Faculty Publications: November, 2014

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Title:
Sharper Fermi LAT Images: Instrument Response Functions for an Improved Event Selection
Authors:
Portillo, Stephen K. N.; Finkbeiner, Douglas P.
Publication:
The Astrophysical Journal, Volume 796, Issue 1, article id. 54, 6 pp. (2014). (ApJ Homepage)
Publication Date:
11/2014
Origin:
IOP
Astronomy Keywords:
gamma rays: general, methods: data analysis, surveys
DOI:
10.1088/0004-637X/796/1/54
Bibliographic Code:
2014ApJ...796...54P

Abstract

The Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope has a point-spread function (PSF) with large tails, consisting of events affected by tracker inefficiencies, inactive volumes, and hard scattering; these tails can make source confusion a limiting factor. The parameter CTBCORE, available in the publicly available Extended Fermi LAT data (available at http://fermi.gsfc.nasa.gov/ssc/data/access/), estimates the quality of each event's direction reconstruction; by implementing a cut in this parameter, the tails of the PSF can be suppressed at the cost of losing effective area. We implement cuts on CTBCORE and present updated instrument response functions derived from the Fermi LAT data itself, along with all-sky maps generated with these cuts. Having shown the effectiveness of these cuts, especially at low energies, we encourage their use in analyses where angular resolution is more important than Poisson noise.

 

Title:
Measurement of the muon reconstruction performance of the ATLAS detector using 2011 and 2012 LHC proton-proton collision data
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Barreiro Guimarães da Costa, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... ; and 2884 coauthors
Publication:
The European Physical Journal C, Volume 74, article id. #3130, 34 pp. (EPJC Homepage)
Publication Date:
11/2014
Origin:
SPRINGER
Abstract Copyright:
(c) 2014: CERN for the benefit of the ATLAS collaboration
DOI:
10.1140/epjc/s10052-014-3130-x
Bibliographic Code:
2014EPJC...74.3130A

Abstract

This paper presents the performance of the ATLAS muon reconstruction during the LHC run with collisions at -8 TeV in 2011-2012, focusing mainly on data collected in 2012. Measurements of the reconstruction efficiency and of the momentum scale and resolution, based on large reference samples of , and decays, are presented and compared to Monte Carlo simulations. Corrections to the simulation, to be used in physics analysis, are provided. Over most of the covered phase space (muon and GeV) the efficiency is above and is measured with per-mille precision. The momentum resolution ranges from at central rapidity and for transverse momentum GeV, to at large rapidity and GeV. The momentum scale is known with an uncertainty of to depending on rapidity. A method for the recovery of final state radiation from the muons is also presented.

 

Title:
Measurement of flow harmonics with multi-particle cumulants in Pb+Pb collisions at TeV with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Barreiro Guimarães da Costa, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... ; and 2881 coauthors
Publication:
The European Physical Journal C, Volume 74, article id. #3157, 28 pp. (EPJC Homepage)
Publication Date:
11/2014
Origin:
SPRINGER
Abstract Copyright:
(c) 2014: CERN for the benefit of the ATLAS collaboration
DOI:
10.1140/epjc/s10052-014-3157-z
Bibliographic Code:
2014EPJC...74.3157A

Abstract

ATLAS measurements of the azimuthal anisotropy in lead-lead collisions at TeV are shown using a dataset of approximately 7 b collected at the LHC in 2010. The measurements are performed for charged particles with transverse momenta GeV and in the pseudorapidity range . The anisotropy is characterized by the Fourier coefficients, , of the charged-particle azimuthal angle distribution for -4. The Fourier coefficients are evaluated using multi-particle cumulants calculated with the generating function method. Results on the transverse momentum, pseudorapidity and centrality dependence of the coefficients are presented. The elliptic flow, , is obtained from the two-, four-, six- and eight-particle cumulants while higher-order coefficients, and , are determined with two- and four-particle cumulants. Flow harmonics measured with four-particle cumulants are significantly reduced compared to the measurement involving two-particle cumulants. A comparison to measurements obtained using different analysis methods and previously reported by the LHC experiments is also shown. Results of measurements of flow fluctuations evaluated with multi-particle cumulants are shown as a function of transverse momentum and the collision centrality. Models of the initial spatial geometry and its fluctuations fail to describe the flow fluctuations measurements.

 

Title:
Search for long-lived neutral particles decaying into lepton jets in proton-proton collisions at TeV with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Barreiro Guimarães da Costa, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... ; and 2897 coauthors
Publication:
Journal of High Energy Physics, Volume 2014, article id. #88, 48 pp.
Publication Date:
11/2014
Origin:
SPRINGER
Keywords:
Hadron-Hadron Scattering
Abstract Copyright:
(c) 2014: The Author(s)
DOI:
10.1007/JHEP11(2014)088
Bibliographic Code:
2014JHEP...11..088A

Abstract

Several models of physics beyond the Standard Model predict neutral particles that decay into final states consisting of collimated jets of light leptons and hadrons (so-called "lepton jets"). These particles can also be long-lived with decay length comparable to, or even larger than, the LHC detectors' linear dimensions. This paper presents the results of a search for lepton jets in proton-proton collisions at the centre-of-mass energy of TeV in a sample of 20.3 fb-1 collected during 2012 with the ATLAS detector at the LHC. Limits on models predicting Higgs boson decays to neutral long-lived lepton jets are derived as a function of the particle's proper decay length. [Figure not available: see fulltext.]

 

Title:
Search for pair and single production of new heavy quarks that decay to a Z boson and a third-generation quark in pp collisions at TeV with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Barreiro Guimarães da Costa, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... ; and 2890 coauthors
Publication:
Journal of High Energy Physics, Volume 2014, article id. #104, 54 pp.
Publication Date:
11/2014
Origin:
SPRINGER
Keywords:
Hadron-Hadron Scattering
Abstract Copyright:
(c) 2014: The Author(s)
DOI:
10.1007/JHEP11(2014)104
Bibliographic Code:
2014JHEP...11..104A

Abstract

A search is presented for the production of new heavy quarks that decay to a Z boson and a third-generation Standard Model quark. In the case of a new charge +2 /3 quark ( T ), the decay targeted is T --> Zt, while the decay targeted for a new charge -1 /3 quark ( B) is B --> Zb. The search is performed with a dataset corresponding to 20 .3 fb-1 of pp collisions at TeV recorded in 2012 with the ATLAS detector at the CERN Large Hadron Collider. Selected events contain a high transverse momentum Z boson candidate reconstructed from a pair of oppositely charged same-flavor leptons (electrons or muons), and are analyzed in two channels defined by the absence or presence of a third lepton. Hadronic jets, in particular those with properties consistent with the decay of a b-hadron, are also required to be present in selected events. Different requirements are made on the jet activity in the event in order to enhance the sensitivity to either heavy quark pair production mediated by the strong interaction, or single production mediated by the electroweak interaction. No significant excess of events above the Standard Model expectation is observed, and lower limits are derived on the mass of vector-like T and B quarks under various branching ratio hypotheses, as well as upper limits on the magnitude of electroweak coupling parameters. [Figure not available: see fulltext.]

 

Title:
Search for top squark pair production in final states with one isolated lepton, jets, and missing transverse momentum in = 8 TeV pp collisions with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Barreiro Guimarães da Costa, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... ; and 2884 coauthors
Publication:
Journal of High Energy Physics, Volume 2014, article id. #118, 87 pp.
Publication Date:
11/2014
Origin:
SPRINGER
Keywords:
Hadron-Hadron Scattering, proton-proton scattering, supersymmetry, top squark
Abstract Copyright:
(c) 2014: The Author(s)
DOI:
10.1007/JHEP11(2014)118
Bibliographic Code:
2014JHEP...11..118A

Abstract

The results of a search for top squark (stop) pair production in final states with one isolated lepton, jets, and missing transverse momentum are reported. The analysis is performed with proton-proton collision data at = 8 TeV collected with the ATLAS detector at the LHC in 2012 corresponding to an integrated luminosity of 20 fb-1. The lightest supersymmetric particle (LSP) is taken to be the lightest neutralino which only interacts weakly and is assumed to be stable. The stop decay modes considered are those to a top quark and the LSP as well as to a bottom quark and the lightest chargino, where the chargino decays to the LSP by emitting a W boson. A wide range of scenarios with different mass splittings between the stop, the lightest neutralino and the lightest chargino are considered, including cases where the W bosons or the top quarks are off-shell. Decay modes involving the heavier charginos and neutralinos are addressed using a set of phenomenological models of supersymmetry. No significant excess over the Standard Model prediction is observed. A stop with a mass between 210 and 640 GeV decaying directly to a top quark and a massless LSP is excluded at 95% confidence level, and in models where the mass of the lightest chargino is twice that of the LSP, stops are excluded at 95% confidence level up to a mass of 500 GeV for an LSP mass in the range of 100 to 150 GeV. Stringent exclusion limits are also derived for all other stop decay modes considered, and model-independent upper limits are set on the visible cross-section for processes beyond the Standard Model. [Figure not available: see fulltext.]

 

Title:
BPS degeneracies and superconformal index in diverse dimensions
Authors:
Iqbal, Amer; Vafa, Cumrun
Publication:
Physical Review D, Volume 90, Issue 10, id.105031 (PhRvD Homepage)
Publication Date:
11/2014
Origin:
APS
PACS Keywords:
Supersymmetric models, Field theories in dimensions other than four
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevD.90.105031
Bibliographic Code:
2014PhRvD..90j5031I

Abstract

We present a unifying theme relating BPS partition functions and superconformal indices. In the case with complex supersymmetry central charges (as in N =2 in d =4 and N =(2 ,2 ) in d =2 ), the known results can be reinterpreted as the statement that the BPS partition functions can be used to compute a specialization of the superconformal indices. We argue that in the case with real central charge in the supersymmetry algebra, as in N =1 in d =5 (or the N =2 in d =3 ), the BPS degeneracy captures the full superconformal index. Furthermore, we argue that refined topological strings, which capture five-dimensional (5d) BPS degeneracies of M theory on Calabi-Yau 3-folds, can be used to compute a 5d supersymmetric index including in the sectors with three-dimensional defects for a large class of 5d superconformal theories. Moreover, we provide evidence that distinct Calabi-Yau singularities which are expected to lead to the same Superconformal field theory yield the same index.

 

Title:
Possible Futures of Electroweak Precision: ILC, FCC-ee, and CEPC
Authors:
Fan, JiJi; Reece, Matthew; Wang, Lian-Tao
Publication:
eprint arXiv:1411.1054
Publication Date:
11/2014
Origin:
ARXIV
Keywords:
High Energy Physics - Phenomenology
Comment:
26 pages, 6 figures
Bibliographic Code:
2014arXiv1411.1054F

Abstract

The future of high-precision electroweak physics lies in e+e- collider measurements of properties of the Z boson, the W boson, the Higgs boson, and the top quark. We estimate the expected performance of three possible future colliders: the ILC, FCC-ee (formerly known as TLEP), and CEPC. In particular, we present the first estimates of the possible reach of CEPC, China's proposed Circular Electron-Positron Collider, for the oblique parameters S and T and for seven-parameter fits of Higgs couplings. These results allow the physics potential for CEPC to be compared with that of the ILC and FCC-ee. We also show how the constraints on S and T would evolve as the uncertainties on each of the most important input measurements change separately. This clarifies the basic physics goals for future colliders. To improve on the current precision, the highest priorities are improving the uncertainties on the W mass and effective weak mixing angle. At the same time, improved measurements of the top mass, the Z mass, the running of alpha, and the Z width will offer further improvement which will determine the ultimate reach. Each of the possible future colliders we consider has strong prospects for probing TeV-scale electroweak physics.

 

Title:
How the velvet worm squirts slime
Authors:
Concha, Andrés; Mellado, Paula; Morera-Brenes, Bernal; Sampaio Costa, Cristiano; Mahadevan, L.; Monge-Nájera, Julián
Publication:
eprint arXiv:1411.1750
Publication Date:
11/2014
Origin:
ARXIV
Keywords:
Physics - Fluid Dynamics, Condensed Matter - Soft Condensed Matter, Physics - Biological Physics
Comment:
3 pages, 3 figures
Bibliographic Code:
2014arXiv1411.1750C

Abstract

The rapid squirt of a proteinaceous slime jet endows the ancient velvet worms (Onychophora) with a unique mechanism for defense from predators and for capturing prey by entangling them in a disordered web that immobilizes their target. However, to date neither qualitative nor quantitative descriptions have been provided for this unique adaptation. Here we investigate the fast oscillatory motion of the oral papillae and the exiting liquid jet that oscillates with frequencies $f\sim 30-60$ Hz. Using anatomical images, high speed videography, theoretical analysis and a physical simulacrum we show that this fast oscillatory motion is the result of an elastohydrodynamic instability driven by the interplay between the elasticity of oral papillae and the fast unsteady flow during squirting. Our results demonstrate how passive strategies can be cleverly harnessed by organisms, while suggesting future oscillating micro-fluidic devices as well as novel ways for micro and nano fiber production using bioinspired strategies.

 

Title:
Elliptic Genus of E-strings
Authors:
Kim, Joonho; Kim, Seok; Lee, Kimyeong; Park, Jaemo; Vafa, Cumrun
Publication:
eprint arXiv:1411.2324
Publication Date:
11/2014
Origin:
ARXIV
Keywords:
High Energy Physics - Theory
Comment:
47 pages, 2 figures
Bibliographic Code:
2014arXiv1411.2324K

Abstract

We study a family of 2d N=(0,4) gauge theories which describes at low energy the dynamics of E-strings, the M2-branes suspended between a pair of M5 and M9 branes. The gauge theory is engineered using a duality with type IIA theory, leading to the D2-branes suspended between an NS5-brane and 8 D8-branes on an O8-plane. We compute the elliptic genus of this family of theories, and find agreement with the known results for single and two E-strings. The partition function can in principle be computed for arbitrary number of E-strings, and we compute them explicitly for low numbers. We test our predictions against the partially known results from topological strings, as well as from the instanton calculus of 5d Sp(1) gauge theory. Given the relation to topological strings, our computation provides the all genus partition function of the refined topological strings on the canonical bundle over 1/2 K3.

 

Title:
Electron-phonon processes of the silicon-vacancy centre in diamond
Authors:
Jahnke, Kay D.; Sipahigil, Alp; Binder, Jan M.; Doherty, Marcus W.; Metsch, Mathias; Rogers, Lachlan J.; Manson, Neil B.; Lukin, Mikhail D.; Jelezko, Fedor
Publication:
eprint arXiv:1411.2871
Publication Date:
11/2014
Origin:
ARXIV
Keywords:
Quantum Physics, Condensed Matter - Materials Science, Physics - Optics
Comment:
19 pages, 6 figures
Bibliographic Code:
2014arXiv1411.2871J

Abstract

We investigate phonon induced electronic dynamics in the ground and excited states of the negatively charged silicon-vacancy ($\mathrm{SiV}^-$) centre in diamond. Optical transition line widths, transition wavelength and excited state lifetimes are measured for the temperature range 4-350 K. The ground state orbital relaxation rates are measured using time-resolved fluorescence techniques. A microscopic model of the thermal broadening in the excited and ground states of the $\mathrm{SiV}^-$ centre is developed. A vibronic process involving single-phonon transitions is found to determine orbital relaxation rates for both the ground and the excited states at cryogenic temperatures. We discuss the implications of our findings for coherence of qubit states in the ground states and propose methods to extend coherence times of $\mathrm{SiV}^-$ qubits.

 

Title:
Conductivity of weakly disordered strange metals: from conformal to hyperscaling-violating regimes
Authors:
Lucas, Andrew; Sachdev, Subir
Publication:
eprint arXiv:1411.3331
Publication Date:
11/2014
Origin:
ARXIV
Keywords:
High Energy Physics - Theory, Condensed Matter - Strongly Correlated Electrons, General Relativity and Quantum Cosmology
Comment:
31 pages, 6 figures
Bibliographic Code:
2014arXiv1411.3331L

Abstract

We present a semi-analytic method for constructing holographic black holes that interpolate from anti-de Sitter space to hyperscaling-violating geometries. These are holographic duals of conformal field theories in the presence of an applied chemical potential, $\mu$, at a non-zero temperature, $T$, and allow us to describe the crossover from `strange metal' physics at $T \ll \mu$, to conformal physics at $T \gg \mu$. Our holographic technique adds an extra gauge field and exploits structure of the Einstein-Maxwell system to manifestly find 1-parameter families of solutions of the Einstein-matter system in terms of a small family of functions, obeying a nested set of differential equations. Using these interpolating geometries, we re-consider holographically some recent questions of interest about hyperscaling-violating field theories. Our focus is a more detailed holographic computation of the conductivity of strange metals, weakly perturbed by disorder coupled to scalar operators, including both the average conductivity as well as sample-to-sample fluctuations. Our findings are consistent with previous scaling arguments, though we point out logarithmic corrections in some special (holographic) cases. We also discuss the nature of superconducting instabilities in hyperscaling-violating geometries with appropriate choices of scalar couplings.

 

Title:
Dynamical instabilities and transient short-range order in the fermionic Hubbard model
Authors:
Bauer, Johannes; Babadi, Mehrtash; Demler, Eugene
Publication:
eprint arXiv:1411.4049
Publication Date:
11/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Other Condensed Matter, Condensed Matter - Quantum Gases, Condensed Matter - Statistical Mechanics
Comment:
4 pages, 3 figures
Bibliographic Code:
2014arXiv1411.4049B

Abstract

We study the dynamics of magnetic correlations in the half-filled fermionic Hubbard model following a fast ramp of the repulsive interaction. We use Schwinger-Keldysh self-consistent second-order perturbation theory to investigate the evolution of single-particle Green's functions and solve the non-equilibrium Bethe-Salpeter equation to study the dynamics of magnetic correlations. This approach gives us new insights into the interplay between single-particle relaxation dynamics and the growth of antiferromagnetic correlations. Depending on the ramping time and the final value of the interaction, we find different dynamical behavior which we illustrate using a dynamical phase diagram. Of particular interest is the emergence of a transient short-range ordered regime characterized by the strong initial growth of antiferromagnetic correlations followed by a decay of correlations upon thermalization. The discussed phenomena can be probed in experiments with ultracold atoms in optical lattices.

 

Title:
Neuromimetic Circuits with Synaptic Devices based on Strongly Correlated Electron Systems
Authors:
Ha, Sieu D.; Shi, Jian; Meroz, Yasmine; Mahadevan, L.; Ramanathan, Shriram
Publication:
eprint arXiv:1411.4179
Publication Date:
11/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Strongly Correlated Electrons, Computer Science - Emerging Technologies, Quantitative Biology - Neurons and Cognition
Bibliographic Code:
2014arXiv1411.4179H

Abstract

Strongly correlated electron systems such as the rare-earth nickelates (RNiO3, R = rare-earth element) can exhibit synapse-like continuous long term potentiation and depression when gated with ionic liquids; exploiting the extreme sensitivity of coupled charge, spin, orbital, and lattice degrees of freedom to stoichiometry. We present experimental real-time, device-level classical conditioning and unlearning using nickelate-based synaptic devices in an electronic circuit compatible with both excitatory and inhibitory neurons. We establish a physical model for the device behavior based on electric-field driven coupled ionic-electronic diffusion that can be utilized for design of more complex systems. We use the model to simulate a variety of associate and non-associative learning mechanisms, as well as a feedforward recurrent network for storing memory. Our circuit intuitively parallels biological neural architectures, and it can be readily generalized to other forms of cellular learning and extinction. The simulation of neural function with electronic device analogues may provide insight into biological processes such as decision making, learning and adaptation, while facilitating advanced parallel information processing in hardware.

 

Title:
Oscillatory Non-collinear Magnetism Induced by Interfacial Charge Transfer in Metallic Oxide Superlattices
Authors:
Hoffman, J.; Kirby, B. J.; Kwon, J.; Freeland, J. W.; Martin, I.; Heinonen, O. G.; Steadman, P.; Zhou, H.; Schlepuetz, C. M.; te Velthuis, S. G. E; Zuo, J.-M.; Bhattacharya, A.
Publication:
eprint arXiv:1411.4344
Publication Date:
11/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Materials Science
Bibliographic Code:
2014arXiv1411.4344H

Abstract

Interfaces between correlated complex oxides are promising avenues to realize new forms of magnetism that arise as a result of charge transfer, proximity effects and locally broken symmetries. We report upon the discovery of a non-collinear magnetic structure in superlattices of the ferromagnetic metallic oxide La2/3Sr1/3MnO3 (LSMO) and the correlated metal LaNiO3 (LNO). The exchange interaction between LSMO layers is mediated by the intervening LNO, such that the angle between the magnetization of neighboring LSMO layers varies in an oscillatory manner with the thickness of the LNO layer. The magnetic field, temperature, and spacer thickness dependence of the non-collinear structure are inconsistent with the bilinear and biquadratic interactions that are used to model the magnetic structure in conventional metallic multilayers. A model that couples the LSMO layers to a helical spin state within the LNO fits the observed behavior. We propose that the spin-helix results from the interaction between a spatially varying spin susceptibility within the LNO and interfacial charge transfer that creates localized Ni2+ states. This provides a new approach to engineering non-collinear spin textures in metallic oxide heterostructures that can be exploited in devices based on both spin and

 

Title:
Development of high frequency and wide bandwidth Johnson noise thermometry
Authors:
Crossno, Jesse; Liu, Xiaomeng; Ohki, Thomas A.; Kim, Philip; Chung Fong, Kin
Publication:
eprint arXiv:1411.4596
Publication Date:
11/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Mesoscale and Nanoscale Physics
Comment:
4 pages, 4 figures
Bibliographic Code:
2014arXiv1411.4596C

Abstract

We develop a high frequency, wide bandwidth radiometer operating at room temperature, which augments the traditional technique of Johnson noise thermometry for nanoscale thermal transport studies. Employing SiGe low noise amplifiers and an analog multiplier operating at 2 GHz, auto- and cross-correlated Johnson noise measurements are performed in the temperature range of 3 to 300 K, achieving a sensitivity of 5.5 mK (110 ppm) in 1 second of integration time. The versatility of the noise thermometry developed in this study is demonstrated by measuring the electron temperature of a mesoscopic graphene device under Joule heating, from which the electronic thermal conductance is determined over a wide temperature range.

 

Title:
Evaporation-driven ring and film deposition from colloidal droplets
Authors:
Nadir Kaplan, C.; Mahadevan, L.
Publication:
eprint arXiv:1411.4748
Publication Date:
11/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Soft Condensed Matter, Condensed Matter - Materials Science
Comment:
8 pages, 5 figures
Bibliographic Code:
2014arXiv1411.4748N

Abstract

Evaporating suspensions of colloidal particles lead to the formation of a variety of patterns, ranging from a left-over ring of a dried coffee drop to uniformly distributed solid pigments left behind wet paint. To characterize the transition between single rings, multiple concentric rings, broad bands, and uniform deposits, we investigate the dynamics of a drying droplet via a multiphase model of colloidal particles in a solvent. Our theory couples the inhomogeneous evaporation at the evolving droplet interface to the dynamics inside the drop, i.e. the liquid flow, local variations of the particle concentration, and the propagation of the deposition front where the solute forms an incompressible porous medium at high concentrations. A dimensionless parameter combining the capillary number and the droplet aspect ratio captures the formation conditions of different pattern types.

 

Title:
Volume doubling, Poincar\'{e} inequality and Guassian heat kernel estimate for nonnegative curvature graphs
Authors:
Horn, Paul; Lin, Yong; Liu, Shuang; Yau, Shing-Tung
Publication:
eprint arXiv:1411.5087
Publication Date:
11/2014
Origin:
ARXIV
Keywords:
Mathematics - Differential Geometry, Mathematics - Combinatorics, Mathematics - Metric Geometry
Comment:
38 pages. arXiv admin note: text overlap with arXiv:0801.0812, arXiv:0911.1819 by other authors
Bibliographic Code:
2014arXiv1411.5087H

Abstract

By studying the heat semigroup, we prove Li-Yau type estimates for bounded and positive solutions of the heat equation on graphs, under the assumption of the curvature-dimension inequality $CDE'(n,0)$, which can be consider as a notion of curvature for graphs. Furthermore, we derive that if a graph has nonnegative curvature then it has the volume doubling property, from this we can prove the Guassian estimate for heat kernel, and then Poincar\'{e} inequality and Harnack inequality. Under the assumption of positive curvature on graphs, we derive the Bonnet-Myers type theorem that the diameter of graphs is finite by proving some Log Sobolev inequalities.

 

Title:
3D Dust Mapping Reveals that Orion Forms Part of a Large Ring of Dust
Authors:
Schlafly, E. F.; Green, G.; Finkbeiner, D. P.; Rix, H.-W.; Burgett, W. S.; Chambers, K. C.; Draper, P. W.; Kaiser, N.; Martin, N. F.; Metcalfe, N.; Morgan, J. S.; Price, P. A.; Tonry, J. L.; Wainscoat, R. J.; Waters, C.
Publication:
eprint arXiv:1411.5402
Publication Date:
11/2014
Origin:
ARXIV
Keywords:
Astrophysics - Astrophysics of Galaxies
Comment:
13 pages, 8 figures, accepted for publication in ApJ
Bibliographic Code:
2014arXiv1411.5402S

Abstract

The Orion Molecular Complex is the nearest site of ongoing high-mass star formation, making it one of the most extensively studied molecular complexes in the Galaxy. We have developed a new technique for mapping the 3D distribution of dust in the Galaxy using Pan-STARRS1 photometry. We isolate the dust at the distance to Orion using this technique, revealing a large (100 pc, 14 degree diameter), previously unrecognized ring of dust, which we term the "Orion dust ring." The ring includes Orion A and B, and is not coincident with current H-alpha features. The circular morphology suggests formation as an ancient bubble in the interstellar medium, though we have not been able to conclusively identify the source of the bubble. This hint at the history of Orion may have important consequences for models of high-mass star formation and triggered star formation.

 

Title:
Two-Dimensional Clusters of Colloidal Spheres: Ground States, Excited States, and Structural Rearrangements
Authors:
Perry, Rebecca W.; Holmes-Cerfon, Miranda C.; Brenner, Michael P.; Manoharan, Vinothan N.
Publication:
eprint arXiv:1411.5680
Publication Date:
11/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Soft Condensed Matter, Condensed Matter - Statistical Mechanics
Comment:
12 pages, 5 figures
Bibliographic Code:
2014arXiv1411.5680P

Abstract

We study experimentally what is arguably the simplest yet non-trivial colloidal system: two-dimensional clusters of 6 spherical particles bound by depletion interactions. These clusters have multiple, degenerate ground states whose equilibrium distribution is determined by entropic factors, principally the symmetry. In equilibrium, they rearrange between these ground state configurations. We observe these rearrangements as well as all of the low-lying excited states. In contrast to the ground states, the excited states have soft modes and low symmetry, and their occupation probabilities depend on the size of the configuration space reached through internal degrees of freedom, as well as a single "sticky parameter" encapsulating the depth and curvature of the potential. Using a geometrical model that accounts for the entropy of the soft modes and the diffusion rates along them, we accurately reproduce the measured, absolute rearrangement rates. The success of this model, which requires no fitting parameters or measurements of the potential, shows that the free-energy landscape of colloidal systems and the dynamics it governs can be understood geometrically.

 

Title:
Wess-Zumino-Witten terms in graphene Landau levels
Authors:
Lee, Junhyun; Sachdev, Subir
Publication:
eprint arXiv:1411.5684
Publication Date:
11/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Mesoscale and Nanoscale Physics
Comment:
5 pages, 2 figures with supplement
Bibliographic Code:
2014arXiv1411.5684L

Abstract

We consider the interplay between the antiferromagnetic and Kekul\'e valence bond solid orderings in the zero energy Landau levels of neutral monolayer and bilayer graphene. We establish the presence of Wess-Zumino-Witten terms between these orders: this implies that their quantum fluctuations are described by the deconfined critical theories of quantum spin systems. We present implications for experiments, including the possible presence of excitonic superfluidity in bilayer graphene.

 

Title:
Gravitational Memory, BMS Supertranslations and Soft Theorems
Authors:
Strominger, Andrew; Zhiboedov, Alexander
Publication:
eprint arXiv:1411.5745
Publication Date:
11/2014
Origin:
ARXIV
Keywords:
High Energy Physics - Theory, General Relativity and Quantum Cosmology
Comment:
18 pages, 2 figures
Bibliographic Code:
2014arXiv1411.5745S

Abstract

The transit of a gravitating radiation pulse past arrays of detectors stationed near future null infinity in the vacuum is considered. It is shown that the relative positions and clock times of the detectors before and after the radiation transit differ by a BMS supertranslation. An explicit expression for the supertranslation in terms of moments of the radiation energy flux is given. The relative spatial displacement found for a pair of nearby detectors reproduces the well-known and potentially measurable gravitational memory effect. The displacement memory formula is shown to be equivalent to Weinberg's formula for soft graviton production.

 

Title:
A special Lagrangian type equation for holomorphic line bundles
Authors:
Jacob, Adam; Yau, Shing-Tung
Publication:
eprint arXiv:1411.7457
Publication Date:
11/2014
Origin:
ARXIV
Keywords:
Mathematics - Differential Geometry
Comment:
29 pages
Bibliographic Code:
2014arXiv1411.7457J

Abstract

Let $L$ be a holomorphic line bundle over a compact K\"ahler manifold $X$. Motivated by mirror symmetry, we study the deformed Hermitian-Yang-Mills equation on $L$, which is the line bundle analogue of the special Lagrangian equation in the case that $X$ is Calabi-Yau. We show that this equation is the Euler-Lagrange equation for a positive functional, and that solutions are unique global minimizers. We provide a necessary and sufficient criterion for existence in the case that $X$ is a K\"ahler surface. For the higher dimensional cases, we introduce a line bundle version of the Lagrangian mean curvature flow, and prove convergence when $L$ is ample and $X$ has non-negative orthogonal bisectional curvature.

 

Title:
Landau level spectroscopy of electron-electron interactions in graphene
Authors:
Faugeras, C.; Berciaud, S.; Leszczynski, P.; Henni, Y.; Nogajewski, K.; Orlita, M.; Taniguchi, T.; Watanabe, K.; Forsythe, C.; Kim, P.; Jalil, R.; Geim, A. K.; Basko, D. M.; Potemski, M.
Publication:
eprint arXiv:1412.0115
Publication Date:
11/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Strongly Correlated Electrons
Comment:
5+2 pages, 2 figures
Bibliographic Code:
2014arXiv1412.0115F

Abstract

We present magneto-Raman scattering studies of electronic inter Landau level excitations in quasi-neutral graphene samples with different strengths of Coulomb interaction. The band velocity associated with these excitations is found to depend on the dielectric environment, on the index of Landau level involved, and to vary as a function of the magnetic field. This contradicts the single-particle picture of non-interacting massless Dirac electrons, but is accounted for by theory when the effect of electron-electron interaction is taken into account. Raman active, zero-momentum inter Landau level excitations in graphene are sensitive to electron-electron interactions due to the non-applicability of the Kohn theorem in this system, with a clearly non-parabolic dispersion relation.

 

Title:
Elastohydrodynamics of a sliding, spinning, sedimenting particle near a soft wall
Authors:
Salez, Thomas; Mahadevan, L.
Publication:
eprint arXiv:1412.0162
Publication Date:
11/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Soft Condensed Matter, Physics - Fluid Dynamics, Physics - Geophysics
Bibliographic Code:
2014arXiv1412.0162S

Abstract

We address the free motion of a negatively buoyant particle inside a viscous fluid, in the vicinity of a thin compressible elastic wall, a situation that arises in a variety of technological and natural settings. We use scaling arguments to establish different regimes of sedimentation and sliding, and then use thin-film lubrication dynamics to determine an asymptotic theory for the sedimentation, sliding, and rolling motions of a cylinder that takes the form of three coupled nonlinear singular-differential equations. Numerical integration of the resulting equations confirms our scaling relations and further yields a range of unexpected behaviors. Despite the low-Reynolds feature of the flow, we show that the particle can spontaneously oscillate when sliding, can generate lift via a Magnus-like effect, can ricochet, and also show an unusual sedimentation singularity. Finally, we use simple generalization of our model to account for poroelasticity, and also address a sedimentation-sliding transition that can lead to the particle coasting over very long distances, similar to certain geophysical phenomena.

 

Title:
Design and performance of a cryogenic apparatus for magnetically trapping ultracold neutrons
Authors:
Huffman, P. R.; Coakley, K. J.; Doyle, J. M.; Huffer, C. R.; Mumm, H. P.; O'Shaughnessy, C. M.; Schelhammer, K. W.; Seo, P.-N.; Yang, L.
Publication:
Cryogenics, Volume 64, p. 40-50.
Publication Date:
11/2014
Origin:
ELSEVIER
Abstract Copyright:
(c) 2014 Elsevier Ltd
DOI:
10.1016/j.cryogenics.2014.09.008
Bibliographic Code:
2014Cryo...64...40H

Abstract

The cryogenic design and performance of an apparatus used to magnetically confine ultracold neutrons (UCN) is presented. The apparatus is part of an effort to measure the beta-decay lifetime of the free neutron and is comprised of a high-current superconducting magnetic trap that surrounds ~21 l of isotopically pure 4He cooled to approximately 250 mK. A 0.89 nm neutron beam can enter the apparatus from one end of the magnetic trap and a light collection system allows visible light generated within the helium by decays to be transported to detectors at room temperature. Two cryocoolers are incorporated to reduce liquid helium consumption.

 

Title:
The Physics of the B Factories
Authors:
Bevan, A. J.; Golob, B.; Mannel, Th.; Prell, S.;... Morii, M.;... and 2008 coauthors
Publication:
The European Physical Journal C, Volume 74, article id. #3026, 928 pp. (EPJC Homepage)
Publication Date:
11/2014
Origin:
SPRINGER
Abstract Copyright:
(c) 2014: The Author(s)
DOI:
10.1140/epjc/s10052-014-3026-9
Bibliographic Code:
2014EPJC...74.3026B

Abstract

This work is on the Physics of the B Factories. Part A of this book contains a brief description of the SLAC and KEK B Factories as well as their detectors, BaBar and Belle, and data taking related issues. Part B discusses tools and methods used by the experiments in order to obtain results. The results themselves can be found in Part C.

 

Title:
Measurements of jet vetoes and azimuthal decorrelations in dijet events produced in collisions at using the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Barreiro Guimarães da Costa, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... ; and 2882 coauthors
Publication:
The European Physical Journal C, Volume 74, article id. #3117, 27 pp. (EPJC Homepage)
Publication Date:
11/2014
Origin:
SPRINGER
Abstract Copyright:
(c) 2014: CERN for the benefit of the ATLAS collaboration
DOI:
10.1140/epjc/s10052-014-3117-7
Bibliographic Code:
2014EPJC...74.3117A

Abstract

Additional jet activity in dijet events is measured using $pp$ collisions at ATLAS at a centre-of-mass energy of 7 TeV, for jets reconstructed using the anti-kt algorithm with radius parameter R=0.6. This is done using variables such as the fraction of dijet events without an additional jet in the rapidity interval bounded by the dijet subsystem and correlations between the azimuthal angles of the dijets. They are presented, both with and without a veto on additional jet activity in the rapidity interval, as a function of the mean transverse momentum of the dijets and of the rapidity interval size. The double differential dijet cross section is also measured as a function of the interval size and the azimuthal angle between the dijets. These variables probe differences in the approach to resummation of large logarithms when performing QCD calculations. The data are compared to POWHEG, interfaced to the PYTHIA 8 and HERWIG parton shower generators, as well as to HEJ with and without interfacing it to the ARIADNE parton shower generator. None of the theoretical predictions agree with the data across the full phase-space considered; however, POWHEG+PYTHIA 8 and HEJ+ARIADNE are found to provide the best agreement with the data.These measurements use the full data sample collected with the ATLAS detector in 7 TeV $pp$ collisions at the LHC and correspond to integrated luminosities of 36.1 pb$^-1$ and 4.5 fb$^-1$ for data collected during 2010 and 2011 respectively.

 

Title:
Communication: HK propagator uniformized along a one-dimensional manifold in weakly anharmonic systems
Authors:
Kocia, Lucas; Heller, Eric J.
Publication:
The Journal of Chemical Physics, Volume 141, Issue 18, id.181102 (JChPh Homepage)
Publication Date:
11/2014
Origin:
AIP
Abstract Copyright:
2014: AIP Publishing LLC
DOI:
10.1063/1.4901301
Bibliographic Code:
2014JChPh.141r1102K

Abstract

A simplification of the Heller-Herman-Kluk-Kay (HK) propagator is presented that does not suffer from the need for an increasing number of trajectories with dimensions of the system under study. This is accomplished by replacing HK's uniformizing integral over all of phase space by a one-dimensional curve that is appropriately selected to lie along the fastest growing manifold of a defining trajectory. It is shown that this modification leads to eigenspectra of quantum states in weakly anharmonic systems that can outperform the comparatively computationally cheap thawed Gaussian approximation method and frequently approach the accuracy of spectra obtained with the full HK propagator.

 

Title:
Search for neutral Higgs bosons of the minimal supersymmetric standard model in pp collisions at TeV with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Barreiro Guimarães da Costa, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... ; and 2887 coauthors
Publication:
Journal of High Energy Physics, Volume 2014, article id. #56, 47 pp.
Publication Date:
11/2014
Origin:
SPRINGER
Keywords:
Hadron-Hadron Scattering
Abstract Copyright:
(c) 2014: The Author(s)
DOI:
10.1007/JHEP11(2014)056
Bibliographic Code:
2014JHEP...11..056A

Abstract

A search for the neutral Higgs bosons predicted by the Minimal Supersymmetric Standard Model (MSSM) is reported. The analysis is performed on data from proton-proton collisions at a centre-of-mass energy of 8 TeV collected with the ATLAS detector at the Large Hadron Collider. The samples used for this search were collected in 2012 and correspond to integrated luminosities in the range 19.5-20.3 fb-1. The MSSM Higgs bosons are searched for in the tau tau final state. No significant excess over the expected background is observed, and exclusion limits are derived for the production cross section times branching fraction of a scalar particle as a function of its mass. The results are also interpreted in the MSSM parameter space for various benchmark scenarios. [Figure not available: see fulltext.]

 

Title:
All-Optical Sensing of a Single-Molecule Electron Spin
Authors:
Sushkov, A. O.; Chisholm, N.; Lovchinsky, I.; Kubo, M.; Lo, P. K.; Bennett, S. D.; Hunger, D.; Akimov, A.; Walsworth, R. L.; Park, H.; Lukin, M. D.
Publication:
Nano Letters, vol. 14, issue 11, pp. 6443-6448
Publication Date:
11/2014
Origin:
CROSSREF
DOI:
10.1021/nl502988n
Bibliographic Code:
2014NanoL..14.6443S

Abstract

We demonstrate an all-optical method for magnetic sensing of individual molecules in ambient conditions at room temperature. Our approach is based on shallow nitrogen-vacancy (NV) centers near the surface of a diamond crystal, which we use to detect single paramagnetic molecules covalently attached to the diamond surface. The manipulation and readout of the NV centers is all-optical and provides a sensitive probe of the magnetic field fluctuations stemming from the dynamics of the electronic spins of the attached molecules. As a specific example, we demonstrate detection of a single paramagnetic molecule containing a gadolinium (Gd$^{3+}$) ion. We confirm single-molecule resolution using optical fluorescence and atomic force microscopy to co-localize one NV center and one Gd$^{3+}$-containing molecule. Possible applications include nanoscale and in vivo magnetic spectroscopy and imaging of individual molecules.

 

Title:
Measurement of the cross-section of high transverse momentum vector bosons reconstructed as single jets and studies of jet substructure in pp collisions at \sqrt{s} = 7 TeV with the ATLAS detector
Authors:
Aad, G.; Abajyan, T.; Abbott, B.;... Barreiro Guimarães da Costa, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2849 coauthors
Publication:
New Journal of Physics, Volume 16, Issue 11, article id. 113013 (2014).
Publication Date:
11/2014
Origin:
IOP
DOI:
10.1088/1367-2630/16/11/113013
Bibliographic Code:
2014NJPh...16k3013A

Abstract

This paper presents a measurement of the cross-section for high transverse momentum W and Z bosons produced in pp collisions and decaying to all-hadronic final states. The data used in the analysis were recorded by the ATLAS detector at the CERN Large Hadron Collider at a centre-of-mass energy of \sqrt{s}=7 TeV and correspond to an integrated luminosity of 4.6 f{{b}-1}. The measurement is performed by reconstructing the boosted W or Z bosons in single jets. The reconstructed jet mass is used to identify the W and Z bosons, and a jet substructure method based on energy cluster information in the jet centre-of-mass frame is used to suppress the large multi-jet background. The cross-section for events with a hadronically decaying W or Z boson, with transverse momentum {{p}T}\gt 320 GeV and pseudorapidity |eta |\lt 1.9, is measured to be {{sigma }W+Z}=8.5+/- 1.7 pb and is compared to next-to-leading-order calculations. The selected events are further used to study jet grooming techniques.

 

Title:
Measurement of the cross section of high transverse momentum Z -->b b bar production in proton-proton collisions at &surd;{s }=8 TeV with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Barreiro Guimarães da Costa, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2870 coauthors
Publication:
Physics Letters B, Volume 738, p. 25-43.
Publication Date:
11/2014
Origin:
ELSEVIER
Keywords:
LHC, Boosted b b bar topologies
Abstract Copyright:
(c) 2014 Elsevier Science B.V. All rights reserved.
DOI:
10.1016/j.physletb.2014.09.020
Bibliographic Code:
2014PhLB..738...25A

Abstract

This Letter reports the observation of a high transverse momentum Z --> b b bar signal in proton-proton collisions at &surd;{ s} = 8 TeV and the measurement of its production cross section. The data analysed were collected in 2012 with the ATLAS detector at the LHC and correspond to an integrated luminosity of 19.5 fb-1. The Z --> b b bar decay is reconstructed from a pair of b-tagged jets, clustered with the anti-kt jet algorithm with R = 0.4, that have low angular separation and form a dijet with pT > 200 GeV. The signal yield is extracted from a fit to the dijet invariant mass distribution, with the dominant, multi-jet background mass shape estimated by employing a fully data-driven technique that reduces the dependence of the analysis on simulation. The fiducial cross section is determined to b

 

Title:
Search for the Standard Model Higgs boson decay to mu+mu- with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Barreiro Guimarães da Costa, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2882 coauthors
Publication:
Physics Letters B, Volume 738, p. 68-86.
Publication Date:
11/2014
Origin:
ELSEVIER
Abstract Copyright:
(c) 2014 Elsevier Science B.V. All rights reserved.
DOI:
10.1016/j.physletb.2014.09.008
Bibliographic Code:
2014PhLB..738...68A

Abstract

A search is reported for Higgs boson decay to mu+mu- using data with an integrated luminosity of 24.8 fb-1 collected with the ATLAS detector in pp collisions at &surd;{ s} = 7and 8 TeV at the CERN Large Hadron Collider. The observed dimuon invariant mass distribution is consistent with the Standard Model background-only hypothesis in the 120-150 GeV search range. For a Higgs boson with a mass of 125.5 GeV, the observed (expected) upper limit at the 95% confidence level is 7.0 (7.2) times the Standard Model expectation. This corresponds to an upper limit on the branching ratio BR (H -->mu+mu-) of 1.5 ×10-3.

 

Title:
Fiducial and differential cross sections of Higgs boson production measured in the four-lepton decay channel in pp collisions at &surd;{s }=8 TeV with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Barreiro Guimarães da Costa, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2894 coauthors
Publication:
Physics Letters B, Volume 738, p. 234-253.
Publication Date:
11/2014
Origin:
ELSEVIER
Abstract Copyright:
(c) 2014 Elsevier Science B.V. All rights reserved.
DOI:
10.1016/j.physletb.2014.09.054
Bibliographic Code:
2014PhLB..738..234A

Abstract

Measurements of fiducial and differential cross sections of Higgs boson production in the H --> ZZ* --> 4 l decay channel are presented. The cross sections are determined within a fiducial phase space and corrected for detection efficiency and resolution effects. They are based on 20.3 fb-1 of pp collision data, produced at &surd;{ s} = 8 TeV centre-of-mass energy at the LHC and recorded by the ATLAS detector. The differential measurements are performed in bins of transverse momentum and rapidity of the four-lepton system, the invariant mass of the subleading lepton pair and the decay angle of the leading lepton pair with respect to the beam line in the four-lepton rest frame, as well as the number of jets and the transverse momentum of the leading jet. The measured cross sections are compared to selected theoretical calculations of the Standard Model expectations. No significant deviation from any of the tested predictions is found.

 

Title:
Search for new resonances in Wgamma and Zgamma final states in pp collisions at &surd;{ s} = 8 TeV with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Barreiro Guimarães da Costa, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2886 coauthors
Publication:
Physics Letters B, Volume 738, p. 428-447.
Publication Date:
11/2014
Origin:
ELSEVIER
Abstract Copyright:
(c) 2014 Elsevier Science B.V. All rights reserved.
DOI:
10.1016/j.physletb.2014.10.002
Bibliographic Code:
2014PhLB..738..428A

Abstract

This Letter presents a search for new resonances decaying to final states with a vector boson produced in association with a high transverse momentum photon, Vgamma, with V = W (--> lnu) or Z (-->l+l-), where l = e or mu. The measurements use 20.3 fb-1 of proton-proton collision data at a center-of-mass energy of &surd;{ s} = 8 TeV recorded with the ATLAS detector. No deviations from the Standard Model expectations are found, and production cross section limits are set at 95% confidence level. Masses of the hypothetical aT and omegaT states of a benchmark Low Scale Technicolor model are excluded in the ranges [ 275 , 960 ] GeV and [ 200 , 700 ] ∪ [ 750 , 890 ] GeV, respectively. Limits at 95% confidence level on the production cross section of a singlet scalar resonance decaying to Zgamma final states have also been obtained for masses below 1180 GeV.

 

Title:
Dissipative phase transitions: Independent versus collective decay and spin squeezing
Authors:
Lee, Tony E.; Chan, Ching-Kit; Yelin, Susanne F.
Publication:
Physical Review A, Volume 90, Issue 5, id.052109 (PhRvA Homepage)
Publication Date:
11/2014
Origin:
APS
PACS Keywords:
Decoherence, open systems, quantum statistical methods, Magnetic phase boundaries, Entanglement production characterization and manipulation, Nonclassical states of the electromagnetic field including entangled photon states, quantum state engineering and measurements
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevA.90.052109
Bibliographic Code:
2014PhRvA..90e2109L

Abstract

We study the X Y model with infinite-range interactions (Lipkin-Meshkov-Glick model) in the presence of dissipation from spontaneous decay. We show that independent and collective decay lead to qualitatively different phase transitions of the steady state, even though the phase boundary is the same. Independent decay leads to a second-order phase transition to a ferromagnet, while collective decay leads to a first-order transition to a time-dependent oscillatory phase. Then we show that the addition of a drive leads to infinite spin squeezing for collective decay in the thermodynamic limit. Our results can be experimentally seen in trapped-ion and cavity-QED experiments.

 

Title:
Scattering resonances and bound states for strongly interacting Rydberg polaritons
Authors:
Bienias, P.; Choi, S.; Firstenberg, O.; Maghrebi, M. F.; Gullans, M.; Lukin, M. D.; Gorshkov, A. V.; Büchler, H. P.
Publication:
Physical Review A, Volume 90, Issue 5, id.053804 (PhRvA Homepage)
Publication Date:
11/2014
Origin:
APS
PACS Keywords:
Quantum optical phenomena in absorbing dispersive and conducting media, Rydberg states, Interatomic potentials and forces, Effects of atomic coherence on propagation absorption and amplification of light, electromagnetically induced transparency and absorption
Abstract Copyright:
(c) 2014: American Physical Society
DOI:
10.1103/PhysRevA.90.053804
Bibliographic Code:
2014PhRvA..90e3804B

Abstract

We provide a theoretical framework describing slow-light polaritons interacting via atomic Rydberg states. The method allows us to analytically derive the scattering properties of two polaritons. We identify parameter regimes where polariton-polariton interactions are repulsive. Furthermore, in the regime of attractive interactions, we identify multiple two-polariton bound states, calculate their dispersion, and study the resulting scattering resonances. Finally, the two-particle scattering properties allow us to derive the effective low-energy many-body Hamiltonian. This theoretical platform is applicable to ongoing experiments.

 

Title:
Deconfined criticality in bilayer graphene
Authors:
Lee, Junhyun; Sachdev, Subir
Publication:
Physical Review B, Volume 90, Issue 19, id.195427 (PhRvB Homepage)
Publication Date:
11/2014
Origin:
APS
PACS Keywords:
Quantized spin models, Strongly correlated electron systems, heavy fermions, Magnetic phase boundaries
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevB.90.195427
Bibliographic Code:
2014PhRvB..90s5427L

Abstract

We propose that bilayer graphene can provide an experimental realization of deconfined criticality. Current experiments indicate the presence of Néel order in the presence of a moderate magnetic field. The Néel order can be destabilized by application of a transverse electric field. The resulting electric field induced state is likely to have valence bond solid order, and the transition can acquire the emergent fractionalized and gauge excitations of deconfined criticality.

 

Title:
Measurement of the top-quark mass in the all-hadronic channel using the full CDF data set
Authors:
Aaltonen, T.; Amerio, S.; Amidei, D.;... Franklin, M.;... Guimaraes da Costa, J.;... and 397 coauthors
Publication:
Physical Review D, Volume 90, Issue 9, id.091101 (PhRvD Homepage)
Publication Date:
11/2014
Origin:
APS
PACS Keywords:
Top quarks, Inclusive production with identified hadrons, Inclusive production with identified leptons photons or other nonhadronic particles
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevD.90.091101
Bibliographic Code:
2014PhRvD..90i1101A

Abstract

The top-quark mass Mtop is measured using top quark-antiquark pairs produced in proton-antiproton collisions at a center-of-mass energy of 1.96 TeV and that decay into a fully hadronic final state. The full data set collected with the CDF II detector at the Fermilab Tevatron Collider, corresponding to an integrated luminosity of 9.3 fb-1 , is used. Events are selected that have six to eight jets, at least one of which is identified as having originated from a b quark. In addition, a multivariate algorithm, containing multiple kinematic variables as inputs, is used to discriminate signal events from background events due to QCD multijet production. Templates for the reconstructed top-quark mass are combined in a likelihood fit to measure Mtop with a simultaneous calibration of the jet energy scale. A value of Mtop=175.07 ±1.19 (stat )-1.58+1.55(syst ) GeV /c2 is obtained for the top-quark mass.

 

Title:
Measurements of direct C P asymmetries in B -->Xsgamma decays using sum of exclusive decays
Authors:
Lees, J. P.; Poireau, V.; Tisserand, V.;... Morii, M.;... and 337 coauthors
Publication:
Physical Review D, Volume 90, Issue 9, id.092001 (PhRvD Homepage)
Publication Date:
11/2014
Origin:
APS
PACS Keywords:
Leptonic semileptonic and radiative decays of mesons, Decays of bottom mesons
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevD.90.092001
Bibliographic Code:
2014PhRvD..90i2001L

Abstract

We measure the direct C P violation asymmetry, AC P, in B -->Xsgamma and the isospin difference of the asymmetry, Delta AC P, using 429 fb-1. of data collected at Upsilon (4 S ) resonance with the BABAR detector at the PEP-II asymmetric-energy e+e- storage rings operating at the SLAC National Accelerator Laboratory. B mesons are reconstructed from ten charged B final states and six neutral B final states. We find AC P=+(1.7 ±1.9 ±1.0 )% , which is in agreement with the Standard Model prediction and provides an improvement on the world average. Moreover, we report the first measurement of the difference between AC P for charged and neutral decay modes, Delta AC P=+(5.0 ±3.9 ±1.5 )% . Using the value of Delta AC P, we also provide 68% and 90% confidence intervals on the imaginary part of the ratio of the Wilson coefficients corresponding to the chromomagnetic dipole and the electromagnetic dipole transitions.

 

Title:
Hard-soft-collinear factorization to all orders
Authors:
Feige, Ilya; Schwartz, Matthew D.
Publication:
Physical Review D, Volume 90, Issue 10, id.105020 (PhRvD Homepage)
Publication Date:
11/2014
Origin:
APS
PACS Keywords:
General properties of QCD, Quantum chromodynamics, Gauge field theories
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevD.90.105020
Bibliographic Code:
2014PhRvD..90j5020F

Abstract

We provide a precise statement of hard-soft-collinear factorization of scattering amplitudes and prove it to all orders in perturbation theory. Factorization is formulated as the equality at leading power of scattering amplitudes in QCD with other amplitudes in QCD computed from a product of operator matrix elements. The equivalence is regulator independent and gauge independent. As the formulation relates amplitudes to the same amplitudes with additional soft or collinear particles, it includes as special cases the factorization of soft currents and collinear splitting functions from generic matrix elements, both of which are shown to be process independent to all orders. We show that the overlapping soft-collinear region is naturally accounted for by vacuum matrix elements of kinked Wilson lines. Although the proof is self-contained, it combines techniques developed for the study of pinch surfaces, scattering amplitudes, and effective field theory.

 

Title:
Resonances and circuit theory for the interaction of metallic disks and annuli with an electromagnetic field
Authors:
Chui, S. T.; Du, J. J.; Yau, S. T.
Publication:
Physical Review E, Volume 90, Issue 5, id.053202 (PhRvE Homepage)
Publication Date:
11/2014
Origin:
APS
PACS Keywords:
Electromagnetic wave propagation, radiowave propagation, Theory models and numerical simulation, Optical properties of low-dimensional mesoscopic and nanoscale materials and structures
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevE.90.053202
Bibliographic Code:
2014PhRvE..90e3202C

Abstract

To understand the nature of the electromagnetic resonances of finite metallic surfaces, we formulate a rigorous and rapidly convergent circuit theory for the interaction of a metallic disk and a metallic annulus with an electromagnetic field. Expressions for the current induced and the resonance condition are derived. A new understanding of the nature of the resonances is obtained. For half of the resonances we find a divergent electric field at the edge of the disk, even though it is smooth in shape. For the disk, we compare with previous results using vector spheroidal wave functions and found good agreement for the resonance condition. Our approach can be generalized to other finite surfaces.

 

Title:
Chiral Prethermalization in Supersonically Split Condensates
Authors:
Agarwal, Kartiek; Torre, Emanuele G. Dalla; Rauer, Bernhard; Langen, Tim; Schmiedmayer, Jörg; Demler, Eugene
Publication:
Physical Review Letters, Volume 113, Issue 19, id.190401 (PhRvL Homepage)
Publication Date:
11/2014
Origin:
APS
PACS Keywords:
Dynamic properties of condensates, collective and hydrodynamic excitations superfluid flow, Boson systems, Nonequilibrium and irreversible thermodynamics
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevLett.113.190401
Bibliographic Code:
2014PhRvL.113s0401A

Abstract

We study the dynamics of phase relaxation between a pair of one-dimensional condensates created by a supersonic unzipping of a single condensate. We use the Lorentz invariance of the low energy sector of such systems to show that dephasing results in an unusual prethermal state, in which right- and left-moving excitations have different, Doppler-shifted temperatures. The chirality of these modes can be probed experimentally by measuring the interference fringe contrasts with the release point of the split condensates moving at another supersonic velocity. Further, an accelerated motion of the release point can be used to observe a spacelike analog of the Unruh effect. A concrete experimental realization of the quantum zipper for a BEC of trapped atoms on an atom chip is outlined.

 

Title:
Many-Body Dynamics of Dipolar Molecules in an Optical Lattice
Authors:
Hazzard, Kaden R. A.; Gadway, Bryce; Foss-Feig, Michael; Yan, Bo; Moses, Steven A.; Covey, Jacob P.; Yao, Norman Y.; Lukin, Mikhail D.; Ye, Jun; Jin, Deborah S.; Rey, Ana Maria
Publication:
Physical Review Letters, Volume 113, Issue 19, id.195302 (PhRvL Homepage)
Publication Date:
11/2014
Origin:
APS
PACS Keywords:
Ultracold gases trapped gases, Decoherence, open systems, quantum statistical methods, Ion trapping, Quantized spin models
Abstract Copyright:
(c) 2014: American Physical Society
DOI:
10.1103/PhysRevLett.113.195302
Bibliographic Code:
2014PhRvL.113s5302H

Abstract

We use Ramsey spectroscopy to experimentally probe the quantum dynamics of disordered dipolar-interacting ultracold molecules in a partially filled optical lattice, and we compare the results to theory. We report the capability to control the dipolar interaction strength. We find excellent agreement between our measurements of the spin dynamics and theoretical calculations with no fitting parameters, including the dynamics' dependence on molecule number and on the dipolar interaction strength. This agreement verifies the microscopic model expected to govern the dynamics of dipolar molecules, even in this strongly correlated beyond-mean-field regime, and represents the first step towards using this system to explore many-body dynamics in regimes that are inaccessible to current theoretical techniques.

 

Title:
Revealing Topological Superconductivity in Extended Quantum Spin Hall Josephson Junctions
Authors:
Lee, Shu-Ping; Michaeli, Karen; Alicea, Jason; Yacoby, Amir
Publication:
Physical Review Letters, Volume 113, Issue 19, id.197001 (PhRvL Homepage)
Publication Date:
11/2014
Origin:
APS
PACS Keywords:
Proximity effects, Andreev effect, SN and SNS junctions, Tunneling phenomena, point contacts weak links Josephson effects
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevLett.113.197001
Bibliographic Code:
2014PhRvL.113s7001L

Abstract

Quantum spin Hall-superconductor hybrids are promising sources of topological superconductivity and Majorana modes, particularly given recent progress on HgTe and InAs/GaSb. We propose a new method of revealing topological superconductivity in extended quantum spin Hall Josephson junctions supporting "fractional Josephson currents." Specifically, we show that as one threads magnetic flux between the superconductors, the critical current traces an interference pattern featuring sharp fingerprints of topological superconductivity---even when noise spoils parity conservation.

 

Title:
Magnetic Resonance Detection of Individual Proton Spins Using Quantum Reporters
Authors:
Sushkov, A. O.; Lovchinsky, I.; Chisholm, N.; Walsworth, R. L.; Park, H.; Lukin, M. D.
Publication:
Physical Review Letters, Volume 113, Issue 19, id.197601 (PhRvL Homepage)
Publication Date:
11/2014
Origin:
APS
PACS Keywords:
Color centers and other defects, Magnetometers for susceptibility magnetic moment and magnetization measurements, Spin echoes, Structure determination with NMR
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevLett.113.197601
Bibliographic Code:
2014PhRvL.113s7601S

Abstract

We demonstrate a method of magnetic resonance imaging with single nuclear-spin sensitivity under ambient conditions. Our method employs isolated electronic-spin quantum bits (qubits) as magnetic resonance "reporters" on the surface of high purity diamond. These spin qubits are localized with nanometer-scale uncertainty, and their quantum state is coherently manipulated and measured optically via a proximal nitrogen-vacancy color center located a few nanometers below the diamond surface. This system is then used for sensing, coherent coupling, and imaging of individual proton spins on the diamond surface with angstrom resolution. Our approach may enable direct structural imaging of complex molecules that cannot be accessed from bulk studies. It realizes a new platform for probing novel materials, monitoring chemical reactions, and manipulation of complex systems on surfaces at a quantum level.

 

Title:
Search for a Dark Photon in e+e- Collisions at BaBar
Authors:
Lees, J. P.; Poireau, V.; Tisserand, V.;... Morii, M.;... and 310 coauthors
Publication:
Physical Review Letters, Volume 113, Issue 20, id.201801 (PhRvL Homepage)
Publication Date:
11/2014
Origin:
APS
PACS Keywords:
Production of non-standard model particles in e-e+ interactions, Extensions of electroweak gauge sector, Other particles, Dark matter
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevLett.113.201801
Bibliographic Code:
2014PhRvL.113t1801L

Abstract

Dark sectors charged under a new Abelian interaction have recently received much attention in the context of dark matter models. These models introduce a light new mediator, the so-called dark photon (A'), connecting the dark sector to the standard model. We present a search for a dark photon in the reaction e+e--->gamma A' , A'-->e+e- , mu+mu- using 514 fb-1 of data collected with the BABAR detector. We observe no statistically significant deviations from the standard model predictions, and we set 90% confidence level upper limits on the mixing strength between the photon and dark photon at the level of 1 0-4-1 0-3 for dark photon masses in the range 0.02 - 10.2 GeV . We further constrain the range of the parameter space favored by interpretations of the discrepancy between the calculated and measured anomalous magnetic moment of the muon.

 

Title:
Observation of an Excited Bc± Meson State with the ATLAS Detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.; Barreiro Guimarães da Costa, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2878 coauthors
Publication:
Physical Review Letters, Volume 113, Issue 21, id.212004 (PhRvL Homepage)
Publication Date:
11/2014
Origin:
APS
PACS Keywords:
Bottom mesons
Abstract Copyright:
2014: CERN
DOI:
10.1103/PhysRevLett.113.212004
Bibliographic Code:
2014PhRvL.113u2004A

Abstract

A search for excited states of the Bc± meson is performed using 4.9 fb-1 of 7 TeV and 19.2 fb-1 of 8 TeV p p collision data collected by the ATLAS experiment at the LHC. A new state is observed through its hadronic transition to the ground state, with the latter detected in the decay Bc±-->J /psi pi± . The state appears in the m (Bc±pi+pi-)-m (Bc±)-2 m (pi±) mass difference distribution with a significance of 5.2 standard deviations. The mass of the observed state is 6842 ±4 ±5 MeV , where the first error is statistical and the second is systematic. The mass and decay of this state are consistent with expectations for the second S -wave state of the Bc± meson, Bc±(2 S ).

 

Title:
La2-xSrxCuO4 superconductor nanowire devices
Authors:
Litombe, N. E.; Bollinger, A. T.; Hoffman, J. E.; Bozovic, I.
Publication:
Physica C: Superconductivity and its applications, Volume 506, p. 169-173.
Publication Date:
11/2014
Origin:
ELSEVIER
Abstract Copyright:
(c) 2014 Elsevier B.V.
DOI:
10.1016/j.physc.2014.06.010
Bibliographic Code:
2014PhyC..506..169L

Abstract

La2-xSrxCuO4 nanowire devices have been fabricated and characterized using electrical transport measurements. Nanowires with widths down to 80 nm are patterned using high-resolution electron beam lithography. However, the narrowest nanowires show incomplete superconducting transitions with some residual resistance at T = 4 K. Here, we report on the refinement of the fabrication process to achieve narrower nanowire devices with complete superconducting transitions, opening the path to the study of novel physics arising from dimension-limited superconductivity on the nanoscale.

 

Title:
Field-effect-induced two-dimensional electron gas utilizing modulation-doped ohmic contacts
Authors:
Mondal, Sumit; Gardner, Geoffrey C.; Watson, John D.; Fallahi, Saeed; Yacoby, Amir; Manfra, Michael J.
Publication:
Solid State Communications, Volume 197, p. 20-24.
Publication Date:
11/2014
Origin:
ELSEVIER
Abstract Copyright:
(c) 2014 Elsevier Ltd
DOI:
10.1016/j.ssc.2014.08.011
Bibliographic Code:
2014SSCom.197...20M

Abstract

Modulation-doped AlGaAs/GaAs heterostructures are utilized extensively in the study of quantum transport in nanostructures, but charge fluctuations associated with remote ionized dopants often produce deleterious effects. Electric field-induced carrier systems offer an attractive alternative if certain challenges can be overcome. We demonstrate a field-effect transistor in which the active channel is locally devoid of modulation-doping, but silicon dopant atoms are retained in the ohmic contact region to facilitate reliable low-resistance contacts. A high quality two-dimensional electron gas is induced by a field-effect and is tunable over a wide range of density. Device design, fabrication, and low temperature (T=0.3 K) transport data are reported.


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