Faculty Publications: February, 2015

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

The following are Harvard Physics faculty members' publications, added to the ADS database last month. Please note that some publications which appeared in print last month may not be included in the database (and therefore may not appear on this list) until the following month.

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Jan 2015 |


Title:
Three-dimensional Dust Mapping reveals that Orion Forms Part of a Large Ring of Dust
Authors:
Schlafly, E. F.; Green, G.; Finkbeiner, D. P.; Rix, H.-W.; Burgett, W. S.; Chambers, K. C.; Draper, P. W.; Kaiser, N.; Martin, N. F.; Metcalfe, N.; Morgan, J. S.; Price, P. A.; Tonry, J. L.; Wainscoat, R. J.; Waters, C.
Publication:
The Astrophysical Journal, Volume 799, Issue 2, article id. 116, 12 pp. (2015). (ApJ Homepage)
Publication Date:
02/2015
Origin:
IOP
Astronomy Keywords:
dust, extinction, ISM: bubbles, ISM: clouds
DOI:
10.1088/0004-637X/799/2/116
Bibliographic Code:
2015ApJ...799..116S

Abstract

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

 

Title:
Creating femtosecond-laser-hyperdoped silicon with a homogeneous doping profile
Authors:
Lin, Yu-Ting; Mangan, Niall; Marbach, Sophie; Schneider, Tobias M.; Deng, Guoliang; Zhou, Shouhuan; Brenner, Michael P.; Mazur, Eric
Publication:
Applied Physics Letters, Volume 106, Issue 6, id.062105 (ApPhL Homepage)
Publication Date:
02/2015
Origin:
AIP
Abstract Copyright:
2015: AIP Publishing LLC
DOI:
10.1063/1.4907988
Bibliographic Code:
2015ApPhL.106f2105L

Abstract

Femtosecond-laser hyperdoping of sulfur in silicon typically produces a concentration gradient that results in undesirable inhomogeneous material properties. Using a mathematical model of the doping process, we design a fabrication method consisting of a sequence of laser pulses with varying sulfur concentrations in the atmosphere, which produces hyperdoped silicon with a uniform concentration depth profile. Our measurements of the evolution of the concentration profiles with each laser pulse are consistent with our mathematical model of the doping mechanism, based on classical heat and solute diffusion coupled to the far-from-equilibrium dopant incorporation. The use of optimization methods opens an avenue for creating controllable hyperdoped materials on demand.

 

Title:
BICEP2/Keck Array IV: Optical Characterization and Performance of the BICEP2 and Keck Array Experiments
Authors:
BICEP2, The; Keck Array Collaborations; :; Ade, P. A. R.; Aikin, R. W.; Barkats, D.;... Kovac, J. M.;... ; and 47 coauthors
Publication:
eprint arXiv:1502.00596
Publication Date:
02/2015
Origin:
ARXIV
Keywords:
Astrophysics - Instrumentation and Methods for Astrophysics, Astrophysics - Cosmology and Nongalactic Astrophysics
Comment:
20 pages, 24 figures
Bibliographic Code:
2015arXiv150200596B

Abstract

BICEP2 and the Keck Array are polarization-sensitive microwave telescopes that observe the cosmic microwave background (CMB) from the South Pole at degree angular scales in search of a signature of inflation imprinted as B-mode polarization in the CMB. BICEP2 was deployed in late 2009, observed for three years until the end of 2012 at 150 GHz with 512 antenna-coupled transition edge sensor bolometers, and has reported a detection of B-mode polarization on degree angular scales. The Keck Array was first deployed in late 2010 and will observe through 2016 with five receivers at several frequencies (95, 150, and 220 GHz). BICEP2 and the Keck Array share a common optical design and employ the field-proven BICEP1 strategy of using small-aperture, cold, on-axis refractive optics, providing excellent control of systematics while maintaining a large field of view. This design allows for full characterization of far-field optical performance using microwave sources on the ground. Here we describe the optical design of both instruments and report a full characterization of the optical performance and beams of BICEP2 and the Keck Array at 150 GHz.

 

Title:
BICEP2 III: Instrumental Systematics
Authors:
BICEP2 Collaboration; Ade, P. A. R.; Aikin, R. W.; Barkats, D.;... Kovac, J. M.;... ; and 40 coauthors
Publication:
eprint arXiv:1502.00608
Publication Date:
02/2015
Origin:
ARXIV
Keywords:
Astrophysics - Instrumentation and Methods for Astrophysics, Astrophysics - Cosmology and Nongalactic Astrophysics
Comment:
26 pages, 16 figures, higher quality figures available at http://bicepkeck.org
Bibliographic Code:
2015arXiv150200608B

Abstract

In a companion paper we have reported a $>5\sigma$ detection of degree scale $B $-mode polarization at 150 GHz by the BICEP2 experiment. Here we provide a detailed study of potential instrumental systematic contamination to that measurement. We focus extensively on spurious polarization that can potentially arise from beam imperfections. We present a heuristic classification of beam imperfections according to their symmetries and uniformities, and discuss how resulting contamination adds or cancels in maps that combine observations made at multiple orientations of the telescope about its boresight axis. We introduce a technique, which we call "deprojection", for filtering the leading order beam-induced contamination from time ordered data, and show that it removes power from BICEP2's $BB$ spectrum consistent with predictions using high signal-to-noise beam shape measurements. We detail the simulation pipeline that we use to directly simulate instrumental systematics and the calibration data used as input to that pipeline. Finally, we present the constraints on $BB$ contamination from individual sources of potential systematics. We find that systematics contribute $BB$ power that is a factor $\sim10\times$ below BICEP2's 3-year statistical uncertainty, and negligible compared to the observed $BB$ signal. The contribution to the best-fit tensor/scalar ratio is at a level equivalent to $r=(3-6)\times10^{-3}$.

 

Title:
A Joint Analysis of BICEP2/Keck Array and Planck Data
Authors:
BICEP2/Keck; Planck Collaborations; :; Ade, P. A. R.; Aghanim, N.; Ahmed, Z.;... Kovac, J. M.;... ; and 269 coauthors
Publication:
eprint arXiv:1502.00612
Publication Date:
02/2015
Origin:
ARXIV
Keywords:
Astrophysics - Cosmology and Nongalactic Astrophysics, General Relativity and Quantum Cosmology, High Energy Physics - Phenomenology, High Energy Physics - Theory
Comment:
Provisionally accepted by PRL. Data and figures available for download at http://bicepkeck.org and http://pla.esac.esa.int/pla
Bibliographic Code:
2015arXiv150200612B

Abstract

We report the results of a joint analysis of data from BICEP2/Keck Array and Planck. BICEP2 and Keck Array have observed the same approximately 400 deg$^2$ patch of sky centered on RA 0h, Dec. $-57.5\deg$. The combined maps reach a depth of 57 nK deg in Stokes $Q$ and $U$ in a band centered at 150 GHz. Planck has observed the full sky in polarization at seven frequencies from 30 to 353 GHz, but much less deeply in any given region (1.2 $\mu$K deg in $Q$ and $U$ at 143 GHz). We detect 150$\times$353 cross-correlation in $B$-modes at high significance. We fit the single- and cross-frequency power spectra at frequencies above 150 GHz to a lensed-$\Lambda$CDM model that includes dust and a possible contribution from inflationary gravitational waves (as parameterized by the tensor-to-scalar ratio $r$). We probe various model variations and extensions, including adding a synchrotron component in combination with lower frequency data, and find that these make little difference to the $r$ constraint. Finally we present an alternative analysis which is similar to a map-based cleaning of the dust contribution, and show that this gives similar constraints. The final result is expressed as a likelihood curve for $r$, and yields an upper limit $r_{0.05}<0.12$ at 95% confidence. Marginalizing over dust and $r$, lensing $B$-modes are detected at $7.0\,\sigma$ significance.

 

Title:
Antenna-coupled TES bolometers used in BICEP2, Keck array, and SPIDER
Authors:
Ade, P. A. R.; Aikin, R. W.; Amiri, M.; Barkats, D.;... Kovac, J. M.;... and 63 coauthors
Publication:
eprint arXiv:1502.00619
Publication Date:
02/2015
Origin:
ARXIV
Keywords:
Astrophysics - Instrumentation and Methods for Astrophysics
Comment:
16 pgs, 20 figs
Bibliographic Code:
2015arXiv150200619A

Abstract

We have developed antenna-coupled transition-edge sensor (TES) bolometers for a wide range of cosmic microwave background (CMB) polarimetry experiments, including BICEP2, Keck Array, and the balloon borne SPIDER. These detectors have reached maturity and this paper reports on their design principles, overall performance, and key challenges associated with design and production. Our detector arrays repeatedly produce spectral bands with 20%-30% bandwidth at 95, 150, or 220~GHz. The integrated antenna arrays synthesize symmetric co-aligned beams with controlled side-lobe levels. Cross-polarized response on boresight is typically ~0.5%, consistent with cross-talk in our multiplexed readout system. End-to-end optical efficiencies in our cameras are routinely 35% or higher, with per detector sensitivities of NET~300 uKrts. Thanks to the scalability of this design, we have deployed 2560 detectors as 1280 matched pairs in Keck Array with a combined instantaneous sensitivity of ~9 uKrts, as measured directly from CMB maps in the 2013 season. Similar arrays have recently flown in the SPIDER instrument, and development of this technology is ongoing.

 

Title:
BICEP2 / Keck Array V: Measurements of B-mode Polarization at Degree Angular Scales and 150 GHz by the Keck Array
Authors:
Ade, P. A. R.; Ahmed, Z.; Aikin, R. W.;... Kovac, J. M.;... ; and 55 coauthors
Publication:
eprint arXiv:1502.00643
Publication Date:
02/2015
Origin:
ARXIV
Keywords:
Astrophysics - Cosmology and Nongalactic Astrophysics
Comment:
13 pages, 9 figures
Bibliographic Code:
2015arXiv150200643A

Abstract

The Keck Array is a system of cosmic microwave background (CMB) polarimeters, each similar to the BICEP2 experiment. In this paper we report results from the 2012 and 2013 observing seasons, during which the Keck Array consisted of five receivers all operating in the same (150 GHz) frequency band and observing field as BICEP2. We again find an excess of B-mode power over the lensed-$\Lambda$CDM expectation of $> 5 \sigma$ in the range $30 < \ell < 150$ and confirm that this is not due to systematics using jackknife tests and simulations based on detailed calibration measurements. In map difference and spectral difference tests these new data are shown to be consistent with BICEP2. Finally, we combine the maps from the two experiments to produce final Q and U maps which have a depth of 57 nK deg (3.4 $\mu$K arcmin) over an effective area of 400 deg$^2$ for an equivalent survey weight of 250,000 $\mu$K$^{-2}$. The final BB band powers have noise uncertainty a factor of 2.3 times better than the previous results, and a significance of detection of excess power of $> 6\sigma$.

 

Title:
Measurement of central exclusive pi+pi- production in p-pbar collisions at sqrt(s) = 0.9 and 1.96 TeV at CDF
Authors:
CDF Collaboration; Aaltonen, T.; Amerio, S.; Amidei, D.;... Franklin, M.;... Guimaraes da Costa, J.;... ; and 400 coauthors
Publication:
eprint arXiv:1502.01391
Publication Date:
02/2015
Origin:
ARXIV
Keywords:
High Energy Physics - Experiment
Comment:
7 pages, 4 figures, submitted to Phys. Rev. Lett
Bibliographic Code:
2015arXiv150201391C

Abstract

We measure exclusive $\pi^+\pi^-$ production in proton-antiproton collisions at center-of-mass energies $\sqrt{s}$ = 0.9 and 1.96 TeV in the Collider Detector at Fermilab. We select events with two oppositely-charged particles, assumed to be pions, with pseudorapidity $|\eta| < 1.3$ and with no other particles detected in $|\eta| < 5.9$. We require the \pipi system to have rapidity $|y|<$ 1.0. The production mechanism of these events is expected to be dominated by double pomeron exchange, which constrains the quantum numbers of the central state. The data are potentially valuable for isoscalar meson spectroscopy, and for understanding the pomeron in a region of transition between nonperturbative and perturbative quantum chromodynamics. The data extend up to dipion mass $M(\pi^+\pi^-)$ = 5000 MeV/$c^2$, and show resonance structures attributed to $f_0$ and $f_2(1270)$ mesons. From the $\pi^+\pi^-$ and $K^+K^-$ spectra we place upper limits on exclusive $\chi_{c0}(3415)$ production.

 

Title:
Imprint of topological degeneracy in quasi-one-dimensional fractional quantum Hall states
Authors:
Sagi, Eran; Oreg, Yuval; Stern, Ady; Halperin, Bertrand I.
Publication:
eprint arXiv:1502.01665
Publication Date:
02/2015
Origin:
ARXIV
Keywords:
Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Strongly Correlated Electrons
Bibliographic Code:
2015arXiv150201665S

Abstract

We consider an annular superconductor-insulator-superconductor Josephson-junction, with the insulator being a double layer of electron and holes at Abelian fractional quantum Hall states of identical fillings. When the two superconductors gap out the edge modes, the system has a topological ground state degeneracy in the thermodynamic limit akin to the fractional quantum Hall degeneracy on a torus. In the quasi-one-dimensional limit, where the width of the insulator becomes small, the ground state energies are split. We discuss several implications of the topological degeneracy that survive the crossover to the quasi-one-dimensional limit. In particular, the Josephson effect shows a $2\pi d$-periodicity, where $d$ is the ground state degeneracy in the 2 dimensional limit. We find that at special values of the relative phase between the two superconductors there are protected crossing points in which the degeneracy is not completely lifted. These features occur also if the insulator is a time-reversal-invariant fractional topological insulator. We describe the latter using a construction based on coupled wires. Furthermore, when the superconductors are replaced by systems with an appropriate magnetic order that gap the edges via a spin-flipping backscattering, the Josephson effect is replaced by a spin Josephson effect.

 

Title:
Interpolating the Coulomb Phase of Little String Theory
Authors:
Lin, Ying-Hsuan; Shao, Shu-Heng; Wang, Yifan; Yin, Xi
Publication:
eprint arXiv:1502.01751
Publication Date:
02/2015
Origin:
ARXIV
Keywords:
High Energy Physics - Theory
Comment:
40 pages, 5 figures, 4 tables
Bibliographic Code:
2015arXiv150201751L

Abstract

We study up to 8-derivative terms in the Coulomb branch effective action of (1,1) little string theory, by collecting results of 4-gluon scattering amplitudes from both perturbative 6D super-Yang-Mills theory up to 4-loop order, and tree-level double scaled little string theory (DSLST). In previous work we have matched the 6-derivative term from the 6D gauge theory to DSLST, indicating that this term is protected on the entire Coulomb branch. The 8-derivative term, on the other hand, is unprotected. In this paper we compute the 8-derivative term by interpolating from the two limits, near the origin and near the infinity on the Coulomb branch, numerically from SU(k) SYM and DSLST respectively, for k=2,3,4,5. We discuss the implication of this result on the UV completion of 6D SYM as well as the strong coupling completion of DSLST. We also comment on analogous interpolating functions in the Coulomb phase of circle-compactified (2,0) little string theory.

 

Title:
Constraining Higher Derivative Supergravity with Scattering Amplitudes
Authors:
Wang, Yifan; Yin, Xi
Publication:
eprint arXiv:1502.03810
Publication Date:
02/2015
Origin:
ARXIV
Keywords:
High Energy Physics - Theory
Comment:
9 pages, 2 figures; references add
Bibliographic Code:
2015arXiv150203810W

Abstract

We study supersymmetry constraints on higher derivative deformations of type IIB supergravity by consideration of superamplitudes. Combining constraints of on-shell supervertices and basic results from string perturbation theory, we give a simple argument for the non-renormalization theorem of Green and Sethi, and some of its generalizations.

 

Title:
Phase transition beneath the superconducting dome in BaFe$_2$(As$_{1-x}$P$_x$)$_2$
Authors:
Chowdhury, Debanjan; Orenstein, J.; Sachdev, Subir; Senthil, T.
Publication:
eprint arXiv:1502.04122
Publication Date:
02/2015
Origin:
ARXIV
Keywords:
Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Superconductivity
Comment:
4.5 pages, 3 figures
Bibliographic Code:
2015arXiv150204122C

Abstract

We present a theory for the large suppression of the superfluid-density, $\rho_s$, in BaFe$_2$(As$_{1-x}$P$_x$)$_2$ in the vicinity of a putative spin-density wave quantum critical point at a P-doping, $x=x_{c}$. We argue that the transition becomes weakly first-order in the vicinity of $x_{c}$, and disorder induces puddles of superconducting and antiferromagnetic regions at short length-scales; thus the system becomes an electronic micro-emulsion. We propose that frustrated Josephson couplings between the superconducting grains suppress $\rho_s$. In addition, the presence of 'normal' quasiparticles at the interface of the frustrated Josephson junctions resolves some seemingly contradictory observations between the metallic and the superconducting phases. We propose experiments to test our theory.

 

Title:
Memory matrix theory of magnetotransport in strange metals
Authors:
Lucas, Andrew; Sachdev, Subir
Publication:
eprint arXiv:1502.04704
Publication Date:
02/2015
Origin:
ARXIV
Keywords:
Condensed Matter - Strongly Correlated Electrons, High Energy Physics - Theory
Comment:
17 pages
Bibliographic Code:
2015arXiv150204704L

Abstract

We model strange metals as quantum liquids without quasiparticle excitations, but with slow momentum relaxation, and with charge and energy diffusion. General expressions are obtained for electrical, thermal and thermoelectric transport in the presence of an applied magnetic field using the memory matrix formalism. In the appropriate limits, our expressions agree with previous hydrodynamic and holographic results. Such transport models have been argued to be compatible with thermoelectric and Hall transport measurements in the strange metal phase of the hole-doped cuprates.

 

Title:
Quenching of dynamic nuclear polarization by spin-orbit coupling in GaAs quantum dots
Authors:
Nichol, John M.; Harvey, Shannon P.; Shulman, Michael D.; Pal, Arijeet; Umansky, Vladimir; Rashba, Emmanuel I.; Halperin, Bertrand I.; Yacoby, Amir
Publication:
eprint arXiv:1502.05400
Publication Date:
02/2015
Origin:
ARXIV
Keywords:
Condensed Matter - Mesoscale and Nanoscale Physics
Comment:
5+12 pages, 9 figures
Bibliographic Code:
2015arXiv150205400N

Abstract

The central-spin problem, in which an electron spin interacts with a nuclear spin bath, is a widely studied model of quantum decoherence. Dynamic nuclear polarization (DNP) occurs in central spin systems when electronic angular momentum is transferred to nuclear spins and is exploited in spin-based quantum information processing for coherent electron and nuclear spin control. However, the mechanisms limiting DNP remain only partially understood. Here, we show that spin-orbit coupling quenches DNP in a GaAs double quantum dot, even though spin-orbit coupling in GaAs is weak. Using Landau-Zener sweeps, we measure the dependence of the electron spin-flip probability on the strength and direction of in-plane magnetic field, allowing us to distinguish effects of the spin-orbit and hyperfine interactions. To confirm our interpretation, we measure high-bandwidth correlations in the electron spin-flip probability and attain results consistent with a significant spin-orbit contribution. We observe that DNP is quenched when the spin-orbit component exceeds the hyperfine, in agreement with a theoretical model. Our results shed new light on the surprising competition between the spin-orbit and hyperfine interactions in central-spin systems.

 

Title:
Atomic Classification of 6D SCFTs
Authors:
Heckman, Jonathan J.; Morrison, David R.; Rudelius, Tom; Vafa, Cumrun
Publication:
eprint arXiv:1502.05405
Publication Date:
02/2015
Origin:
ARXIV
Keywords:
High Energy Physics - Theory
Comment:
122 pages, 23 figures. Included with the submission are the Mathematica notebooks "Bases.nb" and "Fiber_Enhancements.nb"
Bibliographic Code:
2015arXiv150205405H

Abstract

We use F-theory to classify possibly all six-dimensional superconformal field theories (SCFTs). This involves a two step process: We first classify all possible tensor branches allowed in F-theory (which correspond to allowed collections of contractible spheres) and then classify all possible configurations of seven-branes wrapped over them. We describe the first step in terms of "atoms" joined into "radicals" and "molecules," using an analogy from chemistry. The second step has an interpretation via quiver-type gauge theories constrained by anomaly cancellation. A very surprising outcome of our analysis is that all of these tensor branches have the structure of a linear chain of intersecting spheres with a small amount of possible decoration at the two ends. The resulting structure of these SCFTs takes the form of a generalized quiver consisting of ADE-type nodes joined by conformal matter. A collection of highly non-trivial examples involving E8 small instantons probing an ADE singularity is shown to have an F-theory realization. This yields a classification of homomorphisms from ADE subgroups of SU(2) into E8 in purely geometric terms, largely matching results obtained in the mathematics literature from an intricate group theory analysis and suggesting a few corrections to those results.

 

Title:
Removing phase-space restrictions in factorized cross sections
Authors:
Feige, Ilya; Schwartz, Matthew D.; Yan, Kai
Publication:
eprint arXiv:1502.05411
Publication Date:
02/2015
Origin:
ARXIV
Keywords:
High Energy Physics - Phenomenology
Comment:
32 pages, 1 figure
Bibliographic Code:
2015arXiv150205411F

Abstract

Factorization in gauge theories holds at the amplitude or amplitude-squared level for states of given soft or collinear momenta. When performing phase-space integrals over such states, one would generally like to avoid putting in explicit cuts to separate soft from collinear momenta. Removing these cuts induces an overcounting of the soft-collinear region and adds new infrared-ultraviolet divergences in the collinear region. In this paper, we first present a regulator-independent subtraction algorithm for removing soft-collinear overlap at the amplitude level which may be useful in pertubative QCD. We then discuss how both the soft-collinear and infrared-ultraviolet overlap can be undone for certain observables in a way which respects factorization. Our discussion clarifies some of the subtleties in phase-space subtractions and includes a proof of the infrared finiteness of a suitably subtracted jet function. These results complete the connection between factorized QCD and Soft-Collinear Effective Theory.

 

Title:
New Gravitational Memories
Authors:
Pasterski, Sabrina; Strominger, Andrew; Zhiboedov, Alexander
Publication:
eprint arXiv:1502.06120
Publication Date:
02/2015
Origin:
ARXIV
Keywords:
High Energy Physics - Theory, General Relativity and Quantum Cosmology
Comment:
17 pages
Bibliographic Code:
2015arXiv150206120P

Abstract

The conventional gravitational memory effect is a relative displacement in the position of two detectors induced by radiative energy flux. We find a new type of gravitational `spin memory' in which beams on clockwise and counterclockwise orbits acquire a relative delay induced by radiative angular momentum flux. It has recently been shown that the displacement memory formula is a Fourier transform in time of Weinberg's soft graviton theorem. Here we see that the spin memory formula is a Fourier transform in time of the recently-discovered subleading soft graviton theorem.

 

Title:
Higher-Dimensional Supertranslations and Weinberg's Soft Graviton Theorem
Authors:
Kapec, Daniel; Lysov, Vyacheslav; Pasterski, Sabrina; Strominger, Andrew
Publication:
eprint arXiv:1502.07644
Publication Date:
02/2015
Origin:
ARXIV
Keywords:
General Relativity and Quantum Cosmology, High Energy Physics - Phenomenology, High Energy Physics - Theory
Comment:
24 pages
Bibliographic Code:
2015arXiv150207644K

Abstract

Asymptotic symmetries of theories with gravity in d=2m+2 spacetime dimensions are reconsidered for m>1 in light of recent results concerning d=4 BMS symmetries. Weinberg's soft graviton theorem in 2m+2 dimensions is re-expressed as a Ward identity for the gravitational S-matrix. The corresponding asymptotic symmetries are identified with 2m+2-dimensional supertranslations. An alternate derivation of these asymptotic symmetries as diffeomorphisms which preserve finite-energy boundary conditions at null infinity and act non-trivially on physical data is given. Our results differ from those of previous analyses whose stronger boundary conditions precluded supertranslations for d>4. We find for all even d that supertranslation symmetry is spontaneously broken in the conventional vacuum and identify soft gravitons as the corresponding Goldstone bosons.

 

Title:
Low-frequency conductivity in many-body localized systems
Authors:
Gopalakrishnan, Sarang; Mueller, Markus; Khemani, Vedika; Knap, Michael; Demler, Eugene; Huse, David A.
Publication:
eprint arXiv:1502.07712
Publication Date:
02/2015
Origin:
ARXIV
Keywords:
Condensed Matter - Disordered Systems and Neural Networks, Condensed Matter - Quantum Gases, Condensed Matter - Statistical Mechanics
Comment:
10 pages, 6 figures
Bibliographic Code:
2015arXiv150207712G

Abstract

We argue that the a.c. conductivity $\sigma(\omega)$ in the many-body localized phase is a power law of frequency $\omega$ at low frequency: specifically, $\sigma(\omega) \sim \omega^\alpha$ with the exponent $\alpha$ approaching 1 at the phase transition to the thermal phase, and asymptoting to 2 deep in the localized phase. We identify two separate mechanisms giving rise to this power law: deep in the localized phase, the conductivity is dominated by rare resonant pairs of configurations; close to the transition, the dominant contributions are rare regions that are locally critical or in the thermal phase. We present numerical evidence supporting these claims, and discuss how these power laws can also be seen through polarization-decay measurements in ultracold atomic systems.

 

Title:
Search for resonant diboson production in the final state in collisions at TeV with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Barreiro Guimarães da Costa, J.;... Franklin, M.;... ; Huth, J.;... Morii, M.;...; and 2891 coauthors
Publication:
The European Physical Journal C, Volume 75, article id. #69, 20 pp. (EPJC Homepage)
Publication Date:
02/2015
Origin:
SPRINGER
Abstract Copyright:
(c) 2015: CERN for the benefit of the ATLAS collaboration
DOI:
10.1140/epjc/s10052-015-3261-8
Bibliographic Code:
2015EPJC...75...69A

Abstract

This paper reports on a search for narrow resonances in diboson production in the final state using collision data corresponding to an integrated luminosity of fb collected at TeV with the ATLAS detector at the Large Hadron Collider. No significant excess of data events over the Standard Model expectation is observed. Upper limits at the 95 % confidence level are set on the production cross section times branching ratio for Kaluza-Klein gravitons predicted by the Randall-Sundrum model and for Extended Gauge Model bosons. These results lead to the exclusion of mass values below 740 and 1590 GeV for the graviton and boson respectively.

 

Title:
Search for invisible particles produced in association with single-top-quarks in proton-proton collisions at with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Barreiro Guimarães da Costa, J.;... Franklin, M.;... ; Huth, J.;... Morii, M.;...; and 2872 coauthors
Publication:
The European Physical Journal C, Volume 75, article id. #79, 24 pp. (EPJC Homepage)
Publication Date:
02/2015
Origin:
SPRINGER
Abstract Copyright:
(c) 2015: CERN for the benefit of the ATLAS collaboration
DOI:
10.1140/epjc/s10052-014-3233-4
Bibliographic Code:
2015EPJC...75...79A

Abstract

A search for the production of single-top-quarks in association with missing energy is performed in proton-proton collisions at a centre-of-mass energy of with the ATLAS experiment at the large hadron collider using data collected in 2012, corresponding to an integrated luminosity of fb. In this search, the boson from the top quark is required to decay into an electron or a muon and a neutrino. No deviation from the standard model prediction is observed, and upper limits are set on the production cross-section for resonant and non-resonant production of an invisible exotic state in association with a right-handed top quark. In the case of resonant production, for a spin- resonance with a mass of GeV, an effective coupling strength above is excluded at 95 confidence level for the top quark and an invisible spin- state with mass between and GeV. In the case of non-resonant production, an effective coupling strength above is excluded at 95 confidence level for the top quark and an invisible spin- state with mass between and GeV.

 

Title:
One-dimensional capillary jumps
Authors:
Argentina, M.; Cohen, A.; Bouret, Y.; Fraysse, N.; Raufaste, C.
Publication:
Journal of Fluid Mechanics, vol. 765, pp. 1-16
Publication Date:
02/2015
Origin:
CROSSREF
DOI:
10.1017/jfm.2014.717
Bibliographic Code:
2015JFM...765....1A

Abstract

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Title:
6d Conformal matter
Authors:
Del Zotto, Michele; Heckman, Jonathan J.; Tomasiello, Alessandro; Vafa, Cumrun
Publication:
Journal of High Energy Physics, Volume 2015, article id. #54, 56 pp.
Publication Date:
02/2015
Origin:
SPRINGER
Keywords:
F-Theory, AdS-CFT Correspondence, Field Theories in Higher Dimensions
Abstract Copyright:
(c) 2015: The Author(s)
DOI:
10.1007/JHEP02(2015)054
Bibliographic Code:
2015JHEP...02..054D

Abstract

A single M5-brane probing G, an ADE-type singularity, leads to a system which has G × G global symmetry and can be viewed as "bifundamental" ( G, G) matter. For the A N series, this leads to the usual notion of bifundamental matter. For the other cases it corresponds to a strongly interacting (1 , 0) superconformal system in six dimensions. Similarly, an ADE singularity intersecting the Horava-Witten wall leads to a superconformal matter system with E 8 × G global symmetry. Using the F-theory realization of these theories, we elucidate the Coulomb/tensor branch of ( G, G') conformal matter. This leads to the notion of fractionalization of an M5-brane on an ADE singularity as well as fractionalization of the intersection point of the ADE singularity with the Horava-Witten wall. Partial Higgsing of these theories leads to new 6d SCFTs in the infrared, which we also characterize. This generalizes the class of (1 , 0) theories which can be perturbatively realized by suspended branes in IIA string theory. By reducing on a circle, we arrive at novel duals for 5d affine quiver theories. Introducing many M5-branes leads to large N gravity duals.

 

Title:
Nanoscale NMR spectroscopy and imaging of multiple nuclear species
Authors:
Devience, Stephen J.; Pham, Linh M.; Lovchinsky, Igor; Sushkov, Alexander O.; Bar-Gill, Nir; Belthangady, Chinmay; Casola, Francesco; Corbett, Madeleine; Zhang, Huiliang; Lukin, Mikhail; Park, Hongkun; Yacoby, Amir; Walsworth, Ronald L.
Publication:
Nature Nanotechnology, Volume 10, Issue 2, pp. 129-134 (2015).
Publication Date:
02/2015
Origin:
NATURE
Abstract Copyright:
(c) 2015: Nature Publishing Group
DOI:
10.1038/nnano.2014.313
Bibliographic Code:
2015NatNa..10..129D

Abstract

Nuclear magnetic resonance (NMR) spectroscopy and magnetic resonance imaging (MRI) provide non-invasive information about multiple nuclear species in bulk matter, with wide-ranging applications from basic physics and chemistry to biomedical imaging. However, the spatial resolution of conventional NMR and MRI is limited to several micrometres even at large magnetic fields (>1 T), which is inadequate for many frontier scientific applications such as single-molecule NMR spectroscopy and in vivo MRI of individual biological cells. A promising approach for nanoscale NMR and MRI exploits optical measurements of nitrogen--vacancy (NV) colour centres in diamond, which provide a combination of magnetic field sensitivity and nanoscale spatial resolution unmatched by any existing technology, while operating under ambient conditions in a robust, solid-state system. Recently, single, shallow NV centres were used to demonstrate NMR of nanoscale ensembles of proton spins, consisting of a statistical polarization equivalent to ~100--1,000 spins in uniform samples covering the surface of a bulk diamond chip. Here, we realize nanoscale NMR spectroscopy and MRI of multiple nuclear species (1H, 19F, 31P) in non-uniform (spatially structured) samples under ambient conditions and at moderate magnetic fields (~20 mT) using two complementary sensor modalities.

 

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:
New Journal of Physics, Volume 17, Issue 2, article id. 022001 (2015).
Publication Date:
02/2015
Origin:
IOP
DOI:
10.1088/1367-2630/17/2/022001
Bibliographic Code:
2015NJPh...17b2001D

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). We develop a minimal phenomenological model that allows us to quantitatively describe STM and REXS experiments and discuss their relation with photoemission spectroscopy. Experimental signatures of the incommensurate order are explained in terms of scattering of short-lived quasiparticles from local impurities. We identify the unknown second energy scale with the inverse lifetime of the quasiparticles, refocusing questions about the nature of the pseudogap phase to the study of the origin of inelastic scattering.

 

Title:
All-optical control of a single electron spin in diamond
Authors:
Chu, Y.; Markham, M.; Twitchen, D. J.; Lukin, M. D.
Publication:
Physical Review A, Volume 91, Issue 2, id.021801 (PhRvA Homepage)
Publication Date:
02/2015
Origin:
APS
PACS Keywords:
Effects of atomic coherence on propagation absorption and amplification of light, electromagnetically induced transparency and absorption, Quantum information, Optical implementations of quantum information processing and transfer, Impurity and defect levels
Abstract Copyright:
2015: American Physical Society
DOI:
10.1103/PhysRevA.91.021801
Bibliographic Code:
2015PhRvA..91b1801C

Abstract

Precise coherent control of the individual electronic spins associated with atomlike 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 ˜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:
Measurement of the transverse polarization of Lambda and Lambda ¯ hyperons produced in proton-proton collisions at &surd;{s }=7 TeV using the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Barreiro Guimarães da Costa, J.;... Franklin, M.;... ; Huth, J.;... Morii, M.;...; and 2869 coauthors
Publication:
Physical Review D, Volume 91, Issue 3, id.032004 (PhRvD Homepage)
Publication Date:
02/2015
Origin:
APS
PACS Keywords:
Inclusive production with identified hadrons, Polarization in interactions and scattering, Hyperons
Abstract Copyright:
2015: CERN
DOI:
10.1103/PhysRevD.91.032004
Bibliographic Code:
2015PhRvD..91c2004A

Abstract

The transverse polarization of Lambda and Lambda ¯ hyperons produced in proton-proton collisions at a center-of-mass energy of 7 TeV is measured. The analysis uses 760 mu b-1 of minimum bias data collected by the ATLAS detector at the LHC in the year 2010. The measured transverse polarization averaged over Feynman xF from 5 ×1 0-5 to 0.01 and transverse momentum pT from 0.8 to 15 GeV is -0.010 ±0.005 (stat)±0.004 (syst) for Lambda and 0.002 ±0.006 (stat)±0.004 (syst) for Lambda ¯. It is also measured as a function of xF and pT, but no significant dependence on these variables is observed. Prior to this measurement, the polarization was measured at fixed-target experiments with center-of-mass energies up to about 40 GeV. The ATLAS results are compatible with the extrapolation of a fit from previous measurements to the xF range covered by this measurement.

 

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