 supergravity. A comment, regarding a 6D/7D correspondence, along the line of Ceresole-Ferrara-Marrani used for 4D/5D, ref.arXiv:0707.0964, is made.

El Hassan Saidi

Papers

DFT investigations of the hydrogenation effect on silicene/graphene hybrids

Toric Calabi–Yau supermanifolds and mirror symmetry

NC Branes and Hierarchies in Quantum Hall Fluids

BPS and non BPS 7D Black Attractors in M-Theory on K3

Edge effect on magnetic phases of doped zigzag graphone nanoribbons