Faculty Publications: December, 2014

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Title:
Quantifying the power of multiple event interpretations
Authors:
Chien, Yang-Ting; Farhi, David; Krohn, David; Marantan, Andrew; Mateos, David Lopez; Schwartz, Matthew
Publication:
Journal of High Energy Physics, Volume 2014, article id. #140, 14 pp.
Publication Date:
12/2014
Origin:
SPRINGER
Keywords:
Jets
Abstract Copyright:
(c) 2014: The Author(s)
DOI:
10.1007/JHEP12(2014)140
Bibliographic Code:
2014JHEP...12..140C

Abstract

A number of methods have been proposed recently which exploit multiple highly-correlated interpretations of events, or of jets within an event. For example, Qjets reclusters a jet multiple times and telescoping jets uses multiple cone sizes. Previous work has employed these methods in pseudo-experimental analyses and found that, with a simplified statistical treatment, they give sizable improvements over traditional methods. In this paper, the improvement gain from multiple event interpretations is explored with methods much closer to those used in real experiments. To this end, we derive and study a generalized extended maximum likelihood procedure, and find that using multiple jet radii can provide substantial benefit over a single radius in fitting procedures. Another major concern we address is that multiple event interpretations might be exploiting similar information to that already present in the standard kinematic variables. We perform multivariate analyses (boosted decision trees) on a set of standard kinematic variables, a single observable computed with several different cone sizes, and both sets combined. We find that using multiple radii is still helpful even on top of standard kinematic variables (providing a 12% improvement at low p T and 20% at high p T ). These results suggest that including multiple event interpretations in a realistic search for Higgs to would give additional sensitivity over traditional approaches.

 

Title:
Little string amplitudes (and the unreasonable effectiveness of 6D SYM)
Authors:
Chang, Chi-Ming; Lin, Ying-Hsuan; Shao, Shu-Heng; Wang, Yifan; Yin, Xi
Publication:
Journal of High Energy Physics, Volume 2014, article id. #176, 52 pp.
Publication Date:
12/2014
Origin:
SPRINGER
Keywords:
Supersymmetric gauge theory, Gauge-gravity correspondence, Scattering Amplitudes
Abstract Copyright:
(c) 2014: The Author(s)
DOI:
10.1007/JHEP12(2014)176
Bibliographic Code:
2014JHEP...12..176C

Abstract

We study tree level scattering amplitudes of four massless states in the double scaled little string theory, and compare them to perturbative loop amplitudes in six-dimensional super-Yang-Mills theory. The little string amplitudes are computed from correlators in the cigar coset CFT and in = 2 minimal models. The results are expressed in terms of integrals of conformal blocks and evaluated numerically in the alpha ' expansion. We find striking agreements with up to 2-loop scattering amplitudes of massless gluons in 6D SU( k) SYM at a Z k invariant point on the Coulomb branch. We comment on the issue of UV divergence at higher loop orders in the gauge theory and discuss the implication of our results.

 

Title:
Force-free electrodynamics around extreme Kerr black holes
Authors:
Lupsasca, Alexandru; Rodriguez, Maria J.; Strominger, Andrew
Publication:
Journal of High Energy Physics, Volume 2014, article id. #185, 23 pp.
Publication Date:
12/2014
Origin:
SPRINGER
Keywords:
Black Holes, Conformal and W Symmetry, Integrable Equations in Physics
Abstract Copyright:
(c) 2014: The Author(s)
DOI:
10.1007/JHEP12(2014)185
Bibliographic Code:
2014JHEP...12..185L

Abstract

Plasma-filled magnetospheres can extract energy from a spinning black hole and provide the power source for a variety of observed astrophysical phenomena. These magnetospheres are described by the highly nonlinear equations of force-free electrodynamics, or FFE. Typically these equations can only be solved numerically. In this paper we consider the FFE equations very near the horizon of a maximally spinning black hole, where the energy extraction takes place. Thanks to an enhanced conformal symmetry which appears in this near-horizon region, we are able to analytically obtain several infinite families of exact solutions of the full nonlinear equations.

 

Title:
Measurement of indirect C P -violating asymmetries in D0-->K+K- and D0-->pi+pi- decays at CDF
Authors:
Aaltonen, T.; Amerio, S.; Amidei, D.;... Franklin, M.;... Guimaraes da Costa, J.;... .; and 397 coauthors
Publication:
Physical Review D, Volume 90, Issue 11, id.111103 (PhRvD Homepage)
Publication Date:
12/2014
Origin:
APS
PACS Keywords:
Decays of charmed mesons, Charge conjugation parity time reversal and other discrete symmetries, Charmed mesons
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevD.90.111103
Bibliographic Code:
2014PhRvD..90k1103A

Abstract

We report a measurement of the indirect C P -violating asymmetries (AGamma ) between effective lifetimes of anticharm and charm mesons reconstructed in D0-->K+K- and D0-->pi+pi- decays. We use the full data set of proton-antiproton collisions collected by the Collider Detector at Fermilab experiment and corresponding to 9.7 fb-1 of integrated luminosity. The strong-interaction decay D*+-->D0pi+ is used to identify the meson at production as D0 or D¯ 0 . We statistically subtract D0 and D¯ 0 mesons originating from b -hadron decays and measure the yield asymmetry between anticharm and charm decays as a function of decay time. We measure AGamma(K+K-)=(-0.19 ±0.15 (stat)±0.04 (syst))% and AGamma(pi+pi-)=(-0.01 ±0.18 (stat)±0.03 (syst))% . The results are consistent with the hypothesis of C P symmetry and their combination yields AGamma=(-0.12 ±0.12 )%.

 

Title:
Measurement of the Single Top Quark Production Cross Section and |Vt b| in Events with One Charged Lepton, Large Missing Transverse Energy, and Jets at CDF
Authors:
Aaltonen, T.; Amerio, S.; Amidei, D.;... Franklin, M.;... Guimaraes da Costa, J.;... .; and 398 coauthors
Publication:
Physical Review Letters, Volume 113, Issue 26, id.261804 (PhRvL Homepage)
Publication Date:
12/2014
Origin:
APS
PACS Keywords:
Top quarks, Determination of Kobayashi-Maskawa matrix elements, Applications of electroweak models to specific processes, Inclusive production with identified leptons photons or other nonhadronic particles
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevLett.113.261804
Bibliographic Code:
2014PhRvL.113z1804A

Abstract

We report a measurement of single top quark production in proton-antiproton collisions at a center-of-mass energy of &surd;{s }=1.96 TeV using a data set corresponding to 7.5 fb-1 of integrated luminosity collected by the Collider Detector at Fermilab. We select events consistent with the single top quark decay process t -->W b -->lnu b by requiring the presence of an electron or muon, a large imbalance of transverse momentum indicating the presence of a neutrino, and two or three jets including at least one originating from a bottom quark. An artificial neural network is used to discriminate the signal from backgrounds. We measure a single top quark production cross section of 3.0 4-0.53+0.57 pb and set a lower limit on the magnitude of the coupling between the top quark and bottom quark |Vt b|>0.78 at the 95% credibility level.

 

Title:
Conceptual question response times in Peer Instruction classrooms
Authors:
Miller, Kelly; Lasry, Nathaniel; Lukoff, Brian; Schell, Julie; Mazur, Eric
Publication:
Physical Review Special Topics - Physics Education Research, Volume 10, Issue 2, id.020113
Publication Date:
12/2014
Origin:
APS
PACS Keywords:
Research in physics education
Abstract Copyright:
2014: authors
DOI:
10.1103/PhysRevSTPER.10.020113
Bibliographic Code:
2014PRSTP..10b0113M

Abstract

Classroom response systems are widely used in interactive teaching environments as a way to engage students by asking them questions. Previous research on the time taken by students to respond to conceptual questions has yielded insights on how students think and change conceptions. We measure the amount of time students take to respond to in-class, conceptual questions [ConcepTests (CTs)] in two introductory physics courses taught using Peer Instruction and use item response theory to determine the difficulty of the CTs. We examine response time differences between correct and incorrect answers both before and after the peer discussion for CTs of varying difficulty. We also determine the relationship between response time and student performance on a standardized test of incoming physics knowledge, precourse self-efficacy, and gender. Our data reveal three results of interest. First, response time for correct answers is significantly faster than for incorrect answers, both before and after peer discussion, especially for easy CTs. Second, students with greater incoming physics knowledge and higher self-efficacy respond faster in both rounds. Third, there is no gender difference in response rate after controlling for incoming physics knowledge scores, although males register significantly more attempts before committing to a final answer than do female students. These results provide insight into effective CT pacing during Peer Instruction. In particular, in order to maintain a pace that keeps everyone engaged, students should not be given too much time to respond. When around 80% of the answers are in, the ratio of correct to incorrect responses rapidly approaches levels indicating random guessing and instructors should close the poll.

 

Title:
Fusing E-strings to heterotic strings: E +E -->H
Authors:
Haghighat, Babak; Lockhart, Guglielmo; Vafa, Cumrun
Publication:
Physical Review D, Volume 90, Issue 12, id.126012 (PhRvD Homepage)
Publication Date:
12/2014
Origin:
APS
PACS Keywords:
M theory
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevD.90.126012
Bibliographic Code:
2014PhRvD..90l6012H

Abstract

E-strings arise from M2 branes suspended between an M5 brane and an M9 plane. In this paper we obtain explicit expressions for the elliptic genus of two E-strings using a series of string dualities. Moreover we show how this can be used to recover the elliptic genus of two E8×E8 heterotic strings using the Horava-Witten realization of heterotic strings in M-theory. This involves highly nontrivial identities among Jacobi forms and is remarkable in light of the fact that E-strings are "sticky" and form bound states whereas heterotic strings do not form bound states.

 

Title:
High Efficiency Positron Accumulation for High-Precision Measurements
Authors:
Fogwell Hoogerheide, S.; Dorr, J. C.; Novitski, E.; Gabrielse, G.
Publication:
eprint arXiv:1501.00096
Publication Date:
12/2014
Origin:
ARXIV
Keywords:
Physics - Instrumentation and Detectors, Physics - Atomic Physics
Comment:
7 pages, 9 figures
Bibliographic Code:
2015arXiv150100096F

Abstract

Positrons are accumulated within a Penning trap designed to make more precise measurements of the positron and electron magnetic moments. The retractable radioactive source used is weak enough to require no license for handling radioactive material and the radiation dosage one meter from the source gives an exposure several times smaller than the average radiation dose on the earth's surface. The 100 mK trap is mechanically aligned with the 4.2 K superconducting solenoid that produces a 6 tesla magnetic trapping field with a direct mechanical coupling.

 

Title:
The enigma of the pseudogap phase of the cuprate superconductors
Authors:
Chowdhury, Debanjan; Sachdev, Subir
Publication:
eprint arXiv:1501.00002
Publication Date:
12/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Superconductivity
Comment:
37 pages, 19 figures, 100+ references. Proceedings of the 50th Karpacz Winter School of Theoretical Physics, 2-9 March 2014, Karpacz, Poland
Bibliographic Code:
2015arXiv150100002C

Abstract

The last few years have seen significant experimental progress in characterizing the copper-based hole-doped high temperature superconductors in the regime of low hole density, p. Quantum oscillations, NMR, X-ray, and STM experiments have shed much light on the nature of the ordering at low temperatures. We review evidence that the order parameter in the non-Lanthanum-based cuprates is a d-form factor density-wave. This novel order acts as an unexpected window into the electronic structure of the pseudogap phase at higher temperatures in zero field: we argue in favor of a `fractionalized Fermi liquid' (FL*) with 4 pockets of spin S=1/2, charge +e fermions enclosing an area specified by p.

 

Title:
Neuromimetic Circuits with Synaptic Devices Based on Strongly Correlated Electron Systems
Authors:
Ha, Sieu D.; Shi, Jian; Meroz, Yasmine; Mahadevan, L.; Ramanathan, Shriram
Publication:
Physical Review Applied, Volume 2, Issue 6, id.064003
Publication Date:
12/2014
Origin:
APS
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevApplied.2.064003
Bibliographic Code:
2014PhRvP...2f4003H

Abstract

Strongly correlated electron systems such as the rare-earth nickelates (R NiO3 , R denotes a rare-earth element) can exhibit synapselike continuous long-term potentiation and depression when gated with ionic liquids; exploiting the extreme sensitivity of coupled charge, spin, orbital, and lattice degrees of freedom to stoichiometry. We present experimental real-time, device-level classical conditioning and unlearning using nickelate-based synaptic devices in an electronic circuit compatible with both excitatory and inhibitory neurons. We establish a physical model for the device behavior based on electric-field-driven coupled ionic-electronic diffusion that can be utilized for design of more complex systems. We use the model to simulate a variety of associate and nonassociative learning mechanisms, as well as a feedforward recurrent network for storing memory. Our circuit intuitively parallels biological neural architectures, and it can be readily generalized to other forms of cellular learning and extinction. The simulation of neural function with electronic device analogs may provide insight into biological processes such as decision making, learning, and adaptation, while facilitating advanced parallel information processing in hardware.

 

Title:
All-Optical Initialization, Readout, and Coherent Preparation of Single Silicon-Vacancy Spins in Diamond
Authors:
Rogers, Lachlan J.; Jahnke, Kay D.; Metsch, Mathias H.; Sipahigil, Alp; Binder, Jan M.; Teraji, Tokuyuki; Sumiya, Hitoshi; Isoya, Junichi; Lukin, Mikhail D.; Hemmer, Philip; Jelezko, Fedor
Publication:
Physical Review Letters, Volume 113, Issue 26, id.263602 (PhRvL Homepage)
Publication Date:
12/2014
Origin:
APS
PACS Keywords:
Effects of atomic coherence on propagation absorption and amplification of light, electromagnetically induced transparency and absorption, Quantum computation, Optical implementations of quantum information processing and transfer, Color centers
Abstract Copyright:
2014: authors
DOI:
10.1103/PhysRevLett.113.263602
Bibliographic Code:
2014PhRvL.113z3602R

Abstract

The silicon-vacancy (SiV- ) color center in diamond has attracted attention because of its unique optical properties. It exhibits spectral stability and indistinguishability that facilitate efficient generation of photons capable of demonstrating quantum interference. Here we show optical initialization and readout of electronic spin in a single SiV- center with a spin relaxation time of T1=2.4 ±0.2 ms . Coherent population trapping (CPT) is used to demonstrate coherent preparation of dark superposition states with a spin coherence time of T2*=35 ±3 ns . This is fundamentally limited by orbital relaxation, and an understanding of this process opens the way to extend coherence by engineering interactions with phonons. Hyperfine structure is observed in CPT measurements with the <mml:mmultiscripts>Si 29 </mml:mmultiscripts> isotope which allows access to nuclear spin. These results establish the SiV- center as a solid-state spin-photon interface.

 

Title:
Many-Body Localization in Dipolar Systems
Authors:
Yao, N. Y.; Laumann, C. R.; Gopalakrishnan, S.; Knap, M.; Müller, M.; Demler, E. A.; Lukin, M. D.
Publication:
Physical Review Letters, Volume 113, Issue 24, id.243002 (PhRvL Homepage)
Publication Date:
12/2014
Origin:
APS
PACS Keywords:
Ultracold gases trapped gases, Boson systems, Lattice fermion models, Weak or Anderson localization
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevLett.113.243002
Bibliographic Code:
2014PhRvL.113x3002Y

Abstract

Systems of strongly interacting dipoles offer an attractive platform to study many-body localized phases, owing to their long coherence times and strong interactions. We explore conditions under which such localized phases persist in the presence of power-law interactions and supplement our analytic treatment with numerical evidence of localized states in one dimension. We propose and analyze several experimental systems that can be used to observe and probe such states, including ultracold polar molecules and solid-state magnetic spin impurities.

 

Title:
Measurements of Direct C P -Violating Asymmetries in Charmless Decays of Bottom Baryons
Authors:
Aaltonen, T.; Amerio, S.; Amidei, D....; Franklin, M.;... Guimaraes da Costa, J.;.. ; and 403 coauthors.
Publication:
Physical Review Letters, Volume 113, Issue 24, id.242001 (PhRvL Homepage)
Publication Date:
12/2014
Origin:
APS
PACS Keywords:
Bottom baryons, Bottom mesons, Charge conjugation parity time reversal and other discrete symmetries
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevLett.113.242001
Bibliographic Code:
2014PhRvL.113x2001A

Abstract

We report final measurements of direct C P -violating asymmetries in charmless decays of neutral bottom hadrons to pairs of charged hadrons with the upgraded Collider Detector at the Fermilab Tevatron. Using the complete &surd;{s }=1.96 TeV proton-antiproton collisions data set, corresponding to 9.3 fb-1 of integrated luminosity, we measure A (Lambdab0-->p pi- )=+0.06 ±0.07 (stat)±0.03 (syst) and A (Lambdab0-->p K- )=-0.10 ±0.08 (stat)±0.04 (syst) , compatible with no asymmetry. In addition we measure the C P -violating asymmetries in Bs0-->K-pi+ and B0-->K+pi- decays to be A (Bs0-->K-pi+ )=+0.22 ±0.07 (stat)±0.02 (syst) and A (B0-->K+pi- )=-0.083 ±0.013 (stat)±0.004 (syst), respectively, which are significantly different from zero and consistent with current world averages.

 

Title:
Consistent Use of the Standard Model Effective Potential
Authors:
Andreassen, Anders; Frost, William; Schwartz, Matthew D.
Publication:
Physical Review Letters, Volume 113, Issue 24, id.241801 (PhRvL Homepage)
Publication Date:
12/2014
Origin:
APS
PACS Keywords:
Electroweak radiative corrections, Spontaneous and radiative symmetry breaking
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevLett.113.241801
Bibliographic Code:
2014PhRvL.113x1801A

Abstract

The stability of the standard model is determined by the true minimum of the effective Higgs potential. We show that the potential at its minimum when computed by the traditional method is strongly dependent on the gauge parameter. It moreover depends on the scale where the potential is calculated. We provide a consistent method for determining absolute stability independent of both gauge and calculation scale, order by order in perturbation theory. This leads to a revised stability bounds mhpole>(129.4 ±2.3 ) GeV and mtpole<(171.2 ±0.3 ) GeV . We also show how to evaluate the effect of new physics on the stability bound without resorting to unphysical field values.

 

Title:
Absence of red structural color in photonic glasses, bird feathers, and certain beetles
Authors:
Magkiriadou, Sofia; Park, Jin-Gyu; Kim, Young-Seok; Manoharan, Vinothan N.
Publication:
Physical Review E, Volume 90, Issue 6, id.062302 (PhRvE Homepage)
Publication Date:
12/2014
Origin:
APS
PACS Keywords:
Colloids, Multilayers, superlattices, Diffraction and scattering, Wave propagation in random media
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevE.90.062302
Bibliographic Code:
2014PhRvE..90f2302M

Abstract

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

 

Title:
Measurements of spin correlation in top-antitop quark events from 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 2877 coauthors
Publication:
Physical Review D, Volume 90, Issue 11, id.112016 (PhRvD Homepage)
Publication Date:
12/2014
Origin:
APS
PACS Keywords:
Top quarks, Experimental tests, Inclusive production with identified leptons photons or other nonhadronic particles
Abstract Copyright:
2014: CERN
DOI:
10.1103/PhysRevD.90.112016
Bibliographic Code:
2014PhRvD..90k2016A

Abstract

Measurements of spin correlation in top quark pair production are presented using data collected with the ATLAS detector at the LHC with proton-proton collisions at a center-of-mass energy of 7 TeV, corresponding to an integrated luminosity of 4.6 fb-1. Events are selected in final states with two charged leptons and at least two jets and in final states with one charged lepton and at least four jets. Four different observables sensitive to different properties of the top quark pair production mechanism are used to extract the correlation between the top and antitop quark spins. Some of these observables are measured for the first time. The measurements are in good agreement with the Standard Model prediction at next-to-leading-order accuracy.

 

Title:
Measurement of Higgs boson production in the diphoton decay channel in p p collisions at center-of-mass energies of 7 and 8 TeV with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.; ... Barreiro Guimarães da Costa, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... ; and 2895 coauthors
Publication:
Physical Review D, Volume 90, Issue 11, id.112015 (PhRvD Homepage)
Publication Date:
12/2014
Origin:
APS
PACS Keywords:
Standard-model Higgs bosons
Abstract Copyright:
2014: CERN
DOI:
10.1103/PhysRevD.90.112015
Bibliographic Code:
2014PhRvD..90k2015A

Abstract

A measurement of the production processes of the recently discovered Higgs boson is performed in the two-photon final state using 4.5 fb-1 of proton-proton collisions data at &surd;{s }=7 TeV and 20.3 fb-1 at &surd;{s }=8 TeV collected by the ATLAS detector at the Large Hadron Collider. The number of observed Higgs boson decays to diphotons divided by the corresponding Standard Model prediction, called the signal strength, is found to be mu =1.17 ±0.27 at the value of the Higgs boson mass measured by ATLAS, mH=125.4 GeV . The analysis is optimized to measure the signal strengths for individual Higgs boson production processes at this value of mH. They are found to be muggF=1.32 ±0.38 , muVBF=0.8 ±0.7 , muW H=1.0 ±1.6 , muZ H=0.1-0.1+3.7 , and mut t ¯ H=1.6-1.8+2.7 , for Higgs boson production through gluon fusion, vector-boson fusion, and in association with a W or Z boson or a top-quark pair, respectively. Compared with the previously published ATLAS analysis, the results reported here also benefit from a new energy calibration procedure for photons and the subsequent reduction of the systematic uncertainty on the diphoton mass resolution. No significant deviations from the predictions of the Standard Model are found.

 

Title:
Comprehensive measurements of t -channel single top-quark production cross sections at &surd;{s }=7 TeV with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.; ... Barreiro Guimarães da Costa, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... ; and 2882 coauthors
Publication:
Physical Review D, Volume 90, Issue 11, id.112006 (PhRvD Homepage)
Publication Date:
12/2014
Origin:
APS
PACS Keywords:
Top quarks, Determination of Kobayashi-Maskawa matrix elements, Inclusive production with identified leptons photons or other nonhadronic particles, Protons and neutrons
Abstract Copyright:
2014: CERN
DOI:
10.1103/PhysRevD.90.112006
Bibliographic Code:
2014PhRvD..90k2006A

Abstract

This article presents measurements of the t -channel single top-quark (t ) and top-antiquark (t ¯) total production cross sections sigma (t q ) and sigma (t ¯q ), their ratio Rt=sigma (t q )/sigma (t ¯q ), and a measurement of the inclusive production cross section sigma (t q +t ¯q ) in proton-proton collisions at &surd;{s }=7 TeV at the LHC. Differential cross sections for the t q and t ¯q processes are measured as a function of the transverse momentum and the absolute value of the rapidity of t and t ¯, respectively. The analyzed data set was recorded with the ATLAS detector and corresponds to an integrated luminosity of 4.59 fb-1 . Selected events contain one charged lepton, large missing transverse momentum, and two or three jets. The cross sections are measured by performing a binned maximum-likelihood fit to the output distributions of neural networks. The resulting measurements are sigma (t q )=46 ±1 (stat)±6 (syst) pb , sigma (t ¯ q )=23 ±1 (stat)±3 (syst) pb , Rt=2.04 ±0.13 (stat)±0.12 (syst) , and sigma (t q +t ¯ q )=68 ±2 (stat)±8 (syst) pb , consistent with the Standard Model expectation. The uncertainty on the measured cross sections is dominated by systematic uncertainties, while the uncertainty on Rt is mainly statistical. Using the ratio of sigma (t q +t ¯q ) to its theoretical prediction, and assuming that the top-quark-related CKM matrix elements obey the relation |Vt b|≫|Vt s|,|Vt d| , we determine |Vt b|=1.02 ±0.07.

 

Title:
Search for nonpointing and delayed photons in the diphoton and missing transverse momentum final state in 8 TeV p p collisions at the LHC using the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.; ... Barreiro Guimarães da Costa, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... ; and 2885 coauthors
Publication:
Physical Review D, Volume 90, Issue 11, id.112005 (PhRvD Homepage)
Publication Date:
12/2014
Origin:
APS
PACS Keywords:
Supersymmetric models, Inclusive production with identified leptons photons or other nonhadronic particles, Limits on production of particles
Abstract Copyright:
2014: CERN
DOI:
10.1103/PhysRevD.90.112005
Bibliographic Code:
2014PhRvD..90k2005A

Abstract

A search has been performed, using the full 20.3 fb-1 data sample of 8 TeV proton-proton collisions collected in 2012 with the ATLAS detector at the LHC, for photons originating from a displaced vertex due to the decay of a neutral long-lived particle into a photon and an invisible particle. The analysis investigates the diphoton plus missing transverse momentum final state, and is therefore most sensitive to pair production of long-lived particles. The analysis technique exploits the capabilities of the ATLAS electromagnetic calorimeter to make precise measurements of the flight direction, as well as the time of flight, of photons. No excess is observed over the Standard Model predictions for background. Exclusion limits are set within the context of gauge mediated supersymmetry breaking models, with the lightest neutralino being the next-to-lightest supersymmetric particle and decaying into a photon and gravitino with a lifetime in the range from 250 ps to about 100 ns.

 

Title:
Density-wave instabilities of fractionalized Fermi liquids
Authors:
Chowdhury, Debanjan; Sachdev, Subir
Publication:
Physical Review B, Volume 90, Issue 24, id.245136 (PhRvB Homepage)
Publication Date:
12/2014
Origin:
APS
PACS Keywords:
Non-Fermi-liquid ground states electron phase diagrams and phase transitions in model systems, Lattice fermion models
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevB.90.245136
Bibliographic Code:
2014PhRvB..90x5136C

Abstract

Recent experiments in the underdoped regime of the hole-doped cuprates have found evidence for an incommensurate charge density-wave state. We present an analysis of the charge ordering instabilities in a metal with antiferromagnetic correlations, where the electronic excitations are coupled to the fractionalized excitations of a quantum fluctuating antiferromagnet on the square lattice. The resulting charge density-wave state emerging out of such a fractionalized Fermi liquid (FL*) has wave vectors of the form (±Q0,0 ) ,(0 ,±Q0) , with a predominantly d -form factor, in agreement with experiments on a number of different families of the cuprates. In contrast, as previously shown, the charge density-wave instability of a nearly antiferromagnetic metal with a large Fermi surface, interacting via short-range interactions, has wave vectors of the type (±Q0,±Q0) . Our results show that the observed charge density-wave appears as a low-energy instability of a fractionalized metallic state linked to the proximity to an antiferromagnetic insulator, and the pseudogap regime can be described by such a metal at least over intermediate length and energy scales.

 

Title:
Conformal field theories at nonzero temperature: Operator product expansions, Monte Carlo, and holography
Authors:
Katz, Emanuel; Sachdev, Subir; Sørensen, Erik S.; Witczak-Krempa, William
Publication:
Physical Review B, Volume 90, Issue 24, id.245109 (PhRvB Homepage)
Publication Date:
12/2014
Origin:
APS
PACS Keywords:
Conformal field theory algebraic structures
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevB.90.245109
Bibliographic Code:
2014PhRvB..90x5109K

Abstract

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

 

Title:
Phase diagram and excitations of a Shiba molecule
Authors:
Yao, N. Y.; Moca, C. P.; Weymann, I.; Sau, J. D.; Lukin, M. D.; Demler, E. A.; Zaránd, G.
Publication:
Physical Review B, Volume 90, Issue 24, id.241108 (PhRvB Homepage)
Publication Date:
12/2014
Origin:
APS
PACS Keywords:
Magnetic impurity interactions, Electric and magnetic moments polarizability and magnetic susceptibility, Exchange and superexchange interactions
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevB.90.241108
Bibliographic Code:
2014PhRvB..90x1108Y

Abstract

We analyze the phase diagram associated with a pair of magnetic impurities trapped in a superconducting host. The natural interplay between Kondo screening, superconductivity, and exchange interactions leads to a rich array of competing phases, whose transitions are characterized by discontinuous changes of the total spin. Our analysis is based on a combination of numerical renormalization group techniques as well as semiclassical analytics. In addition to the expected screened and unscreened phases, we observe a new molecular doublet phase where the impurity spins are only partially screened by a single extended quasiparticle. Direct signatures of the various Shiba molecule states can be observed via radio-frequency spectroscopy.

 

Title:
Bloch oscillations of bosonic lattice polarons
Authors:
Grusdt, F.; Shashi, A.; Abanin, D.; Demler, E.
Publication:
Physical Review A, Volume 90, Issue 6, id.063610 (PhRvA Homepage)
Publication Date:
12/2014
Origin:
APS
PACS Keywords:
Ultracold gases trapped gases, Large or Frohlich polarons, Quantum transport
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevA.90.063610
Bibliographic Code:
2014PhRvA..90f3610G

Abstract

We consider a single-impurity atom confined to an optical lattice and immersed in a homogeneous Bose-Einstein condensate (BEC). Interaction of the impurity with the phonon modes of the BEC leads to the formation of a stable quasiparticle, the polaron. We use a variational mean-field approach to study dispersion renormalization and derive equations describing nonequilibrium dynamics of polarons by projecting equations of motion into mean-field-type wave functions. As a concrete example, we apply our method to study dynamics of impurity atoms in response to a suddenly applied force and explore the interplay of coherent Bloch oscillations and incoherent drift. We obtain a nonlinear dependence of the drift velocity on the applied force, including a sub-Ohmic dependence for small forces for dimensionality d >1 of the BEC. For the case of heavy impurity atoms, we derive a closed analytical expression for the drift velocity. Our results show considerable differences with the commonly used phenomenological Esaki-Tsu model.

 

Title:

Measurement of inclusive jet charged-particle fragmentation functions in Pb+Pb collisions at &surd;{sNN} = 2.76 TeV with 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:
Physics Letters B, Volume 739, p. 320-342.
Publication Date:
12/2014
Origin:
ELSEVIER
Abstract Copyright:
(c) 2014 The Authors
DOI:
10.1016/j.physletb.2014.10.065
Bibliographic Code:
2014PhLB..739..320A

Abstract

Measurements of charged-particle fragmentation functions of jets produced in ultra-relativistic nuclear collisions can provide insight into the modification of parton showers in the hot, dense medium created in the collisions. ATLAS has measured jets in &surd;{sNN} = 2.76 TeV Pb+Pb collisions at the LHC using a data set recorded in 2011 with an integrated luminosity of 0.14 nb-1. Jets were reconstructed using the anti-kt algorithm with distance parameter values R = 0.2 , 0.3 ,and 0.4. Distributions of charged-particle transverse momentum and longitudinal momentum fraction are reported for seven bins in collision centrality for R = 0.4 jets with pTjet> 100 GeV. Commensurate minimum pT values are used for the other radii. Ratios of fragment distributions in each centrality bin to those measured in the most peripheral bin are presented. These ratios show a reduction of fragment yield in central collisions relative to peripheral collisions at intermediate z values, 0.04 ≲ z ≲ 0.2, and an enhancement in fragment yield for z ≲ 0.04. A smaller, less significant enhancement is observed at large z and large pT in central collisions.

 

Title:

Measurement of the total cross section from elastic scattering in pp collisions at &surd;{ s} = 7 TeV with the ATLAS detector

Authors:
Aad, G.; Abbott, B.; Abdallah, J.; ... Barreiro Guimarães da Costa, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... ; and 2893 coauthors
Publication:
Nuclear Physics, Section B, Volume 889, p. 486-548.
Publication Date:
12/2014
Origin:
ELSEVIER
Abstract Copyright:
(c) 2014 The Authors
DOI:
10.1016/j.nuclphysb.2014.10.019
Bibliographic Code:
2014NuPhB.889..486A

Abstract

A measurement of the total pp cross section at the LHC at &surd;{ s} = 7 TeV is presented. In a special run with high-beta* beam optics, an integrated luminosity of 80 mub-1 was accumulated in order to measure the differential elastic cross section as a function of the Mandelstam momentum transfer variable t. The measurement is performed with the ALFA sub-detector of ATLAS. Using a fit to the differential elastic cross section in the | t | range from 0.01 GeV2 to 0.1 GeV2 to extrapolate to | t | --> 0, the total cross section, sigmatot (pp --> X), is measured via the optical theorem to be:<ce:display><ce:formula.

 

Title:
Inverse Ising inference with correlated samples
Authors:
Obermayer, Benedikt; Levine, Erel
Publication:
New Journal of Physics, Volume 16, Issue 12, article id. 123017 (2014).
Publication Date:
12/2014
Origin:
IOP
DOI:
10.1088/1367-2630/16/12/123017
Bibliographic Code:
2014NJPh...16l3017O

Abstract

Correlations between two variables of a high-dimensional system can be indicative of an underlying interaction, but can also result from indirect effects. Inverse Ising inference is a method to distinguish one from the other. Essentially, the parameters of the least constrained statistical model are learned from the observed correlations such that direct interactions can be separated from indirect correlations. Among many other applications, this approach has been helpful for protein structure prediction, because residues which interact in the 3D structure often show correlated substitutions in a multiple sequence alignment. In this context, samples used for inference are not independent but share an evolutionary history on a phylogenetic tree. Here, we discuss the effects of correlations between samples on global inference. Such correlations could arise due to phylogeny but also via other slow dynamical processes. We present a simple analytical model to address the resulting inference biases, and develop an exact method accounting for background correlations in alignment data by combining phylogenetic modeling with an adaptive cluster expansion algorithm. We find that popular reweighting schemes are only marginally effective at removing phylogenetic bias, suggest a rescaling strategy that yields better results, and provide evidence that our conclusions carry over to the frequently used mean-field approach to the inverse Ising problem.

 

Title:
Connecting high-field quantum oscillations to zero-field electron spectral functions in the underdoped cuprates
Authors:
Allais, Andrea; Chowdhury, Debanjan; Sachdev, Subir
Publication:
Nature Communications, Volume 5, id. 5771 (2014).
Publication Date:
12/2014
Origin:
NATURE
Abstract Copyright:
(c) 2014: Nature Publishing Group, a division of Macmillan Publishers Limited. All Rights Reserved.
DOI:
10.1038/ncomms6771
Bibliographic Code:
2014NatCo...5E5771A

Abstract

The nature of the pseudogap regime of cuprate superconductors at low hole density remains unresolved. It has a number of seemingly distinct experimental signatures: a suppression of the paramagnetic spin susceptibility at high temperatures, low-energy electronic excitations that extend over arcs in the Brillouin zone, X-ray detection of charge-density wave order at intermediate temperatures and quantum oscillations at high magnetic fields and low temperatures. Here we show that a model of competing charge-density wave and superconducting orders provides a unified description of the intermediate and low-temperature regimes. We treat quantum oscillations at high field beyond semiclassical approximations, and find clear and robust signatures of an electron pocket compatible with existing observations; we also predict oscillations due to additional hole pockets. In the zero-field and intermediate temperature regime, we compute the electronic spectrum in the presence of thermally fluctuating charge-density and superconducting orders. Our results are compatible with experimental trends.

 

Title:
High quality-factor optical nanocavities in bulk single-crystal diamond
Authors:
Burek, Michael J.; Chu, Yiwen; Liddy, Madelaine S. Z.; Patel, Parth; Rochman, Jake; Meesala, Srujan; Hong, Wooyoung; Quan, Qimin; Lukin, Mikhail D.; Loncar, Marko
Publication:
Nature Communications, Volume 5, id. 5718 (2014).
Publication Date:
12/2014
Origin:
NATURE
Abstract Copyright:
(c) 2014: Nature Publishing Group, a division of Macmillan Publishers Limited. All Rights Reserved.
DOI:
10.1038/ncomms6718
Bibliographic Code:
2014NatCo...5E5718B

Abstract

Single-crystal diamond, with its unique optical, mechanical and thermal properties, has emerged as a promising material with applications in classical and quantum optics. However, the lack of heteroepitaxial growth and scalable fabrication techniques remains the major limiting factors preventing more wide-spread development and application of diamond photonics. In this work, we overcome this difficulty by adapting angled-etching techniques, previously developed for realization of diamond nanomechanical resonators, to fabricate racetrack resonators and photonic crystal cavities in bulk single-crystal diamond. Our devices feature large optical quality factors, in excess of 105, and operate over a wide wavelength range, spanning visible and telecom. These newly developed high-Q diamond optical nanocavities open the door for a wealth of applications, ranging from nonlinear optics and chemical sensing, to quantum information processing and cavity optomechanics.

 

Title:
Low-Temperature Scanning Capacitance Probe for Imaging Electron Motion
Authors:
Bhandari, S.; Westervelt, R. M.
Publication:
Journal of Physics: Conference Series, Volume 568, Issue 3, article id. 032005 (2014).
Publication Date:
12/2014
Origin:
IOP
DOI:
10.1088/1742-6596/568/3/032005
Bibliographic Code:
2014JPhCS.568c2005B

Abstract

Novel techniques to probe electronic properties at the nanoscale can shed light on the physics of nanoscale devices. In particular, studying the scattering of electrons from edges and apertures at the nanoscale and imaging the electron profile in a quantum dot, have been of interest [1]. In this paper, we present the design and implementation of a cooled scanning capacitance probe that operates at liquid He temperatures to image electron waves in nanodevices. The conducting tip of a scanned probe microscope is held above the nanoscale structure, and an applied sample-to-tip voltage creates an image charge that is measured by a cooled charge amplifier [2] adjacent to the tip. The circuit is based on a low-capacitance, high- electron-mobility transistor (Fujitsu FHX35X). The input is a capacitance bridge formed by a low capacitance pinched-off HEMT transistor and tip-sample capacitance. We have achieved low noise level (0.13 e/VHz) and high spatial resolution (100 nm) for this technique, which promises to be a useful tool to study electronic behavior in nanoscale devices.

 

Title:
Stabilization of Multi-electron Bubbles in Superfluid Helium
Authors:
Silvera, Isaac F.; Fang, Jieping; Tempere, Jacques
Publication:
Journal of Physics: Conference Series, Volume 568, Issue 1, article id. 012016 (2014).
Publication Date:
12/2014
Origin:
IOP
DOI:
10.1088/1742-6596/568/1/012016
Bibliographic Code:
2014JPhCS.568a2016S

Abstract

Multielectron bubbles (MEBs) in liquid helium were first observed in the late 1970s, but their properties have never been explored experimentally due to their short lifetimes and the difficulty to localize them. We report the observation of long- lived MEBs in a novel cell filled with superfluid helium at static negative pressures. MEBs were extracted from the electron filled vapor sheath of a heated filament loop embedded in the superfluid helium and observed by high-speed photography. MEBs are 2D electron gases on the 3D surface of hollow helium bubbles. Diameters can range from nanometers to millimeters, depending on the number of enclosed electrons. Electrons move in angular momentum states; deformations of the surface are called spherical ripplons. The attractive electron-ripplon interaction leads to an unusual form of superconductivity. If they can be compressed, Wigner crystallization and quantum melting can be observed, as well as a new phase for localization called the ripplo- polaron lattice. MEBs are unstable to tunneling discharge when pressed against a surface. Just as Bose gases are captured in a trap for study, MEBs must also be localized away from walls. We shall discuss methods of capturing them in an electromagnetic trap embedded in the liquid helium.

 

Title:
Review of the highlights of X-ray studies of liquid metal surfaces
Authors:
Pershan, P. S.
Publication:
Journal of Applied Physics, Volume 116, Issue 22, id.222201 (JAP Homepage)
Publication Date:
12/2014
Origin:
AIP
Abstract Copyright:
2014: AIP Publishing LLC
DOI:
10.1063/1.4902958
Bibliographic Code:
2014JAP...116v2201P

Abstract

X-ray studies of the interface between liquid metals and their coexisting vapor are reviewed. After a brief discussion of the few elemental liquid metals for which the surface Debye-Waller effect is sufficiently weak to allow measurement, this paper will go on to discuss the various types of surface phenomena that have been observed for liquid metal alloys. These include surface adsorption, surface freezing, surface aggregation of nm size atomic clusters, and surface chemistry that leads to new 3D crystalline phases.

 

Title:

Measurement of distributions sensitive to the underlying event in inclusive Z-boson production 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 2888 coauthors
Publication:
The European Physical Journal C, Volume 74, article id. #3195, 33 pp. (EPJC Homepage)
Publication Date:
12/2014
Origin:
SPRINGER
Abstract Copyright:
(c) 2014: CERN for the benefit of the ATLAS collaboration
DOI:
10.1140/epjc/s10052-014-3195-6
Bibliographic Code:
2014EPJC...74.3195A

Abstract

A measurement of charged-particle distributions sensitive to the properties of the underlying event is presented for an inclusive sample of events containing a -boson, decaying to an electron or muon pair. The measurement is based on data collected using the ATLAS detector at the LHC in proton-proton collisions at a centre-of-mass energy of TeV with an integrated luminosity of fb. Distributions of the charged particle multiplicity and of the charged particle transverse momentum are measured in regions of azimuthal angle defined with respect to the -boson direction. The measured distributions are compared to similar distributions measured in jet events, and to the predictions of various Monte Carlo generators implementing different underlying event models.

 

Title:

A measurement of the ratio of the production cross sections for and bosons in association with jets 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 74, article id. #3168, 31 pp. (EPJC Homepage)
Publication Date:
12/2014
Origin:
SPRINGER
Abstract Copyright:
(c) 2014: CERN for the benefit of the ATLAS collaboration
DOI:
10.1140/epjc/s10052-014-3168-9
Bibliographic Code:
2014EPJC...74.3168A

Abstract

The ratio of the production cross sections for and bosons in association with jets has been measured in proton-proton collisions at with the ATLAS experiment at the Large Hadron Collider. The measurement is based on the entire 2011 dataset, corresponding to an integrated luminosity of . Inclusive and differential cross-section ratios for massive vector bosons decaying to electrons and muons are measured in association with jets with transverse momentum and jet rapidity . The measurements are compared to next-to-leading-order perturbative QCD calculations and to predictions from different Monte Carlo generators implementing leading-order matrix elements supplemented by parton showers.

 

Title:
Exactly isochoric deformations of soft solids
Authors:
Biggins, John S.; Wei, Z.; Mahadevan, L.
Publication:
Europhysics Letters, Volume 108, Issue 6, article id. 64001 (2014).
Publication Date:
12/2014
Origin:
IOP
DOI:
10.1209/0295-5075/108/64001
Bibliographic Code:
2014EL....10864001B

Abstract

Many materials of contemporary interest, such as gels, biological tissues and elastomers, are easily deformed but essentially incompressible. Traditional linear theory of elasticity implements incompressibility only to first order and thus permits some volume changes, which become problematically large even at very small strains. Using a mixed coordinate transformation originally due to Gauss, we enforce the constraint of isochoric deformations exactly to develop a linear theory with perfect volume conservation that remains valid until strains become geometrically large. We demonstrate the utility of this approach by calculating the response of an infinite soft isochoric solid to a point force that leads to a nonlinear generalization of the Kelvin solution. Our approach naturally generalizes a range of problems involving deformations of soft solids and interfaces in two-dimensional and axisymmetric geometries, which we exemplify by determining the solution to a distributed load that mimics muscular contraction within the bulk of a soft solid.

 

Title:
The Gravity Duals of Modular Hamiltonians
Authors:
Jafferis, Daniel L.; Suh, S. Josephine
Publication:
eprint arXiv:1412.8465
Publication Date:
12/2014
Origin:
ARXIV
Keywords:
High Energy Physics - Theory
Comment:
20 pages + appendices, 6 figures
Bibliographic Code:
2014arXiv1412.8465J

Abstract

In this work, we investigate modular Hamiltonians defined with respect to arbitrary spatial regions in quantum field theory states which have semi-classical gravity duals. We find prescriptions in the gravity dual for calculating the action of the modular Hamiltonian on its defining state, including its dual metric, and also on small excitations around the state. Curiously, use of the covariant holographic entanglement entropy formula leads us to the conclusion that the modular Hamiltonian, which in the quantum field theory acts only in the causal completion of the region, does not commute with bulk operators whose entire gauge-invariant description is space-like to the causal completion of the region.

 

Title:
Heterotic String Compactification and New Vector Bundles
Authors:
Lin, Hai; Wu, Baosen; Yau, Shing-Tung
Publication:
eprint arXiv:1412.8000
Publication Date:
12/2014
Origin:
ARXIV
Keywords:
High Energy Physics - Theory, Mathematics - Algebraic Geometry, Mathematics - Differential Geometry
Comment:
25 pages
Bibliographic Code:
2014arXiv1412.8000L

Abstract

We propose a construction of K\"ahler and non-K\"ahler Calabi-Yau manifolds by branched double covers of twistor spaces. In this construction we use the twistor spaces of four-manifolds with self-dual conformal structures, with the examples of connected sum of $n$ $\mathbb{P}^{2}$s. We also construct $K3$-fibered Calabi-Yau manifolds from the branched double covers of the blow-ups of the twistor spaces. These manifolds can be used in heterotic string compactifications to four dimensions. We also construct stable and polystable vector bundles. Some classes of these vector bundles can give rise to supersymmetric grand unified models with three generations of quarks and leptons in four dimensions.

 

Title:
Optimal control of plate shape with incompatible strain fields
Authors:
Wyn Jones, Gareth; Mahadevan, L.
Publication:
eprint arXiv:1412.6940
Publication Date:
12/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Soft Condensed Matter, Mathematics - Optimization and Control
Comment:
21 pages, 6 figures
Bibliographic Code:
2014arXiv1412.6940W

Abstract

A flat plate can bend into a curved surface if it experiences an inhomogeneous growth field. In this article a method is described that numerically determines the optimal growth field giving rise to an arbitrary target shape, optimizing for closeness to the target shape and for growth field smoothness. Numerical solutions are presented, for the full non-symmetric case as well as for simplified one-dimensional and axisymmetric geometries. This system can also be solved semi-analytically by positing an ansatz for the deformation and growth fields in a circular disk with given thickness profile. Paraboloidal, cylindrical and saddle-shaped target shapes are presented as examples, of which the last two exemplify a soft mode arising from a non-axisymmetric deformation of a structure with axisymmetric material properties.

 

Title:
Inhomogeneous broadening of optical transitions of 87Rb atoms in an optical nanofiber trap
Authors:
Lee, J.; Grover, J. A.; Hoffman, J. E.; Orozco, L. A.; Rolston, S. L.
Publication:
eprint arXiv:1412.6754
Publication Date:
12/2014
Origin:
ARXIV
Keywords:
Physics - Atomic Physics, Physics - Optics, Quantum Physics
Comment:
5 pages, 4 figures
Bibliographic Code:
2014arXiv1412.6754L

Abstract

We experimentally demonstrate optical trapping of 87Rb atoms using a two-color evanescent field around an optical nanofiber. In our trapping geometry, a blue-detuned traveling wave whose polarization is nearly parallel to the polarization of a red-detuned standing wave produce significant vector light shifts that lead to broadening of the absorption profile of a near-resonant beam at the trapping site. A model that includes scalar, vector, and tensor light shifts of the probe transition $5S_{1/2}$-$5P_{3/2}$ from the trapping beams; weighted by the temperature-dependent position of the atoms in the trap qualitatively describe the observed asymmetric profile, and explained differences with previous experiments that used Cs atoms. The model provides a consistent way to extract the number of atoms in the trap.

 

Title:
Evolutionary Dynamics with Fluctuating Population Sizes
Authors:
Chotibut, Thiparat; Nelson, David R.
Publication:
eprint arXiv:1412.6688
Publication Date:
12/2014
Origin:
ARXIV
Keywords:
Quantitative Biology - Populations and Evolution, Condensed Matter - Statistical Mechanics, Physics - Biological Physics
Comment:
51 pages, 12 figures, submitted to Physical Review E
Bibliographic Code:
2014arXiv1412.6688C

Abstract

Game theory ideas provide a useful framework for studying evolutionary dynamics in a well-mixed environment. This approach, however, typically enforces a strictly fixed overall population size, deemphasizing natural growth processes. We study a competitive Lotka-Volterra model, with number fluctuations, that accounts for natural population growth and encompasses interaction scenarios typical of evolutionary games. In an appropriate limit, the model describes standard evolutionary games with both genetic drift and overall population size fluctuations. We demonstrate a novel mechanism for neutral evolution in a well-mixed Moran model such that population size fluctuations favor a fixation of one species over the other. We derive an effective evolutionary dynamics for fluctuation-induced selection by adiabatic elimination of a fast variable. The method can be extended to study the interplay between selection, genetic drift, and population size fluctuations in other scenarios. We also investigate strong mutualism, in a limit where a varying population size can strongly influence the evolutionary dynamics. We analytically and numerically determine fixation probabilities as well as mean fixation times using matched asymptotic expansions, taking into account the population size degree of freedom. These results elucidate the interplay between population dynamics and evolutionary dynamics in well-mixed systems.

 

Title:
Warped Dipole Completed, with a Tower of Higgs Bosons
Authors:
Agashe, Kaustubh; Azatov, Aleksandr; Cui, Yanou; Randall, Lisa; Son, Minho
Publication:
eprint arXiv:1412.6468
Publication Date:
12/2014
Origin:
ARXIV
Keywords:
High Energy Physics - Phenomenology, High Energy Physics - Theory
Comment:
Main text 35 pages, 9 figures
Bibliographic Code:
2014arXiv1412.6468A

Abstract

In the context of warped extra-dimensional models which address both the Planck-weak- and flavor-hierarchies of the Standard Model (SM), it has been argued that certain observables can be calculated within the 5D effective field theory only with the Higgs field propagating in the bulk of the extra dimension, just like other SM fields. The related studies also suggested an interesting form of decoupling of the heavy Kaluza-Klein (KK) fermion states in the warped 5D SM in the limit where the profile of the SM Higgs approaches the IR brane. We demonstrate that a similar phenomenon occurs when we include the mandatory KK excitations of the SM Higgs in loop diagrams giving dipole operators for SM fermions, where the earlier work only considered the SM Higgs (zero mode). In particular, in the limit of a quasi IR-localized SM Higgs, the effect from summing over KK Higgs modes is unsuppressed (yet finite), in contrast to the naive expectation that KK Higgs modes decouple as their masses become large. In this case, a wide range of KK Higgs modes have quasi-degenerate masses and enhanced couplings to fermions relative to those of the SM Higgs, which contribute to the above remarkable result. In addition, we find that the total contribution from KK Higgs modes in general can be comparable to that from the SM Higgs alone. It is also interesting that KK Higgs couplings to KK fermions of the same chirality as the corresponding SM modes have an unsuppressed overall contribution, in contrast to the result from the earlier studies involving the SM Higgs. Our studies suggest that KK Higgs bosons are generally an indispensable part of the warped 5D SM, and their phenomenology such as signals at the LHC are worth further investigation.

 

Title:
Nanoscale interplay of strain and doping in a high-temperature superconductor
Authors:
Zeljkovic, Ilija; Nieminen, Jouko; Huang, Dennis; Chang, Tay-Rong; He, Yang; Jeng, Horng-Tay; Xu, Zhijun; Wen, Jinsheng; Gu, Genda; Lin, Hsin; Markiewicz, Robert S.; Bansil, Arun; Hoffman, Jennifer E.
Publication:
eprint arXiv:1412.6088
Publication Date:
12/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Materials Science, Condensed Matter - Superconductivity
Comment:
Nano Letters 14, 6749 (2014); doi:10.1021/nl501890k
Bibliographic Code:
2014arXiv1412.6088Z

Abstract

The highest temperature superconductors are electronically inhomogeneous at the nanoscale, suggesting the existence of a local variable which could be harnessed to enhance the superconducting pairing. Here we report the relationship between local doping and local strain in the cuprate superconductor Bi$_2$Sr$_2$CaCu$_2$O$_{8+x}$. We use scanning tunneling microscopy to discover that the crucial oxygen dopants are periodically distributed, in correlation with local strain. Our picoscale investigation of the intra-unit-cell positions of all oxygen dopants provides essential structural input for a complete microscopic theory.

 

Title:
Multi-terminal electrical transport measurements of molybdenum disulphide using van der Waals heterostructure device platform
Authors:
Cui, Xu; Lee, Gwan-Hyoung; Duck Kim, Young; Arefe, Ghidewon; Huang, Pinshane Y.; Lee, Chul-Ho; Chenet, Daniel A.; Zhang, Xian; Wang, Lei; Ye, Fan; Pizzocchero, Filippo; Jessen, Bjarke S.; Watanabe, Kenji; Taniguchi, Takashi; Muller, David A.; Low, Tony; Kim, Philip; Hone, James
Publication:
eprint arXiv:1412.5977
Publication Date:
12/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Materials Science, Condensed Matter - Mesoscale and Nanoscale Physics
Comment:
21 pages, 4 figures, 1 table; fix the affiliation and acknowledgements;remove the refs. 36 on page 7
Bibliographic Code:
2014arXiv1412.5977C

Abstract

Atomically thin two-dimensional (2D) semiconductors such as molybdenum disulphide (MoS2) hold great promise in electrical, optical, and mechanical devices and display novel physical phenomena such as coupled spin-valley physics and the valley Hall effect. However, the electron mobility of mono- and few-layer MoS2 has so far been substantially below theoretically predicted limits, particularly at low temperature (T), which has hampered efforts to observe its intrinsic quantum transport behaviors. Potential sources of disorder and scattering include both defects such as sulfur vacancies in the MoS2 itself, and extrinsic sources such as charged impurities and remote optical phonons from oxide dielectrics. To reduce extrinsic scattering and approach the intrinsic limit, we developed a van der Waals (vdW) heterostructure device platform where MoS2 layers are fully encapsulated within hexagonal boron nitride (hBN), and electrically contacted in a multi-terminal geometry using gate-tunable graphene electrodes. Multi-terminal magneto-transport measurements show dramatic improvements in performance, including a record-high Hall mobility reaching 34,000 cm2/Vs for 6-layer MoS2 at low T. Comparison to theory shows a decrease of 1-2 orders of magnitude in the density of charged impurities, indicating that performance at low T in previous studies was limited by extrinsic factors rather than defects in the MoS2. We also observed Shubnikov-de Haas (SdH) oscillations for the first time in high-mobility monolayer and few-layer MoS2. This novel device platform therefore opens up a new way toward measurements of intrinsic properties and the study of quantum transport phenomena in 2D semiconducting materials.

 

Title:
State-selective intersystem crossing in nitrogen-vacancy centers
Authors:
Goldman, M. L.; Doherty, M. W.; Sipahigil, A.; Yao, N. Y.; Bennett, S. D.; Manson, N. B.; Kubanek, A.; Lukin, M. D.
Publication:
eprint arXiv:1412.4865
Publication Date:
12/2014
Origin:
ARXIV
Keywords:
Quantum Physics, Condensed Matter - Mesoscale and Nanoscale Physics
Bibliographic Code:
2014arXiv1412.4865G

Abstract

The intersystem crossing (ISC) is an important process in many solid-state atomlike impurities. For example, it allows the electronic spin state of the nitrogen-vacancy (NV) center in diamond to be initialized and read out using optical fields at ambient temperatures. This capability has enabled a wide array of applications in metrology and quantum information science. Here, we develop a microscopic model of the state-selective ISC from the optical excited state manifold of the NV center. By correlating the electron-phonon interactions that mediate the ISC with those that induce population dynamics within the NV center's excited state manifold and those that produce the phonon sidebands of its optical transitions, we quantitatively demonstrate that our model is consistent with recent ISC measurements. Furthermore, our model constrains the unknown energy spacings between the center's spin-singlet and spin-triplet levels. Finally, we discuss prospects to engineer the ISC in order to improve the spin initialization and readout fidelities of NV centers.

 

Title:
Twistorial Topological Strings and a tt* Geometry for N=2 Theories in 4d
Authors:
Cecotti, Sergio; Neitzke, Andrew; Vafa, Cumrun
Publication:
eprint arXiv:1412.4793
Publication Date:
12/2014
Origin:
ARXIV
Keywords:
High Energy Physics - Theory
Comment:
100 pages
Bibliographic Code:
2014arXiv1412.4793C

Abstract

We define twistorial topological strings by considering tt* geometry of the 4d N=2 supersymmetric theories on the Nekrasov-Shatashvili half-Omega background, which leads to quantization of the associated hyperKahler geometries. We show that in one limit it reduces to the refined topological string amplitude. In another limit it is a solution to a quantum Riemann-Hilbert problem involving quantum Kontsevich-Soibelman operators. In a further limit it encodes the hyperKahler integrable systems studied by GMN. In the context of AGT conjecture, this perspective leads to a twistorial extension of Toda. The 2d index of the half-Omega theory leads to the recently introduced index for N=2 theories in 4d. The twistorial topological string can alternatively be viewed, using the work of Nekrasov-Witten, as studying the vacuum geometry of 4d N=2 supersymmetric theories on T^2x I where I is an interval with specific boundary conditions at the two ends.

 

Title:
The competition between simple and complex evolutionary trajectories in asexual populations
Authors:
Ochs, Ian E.; Desai, Michael M.
Publication:
eprint arXiv:1412.3893
Publication Date:
12/2014
Origin:
ARXIV
Keywords:
Quantitative Biology - Populations and Evolution
Comment:
8 pages, 3 figures
Bibliographic Code:
2014arXiv1412.3893O

Abstract

On rugged fitness landscapes where sign epistasis is common, adaptation can often involve either individually beneficial "uphill" mutations or more complex mutational trajectories involving fitness valleys or plateaus. The dynamics of the evolutionary process determine the probability that evolution will take any specific path among a variety of competing possible trajectories. Understanding this evolutionary choice is essential if we are to understand the outcomes and predictability of adaptation on rugged landscapes. We present a simple model to analyze the probability that evolution will eschew immediately uphill paths in favor of crossing fitness valleys or plateaus that lead to higher fitness but less accessible genotypes. We calculate how this probability depends on the population size, mutation rates, and relevant selection pressures, and compare our analytical results to Wright-Fisher simulations. We find that the probability of valley crossing depends nonmonotonically on population size: intermediate size populations are most likely to follow a "greedy" strategy of acquiring immediately beneficial mutations even if they lead to evolutionary dead ends, while larger and smaller populations are more likely to cross fitness valleys to reach distant advantageous genotypes. We explicitly identify the boundaries between these different regimes in terms of the relevant evolutionary parameters. Above a certain threshold population size, we show that the degree of evolutionary "foresight" depends only on a single simple combination of the relevant parameters.

 

Title:
Strings of Minimal 6d SCFTs
Authors:
Haghighat, Babak; Klemm, Albrecht; Lockhart, Guglielmo; Vafa, Cumrun
Publication:
eprint arXiv:1412.3152
Publication Date:
12/2014
Origin:
ARXIV
Keywords:
High Energy Physics - Theory
Comment:
50+1 pages, 8 figures
Bibliographic Code:
2014arXiv1412.3152H

Abstract

We study strings associated with minimal 6d SCFTs, which by definition have only one string charge and no Higgs branch. These theories are labelled by a number n with 1 <= n <= 8 or n = 12. Quiver theories have previously been proposed which describe strings of SCFTs for n = 1, 2. For n > 2 the strings interact with the bulk gauge symmetry. In this paper we find a quiver description for the n = 4 string using Sen's limit of F-theory and calculate its elliptic genus with localization techniques. This result is checked using the duality of F-theory with M-theory and topological string theory whose refined BPS partition function captures the elliptic genus of the SCFT strings. We use the topological string theory to gain insight into the elliptic genus for other values of n.

 

Title:
Precision Natural SUSY at CEPC, FCC-ee, and ILC
Authors:
Fan, JiJi; Reece, Matthew; Wang, Lian-Tao
Publication:
eprint arXiv:1412.3107
Publication Date:
12/2014
Origin:
ARXIV
Keywords:
High Energy Physics - Phenomenology
Comment:
26 pages, 9 figures
Bibliographic Code:
2014arXiv1412.3107F

Abstract

Testing the idea of naturalness is and will continue to be one of the most important goals of high energy physics experiments. It will play a central role in the physics program of future colliders. In this paper, we present projections of the reach of natural SUSY at future lepton colliders: CEPC, FCC-ee and ILC. We focus on the observables which give the strongest reach, the electroweak precision observables (for left-handed stops), and Higgs to gluon and photon decay rates (for both left- and right-handed stops). There is a "blind spot" when the stop mixing parameter Xt is approximately equal to the average stop mass. We argue that in natural scenarios, bounds on the heavy Higgs bosons from tree-level mixing effects that modify the bottom Yukawa coupling together with bounds from b to s gamma play a complementary role in probing the blind spot region. For specific natural SUSY scenarios such as folded SUSY in which the top partners do not carry Standard Model color charges, electroweak precision observables could be the most sensitive probe. In all the scenarios discussed in this paper, the combined set of precision measurements will probe down to a few percent in fine-tuning.

 

Title:
Asymptotic Symmetries of Massless QED in Even Dimensions
Authors:
Kapec, Daniel; Lysov, Vyacheslav; Strominger, Andrew
Publication:
eprint arXiv:1412.2763
Publication Date:
12/2014
Origin:
ARXIV
Keywords:
High Energy Physics - Theory, General Relativity and Quantum Cosmology, High Energy Physics - Phenomenology
Comment:
18 pages
Bibliographic Code:
2014arXiv1412.2763K

Abstract

We consider the scattering of massless particles coupled to an abelian gauge field in 2n-dimensional Minkowski spacetime. Weinberg's soft photon theorem is recast as Ward identities for infinitely many new nontrivial symmetries of the massless QED S-matrix, with one such identity arising for each propagation direction of the soft photon. These symmetries are identified as large gauge transformations with angle-dependent gauge parameters that are constant along the null generators of null infinity. Almost all of the symmetries are spontaneously broken in the standard vacuum and the soft photons are the corresponding Goldstone bosons. Our result establishes a relationship between soft theorems and asymptotic symmetry groups in any even dimension.

 

Title:
Dissipative Dark Matter and the Andromeda Plane of Satellites
Authors:
Randall, Lisa; Scholtz, Jakub
Publication:
eprint arXiv:1412.1839
Publication Date:
12/2014
Origin:
ARXIV
Keywords:
Astrophysics - Astrophysics of Galaxies, Astrophysics - Cosmology and Nongalactic Astrophysics, High Energy Physics - Phenomenology
Comment:
13 pages, 12 figures
Bibliographic Code:
2014arXiv1412.1839R

Abstract

We show that dissipative dark matter can potentially explain the large observed mass to light ratio of the dwarf satellite galaxies that have been observed in the recently identified planar structure around Andromeda, which are thought to result from tidal forces during a galaxy merger. Whereas dwarf galaxies created from ordinary disks would be dark matter poor, dark matter inside the galactic plane not only provides a source of dark matter, but one that is more readily bound due to the dark matter's lower velocity. This initial N-body study shows that with a thin disk of dark matter inside the baryonic disk, mass-to-light ratios as high as O(30) can be generated when tidal forces pull out patches of sizes similar to the scales of Toomre instabilities of the dark disk. A full simulation will be needed to confirm this result.

 

Title:
Dynamics of evaporative colloidal patterning
Authors:
Nadir Kaplan, C.; Wu, Ning; Mandre, Shreyas; Aizenberg, Joanna; Mahadevan, L.
Publication:
eprint arXiv:1412.1813
Publication Date:
12/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Soft Condensed Matter, Condensed Matter - Materials Science
Comment:
11 pages, 7 figures, 2 tables
Bibliographic Code:
2014arXiv1412.1813N

Abstract

Drying suspensions often leave behind complex patterns of particulates, as might be seen in the coffee stains on a table. Here we consider the dynamics of periodic band or uniform solid film formation on a vertical plate suspended partially in a drying colloidal solution. Direct observations allow us to visualize the dynamics of the band and film deposition, and the transition in between when the colloidal concentration is varied. A minimal theory of the liquid meniscus motion along the plate reveals the dynamics of the banding and its transition to the filming as a function of the ratio of deposition and evaporation rates. We also provide a complementary multiphase model of colloids dissolved in the liquid, which couples the inhomogeneous evaporation at the evolving meniscus to the fluid and particulate flows and the transition from a dilute suspension to a porous plug. This allows us to determine the concentration dependence of the bandwidth and the deposition rate. Together, our findings allow for the control of drying-induced patterning as a function of the colloidal concentration and evaporation rate.

 

Title:
Higgs criticality in a two-dimensional metal
Authors:
Chowdhury, Debanjan; Sachdev, Subir
Publication:
eprint arXiv:1412.1086
Publication Date:
12/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Strongly Correlated Electrons, High Energy Physics - Theory
Comment:
27 pages, 6 figures
Bibliographic Code:
2014arXiv1412.1086C

Abstract

We analyze a candidate theory for the strange metal near optimal hole-doping in the cuprate superconductors. The theory contains a quantum phase transition between metals with `large' and `small' Fermi surfaces, but the transition does not directly involve any broken global symmetries. The two metals have emergent SU(2) and U(1) gauge fields respectively, and the transition is driven by the condensation of a real Higgs field, carrying a finite lattice momentum and an adjoint SU(2) gauge charge. This Higgs field measures the local antiferromagnetic correlations in a `rotating reference frame'. We propose a global phase diagram around this Higgs transition, and describe its relationship to a variety of recent experiments on the cuprate superconductors.

 

Title:
D-branes and Azumaya/matrix noncommutative differential geometry,II: Azumaya/matrix supermanifolds and differentiable maps therefrom -- with a view toward dynamical fermionic D-branes in string theory
Authors:
Liu, Chien-Hao; Yau, Shing-Tung
Publication:
eprint arXiv:1412.0771
Publication Date:
12/2014
Origin:
ARXIV
Keywords:
High Energy Physics - Theory, Mathematics - Algebraic Geometry, Mathematics - Differential Geometry, Mathematics - Symplectic Geometry, 81T30, 58A40, 14A22, 58A50, 16S50, 51K10, 46L87, 81T60, 81T75, 81V22
Comment:
70+2 pages, 8 figures
Bibliographic Code:
2014arXiv1412.0771L

Abstract

In this Part II of D(11), we introduce new objects: super-$C^k$-schemes and Azumaya super-$C^k$-manifolds with a fundamental module (or, synonymously, matrix super-$C^k$-manifolds with a fundamental module), and extend the study in D(11.1) ([L-Y3], arXiv:1406.0929 [math.DG]) to define the notion of `differentiable maps from an Azumaya/matrix supermanifold with a fundamental module to a real manifold or supermanifold'. This allows us to introduce the notion of `fermionic D-branes' in two different styles, one parallels Ramond-Neveu-Schwarz fermionic string and the other Green-Schwarz fermionic string. A more detailed discussion on the Higgs mechanism on dynamical D-branes in our setting, taking maps from the D-brane world-volume to the space-time in question and/or sections of the Chan-Paton bundle on the D-brane world-volume as Higgs fields, is also given for the first time in the D-project. Finally note that mathematically string theory begins with the notion of a differentiable map from a string world-sheet (a $2$-manifold) to a target space-time (a real manifold). In comparison to this, D(11.1) and the current D(11.2) together bring us to the same starting point for studying D-branes in string theory as dynamical objects.

 

Title:
Time-dependent Hermite-Galerkin spectral method and its applications
Authors:
Luo, Xue; Yau, Shing-Tung; Yau, Stephen S.-T.
Publication:
eprint arXiv:1412.0427
Publication Date:
12/2014
Origin:
ARXIV
Keywords:
Mathematics - Numerical Analysis, 65N35, 65N22, 65M70
Comment:
16 pages, 7 tables
Bibliographic Code:
2014arXiv1412.0427L

Abstract

A time-dependent Hermite-Galerkin spectral method (THGSM) is investigated in this paper for the nonlinear convection-diffusion equations in the unbounded domains. The time-dependent scaling factor and translating factor are introduced in the definition of the generalized Hermite functions (GHF). As a consequence, the THGSM based on these GHF has many advantages, not only in theorethical proofs, but also in numerical implementations. The stability and spectral convergence of our proposed method have been established in this paper. The Korteweg-de Vries-Burgers (KdVB) equation and its special cases, including the heat equation and the Burgers' equation, as the examples, have been numerically solved by our method. The numerical results are presented, and it surpasses the existing methods in accuracy. Our theoretical proof of the spectral convergence has been supported by the numerical results.

 

Title:
Studying non-equilibrium many-body dynamics using one-dimensional Bose gases
Authors:
Langen, Tim; Gring, Michael; Kuhnert, Maximilian; Rauer, Bernhard; Geiger, Remi; Mazets, Igor; Smith, David Adu; Kitagawa, Takuya; Demler, Eugene; Schmiedmayer, Jörg
Publication:
AIP Conference Proceedings, Volume 1633, Issue 1, p.11-15 (AIPC Homepage)
Publication Date:
12/2014
Origin:
AIP
Abstract Copyright:
2014: AIP Publishing LLC
DOI:
10.1063/1.4903080
Bibliographic Code:
2014AIPC.1633...11L

Abstract

Non-equilibrium dynamics of isolated quantum many-body systems play an important role in many areas of physics. However, a general answer to the question of how these systems relax is still lacking. We experimentally study the dynamics of ultracold one-dimensional (1D) Bose gases. This reveals the existence of a quasi-steady prethermalized state which differs significantly from the thermal equilibrium of the system. Our results demonstrate that the dynamics of non-equilibrium quantum many-body systems is a far richer process than has been assumed in the past.


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