Faculty Publications: May, 2014

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Title:
Transport in two-dimensional disordered semimetals
Authors:
Knap, Michael; Sau, Jay D.; Halperin, Bertrand I.; Demler, Eugene
Publication:
eprint arXiv:1405.0277
Publication Date:
05/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Disordered Systems and Neural Networks
Comment:
5 pages, 4 figures, plus supplemental material. V2: minor clarifications and an additional reference
Bibliographic Code:
2014arXiv1405.0277K

Abstract

We theoretically study transport in two-dimensional semimetals. Typically, electron and hole puddles emerge in the transport layer of these systems due to smooth fluctuations in the potential. We calculate the electric response of the electron-hole liquid subject to zero and finite perpendicular magnetic fields using an effective medium approximation and a complimentary mapping on resistor networks. In the presence of smooth disorder and in the limit of weak electron-hole recombination rate, we find for small but finite overlap of the electron and hole bands an abrupt upturn in resistivity when lowering the temperature but no divergence at zero temperature. We discuss how this behavior is relevant for several experimental realizations and introduce a simple physical explanation for this effect.

 

Title:
Heisenberg-Limited Atom Clocks Based on Entangled Qubits
Authors:
Kessler, E. M.; Kómár, P.; Bishof, M.; Jiang, L.; Sørensen, A. S.; Ye, J.; Lukin, M. D.
Publication:
Physical Review Letters, Volume 112, Issue 19, id.190403 (PhRvL Homepage)
Publication Date:
05/2014
Origin:
APS
PACS Keywords:
Entanglement and quantum nonlocality, Metrology, Time and frequency, Nonclassical states of the electromagnetic field including entangled photon states, quantum state engineering and measurements
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevLett.112.190403
Bibliographic Code:
2014PhRvL.112s0403K

Abstract

We present a quantum-enhanced atomic clock protocol based on groups of sequentially larger Greenberger-Horne-Zeilinger (GHZ) states that achieves the best clock stability allowed by quantum theory up to a logarithmic correction. Importantly the protocol is designed to work under realistic conditions where the drift of the phase of the laser interrogating the atoms is the main source of decoherence. The simultaneous interrogation of the laser phase with a cascade of GHZ states realizes an incoherent version of the phase estimation algorithm that enables Heisenberg-limited operation while extending the coherent interrogation time beyond the laser noise limit. We compare and merge the new protocol with existing state of the art interrogation schemes, and identify the precise conditions under which entanglement provides an advantage for clock stabilization: it allows a significant gain in the stability for short averaging time.

 

Title:
Measurement of the B→Xs+- Branching Fraction and Search for Direct CP Violation from a Sum of Exclusive Final State
Authors:
Lees, J. P.; Poireau, V.; Tisserand, V.;....; Morii, M.; and 334 coauthors
Publication:
Physical Review Letters, Volume 112, Issue 21, id.211802 (PhRvL Homepage)
Publication Date:
05/2014
Origin:
APS
PACS Keywords:
Decays of bottom mesons, Charge conjugation parity time reversal and other discrete symmetries
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevLett.112.211802
Bibliographic Code:
2014PhRvL.112u1802L

Abstract

We measure the total branching fraction of the flavor-changing neutral-current process B→Xs+-, along with partial branching fractions in bins of dilepton and hadronic system (Xs) mass, using a sample of 471×106 ϒ(4S)→BB ¯ events recorded with the BABAR detector. The admixture of charged and neutral B mesons produced at PEP-II2 are reconstructed by combining a dilepton pair with 10 different Xs final states. Extrapolating from a sum over these exclusive modes, we measure a lepton-flavor-averaged inclusive branching fraction B(B→Xs+-)=[6.73-0.64+0.70(stat)-0.25+0.34(exp syst)±0.50(model syst)]×10-6 for mℓ+-2>0.1 GeV2/c4. Restricting our analysis exclusively to final states from which a decaying B meson's flavor can be inferred, we additionally report measurements of the direct CP asymmetry ACP in bins of dilepton mass; over the full dilepton mass range, we find ACP=0.04±0.11±0.01 for a lepton-flavor-averaged sample.

 

Title:
tt * geometry in 3 and 4 dimensions
Authors:
Cecotti, Sergio; Gaiotto, Davide; Vafa, Cumrun
Publication:
Journal of High Energy Physics, Volume 2014, article id. #55
Publication Date:
05/2014
Origin:
SPRINGER
Keywords:
Supersymmetry and Duality, Supersymmetric gauge theory, Extended Supersymmetry, Nonperturbative Effects
Abstract Copyright:
(c) 2014: The Author(s)
DOI:
10.1007/JHEP05(2014)055
Bibliographic Code:
2014JHEP...05..055C

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 × ) N and the vacuum geometry turns out to be a solution to a generalization of monopole equations in 3 N 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 × 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 X M,N = ( T 3 × ) M × T 3 N , 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:
Measurement of dijet cross-sections in pp collisions at 7 TeV centre-of-mass energy using the ATLAS detector
Authors:
Aad, G.; Abajyan, T.; Abbott, B.; ... ; Franklin, M.;... Guimarães da Costa, J.;... Huth, J.;...; Morii, M.; and 2944 coauthors
Publication:
Journal of High Energy Physics, Volume 2014, article id. #59
Publication Date:
05/2014
Origin:
SPRINGER
Keywords:
Jets, Jet physics, Hadron-Hadron Scattering
Abstract Copyright:
(c) 2014: The Author(s)
DOI:
10.1007/JHEP05(2014)059
Bibliographic Code:
2014JHEP...05..059A

Abstract

Double-differential dijet cross-sections measured in pp collisions at the LHC with a 7 TeV centre-of-mass energy are presented as functions of dijet mass and half the rapidity separation of the two highest- p T jets. These measurements are obtained using data corresponding to an integrated luminosity of 4.5 fb-1, recorded by the ATLAS detector in 2011. The data are corrected for detector effects so that cross-sections are presented at the particle level. Cross-sections are measured up to 5 TeV dijet mass using jets reconstructed with the anti- k t algorithm for values of the jet radius parameter of 0.4 and 0.6. The cross-sections are compared with next-to-leading-order perturbative QCD calculations by NLOJet++ corrected to account for non-perturbative effects. Comparisons with POWHEG predictions, using a next-to-leading-order matrix element calculation interfaced to a parton-shower Monte Carlo simulation, are also shown. Electroweak effects are accounted for in both cases. The quantitative comparison of data and theoretical predictions obtained using various parameterizations of the parton distribution functions is performed using a frequentist method. In general, good agreement with data is observed for the NLOJet++ theoretical predictions when using the CT10, NNPDF2.1 and MSTW 2008 PDF sets. Disagreement is observed when using the ABM11 and HERAPDF1.5 PDF sets for some ranges of dijet mass and half the rapidity separation. An example setting a lower limit on the compositeness scale for a model of contact interactions is presented, showing that the unfolded results can be used to constrain contributions to dijet production beyond that predicted by the Standard Model. [Figure not available: see fulltext.]

 

Title:
Measurement of the production of a W boson in association with a charm quark in pp collisions at = 7 TeV with the ATLAS detector
Authors:
Aad, G.; Abajyan, T.; Abbott, B.; ... ; Franklin, M.;... Guimarães da Costa, J.;... Huth, J.;...; Morii, M.; and 2894 coauthors
Publication:
Journal of High Energy Physics, Volume 2014, article id. #68
Publication Date:
05/2014
Origin:
SPRINGER
Keywords:
Electroweak interaction, Hadron-Hadron Scattering, Charm physics
Abstract Copyright:
(c) 2014: The Author(s)
DOI:
10.1007/JHEP05(2014)068
Bibliographic Code:
2014JHEP...05..068A

Abstract

The production of a W boson in association with a single charm quark is studied using 4.6 fb-1 of pp collision data at = 7 TeV collected with the ATLAS detector at the Large Hadron Collider. In events in which a W boson decays to an electron or muon, the charm quark is tagged either by its semileptonic decay to a muon or by the presence of a charmed meson. The integrated and differential cross sections as a function of the pseudorapidity of the lepton from the W-boson decay are measured. Results are compared to the predictions of next-to-leading-order QCD calculations obtained from various parton distribution function parameterisations. The ratio of the strange-to-down sea-quark distributions is determined to be at Q 2 = 1.9 GeV2, which supports the hypothesis of an SU(3)-symmetric composition of the light-quark sea. Additionally, the cross-section ratio σ( W + +)/ σ( W - + c) is compared to the predictions obtained using parton distribution function parameterisations with different assumptions about the quark asymmetry. [Figure not available: see fulltext.]

 

Title:
Search for direct production of charginos, neutralinos and sleptons in final states with two leptons and missing transverse momentum in pp collisions at = 8TeV with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... ; Franklin, M.;... Guimarães da Costa, J.;... Huth, J.;...; Morii, M.; and 2880 coauthors
Publication:
Journal of High Energy Physics, Volume 2014, article id. #71
Publication Date:
05/2014
Origin:
SPRINGER
Keywords:
Supersymmetry, Hadron-Hadron Scattering
Abstract Copyright:
(c) 2014: The Author(s)
DOI:
10.1007/JHEP05(2014)071
Bibliographic Code:
2014JHEP...05..071A

Abstract

Searches for the electroweak production of charginos, neutralinos and sleptons in final states characterized by the presence of two leptons (electrons and muons) and missing transverse momentum are performed using 20.3 fb-1 of proton-proton collision data at = 8 TeV recorded with the ATLAS experiment at the Large Hadron Collider. No significant excess beyond Standard Model expectations is observed. Limits are set on the masses of the lightest chargino, next-to-lightest neutralino and sleptons for different lightest-neutralino mass hypotheses in simplified models. Results are also interpreted in various scenarios of the phenomenological Minimal Supersymmetric Standard Model. [Figure not available: see fulltext.]

 

Title:
Density-Gradient-Free Microfluidic Centrifugation for Analytical and Preparative Separation of Nanoparticles
Authors:
Arosio, Paolo; Müller, Thomas; Mahadevan, L.; Knowles, Tuomas P. J.
Publication:
Nano Letters, vol. 14, issue 5, pp. 2365-2371
Publication Date:
05/2014
Origin:
CROSSREF
DOI:
10.1021/nl404771g
Bibliographic Code:
2014NanoL..14.2365A

Abstract

Not Available

 

Title:
Radio-frequency spectroscopy of polarons in ultracold Bose gases
Authors:
Shashi, Aditya; Grusdt, Fabian; Abanin, Dmitry A.; Demler, Eugene
Publication:
Physical Review A, Volume 89, Issue 5, id.053617 (PhRvA Homepage)
Publication Date:
05/2014
Origin:
APS
PACS Keywords:
Ultracold gases trapped gases, Absorption and reflection spectra: visible and ultraviolet, Nonequilibrium gas dynamics, Scattering by phonons magnons and other nonlocalized excitations
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevA.89.053617
Bibliographic Code:
2014PhRvA..89e3617S

Abstract

Recent experimental advances enabled the realization of mobile impurities immersed in a Bose-Einstein condensate (BEC) of ultracold atoms. Here, we consider impurities with two or more internal hyperfine states, and study their radio-frequency (rf) absorption spectra, which correspond to transitions between two different hyperfine states. We calculate rf spectra for the case when one of the hyperfine states involved interacts with the BEC, while the other state is noninteracting, by performing a nonperturbative resummation of the probabilities of exciting different numbers of phonon modes. In the presence of interactions, the impurity gets dressed by Bogoliubov excitations of the BEC, and forms a polaron. The rf signal contains a δ-function peak centered at the energy of the polaron measured relative to the bare impurity transition frequency with a weight equal to the amount of bare impurity character in the polaron state. The rf spectrum also has a broad incoherent part arising from the background excitations of the BEC, with a characteristic power-law tail that appears as a consequence of the universal physics of contact interactions. We discuss both the direct rf measurement, in which the impurity is initially in an interacting state, and the inverse rf measurement, in which the impurity is initially in a noninteracting state. In the latter case, in order to calculate the rf spectrum, we solve the problem of polaron formation: a mobile impurity is suddenly introduced in a BEC, and dynamically gets dressed by Bogoliubov phonons. Our solution is based on a time-dependent variational ansatz of coherent states of Bogoliubov phonons, which becomes exact when the impurity is localized. Moreover, we show that such an ansatz compares well with a semiclassical estimate of the propagation amplitude of a mobile impurity in the BEC. Our technique can be extended to cases when both initial and final impurity states are interacting with the BEC.

 

Title:
Study of top quark production and decays involving a tau lepton at CDF and limits on a charged Higgs boson contribution
Authors:
Aaltonen, T.; Amerio, S.; Amidei, D.;... Franklin, M.;... Guimaraes da Costa, J.;... ; and 404 coauthors
Publication:
Physical Review D, Volume 89, Issue 9, id.091101 (PhRvD Homepage)
Publication Date:
05/2014
Origin:
APS
PACS Keywords:
Top quarks
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevD.89.091101
Bibliographic Code:
2014PhRvD..89i1101A

Abstract

We present an analysis of top-antitop quark production and decay into a tau lepton, tau neutrino, and bottom quark using data from 9 fb-1 of integrated luminosity at the Collider Detector at Fermilab. Dilepton events, where one lepton is an energetic electron or muon and the other a hadronically decaying tau lepton, originating from proton-antiproton collisions at √s =1.96 TeV, are used. A top-antitop quark production cross section of 8.1±2.1 pb is measured, assuming standard-model top quark decays. By separately identifying for the first time the single-tau and the ditau components, we measure the branching fraction of the top quark into the tau lepton, tau neutrino, and bottom quark to be (9.6±2.8)%. The branching fraction of top quark decays into a charged Higgs boson and a bottom quark, which would imply violation of lepton universality, is limited to be less than 5.9% at a 95% confidence level [for B(H-→τν¯)=1].

 

Title:
Measurement of the parity-violating asymmetry parameter αb and the helicity amplitudes for the decay Λb0→J/ψΛ0 with the ATLAS detector
Authors:
Aad, G.; Abajyan, T.; Abbott, B.; ... ; Franklin, M.;... Guimarães da Costa, J.;... Huth, J.;...; Morii, M.; and 2892 coauthors
Publication:
Physical Review D, Volume 89, Issue 9, id.092009 (PhRvD Homepage)
Publication Date:
05/2014
Origin:
APS
PACS Keywords:
Bottom baryons
Abstract Copyright:
2014: CERN
DOI:
10.1103/PhysRevD.89.092009
Bibliographic Code:
2014PhRvD..89i2009A

Abstract

A measurement of the parity-violating decay asymmetry parameter, αb, and the helicity amplitudes for the decay Λb0→J/ψ(μ+μ-0(pπ-) is reported. The analysis is based on 1400 Λb0 and Λ ¯b0 baryons selected in 4.6 fb-1 of proton-proton collision data with a center-of-mass energy of 7 TeV recorded by the ATLAS experiment at the LHC. By combining the Λb0 and Λ ¯b0 samples under the assumption of CP conservation, the value of αb is measured to be 0.30±0.16(stat)±0.06(syst). This measurement provides a test of theoretical models based on perturbative QCD or heavy-quark effective theory.

 

Title:
Suppressing qubit dephasing using real-time Hamiltonian estimation
Authors:
Shulman, Michael D.; Harvey, Shannon P.; Nichol, John M.; Bartlett, Stephen D.; Doherty, Andrew C.; Umansky, Vladimir; Yacoby, Amir
Publication:
eprint arXiv:1405.0485
Publication Date:
05/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Mesoscale and Nanoscale Physics, Quantum Physics
Bibliographic Code:
2014arXiv1405.0485S

Abstract

Unwanted interaction between a quantum system and its fluctuating environment leads to decoherence and is the primary obstacle to establishing a scalable quantum information processing architecture. Strategies such as environmental and materials engineering, quantum error correction and dynamical decoupling can mitigate decoherence, but generally increase experimental complexity. Here we improve coherence in a qubit using real-time Hamiltonian parameter estimation. Using a rapidly converging Bayesian approach, we precisely measure the splitting in a singlet-triplet spin qubit faster than the surrounding nuclear bath fluctuates. We continuously adjust qubit control parameters based on this information, thereby improving the inhomogenously broadened coherence time ($T_{2}^{*}$) from tens of nanoseconds to above 2 $\mu$s and demonstrating the effectiveness of Hamiltonian estimation in reducing the effects of correlated noise in quantum systems. Because the technique demonstrated here is compatible with arbitrary qubit operations, it is a natural complement to quantum error correction and can be used to improve the performance of a wide variety of qubits in both metrological and quantum-information-processing applications.

 

Title:
Field-effect-induced two-dimensional electron gas utilizing modulation doping for improved ohmic contacts
Authors:
Mondal, Sumit; Gardner, Geoffrey C.; Watson, John D.; Fallahi, Saeed; Yacoby, Amir; Manfra, Michael J.
Publication:
eprint arXiv:1405.1273
Publication Date:
05/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Mesoscale and Nanoscale Physics
Comment:
8 pages, 3 figures
Bibliographic Code:
2014arXiv1405.1273M

Abstract

Modulation-doped AlGaAs/GaAs heterostructures are utilized extensively in the study of quantum transport in nanostructures, but charge fluctuations associated with remote ionized dopants often produce deleterious effects. Electric field-induced carrier systems offer an attractive alternative if certain challenges can be overcome. We demonstrate a field-effect transistor in which the active channel is locally devoid of modulation-doping, but silicon dopant atoms are retained in the ohmic contact region to facilitate reliable low-resistance contacts. A high quality two-dimensional electron gas is induced by a field-effect and is tunable over a wide range of density. Device design, fabrication, and low temperature (T= 0.3K) transport data are reported.

 

Title:
BICEP2 and the Central Charge of Holographic Inflation
Authors:
Larsen, Finn; Strominger, Andrew
Publication:
eprint arXiv:1405.1762
Publication Date:
05/2014
Origin:
ARXIV
Keywords:
High Energy Physics - Theory
Bibliographic Code:
2014arXiv1405.1762L

Abstract

Holographic inflation posits that the inflationary deSitter era of our universe is approximately described by a dual three-dimensional Euclidean CFT living on the spatial slice at the end of inflation. We point out that the BICEP2 results determine the central charge of this putative CFT to be given by $C_T=3 \times 10^8$.

 

Title:
Shaping Electromagnetic Fields
Authors:
Liu, Bo; Heller, Eric J.
Publication:
eprint arXiv:1405.2807
Publication Date:
05/2014
Origin:
ARXIV
Keywords:
Physics - Optics
Bibliographic Code:
2014arXiv1405.2807L

Abstract

The ability to control electromagnetic fields on the subwavelength scale could open exciting new venues in many fields of science. Transformation optics provides one way to attain such control through the local variation of the permittivity and permeability of a material. Here, we demonstrate another way to shape electromagnetic fields, taking advantage of the enormous size of the configuration space in combinatorial problems and the resonant scattering properties of metallic nanoparticles. Our design does not require the engineering of a material's electromagnetic properties and has relevance to the design of more flexible platforms for probing light-matter interaction and many body physics.

 

Title:
A Map of Dust Reddening to 4.5 kpc from Pan-STARRS1
Authors:
Schlafly, E. F.; Green, G.; Finkbeiner, D. P.; Juric, M.; Rix, H.-W.; Martin, N. F.; Burgett, W. S.; Chambers, K. C.; Draper, P. W.; Hodapp, K. W.; Kaiser, N.; Kudritzki, R.-P.; Magnier, E. A.; Metcalfe, N.; Morgan, J. S.; Price, P. A.; Stubbs, C. W.; Tonry, J. L.; Wainscoat, R. J.; Waters, C.
Publication:
eprint arXiv:1405.2922
Publication Date:
05/2014
Origin:
ARXIV
Keywords:
Astrophysics - Astrophysics of Galaxies
Comment:
10 pages, 7 figures, accepted for publication in ApJ
Bibliographic Code:
2014arXiv1405.2922S

Abstract

We present a map of the dust reddening to 4.5 kpc derived from Pan-STARRS1 stellar photometry. The map covers almost the entire sky north of declination -30 degrees at a resolution of 7' to 14', and is based on the estimated distances and reddenings to more than 500 million stars. The technique is designed to map dust in the Galactic plane, where many other techniques are stymied by the presence of multiple dust clouds at different distances along each line of sight. This reddening-based dust map agrees closely with the Schlegel, Finkbeiner, and Davis (SFD; 1998) far-infrared emission-based dust map away from the Galactic plane, and the most prominent differences between the two maps stem from known limitations of SFD in the plane. We also compare the map with Planck, finding likewise good agreement in general at high latitudes. The use of optical data from Pan-STARRS1 yields reddening uncertainty as low as 25 mmag E(B-V).

 

Title:
Ultrahigh Transmission Optical Nanofibers
Authors:
Hoffman, J. E.; Ravets, S.; Grover, J. A.; Solano, P.; Kordell, P. R.; Wong-Campos, J. D.; Orozco, L. A.; Rolston, S. L.
Publication:
eprint arXiv:1405.3258
Publication Date:
05/2014
Origin:
ARXIV
Keywords:
Physics - Optics, Physics - Atomic Physics
Comment:
32 pages, 10 figures, accepted to AIP Advances
Bibliographic Code:
2014arXiv1405.3258H

Abstract

We present a procedure for reproducibly fabricating ultrahigh transmission optical nanofibers (530 nm diameter and 84 mm stretch) with single-mode transmissions of 99.95 $ \pm$ 0.02%, which represents a loss from tapering of 2.6 $\,\times \,$ 10$^{-5}$ dB/mm when normalized to the entire stretch. When controllably launching the next family of higher-order modes on a fiber with 195 mm stretch, we achieve a transmission of 97.8 $\pm$ 2.8%, which has a loss from tapering of 5.0 $\,\times \,$ 10$^{-4}$ dB/mm when normalized to the entire stretch. Our pulling and transfer procedures allow us to fabricate optical nanofibers that transmit more than 400 mW in high vacuum conditions. These results, published as parameters in our previous work, present an improvement of two orders of magnitude less loss for the fundamental mode and an increase in transmission of more than 300% for higher-order modes, when following the protocols detailed in this paper. We extract from the transmission during the pull, the only reported spectrogram of a fundamental mode launch that does not include excitation to asymmetric modes; in stark contrast to a pull in which our cleaning protocol is not followed. These results depend critically on the pre-pull cleanliness and when properly following our pulling protocols are in excellent agreement with simulations.

 

Title:
Deleterious passengers in adapting populations
Authors:
Good, Benjamin H; Desai, Michael M
Publication:
eprint arXiv:1405.3902
Publication Date:
05/2014
Origin:
ARXIV
Keywords:
Quantitative Biology - Populations and Evolution
Bibliographic Code:
2014arXiv1405.3902G

Abstract

Most new mutations are deleterious and are eventually eliminated by natural selection. But in an adapting population, the rapid amplification of beneficial mutations can hinder the removal of deleterious variants in nearby regions of the genome, altering the patterns of sequence evolution. Here, we analyze the interactions between beneficial "driver" mutations and linked deleterious "passengers" during the course of adaptation. We derive analytical expressions for the substitution rate of a deleterious mutation as a function of its fitness cost, as well as the reduction in the beneficial substitution rate due to the genetic load of the passengers. We find that the fate of each deleterious mutation varies dramatically with the rate and spectrum of beneficial mutations, with a non-monotonic dependence on both the population size and the rate of adaptation. By quantifying this dependence, our results allow us to estimate which deleterious mutations will be likely to fix, and how many of these mutations must arise before the progress of adaptation is significantly reduced.

 

Title:
Compton Scattering from \nuc{6}{Li} at 86 MeV
Authors:
Myers, L. S.; Ahmed, M. W.; Feldman, G.; Kafkarkou, A.; Kendellen, D. P.; Mazumdar, I.; Mueller, J. M.; Sikora, M. H.; Weller, H. R.; Zimmerman, W. R.
Publication:
eprint arXiv:1405.5049
Publication Date:
05/2014
Origin:
ARXIV
Keywords:
Nuclear Experiment
Comment:
5 pages, 5 figures, submission to Phys. Rev. C
Bibliographic Code:
2014arXiv1405.5049M

Abstract

Cross sections for \nuc{6}{Li}($\gamma$,$\gamma$)\nuc{6}{Li} have been measured at the High Intensity Gamma-Ray Source (\HIGS) and the sensitivity of these cross sections to the nucleon isoscalar polarizabilities was studied. Data were collected using a quasi-monoenergetic 86 MeV photon beam at photon scattering angles of 40$^{\circ}$--160$^{\circ}$. These results are an extension of a previous measurement at a lower energy. The earlier work indicated that the \nuc{6}{Li}($\gamma$,$\gamma$)\nuc{6}{Li} reaction at 60 MeV provides a means of extracting the nucleon polarizabilities; this work demonstrates that the sensitivity of the cross section to the polarizabilities is increased at 86 MeV. A full theoretical treatment is needed to verify this conclusion and produce values of the polarizabilities.

 

Title:
Spin Squeezing by means of Driven Superradiance
Authors:
Wolfe, Elie; Yelin, S. F.
Publication:
eprint arXiv:1405.5288
Publication Date:
05/2014
Origin:
ARXIV
Keywords:
Quantum Physics, Mathematical Physics
Comment:
5+2 pages, 2 color figures. Includes analytic constructions of both the coupled first-order rate equations as well as the spin squeezing parameter explicitly in terms of the matrix elements. We appreciate and actively welcome all comments
Bibliographic Code:
2014arXiv1405.5288W

Abstract

We discuss the possibility of generating entanglement by means of driven superradiance. In an earlier paper [Phys. Rev. Lett. 112, 140402 (2014)] the authors determined that spontaneous purely-dissipative Dicke model superradiance failed to generate any entanglement over the course of the system's time evolution. In this article we show that by adding a driving field, however, the Dicke model system can be tuned to evolve into an entangled steady state. We discuss how to optimize the driving frequency to maximize the entanglement. We show that the resulting entanglement is fairly strong, in that it leads to spin squeezing.

 

Title:
A Construction of stable bundles and reflexive sheaves on Calabi-Yau threefolds
Authors:
Wu, Baosen; Yau, Shing Tung
Publication:
eprint arXiv:1405.5676
Publication Date:
05/2014
Origin:
ARXIV
Keywords:
Mathematics - Algebraic Geometry, High Energy Physics - Theory
Comment:
16 pages
Bibliographic Code:
2014arXiv1405.5676W

Abstract

We use Serre construction and deformation to construct stable bundles and reflexive sheaves on Calabi-Yau threefolds.

 

Title:
Mobile magnetic impurities in a Fermi superfluid: a route to designer molecules
Authors:
Gopalakrishnan, Sarang; Parker, Colin V.; Demler, Eugene
Publication:
eprint arXiv:1405.6717
Publication Date:
05/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Quantum Gases, Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Superconductivity, Quantum Physics
Comment:
5pp., 4 figures, plus appendix
Bibliographic Code:
2014arXiv1405.6717G

Abstract

A magnetic impurity in a fermionic superfluid hosts bound quasiparticle states known as Yu-Shiba-Rusinov (YSR) states. We argue here that, if the impurity is mobile (i.e., has a finite mass), the impurity and its bound YSR quasiparticle move together as a midgap molecule, which has an unusual "Mexican-hat" dispersion that is tunable via the fermion density. We map out the impurity dispersion, which consists of an "atomic" branch (in which the impurity is dressed by quasiparticle pairs) and a "molecular" branch (in which the impurity binds a quasiparticle). We discuss the experimental realization and detection of midgap Shiba molecules, focusing on lithium-cesium mixtures, and comment on the prospects they offer for realizing exotic many-body states.

 

Title:
A Synopsis of the Minimal Modal Interpretation of Quantum Theory
Authors:
Barandes, Jacob A.; Kagan, David
Publication:
eprint arXiv:1405.6754
Publication Date:
05/2014
Origin:
ARXIV
Keywords:
Quantum Physics, General Relativity and Quantum Cosmology
Comment:
7 pages + references, 2 figures; cosmetic changes, added figure, updated references, generalized conditional probabilities with attendant changes to the section on Lorentz invariance; this letter summarizes the more comprehensive companion paper at arXiv:1405.6755
Bibliographic Code:
2014arXiv1405.6754B

Abstract

We summarize a new realist interpretation of quantum theory that builds on the existing physical structure of the theory and allows experiments to have definite outcomes, but leaves the theory's basic dynamical content essentially intact. Much as classical systems have specific states that evolve along definite trajectories through configuration spaces, the traditional formulation of quantum theory asserts that closed quantum systems have specific states that evolve unitarily along definite trajectories through Hilbert spaces, and our interpretation extends this intuitive picture of states and Hilbert-space trajectories to the case of open quantum systems as well. Our interpretation---which we claim is ultimately compatible with Lorentz invariance---reformulates wave-function collapse in terms of an underlying interpolating dynamics, makes it possible to derive the Born rule from deeper principles, and resolves several open questions regarding ontological stability and dynamics.

 

Title:
The Minimal Modal Interpretation of Quantum Theory
Authors:
Barandes, Jacob A.; Kagan, David
Publication:
eprint arXiv:1405.6755
Publication Date:
05/2014
Origin:
ARXIV
Keywords:
Quantum Physics, General Relativity and Quantum Cosmology
Comment:
73 pages + references, 9 figures; cosmetic changes, added figure, updated references, generalized conditional probabilities with attendant changes to the sections on the EPR-Bohm thought experiment and Lorentz invariance; for a concise summary, see the companion letter at arXiv:1405.6754
Bibliographic Code:
2014arXiv1405.6755B

Abstract

We introduce a realist, unextravagant interpretation of quantum theory that builds on the existing physical structure of the theory and allows experiments to have definite outcomes, but leaves the theory's basic dynamical content essentially intact. Much as classical systems have specific states that evolve along definite trajectories through configuration spaces, the traditional formulation of quantum theory asserts that closed quantum systems have specific states that evolve unitarily along definite trajectories through Hilbert spaces, and our interpretation extends this intuitive picture of states and Hilbert-space trajectories to the case of open quantum systems as well. We provide independent justification for the partial-trace operation for density matrices, reformulate wave-function collapse in terms of an underlying interpolating dynamics, derive the Born rule from deeper principles, resolve several open questions regarding ontological stability and dynamics, address a number of familiar no-go theorems, and argue that our interpretation is ultimately compatible with Lorentz invariance. Along the way, we also investigate a number of unexplored features of quantum theory, including an interesting geometrical structure---which we call subsystem space---that we believe merits further study. We include an appendix that briefly reviews the traditional Copenhagen interpretation and the measurement problem of quantum theory, as well as the instrumentalist approach and a collection of foundational theorems not otherwise discussed in the main text.

 

Title:
Structural stability and electronic properties of low-index surfaces of SnS
Authors:
Tritsaris, Georgios A.; Malone, Brad D.; Kaxiras, Efthimios
Publication:
Journal of Applied Physics, Volume 115, Issue 17, id.173702 (JAP Homepage)
Publication Date:
05/2014
Origin:
AIP
Abstract Copyright:
2014: AIP Publishing LLC
DOI:
10.1063/1.4874775
Bibliographic Code:
2014JAP...115q3702T

Abstract

Thin film photovoltaic cells are increasingly important for cost-effective solar energy harvesting. Layered SnS is a promising absorber material due to its high optical absorption in the visible and good doping characteristics. We use first-principles calculations based on density functional theory to study structures of low-index surfaces of SnS using stoichiometric and oxygen-containing structural models, in order to elucidate their possible effect on the efficiency of the photovoltaic device. We find that the surface energy is minimized for the surface with orientation parallel to the layer stacking direction. Compared to stoichiometric surfaces, the oxygen-containing surfaces exhibit fewer electronic states near the band gap. This reduction of near-gap surface states by oxygen should reduce recombination losses at grain boundaries and interfaces of the SnS absorber, and should be beneficial to the efficiency of the solar cell.

 

Title:
Tangles, generalized Reidemeister moves, and three-dimensional mirror symmetry
Authors:
Córdova, Clay; Espahbodi, Sam; Haghighat, Babak; Rastogi, Ashwin; Vafa, Cumrun
Publication:
Journal of High Energy Physics, Volume 2014, article id. #14
Publication Date:
05/2014
Origin:
SPRINGER
Keywords:
Supersymmetry and Duality, Field Theories in Lower Dimensions, Extended Supersymmetry, M-Theory
Abstract Copyright:
(c) 2014: The Author(s)
DOI:
10.1007/JHEP05(2014)014
Bibliographic Code:
2014JHEP...05..014C

Abstract

Three-dimensional = 2 superconformal field theories are constructed by compactifying M5-branes on three-manifolds. In the infrared the branes recombine, and the physics is captured by a single M5-brane on a branched cover of the original ultraviolet geometry. The branch locus is a tangle, a one-dimensional knotted submanifold of the ultraviolet geometry. A choice of branch sheet for this cover yields a Lagrangian for the theory, and varying the branch sheet provides dual descriptions. Massless matter arises from vanishing size M2-branes and appears as singularities of the tangle where branch lines collide. Massive deformations of the field theory correspond to resolutions of singularities resulting in distinct smooth manifolds connected by geometric transitions. A generalization of Reidemeister moves for singular tangles captures mirror symmetries of the underlying theory yielding a geometric framework where dualities are manifest.

 

Title:
On the classification of 6D SCFTs and generalized ADE orbifolds
Authors:
Heckman, Jonathan J.; Morrison, David R.; Vafa, Cumrun
Publication:
Journal of High Energy Physics, Volume 2014, article id. #28
Publication Date:
05/2014
Origin:
SPRINGER
Keywords:
F-Theory, Differential and Algebraic Geometry, Field Theories in Higher Dimensions
Abstract Copyright:
(c) 2014: The Author(s)
DOI:
10.1007/JHEP05(2014)028
Bibliographic Code:
2014JHEP...05..028H

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 ℂ2/Γ with Γ a discrete subgroup of U(2). When Γ 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 Γ 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:
Exact results for five-dimensional superconformal field theories with gravity duals
Authors:
Jafferis, Daniel L.; Pufu, Silviu S.
Publication:
Journal of High Energy Physics, Volume 2014, article id. #32
Publication Date:
05/2014
Origin:
SPRINGER
Keywords:
Matrix Models, Supersymmetric gauge theory, AdS-CFT Correspondence, Extended Supersymmetry
Abstract Copyright:
(c) 2014: The Author(s)
DOI:
10.1007/JHEP05(2014)032
Bibliographic Code:
2014JHEP...05..032J

Abstract

We apply the technique of supersymmetric localization to exactly compute the S 5 partition function of several large N superconformal field theories in five dimensions that have AdS6 duals in massive type IIA supergravity. The localization computations are performed in the non-renormalizable effective field theories obtained through relevant deformations of the UV superconformal field theories. We compare the S 5 free energy to a holographic computation of entanglement entropy in the AdS6 duals and find perfect agreement. In particular, we reproduce the N 5/2 scaling of the S 5 free energy that was expected from supergravity.

 

Title:
The dynamics of quantum criticality revealed by quantum Monte Carlo and holography
Authors:
Witczak-Krempa, William; Sørensen, Erik S.; Sachdev, Subir
Publication:
Nature Physics, Volume 10, Issue 5, pp. 361-366 (2014).
Publication Date:
05/2014
Origin:
NATURE
Abstract Copyright:
(c) 2014: Nature Publishing Group
DOI:
10.1038/nphys2913
Bibliographic Code:
2014NatPh..10..361W

Abstract

Understanding the dynamics of quantum systems without long-lived excitations (quasiparticles) constitutes an important yet challenging problem. Although numerical techniques can yield results for the dynamics in imaginary time, their reliable continuation to real time has proved difficult. We tackle this issue using the superfluid-insulator quantum critical point of bosons on a two-dimensional lattice, where quantum fluctuations destroy quasiparticles. We present quantum Monte Carlo simulations for two separate lattice realizations. Their low-frequency conductivities turn out to have the same universal dependence on imaginary frequency and temperature. Using the structure of the real-time dynamics of conformal field theories described by the holographic gauge/gravity duality, we then make progress on the problem of analytically continuing the numerical data to real time. Our method yields quantitative and experimentally testable results on the frequency-dependent conductivity near the quantum critical point. Extensions to other observables and universality classes are discussed.

 

Title:
Search for Higgs boson decays to a photon and a Z boson in pp collisions at s=7 and 8 TeV with the ATLAS detector
Authors:
Aad, G.; Abajyan, T.; Abbott, B.;... ; Franklin, M.;... Guimarães da Costa, J.;... Huth, J.;...; Morii, M.; and 2898 coauthors
Publication:
Physics Letters B, Volume 732, p. 8-27.
Publication Date:
05/2014
Origin:
ELSEVIER
Abstract Copyright:
The Authors
DOI:
10.1016/j.physletb.2014.03.015
Bibliographic Code:
2014PhLB..732....8A

Abstract

A search is reported for a neutral Higgs boson in the decay channel H→Zγ, Z→ℓ+ (ℓ=e,μ), using 4.5 fb‑1 of pp collisions at s=7 TeV and 20.3 fb‑1 of pp collisions at s=8 TeV, recorded by the ATLAS detector at the CERN Large Hadron Collider. The observed distribution of the invariant mass of the three final-state particles, m, is consistent with the Standard Model hypothesis in the investigated mass range of 120–150 GeV. For a Higgs boson with a mass of 125.5 GeV, the observed upper limit at the 95% confidence level is 11 times the Standard Model expectation. Upper limits are set on the cross section times branching ratio of a neutral Higgs boson with mass in the range 120–150 GeV between 0.13 and 0.5 pb for s=8 TeV at 95% confidence level.

 

Title:
Invariant-mass distribution of jet pairs produced in association with a W boson in pp ¯ collisions at √s =1.96 TeV using the full CDF Run II data set
Authors:
Aaltonen, T.; Amerio, S.; Amidei, D.;... ... Franklin, M.;... ; Guimaraes da Costa, J.;... and 403 coauthors
Publication:
Physical Review D, Volume 89, Issue 9, id.092001 (PhRvD Homepage)
Publication Date:
05/2014
Origin:
APS
PACS Keywords:
Applications of electroweak models to specific processes, Experimental tests, Other particles
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevD.89.092001
Bibliographic Code:
2014PhRvD..89i2001A

Abstract

We report on a study of the dijet invariant-mass distribution in events with one identified lepton, a significant imbalance in the total event transverse momentum, and two jets. This distribution is sensitive to the possible production of a new particle in association with a W boson, where the boson decays leptonically. We use the full data set of proton-antiproton collisions at 1.96 TeV center-of-mass energy collected by the Collider Detector at the Fermilab Tevatron, corresponding to an integrated luminosity of 8.9 fb-1. The data are found to be consistent with standard model expectations, and a 95% confidence level upper limit is set on the production cross section of a W boson in association with a new particle decaying into two jets.

 

Title:
Cross sections for the reactions e+e-→KS0KL0, KS0KL0π+π-, KS0KS0π+π-, and KS0KS0K+K- from events with initial-state radiation
Authors:
Lees, J. P.; Poireau, V.; Tisserand, V.;... ... Morii, M.;... and 310 coauthors (Babar Collaboration)
Publication:
Physical Review D, Volume 89, Issue 9, id.092002 (PhRvD Homepage)
Publication Date:
05/2014
Origin:
APS
PACS Keywords:
Hadron production in e-e+ interactions, Decays of other mesons, Mesons
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevD.89.092002
Bibliographic Code:
2014PhRvD..89i2002L

Abstract

We study the processes e+e-→KS0KL0γ, KS0KL0π+π-γ, KS0KS0π+π-γ, and KS0KS0K+K-γ, where the photon is radiated from the initial state, providing cross section measurements for the hadronic states over a continuum of center-of-mass energies. The results are based on 469 fb-1 of data collected with the BABAR detector at SLAC. We observe the ϕ(1020) resonance in the KS0KL0 final state and measure the product of its electronic width and branching fraction with about 3% uncertainty. We present a measurement of the e +e-→KS0KL0 cross section in the energy range from 1.06 to 2.2 GeV and observe the production of a resonance at 1.67 GeV. We present the first measurements of the e+e-→KS0KL0π+π-, KS0KS0π+π-, and KS0KS0K+K- cross sections and study the intermediate resonance structures. We obtain the first observations of J/ψ decay to the KS0KL0π +π-, KS0KS0π+π-, and KS0KS0K+K- final states.

 

Title:
Combined Analysis of νμ Disappearance and νμ→νe Appearance in MINOS Using Accelerator and Atmospheric Neutrinos
Authors:
Adamson, P.; Anghel, I.; Aurisano, A.;... Feldman, G. J.;... and 85 coauthors (Minos Collaboration)
Publication:
Physical Review Letters, Volume 112, Issue 19, id.191801 (PhRvL Homepage)
Publication Date:
05/2014
Origin:
APS
PACS Keywords:
Neutrino mass and mixing
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevLett.112.191801
Bibliographic Code:
2014PhRvL.112s1801A

Abstract

We report on a new analysis of neutrino oscillations in MINOS using the complete set of accelerator and atmospheric data. The analysis combines the νμ disappearance and νe appearance data using the three-flavor formalism. We measure |Δm322|=[2.28-2.46]×10-3 eV2 (68% C.L.) and sin2θ23=0.35-0.65 (90% C.L.) in the normal hierarchy, and |Δm322|=[2.32-2.53]×10-3 eV2 (68% C.L.) and sin2θ23=0.34-0.67 (90% C.L.) in the inverted hierarchy. The data also constrain δCP, the θ23 octant degeneracy and the mass hierarchy; we disfavor 36% (11%) of this three-parameter space at 68% (90%) C.L.

 

Title:
Search for Invisible Decays of a Higgs Boson Produced in Association with a Z Boson in ATLAS
Authors:
Aad, G.; Abajyan, T.; Abbott, B.;... ; Franklin, M.;... Guimarães da Costa, J.;... Huth, J.;...; Morii, M.; and 2912 coauthors
Publication:
Physical Review Letters, Volume 112, Issue 20, id.201802 (PhRvL Homepage)
Publication Date:
05/2014
Origin:
APS
PACS Keywords:
Standard-model Higgs bosons, Extensions of electroweak Higgs sector, Dark matter
Abstract Copyright:
2014: CERN
DOI:
10.1103/PhysRevLett.112.201802
Bibliographic Code:
2014PhRvL.112t1802A

Abstract

A search for evidence of invisible-particle decay modes of a Higgs boson produced in association with a Z boson at the Large Hadron Collider is presented. No deviation from the standard model expectation is observed in 4.5 fb-1 (20.3 fb-1) of 7 (8) TeV pp collision data collected by the ATLAS experiment. Assuming the standard model rate for ZH production, an upper limit of 75%, at the 95% confidence level is set on the branching ratio to invisible-particle decay modes of the Higgs boson at a mass of 125.5 GeV. The limit on the branching ratio is also interpreted in terms of an upper limit on the allowed dark matter-nucleon scattering cross section within a Higgs-portal dark matter scenario. Within the constraints of such a scenario, the results presented in this Letter provide the strongest available limits for low-mass dark matter candidates. Limits are also set on an additional neutral Higgs boson, in the mass range 110<mH<400 GeV, produced in association with a Z boson and decaying to invisible particles.

 


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