Faculty Publications: August, 2014

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Title:
Consistent Use of Effective Potentials
Authors:
Andreassen, Anders; Frost, William; Schwartz, Matthew D.
Publication:
eprint arXiv:1408.0287
Publication Date:
08/2014
Origin:
ARXIV
Keywords:
High Energy Physics - Phenomenology
Comment:
37 pages, 3 figures
Bibliographic Code:
2014arXiv1408.0287A

Abstract

It is well known that effective potentials can be gauge-dependent while their values at extrema should be gauge-invariant. Unfortunately, establishing this invariance in perturbation theory is not straightforward, since contributions from arbitrarily high- order loops can be of the same size. We show in massless scalar QED that an infinite class of loops can be summed (and must be summed) to give a gauge invariant value for the potential at its minimum. In addition, we show that the exact potential depends on both the scale at which it is calculated and the normalization of the fields, but the vacuum energy does not. Using these insights, we propose a method to extract some physical quantities from effective potentials which is self-consistent order-by-order in perturbation theory, including improvement with the renormalization group.

 

Title:
Osmotic Pressure in a Bacterial Swarm
Authors:
Ping, Liyan; Wu, Yilin; Hosu, Basarab G.; Tang, Jay X.; Berg, Howard C.
Publication:
Biophysical Journal, vol. 107, issue 4, pp. 871-878
Publication Date:
08/2014
Origin:
CROSSREF
DOI:
10.1016/j.bpj.2014.05.052
Bibliographic Code:
2014BpJ...107..871P

Abstract

Not Available

 

Title:
Measurement of the underlying event in jet events from 7 proton-proton collisions with the ATLAS detector
Authors:
Aad, G.; Abajyan, T.; Abbott, B.;... Franklin, M.;... Guimarães da Costa, J.;... Huth, J.;...; Morii, M.; and 2868 coauthors
Publication:
The European Physical Journal C, Volume 74, article id.2965, 29 pp. (EPJC Homepage)
Publication Date:
08/2014
Origin:
SPRINGER
Abstract Copyright:
(c) 2014: The Author(s)
DOI:
10.1140/epjc/s10052-014-2965-5
Bibliographic Code:
2014EPJC...74.2965A

Abstract

Distributions sensitive to the underlying event in QCD jet events have been measured with the ATLAS detector at the LHC, based on of proton-proton collision data collected at a centre-of-mass energy of 7 . Charged-particle mean and densities of all-particle and charged-particle multiplicity and have been measured in regions azimuthally transverse to the hardest jet in each event. These are presented both as one-dimensional distributions and with their mean values as functions of the leading-jet transverse momentum from 20 to 800 . The correlation of charged-particle mean with charged-particle multiplicity is also studied, and the densities include the forward rapidity region; these features provide extra data constraints for Monte Carlo modelling of colour reconnection and beam-remnant effects respectively. For the first time, underlying event observables have been computed separately for inclusive jet and exclusive dijet event selections, allowing more detailed study of the interplay of multiple partonic scattering and QCD radiation contributions to the underlying event. Comparisons to the predictions of different Monte Carlo models show a need for further model tuning, but the standard approach is found to generally reproduce the features of the underlying event in both types of event selection.

 

Title:
Measurement of the centrality and pseudorapidity dependence of the integrated elliptic flow in lead-lead collisions at TeV with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Guimarães da Costa, J.;... Huth, J.;...; Morii, M.; and 2855 coauthors
Publication:
The European Physical Journal C, Volume 74, article id.2982, 25 pp. (EPJC Homepage)
Publication Date:
08/2014
Origin:
SPRINGER
Abstract Copyright:
(c) 2014: The Author(s)
DOI:
10.1140/epjc/s10052-014-2982-4
Bibliographic Code:
2014EPJC...74.2982A

Abstract

Not Available

 

Title:
Light-quark and gluon jet discrimination in collisions at with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Guimarães da Costa, J.;... Huth, J.;...; Morii, M.; and 2872 coauthors
Publication:
The European Physical Journal C, Volume 74, article id.3023, 29 pp. (EPJC Homepage)
Publication Date:
08/2014
Origin:
SPRINGER
Abstract Copyright:
(c) 2014: The Author(s)
DOI:
10.1140/epjc/s10052-014-3023-z
Bibliographic Code:
2014EPJC...74.3023A

Abstract

Not Available

 

Title:
A preliminary design for the GMT-Consortium Large Earth Finder (G-CLEF)
Authors:
Szentgyorgyi, Andrew; Barnes, Stuart; Bean, Jacob; Bigelow, Bruce; Bouchez, Antonin; Chun, Moo-Young; Crane, Jeffrey D.; Epps, Harland; Evans, Ian; Evans, Janet; Frebel, Anna; Furesz, Gabor; Glenday, Alex; Guzman, Dani; Hare, Tyson; Jang, Bi-Ho; Jang, Jeong-Gyun; Jeong, Ueejong; Jordan, Andres; Kim, Kang-Min; Kim, Jihun; Li, Chih-Hao; Lopez-Morales, Mercedes; McCracken, Kenneth; McLeod, Brian; Mueller, Mark; Nah, Jakyung; Norton, Timothy; Oh, Heeyoung; Oh, Jae Sok; Ordway, Mark; Park, Byeong-Gon; Park, Chan; Park, Sung-Joon; Phillips, David; Plummer, David; Podgorski, William; Rodler, Florian; Seifahrt, Andreas; Tak, Kyung-Mo; Uomoto, Alan; Van Dam, Marcos A.; Walsworth, Ronald; Yu, Young Sam; Yuk, In-Soo
Publication:
Proceedings of the SPIE, Volume 9147, id. 914726 16 pp. (2014). (SPIE Homepage)
Publication Date:
08/2014
Origin:
SPIE
Abstract Copyright:
(c) 2014: SPIE. Downloading of the abstract is permitted for personal use only.
Comment:
ISBN: 9780819496157
DOI:
10.1117/12.2056741
Bibliographic Code:
2014SPIE.9147E..26S

Abstract

The GMT-Consortium Large Earth Finder (G-CLEF) is an optical-band echelle spectrograph that has been selected as the first light instrument for the Giant Magellan Telescope (GMT). G-CLEF is a general-purpose, high dispersion spectrograph that is fiber fed and capable of extremely precise radial velocity measurements. The G-CLEF Concept Design (CoD) was selected in Spring 2013. Since then, G-CLEF has undergone science requirements and instrument requirements reviews and will be the subject of a preliminary design review (PDR) in March 2015. Since CoD review (CoDR), the overall G-CLEF design has evolved significantly as we have optimized the constituent designs of the major subsystems, i.e. the fiber system, the telescope interface, the calibration system and the spectrograph itself. These modifications have been made to enhance G-CLEF's capability to address frontier science problems, as well as to respond to the evolution of the GMT itself and developments in the technical landscape. G-CLEF has been designed by applying rigorous systems engineering methodology to flow Level 1 Scientific Objectives to Level 2 Observational Requirements and thence to Level 3 and Level 4. The rigorous systems approach applied to G-CLEF establishes a well defined science requirements framework for the engineering design. By adopting this formalism, we may flexibly update and analyze the capability of G-CLEF to respond to new scientific discoveries as we move toward first light. G-CLEF will exploit numerous technological advances and features of the GMT itself to deliver an efficient, high performance instrument, e.g. exploiting the adaptive optics secondary system to increase both throughput and radial velocity measurement precision.

 

Title:
Green astro-comb for HARPS-N
Authors:
Langellier, Nicholas; Li, Chih-Hao; Glenday, Alexander G.; Chang, Guoqing; Chen, Hung-Wen; Lim, Jinkang; Furesz, Gabor; Kärtner, Franz; Phillips, David F.; Sasselov, Dimitar; Szentgyorgyi, Andrew; Walsworth, Ronald
Publication:
Proceedings of the SPIE, Volume 9147, id. 91478N 9 pp. (2014). (SPIE Homepage)
Publication Date:
08/2014
Origin:
SPIE
Abstract Copyright:
(c) 2014: SPIE. Downloading of the abstract is permitted for personal use only.
Comment:
ISBN: 9780819496157
DOI:
10.1117/12.2056548
Bibliographic Code:
2014SPIE.9147E..8NL

Abstract

We report the design, installation and testing of a broadband green astro-comb on the HARPS-N spectrograph at the TNG telescope. The astro-comb consists of over 7000 narrow lines (<10-6 nm width) spaced by 16 GHz (0.02 nm at 550 nm) with wavelengths stabilized to the Global Positioning System (GPS) and with flat power from 500 to 620 nm. The narrow lines are used to calibrate the spectrograph and measure its line profile. The short term sensitivity of HARPS-N is measured to be less than 2 cm/s and the long-term drift of the spectrograph is approximately 10 cm/s/day. The astrocomb has been partially automated with future work planned to turn the astro-comb into a fully automated, push button instrument.

 

Title:
Consistent Use of the Standard Model Effective Potential
Authors:
Andreassen, Anders; Frost, William; Schwartz, Matthew D.
Publication:
eprint arXiv:1408.0292
Publication Date:
08/2014
Origin:
ARXIV
Keywords:
High Energy Physics - Phenomenology
Comment:
5 pages, 5 figures
Bibliographic Code:
2014arXiv1408.0292A

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 mH > (129.4 \pm 2.3) GeV and mt < (171.2 \pm 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:
Elastocapillary coalescence of plates and pillars
Authors:
Wei, Zhiyan; Schneider, Tobias; Kim, Jungchul; Kim, Ho-Young; Aizenberg, Joanna; Mahadevan, L.
Publication:
eprint arXiv:1408.0748
Publication Date:
08/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Soft Condensed Matter
Bibliographic Code:
2014arXiv1408.0748W

Abstract

When a fluid-immersed array of lamellae or filaments that is attached to a substrate is dried, evaporation leads to the formation of menisci on the tips of the plates or pillars that bring them together. Similarly, when hair dries it clumps together due to capillary forces induced by the liquid menisci between the flexible hairs. Building on prior experimental observations, we use a combination of theory and computation to understand the nature of this instability and its evolution in both the two-dimensional and three-dimensional setting of the problem. For the case of lamellae, we explicitly derive the interaction torques based on the relevant physical parameters. A Bloch-wave analysis for our periodic mechanical system captures the critical volume of the liquid and the 2-plate-collapse eigenmode at the onset of instability. We study the evolution of clusters and their arrest using numerical simulations to explain the hierarchical cluster formation and characterize the sensitive dependence of the final structures on the initial perturbations. We then generalize our analysis to treat the problem of pillar collapse in 3D, where the fluid domain is completely connected and the interface is a surface with the uniform mean curvature. Our theory and simulations capture the salient features of both previous experimental observations and our own in terms of the key parameters that can be used to control the kinetics of the process.

 

Title:
A Simple Alternative to Jet-Clustering Algorithms
Authors:
Georgi, Howard
Publication:
eprint arXiv:1408.1161
Publication Date:
08/2014
Origin:
ARXIV
Keywords:
High Energy Physics - Phenomenology
Comment:
7 pages, 0 figures
Bibliographic Code:
2014arXiv1408.1161G

Abstract

I describe a class of iterative jet algorithms that are based on maximizing a fixed function of the total 4-momentum rather than clustering of pairs of jets. I describe some of the properties of the simplest examples of this class, appropriate for jets at an $e^+e^-$ machine. These examples are sufficiently simple that many features of the jets that they define can be determined analytically with ease. The jets constructed in this way have some potentially useful properties, including a strong form of infrared safety.

 

Title:
Anomalous diffusion and Griffiths effects near the many-body localization transition
Authors:
Agarwal, Kartiek; Gopalakrishnan, Sarang; Knap, Michael; Mueller, Markus; Demler, Eugene
Publication:
eprint arXiv:1408.3413
Publication Date:
08/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Disordered Systems and Neural Networks, Condensed Matter - Statistical Mechanics, Condensed Matter - Strongly Correlated Electrons
Comment:
6 pages, 3 figures + Supplemental Material
Bibliographic Code:
2014arXiv1408.3413A

Abstract

We explore the high-temperature dynamics of the disordered, one-dimensional XXZ model near the many-body localization (MBL) transition, focusing on the delocalized (i.e., "metallic") phase. In the vicinity of the transition, we find that this phase has the following properties: (i) Local magnetization fluctuations relax subdiffusively; (ii) the a.c. conductivity vanishes near zero frequency as a power law; (iii) the distribution of resistances becomes increasingly broad at low frequencies, approaching a power law in the zero-frequency limit. We argue that these effects can be understood in a unified way if the metallic phase near the MBL transition is a Griffiths phase. We establish scaling relations between the associated exponents, using exact linear-response arguments as well as a phenomenological resistor-capacitor model.

 

Title:
The impact of macroscopic epistasis on long-term evolutionary dynamics
Authors:
Good, Benjamin H.; Desai, Michael M.
Publication:
eprint arXiv:1408.4108
Publication Date:
08/2014
Origin:
ARXIV
Keywords:
Quantitative Biology - Populations and Evolution
Bibliographic Code:
2014arXiv1408.4108G

Abstract

Genetic interactions can strongly influence the fitness effects of individual mutations, yet the impact of these epistatic interactions on evolutionary dynamics remains poorly understood. Here we investigate the evolutionary role of epistasis over 50,000 generations in a well-studied laboratory evolution experiment in E. coli. The extensive duration of this experiment provides a unique window into the effects of epistasis during long-term adaptation to a constant environment. Guided by analytical results in the weak-mutation limit, we develop a computational framework to assess the compatibility of a given epistatic model with the observed patterns of fitness gain and mutation accumulation through time. We find that the average fitness trajectory alone provides little power to distinguish between competing models, including those that lack any direct epistatic interactions between mutations. However, when combined with the mutation trajectory, these observables place strong constraints on the set of possible models of epistasis, ruling out most existing explanations of the data. Instead, we find the strongest support for a "two-epoch" model of adaptation, in which an initial burst of diminishing returns epistasis is followed by a steady accumulation of mutations under a constant distribution of fitness effects. Our results highlight the need for additional DNA sequencing of these populations, as well as for more sophisticated models of epistasis that are compatible with all of the experimental data.

 

Title:
High-Q 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.; Lončar, Marko
Publication:
eprint arXiv:1408.5973
Publication Date:
08/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Mesoscale and Nanoscale Physics, Physics - Optics
Bibliographic Code:
2014arXiv1408.5973B

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 remain 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 10^5, 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:
Survival Probabilities at Spherical Frontiers
Authors:
Lavrentovich, Maxim O.; Nelson, David R.
Publication:
eprint arXiv:1408.6006
Publication Date:
08/2014
Origin:
ARXIV
Keywords:
Quantitative Biology - Populations and Evolution, Condensed Matter - Statistical Mechanics
Comment:
41 pages, 12 figures
Bibliographic Code:
2014arXiv1408.6006L

Abstract

Motivated by tumor growth and spatial population genetics, we study the interplay between evolutionary and spatial dynamics at the surfaces of three-dimensional, spherical range expansions. We consider an arbitrary time dependence of the range expansion radius $R(t)=R_0(1+t/t^*)^{\Theta}$, where $t^*$ is a cross-over time, $\Theta$ is a growth exponent, and $R_0$ is the initial radius. Guided by recent results for two-dimensional inflating range expansions, we identify the key dimensionless parameters and universal functions that describe the survival probability of a mutant cell with a selective advantage $s$ arising at the population frontier in the limit of small selective advantage $s$. We focus on linearly inflating expansions ($\Theta=1$ spherical Fisher-Kolmogorov-Petrovsky-Piscunov waves), treadmilling expansions ($\Theta=0$, with cells in the interior removed by apoptosis or a similar process), and "marginally inflating" $(\Theta=1/2)$ expansions. We find that inflating fronts can enhance mutant survival probabilities by factors of 100 or more.

 

Title:
DC resistivity at the onset of spin density wave order in two-dimensional metals
Authors:
Patel, Aavishkar A.; Sachdev, Subir
Publication:
eprint arXiv:1408.6549
Publication Date:
08/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Strongly Correlated Electrons, High Energy Physics - Theory
Comment:
25 pages, 5 figures
Bibliographic Code:
2014arXiv1408.6549P

Abstract

The theory for the onset of spin density wave order in a metal in two dimensions flows to strong coupling, with strong interactions not only at the `hot spots', but on the entire Fermi surface. We advocate the computation of DC transport in a regime where there is rapid relaxation to local equilibrium around the Fermi surface by processes which conserve total momentum. The DC resistivity is then controlled by weaker perturbations which do not conserve momentum. We consider variations in the local position of the quantum critical point, induced by long-wavelength disorder, and find a contribution to the resistivity which is linear in temperature (up to logarithmic corrections) at low temperature. Scattering of fermions between hot spots, by short-wavelength disorder, leads to a residual resistivity and a correction which is linear in temperature.

 

Title:
Dissipative phase transitions: independent vs. collective decay and spin squeezing
Authors:
Lee, Tony E.; Chan, Ching-Kit; Yelin, Susanne F.
Publication:
eprint arXiv:1408.6830
Publication Date:
08/2014
Origin:
ARXIV
Keywords:
Quantum Physics, Condensed Matter - Quantum Gases, Nonlinear Sciences - Chaotic Dynamics
Comment:
9 pages, 6 figures
Bibliographic Code:
2014arXiv1408.6830L

Abstract

We study the XY model with infinite-range interactions (Lipkin-Meshkov-Glick model) in the presence of dissipation from spontaneous decay. We show that independent and collective decay lead to qualitatively different phase transitions of the steady state, even though the phase boundary is the same. Independent decay leads to a second-order phase transition to a ferromagnet, while collective decay leads to a first-order transition to a time-dependent oscillatory phase. Then we show that the addition of a drive leads to infinite spin squeezing for collective decay in the thermodynamic limit. The combination of spin-spin interaction and drive leads to more spin squeezing than each by itself. Our results can be experimentally seen in trapped-ion and cavity-QED experiments.

 

Title:
Multifarious Assembly Mixtures: Systems Allowing Retrieval of Diverse Stored Structures
Authors:
Murugan, Arvind; Zeravcic, Zorana; Brenner, Michael P.; Leibler, Stanislas
Publication:
eprint arXiv:1408.6893
Publication Date:
08/2014
Origin:
ARXIV
Keywords:
Condensed Matter - Disordered Systems and Neural Networks, Condensed Matter - Soft Condensed Matter, Condensed Matter - Statistical Mechanics
Comment:
Paper + SI. Figures at the end
Bibliographic Code:
2014arXiv1408.6893M

Abstract

Self-assembly materials are traditionally designed so that molecular or meso-scale components form a single kind of large structure. Here, we propose a scheme to create "multifarious assembly mixtures", which self-assemble many different large structures from a set of shared components. We show that the number of multifarious structures stored in the solution of components increases rapidly with the number of different types of components. Yet, each stored structure can be retrieved by tuning only a few parameters, the number of which is only weakly dependent on the size of the assembled structure. Implications for artificial and biological self-assembly are discussed.

 

Title:
Measurement of collective dynamical mass of Dirac fermions in graphene
Authors:
Yoon, Hosang; Forsythe, Carlos; Wang, Lei; Tombros, Nikolaos; Watanabe, Kenji; Taniguchi, Takashi; Hone, James; Kim, Philip; Ham, Donhee
Publication:
Nature Nanotechnology, Volume 9, Issue 8, pp. 594-599 (2014).
Publication Date:
08/2014
Origin:
NATURE
Abstract Copyright:
(c) 2014: Nature Publishing Group
DOI:
10.1038/nnano.2014.112
Bibliographic Code:
2014NatNa...9..594Y

Abstract

Individual electrons in graphene behave as massless quasiparticles. Unexpectedly, it is inferred from plasmonic investigations that electrons in graphene must exhibit a non-zero mass when collectively excited. The inertial acceleration of the electron collective mass is essential to explain the behaviour of plasmons in this material, and may be directly measured by accelerating it with a time-varying voltage and quantifying the phase delay of the resulting current. This voltage-current phase relation would manifest as a kinetic inductance, representing the reluctance of the collective mass to accelerate. However, at optical (infrared) frequencies, phase measurements of current are generally difficult, and, at microwave frequencies, the inertial phase delay has been buried under electron scattering. Therefore, to date, the collective mass in graphene has defied unequivocal measurement. Here, we directly and precisely measure the kinetic inductance, and therefore the collective mass, by combining device engineering that reduces electron scattering and sensitive microwave phase measurements. Specifically, the encapsulation of graphene between hexagonal boron nitride layers, one-dimensional edge contacts and a proximate top gate configured as microwave ground together enable the inertial phase delay to be resolved from the electron scattering. Beside its fundamental importance, the kinetic inductance is found to be orders of magnitude larger than the magnetic inductance, which may be utilized to miniaturize radiofrequency integrated circuits. Moreover, its bias dependency heralds a solid-state voltage-controlled inductor to complement the prevalent voltage-controlled capacitor.

 

Title:
A quantum network of clocks
Authors:
Kómár, P.; Kessler, E. M.; Bishof, M.; Jiang, L.; Sørensen, A. S.; Ye, J.; Lukin, M. D.
Publication:
Nature Physics, Volume 10, Issue 8, pp. 582-587 (2014).
Publication Date:
08/2014
Origin:
NATURE
Abstract Copyright:
(c) 2014: Nature Publishing Group
DOI:
10.1038/nphys3000
Bibliographic Code:
2014NatPh..10..582K

Abstract

The development of precise atomic clocks plays an increasingly important role in modern society. Shared timing information constitutes a key resource for navigation with a direct correspondence between timing accuracy and precision in applications such as the Global Positioning System. By combining precision metrology and quantum networks, we propose a quantum, cooperative protocol for operating a network of geographically remote optical atomic clocks. Using nonlocal entangled states, we demonstrate an optimal utilization of global resources, and show that such a network can be operated near the fundamental precision limit set by quantum theory. Furthermore, the internal structure of the network, combined with quantum communication techniques, guarantees security both from internal and external threats. Realization of such a global quantum network of clocks may allow construction of a real-time single international time scale (world clock) with unprecedented stability and accuracy.

 

Title:
Measurement of event-plane correlations in √sNN =2.76 TeV lead-lead collisions with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Guimarães da Costa, J.;... Huth, J.;...; Morii, M.; and 2878 coauthors
Publication:
Physical Review C, Volume 90, Issue 2, id.024905 (PhRvC Homepage)
Publication Date:
08/2014
Origin:
APS
PACS Keywords:
Particle and resonance production, Particle correlations
Abstract Copyright:
2014: CERN
DOI:
10.1103/PhysRevC.90.024905
Bibliographic Code:
2014PhRvC..90b4905A

Abstract

A measurement of event-plane correlations involving two or three event planes of different order is presented as a function of centrality for 7 μb-1 Pb +Pb collision data at √sNN =2.76 TeV, recorded by the ATLAS experiment at the Large Hadron Collider. Fourteen correlators are measured using a standard event-plane method and a scalar-product method, and the latter method is found to give a systematically larger correlation signal. Several different trends in the centrality dependence of these correlators are observed. These trends are not reproduced by predictions based on the Glauber model, which includes only the correlations from the collision geometry in the initial state. Calculations that include the final-state collective dynamics are able to describe qualitatively, and in some cases also quantitatively, the centrality dependence of the measured correlators. These observations suggest that both the fluctuations in the initial geometry and the nonlinear mixing between different harmonics in the final state are important for creating these correlations in momentum space.

 

Title:
Measurement of charged pion production yields off the NuMI target
Authors:
Paley, J. M.; Messier, M. D.; Raja, R.;... Feldman, G. J.;... and 53 coauthors (MIPP Collaboration)
Publication:
Physical Review D, Volume 90, Issue 3, id.032001 (PhRvD Homepage)
Publication Date:
08/2014
Origin:
APS
PACS Keywords:
Inelastic proton scattering, Monte Carlo simulations, Neutrino scattering
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevD.90.032001
Bibliographic Code:
2014PhRvD..90c2001P

Abstract

The fixed-target Main Injector Particle Production (MIPP) experiment, Fermilab E907, was designed to measure the production of hadrons from the collisions of hadrons of momenta ranging from 5 to 120 GeV/c on a variety of nuclei. These data will generally improve the simulation of particle detectors and predictions of particle beam fluxes at accelerators. The spectrometer momentum resolution is between 3% and 4%, and particle identification is performed for particles ranging between 0.3 and 80 GeV/c using dE/dx, time-of-flight, and Cherenkov radiation measurements. MIPP collected 1.42×106 events of 120 GeV Main Injector protons striking a target used in the Neutrinos at the Main Injector facility at Fermilab. The data have been analyzed and we present here charged pion yields per proton on target determined in bins of longitudinal and transverse momentum between 0.5 and 80 GeV/c, with combined statistical and systematic relative uncertainties between 5% and 10%.

 

Title:
Gravity waves from the Kerr/CFT correspondence
Authors:
Porfyriadis, Achilleas P.; Strominger, Andrew
Publication:
Physical Review D, Volume 90, Issue 4, id.044038 (PhRvD Homepage)
Publication Date:
08/2014
Origin:
APS
PACS Keywords:
Gravitational waves: theory, Quantum gravity
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevD.90.044038
Bibliographic Code:
2014PhRvD..90d4038P

Abstract

Dynamics at large redshift near the horizon of an extreme Kerr black hole are governed by an infinite-dimensional conformal symmetry. This symmetry may be exploited to analytically, rather than numerically, compute a variety of potentially observable processes. In this paper we compute and study the conformal transformation properties of the gravitational radiation emitted by an orbiting mass in the large-redshift near-horizon region.

 

Title:
RecA-mediated sequence homology recognition as an example of how searching speed in self-assembly systems can be optimized by balancing entropic and enthalpic barriers
Authors:
Jiang, Lili; Prentiss, Mara
Publication:
Physical Review E, Volume 90, Issue 2, id.022704 (PhRvE Homepage)
Publication Date:
08/2014
Origin:
APS
PACS Keywords:
Monte Carlo simulations, Monte Carlo simulations, Monte Carlo calculations, Stochastic modeling
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevE.90.022704
Bibliographic Code:
2014PhRvE..90b2704J

Abstract

Ideally, self-assembly should rapidly and efficiently produce stable correctly assembled structures. We study the tradeoff between enthalpic and entropic cost in self-assembling systems using RecA-mediated homology search as an example. Earlier work suggested that RecA searches could produce stable final structures with high stringency using a slow testing process that follows an initial rapid search of ˜9-15 bases. In this work, we will show that as a result of entropic and enthalpic barriers, simultaneously testing all ˜9-15 bases as separate individual units results in a longer overall searching time than testing them in groups and stages.

 

Title:
Unstable Avoided Crossing in Coupled Spinor Condensates
Authors:
Bernier, Nathan R.; Dalla Torre, Emanuele G.; Demler, Eugene
Publication:
Physical Review Letters, Volume 113, Issue 6, id.065303 (PhRvL Homepage)
Publication Date:
08/2014
Origin:
APS
PACS Keywords:
Dynamic properties of condensates, excitations and superfluid flow, Multicomponent condensates, spinor condensates, Pattern selection, pattern formation
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevLett.113.065303
Bibliographic Code:
2014PhRvL.113f5303B

Abstract

We consider the dynamics of a Bose-Einstein condensate with two internal states, coupled through a coherent drive. We focus on a specific quench protocol, in which the sign of the coupling field is suddenly changed. At a mean-field level, the system is transferred from a minimum to a maximum of the coupling energy and can remain dynamically stable, in spite of the development of negative-frequency modes. In the presence of a nonzero detuning between the two states, the "charge" and "spin" modes couple, giving rise to an unstable avoided crossing. This phenomenon is generic to systems with two dispersing modes away from equilibrium and constitutes an example of class-Io nonequilibrium pattern formation in quantum systems.

 

Title:
Gopalakrishnan, Martin, and Demler Reply:
Authors:
Gopalakrishnan, Sarang; Martin, Ivar; Demler, Eugene A.
Publication:
Physical Review Letters, Volume 113, Issue 7, id.079603 (PhRvL Homepage)
Publication Date:
08/2014
Origin:
APS
PACS Keywords:
Ultracold gases trapped gases, Multicomponent condensates, spinor condensates, Spin-orbit coupling Zeeman and Stark splitting Jahn-Teller effect
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevLett.113.079603
Bibliographic Code:
2014PhRvL.113g9603G

Abstract

A Reply to the Comments by M. Sandbrink et al. and R. Lifshitz.

 

Title:
Enhanced Antiferromagnetic Exchange between Magnetic Impurities in a Superconducting Host
Authors:
Yao, N. Y.; Glazman, L. I.; Demler, E. A.; Lukin, M. D.; Sau, J. D.
Publication:
Physical Review Letters, Volume 113, Issue 8, id.087202 (PhRvL Homepage)
Publication Date:
08/2014
Origin:
APS
PACS Keywords:
Magnetic impurity interactions, Electric and magnetic moments polarizability and magnetic susceptibility, Magnetic properties, Exchange and superexchange interactions
Abstract Copyright:
2014: American Physical Society
DOI:
10.1103/PhysRevLett.113.087202
Bibliographic Code:
2014PhRvL.113h7202Y

Abstract

It is generally believed that superconductivity only weakly affects the indirect exchange between magnetic impurities. If the distance r between impurities is smaller than the superconducting coherence length (r≲ξ), this exchange is thought to be dominated by Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions, identical to the those in a normal metallic host. This perception is based on a perturbative treatment of the exchange interaction. Here, we provide a nonperturbative analysis and demonstrate that the presence of Yu-Shiba-Rusinov bound states induces a strong 1/r2 antiferromagnetic interaction that can dominate over conventional RKKY even at distances significantly smaller than the coherence length (r≪ξ). Experimental signatures, implications, and applications are discussed.

 

Title:
Parallel in time approximation of the lattice Boltzmann method for laminar flows
Authors:
Randles, A.; Kaxiras, E.
Publication:
Journal of Computational Physics 1 Aug. 2014, vol.270, pp. 577-86. ISSN: 0021-9991
Publication Date:
08/2014
Publisher:
Elsevier
Database:
Inspec
Inspec Headings:
flow simulation; laminar flow; lattice Boltzmann methods; mesh generation; predictor-corrector methods; shapes (structures)
DOI:
10.1016/j.jcp.2014.04.006

Abstract

Fluid dynamics simulations using grid-based methods, such as the lattice Boltzmann equation, can benefit from parallel-in-space computation. However, for a fixed-size simulation of this type, the efficiency of larger processor counts will saturate when the number of grid points per core becomes too small. To overcome this fundamental strong scaling limit in space-parallel approaches, we present a novel time-parallel version of the lattice Boltzmann method using the parareal algorithm. This method is based on a predictor-corrector scheme combined with mesh refinement to enable the simulation of larger number of time steps. We present results of up to a 32× increase in speed for a model system consisting of a cylinder with conditions for laminar flow. The parallel gain obtainable is predicted with strong accuracy, providing a quantitative understanding of the potential impact of this method. [All rights reserved Elsevier].


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