Faculty Publications: October, 2015

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Title:
BICEP2/Keck Array V: Measurements of B-mode Polarization at Degree Angular Scales and 150 GHz by the Keck Array
Authors:
BICEP2 and Keck Array Collaborations; Ade, P. A. R.; Ahmed, Z.; Aikin, R. W.;... Dvorkin, C.;... Kovac, J. M.;... and 55 coauthors
Publication:
The Astrophysical Journal, Volume 811, Issue 2, article id. 126, 13 pp. (2015). (ApJ Homepage)
Publication Date:
10/2015
Origin:
IOP
Astronomy Keywords:
cosmic background radiation, cosmology: observations, gravitational waves, inflation, polarization
DOI:
10.1088/0004-637X/811/2/126
Bibliographic Code:
2015ApJ...811..126B

Abstract

The Keck Array is a system of cosmic microwave background polarimeters, each similar to the Bicep2 experiment. In this paper we report results from the 2012 to 2013 observing seasons, during which the Keck Array consisted of five receivers all operating in the same (150 GHz) frequency band and observing field as Bicep2. We again find an excess of B-mode power over the lensed-ΛCDM expectation of >5σ in the range 30 < ℓ < 150 and confirm that this is not due to systematics using jackknife tests and simulations based on detailed calibration measurements. In map difference and spectral difference tests these new data are shown to be consistent with Bicep2. Finally, we combine the maps from the two experiments to produce final Q and U maps which have a depth of 57 nK deg (3.4 μK arcmin) over an effective area of 400 deg2 for an equivalent survey weight of 250,000 μK-2. The final BB band powers have noise uncertainty a factor of 2.3 times better than the previous results, and a significance of detection of excess power of >6σ.

 

Title:
Antenna-coupled TES Bolometers Used in BICEP2, Keck Array, and Spider
Authors:
Ade, P. A. R.; Aikin, R. W.; Amiri, M.;... Kovac, J. M.;... Bicep2, Keck Array, Spider Collaborations
Publication:
The Astrophysical Journal, Volume 812, Issue 2, article id. 176, 17 pp. (2015). (ApJ Homepage)
Publication Date:
10/2015
Origin:
IOP
Astronomy Keywords:
cosmic background radiation, instrumentation: detectors, instrumentation: polarimeters, methods: laboratory: solid state, techniques: polarimetric
DOI:
10.1088/0004-637X/812/2/176
Bibliographic Code:
2015ApJ...812..176A

Abstract

We have developed antenna-coupled transition-edge sensor bolometers for a wide range of cosmic microwave background (CMB) polarimetry experiments, including Bicep2, Keck Array, and the balloon borne Spider. These detectors have reached maturity and this paper reports on their design principles, overall performance, and key challenges associated with design and production. Our detector arrays repeatedly produce spectral bands with 20%–30% bandwidth at 95, 150, or 230 GHz. The integrated antenna arrays synthesize symmetric co-aligned beams with controlled side-lobe levels. Cross-polarized response on boresight is typically ∼ 0.5%, consistent with cross-talk in our multiplexed readout system. End-to-end optical efficiencies in our cameras are routinely 35% or higher, with per detector sensitivities of NET ∼ 300 μ {{{K}}}{CMB}\sqrt{{{s}}}. Thanks to the scalability of this design, we have deployed 2560 detectors as 1280 matched pairs in Keck Array with a combined instantaneous sensitivity of ∼ 9 μ {{{K}}}{CMB}\sqrt{{{s}}}, as measured directly from CMB maps in the 2013 season. Similar arrays have recently flown in the Spider instrument, and development of this technology is ongoing.

 

Title:
Evaluating small sphere limit of the Wang-Yau quasi-local energy
Authors:
Chen, PoNing; Wang, Mu-Tao; Yau, Shing-Tung
Publication:
eprint arXiv:1510.00904
Publication Date:
10/2015
Origin:
ARXIV
Keywords:
Mathematics - Differential Geometry, General Relativity and Quantum Cosmology
Comment:
43 pages
Bibliographic Code:
2015arXiv151000904C

Abstract

In this article, we study the small sphere limit of the Wang-Yau quasi-local energy defined in [18,19]. Given a point $p$ in a spacetime $N$, we consider a canonical family of surfaces approaching $p$ along its future null cone and evaluate the limit of the Wang-Yau quasi-local energy. The evaluation relies on solving an "optimal embedding equation" whose solutions represent critical points of the quasi-local energy. For a spacetime with matter fields, the scenario is similar to that of the large sphere limit found in [7]. Namely, there is a natural solution which is a local minimum, and the limit of its quasi-local energy recovers the stress-energy tensor at $p$. For a vacuum spacetime, the quasi-local energy vanishes to higher order and the solution of the optimal embedding equation is more complicated. Nevertheless, we are able to show that there exists a solution which is a local minimum and that the limit of its quasi-local energy is related to the Bel-Robinson tensor. Together with earlier work [7], this completes the consistency verification of the Wang-Yau quasi-local energy with all classical limits.

 

Title:
4d N=2 SCFT and singularity theory Part I: Classification
Authors:
Xie, Dan; Yau, Shing-Tung
Publication:
eprint arXiv:1510.01324
Publication Date:
10/2015
Origin:
ARXIV
Keywords:
High Energy Physics - Theory, Mathematics - Algebraic Geometry
Comment:
52 pages, 7 figures
Bibliographic Code:
2015arXiv151001324X

Abstract

This is the first of a series of papers in which we systematically use singularity theory to study four dimensional N=2 superconformal field theories. Our main focus in this paper is to identify what kind of singularity is needed to define a SCFT. The constraint for a hypersurface singularity has been found by Sharpere and Vafa, and here the complete set of solutions are listed using a related mathematical result of Stephen S. T. Yau and Yu. We also study other type of singularities such as the complete intersection, quotient of hypersurface singularity by a finite group and non-isolated singularity. We finally conjecture that any three dimensional rational Gorenstein graded isolated singularity should define a N=2 SCFT. We explain how to extract various interesting physical quantities such as Seiberg-Witten geometry, central charges, exact marginal deformations, BPS quiver, RG flow trajectory, etc from the properties of singularity.

 

Title:
Transport in inhomogeneous quantum critical fluids and in the Dirac fluid in graphene
Authors:
Lucas, Andrew; Crossno, Jesse; Chung Fong, Kin; Kim, Philip; Sachdev, Subir
Publication:
eprint arXiv:1510.01738
Publication Date:
10/2015
Origin:
ARXIV
Keywords:
Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Mesoscale and Nanoscale Physics, High Energy Physics - Theory
Comment:
19 + 11 pages; 8 + 3 figures
Bibliographic Code:
2015arXiv151001738L

Abstract

We develop a general hydrodynamic framework for computing direct current thermal and electric transport in a strongly interacting finite temperature quantum system near a Lorentz-invariant quantum critical point. Our framework is non-perturbative in the strength of long wavelength fluctuations in the background charge density of the electronic fluid, and requires the rate of electron-electron scattering to be faster than the rate of electron-impurity scattering. We use this formalism to compute transport coefficients in the Dirac fluid in clean samples of graphene near the charge neutrality point, and find results insensitive to long range Coulomb interactions. Numerical results are compared to recent experimental data on thermal and electrical conductivity in the Dirac fluid in graphene and substantially improved quantitative agreement over existing hydrodynamic theories is found. We comment on the interplay between the Dirac fluid and acoustic and optical phonons, and qualitatively explain experimentally observed effects. Our work paves the way for quantitative contact between experimentally realized condensed matter systems and the wide body of high energy inspired theories on transport in interacting many-body quantum systems.

 

Title:
Superconductivity and other phase transitions in a hybrid Bose-Fermi mixture formed by a polariton condensate and an electron system in two dimensions
Authors:
Cotleţ, Ovidiu; Zeytinoǧlu, Sina; Sigrist, Manfred; Demler, Eugene; Imamoǧlu, Ataç
Publication:
eprint arXiv:1510.02001
Publication Date:
10/2015
Origin:
ARXIV
Keywords:
Condensed Matter - Quantum Gases, Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Superconductivity, Quantum Physics
Comment:
20 pages, 6 figures
Bibliographic Code:
2015arXiv151002001C

Abstract

Interacting Bose-Fermi systems play a central role in condensed matter physics. Here, we analyze a novel Bose-Fermi mixture formed by a cavity exciton-polariton condensate interacting with a two-dimensional electron system. We show that that previous predictions of superconductivity [F.P. Laussy, Phys. Rev. Lett. 10, 104 (2010)] and excitonic supersolid formation [I.A. Shelykh, Phys. Rev. Lett. 14, 105 (2010)] in this system are closely intertwined- resembling the predictions for strongly correlated electron systems such as high temperature superconductors. In stark contrast to a large majority of Bose-Fermi systems analyzed in solids and ultracold atomic gases, the renormalized interaction between the polaritons and electrons in our system is long-ranged and strongly peaked at a tunable wavevector, which can be rendered incommensurate with the Fermi momentum. We analyze the prospects for experimental observation of superconductivity and find that critical temperatures on the order of a few Kelvins can be achieved in heterostructures consisting of transition metal dichalcogenide monolayers that are embedded in an open cavity structure. All optical control of superconductivity in semiconductor heterostructures could enable the realization of new device concepts compatible with semiconductor nanotechnology. In addition the possibility to interface quantum Hall physics, superconductivity and nonequilibrium polariton condensates is likely to provide fertile ground for investigation of completely new physical phenomena.

 

Title:
New theoretical approaches to Bose polarons
Authors:
Grusdt, Fabian; Demler, Eugene
Publication:
eprint arXiv:1510.04934
Publication Date:
10/2015
Origin:
ARXIV
Keywords:
Condensed Matter - Quantum Gases, Condensed Matter - Other Condensed Matter
Comment:
79 pages, 19 figures. Based on a course presented at the International School of Physics Enrico Fermi, Varenna, Italy 2014
Bibliographic Code:
2015arXiv151004934G

Abstract

The Fr\"ohlich polaron model describes a ubiquitous class of problems concerned with understanding properties of a single mobile particle interacting with a bosonic reservoir. Originally introduced in the context of electrons interacting with phonons in crystals, this model found applications in such diverse areas as strongly correlated electron systems, quantum information, and high energy physics. In the last few years this model has been applied to describe impurity atoms immersed in Bose-Einstein condensates of ultracold atoms. The tunability of microscopic parameters in ensembles of ultracold atoms and the rich experimental toolbox of atomic physics should allow to test many theoretical predictions and give us new insights into equilibrium and dynamical properties of polarons. In these lecture notes we provide an overview of common theoretical approaches that have been used to study BEC polarons, including Rayleigh-Schr\"odinger and Green's function perturbation theories, self-consistent Born approximation, mean-field approach, Feynman's variational path integral approach, Monte Carlo simulations, renormalization group calculations, and Gaussian variational ansatz. We focus on the renormalization group approach and provide details of analysis that have not been presented in earlier publications. We show that this method helps to resolve striking discrepancy in polaron energies obtained using mean-field approximation and Monte Carlo simulations. We also discuss applications of this method to the calculation of the effective mass of BEC polarons. As one experimentally relevant example of a non-equililbrium problem we consider Bloch oscillations of Bose polarons and demonstrate that one should find considerable deviations from the commonly accepted phenomenological Esaki-Tsu model. We review which parameter regimes of Bose polarons can be achieved in various atomic mixtures.

 

Title:
Imaging Cyclotron Orbits of Electrons in Graphene
Authors:
Bhandari, S.; Lee, G. H.; Klales, A.; Watanabe, K.; Taniguchi, T.; Heller, E.; Kim, P.; Westervelt, R. M.
Publication:
eprint arXiv:1510.05197
Publication Date:
10/2015
Origin:
ARXIV
Keywords:
Condensed Matter - Mesoscale and Nanoscale Physics
Comment:
19 pages, 4 figures, submitted for publication
Bibliographic Code:
2015arXiv151005197B

Abstract

Electrons in graphene can travel for several microns without scattering at low temperatures, and their motion becomes ballistic, following classical trajectories. When a magnetic field B is applied perpendicular to the plane, electrons follow cyclotron orbits. Magnetic focusing occurs when electrons injected from one narrow contact focus onto a second contact located an integer number of cyclotron diameters away. By tuning the magnetic field B and electron density n in the graphene layer, we observe magnetic focusing peaks. We use a cooled scanning gate microscope to image cyclotron trajectories in graphene at 4.2 K. The tip creates a local change in density that casts a shadow by deflecting electrons flowing nearby; an image of flow can be obtained by measuring the transmission between contacts as the tip is raster scanned across the sample. On the first magnetic focusing peak, we image a cyclotron orbit that extends from one point contact to the other. In addition, we study the geometry of orbits deflected into the second point contact by the tip.

 

Title:
Thermodynamic properties of a quantum Hall anti-dot interferometer
Authors:
Levy Schreier, Sarah; Stern, Ady; Rosenow, Bernd; Halperin, Bertrand. I.
Publication:
eprint arXiv:1510.05241
Publication Date:
10/2015
Origin:
ARXIV
Keywords:
Condensed Matter - Mesoscale and Nanoscale Physics
Comment:
3 figures
Bibliographic Code:
2015arXiv151005241L

Abstract

We study quantum Hall interferometers in which the interference loop encircles a quantum anti-dot. We base our study on thermodynamic considerations, which we believe reflect the essential aspects of interference transport phenomena. We find that similar to the more conventional Fabry-Perot quantum Hall interferometers, in which the interference loop forms a quantum dot, the anti-dot interferometer is affected by the electro-static Coulomb interaction between the edge modes defining the loop. We show that in the Aharonov-Bohm regime, in which effects of fractional statistics should be visible, is easier to access in interferometers based on anti-dots than in those based on dots. We discuss the relevance of our results to recent measurements on anti-dots interferometers.

 

Title:
New Phases and Dissociation-Recombination of Hydrogen Deuteride to 3.4 Megabar
Authors:
Dias, Ranga P.; Noked, Ori; Silvera, Isaac F.
Publication:
eprint arXiv:1510.05686
Publication Date:
10/2015
Origin:
ARXIV
Keywords:
Condensed Matter - Other Condensed Matter, Condensed Matter - Quantum Gases
Comment:
11 pages, 4 figures, submitted
Bibliographic Code:
2015arXiv151005686D

Abstract

We present infrared absorption studies of solid hydrogen deuteride to pressures as high as 3.4 megabar in a diamond anvil cell and temperatures in the range 5 to 295 K. Above 198 GPa the sample transforms to a mixture of HD ,H2 and D2, interpreted as a process of dissociation and recombination. Three new phases-lines are observed, two of which differ remarkably from those of the high-pressure homonuclear species, but none are metallic. The time-dependent spectral changes are analyzed to determine the molecular concentrations as a function of time; the nucleon exchange achieves steady state concentrations in ~20 hours at ~200 GPa.

 

Title:
Semicontinuity of 4d N=2 spectrum under renormalization group flow
Authors:
Xie, Dan; Yau, Shing-Tung
Publication:
eprint arXiv:1510.06036
Publication Date:
10/2015
Origin:
ARXIV
Keywords:
High Energy Physics - Theory, Mathematics - Algebraic Geometry
Comment:
12 pages
Bibliographic Code:
2015arXiv151006036X

Abstract

We study renormalization group flow of four dimensional N=2 SCFTs defined by isolated hypersurface three-fold singularities. We define the spectrum of N=2 theory as the set of scaling dimensions of the parameters on the Coulomb branch, which include Coulomb branch moduli, mass parameters and coupling constants. We prove that the spectrum of those theories is semicontinous under the RG flow on the Coulomb branch using the mathematical result about the singularity spectra under deformation. The semicontinuity behavior of N=2 spectrum implies a theorem under relevant and Coulomb branch moduli deformation, the absence of dangerous irrelevant deformations and can be taken as the necessary condition for the ending point of a RG flow. This behavior is also true for (c,c) ring deformation of two dimensional Landau-Ginzburg model with (2,2) supersymmetry.

 

Title:
A mesoscopic Rydberg impurity in an atomic quantum gas
Authors:
Schmidt, Richard; Sadeghpour, H. R.; Demler, E.
Publication:
eprint arXiv:1510.09183
Publication Date:
10/2015
Origin:
ARXIV
Keywords:
Condensed Matter - Quantum Gases, Condensed Matter - Mesoscale and Nanoscale Physics, Physics - Atomic Physics, Quantum Physics
Comment:
7+3 pages, 5 figures
Bibliographic Code:
2015arXiv151009183S

Abstract

Giant impurity excitations with large binding energies are powerful probes for exploring new regimes of far out of equilibrium dynamics in few- and many-body quantum systems, as well as for in-situ observations of correlations. Motivated by recent experimental progress in spectroscopic studies of Rydberg excitations in ensembles of ultracold atoms, we develop a new theoretical approach for describing multiscale dynamics of Rydberg excitations in quantum Bose gases. We find that the crossover from few- to many-body dynamics manifests in a dramatic change in spectral profile from resolved molecular lines to broad Gaussian distributions representing a superpolaronic state in which many atoms bind to the Rydberg impurity. We discuss signatures of this crossover in the temperature and density dependence of the spectra.

 

Title:
BICEP2 / Keck Array VI: Improved Constraints On Cosmology and Foregrounds When Adding 95 GHz Data From Keck Array
Authors:
Array, Keck; BICEP2 Collaborations; :; Ade, P. A. R.; Ahmed, Z.; Aikin, R. W.; Alexander, K. D.; Barkats, D.; Benton, S. J.; Bischoff, C. A.; Bock, J. J.; Bowens-Rubin, R.; Brevik, J. A.; Buder, I.; Bullock, E.; Buza, V.; Connors, J.; Crill, B. P.; Duband, L.; Dvorkin, C.; Filippini, J. P.; Fliescher, S.; Grayson, J.; Halpern, M.; Harrison, S.; Hilton, G. C.; Hui, H.; Irwin, K. D.; Karkare, K. S.; Karpel, E.; Kaufman, J. P.; Keating, B. G.; Kefeli, S.; Kernasovskiy, S. A.; Kovac, J. M.; Kuo, C. L.; Leitch, E. M.; Lueker, M.; Megerian, K. G.; Netterfield, C. B.; Nguyen, H. T.; O'Brient, R.; Ogburn, R. W., IV; Orlando, A.; Pryke, C.; Richter, S.; Schwarz, R.; Sheehy, C. D.; Staniszewski, Z. K.; Steinbach, B.; Sudiwala, R. V.; Teply, G. P.; Thompson, K. L.; Tolan, J. E.; Tucker, C.; Turner, A. D.; Vieregg, A. G.; Weber, A. C.; Wiebe, D. V.; Willmert, J.; Wong, C. L.; Wu, W. L. K.; Yoon, K. W.
Publication:
eprint arXiv:1510.09217
Publication Date:
10/2015
Origin:
ARXIV
Keywords:
Astrophysics - Cosmology and Nongalactic Astrophysics
Comment:
17 pages, 18 figures, to be submitted to PRL
Bibliographic Code:
2015arXiv151009217A

Abstract

We present results from an analysis of all data taken by the BICEP2 & Keck Array CMB polarization experiments up to and including that taken during the 2014 observing season. This includes the first Keck Array observations at 95 GHz. The maps reach a depth of 50 nK deg in Stokes $Q$ and $U$ in the 150 GHz band and 127 nK deg in the 95 GHz band. We take auto- and cross-spectra between these maps and publicly available maps from WMAP and Planck at frequencies from 23 GHz to 353 GHz. An excess over lensed-LCDM is detected at modest significance in the 95x150 $BB$ spectrum, and is consistent with the dust contribution expected from our previous work. No significant evidence for synchrotron emission is found in spectra such as 23x95, or for dust/sync correlation in spectra such as 23x353. We take the likelihood of all the spectra for a multi-component model including lensed-LCDM, dust, synchrotron and a possible contribution from inflationary gravitational waves (as parametrized by the tensor-to-scalar ratio $r$), using priors on the frequency spectral behaviors of dust and synchrotron emission from previous analyses of WMAP and Planck data in other regions of the sky. This analysis yields an upper limit $r_{0.05}<0.09$ at 95% confidence, which is robust to variations explored in analysis and priors. Combining these $B$-mode results with the (more model-dependent) constraints from Planck analysis of CMB temperature and other evidence yields a combined limit $r_{0.05}<0.07$. These are the strongest constraints to date on inflationary gravitational waves.

 

Title:
Imprint of inflation on galaxy shape correlations
Authors:
Schmidt, Fabian; Chisari, Nora Elisa; Dvorkin, Cora
Publication:
Journal of Cosmology and Astroparticle Physics, Issue 10, article id. 032, pp. (2015). (JCAP Homepage)
Publication Date:
10/2015
Origin:
IOP
DOI:
10.1088/1475-7516/2015/10/032
Bibliographic Code:
2015JCAP...10..032S

Abstract

We show that intrinsic (not lensing-induced) correlations between galaxy shapes offer a new probe of primordial non-Gaussianity and inflationary physics which is complementary to galaxy number counts. Specifically, intrinsic alignment correlations are sensitive to an anisotropic squeezed limit bispectrum of the primordial perturbations. Such a feature arises in solid inflation, as well as more broadly in the presence of light higher spin fields during inflation (as pointed out recently by Arkani-Hamed and Maldacena). We present a derivation of the all-sky two-point correlations of intrinsic shapes and number counts in the presence of non-Gaussianity with general angular dependence, and show that a quadrupolar (spin-2) anisotropy leads to the analog in galaxy shapes of the well-known scale-dependent bias induced in number counts by isotropic (spin-0) non-Gaussianity. Moreover, in the presence of non-zero anisotropic non-Gaussianity, the quadrupole of galaxy shapes becomes sensitive to far superhorizon modes. These effects come about because long-wavelength modes induce a local anisotropy in the initial power spectrum, with which galaxies will correlate. We forecast that future imaging surveys could provide constraints on the amplitude of anisotropic non-Gaussianity that are comparable to those from the Cosmic Microwave Background (CMB). These are complementary as they probe different physical scales. The constraints, however, depend on the sensitivity of galaxy shapes to the initial conditions which we only roughly estimate from observed tidal alignments.

 

Title:
Evaporation-driven ring and film deposition from colloidal droplets
Authors:
Kaplan, C. Nadir; Mahadevan, L.
Publication:
Journal of Fluid Mechanics, vol. 781, id. R2
Publication Date:
10/2015
Origin:
CROSSREF
DOI:
10.1017/jfm.2015.496
Bibliographic Code:
2015JFM...781R...2K

Abstract

Not Available

 

Title:
Erratum: Nanometre-scale probing of spin waves using single electron spins
Authors:
van der Sar, Toeno; Casola, Francesco; Walsworth, Ronald; Yacoby, Amir
Publication:
Nature Communications, Volume 6, id. 8426 (2015).
Publication Date:
10/2015
Origin:
NATURE
Abstract Copyright:
(c) 2015: Nature Publishing Group, a division of Macmillan Publishers Limited. All Rights Reserved.
DOI:
10.1038/ncomms9426
Bibliographic Code:
2015NatCo...6E8426V

Abstract

Not Available

 

Title:
Unjamming and cell shape in the asthmatic airway epithelium
Authors:
Park, Jin-Ah; Kim, Jae Hun; Bi, Dapeng; Mitchel, Jennifer A.; Qazvini, Nader Taheri; Tantisira, Kelan; Park, Chan Young; McGill, Maureen; Kim, Sae-Hoon; Gweon, Bomi; Notbohm, Jacob; Steward, Robert, Jr.; Burger, Stephanie; Randell, Scott H.; Kho, Alvin T.; Tambe, Dhananjay T.; Hardin, Corey; Shore, Stephanie A.; Israel, Elliot; Weitz, David A.; Tschumperlin, Daniel J.; Henske, Elizabeth P.; Weiss, Scott T.; Manning, M. Lisa; Butler, James P.; Drazen, Jeffrey M.; Fredberg, Jeffrey J.
Publication:
Nature Materials, Volume 14, Issue 10, pp. 1040-1048 (2015).
Publication Date:
10/2015
Origin:
NATURE
Abstract Copyright:
(c) 2015: Nature Publishing Group
DOI:
10.1038/nmat4357
Bibliographic Code:
2015NatMa..14.1040P

Abstract

From coffee beans flowing in a chute to cells remodelling in a living tissue, a wide variety of close-packed collective systems--both inert and living--have the potential to jam. The collective can sometimes flow like a fluid or jam and rigidify like a solid. The unjammed-to-jammed transition remains poorly understood, however, and structural properties characterizing these phases remain unknown. Using primary human bronchial epithelial cells, we show that the jamming transition in asthma is linked to cell shape, thus establishing in that system a structural criterion for cell jamming. Surprisingly, the collapse of critical scaling predicts a counter-intuitive relationship between jamming, cell shape and cell-cell adhesive stresses that is borne out by direct experimental observations. Cell shape thus provides a rigorous structural signature for classification and investigation of bronchial epithelial layer jamming in asthma, and potentially in any process in disease or development in which epithelial dynamics play a prominent role.

 

Title:
Fourier magnetic imaging with nanoscale resolution and compressed sensing speed-up using electronic spins in diamond
Authors:
Arai, K.; Belthangady, C.; Zhang, H.; Bar-Gill, N.; Devience, S. J.; Cappellaro, P.; Yacoby, A.; Walsworth, R. L.
Publication:
Nature Nanotechnology, Volume 10, Issue 10, pp. 859-864 (2015).
Publication Date:
10/2015
Origin:
NATURE
Abstract Copyright:
(c) 2015: Nature Publishing Group
DOI:
10.1038/nnano.2015.171
Bibliographic Code:
2015NatNa..10..859A

Abstract

Optically detected magnetic resonance using nitrogen-vacancy (NV) colour centres in diamond is a leading modality for nanoscale magnetic field imaging, as it provides single electron spin sensitivity, three-dimensional resolution better than 1 nm (ref. 5) and applicability to a wide range of physical and biological samples under ambient conditions. To date, however, NV-diamond magnetic imaging has been performed using ‘real-space’ techniques, which are either limited by optical diffraction to ˜250 nm resolution or require slow, point-by-point scanning for nanoscale resolution, for example, using an atomic force microscope, magnetic tip, or super-resolution optical imaging. Here, we introduce an alternative technique of Fourier magnetic imaging using NV-diamond. In analogy with conventional magnetic resonance imaging (MRI), we employ pulsed magnetic field gradients to phase-encode spatial information on NV electronic spins in wavenumber or ‘k-space’ followed by a fast Fourier transform to yield real-space images with nanoscale resolution, wide field of view and compressed sensing speed-up.

 

Title:
Measurement of exclusive γγ →ℓ+ℓ- production in proton-proton collisions at √{ s} = 7 TeV with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2844 coauthors
Publication:
Physics Letters B, Volume 749, p. 242-261.
Publication Date:
10/2015
Origin:
ELSEVIER
Abstract Copyright:
(c) 2015 CERN for the benefit of the ATLAS Collaboration.
DOI:
10.1016/j.physletb.2015.07.069
Bibliographic Code:
2015PhLB..749..242A

Abstract

This Letter reports a measurement of the exclusive γγ→ℓ+- (ℓ = e, μ) cross-section in proton-proton collisions at a centre-of-mass energy of 7 TeV by the ATLAS experiment at the LHC, based on an integrated luminosity of 4.6 fb-1. For the electron or muon pairs satisfying exclusive selection criteria, a fit to the dilepton acoplanarity distribution is used to extract the fiducial cross-sections. The cross-section in the electron channel is determined to be σγγ →e+e- excl. = 0.428 ± 0.035 (stat.) ± 0.018 (syst.) pb for a phase-space region with invariant mass of the electron pairs greater than 24 GeV, in which both electrons have transverse momentum pT > 12 GeV and pseudorapidity | η | < 2.4. For muon pairs with invariant mass greater than 20 GeV, muon transverse momentum pT > 10 GeV and pseudorapidity | η | < 2.4, the cross-section is determined to be σγγ →μ+μ- excl. = 0.628 ± 0.032 (stat.) ± 0.021 (syst.) pb. When proton absorptive effects due to the finite size of the proton are taken into account in the theory calculation, the measured cross-sections are found to be consistent with the theory prediction.

 

Title:
Search for the associated production of the Higgs boson with a top quark pair in multilepton final states with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2822 coauthors
Publication:
Physics Letters B, Volume 749, p. 519-541.
Publication Date:
10/2015
Origin:
ELSEVIER
Abstract Copyright:
(c) 2015 CERN for the benefit of the ATLAS Collaboration.
DOI:
10.1016/j.physletb.2015.07.079
Bibliographic Code:
2015PhLB..749..519A

Abstract

A search for the associated production of the Higgs boson with a top quark pair is performed in multilepton final states using 20.3 fb-1 of proton-proton collision data recorded by the ATLAS experiment at √{ s} = 8 TeV at the Large Hadron Collider. Five final states, targeting the decays H → WW*,ττ, and ZZ*, are examined for the presence of the Standard Model (SM) Higgs boson: two same-charge light leptons (e or μ) without a hadronically decaying τ lepton; three light leptons; two same-charge light leptons with a hadronically decaying τ lepton; four light leptons; and one light lepton and two hadronically decaying τ leptons. No significant excess of events is observed above the background expectation. The best fit for the t t bar H production cross section, assuming a Higgs boson mass of 125 GeV, is 2.1-1.2+1.4 times the SM expectation, and the observed (expected) upper limit at the 95% confidence level is 4.7 (2.4) times the SM rate. The p-value for compatibility with the background-only hypothesis is 1.8σ; the expectation in the presence of a Standard Model signal is 0.9σ.

 

Title:
Hyperscaling at the spin density wave quantum critical point in two-dimensional metals
Authors:
Patel, Aavishkar A.; Strack, Philipp; Sachdev, Subir
Publication:
Physical Review B, Volume 92, Issue 16, id.165105 (PhRvB Homepage)
Publication Date:
10/2015
Origin:
APS
PACS Keywords:
Non-Fermi-liquid ground states electron phase diagrams and phase transitions in model systems
Abstract Copyright:
2015: American Physical Society
DOI:
10.1103/PhysRevB.92.165105
Bibliographic Code:
2015PhRvB..92p5105P

Abstract

The hyperscaling property implies that spatially isotropic critical quantum states in d spatial dimensions have a specific heat, which scales with temperature as Td /z, and an optical conductivity, which scales with frequency as ω(d -2 )/z for ω ≫T , where z is the dynamic critical exponent. We examine the spin density wave critical fixed point of metals in d =2 found by Sur and Lee [Phys. Rev. B 91, 125136 (2015), 10.1103/PhysRevB.91.125136] in an expansion in ɛ =3 -d . We find that the contributions of the "hot spots" on the Fermi surface to the optical conductivity and specific heat obey hyperscaling (up to logarithms), and agree with the results of the large N analysis of the optical conductivity by Hartnoll et al. [ Phys. Rev. B 84, 125115 (2011), 10.1103/PhysRevB.84.125115]. With a small bare velocity of the boson associated with the spin density wave order, there is an intermediate energy regime where hyperscaling is violated with d →dt , where dt=1 is the number of dimensions transverse to the Fermi surface. We also present a Boltzmann equation analysis which indicates that the hot-spot contribution to the dc conductivity has the same scaling as the optical conductivity, with T replacing ω.

 

Title:
Probing excitations in insulators via injection of spin currents
Authors:
Chatterjee, Shubhayu; Sachdev, Subir
Publication:
Physical Review B, Volume 92, Issue 16, id.165113 (PhRvB Homepage)
Publication Date:
10/2015
Origin:
APS
PACS Keywords:
Spin transport through interfaces, Current-driven spin pumping
Abstract Copyright:
2015: American Physical Society
DOI:
10.1103/PhysRevB.92.165113
Bibliographic Code:
2015PhRvB..92p5113C

Abstract

We propose a spin transport experiment to measure the low-energy excitations in insulators with spin degrees of freedom, with a focus on detecting ground states that lack magnetic order. A general formalism to compute the spin current from a metal with a nonequilibrium distribution of spins to an insulator is developed. It is applied to insulating states with and without long range magnetic order, and salient features in the spin conductance are noted.

 

Title:
Search for photonic signatures of gauge-mediated supersymmetry in 8 TeV p p collisions with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2850 coauthors
Publication:
Physical Review D, Volume 92, Issue 7, id.072001 (PhRvD Homepage)
Publication Date:
10/2015
Origin:
APS
PACS Keywords:
Supersymmetric models, Limits on production of particles
Abstract Copyright:
2015: CERN
DOI:
10.1103/PhysRevD.92.072001
Bibliographic Code:
2015PhRvD..92g2001A

Abstract

A search is presented for photonic signatures motivated by generalized models of gauge-mediated supersymmetry breaking. This search makes use of 20.3 fb-1 of proton-proton collision data at √{s }=8 TeV recorded by the ATLAS detector at the LHC, and explores models dominated by both strong and electroweak production of supersymmetric partner states. Four experimental signatures incorporating an isolated photon and significant missing transverse momentum are explored. These signatures include events with an additional photon, lepton, b -quark jet, or jet activity not associated with any specific underlying quark flavor. No significant excess of events is observed above the Standard Model prediction and model-dependent 95% confidence-level exclusion limits are set.

 

Title:
Search for massive, long-lived particles using multitrack displaced vertices or displaced lepton pairs in p p collisions at √{s }=8 TeV with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2820 coauthors
Publication:
Physical Review D, Volume 92, Issue 7, id.072004 (PhRvD Homepage)
Publication Date:
10/2015
Origin:
APS
PACS Keywords:
Supersymmetric models, Limits on production of particles, Supersymmetric partners of known particles
Abstract Copyright:
2015: CERN
DOI:
10.1103/PhysRevD.92.072004
Bibliographic Code:
2015PhRvD..92g2004A

Abstract

Many extensions of the Standard Model posit the existence of heavy particles with long lifetimes. This article presents the results of a search for events containing at least one long-lived particle that decays at a significant distance from its production point into two leptons or into five or more charged particles. This analysis uses a data sample of proton-proton collisions at √{s }=8 TeV corresponding to an integrated luminosity of 20.3 fb-1 collected in 2012 by the ATLAS detector operating at the Large Hadron Collider. No events are observed in any of the signal regions, and limits are set on model parameters within supersymmetric scenarios involving R -parity violation, split supersymmetry, and gauge mediation. In some of the search channels, the trigger and search strategy are based only on the decay products of individual long-lived particles, irrespective of the rest of the event. In these cases, the provided limits can easily be reinterpreted in different scenarios.

 

Title:
Tevatron Combination of Single-Top-Quark Cross Sections and Determination of the Magnitude of the Cabibbo-Kobayashi-Maskawa Matrix Element Vt b
Authors:
Aaltonen, T.; Abazov, V. M.; Abbott, B.;... Franklin, M.;... ; and 2850 coauthors
Publication:
Physical Review Letters, Volume 115, Issue 15, id.152003 (PhRvL Homepage)
Publication Date:
10/2015
Origin:
APS
PACS Keywords:
Top quarks, Applications of electroweak models to specific processes, Inclusive production with identified leptons photons or other nonhadronic particles, Determination of Kobayashi-Maskawa matrix elements
Abstract Copyright:
2015: American Physical Society
DOI:
10.1103/PhysRevLett.115.152003
Bibliographic Code:
2015PhRvL.115o2003A

Abstract

We present the final combination of CDF and D0 measurements of cross sections for single-top-quark production in proton-antiproton collisions at a center-of-mass energy of 1.96 TeV. The data correspond to total integrated luminosities of up to 9.7 fb-1 per experiment. The t -channel cross section is measured to be σt=2.2 5-0.31+0.29 pb . We also present the combinations of the two-dimensional measurements of the s - vs t -channel cross section. In addition, we give the combination of the s +t channel cross section measurement resulting in σs +t=3.3 0-0.40+0.52 pb , without assuming the standard model value for the ratio σst. The resulting value of the magnitude of the top-to-bottom quark coupling is |Vt b|=1.0 2-0.05+0.06, corresponding to |Vt b|>0.92 at the 95% C.L.

 

Title:
Far-from-Equilibrium Field Theory of Many-Body Quantum Spin Systems: Prethermalization and Relaxation of Spin Spiral States in Three Dimensions
Authors:
Babadi, Mehrtash; Demler, Eugene; Knap, Michael
Publication:
Physical Review X, Volume 5, Issue 4, id.041005
Publication Date:
10/2015
Origin:
APS
PACS Keywords:
Quantized spin models, Fluctuation phenomena random processes noise and Brownian motion, Nonequilibrium and irreversible thermodynamics
Abstract Copyright:
2015: authors
DOI:
10.1103/PhysRevX.5.041005
Bibliographic Code:
2015PhRvX...5d1005B

Abstract

We study theoretically the far-from-equilibrium relaxation dynamics of spin spiral states in the three-dimensional isotropic Heisenberg model. The investigated problem serves as an archetype for understanding quantum dynamics of isolated many-body systems in the vicinity of a spontaneously broken continuous symmetry. We present a field-theoretical formalism that systematically improves on the mean field for describing the real-time quantum dynamics of generic spin-1 /2 systems. This is achieved by mapping spins to Majorana fermions followed by a 1 /N expansion of the resulting two-particle-irreducible effective action. Our analysis reveals rich fluctuation-induced relaxation dynamics in the unitary evolution of spin spiral states. In particular, we find the sudden appearance of long-lived prethermalized plateaus with diverging lifetimes as the spiral winding is tuned toward the thermodynamically stable ferro- or antiferromagnetic phases. The emerging prethermalized states are characterized by different bosonic modes being thermally populated at different effective temperatures and by a hierarchical relaxation process reminiscent of glassy systems. Spin-spin correlators found by solving the nonequilibrium Bethe-Salpeter equation provide further insight into the dynamic formation of correlations, the fate of unstable collective modes, and the emergence of fluctuation-dissipation relations. Our predictions can be verified experimentally using recent realizations of spin spiral states with ultracold atoms in a quantum gas microscope [S. Hild et al., Phys. Rev. Lett. 113, 147205 (2014), 10.1103/PhysRevLett.113.147205].

 

Title:
Intensity-intensity correlations determined by dimension of quantum state in phase space: P-distribution
Authors:
Leuchs, Gerd; Glauber, Roy J.; Schleich, Wolfgang P.
Publication:
Physica Scripta, Volume 90, Issue 10, article id. 108007 (2015).
Publication Date:
10/2015
Origin:
IOP
DOI:
10.1088/0031-8949/90/10/108007
Bibliographic Code:
2015PhyS...90j8007L

Abstract

We use the P-distribution to show that the familiar values 1, 2 and 3 of the normalized second order correlation function at equal times {g}(2)(0) corresponding to a coherent state, a thermal state and a highly squeezed vacuum are a consequence of the number of dimensions these states take up in quantum phase space. Whereas the thermal state exhibits rotational symmetry and thus extends over two dimensions, the squeezed vacuum factorizes into two independent one-dimensional phase space variables, and in the limit of large squeezing is therefore a one-dimensional object. The coherent state is a point in the phase space of the P-distribution and thus has zero dimensions. The fact that for photon number states the P-distribution is even narrower than that of the zero-dimensional coherent state suggests the notion of ‘negative’ dimensions.


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