Faculty Publications: September, 2014

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Title:
BICEP2. II. Experiment and three-year Data Set
Authors:
Ade, P. A. R.; Aikin, R. W.; Amiri, M.;...; Kovac, J. M.;... and 48 coauthors; Bicep2 Collaboration
Publication:
The Astrophysical Journal, Volume 792, Issue 1, article id. 62, 29 pp. (2014). (ApJ Homepage)
Publication Date:
09/2014
Origin:
IOP
Astronomy Keywords:
cosmic background radiation, cosmology: observations, gravitational waves, inflation, instrumentation: polarimeters, telescopes
DOI:
10.1088/0004-637X/792/1/62
Bibliographic Code:
2014ApJ...792...62A

Abstract

We report on the design and performance of the BICEP2 instrument and on its three-year data set. BICEP2 was designed to measure the polarization of the cosmic microwave background (CMB) on angular scales of 1°-5°(l = 40-200), near the expected peak of the B-mode polarization signature of primordial gravitational waves from cosmic inflation. Measuring B-modes requires dramatic improvements in sensitivity combined with exquisite control of systematics. The BICEP2 telescope observed from the South Pole with a 26 cm aperture and cold, on-axis, refractive optics. BICEP2 also adopted a new detector design in which beam-defining slot antenna arrays couple to transition-edge sensor (TES) bolometers, all fabricated on a common substrate. The antenna-coupled TES detectors supported scalable fabrication and multiplexed readout that allowed BICEP2 to achieve a high detector count of 500 bolometers at 150 GHz, giving unprecedented sensitivity to B-modes at degree angular scales. After optimization of detector and readout parameters, BICEP2 achieved an instrument noise-equivalent temperature of 15.8\ \mu {K}\sqrt{{s}}. The full data set reached Stokes Q and U map depths of 87.2 nK in square-degree pixels (5.'2 μK) over an effective area of 384 deg2 within a 1000 deg2 field. These are the deepest CMB polarization maps at degree angular scales to date. The power spectrum analysis presented in a companion paper has resulted in a significant detection of B-mode polarization at degree scales.

 

Title:
Random-subset fitting of digital holograms for fast three-dimensional particle tracking [Invited]
Authors:
Dimiduk, Thomas G.; Perry, Rebecca W.; Fung, Jerome; Manoharan, Vinothan N.
Publication:
Applied Optics, vol. 53, issue 27, p. G177
Publication Date:
09/2014
Origin:
CROSSREF
DOI:
10.1364/AO.53.00G177
Bibliographic Code:
2014ApOpt..53G.177D

Abstract

Not Available

 

Title:
High-efficiency resonant amplification of weak magnetic fields for single spin magnetometry
Authors:
Trifunovic, Luka; Pedrocchi, Fabio L.; Hoffman, Silas; Maletinsky, Patrick; Yacoby, Amir; Loss, Daniel
Publication:
eprint arXiv:1409.1497
Publication Date:
09/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Other Condensed Matter
Comment:
11 pages, 7 figures
Bibliographic Code:
2014arXiv1409.1497T

Abstract

We demonstrate theoretically that by placing a ferromagnetic particle between a nitrogen-vacancy (NV) magnetometer and a target spin, the magnetometer sensitivity is increased dramatically. Specifically, using materials and techniques already experimentally available, we find that by taking advantage of the ferromagnetic resonance the minimum magnetic moment that can be measured is smaller by four orders of magnitude in comparison to current state-of-the-art magnetometers. As such, our proposed setup is sensitive enough to detect a single nuclear spin at a distance of $30$~nm from the surface within less than one second of data acquisition at room temperature. Our proposal opens the door for nanoscale NMR on biological material under ambient conditions.

 

Title:
Non-Unitary Holography
Authors:
Vafa, Cumrun
Publication:
eprint arXiv:1409.1603
Publication Date:
09/2014
Origin:
ARXIV
Keywords:
High Energy Physics - Theory
Comment:
13 pages, note added and additional references and minor edits
Bibliographic Code:
2014arXiv1409.1603V

Abstract

We propose gauge theory/gravity duality involving conformal theories based on U(N+k|k) gauge groups. We show that to all orders in 1/N these non-unitary theories based on supergroups are indistinguishable from the corresponding unitary theories where the gauge group is replaced by U(N). This leads to non-unitary gravity duals which to all orders in 1/N are indistinguishable from their unitary cousins. They are distinguished by operators whose correlation functions differ by O(exp(-aN)). The celebrated type IIB on AdS^5 x S^5 and M-theory on AdS^4 x S^7 fall in this class and thus seem to also admit non-unitary non-perturbative completions. It is tempting to conjecture that this setup may provide a non-unitary model for black hole evaporation.

 

Title:
Conserved quantities on asymptotically hyperbolic initial data sets
Authors:
Chen, Po-Ning; Wang, Mu-Tao; Yau, Shing-Tung
Publication:
eprint arXiv:1409.1812
Publication Date:
09/2014
Origin:
ARXIV
Keywords:
Mathematics - Differential Geometry, General Relativity and Quantum Cosmology
Comment:
30 pages
Bibliographic Code:
2014arXiv1409.1812C

Abstract

In this article, we consider the limit of quasi-local conserved quantities [31,9] at the infinity of an asymptotically hyperbolic initial data set in general relativity. These give notions of total energy-momentum, angular momentum, and center of mass. Our assumption on the asymptotics is less stringent than any previous ones to validate a Bondi-type mass loss formula. The Lorentz group acts on the asymptotic infinity through the exchange of foliations by coordinate spheres. For foliations aligning with the total energy-momentum vector, we prove that the limits of quasi-local center of mass and angular momentum are finite, and evaluate the limits in terms of the expansion coefficients of the metric and the second fundamental form.

 

Title:
Exploring dynamical phase transitions and prethermalization with quantum noise of excitations
Authors:
Smacchia, Pietro; Knap, Michael; Demler, Eugene; Silva, Alessandro
Publication:
eprint arXiv:1409.1883
Publication Date:
09/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Statistical Mechanics, Condensed Matter - Quantum Gases
Comment:
5 + 6 pages; 4+ 5 figures
Bibliographic Code:
2014arXiv1409.1883S

Abstract

Dynamical phase transitions can occur in isolated quantum systems following a sudden change of the system parameters. We discuss the characterization of such dynamical phase transitions based on the statistics of excitations produced in a quantum quench. We consider a specific case of an $O(N)$ model in the large $N$ limit and show that the transition manifests itself most dramatically not in the average number of defects but in the higher moments. We argue that the growth of the second moment of the defect density in time following a quench is a signature of a prethermal state. Our theoretical results should be relevant to quench experiments with ultracold bosonic atoms in optical lattices from the Mott insulating to the superfluid phase.

 

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:
eprint arXiv:1409.2749
Publication Date:
09/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Mesoscale and Nanoscale Physics, Quantum Physics
Comment:
31 pages, 10 figures
Bibliographic Code:
2014arXiv1409.2749A

Abstract

Optically-detected magnetic resonance using Nitrogen Vacancy (NV) color 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, 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, e.g., 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 (FOV), and compressed sensing speed-up.

 

Title:
Non-Kaehler SYZ mirror symmetry
Authors:
Lau, Siu-Cheong; Tseng, Li-Sheng; Yau, Shing-Tung
Publication:
eprint arXiv:1409.2765
Publication Date:
09/2014
Origin:
ARXIV
Keywords:
Mathematics - Differential Geometry, High Energy Physics - Theory, Mathematics - Algebraic Geometry, 53D37, 14J33, 53Z05
Comment:
24 pages
Bibliographic Code:
2014arXiv1409.2765L

Abstract

We study SYZ mirror symmetry in the context of non-Kaehler Calabi-Yau manifolds. In particular, we study the six-dimensional Type II supersymmetric $SU(3)$ systems with Ramond-Ramond fluxes, and generalized them to higher dimensions. We show that Fourier-Mukai transform provides the mirror map between these Type IIA and Type IIB supersymmetric systems in the semi-flat setting. This is concretely exhibited by nilmanifolds.

 

Title:
Strongly Correlated Quantum Walks in Optical Lattices
Authors:
Preiss, Philipp M.; Ma, Ruichao; Tai, M. Eric; Lukin, Alexander; Rispoli, Matthew; Zupancic, Philip; Lahini, Yoav; Islam, Rajibul; Greiner, Markus
Publication:
eprint arXiv:1409.3100
Publication Date:
09/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Quantum Gases
Comment:
8 pages, 4 figures, 1 table
Bibliographic Code:
2014arXiv1409.3100P

Abstract

Full control over the dynamics of interacting, indistinguishable quantum particles is an important prerequisite for the experimental study of strongly correlated quantum matter and the implementation of high-fidelity quantum information processing. Here we demonstrate such control over the quantum walk - the quantum mechanical analogue of the classical random walk - in the strong interaction regime. We directly observe fundamental effects such as the emergence of correlations due to quantum statistics and interactions in two-particle quantum walks, as well as strongly correlated Bloch oscillations in tilted optical lattices. Our approach can be scaled to larger systems, greatly extending the class of problems accessible via quantum walks, which can now serve as a basis for universal quantum computation and as a quantum simulator for strongly correlated many-body dynamics.

 

Title:
Conformal field theories at non-zero temperature: operator product expansions, Monte Carlo, and holography
Authors:
Katz, Emanuel; Sachdev, Subir; Sorensen, Erik S.; Witczak-Krempa, William
Publication:
eprint arXiv:1409.3841
Publication Date:
09/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Strongly Correlated Electrons, General Relativity and Quantum Cosmology, High Energy Physics - Lattice, High Energy Physics - Theory
Comment:
25+12 pages; 5+2 figures. Single column
Bibliographic Code:
2014arXiv1409.3841K

Abstract

We compute the non-zero temperature conductivity of conserved flavor currents in conformal field theories (CFTs) in 2+1 spacetime dimensions. At frequencies much greater than the temperature, $\hbar\omega>> k_B T$, the $\omega$ dependence can be computed from the operator product expansion (OPE) between the currents and operators which acquire a non-zero expectation value at T > 0. Such results are found to be in excellent agreement with quantum Monte Carlo studies of the O(2) Wilson-Fisher CFT. Results for the conductivity and other observables are also obtained in vector 1/N expansions. We match these large $\omega$ results to the corresponding correlators of holographic representations of the CFT: the holographic approach then allows us to extrapolate to small $\hbar \omega/(k_B T)$. Other holographic studies implicitly only used the OPE between the currents and the energy-momentum tensor, and this yields the correct leading large $\omega$ behavior for a large class of CFTs. However, for the Wilson-Fisher CFT a relevant "thermal" operator must also be considered, and then consistency with the Monte Carlo results is obtained without a previously needed ad hoc rescaling of the T value. We also establish sum rules obeyed by the conductivity of a wide class of CFTs.

 

Title:
Measurement of differential production cross section for $Z/\gamma^*$ bosons in association with jets in $p\bar{p}$ collisions at $\sqrt{s}=1.96$ TeV
Authors:
CDF Collaboration; Aaltonen, T.; Amerio, S.; Amidei, D.;... Franklin, M.;... Guimaraes da Costa, J.;... and 398 coauthors;
Publication:
eprint arXiv:1409.4359
Publication Date:
09/2014
Origin:
ARXIV
Keywords:
High Energy Physics - Experiment
Comment:
submitted to Phys. Rev. D
Bibliographic Code:
2014arXiv1409.4359C

Abstract

Differential cross sections for the production of $Z$ bosons or off-shell photons $\gamma^*$ in association with jets are measured in proton-antiproton collisions at center-of-mass energy $\sqrt{s}=1.96$ TeV using the full data set collected with the Collider Detector at Fermilab in Tevatron Run II, and corresponding to 9.6 fb$^{-1}$ of integrated luminosity. Results include first measurements at CDF of differential cross sections in events with a $Z/\gamma^*$ boson and three or more jets, the inclusive cross section for production of $Z/\gamma^*$ and four or more jets, and cross sections as functions of various angular observables in lower jet-multiplicity final states. Measured cross sections are compared to several theoretical predictions.

 

Title:
Measurement of the Top-Quark Mass in the All-Hadronic Channel using the full CDF data set
Authors:
CDF Collaboration; Aaltonen, T.; Amerio, S.; Amidei, D.; Anastassov, A.;... Franklin, M.;... Guimaraes da Costa, J.;... and 402 coauthors
Publication:
eprint arXiv:1409.4906
Publication Date:
09/2014
Origin:
ARXIV
Keywords:
High Energy Physics - Experiment
Comment:
Minor modifications to the text based on the feedback from the journal referee
Bibliographic Code:
2014arXiv1409.4906C

Abstract

The top-quark mass M_top is measured using top quark-antiquark pairs produced in proton-antiproton collisions at a center-of-mass energy of 1.96 TeV and decaying into a fully hadronic final state. The full data set collected with the CDFII 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 M_top with a simultaneous calibration of the jet-energy scale. A value of M_top = 175.07+- 1.19(stat)+1.55-1.58(syst) GeV/c^2 is obtained for the top-quark mass.

 

Title:
An in situ measurement of the radio-frequency attenuation in ice at Summit Station, Greenland
Authors:
Avva, J.; Kovac, J. M.; Miki, C.; Saltzberg, D.; Vieregg, A. G.
Publication:
eprint arXiv:1409.5413
Publication Date:
09/2014
Origin:
ARXIV
Keywords:
Astrophysics - Instrumentation and Methods for Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, High Energy Physics - Experiment
Comment:
7 pages, 7 figures, submitted to Journal of Glaciology
Bibliographic Code:
2014arXiv1409.5413A

Abstract

We report an in situ measurement of the electric field attenuation length at radio frequencies for the bulk ice at Summit Station, Greenland, made by broadcasting radio-frequency signals vertically through the ice and measuring the relative power in the return ground bounce signal. We find the depth-averaged field attenuation length to be 947 +92/-85 meters at 75 MHz. While this measurement has clear radioglaciological applications, the radio clarity of the ice also has implications for the detection of ultra-high energy (UHE) astrophysical particles via their radio emission in dielectric media such as ice. The measured attenuation length at Summit Station is comparable to previously measured radio-frequency attenuation lengths at candidate particle detector sites around the world, and strengthens the case for Summit Station as the most promising northern site for UHE neutrino detection.

 

Title:
Decoherence imaging of spin ensembles using a scanning single-electron spin in diamond
Authors:
Luan, Lan; Grinolds, Michael S.; Hong, Sungkun; Maletinsky, Patrick; Walsworth, Ronald L.; Yacoby, Amir
Publication:
eprint arXiv:1409.5418
Publication Date:
09/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Mesoscale and Nanoscale Physics
Bibliographic Code:
2014arXiv1409.5418L

Abstract

The nitrogen-vacancy (NV) defect center in diamond has demonstrated great capability for nanoscale magnetic sensing and imaging for both static and periodically modulated target fields. However, it remains a challenge to detect and image randomly fluctuating magnetic fields. Recent theoretical and numerical works have outlined detection schemes that exploit changes in decoherence of the detector spin as a sensitive measure for fluctuating fields. Here we experimentally monitor the decoherence of a scanning NV center in order to image the fluctuating magnetic fields from paramagnetic impurities on an underlying diamond surface. We detect a signal corresponding to roughly 800 ${\mu}_B$ in 2 s of integration time, without any control on the target spins, and obtain magnetic-field spectral information using dynamical decoupling techniques. The extracted spatial and temporal properties of the surface paramagnetic impurities provide insight to prolonging the coherence of near-surface qubits for quantum information and metrology applications.

 

Title:
Density wave instabilities of fractionalized Fermi liquids
Authors:
Chowdhury, Debanjan; Sachdev, Subir
Publication:
eprint arXiv:1409.5430
Publication Date:
09/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Superconductivity
Comment:
20 pages, 6 figures
Bibliographic Code:
2014arXiv1409.5430C

Abstract

Recent experiments in the underdoped regime of the hole-doped cuprates have found evidence for an incommensurate charge density wave state. We present an analysis of the charge ordering instabilities in a metal with antiferromagnetic correlations, where the electronic excitations are coupled to the fractionalized excitations of a quantum fluctuating antiferromagnet on the square lattice. The resulting charge density wave state emerging out of such a fractionalized Fermi-liquid (FL*) has wavevectors of the form $(\pm Q_0,0),~(0,\pm Q_0)$, with a predominantly $d$-form factor, in agreement with experiments on a number of different families of the cuprates. In contrast, as previously shown, the charge density wave instability of a nearly antiferromagnetic metal with a large Fermi surface, interacting via short-range interactions, has wavevectors of the type $(\pm Q_0,\pm Q_0)$. Our results show that the observed charge density wave appears as a low-energy instability of a fractionalized metallic state linked to the proximity to an antiferromagnetic insulator, and the pseudogap regime can be described by such a metal at least over intermediate length and energy scales.

 

Title:
Graph invariant from ideas in quantum field theory
Authors:
Huang, An; Yau, Shing-Tung
Publication:
eprint arXiv:1409.5853
Publication Date:
09/2014
Origin:
ARXIV
Keywords:
Mathematics - Combinatorics, 05C60
Comment:
6 pages
Bibliographic Code:
2014arXiv1409.5853H

Abstract

We propose a polynomial time computable graph invariant, which comes out directly from a modified version of discrete Green's function on a graph. It is our hope that it can help to construct fast algorithms for the graph isomorphism testing. We explain the physics behind this discrete Green's function, which is a very basic idea applied to graphs.

 

Title:
On cohomology theory of (di)graphs
Authors:
Huang, An; Yau, Shing-Tung
Publication:
eprint arXiv:1409.6194
Publication Date:
09/2014
Origin:
ARXIV
Keywords:
Mathematics - Combinatorics, Mathematics - Algebraic Topology, 05C38, 55N99
Comment:
17 pages
Bibliographic Code:
2014arXiv1409.6194H

Abstract

To a digraph with a choice of certain integral basis, we construct a CW complex, whose integral singular cohomology is canonically isomorphic to the path cohomology of the digraph as introduced in \cite{GLMY}. The homotopy type of the CW complex turns out to be independent of the choice of basis. After a very brief discussion of functoriality, this construction immediately implies some of the expected but perhaps combinatorially subtle properties of the digraph cohomology and homotopy proved very recently \cite{GLMY2}. Furthermore, one gets a very simple expected formula for the cup product of forms on the digraph. On the other hand, we present an approach of using sheaf theory to reformulate (di)graph cohomologies. The investigation of the path cohomology from this framework, leads to a subtle version of Poincare lemma for digraphs, which follows from the construction of the CW complex.

 

Title:
All optical control of a single electron spin in diamond
Authors:
Chu, Yiwen; Markham, Matthew; Twitchen, Daniel J.; Lukin, Mikhail D.
Publication:
eprint arXiv:1409.6372
Publication Date:
09/2014
Origin:
ARXIV
Keywords:
Quantum Physics
Bibliographic Code:
2014arXiv1409.6372C

Abstract

Precise coherent control of the individual electronic spins associated with atom-like impurities in the solid state is essential for applications in quantum information processing and quantum metrology. We demonstrate all-optical initialization, fast coherent manipulation, and readout of the electronic spin of the negatively charged nitrogen-vacancy (NV$^-$) center in diamond at T$\sim$7K. We then present the observation of a novel double-dark resonance in the spectroscopy of an individual NV center. These techniques open the door for new applications ranging from robust manipulation of spin states using geometric quantum gates to quantum sensing and information processing.

 

Title:
Identifying structural flow defects in disordered solids using machine learning methods
Authors:
Cubuk, Ekin D.; Schoenholz, Samuel S.; Rieser, Jennifer M.; Malone, Brad D.; Rottler, Joerg; Durian, Douglas J.; Kaxiras, Efthimios; Liu, Andrea J.
Publication:
eprint arXiv:1409.6820
Publication Date:
09/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Soft Condensed Matter
Comment:
4 pages, 4 figures
Bibliographic Code:
2014arXiv1409.6820C

Abstract

We use machine learning methods on local structure to identify flow defects - or regions susceptible to rearrangement - in jammed and glassy systems. We apply this method successfully to two disparate systems: a two dimensional experimental realization of a granular pillar under compression, and a Lennard-Jones glass in both two and three dimensions above and below its glass transition temperature. We also identify characteristics of flow defects that differentiate them from the rest of the sample. Our results show it is possible to discern subtle structural features responsible for heterogeneous dynamics observed across a broad range of disordered materials.

 

Title:
Efficient fiber-optical interface for nanophotonic devices
Authors:
Tiecke, T. G.; Nayak, K. P.; Thompson, J. D.; Peyronel, T.; de Leon, N. P.; Vuletić, V.; Lukin, M. D.
Publication:
eprint arXiv:1409.7698
Publication Date:
09/2014
Origin:
ARXIV
Keywords:
Physics - Optics
Comment:
7 pages, 4 figures, includes supplementary information
Bibliographic Code:
2014arXiv1409.7698T

Abstract

We demonstrate a method for efficient coupling of guided light from a single mode optical fiber to nanophotonic devices. Our approach makes use of single-sided conical tapered optical fibers that are evanescently coupled over the last ~10 um to a nanophotonic waveguide. By means of adiabatic mode transfer using a properly chosen taper, single-mode fiber-waveguide coupling efficiencies as high as 97(1)% are achieved. Efficient coupling is obtained for a wide range of device geometries which are either singly-clamped on a chip or attached to the fiber, demonstrating a promising approach for integrated nanophotonic circuits, quantum optical and nanoscale sensing applications.

 

Title:
Pleiotropic consequences of adaptation across gradations of environmental stress in budding yeast
Authors:
Jerison, Elizabeth R.; Kryazhimskiy, Sergey; Desai, Michael M.
Publication:
eprint arXiv:1409.7839
Publication Date:
09/2014
Origin:
ARXIV
Keywords:
Quantitative Biology - Populations and Evolution
Bibliographic Code:
2014arXiv1409.7839J

Abstract

Adaptation to one environment often results in fitness gains and losses in other conditions. To characterize how these consequences of adaptation depend on the physical similarity between environments, we evolved 180 populations of Saccharomyces cerevisiae at different degrees of stress induced by either salt, temperature, pH, or glucose depletion. We measure how the fitness of clones adapted to each environment depends on the intensity of the corresponding type of stress. We find that clones evolved in a given type and intensity of stress tend to gain fitness in other similar intensities of that stress, and lose progressively more fitness in more physically dissimilar environments. These fitness trade-offs are asymmetric: adaptation to permissive conditions incurred a smaller trade-off in stressful conditions than vice versa. We also find that fitnesses of clones are highly correlated across similar intensities of stress, but these correlations decay towards zero in more dissimilar environments. To interpret these results, we introduce the concept of a joint distribution of fitness effects of new mutations in multiple environments (the JDFE), which describes the probability that a given mutation has particular fitness effects in some set of conditions. We find that our observations are consistent with JDFEs that are highly correlated between physically similar environments, and that become less correlated and asymmetric as the environments become more dissimilar. The JDFE provides a framework for quantifying evolutionary similarity between conditions, and forms a useful basis for theoretical work aimed at predicting the outcomes of evolution in fluctuating environments.

 

Title:
On the Absence of Red Structural Color in Photonic Glasses, Bird Feathers and Certain Beetles
Authors:
Magkiriadou, Sofia; Park, Jin-Gyu; Kim, Young-Seok; Manoharan, Vinothan N.
Publication:
eprint arXiv:1409.8575
Publication Date:
09/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Soft Condensed Matter, Physics - Optics
Comment:
8 pages, 9 figures
Bibliographic Code:
2014arXiv1409.8575M

Abstract

Colloidal glasses, bird feathers, and beetle scales can all show structural colors arising from short-ranged spatial correlations between scattering centers. Unlike the structural colors arising from Bragg diffraction in ordered materials like opals, the colors of these photonic glasses are independent of orientation, owing to their disordered, isotropic microstructures. However, there are few examples of photonic glasses with angle-independent red colors in nature, and colloidal glasses with particle sizes chosen to yield structural colors in the red show weak color saturation. Using scattering theory, we show that the absence of angle-independent red color can be explained by the tendency of individual particles to backscatter light more strongly in the blue. We discuss how the backscattering resonances of individual particles arise from cavity-like modes, and how they interact with the structural resonances to prevent red. Finally, we use the model to develop design rules for colloidal glasses with red, angle-independent structural colors.

 

Title:
A New Model for Elliptic Fibrations with a Rank One Mordell-Weil Group: I. Singular Fibers and Semi-Stable Degenerations
Authors:
Esole, Mboyo; Jinwoo Kang, Monica; Yau, Shing-Tung
Publication:
eprint arXiv:1410.0003
Publication Date:
09/2014
Origin:
ARXIV
Keywords:
High Energy Physics - Theory, Mathematics - Algebraic Geometry
Comment:
24 pages, 3 figures, 2 tables
Bibliographic Code:
2014arXiv1410.0003E

Abstract

We introduce a new model for elliptic fibrations endowed with a Mordell-Weil group of rank one. We call it a Q$_7(\mathscr{L},\mathscr{S})$ model. It naturally generalizes several previous models of elliptic fibrations popular in the F-theory literature. The model is also explicitly smooth, thus relevant physical quantities can be computed in terms of topological invariants in straight manner. Since the general fiber is defined by a cubic curve, basic arithmetic operations on the curve can be done using the chord-tangent group law. We will use this model to determine the spectrum of singular fibers of an elliptic fibration of rank one and compute a generating function for its Euler characteristic. With a view toward string theory, we determine a semi-stable degeneration which is understood as a weak coupling limit in F-theory. We show that it satisfies a non-trivial topological relation at the level of homological Chern classes. This relation ensures that the D3 charge in F-theory is the same as the one in the weak coupling limit.

 

Title:
Evaporative microclimate driven hygrometers and hygromotors
Authors:
Chung, Jun Young; King, Hunter; Mahadevan, L.
Publication:
Europhysics Letters, Volume 107, Issue 6, article id. 64002 (2014).
Publication Date:
09/2014
Origin:
IOP
DOI:
10.1209/0295-5075/107/64002
Bibliographic Code:
2014EL....10764002C

Abstract

A strip of paper placed on a hand spontaneously curls upwards. This simple observation illustrates the ability of a relatively homogeneous hygroscopic structural material, paper, to sense and respond to the microclimate near a non-equilibrium system, a moist evaporative boundary layer. We quantify this interaction using a simple experiment and show that it can be understood in terms of a minimal model. A small modification of this paper hygrometer that makes one or another surface partly hydrophobic using a crayon or tape allows us to create a hygro-oscillator or a hygromotor that converts transverse moisture gradients into lateral oscillations or directed motion. Our study shows how treating paper as a responsive structural material allows us to extract information and work from a microclimatic boundary layer, transforming a messenger to a machine.

 

Title:
Muon reconstruction efficiency and momentum resolution of the ATLAS experiment in proton-proton collisions at TeV in 2010
Authors:
Aad, G.; Abajyan, T.; Abbott, B.;... Franklin, M.;... Barreiro Guimarães da Costa, J.;... Huth, J.;... Morii, M.;... and 2911 coauthors
Publication:
The European Physical Journal C, Volume 74, article id. #3034, 32 pp. (EPJC Homepage)
Publication Date:
09/2014
Origin:
SPRINGER
Abstract Copyright:
(c) 2014: CERN for the benefit of the ATLAS collaboration
DOI:
10.1140/epjc/s10052-014-3034-9
Bibliographic Code:
2014EPJC...74.3034A

Abstract

Not Available

 

Title:
Effective field theory and keV lines from dark matter
Authors:
Krall, Rebecca; Reece, Matthew; Roxlo, Thomas
Publication:
Journal of Cosmology and Astroparticle Physics, Issue 09, article id. 007, pp. (2014). (JCAP Homepage)
Publication Date:
09/2014
Origin:
IOP
DOI:
10.1088/1475-7516/2014/09/007
Bibliographic Code:
2014JCAP...09..007K

Abstract

We survey operators that can lead to a keV photon line from dark matter decay or annihilation. We are motivated in part by recent claims of an unexplained 3.5 keV line in galaxy clusters and in Andromeda, but our results could apply to any hypothetical line observed in this energy range. We find that given the amount of flux that is observable, explanations in terms of decay are more plausible than annihilation, at least if the annihilation is directly to Standard Model states rather than intermediate particles. The decay case can be explained by a scalar or pseudoscalar field coupling to photons suppressed by a scale not far below the reduced Planck mass, which can be taken as a tantalizing hint of high-scale physics. The scalar case is particularly interesting from the effective field theory viewpoint, and we discuss it at some length. Because of a quartically divergent mass correction, naturalness strongly suggests the theory should be cut off at or below the 1000 TeV scale. The most plausible such natural UV completion would involve supersymmetry. These bottom-up arguments reproduce expectations from top-down considerations of the physics of moduli. A keV line could also arise from the decay of a sterile neutrino, in which case a renormalizable UV completion exists and no direct inference about high-scale physics is possible.

 

Title:
Collision dynamics of polyatomic molecules containing carbon rings at low temperatures
Authors:
Li, Zhiying; Krems, Roman V.; Heller, Eric J.
Publication:
The Journal of Chemical Physics, Volume 141, Issue 10, id.104317 (JChPh Homepage)
Publication Date:
09/2014
Origin:
AIP
Abstract Copyright:
2014: AIP Publishing LLC
DOI:
10.1063/1.4894793
Bibliographic Code:
2014JChPh.141j4317L

Abstract

We explore the collision dynamics of complex hydrocarbon molecules (benzene, coronene, adamantane, and anthracene) containing carbon rings in a cold buffer gas of 3He. For benzene, we present a comparative analysis of the fully classical and fully quantum calculations of elastic and inelastic scattering cross sections at collision energies between 1 and 10 cm-1. The quantum calculations are performed using the time-independent coupled channel approach and the coupled-states approximation. We show that the coupled-states approximation is accurate at collision energies between 1 and 20 cm-1. For the classical dynamics calculations, we develop an approach exploiting the rigidity of the carbon rings and including low-energy vibrational modes without holonomic constraints. Our results illustrate the effect of the molecular shape and the vibrational degrees of freedom on the formation of long-lived resonance states that lead to low-temperature clustering.

 

Title:
Search for direct pair production of the top squark in all-hadronic final states in proton-proton collisions at = 8 TeV with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Barreiro Guimarães da Costa, J.;... Huth, J.;... Morii, M.;... and 2876 coauthors
Publication:
Journal of High Energy Physics, Volume 2014, article id. #15, 51 pp.
Publication Date:
09/2014
Origin:
SPRINGER
Keywords:
Hadron-Hadron Scattering, Supersymmetry, Top squark, Proton-proton scattering
Abstract Copyright:
(c) 2014: The Author(s)
DOI:
10.1007/JHEP09(2014)015
Bibliographic Code:
2014JHEP...09..015A

Abstract

Not Available

 

Title:
Search for new particles in events with one lepton and missing transverse momentum in pp collisions at = 8 TeV with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Barreiro Guimarães da Costa, J.;... Huth, J.;... Morii, M.;... and 2876 coauthors
Publication:
Journal of High Energy Physics, Volume 2014, article id. #37, 43 pp.
Publication Date:
09/2014
Origin:
SPRINGER
Keywords:
Hadron-Hadron Scattering, Beyond Standard Model
Abstract Copyright:
(c) 2014: The Author(s)
DOI:
10.1007/JHEP09(2014)037
Bibliographic Code:
2014JHEP...09..037A

Abstract

Not Available

 

Title:
Measurement of the production cross-section of ψ(2S) → J/ψ(→ μ+ μ- ) π+ π- in pp collisions at = 7 TeV at ATLAS
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Barreiro Guimarães da Costa, J.;... Huth, J.;... Morii, M.;... and 2876 coauthors
Publication:
Journal of High Energy Physics, Volume 2014, article id. #79, 49 pp.
Publication Date:
09/2014
Origin:
SPRINGER
Keywords:
Hadron-Hadron Scattering
Abstract Copyright:
(c) 2014: The Author(s)
DOI:
10.1007/JHEP09(2014)079
Bibliographic Code:
2014JHEP...09..079A

Abstract

Not Available

 

Title:
Measurements of fiducial and differential cross sections for Higgs boson production in the diphoton decay channel at TeV with ATLAS
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Barreiro Guimarães da Costa, J.;... Huth, J.;... Morii, M.;... and 2885 coauthors
Publication:
Journal of High Energy Physics, Volume 2014, article id. #112, 61 pp.
Publication Date:
09/2014
Origin:
SPRINGER
Keywords:
Hadron-Hadron Scattering
Abstract Copyright:
(c) 2014: The Author(s)
DOI:
10.1007/JHEP09(2014)112
Bibliographic Code:
2014JHEP...09..112A

Abstract

Measurements of fiducial and differential cross sections are presented for Higgs boson production in proton-proton collisions at a centre-of-mass energy of TeV. The analysis is performed in the H --> gammagamma decay channel using 20.3 fb-1 of data recorded by the ATLAS experiment at the CERN Large Hadron Collider. The signal is extracted using a fit to the diphoton invariant mass spectrum assuming that the width of the resonance is much smaller than the experimental resolution. The signal yields are corrected for the effects of detector inefficiency and resolution. The pp --> H --> gammagamma fiducial cross section is measured to be 43.2 ±9.4(stat.) {-/2.9 + 3.2} (syst.) ±1.2(lumi)fb for a Higgs boson of mass 125.4GeV decaying to two isolated photons that have transverse momentum greater than 35% and 25% of the diphoton invariant mass and each with absolute pseudorapidity less than 2.37. Four additional fiducial cross sections and two cross-section limits are presented in phase space regions that test the theoretical modelling of different Higgs boson production mechanisms, or are sensitive to physics beyond the Standard Model. Differential cross sections are also presented, as a function of variables related to the diphoton kinematics and the jet activity produced in the Higgs boson events. The observed spectra are statistically limited but broadly in line with the theoretical expectations. [Figure not available: see fulltext.]

 

Title:
Measurement of the Z/ gamma * boson transverse momentum distribution in pp collisions at TeV with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Barreiro Guimarães da Costa, J.;... Huth, J.;... Morii, M.;... and 2872 coauthors
Publication:
Journal of High Energy Physics, Volume 2014, article id. #145, 47 pp.
Publication Date:
09/2014
Origin:
SPRINGER
Keywords:
Hadron-Hadron Scattering
Abstract Copyright:
(c) 2014: The Author(s)
DOI:
10.1007/JHEP09(2014)145
Bibliographic Code:
2014JHEP...09..145A

Abstract

This paper describes a measurement of the Z/ gamma * boson transverse momentum spectrum using ATLAS proton-proton collision data at a centre-of-mass energy of TeV at the LHC. The measurement is performed in the Z/ gamma * --> e + e - and Z/ gamma * --> mu + mu - channels, using data corresponding to an integrated luminosity of 4.7 fb-1. Normalized differential cross sections as a function of the Z/ gamma * boson transverse momentum are measured for transverse momenta up to 800 GeV. The measurement is performed inclusively for Z/ gamma * rapidities up to 2.4, as well as in three rapidity bins. The channel results are combined, compared to perturbative and resummed QCD calculations and used to constrain the parton shower parameters of Monte Carlo generators. [Figure not available: see fulltext.]

 

Title:
Search for squarks and gluinos with the ATLAS detector in final states with jets and missing transverse momentum using TeV proton-proton collision data
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Barreiro Guimarães da Costa, J.;... Huth, J.;... Morii, M.;... and 2871 coauthors
Publication:
Journal of High Energy Physics, Volume 2014, article id. #176, 52 pp.
Publication Date:
09/2014
Origin:
SPRINGER
Keywords:
Hadron-Hadron Scattering, Supersymmetry
Abstract Copyright:
(c) 2014: The Author(s)
DOI:
10.1007/JHEP09(2014)176
Bibliographic Code:
2014JHEP...09..176A

Abstract

A search for squarks and gluinos in final states containing high- p T jets, missing transverse momentum and no electrons or muons is presented. The data were recorded in 2012 by the ATLAS experiment in TeV proton-proton collisions at the Large Hadron Collider, with a total integrated luminosity of 20 .3 fb-1. Results are interpreted in a variety of simplified and specific supersymmetry-breaking models assuming that R-parity is conserved and that the lightest neutralino is the lightest supersymmetric particle. An exclusion limit at the 95% confidence level on the mass of the gluino is set at 1330 GeV for a simplified model incorporating only a gluino and the lightest neutralino. For a simplified model involving the strong production of first- and second-generation squarks, squark masses below 850 GeV (440 GeV) are excluded for a massless lightest neutralino, assuming mass degenerate (single light-flavour) squarks. In mSUGRA/CMSSM models with tan beta = 30, A 0 = -2 m 0 and mu > 0, squarks and gluinos of equal mass are excluded for masses below 1700 GeV. Additional limits are set for non-universal Higgs mass models with gaugino mediation and for simplified models involving the pair production of gluinos, each decaying to a top squark and a top quark, with the top squark decaying to a charm quark and a neutralino. These limits extend the region of supersymmetric parameter space excluded by previous searches with the ATLAS detector. [Figure not available: see fulltext.]

 

Title:
Search for supersymmetry in events with large missing transverse momentum, jets, and at least one tau lepton in 20 fb-1 of = 8 TeV proton-proton collision data with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Barreiro Guimarães da Costa, J.;... Huth, J.;... Morii, M.;... and 2876 coauthors
Publication:
Journal of High Energy Physics, Volume 2014, article id. #103, 54 pp.
Publication Date:
09/2014
Origin:
SPRINGER
Keywords:
Hadron-Hadron Scattering, Tau Physics, Beyond Standard Model
Abstract Copyright:
(c) 2014: The Author(s)
DOI:
10.1007/JHEP09(2014)103
Bibliographic Code:
2014JHEP...09..103A

Abstract

[Figure not available: see fulltext.]

 

Title:
Quantum nonlinear optics -- photon by photon
Authors:
Chang, Darrick E.; Vuletić, Vladan; Lukin, Mikhail D.
Publication:
Nature Photonics, Volume 8, Issue 9, pp. 685-694 (2014).
Publication Date:
09/2014
Origin:
NATURE
Abstract Copyright:
(c) 2014: Nature Publishing Group, a division of Macmillan Publishers Limited. All Rights Reserved.
DOI:
10.1038/nphoton.2014.192
Bibliographic Code:
2014NaPho...8..685C

Abstract

The realization of strong interactions between individual photons is a long-standing goal of both fundamental and technological significance. Scientists have known for over half a century that light fields can interact inside nonlinear optical media, but the nonlinearity of conventional materials is negligible at the light powers associated with individual photons. Nevertheless, remarkable advances in quantum optics have recently culminated in the demonstration of several methods for generating optical nonlinearities at the level of individual photons. Systems exhibiting strong photon-photon interactions enable a number of unique applications, including quantum-by-quantum control of light fields, single-photon switches and transistors, all-optical deterministic quantum logic, and the realization of strongly correlated states of light and matter.

 

Title:
Induced superconductivity in the quantum spin Hall edge
Authors:
Hart, Sean; Ren, Hechen; Wagner, Timo; Leubner, Philipp; Mühlbauer, Mathias; Brüne, Christoph; Buhmann, Hartmut; Molenkamp, Laurens W.; Yacoby, Amir
Publication:
Nature Physics, Volume 10, Issue 9, pp. 638-643 (2014).
Publication Date:
09/2014
Origin:
NATURE
Abstract Copyright:
(c) 2014: Nature Publishing Group
DOI:
10.1038/nphys3036
Bibliographic Code:
2014NatPh..10..638H

Abstract

Topological insulators are a newly discovered phase of matter characterized by gapped bulk states surrounded by conducting boundary states. Since their theoretical discovery, these materials have encouraged intense efforts to study their properties and capabilities. Among the most striking results of this activity are proposals to engineer a new variety of superconductor at the surfaces of topological insulators. These topological superconductors would be capable of supporting localized Majorana fermions, particles whose braiding properties have been proposed as the basis of a fault-tolerant quantum computer. Despite the clear theoretical motivation, a conclusive realization of topological superconductivity remains an outstanding experimental goal. Here we present measurements of superconductivity induced in two-dimensional HgTe/HgCdTe quantum wells, a material that becomes a quantum spin Hall insulator when the well width exceeds dC = 6.3 nm (ref. ). In wells that are 7.5 nm wide, we find that supercurrents are confined to the one-dimensional sample edges as the bulk density is depleted. However, when the well width is decreased to 4.5 nm the edge supercurrents cannot be distinguished from those in the bulk. Our results provide evidence for supercurrents induced in the helical edges of the quantum spin Hall effect, establishing this system as a promising avenue towards topological superconductivity. In addition to directly confirming the existence of the topological edge channels, our results also provide a measurement of their widths, which range from 180 nm to 408 nm.

 

Title:
Condensed-matter physics: Catching relativistic electrons
Authors:
Zhu, Zhihuai; Hoffman, Jennifer E.
Publication:
Nature, Volume 513, Issue 7518, pp. 319-320 (2014). (Nature Homepage)
Publication Date:
09/2014
Origin:
NATURE
Abstract Copyright:
(c) 2014: Nature Publishing Group, a division of Macmillan Publishers Limited. All Rights Reserved.
DOI:
10.1038/513319a
Bibliographic Code:
2014Natur.513..319Z

Abstract

Low-energy electrons have been found to mimic relativistic high-energy particles in cadmium arsenide. This defines the first stable '3D Dirac semimetal', which holds promise for fundamental-physics exploration and practical applications.

 

Title:
Properties of the ground 3F2 state and the excited 3P0 state of atomic thorium in cold collisions with He3
Authors:
Au, Yat Shan; Connolly, Colin B.; Ketterle, Wolfgang; Doyle, John M.
Publication:
Physical Review A, Volume 90, Issue 3, id.032702 (PhRvA Homepage)
Publication Date:
09/2014
Origin:
APS
PACS Keywords:
Elastic, ultracold collisions, Atom cooling methods, Zeeman and Stark effects
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevA.90.032702
Bibliographic Code:
2014PhRvA..90c2702A

Abstract

Inelastic cross sections for collisions between thorium (Th) and helium (He3) are measured. For Th[3F2]-He3, we determine the ratio of momentum transfer to Zeeman relaxation cross sections to be gamma ˜500 at 800 mK. For Th[3P0]-He3, we find no quenching of this metastable state during 106 collisions. We measure the radiative lifetime of Th[3P0] to be tau >130 ms. The observed stability of Th[3P0] opens up the possibility of trapping this metastable species.

 

Title:
Vibrational quenching of the electronic ground state in ThO in cold collisions with He3
Authors:
Au, Yat Shan; Connolly, Colin B.; Ketterle, Wolfgang; Doyle, John M.
Publication:
Physical Review A, Volume 90, Issue 3, id.032703 (PhRvA Homepage)
Publication Date:
09/2014
Origin:
APS
PACS Keywords:
Elastic, ultracold collisions, Atom cooling methods, Zeeman and Stark effects
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevA.90.032703
Bibliographic Code:
2014PhRvA..90c2703A

Abstract

We measure the ratio gamma of the momentum transfer-to-vibrational quenching cross section for molecular thorium monoxide (ThO) [X(1Sigma+), v =1, J =0] in collisions with atomic helium between 800 mK and 2.4 K. We find gamma ˜104. We also observe indirect evidence for ThO-He van der Waals complex formation, which has been predicted by theory [Tscherbul, Sayfutyarova, Buchachenko, and Dalgarno, J. Chem. Phys. 134, 144301 (2011), 10.1063/1.3575399], and in conjunction, we determine the three-body recombination rate constant at 2.4 K, Gamma3=8±2×10-33 cm6 s-1.

 

Title:
Superfluid spin transport through antiferromagnetic insulators
Authors:
Takei, So; Halperin, Bertrand I.; Yacoby, Amir; Tserkovnyak, Yaroslav
Publication:
Physical Review B, Volume 90, Issue 9, id.094408 (PhRvB Homepage)
Publication Date:
09/2014
Origin:
APS
PACS Keywords:
Magnetic properties of monolayers and thin films, Magnetoelectronics, spintronics: devices exploiting spin polarized transport or integrated magnetic fields
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevB.90.094408
Bibliographic Code:
2014PhRvB..90i4408T

Abstract

A theoretical proposal for realizing and detecting spin supercurrent in an isotropic antiferromagnetic insulator is reported. Superfluid spin transport is achieved by inserting the antiferromagnet between two metallic reservoirs and establishing a spin accumulation in one reservoir such that a spin bias is applied across the magnet. We consider a class of bipartite antiferromagnets with Néel ground states, and temperatures well below the ordering temperature, where spin transport is mediated essentially by the condensate. Landau-Lifshitz and magnetocircuit theories are used to directly relate spin current in different parts of the heterostructure to the spin-mixing conductances characterizing the antiferromagnet|metal interfaces and the antiferromagnet bulk damping parameters, quantities all obtainable from experiments. We study the efficiency of spin angular-momentum transfer at an antiferromagnet|metal interface by developing a microscopic scattering theory for the interface and extracting the spin-mixing conductance for a simple model. Within the model, a quantitative comparison between the spin-mixing conductances obtained for the antiferromagnet|metal and ferromagnet|metal interfaces is made.

 

Title:
Diamagnetism and density-wave order in the pseudogap regime of YBa2Cu3O6+x
Authors:
Hayward, Lauren E.; Achkar, Andrew J.; Hawthorn, David G.; Melko, Roger G.; Sachdev, Subir
Publication:
Physical Review B, Volume 90, Issue 9, id.094515 (PhRvB Homepage)
Publication Date:
09/2014
Origin:
APS
PACS Keywords:
Classical spin models, Diamagnetism paramagnetism and superparamagnetism
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevB.90.094515
Bibliographic Code:
2014PhRvB..90i4515H

Abstract

Clear experimental evidence of charge density-wave correlations competing with superconducting order in YBCO have thrust their relationship with the pseudogap regime into the spotlight. To aid in characterizing the pseudogap regime, we propose a dimensionless ratio of the diamagnetic susceptibility to the correlation length of the charge density-wave correlations. Using Monte Carlo simulations, we compute this ratio on the classical model of Hayward et al. [Science 343, 1336 (2014), 10.1126/science.1246310], which describes angular fluctuations of a multicomponent order, capturing both superconducting and density-wave correlations. We compare our results with available data on YBa2Cu3O6+x, and propose experiments to clarify the value of this dimensionless ratio using existing samples and techniques.

 

Title:
Renormalization group analysis of a fermionic hot-spot model
Authors:
Whitsitt, Seth; Sachdev, Subir
Publication:
Physical Review B, Volume 90, Issue 10, id.104505 (PhRvB Homepage)
Publication Date:
09/2014
Origin:
APS
PACS Keywords:
Cuprate superconductors, Nonconventional mechanisms
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevB.90.104505
Bibliographic Code:
2014PhRvB..90j4505W

Abstract

We present a renormalization group (RG) analysis of a fermionic "hot-spot" model of interacting electrons on the square lattice. We truncate the Fermi-surface excitations to linearly dispersing quasiparticles in the vicinity of eight hot spots on the Fermi surface, with each hot spot separated from another by the wave vector (π,π). This is motivated by the importance of these Fermi-surface locations to the onset of antiferromagnetic order; however, we allow for all possible quartic interactions between the fermions, and also for all possible ordering instabilities. We compute the RG equations for our model, which depend on whether or not the hot spots are perfectly nested, and relate our results to earlier models. We also compute the RG flow of the relevant order parameters for both Hubbard and J,V interactions, and present our results for the dominant instabilities in the nested and non-nested cases. In particular, we find that non-nested hot spots with J,V interactions have competing singlet dx2-y2 superconducting and d-form factor incommensurate density wave instabilities. We also investigate the enhancement of incommensurate density waves near experimentally observed wave vectors, and find dominant d-form factor enhancement for a range of couplings.

 

Title:
Search for supersymmetry in events with four or more leptons in √s =8 TeV pp collisions with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.; ... Franklin, M.;... Barreiro Guimarães da Costa, J.;... Huth, J.;... Morii, M.;... and 2876 coauthors
Publication:
Physical Review D, Volume 90, Issue 5, id.052001 (PhRvD Homepage)
Publication Date:
09/2014
Origin:
APS
PACS Keywords:
Supersymmetric models, Limits on production of particles, Supersymmetric partners of known particles
Abstract Copyright:
2014: CERN
DOI:
10.1103/PhysRevD.90.052001
Bibliographic Code:
2014PhRvD..90e2001A

Abstract

Results from a search for supersymmetry in events with four or more leptons including electrons, muons and taus are presented. The analysis uses a data sample corresponding to 20.3 fb-1 of proton-proton collisions delivered by the Large Hadron Collider at √s =8 TeV and recorded by the ATLAS detector. Signal regions are designed to target supersymmetric scenarios that can be either enriched in or depleted of events involving the production of a Z boson. No significant deviations are observed in data from standard model predictions and results are used to set upper limits on the event yields from processes beyond the standard model. Exclusion limits at the 95% confidence level on the masses of relevant supersymmetric particles are obtained. In R-parity-violating simplified models with decays of the lightest supersymmetric particle to electrons and muons, limits of 1350 and 750 GeV are placed on gluino and chargino masses, respectively. In R-parity-conserving simplified models with heavy neutralinos decaying to a massless lightest supersymmetric particle, heavy neutralino masses up to 620 GeV are excluded. Limits are also placed on other supersymmetric scenarios.

 

Title:
Measurement of Collins asymmetries in inclusive production of charged pion pairs in e+e- annihilation at BABAR
Authors:
Lees, J. P.; Poireau, V.; Tisserand, V.;... Morii, M.;... and 331 coauthors; Babar Collaboration
Publication:
Physical Review D, Volume 90, Issue 5, id.052003 (PhRvD Homepage)
Publication Date:
09/2014
Origin:
APS
PACS Keywords:
Hadron production in e-e+ interactions, Fragmentation into hadrons, Polarization in interactions and scattering, Quarks
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevD.90.052003
Bibliographic Code:
2014PhRvD..90e2003L

Abstract

We present measurements of Collins asymmetries in the inclusive process e+e-→ππX, where π stands for charged pions, at a center-of-mass energy of 10.6 GeV. We use a data sample of 468 fb-1 collected by the BABAR experiment at the PEP-II B factory at SLAC, and consider pairs of charged pions produced in opposite hemispheres of hadronic events. We observe clear asymmetries in the distributions of the azimuthal angles in two distinct reference frames. We study the dependence of the asymmetry on several kinematic variables, finding that it increases with increasing pion momentum and momentum transverse to the analysis axis, and with increasing angle between the thrust and beam axis.

 

Title:
Measurement of the Higgs boson mass from the H→γγ and H→ZZ*→4ℓ channels in pp collisions at center-of-mass energies of 7 and 8 TeV with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.; ... Franklin, M.;... Barreiro Guimarães da Costa, J.;... Huth, J.;... Morii, M.;... and 2883 coauthors
Publication:
Physical Review D, Volume 90, Issue 5, id.052004 (PhRvD Homepage)
Publication Date:
09/2014
Origin:
APS
PACS Keywords:
Standard-model Higgs bosons
Abstract Copyright:
2014: CERN
DOI:
10.1103/PhysRevD.90.052004
Bibliographic Code:
2014PhRvD..90e2004A

Abstract

An improved measurement of the mass of the Higgs boson is derived from a combined fit to the reconstructed invariant mass spectra of the decay channels H→γγ and H→ZZ*→4ℓ. The analysis uses the pp collision data sample recorded by the ATLAS experiment at the CERN Large Hadron Collider at center-of-mass energies of 7 TeV and 8 TeV, corresponding to an integrated luminosity of 25 fb-1. The measured value of the Higgs boson mass is mH=125.36±0.37(stat)±0.18(syst) GeV. This result is based on improved energy-scale calibrations for photons, electrons, and muons as well as other analysis improvements, and supersedes the previous result from ATLAS. Upper limits on the total width of the Higgs boson are derived from fits to the invariant mass spectra of the H→γγ and H→ZZ*→4ℓ decay channels.

 

Title:
Search for high-mass dilepton resonances in pp collisions at √s =8 TeV with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.; ... Franklin, M.;... Barreiro Guimarães da Costa, J.;... Huth, J.;... Morii, M.;... and 2875 coauthors
Publication:
Physical Review D, Volume 90, Issue 5, id.052005 (PhRvD Homepage)
Publication Date:
09/2014
Origin:
APS
PACS Keywords:
Extensions of electroweak gauge sector, Inclusive production with identified leptons photons or other nonhadronic particles
Abstract Copyright:
2014: CERN
DOI:
10.1103/PhysRevD.90.052005
Bibliographic Code:
2014PhRvD..90e2005A

Abstract

The ATLAS detector at the Large Hadron Collider is used to search for high-mass resonances decaying to dielectron or dimuon final states. Results are presented from an analysis of proton-proton (pp) collisions at a center-of-mass energy of 8 TeV corresponding to an integrated luminosity of 20.3 fb-1 in the dimuon channel. A narrow resonance with Standard Model Z couplings to fermions is excluded at 95% confidence level for masses less than 2.79 TeV in the dielectron channel, 2.53 TeV in the dimuon channel, and 2.90 TeV in the two channels combined. Limits on other model interpretations are also presented, including a grand-unification model based on the E6 gauge group, Z* bosons, minimal Z ' models, a spin-2 graviton excitation from Randall-Sundrum models, quantum black holes, and a minimal walking technicolor model with a composite Higgs boson.

 

Title:
Flavor tagged time-dependent angular analysis of the Bs0→J/ψϕ decay and extraction of ΔΓs and the weak phase ϕs in ATLAS
Authors:
Aad, G.; Abajyan, T.; Abbott, B.; ... Franklin, M.;... Barreiro Guimarães da Costa, J.;... Huth, J.;... Morii, M.;... and 2892 coauthors
Publication:
Physical Review D, Volume 90, Issue 5, id.052007 (PhRvD Homepage)
Publication Date:
09/2014
Origin:
APS
PACS Keywords:
Bottom mesons
Abstract Copyright:
2014: CERN
DOI:
10.1103/PhysRevD.90.052007
Bibliographic Code:
2014PhRvD..90e2007A

Abstract

A measurement of the Bs0→J /ψϕ decay parameters, updated to include flavor tagging is reported using 4.9 fb-1 of integrated luminosity collected by the ATLAS detector from √s =7 TeV pp collisions recorded in 2011 at the LHC. The values measured for the physical parameters are ϕs=0.12±0.25(stat)±0.05(syst) radΔΓs=0.053±0.021(stat)±0.010(syst) ps-1Γs=0.677±0.007(stat)±0.004(syst) ps-1|A∥(0)|2=0.220±0.008(stat)±0.009(syst)|A0(0)|2=0.529±0.006(stat)±0.012(syst)δ⊥=3.89±0.47(stat)±0.11(syst) rad where the parameter ΔΓs is constrained to be positive. The S-wave contribution was measured and found to be compatible with zero. Results for ϕs and ΔΓs are also presented as 68% and 95% likelihood contours, which show agreement with the Standard Model expectations.

 

Title:
Search for pair-produced third-generation squarks decaying via charm quarks or in compressed supersymmetric scenarios in pp collisions at √s =8 TeV with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.; ... Franklin, M.;... Barreiro Guimarães da Costa, J.;... Huth, J.;... Morii, M.;... and 2884 coauthors
Publication:
Physical Review D, Volume 90, Issue 6, id.062009 (PhRvD Homepage)
Publication Date:
09/2014
Origin:
APS
PACS Keywords:
Dark matter, Elementary particle processes, Models beyond the standard model, Cosmology
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevD.90.062009
Bibliographic Code:
2014PhRvD..90f2009A

Abstract

Results of a search for supersymmetry via direct production of third-generation squarks are reported, using 20.3 fb-1 of proton-proton collision data at √s =8 TeV recorded by the ATLAS experiment at the LHC in 2012. Two different analysis strategies based on monojetlike and c-tagged event selections are carried out to optimize the sensitivity for direct top squark-pair production in the decay channel to a charm quark and the lightest neutralino (t ˜1→c +χ ˜10) across the top squark-neutralino mass parameter space. No excess above the Standard Model background expectation is observed. The results are interpreted in the context of direct pair production of top squarks and presented in terms of exclusion limits in the (mt ˜1, mχ ˜10) parameter space. A top squark of mass up to about 240 GeV is excluded at 95% confidence level for arbitrary neutralino masses, within the kinematic boundaries. Top squark masses up to 270 GeV are excluded for a neutralino mass of 200 GeV. In a scenario where the top squark and the lightest neutralino are nearly degenerate in mass, top squark masses up to 260 GeV are excluded. The results from the monojetlike analysis are also interpreted in terms of compressed scenarios for top squark-pair production in the decay channel t ˜1→b +ff'+χ ˜10 and sbottom pair production with b ˜1→b +χ ˜10, leading to a similar exclusion for nearly mass-degenerate third-generation squarks and the lightest neutralino. The results in this paper significantly extend previous results at colliders.

 

Title:
Gravity waves from extreme-mass-ratio plunges into Kerr black holes
Authors:
Hadar, Shahar; Porfyriadis, Achilleas P.; Strominger, Andrew
Publication:
Physical Review D, Volume 90, Issue 6, id.064045 (PhRvD Homepage)
Publication Date:
09/2014
Origin:
APS
PACS Keywords:
Gravitational waves: theory, Quantum gravity
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevD.90.064045
Bibliographic Code:
2014PhRvD..90f4045H

Abstract

Massive objects orbiting a near-extreme Kerr black hole quickly plunge into the horizon after passing the innermost stable circular orbit. The plunge trajectory is shown to be related by a conformal map to a circular orbit. Conformal symmetry of the near-horizon region is then used to compute the gravitational radiation produced during the plunge phase.

 

 

Title:
Nonglobal logarithms at three loops, four loops, five loops, and beyond
Authors:
Schwartz, Matthew D.; Zhu, Hua Xing
Publication:
Physical Review D, Volume 90, Issue 6, id.065004 (PhRvD Homepage)
Publication Date:
09/2014
Origin:
APS
PACS Keywords:
Quantum chromodynamics
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevD.90.065004
Bibliographic Code:
2014PhRvD..90f5004S

Abstract

We calculate the coefficients of the leading nonglobal logarithms for the hemisphere mass distribution analytically at 3, 4, and 5 loops at large Nc. We confirm that the integrand derived with the strong-energy-ordering approximation and fixed-order iteration of the Banfi-Marchesini-Syme (BMS) equation agree. Our calculation exploits a hidden PSL(2,R) symmetry associated with the jet directions, apparent in the BMS equation after a stereographic projection to the Poincaré disk. The required integrals have an iterated form, leading to functions of uniform transcendentality. This allows us to extract the coefficients, and some functional dependence on the jet directions, by computing the symbols and coproducts of appropriate expressions involving classical and Goncharov polylogarithms. Convergence of the series to a numerical solution of the BMS equation is also discussed.

 

Title:
Jet cleansing: Separating data from secondary collision induced radiation at high luminosity
Authors:
Krohn, David; Schwartz, Matthew D.; Low, Matthew; Wang, Lian-Tao
Publication:
Physical Review D, Volume 90, Issue 6, id.065020 (PhRvD Homepage)
Publication Date:
09/2014
Origin:
APS
PACS Keywords:
Jets in large-Q2 scattering, Fragmentation into hadrons
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevD.90.065020
Bibliographic Code:
2014PhRvD..90f5020K

Abstract

One of the greatest impediments to extracting useful information from high luminosity hadron-collider data is radiation from secondary collisions (i.e. pileup) which can overlap with that of the primary interaction. In this paper we introduce a simple jet-substructure technique termed cleansing which can consistently correct for large amounts of pileup in an observable independent way. Cleansing works at the subjet level, combining tracker and calorimeter-based data to reconstruct the pileup-free primary interaction. The technique can be used on its own, with various degrees of sophistication, or in concert with jet grooming. We apply cleansing to both kinematic and jet shape reconstruction, finding in all cases a marked improvement over previous methods both in the correlation of the cleansed data with uncontaminated results and in measures like S/√B . Cleansing should improve the sensitivity of new-physics searches at high luminosity and could also aid in the comparison of precision QCD calculations to collider data.

 

Title:
Low's Subleading Soft Theorem as a Symmetry of QED
Authors:
Lysov, Vyacheslav; Pasterski, Sabrina; Strominger, Andrew
Publication:
Physical Review Letters, Volume 113, Issue 11, id.111601 (PhRvL Homepage)
Publication Date:
09/2014
Origin:
APS
PACS Keywords:
S-matrix theory, analytic structure of amplitudes, Symmetry and conservation laws, Quantum electrodynamics
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevLett.113.111601
Bibliographic Code:
2014PhRvL.113k1601L

Abstract

It was shown by Low in the 1950s that the subleading terms of soft-photon S-matrix elements obey a universal linear relation. In this Letter, we give a new interpretation to this old relation, for the case of massless QED, as an infinitesimal symmetry of the S matrix. The symmetry is shown to be locally generated by a vector field on the conformal sphere at null infinity. Explicit expressions are constructed for the associated charges as integrals over null infinity and shown to generate the symmetry. These charges are local generalizations of electric and magnetic dipole charges.

 

Title:
Indistinguishable Photons from Separated Silicon-Vacancy Centers in Diamond
Authors:
Sipahigil, A.; Jahnke, K. D.; Rogers, L. J.; Teraji, T.; Isoya, J.; Zibrov, A. S.; Jelezko, F.; Lukin, M. D.
Publication:
Physical Review Letters, Volume 113, Issue 11, id.113602 (PhRvL Homepage)
Publication Date:
09/2014
Origin:
APS
PACS Keywords:
Photon statistics and coherence theory, Quantum communication, Optical implementations of quantum information processing and transfer, Color centers
Abstract Copyright:
2014: authors
DOI:
10.1103/PhysRevLett.113.113602
Bibliographic Code:
2014PhRvL.113k3602S

Abstract

We demonstrate that silicon-vacancy (SiV) centers in diamond can be used to efficiently generate coherent optical photons with excellent spectral properties. We show that these features are due to the inversion symmetry associated with SiV centers. The generation of indistinguishable single photons from separated emitters at 5 K is demonstrated in a Hong-Ou-Mandel interference experiment. Prospects for realizing efficient quantum network nodes using SiV centers are discussed.

 

Title:
Cross Modulation of Two Laser Beams at the Individual-Photon Level
Authors:
Beck, Kristin M.; Chen, Wenlan; Lin, Qian; Gullans, Michael; Lukin, Mikhail D.; Vuletić, Vladan
Publication:
Physical Review Letters, Volume 113, Issue 11, id.113603 (PhRvL Homepage)
Publication Date:
09/2014
Origin:
APS
PACS Keywords:
Cavity quantum electrodynamics, micromasers, Quantum description of interaction of light and matter, related experiments, Effects of atomic coherence on propagation absorption and amplification of light, electromagnetically induced transparency and absorption
Abstract Copyright:
(c) 2014: us
DOI:
10.1103/PhysRevLett.113.113603
Bibliographic Code:
2014PhRvL.113k3603B

Abstract

Deterministic photon-photon interactions are a long-standing goal in optical science. Using an atomic ensemble inside a cavity, we demonstrate the mutual cross modulation of two continuous light beams at the level of individual photons. The originally uncorrelated beams derived from independent lasers become anticorrelated, as evidenced by an equal-time cross-correlation function g(2)=0.89(1), showing that one photon in one beam extinguishes a photon in the other beam with a probability of 11(1)%. With further technical improvements, our approach should enable the nondestructive continuous detection of traveling optical photons.

 

Title:
The kitchen as a physics classroom
Authors:
Rowat, Amy C.; Sinha, Naveen N.; Sörensen, Pia M.; Campàs, Otger; Castells, Pere; Rosenberg, Daniel; Brenner, Michael P.; Weitz, David A.
Publication:
Physics Education, Volume 49, Issue 5, article id. 512 (2014).
Publication Date:
09/2014
Origin:
IOP
DOI:
10.1088/0031-9120/49/5/512
Bibliographic Code:
2014PhyEd..49..512R

Abstract

Cooking is a tangible, familiar, and delicious tool for teaching physics, which is easy to implement in a university setting. Through our courses at Harvard and UCLA, each year we are engaging hundreds of undergraduate students, primarily non-science majors, in science concepts and the scientific research process. We find that weekly lectures by chefs and professors, paired with edible lab experiments, generate enthusiasm and provide strong motivation for students to learn physics. By the end of the course, students are able to conduct independent scientific research and present their results in a final science fair. Given the considerable broad appeal of food and cooking, the topic could be adapted to other post-secondary as well as secondary-level courses.

 

Title:
Photoresponsive Monodisperse Cholesteric Liquid Crystalline Microshells for Tunable Omnidirectional Lasing Enabled by a Visible Light-Driven Chiral Molecular Switch
Authors:
Lujian Chen; Yannian Li; Jing Fan; Bisoyi, H.K.; Weitz, D.A.; Quan Li
Publication:
Advanced Optical Materials Sept. 2014, vol.2, no.9, pp. 845-8. ISSN: 2195-1071
Publication Date:
09/2014
Publisher:
Wiley-VCH
Database:
Inspec
Inspec Headings:
birefringence; cholesteric liquid crystals; fluorescence; isomerisation; laser beam effects; optical pumping; photonic band gap
DOI:
10.1002/adom.201400166

Abstract

A straightforward approach to fabricate photoresponsive CLC spherical microshells composed of the new visible light-driven chiral molecular switch ( R)-1 and the commercially available fluorescent dye and LC is reported.The resulting microshells are monodisperse and can generate LC lasers with phototunable output wavelength. The photoisomerization of the light-driven switch molecules enables us to shift the wavelength of the LC laser by optical pumping, and fully recover the laser wavelength by keeping the sample in the dark. To the best of our knowledge, this is the first report on photoresponsive liquid crystalline microshells. It is also the first demonstration of a phototunable LC laser in the form of spherical CLC microshells, which is based on an interesting “pumpingself-tuning” mechanism.


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