Faculty Publications: May, 2016

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Title:
Hypercalibration: A Pan-STARRS1-based Recalibration of the Sloan Digital Sky Survey Photometry
Authors:
Finkbeiner, Douglas P.; Schlafly, Edward F.; Schlegel, David J.; Padmanabhan, Nikhil; Jurić, Mario; Burgett, William S.; Chambers, Kenneth C.; Denneau, Larry; Draper, Peter W.; Flewelling, Heather; Hodapp, Klaus W.; Kaiser, Nick; Magnier, E. A.; Metcalfe, N.; Morgan, Jeffrey S.; Price, Paul A.; Stubbs, Christopher W.; Tonry, John L.
Publication:
The Astrophysical Journal, Volume 822, Issue 2, article id. 66, pp. (2016). (ApJ Homepage)
Publication Date:
05/2016
Origin:
IOP
Astronomy Keywords:
methods: data analysis, surveys, techniques: photometric
DOI:
10.3847/0004-637X/822/2/66
Bibliographic Code:
2016ApJ...822...66F

Abstract

We present a recalibration of the Sloan Digital Sky Survey (SDSS) photometry with new flat fields and zero points derived from Pan-STARRS1. Using point-spread function (PSF) photometry of 60 million stars with 16 < r < 20, we derive a model of amplifier gain and flat-field corrections with per-run rms residuals of 3 millimagnitudes (mmag) in griz bands and 15 mmag in u band. The new photometric zero points are adjusted to leave the median in the Galactic north unchanged for compatibility with previous SDSS work. We also identify transient non-photometric periods in SDSS (“contrails”) based on photometric deviations co-temporal in SDSS bands. The recalibrated stellar PSF photometry of SDSS and PS1 has an rms difference of {9, 7, 7, 8} mmag in griz, respectively, when averaged over 15‧ regions.

 

Title:
Hyperscaling violation at the Ising-nematic quantum critical point in two dimensional metals
Authors:
Eberlein, Andreas; Mandal, Ipsita; Sachdev, Subir
Publication:
eprint arXiv:1605.00657
Publication Date:
05/2016
Origin:
ARXIV
Keywords:
Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Quantum Gases, High Energy Physics - Theory
Comment:
28 pages
Bibliographic Code:
2016arXiv160500657E

Abstract

Understanding optical conductivity data in the optimally doped cuprates in the framework of quantum criticality requires a strongly-coupled quantum critical metal which violates hyperscaling. In the simplest scaling framework, hyperscaling violation can be characterized by a single non-zero exponent $\theta$, so that in a spatially isotropic state in $d$ spatial dimensions, the specific heat scales with temperature as $T^{(d-\theta)/z}$, and the optical conductivity scales with frequency as $\omega^{(d-\theta-2)/z}$ for $\omega \gg T$, where $z$ is the dynamic critical exponent. We study the Ising-nematic critical point, using the controlled dimensional regularization method proposed by Dalidovich and Lee (Phys. Rev. B {\bf 88}, 245106 (2013)). We find that hyperscaling is violated, with $\theta =1$ in $d=2$. We expect that similar results apply to Fermi surfaces coupled to gauge fields in $d=2$.

 

Title:
Site-resolved observations of antiferromagnetic correlations in the Hubbard model
Authors:
Parsons, Maxwell F.; Mazurenko, Anton; Chiu, Christie S.; Ji, Geoffrey; Greif, Daniel; Greiner, Markus
Publication:
eprint arXiv:1605.02704
Publication Date:
05/2016
Origin:
ARXIV
Keywords:
Condensed Matter - Quantum Gases
Comment:
6 + 11 pages, 4 + 6 figures, 1 table
Bibliographic Code:
2016arXiv160502704P

Abstract

Quantum many-body systems exhibiting magnetic correlations underlie a wide variety of phenomena. High-temperature superconductivity, for example, can arise from the correlated motion of holes on an antiferromagnetic (AFM) Mott insulator. Ultracold fermionic atoms in optical lattices provide realizations of strongly correlated many-body systems with a tunability that is unparalleled in conventional solid-state systems. Recent experiments exploring the Hubbard model with cold atoms are accessing temperatures where AFM correlations form, but have only observed these correlations via measurements that were averages over inhomogeneous systems. With the advance of quantum gas microscopy we can now take a snapshot of the real-space correlations in a single quantum many-body state at the atomic scale. Here we report site-resolved observations of AFM correlations in a Hubbard-regime optical lattice. The ability to locally measure spin correlations for a many-body state allows us to make unprecedented comparisons to theoretical predictions. We measure the in-situ distributions of the particle density and magnetic correlations, extract thermodynamic quantities from comparisons to theory, directly measure the correlation length, and study how lattice loading dynamics affect our ability to prepare samples in thermal equilibrium. The largest nearest-neighbor spin correlator that we observe is 53 % of the value predicted by quantum Monte Carlo calculations in the zero-temperature limit. Our results demonstrate that quantum gas microscopy is a powerful tool for studying fermionic quantum magnetism. Direct access to many-body physics at the single-particle level and the microscopic study of quantum dynamics will further our understanding of how new states of matter emerge from the interplay of motion and magnetism in quantum many-body systems.

 

Title:
Measurement of $\sin^2\theta^{\rm lept}_{\rm eff}$ using $e^+e^-$ pairs from $\gamma^*/Z$ bosons produced in $p\bar{p}$ collisions at a center-of-momentum energy of 1.96 TeV
Authors:
CDF Collaboration; Aaltonen, T.; Amerio, S.; Amidei, D.;... Franklin, M.;... and 392 coauthors
Publication:
eprint arXiv:1605.02719
Publication Date:
05/2016
Origin:
ARXIV
Keywords:
High Energy Physics - Experiment
Bibliographic Code:
2016arXiv160502719C

Abstract

At the Fermilab Tevatron proton-antiproton ($p\bar{p}$) collider, Drell-Yan lepton pairs are produced in the process $p \bar{p} \rightarrow e^+e^- + X$ through an intermediate $\gamma^*/Z$ boson. The forward-backward asymmetry in the polar-angle distribution of the $e^-$ as a function of the $e^+e^-$-pair mass is used to obtain $\sin^2\theta^{\rm lept}_{\rm eff}$, the effective leptonic determination of the electroweak-mixing parameter $\sin^2\theta_W$. The measurement sample, recorded by the Collider Detector at Fermilab (CDF), corresponds to 9.4~fb$^{-1}$ of integrated luminosity from $p\bar{p}$ collisions at a center-of-momentum energy of 1.96 TeV, and is the full CDF Run II data set. The value of $\sin^2\theta^{\rm lept}_{\rm eff}$ is found to be $0.23248 \pm 0.00053$. The combination with the previous CDF measurement based on $\mu^+\mu^-$ pairs yields $\sin^2\theta^{\rm lept}_{\rm eff} = 0.23221 \pm 0.00046$. This result, when interpreted within the specified context of the standard model assuming $\sin^2 \theta_W = 1 - M_W^2/M_Z^2$ and that the $W$- and $Z$-boson masses are on-shell, yields $\sin^2\theta_W = 0.22400 \pm 0.00045$, or equivalently a $W$-boson mass of $80.328 \pm 0.024 \;{\rm GeV}/c^2$.

 

Title:
Search for time-independent Lorentz violation using muon neutrino to muon antineutrino transitions in MINOS
Authors:
Adamson, P.; Anghel, I.; Aurisano, A.;... Feldman, G. J.;... and 116 coauthors
Publication:
eprint arXiv:1605.03146
Publication Date:
05/2016
Origin:
ARXIV
Keywords:
High Energy Physics - Experiment, High Energy Physics - Phenomenology
Comment:
7 pages, 4 figures
Bibliographic Code:
2016arXiv160503146A

Abstract

Data from the MINOS experiment has been used to search for mixing between muon neutrinos and muon antineutrinos using a time-independent Lorentz-violating formalism derived from the Standard-Model Extension (SME). MINOS is uniquely capable of searching for muon neutrino-antineutrino mixing given its long baseline and ability to distinguish between neutrinos and antineutrinos on an event-by-event basis. Neutrino and antineutrino interactions were observed in the MINOS Near and Far Detectors from an exposure of 10.56$\times10^{20}$ protons-on-target from the NuMI neutrino-optimized beam. No evidence was found for such transitions and new, highly stringent limits were placed on the SME coefficients governing them. We place the first limits on the SME parameters $(c_{L})^{TT}_{\mu\mu} $ and $(c_{L})^{TT}_{\tau\tau}$ at $-8.4\times10^{-23} < (c_{L})^{TT}_{\mu\mu} < 8.0\times10^{-23}$ and $-8.0\times10^{-23} < (c_{L})^{TT}_{\tau\tau} < 8.4\times10^{-23}$, and the world's best limits on the $\tilde{g}^{ZT}_{\mu\overline{\mu}}$ and $\tilde{g}^{ZT}_{\tau\overline{\tau}}$ parameters at $|\tilde{g}^{ZT}_{\mu\overline{\mu}}| < 3.3\times 10^{-23}$ and $|\tilde{g}^{ZT}_{\tau\overline{\tau}}| < 3.3\times 10^{-23}$, all limits quoted at $3\sigma$.

 

Title:
The novel metallic states of the cuprates: topological Fermi liquids and strange metals
Authors:
Sachdev, Subir; Chowdhury, Debanjan
Publication:
eprint arXiv:1605.03579
Publication Date:
05/2016
Origin:
ARXIV
Keywords:
Condensed Matter - Strongly Correlated Electrons, High Energy Physics - Theory
Comment:
34 pages, 11 figures
Bibliographic Code:
2016arXiv160503579S

Abstract

This article is based on a talk by S.S. at the Nambu Memorial Symposium at the University of Chicago. We review ideas on the nature of the metallic states of the hole-doped cuprate high temperature superconductors, with an emphasis on the connections between the Luttinger theorem for the size of the Fermi surface, topological quantum field theories (TQFTs), and critical theories involving changes in the size of the Fermi surface. We begin with the derivation of the Luttinger theorem for a Fermi liquid, using momentum balance during a process of flux-insertion in a lattice electronic model with toroidal boundary conditions. We then review the TQFT of the Z2 spin liquid, and demonstrate its compatibility with the toroidal momentum balance argument. This discussion leads naturally to a simple construction of `topological' Fermi liquid states: the fractionalized Fermi liquid (FL*) and the algebraic charge liquid (ACL). We present arguments for a description of the pseudogap metal of the cuprates using Z2-FL* or Z2-ACL states with Ising-nematic order. These pseudogap metal states are also described as Higgs phases of a SU(2) gauge theory. The Higgs field represents local antiferromagnetism, but the Higgs-condensed phase does not have long-range antiferromagnetic order: the magnitude of the Higgs field determines the pseudogap, the reconstruction of the Fermi surface, and the Ising-nematic order. Finally, we discuss the route to the large Fermi surface Fermi liquid via the critical point where the Higgs condensate and Ising nematic order vanish, and the application of Higgs criticality to the strange metal.

 

Title:
Toda Theory From Six Dimensions
Authors:
Cordova, Clay; Jafferis, Daniel L.
Publication:
eprint arXiv:1605.03997
Publication Date:
05/2016
Origin:
ARXIV
Keywords:
High Energy Physics - Theory
Comment:
40 pages, 2 figures
Bibliographic Code:
2016arXiv160503997C

Abstract

We describe a compactification of the six-dimensional (2,0) theory on a four-sphere which gives rise to a two-dimensional Toda theory at long distances. This construction realizes chiral Toda fields as edge modes trapped near the poles of the sphere. We relate our setup to compactifications of the (2,0) theory on the five and six-sphere. In this way, we explain a connection between half-BPS operators of the (2,0) theory and two-dimensional W-algebras, and derive an equality between their conformal anomalies. As we explain, all such relationships between the six-dimensional (2,0) theory and Toda field theory can be interpreted as statements about the edge modes of complex Chern-Simons on various three-manifolds with boundary.

 

Title:
Axion Experiments to Algebraic Geometry: Testing Quantum Gravity via the Weak Gravity Conjecture
Authors:
Heidenreich, Ben; Reece, Matthew; Rudelius, Tom
Publication:
eprint arXiv:1605.05311
Publication Date:
05/2016
Origin:
ARXIV
Keywords:
High Energy Physics - Theory, General Relativity and Quantum Cosmology
Comment:
Awarded fifth place in the 2016 Gravity Research Foundation Essay Contest; slightly revised for arxiv
Bibliographic Code:
2016arXiv160505311H

Abstract

Common features of known quantum gravity theories may hint at the general nature of quantum gravity. The absence of continuous global symmetries is one such feature. This inspired the Weak Gravity Conjecture, which bounds masses of charged particles. We propose the Lattice Weak Gravity Conjecture, which further requires the existence of an infinite tower of particles of all possible charges under both abelian and nonabelian gauge groups and directly implies a cutoff for quantum field theory. It holds in a wide variety of string theory examples and has testable consequences for the real world and for pure mathematics. We sketch some implications of these ideas for models of inflation, for the QCD axion (and LIGO), for conformal field theory, and for algebraic geometry.

 

Title:
Effective Field Theory for Rydberg Polaritons
Authors:
Gullans, M. J.; Wang, Y.; Thompson, J. D.; Liang, Q.-Y.; Vuletic, V.; Lukin, M. D.; Gorshkov, A. V.
Publication:
eprint arXiv:1605.05651
Publication Date:
05/2016
Origin:
ARXIV
Keywords:
Physics - Atomic Physics, Physics - Optics, Quantum Physics
Comment:
9 pages, 5 figures
Bibliographic Code:
2016arXiv160505651G

Abstract

We study non-perturbative effects in N-body scattering of Rydberg polaritons using effective field theory (EFT). We develop an EFT in one dimension and show how a suitably long medium can be used to prepare shallow N-body bound states. We then derive the effective N-body interaction potential for Rydberg polaritons and the associated N-body contact force that arises in the EFT. We use the contact force to find the leading order corrections to the binding energy of the N-body bound states and determine the photon number at which the EFT description breaks down. We find good agreement throughout between the predictions of EFT and numerical simulations of the exact two and three photon wavefunction transmission.

 

Title:
No "Evidence for a new phase of dense hydrogen above 325 GPa"
Authors:
Dias, Ranga P.; Noked, Ori; Silvera, Isaac F.
Publication:
eprint arXiv:1605.05703
Publication Date:
05/2016
Origin:
ARXIV
Keywords:
Condensed Matter - Other Condensed Matter, Condensed Matter - Materials Science
Comment:
Comment on a published paper
Bibliographic Code:
2016arXiv160505703D

Abstract

In recent years there has been intense experimental activity to observe solid metallic hydrogen. Wigner and Huntington predicted that under extreme pressures insulating molecular hydrogen would dissociate and transition to atomic metallic hydrogen. Recently Dalladay-Simpson, Howie, and Gregoryanz reported a phase transition to an insulating phase in molecular hydrogen at a pressure of 325 GPa and 300 K. Because of its scientific importance we have scrutinized their experimental evidence to determine if their claim is justified. Based on our analysis, we conclude that they have misinterpreted their data: there is no evidence for a phase transition at 325 GPa.

 

Title:
A search for flavor-changing non-standard neutrino interactions using $\nu_{e}$ appearance in MINOS
Authors:
Adamson, P.; Anghel, I.; Aurisano, A.;... Feldman, G. J.; and 116 coauthors
Publication:
eprint arXiv:1605.06169
Publication Date:
05/2016
Origin:
ARXIV
Keywords:
High Energy Physics - Experiment
Comment:
5 pages, 3 figures
Bibliographic Code:
2016arXiv160506169A

Abstract

We report new constraints on flavor-changing non-standard neutrino interactions from the MINOS long-baseline experiment using $\nu_{e}$ appearance candidate events from a predominantly $\nu_{\mu}$ beam. We used a statistical selection algorithm to separate $\nu_{e}$ candidates from background events, enabling an analysis of the combined MINOS neutrino and antineutrino data. We observe no deviations from standard neutrino mixing, and thus place constraints on the non-standard interaction matter effect, $\varepsilon_{e\tau}$, and phase, $(\delta_{CP}+\delta_{e\tau})$, using a thirty-bin likelihood fit.

 

Title:
Evolutionary dynamics on any population structure
Authors:
Allen, Benjamin; Lippner, Gabor; Chen, Yu-Ting; Fotouhi, Babak; Nowak, Martin A.; Yau, Shing-Tung
Publication:
eprint arXiv:1605.06530
Publication Date:
05/2016
Origin:
ARXIV
Keywords:
Quantitative Biology - Populations and Evolution, Mathematics - Probability, 92D15, 05C81
Comment:
38 pages, 6 figures
Bibliographic Code:
2016arXiv160506530A

Abstract

The structure of a biological population affects the outcome of evolutionary processes. Understanding evolution in structured populations is difficult. Precise results have been absent for a long time, but have recently emerged for the special case where each individual has the same number of neighbors. But the general problem of determining natural selection, when the number of neighbors varies, has remained open. For arbitrary selection intensity, the problem is in a computational complexity class which suggests there is no efficient algorithm. But whether there exists a simple solution for weak selection was unanswered. Here we provide, surprisingly, a general formula for weak selection that holds for any graph. Thus, we can predict evolutionary dynamics on any static population structure. Our method uses coalescent theory and relies on calculating the meeting times of random walks. We use our result to design social networks that maximally favor evolution of cooperation. We find that cooperation flourishes most in societies that are based on strong pairwise ties.

 

Title:
Evaluating the paleomagnetic potential of single zircon crystals using the Bishop Tuff
Authors:
Fu, Roger R.; Weiss, Benjamin P.; Lima, Eduardo A.; Kehayias, Pauli; Araujo, Jefferson F. D. F.; Glenn, David R.; Gelb, Jeff; Einsle, Joshua F.; Bauer, Ann M.; Harrison, Richard J.; Ali, Guleed A. H.; Walsworth, Ronald L.
Publication:
eprint arXiv:1605.08479
Publication Date:
05/2016
Origin:
ARXIV
Keywords:
Physics - Geophysics
Comment:
In review in Earth and Planetary Science Letters
Bibliographic Code:
2016arXiv160508479F

Abstract

Zircon crystals offer a unique combination of suitability for high-precision radiometric dating and high resistance to alteration. Paleomagnetic experiments on ancient zircons may potentially constrain the earliest geodynamo, which holds broad implications for the early Earth interior and atmosphere. However, the ability of zircons to record accurately the geomagnetic field has not been fully demonstrated. Here we conduct thermal and room temperature alternating field (AF) paleointensity experiments on 767.1 thousand year old (ka) zircons from the Bishop Tuff, California. The rapid emplacement of these zircons in a well-characterized magnetic field provides a high-fidelity test of the zircons intrinsic paleomagnetic recording accuracy. Successful dual heating experiments on nine zircons measured using a superconducting quantum interference device (SQUID) microscope yield a mean paleointensity of 46.2 +/- 18.8 microtesla (1sigma), which agrees closely with high-precision results from Bishop Tuff whole rock (43.0 +/- 3.2 microtesla). High-resolution quantum diamond magnetic mapping, electron microscopy, and X-ray tomography indicate that the bulk of the remanent magnetization in Bishop Tuff zircons is carried by Fe oxides associated with apatite inclusions, which would be susceptible to destruction via metamorphism and aqueous alteration in older zircons. As such, while zircons can reliably record the geomagnetic field, robust zircon-derived paleomagnetic results require careful characterization of the ferromagnetic carrier and demonstration of their occurrence in primary inclusions. We further conclude that a combination of quantum diamond magnetometry and high-resolution imaging can provide detailed, direct characterization of the ferromagnetic mineralogy of geological samples.

 

Title:
The Future of Primordial Features with Large-Scale Structure Surveys
Authors:
Chen, Xingang; Dvorkin, Cora; Huang, Zhiqi; Namjoo, Mohammad Hossein; Verde, Licia
Publication:
eprint arXiv:1605.09365
Publication Date:
05/2016
Origin:
ARXIV
Keywords:
Astrophysics - Cosmology and Nongalactic Astrophysics
Comment:
31 pages
Bibliographic Code:
2016arXiv160509365C

Abstract

Primordial features are one of the most important extensions of the Standard Model of cosmology, providing a wealth of information on the primordial universe, ranging from discrimination between inflation and alternative scenarios, new particle detection, to fine structures in the inflationary potential. We study the prospects of future large-scale structure (LSS) surveys on the detection and constraints of these features. We classify primordial feature models into several classes, and for each class we present a simple template of power spectrum that encodes the essential physics. We study how well the most ambitious LSS surveys proposed to date, including both spectroscopic and photometric surveys, will be able to improve the constraints with respect to the current Planck data. We find that these LSS surveys will significantly improve the experimental sensitivity on features signals that are oscillatory in scales, due to the 3D information. For a broad range of models, these surveys will be able to reduce the errors of the amplitudes of the features by a factor of 5 or more, including several interesting candidates identified in the recent Planck data. Therefore, LSS surveys offer an impressive opportunity for primordial feature discovery in the next decade or two. We also compare the advantages of both types of surveys.

 

Title:
Eliminating light shifts in single-atom optical traps
Authors:
Hutzler, Nicholas R.; Liu, Lee R.; Yu, Yichao; Ni, Kang-Kuen
Publication:
eprint arXiv:1605.09422
Publication Date:
05/2016
Origin:
ARXIV
Keywords:
Physics - Atomic Physics, Quantum Physics
Bibliographic Code:
2016arXiv160509422H

Abstract

Microscopically controlled neutral atoms in optical tweezers and lattices have led to exciting advances in the study of quantum information and quantum many-body systems. The light shifts of atomic levels from the trapping potential in these systems can result in detrimental effects such as fluctuating dipole force heating, inhomogeneous detunings, and inhibition of laser cooling, which limits the atomic species that can be manipulated. In particular, these light shifts can be large enough to prevent loading into optical tweezers directly from a magneto-optical trap. We present a general solution to these limitations by loading, cooling, and imaging single atoms with temporally alternating beams. Because this technique does not depend on any specific spectral properties, we expect it to enable the optical tweezer method to control nearly any atomic or molecular species that can be laser cooled and optically trapped. Furthermore, we present an analysis of the role of heating and required cooling for single atom tweezer loading.

 

Title:
Probing lepton flavour violation via neutrinoless \varvec{τ longrightarrow 3μ } decays with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2862 coauthors
Publication:
The European Physical Journal C, Volume 76, Issue 5, article id. #232, 25 pp. (EPJC Homepage)
Publication Date:
05/2016
Origin:
SPRINGER
Abstract Copyright:
(c) 2016: CERN for the benefit of the ATLAS collaboration
DOI:
10.1140/epjc/s10052-016-4041-9
Bibliographic Code:
2016EPJC...76..232A

Abstract

This article presents the sensitivity of the ATLAS experiment to the lepton-flavour-violating decays of τ → 3μ . A method utilising the production of τ leptons via W→ τ ν decays is used. This method is applied to the sample of 20.3 fb^{-1} of pp collision data at a centre-of-mass energy of 8 TeV collected by the ATLAS experiment at the LHC in 2012. No event is observed passing the selection criteria, and the observed (expected) upper limit on the τ lepton branching fraction into three muons, Br(τ → 3μ ), is 3.76× 10^{-7} (3.94× 10^{-7}) at 90 % confidence level.

 

Title:
Probing lepton flavour violation via neutrinoless varvec{τ longrightarrow 3μ } decays with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2854 coauthors
Publication:
The European Physical Journal C, Volume 76, Issue 5, article id. #232, 25 pp. (EPJC Homepage)
Publication Date:
05/2016
Origin:
SPRINGER
Abstract Copyright:
(c) 2016: CERN for the benefit of the ATLAS collaboration
DOI:
10.1140/epjc/s10052-016-4041-9
Bibliographic Code:
2016EPJC...76..232A

Abstract

This article presents the sensitivity of the ATLAS experiment to the lepton-flavour-violating decays of τ → 3μ . A method utilising the production of τ leptons via W→ τ ν decays is used. This method is applied to the sample of 20.3 fb^{-1} of pp collision data at a centre-of-mass energy of 8 TeV collected by the ATLAS experiment at the LHC in 2012. No event is observed passing the selection criteria, and the observed (expected) upper limit on the τ lepton branching fraction into three muons, Br(τ → 3μ ), is 3.76× 10^{-7} (3.94× 10^{-7}) at 90 % confidence level.

 

Title:
Probi
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2853 coauthors
Publication:
The European Physical Journal C, Volume 76, Issue 5, article id. #259, 26 pp. (EPJC Homepage)
Publication Date:
05/2016
Origin:
SPRINGER
Abstract Copyright:
(c) 2016: CERN for the benefit of the ATLAS collaboration
DOI:
10.1140/epjc/s10052-016-4095-8
Bibliographic Code:
2016EPJC...76..259A

Abstract

A search for strongly produced supersymmetric particles is conducted using signatures involving multiple energetic jets and either two isolated leptons ( e or μ ) with the same electric charge or at least three isolated leptons. The search also utilises b-tagged jets, missing transverse momentum and other observables to extend its sensitivity. The analysis uses a data sample of proton-proton collisions at √{s}= 13 TeV recorded with the ATLAS detector at the Large Hadron Collider in 2015 corresponding to a total integrated luminosity of 3.2 fb^{-1}. No significant excess over the Standard Model expectation is observed. The results are interpreted in several simplified supersymmetric models and extend the exclusion limits from previous searches. In the context of exclusive production and simplified decay modes, gluino masses are excluded at 95 % confidence level up to 1.1-1.3 TeV for light neutralinos (depending on the decay channel), and bottom squark masses are also excluded up to 540 GeV. In the former scenarios, neutralino masses are also excluded up to 550-850 GeV for gluino masses around 1 TeV.

 

Title:
Negative holomorphic curvature and positive canonical bundle
Authors:
Wu, Damin; Yau, Shing-Tung
Publication:
Inventiones mathematicae, vol. 204, issue 2, pp. 595-604
Publication Date:
05/2016
Origin:
CROSSREF
DOI:
10.1007/s00222-015-0621-9
Bibliographic Code:
2016InMat.204..595W

Abstract

In this note we show that if a projective manifold admits a K\"ahler metric with negative holomorphic sectional curvature then the canonical bundle of the manifold is ample. This confirms a conjecture of the second author.

 

Title:
Patterning Superatom Dopants on Transition Metal Dichalcogenides
Authors:
Yu, Jaeeun; Lee, Chul-Ho; Bouilly, Delphine; Han, Minyong; Kim, Philip; Steigerwald, Michael L.; Roy, Xavier; Nuckolls, Colin
Publication:
Nano Letters, vol. 16, issue 5, pp. 3385-3389
Publication Date:
05/2016
Origin:
CROSSREF
DOI:
10.1021/acs.nanolett.6b01152
Bibliographic Code:
2016NanoL..16.3385Y

Abstract

Not Available

 

Title:
Programming curvature using origami tessellations
Authors:
Dudte, Levi H.; Vouga, Etienne; Tachi, Tomohiro; Mahadevan, L.
Publication:
Nature Materials, Volume 15, Issue 5, pp. 583-588 (2016).
Publication Date:
05/2016
Origin:
NATURE
Abstract Copyright:
(c) 2016: Nature Publishing Group
DOI:
10.1038/nmat4540
Bibliographic Code:
2016NatMa..15..583D

Abstract

Origami describes rules for creating folded structures from patterns on a flat sheet, but does not prescribe how patterns can be designed to fit target shapes. Here, starting from the simplest periodic origami pattern that yields one-degree-of-freedom collapsible structures--we show that scale-independent elementary geometric constructions and constrained optimization algorithms can be used to determine spatially modulated patterns that yield approximations to given surfaces of constant or varying curvature. Paper models confirm the feasibility of our calculations. We also assess the difficulty of realizing these geometric structures by quantifying the energetic barrier that separates the metastable flat and folded states. Moreover, we characterize the trade-off between the accuracy to which the pattern conforms to the target surface, and the effort associated with creating finer folds. Our approach enables the tailoring of origami patterns to drape complex surfaces independent of absolute scale, as well as the quantification of the energetic and material cost of doing so.

 

Title:
Oxygen-activated growth and bandgap tunability of large single-crystal bilayer graphene
Authors:
Hao, Yufeng; Wang, Lei; Liu, Yuanyue; Chen, Hua; Wang, Xiaohan; Tan, Cheng; Nie, Shu; Suk, Ji Won; Jiang, Tengfei; Liang, Tengfei; Xiao, Junfeng; Ye, Wenjing; Dean, Cory R.; Yakobson, Boris I.; McCarty, Kevin F.; Kim, Philip; Hone, James; Colombo, Luigi; Ruoff, Rodney S.
Publication:
Nature Nanotechnology, Volume 11, Issue 5, pp. 426-431 (2016).
Publication Date:
05/2016
Origin:
NATURE
Abstract Copyright:
(c) 2016: Nature Publishing Group
DOI:
10.1038/nnano.2015.322
Bibliographic Code:
2016NatNa..11..426H

Abstract

Bernal (AB)-stacked bilayer graphene (BLG) is a semiconductor whose bandgap can be tuned by a transverse electric field, making it a unique material for a number of electronic and photonic devices. A scalable approach to synthesize high-quality BLG is therefore critical, which requires minimal crystalline defects in both graphene layers and maximal area of Bernal stacking, which is necessary for bandgap tunability. Here we demonstrate that in an oxygen-activated chemical vapour deposition (CVD) process, half-millimetre size, Bernal-stacked BLG single crystals can be synthesized on Cu. Besides the traditional ‘surface-limited’ growth mechanism for SLG (1st layer), we discovered new microscopic steps governing the growth of the 2nd graphene layer below the 1st layer as the diffusion of carbon atoms through the Cu bulk after complete dehydrogenation of hydrocarbon molecules on the Cu surface, which does not occur in the absence of oxygen. Moreover, we found that the efficient diffusion of the carbon atoms present at the interface between Cu and the 1st graphene layer further facilitates growth of large domains of the 2nd layer. The CVD BLG has superior electrical quality, with a device on/off ratio greater than 104, and a tunable bandgap up to ∼100 meV at a displacement field of 0.9 V nm‑1.

 

Title:
A structural approach to relaxation in glassy liquids
Authors:
Schoenholz, S. S.; Cubuk, E. D.; Sussman, D. M.; Kaxiras, E.; Liu, A. J.
Publication:
Nature Physics, Volume 12, Issue 5, pp. 469-471 (2016).
Publication Date:
05/2016
Origin:
NATURE
Abstract Copyright:
(c) 2016: Nature Publishing Group
DOI:
10.1038/nphys3644
Bibliographic Code:
2016NatPh..12..469S

Abstract

In contrast with crystallization, there is no noticeable structural change at the glass transition. Characteristic features of glassy dynamics that appear below an onset temperature, T0 (refs ,,), are qualitatively captured by mean field theory, which assumes uniform local structure. Studies of more realistic systems have found only weak correlations between structure and dynamics. This raises the question: is structure important to glassy dynamics in three dimensions? We answer this question affirmatively, using machine learning to identify a new field, `softness' which characterizes local structure and is strongly correlated with dynamics. We find that the onset of glassy dynamics at T0 corresponds to the onset of correlations between softness (that is, structure) and dynamics. Moreover, we construct a simple model of relaxation that agrees well with our simulation results, showing that a theory of the evolution of softness in time would constitute a theory of glassy dynamics.

 

Title:
Erratum: Topological excitations and the dynamic structure factor of spin liquids on the kagome lattice
Authors:
Punk, Matthias; Chowdhury, Debanjan; Sachdev, Subir
Publication:
Nature Physics, Volume 12, Issue 5, pp. 520 (2016).
Publication Date:
05/2016
Origin:
NATURE
Abstract Copyright:
(c) 2016: Nature Publishing Group, a division of Macmillan Publishers Limited. All Rights Reserved.
DOI:
10.1038/nphys3762
Bibliographic Code:
2016NatPh..12..520P

Abstract

Not Available

 

Title:
Efficient photon triplet generation in integrated nanophotonic waveguides
Authors:
Moebius, Michael G.; Herrera, Felipe; Griesse-Nascimento, Sarah; Reshef, Orad; Evans, Christopher C.; Guerreschi, Gian Giacomo; Aspuru-Guzik, Alán; Mazur, Eric
Publication:
Optics Express, vol. 24, issue 9, p. 9932
Publication Date:
05/2016
Origin:
CROSSREF
DOI:
10.1364/OE.24.009932
Bibliographic Code:
2016OExpr..24.9932M

Abstract

Not Available

 

Title:
Measurement of the dependence of transverse energy production at large pseudorapidity on the hard-scattering kinematics of proton-proton collisions at √{ s} = 2.76 TeV with ATLAS
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2859 coauthors
Publication:
Physics Letters B, Volume 756, p. 10-28.
Publication Date:
05/2016
Origin:
ELSEVIER
Abstract Copyright:
(c) 2016 CERN for the benefit of the ATLAS Collaboration
DOI:
10.1016/j.physletb.2016.02.056
Bibliographic Code:
2016PhLB..756...10A

Abstract

The relationship between jet production in the central region and the underlying-event activity in a pseudorapidity-separated region is studied in 4.0 pb-1 of √{ s} = 2.76 TeVpp collision data recorded with the ATLAS detector at the LHC. The underlying event is characterised through measurements of the average value of the sum of the transverse energy at large pseudorapidity downstream of one of the protons, which are reported here as a function of hard-scattering kinematic variables. The hard scattering is characterised by the average transverse momentum and pseudorapidity of the two highest transverse momentum jets in the event. The dijet kinematics are used to estimate, on an event-by-event basis, the scaled longitudinal momenta of the hard-scattered partons in the target and projectile beam-protons moving toward and away from the region measuring transverse energy, respectively. Transverse energy production at large pseudorapidity is observed to decrease with a linear dependence on the longitudinal momentum fraction in the target proton and to depend only weakly on that in the projectile proton. The results are compared to the predictions of various Monte Carlo event generators, which qualitatively reproduce the trends observed in data but generally underpredict the overall level of transverse energy at forward pseudorapidity.

 

Title:
Measurement of the charge asymmetry in highly boosted top-quark pair production in √{ s} = 8 TeVpp collision data collected by the ATLAS experiment
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2848 coauthors
Publication:
Physics Letters B, Volume 756, p. 52-71.
Publication Date:
05/2016
Origin:
ELSEVIER
Abstract Copyright:
(c) 2016 CERN for the benefit of the ATLAS Collaboration
DOI:
10.1016/j.physletb.2016.02.055
Bibliographic Code:
2016PhLB..756...52A

Abstract

In the pp → t t bar process the angular distributions of top and anti-top quarks are expected to present a subtle difference, which could be enhanced by processes not included in the Standard Model. This Letter presents a measurement of the charge asymmetry in events where the top-quark pair is produced with a large invariant mass. The analysis is performed on 20.3 fb-1 of pp collision data at √{ s} = 8TeV collected by the ATLAS experiment at the LHC, using reconstruction techniques specifically designed for the decay topology of highly boosted top quarks. The charge asymmetry in a fiducial region with large invariant mass of the top-quark pair (mttbar > 0.75 TeV) and an absolute rapidity difference of the top and anti-top quark candidates within - 2 < |yt | - |ytbar | < 2 is measured to be 4.2 ± 3.2%, in agreement with the Standard Model prediction at next-to-leading order. A differential measurement in three t t bar mass bins is also presented.

 

Title:
Evidence for single top-quark production in the s-channel in proton-proton collisions at √{ s} = 8 TeV with the ATLAS detector using the Matrix Element Method
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2866 coauthors
Publication:
Physics Letters B, Volume 756, p. 228-246.
Publication Date:
05/2016
Origin:
ELSEVIER
Abstract Copyright:
(c) 2016 CERN for the benefit of the ATLAS Collaboration
DOI:
10.1016/j.physletb.2016.03.017
Bibliographic Code:
2016PhLB..756..228A

Abstract

This Letter presents evidence for single top-quark production in the s-channel using proton-proton collisions at a centre-of-mass energy of 8 TeV with the ATLAS detector at the CERN Large Hadron Collider. The analysis is performed on events containing one isolated electron or muon, large missing transverse momentum and exactly two b-tagged jets in the final state. The analysed data set corresponds to an integrated luminosity of 20.3 fb-1. The signal is extracted using a maximum-likelihood fit of a discriminant which is based on the matrix element method and optimized in order to separate single-top-quark s-channel events from the main background contributions, which are top-quark pair production and W boson production in association with heavy-flavour jets. The measurement leads to an observed signal significance of 3.2 standard deviations and a measured cross-section of σs = 4.8 ± 0.8(stat.)-1.3+1.6 (syst.) pb, which is consistent with the Standard Model expectation. The expected significance for the analysis is 3.9 standard deviations.

 

Title:
Friedel oscillations as a probe of fermionic quasiparticles
Authors:
Dalla Torre, Emanuele G.; Benjamin, David; He, Yang; Dentelski, David; Demler, Eugene
Publication:
Physical Review B, Volume 93, Issue 20, id.205117 (PhRvB Homepage)
Publication Date:
05/2016
Origin:
APS
Abstract Copyright:
2016: American Physical Society
DOI:
10.1103/PhysRevB.93.205117
Bibliographic Code:
2016PhRvB..93t5117D

Abstract

When immersed in a sea of electrons, local impurities give rise to density modulations known as Friedel oscillations. In spite of the generality of this phenomenon, the exact shape of these modulations is usually computed only for noninteracting electrons with a quadratic dispersion relation. In actual materials, Friedel oscillations are a viable way to access the properties of electronic quasiparticles, including their dispersion relation, lifetime, and pairing. In this work we analyze the signatures of Friedel oscillations in STM and x-ray scattering experiments, focusing on the concrete example of cuprate superconductors. We identify signatures of Friedel oscillations seeded by impurities and vortices, and explain experimental observations that have been previously attributed to a competing charge order.

 

Title:
Photon propagator in light-shell gauge
Authors:
Georgi, Howard; Kestin, Greg; Sajjad, Aqil
Publication:
Physical Review D, Volume 93, Issue 9, id.096002 (PhRvD Homepage)
Publication Date:
05/2016
Origin:
APS
Abstract Copyright:
2016: American Physical Society
DOI:
10.1103/PhysRevD.93.096002
Bibliographic Code:
2016PhRvD..93i6002G

Abstract

We derive the photon propagator in light-shell gauge (LSG) vμAμ=0 , where vμ=(1,r ^ ) μ . This gauge is an important ingredient of the light-shell effective theory—an effective theory for describing high energy jet processes on a 2-dimensional spherical shell expanding at the speed of light around the point of the initial collision producing the jets. Since LSG is a noncovariant gauge, we cannot calculate the LSG propagator by using the standard procedure for covariant gauges. We therefore employ a new technique for computing the propagator, which we hope may be of relevance in other gauges as well.

 


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