Faculty Publications: December, 2013

Query Results from the Smithsonian/NASA Astrophysics Data System (ADS)

 go to Most Recent Faculty Publications

Title:
Single-Photon Nonlinear Optics with Graphene Plasmons
Authors:
Gullans, M.; Chang, D. E.; Koppens, F. H. L.; García de Abajo, F. J.; Lukin, M. D.
Publication:
Physical Review L, Vol. 111, No. 24, id.247401 (PhRvL Homepage)
Publication Date:
12/2013
Origin:
APS
DOI:
10.1103/PhysRevLett.111.247401
Bibliographic Code:
2013PhRvL.111x7401G

Abstract

We show theoretically that it is possible to realize significant nonlinear optical interactions at the few photon level in graphene nanostructures. Our approach takes advantage of the electric field enhancement associated with the strong confinement of graphene plasmons and the large intrinsic nonlinearity of graphene. Such a system could provide a powerful platform for quantum nonlinear optical control of light. As an example, we consider an integrated optical device that exploits this large nonlinearity to realize a single photon switch.

 

Title:
Escape of DNA from a Weakly Biased Thin Nanopore: Experimental Evidence for a Universal Diffusive Behavior
Authors:
Hoogerheide, David P.; Albertorio, Fernando; Golovchenko, Jene A.
Publication:
Physical Review L, Vol. 111, No. 24, id.248301 (PhRvL Homepage)
Publication Date:
12/2013
Origin:
APS
DOI:
10.1103/PhysRevLett.111.248301
Bibliographic Code:
2013PhRvL.111x8301H

Abstract

Not Available

 

Title:   Perseus I: A Distant Satellite Dwarf Galaxy of Andromeda
Authors:   Martin, Nicolas F.; Schlafly, Edward F.; Slater, Colin T.; Bernard, Edouard J.; Rix, Hans-Walter; Bell, Eric F.; Ferguson, Annette M. N.; Finkbeiner, Douglas P.; Laevens, Benjamin P. M.; Burgett, William S.; Chambers, Kenneth C.; Draper, Peter W.; Hodapp, Klaus W.; Kaiser, Nicholas; Kudritzki, Rolf-Peter; Magnier, Eugene A.; Metcalfe, Nigel; Morgan, Jeffrey S.; Price, Paul A.; Tonry, John L.; Wainscoat, Richard J.; Waters, Christopher
Publication:   The Astrophysical Journal Letters, Volume 779, Issue 1, article id. L10, 5 pp. (2013). (ApJL Homepage)
Publication Date:   12/2013
Origin:   IOP
Astronomy Keywords:   galaxies: individual: Perseus I Andromeda XXXIII, Local Group
DOI:   10.1088/2041-8205/779/1/L10
Bibliographic Code:   2013ApJ...779L..10M

Abstract

We present the discovery of a new dwarf galaxy, Perseus I/Andromeda XXXIII, found in the vicinity of Andromeda (M31) in stacked imaging data from the Pan-STARRS1 3π survey. Located 27.°9 away from M31, Perseus I has a heliocentric distance of 785 ± 65 kpc, compatible with it being a satellite of M31 at 374^{+14}_{-10}\,kpc from its host. The properties of Perseus I are typical for a reasonably bright dwarf galaxy (MV = –10.3 ± 0.7), with an exponential half-light radius of rh = 1.7 ± 0.4 arcmin or r_h = 400^{+105}_{-85}\,pc at this distance, and a moderate ellipticity (\epsilon = 0.43^{+0.15}_{-0.17}). The late discovery of Perseus I is due to its fairly low surface brightness (\mu _0=25.7^{+1.0}_{-0.9} mag arcsec–2), and to the previous lack of deep, high quality photometric data in this region. If confirmed to be a companion of M31, the location of Perseus I, far east from its host, could place interesting constraints on the bulk motion of the satellite system of M31.

 

Title:
Dissipative Dynamics of a Driven Quantum Spin Coupled to a Bath of Ultracold Fermions
Authors:
Knap, Michael; Abanin, Dmitry A.; Demler, Eugene
Publication:
Physical Review L, Vol. 111, No. 26, id. 265302 (PhRvL Homepage)
Publication Date:
12/2013
Origin:
APS
DOI:
10.1103/PhysRevLett.111.265302
Bibliographic Code:
2013PhRvL.111z5302K

Abstract

We explore the dynamics and the steady state of a driven quantum spin coupled to a bath of fermions, which can be realized with a strongly imbalanced mixture of ultracold atoms using currently available experimental tools. Radio-frequency driving can be used to induce tunneling between the spin states. The Rabi oscillations are modified due to the coupling of the quantum spin to the environment, which causes frequency renormalization and damping. The spin-bath coupling can be widely tuned by adjusting the scattering length through a Feshbach resonance. When the scattering potential creates a bound state, by tuning the driving frequency it is possible to populate either the ground state, in which the bound state is filled, or a metastable state in which the bound state is empty. In the latter case, we predict an emergent inversion of the steady-state magnetization. Our work shows that different regimes of dissipative dynamics can be explored with a quantum spin coupled to a bath of ultracold fermions.

 

Title:
Electron-Hole Asymmetric Integer and Fractional Quantum Hall Effect in Bilayer Graphene
Authors:
Kou, Angela; Feldman, Benjamin E.; Levin, Andrei J.; Halperin, Bertrand I.; Watanabe, Kenji; Taniguchi, Takashi; Yacoby, Amir
Publication:
eprint arXiv:1312.7033
Publication Date:
12/2013
Origin:
ARXIV
Keywords:
Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Strongly Correlated Electrons
Bibliographic Code:
2013arXiv1312.7033K

Abstract

The nature of fractional quantum Hall (FQH) states is determined by the interplay between the Coulomb interaction and the symmetries of the system. The unique combination of spin, valley, and orbital degeneracies in bilayer graphene is predicted to produce novel and tunable FQH ground states. Here we present local electronic compressibility measurements of the FQH effect in the lowest Landau level of bilayer graphene. We observe incompressible FQH states at filling factors v = 2p + 2/3 with hints of additional states appearing at v = 2p + 3/5, where p = -2,-1, 0, and 1. This sequence of states breaks particle-hole symmetry and instead obeys a v --> v + 2 symmetry, which highlights the importance of the orbital degeneracy for many-body states in bilayer graphene.

 

Title:
Self-Calibration of BICEP1 Three-Year Data and Constraints on Astrophysical Polarization Rotation
Authors:
Kaufman, J. P.; Miller, N. J.; Shimon, M.; Barkats, D.; Bischoff, C.; Buder, I.; Keating, B. G.; Kovac, J. M.; Ade, P. A. R.; Aikin, R.; Battle, J. O.; Bierman, E. M.; Bock, J. J.; Chiang, H. C.; Dowell, C. D.; Duband, L.; Filippini, J.; Hivon, E. F.; Holzapfel, W. L.; Hristov, V. V.; Jones, W. C.; Kernasovskiy, S. S.; Kuo, C. L.; Leitch, E. M.; Mason, P. V.; Matsumura, T.; Nguyen, H. T.; Ponthieu, N.; Pryke, C.; Richter, S.; Rocha, G.; Sheehy, C.; Su, M.; Takahashi, Y. D.; Tolan, J. E.; Yoon, K. W.
Publication:
eprint arXiv:1312.7877
Publication Date:
12/2013
Origin:
ARXIV
Keywords:
Astrophysics - Instrumentation and Methods for Astrophysics, Astrophysics - Cosmology and Extragalactic Astrophysics
Comment:
13 pages, 9 figures
Bibliographic Code:
2013arXiv1312.7877K

Abstract

Cosmic Microwave Background (CMB) polarimeters aspire to measure the faint $B$-mode signature predicted to arise from inflationary gravitational waves. They also have the potential to constrain cosmic birefringence which would produce non-zero expectation values for the CMB's $TB$ and $EB$ spectra. However, instrumental systematic effects can also cause these $TB$ and $EB$ correlations to be non-zero. In particular, an overall miscalibration of the polarization orientation of the detectors produces $TB$ and $EB$ spectra which are degenerate with isotropic cosmological birefringence, while also introducing a small but predictable bias on the $BB$ spectrum. The \bicep three-year spectra, which use our standard calibration of detector polarization angles from a dielectric sheet, are consistent with a polarization rotation of $\alpha = -2.77^\circ \pm 0.86^\circ \text{(statistical)} \pm 1.3^\circ \text{(systematic)}$. We revise the estimate of systematic error on the polarization rotation angle from the two-year analysis by comparing multiple calibration methods. We investigate the polarization rotation for the \bicep 100 GHz and 150 GHz bands separately to investigate theoretical models that produce frequency-dependent cosmic birefringence. We find no evidence in the data supporting either these models or Faraday rotation of the CMB polarization by the Milky Way galaxy's magnetic field. If we assume that there is no cosmic birefringence, we can use the $TB$ and $EB$ spectra to calibrate detector polarization orientations, thus reducing bias of the cosmological $B$-mode spectrum from leaked $E$-modes due to possible polarization orientation miscalibration. After applying this "self-calibration" process, we find that the upper limit on the tensor-to-scalar ratio decreases slightly, from $r<0.70$ to $r<0.65$ at $95\%$ confidence.

 

Title:
Expression Pattern of Entire Cytochrome P450 Genes and Response of Defensomes in the Benzo[a]pyrene-Exposed Monogonont RotiferBrachionus koreanus
Authors:
Kim, Ryeo-Ok; Kim, Bo-Mi; Jeong, Chang-Bum; Nelson, David R.; Lee, Jae-Seong; Rhee, Jae-Sung
Publication:
Environmental Science & Technology, vol. 47, issue 23, pp. 13804-13812
Publication Date:
12/2013
Origin:
CROSSREF
DOI:
10.1021/es403269v
Bibliographic Code:
2013EnST...4713804K

Abstract

Not Available

 

Title:
Measurement of jet shapes in top-quark pair events at using the ATLAS detector
Authors:
Aad, G.; Abajyan, T.; Abbott, B.;... ... Barreiro Guimarães da Costa, J.; ... Franklin, M.; ... Huth, J. ;... Morii, M.; ...; and 2909 coauthors
Publication:
The European Physical Journal C, Volume 73, article id. #2676 (EPJC Homepage)
Publication Date:
12/2013
Origin:
SPRINGER
Abstract Copyright:
(c) 2013: CERN for the benefit of the ATLAS collaboration
DOI:
10.1140/epjc/s10052-013-2676-3
Bibliographic Code:
2013EPJC...73.2676A

Abstract

A measurement of jet shapes in top-quark pair events using 1.8 fb-1 of pp collision data recorded by the ATLAS detector at the LHC is presented. Samples of top-quark pair events are selected in both the single-lepton and dilepton final states. The differential and integrated shapes of the jets initiated by bottom-quarks from the top-quark decays are compared with those of the jets originated by light-quarks from the hadronic W-boson decays in the single-lepton channel. The light-quark jets are found to have a narrower distribution of the momentum flow inside the jet area than b-quark jets.

 

Title:   Exploring Quasiparticles in High-Tc Cuprates Through Photoemission, Tunneling, and X-ray Scattering Experiments
Authors:   Dalla Torre, Emanuele G.; He, Yang; Benjamin, David; Demler, Eugene
Publication:   eprint arXiv:1312.0616
Publication Date:   12/2013
Origin:   ARXIV
Keywords:   Condensed Matter - Superconductivity, Condensed Matter - Strongly Correlated Electrons
Comment:   39 pages, 15 figures, updated references
Bibliographic Code:   2013arXiv1312.0616D

Abstract

One of the key challenges in the field of high-temperature superconductivity is understanding the nature of fermionic quasiparticles. Experiments consistently demonstrate the existence of a second energy scale, distinct from the d-wave superconducting gap, that persists above the transition temperature into the "pseudogap" phase. One common class of models relates this energy scale to the quasiparticle gap due to a competing order, such as the incommensurate "checkerboard" order observed in scanning tunneling microscopy (STM) and resonant elastic X-ray scattering (REXS). In this paper we show that these experiments are better described by identifying the second energy scale with the inverse lifetime of quasiparticles. We develop a minimal phenomenological model that allows us to quantitatively describe STM and REXS experiments and discuss their relation with photoemission spectroscopy. Our study refocuses questions about the nature of the pseudogap phase to the study of the origin of inelastic scattering.

 

Title:   A Full-sky, High-resolution Atlas of Galactic 12 micron Dust Emission with WISE
Authors:   Meisner, Aaron; Finkbeiner, Douglas
Publication:   eprint arXiv:1312.0947
Publication Date:   12/2013
Origin:   ARXIV
Keywords:   Astrophysics - Instrumentation and Methods for Astrophysics, Astrophysics - Galaxy Astrophysics
Comment:   Accepted for publication in ApJ. For data release details and manuscript with high-resolution figures, see http://wise.skymaps.info
Bibliographic Code:   2013arXiv1312.0947M

Abstract

We describe our custom processing of the entire Wide-field Infrared Survey Explorer (WISE) 12 micron imaging data set, and present a high-resolution, full-sky map of diffuse Galactic dust emission that is free of compact sources and other contaminating artifacts. The principal distinctions between our resulting co-added images and the WISE Atlas stacks are our removal of compact sources, including their associated electronic and optical artifacts, and our preservation of spatial modes larger than 1.5 degrees. We provide access to the resulting full-sky map via a set of 430 12.5 degree by 12.5 degree mosaics. These stacks have been smoothed to 15" resolution and are accompanied by corresponding coverage maps, artifact images, and bit-masks for point sources, resolved compact sources, and other defects. When combined appropriately with other mid-infrared and far-infrared data sets, we expect our WISE 12 micron co-adds to form the basis for a full-sky dust extinction map with angular resolution several times better than Schlegel et al. (1998).

 

Title:   Conserved quantities in general relativity: from the quasi-local level to spatial infinity
Authors:   Chen, Po-Ning; Wang, Mu-Tao; Yau, Shing-Tung
Publication:   eprint arXiv:1312.0985
Publication Date:   12/2013
Origin:   ARXIV
Keywords:   Mathematics - Differential Geometry, General Relativity and Quantum Cosmology
Comment:   46 pages
Bibliographic Code:   2013arXiv1312.0985C

Abstract

We define quasi-local conserved quantities in general relativity by using the optimal isometric embedding in [26] to transplant Killing fields in the Minkowski spacetime back to the 2-surface of interest in a physical spacetime. To each optimal isometric embedding, a dual element of the Lie algebra of the Lorentz group is assigned. Quasi-local angular momentum and quasi-local center of mass correspond to pairing this element with rotation Killing fields and boost Killing fields, respectively. They obey classical transformation laws under the action of the Poincar\'e group. We further justify these definitions by considering their limits as the total angular momentum and the total center of mass of an isolated system. These expressions were derived from the Hamilton-Jacobi analysis of gravitation action and thus satisfy conservation laws. As a result, we obtained an invariant total angular momentum theorem in the Kerr spacetime. For a vacuum asymptotically flat initial data set of order $1$, it is shown that the limits are always finite without any extra assumptions. We also study these total conserved quantities on a family of asymptotically flat initial data sets evolving by the vacuum Einstein evolution equation. It is shown that the total angular momentum is conserved under the evolution. For the total center of mass, the classical dynamical formula relating the center of mass, energy, and linear momentum is recovered, in the nonlinear context of initial data sets evolving by the vacuum Einstein evolution equation. The definition of quasi-local angular momentum provides an answer to the second problem in classical general relativity on Penrose's list [18].

 

Title:   Quasilocal angular momentum and center of mass in general relativity
Authors:   Chen, Po-Ning; Wang, Mu-Tao; Yau, Shing-Tung
Publication:   eprint arXiv:1312.0990
Publication Date:   12/2013
Origin:   ARXIV
Keywords:   Mathematics - Differential Geometry, General Relativity and Quantum Cosmology
Comment:   11 pages
Bibliographic Code:   2013arXiv1312.0990C

Abstract

For a spacelike 2-surface in spacetime, we propose a new definition of quasi-local angular momentum and quasi-local center of mass, as an element in the dual space of the Lie algebra of the Lorentz group. Together with previous defined quasi-local energy-momentum, this completes the definition of conserved quantities in general relativity at the quasi-local level. We justify this definition by showing the consistency with the theory of special relativity and expectations on an axially symmetric spacetime. The limits at spatial infinity provide new definitions for total conserved quantities of an isolated system, which do not depend on any asymptotically flat coordinate system or asymptotic Killing field. The new proposal is free of ambiguities found in existing definitions and presents the first definition that precisely describes the dynamics of the Einstein equation.

 

Title:   tt* Geometry in 3 and 4 Dimensions
Authors:   Cecotti, Sergio; Gaiotto, Davide; Vafa, Cumrun
Publication:   eprint arXiv:1312.1008
Publication Date:   12/2013
Origin:   ARXIV
Keywords:   High Energy Physics - Theory
Comment:   125 pages, 23 figures
Bibliographic Code:   2013arXiv1312.1008C

Abstract

We consider the vacuum geometry of supersymmetric theories with 4 supercharges, on a flat toroidal geometry. The 2 dimensional vacuum geometry is known to be captured by the $tt^*$ geometry. In the case of 3 dimensions, the parameter space is $(T^{2}\times {\mathbb R})^N$ and the vacuum geometry turns out to be a solution to a generalization of monopole equations in $3N$ dimensions where the relevant topological ring is that of line operators. We compute the generalization of the 2d cigar amplitudes, which lead to $S^2\times S^1$ or $S^3$ partition functions which are distinct from the supersymmetric partition functions on these spaces, but reduce to them in a certain limit. We show the sense in which these amplitudes generalize the structure of 3d Chern-Simons theories and 2d RCFT's. In the case of 4 dimensions the parameter space is of the form $(T^3\times {\mathbb R})^M\times T^{3N}$, and the vacuum geometry is a solution to a mixture of generalized monopole equations and generalized instanton equations (known as hyper-holomorphic connections). In this case the topological rings are associated to surface operators. We discuss the physical meaning of the generalized Nahm transforms which act on all of these geometries.

 

Title:   Charge order driven by Fermi-arc instability in Bi$_2$Sr$_{2-x}$La$_{x}$CuO$_{6+\delta}$
Authors:   Comin, R.; Frano, A.; Yee, M. M.; Yoshida, Y.; Eisaki, H.; Schierle, E.; Weschke, E.; Sutarto, R.; He, F.; Soumyanarayanan, A.; He, Yang; Le Tacon, M.; Elfimov, I. S.; Hoffman, J. E.; Sawatzky, G. A.; Keimer, B.; Damascelli, A.
Publication:   eprint arXiv:1312.1343
Publication Date:   12/2013
Origin:   ARXIV
Keywords:   Condensed Matter - Superconductivity, Condensed Matter - Strongly Correlated Electrons
Comment:   A high resolution version can be found at http://www.phas.ubc.ca/~quantmat/ARPES/PUBLICATIONS/Articles/Bi2201_CDW_REXS_STM.pdf"
Bibliographic Code:   2013arXiv1312.1343C

Abstract

An understanding of the nature of superconductivity in cuprates has been hindered by the apparent diversity of intertwining electronic orders in these materials. Here we combine resonant X-ray scattering (REXS), scanning-tunneling microscopy (STM), and angle-resolved photoemission spectroscopy (ARPES) to observe a charge order that appears consistently in surface and bulk, as well as momentum and real space, with the Bi$_2$Sr$_{2-x}$La$_{x}$CuO$_{6+\delta}$ cuprate family. The observed wavevector rules out simple antinodal nesting in the single particle limit, but matches well with a phenomenological model of a many-body instability of the Fermi arcs. Combined with earlier observations in other cuprate families, these findings suggest the existence of a generic charge-ordered state in underdoped cuprates, and uncover its connection to the pseudogap regime.

 

Title:   The Photon Propagator in Light-Shell Gauge
Authors:   Georgi, Howard; Kestin, Greg; Sajjad, Aqil
Publication:   eprint arXiv:1312.1741
Publication Date:   12/2013
Origin:   ARXIV
Keywords:   High Energy Physics - Phenomenology, High Energy Physics - Theory
Bibliographic Code:   2013arXiv1312.1741G

Abstract

We derive the photon propagator in light-shell gauge, which was first introduced in the context of light-shell effective theory.

 

Title:   On BMS Invariance of Gravitational Scattering
Authors:   Strominger, Andrew
Publication:   eprint arXiv:1312.2229
Publication Date:   12/2013
Origin:   ARXIV
Keywords:   High Energy Physics - Theory, General Relativity and Quantum Cosmology
Comment:   24 pages, 1 figure
Bibliographic Code:   2013arXiv1312.2229S

Abstract

BMS+ transformations act nontrivially on outgoing gravitational scattering data while preserving intrinsic structure at future null infinity (I+). BMS- transformations similarly act on ingoing data at past null infinity (I-). In this paper we apply - within a suitable finite neighborhood of the Minkowski vacuum - results of Christodoulou and Klainerman to link I+ to I- and thereby identify "diagonal" elements BMS0 of (BMS+)X(BMS-). We argue that BMS0 is a nontrivial infinite-dimensional symmetry of both classical gravitational scattering and the quantum gravity S-matrix. It implies the conservation of net accumulated energy flux at every angle on the conformal S2 at I+. The associated Ward identity is shown to relate S-matrix elements with and without soft gravitons. Finally, BMS0 is recast as a U(1) Kac-Moody symmetry and an expression for the Kac-Moody current is given in terms of a certain soft graviton operator on the boundary of null infinity.

 

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:   eprint arXiv:1312.2559
Publication Date:   12/2013
Origin:   ARXIV
Keywords:   Condensed Matter - Mesoscale and Nanoscale Physics
Comment:   20 pages, 12 figures
Bibliographic Code:   2013arXiv1312.2559H

Abstract

Topological insulators are a newly discovered phase of matter characterized by a gapped bulk surrounded by novel 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 which becomes a quantum spin Hall insulator when the well width exceeds d_{C}=6.3 nm. 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. These results provide evidence for superconductivity induced in the helical edges of the quantum spin Hall effect, a promising step toward the demonstration of one-dimensional topological superconductivity. Our results also provide a direct measurement of the widths of these edge channels, which range from 180 nm to 408 nm.

 

Title:   Thermal Excitations of Warped Membranes
Authors:   Kosmrlj, Andrej; Nelson, David R.
Publication:   eprint arXiv:1312.4089
Publication Date:   12/2013
Origin:   ARXIV
Keywords:   Condensed Matter - Soft Condensed Matter, Condensed Matter - Statistical Mechanics
Comment:   14 pages, 3 figures
Bibliographic Code:   2013arXiv1312.4089K

Abstract

We explore thermal fluctuations of thin planar membranes with a frozen spatially-varying background metric and a shear modulus. We focus on a special class of $D$-dimensional ``warped membranes'' embedded in a $d-$dimensional space with $d\ge D+1$ and a preferred height profile characterized by quenched random Gaussian variables $\{h_\alpha({\bf q})\}$, $\alpha=D+1,\ldots, d$, in Fourier space with zero mean and a power law variance $\overline{ h_\alpha({\bf q}_1) h_\beta({\bf q}_2) } \sim \delta_{\alpha, \beta} \, \delta_{{\bf q}_1, -{\bf q}_2} \, q_1^{-d_h}$. The case $D=2$, $d=3$ with $d_h = 4$ could be realized by flash polymerizing lyotropic smectic liquid crystals. For $D < \max\{4, d_h\}$ the elastic constants are non-trivially renormalized and become scale dependent. Via a self consistent screening approximation we find that the renormalized bending rigidity increases for small wavevectors ${{\bf q}}$ as $\kappa_R \sim q^{-\eta_f}$, while the in-hyperplane elastic constants decrease according to $\lambda_R,\ \mu_R \sim q^{+\eta_u}$. The quenched background metric is relevant (irelevant) for warped membranes characterized by exponent $d_h > 4 - \eta_f^{(F)}$ ($d_h < 4 - \eta_f^{(F)}$), where $\eta_f^{(F)}$ is the scaling exponent for tethered surfaces with a flat background metric, and the scaling exponents are related through $\eta_u + \eta_f = d_h - D$ ($\eta_u + 2 \eta_f=4-D$).

 

Title:   On the Classification of 6D SCFTs and Generalized ADE Orbifolds
Authors:   Heckman, Jonathan J.; Morrison, David R.; Vafa, Cumrun
Publication:   eprint arXiv:1312.5746
Publication Date:   12/2013
Origin:   ARXIV
Keywords:   High Energy Physics - Theory
Comment:   55 pages, 5 figures. Included with the submission is the Mathematica notebook "BlowUpDown.nb"
Bibliographic Code:   2013arXiv1312.5746H

Abstract

We study (1,0) and (2,0) 6D superconformal field theories (SCFTs) that can be constructed in F-theory. Quite surprisingly, all of them involve an orbifold singularity C^2 / G with G a discrete subgroup of U(2). When G is a subgroup of SU(2), all discrete subgroups are allowed, and this leads to the familiar ADE classification of (2,0) SCFTs. For more general U(2) subgroups, the allowed possibilities for G are not arbitrary and are given by certain generalizations of the A- and D-series. These theories should be viewed as the minimal 6D SCFTs. We obtain all other SCFTs by bringing in a number of E-string theories and/or decorating curves in the base by non-minimal gauge algebras. In this way we obtain a vast number of new 6D SCFTs, and we conjecture that our construction provides a full list.

 

Title:   Quasiparticle Theory of Resonant Inelastic X-ray Scattering in high-T$_c$ cuprates
Authors:   Benjamin, David; Klich, Israel; Demler, Eugene
Publication:   eprint arXiv:1312.6642
Publication Date:   12/2013
Origin:   ARXIV
Keywords:   Condensed Matter - Superconductivity, Condensed Matter - Strongly Correlated Electrons
Comment:   6 pages, 3 figures, 2 supplements
Bibliographic Code:   2013arXiv1312.6642B

Abstract

We develop a formalism for calculating resonant inelastic x-ray scattering (RIXS) spectra in systems of itinerant electrons with arbitrary band structures, accounting for the effect of the positively-charged core hole exactly. We apply this formalism to the cuprate superconductors and obtain quantitative agreement with experimental data over a wide range of dopings. We reproduce the dispersing peaks and non-trivial polarization dependence found in RIXS experiments on several materials. Thus we demonstrate that features previously attributed to collective magnetic modes can be explained by band structure alone.

 

Title:   Direct measurement of the Zak phase in topological Bloch bands
Authors:   Atala, Marcos; Aidelsburger, Monika; Barreiro, Julio T.; Abanin, Dmitry; Kitagawa, Takuya; Demler, Eugene; Bloch, Immanuel
Publication:   Nature Physics, Volume 9, Issue 12, pp. 795-800 (2013).
Publication Date:   12/2013
Origin:   NATURE
Abstract Copyright:   (c) 2013: Nature Publishing Group
DOI:   10.1038/nphys2790
Bibliographic Code:   2013NatPh...9..795A

Abstract

Geometric phases that characterize the topological properties of Bloch bands play a fundamental role in the band theory of solids. Here we report on the measurement of the geometric phase acquired by cold atoms moving in one-dimensional optical lattices. Using a combination of Bloch oscillations and Ramsey interferometry, we extract the Zak phase--the Berry phase gained during the adiabatic motion of a particle across the Brillouin zone--which can be viewed as an invariant characterizing the topological properties of the band. For a dimerized lattice, which models polyacetylene, we measure a difference of the Zak phase δφZak=0.97(2)π for the two possible polyacetylene phases with different dimerization. The two dimerized phases therefore belong to different topological classes, such that for a filled band, domain walls have fractional quantum numbers. Our work establishes a new general approach for probing the topological structure of Bloch bands inoptical lattices.

 

Title:   Search for long-lived stopped R-hadrons decaying out of time with pp collisions using the ATLAS detector
Authors:   Aad, G.; Abajyan, T.; Abbott, B.;... Barreiro Guimarães da Costa, J.; ... Franklin, M.; ... Huth, J.; ... Morii, M.; ... ; and 2927 coauthors
Publication:   Physical Review D, vol. 88, Issue 11, id. 112003 (PhRvD Homepage)
Publication Date:   12/2013
Origin:   APS
PACS Keywords:   Supersymmetric partners of known particles
DOI:   10.1103/PhysRevD.88.112003
Bibliographic Code:   2013PhRvD..88k2003A

Abstract

An updated search is performed for gluino, top squark, or bottom squark R-hadrons that have come to rest within the ATLAS calorimeter, and decay at some later time to hadronic jets and a neutralino, using 5.0 and 22.9fb-1 of pp collisions at 7 and 8 TeV, respectively. Candidate decay events are triggered in selected empty bunch crossings of the LHC in order to remove pp collision backgrounds. Selections based on jet shape and muon system activity are applied to discriminate signal events from cosmic ray and beam-halo muon backgrounds. In the absence of an excess of events, improved limits are set on gluino, stop, and sbottom masses for different decays, lifetimes, and neutralino masses. With a neutralino of mass 100 GeV, the analysis excludes gluinos with mass below 832 GeV (with an expected lower limit of 731 GeV), for a gluino lifetime between 10μs and 1000 s in the generic R-hadron model with equal branching ratios for decays to qq¯χ˜0 and gχ˜0. Under the same assumptions for the neutralino mass and squark lifetime, top squarks and bottom squarks in the Regge R-hadron model are excluded with masses below 379 and 344 GeV, respectively.

 

Title:   Search for charginos nearly mass degenerate with the lightest neutralino based on a disappearing-track signature in pp collisions at (s)=8TeV with the ATLAS detector
Authors:   Aad, G.; Abajyan, T.; Abbott, B.; ... Barreiro Guimarães da Costa, J.; ... Franklin, M.; ... Huth, J. ;... Morii, M.; ...; and 2928 coauthors
Publication:   Physical Review D, vol. 88, Issue 11, id. 112006 (PhRvD Homepage)
Publication Date:   12/2013
Origin:   APS
PACS Keywords:   Supersymmetric models, Limits on production of particles
DOI:   10.1103/PhysRevD.88.112006
Bibliographic Code:   2013PhRvD..88k2006A

Abstract

A search is presented for direct chargino production based on a disappearing-track signature using 20.3fb-1 of proton-proton collisions at s=8TeV collected with the ATLAS experiment at the LHC. In anomaly-mediated supersymmetry breaking (AMSB) models, the lightest chargino is nearly mass degenerate with the lightest neutralino and its lifetime is long enough to be detected in the tracking detectors by identifying decays that result in tracks with no associated hits in the outer region of the tracking system. Some models with supersymmetry also predict charginos with a significant lifetime. This analysis attains sensitivity for charginos with a lifetime between 0.1 and 10 ns, and significantly surpasses the reach of the LEP experiments. No significant excess above the background expectation is observed for candidate tracks with large transverse momentum, and constraints on chargino properties are obtained. In the AMSB scenarios, a chargino mass below 270 GeV is excluded at 95% confidence level.

 

Title:   Observation of D0-D¯0 Mixing Using the CDF II Detector
Authors:   Aaltonen, T.; Amerio, S.; Amidei, D.;... Franklin, M.; ... Guimaraes da Costa, J.;... and 398 coauthors
Publication:   Physical Review Letters, vol. 111, Issue 23, id. 231802 (PhRvL Homepage)
Publication Date:   12/2013
Origin:   APS
PACS Keywords:   Quark and lepton masses and mixing, Decays of charmed mesons, Decays of charmed mesons, Charmed mesons
DOI:   10.1103/PhysRevLett.111.231802
Bibliographic Code:   2013PhRvL.111w1802A

Abstract

We measure the time dependence of the ratio of decay rates for D0→K+π- to the Cabibbo-favored decay D0→K-π+. The charge conjugate decays are included. A signal of 3.3×104 D*+→π+D0, D0→K+π- decays is obtained with D0 proper decay times between 0.75 and 10 mean D0 lifetimes. The data were recorded with the CDF II detector at the Fermilab Tevatron and correspond to an integrated luminosity of 9.6fb-1 for pp¯ collisions at s=1.96TeV. Assuming CP conservation, we search for D0-D¯0 mixing and measure the mixing parameters to be RD=(3.51±0.35)×10-3, y'=(4.3±4.3)×10-3, and x'2=(0.08±0.18)×10-3. We report Bayesian probability intervals in the x'2-y' plane and find that the significance of excluding the no-mixing hypothesis is equivalent to 6.1 Gaussian standard deviations, providing the second observation of D0-D¯0 mixing from a single experiment.

 

Title:   Stability of Branched Flow from a Quantum Point Contact
Authors:   Liu, Bo; Heller, Eric J.
Publication:   Physical Review Letters, vol. 111, Issue 23, id. 236804 (PhRvL Homepage)
Publication Date:   12/2013
Origin:   APS
PACS Keywords:   Electronic transport in mesoscopic systems, Quantum chaos, semiclassical methods, Quantum transport, Electronic transport in nanoscale materials and structures
DOI:   10.1103/PhysRevLett.111.236804
Bibliographic Code:   2013PhRvL.111w6804L

Abstract

In classically chaotic systems, small differences in initial conditions are exponentially magnified over time. However, it was observed experimentally that the (necessarily quantum) “branched flow” pattern of electron flux from a quantum point contact (QPC) traveling over a random background potential in two-dimensional electron gases remains substantially invariant to large changes in initial conditions. Since such a potential is classically chaotic and unstable to changes in initial conditions, it was conjectured that the origin of the observed stability is purely quantum mechanical, with no classical analog. In this Letter, we show that the observed stability is a result of the physics of the quantum point contact and the nature of the experiment. We show that the same stability can indeed be reproduced classically, or quantum mechanically. In addition, we explore the stability of the branched flow with regards to changes in the eigenmodes of the quantum point contact.

 

Title:   Measurement of Top Quark Polarization in Top-Antitop Events from Proton-Proton Collisions at s=7TeV Using the ATLAS Detector
    Aad, G.; Abajyan, T.; Abbott, B.; ... Barreiro Guimarães da Costa, J.; ... Franklin, M.; ... Huth, J.; ... ; Morii, M.; ... and 2919 coauthors
Publication:   Physical Review Letters, vol. 111, Issue 23, id. 232002 (PhRvL Homepage)
Publication Date:   12/2013
Origin:   APS
PACS Keywords:   Top quarks, Experimental tests
DOI:   10.1103/PhysRevLett.111.232002
Bibliographic Code:   2013PhRvL.111w2002A

Abstract

This Letter presents measurements of the polarization of the top quark in top-antitop quark pair events, using 4.7fb-1 of proton-proton collision data recorded with the ATLAS detector at the Large Hadron Collider at s=7TeV. Final states containing one or two isolated leptons (electrons or muons) and jets are considered. Two measurements of αP, the product of the leptonic spin-analyzing power and the top quark polarization, are performed assuming that the polarization is introduced by either a CP conserving or a maximally CP violating production process. The measurements obtained, αPCPC=-0.035±0.014(stat)±0.037(syst) and αPCPV=0.020±0.016(stat)-0.017+0.013(syst), are in good agreement with the standard model prediction of negligible top quark polarization.


 go to Most Recent Faculty Publications