Faculty Publications: April, 2016

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

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

Title:
The Optical-infrared Extinction Curve and Its Variation in the Milky Way
Authors:
Schlafly, E. F.; Meisner, A. M.; Stutz, A. M.; Kainulainen, J.; Peek, J. E. G.; Tchernyshyov, K.; Rix, H.-W.; Finkbeiner, D. P.; Covey, K. R.; Green, G. M.; Bell, E. F.; Burgett, W. S.; Chambers, K. C.; Draper, P. W.; Flewelling, H.; Hodapp, K. W.; Kaiser, N.; Magnier, E. A.; Martin, N. F.; Metcalfe, N.; Wainscoat, R. J.; Waters, C.
Publication:
The Astrophysical Journal, Volume 821, Issue 2, article id. 78, 25 pp. (2016). (ApJ Homepage)
Publication Date:
04/2016
Origin:
IOP
Astronomy Keywords:
dust, extinction, ISM: clouds, ISM: structure
DOI:
10.3847/0004-637X/821/2/78
Bibliographic Code:
2016ApJ...821...78S

Abstract

The dust extinction curve is a critical component of many observational programs and an important diagnostic of the physics of the interstellar medium. Here we present new measurements of the dust extinction curve and its variation toward tens of thousands of stars, a hundred-fold larger sample than in existing detailed studies. We use data from the APOGEE spectroscopic survey in combination with ten-band photometry from Pan-STARRS1, the Two Micron All-Sky Survey, and Wide-field Infrared Survey Explorer. We find that the extinction curve in the optical through infrared is well characterized by a one-parameter family of curves described by R(V). The extinction curve is more uniform than suggested in past works, with σ (R(V))=0.18, and with less than one percent of sight lines having R(V)\gt 4. Our data and analysis have revealed two new aspects of Galactic extinction: first, we find significant, wide-area variations in R(V) throughout the Galactic plane. These variations are on scales much larger than individual molecular clouds, indicating that R(V) variations must trace much more than just grain growth in dense molecular environments. Indeed, we find no correlation between R(V) and dust column density up to E(B-V)≈ 2. Second, we discover a strong relationship between R(V) and the far-infrared dust emissivity.

 

Title:
Updated Kinematic Constraints on a Dark Disk
Authors:
Kramer, Eric David; Randall, Lisa
Publication:
eprint arXiv:1604.01407
Publication Date:
04/2016
Origin:
ARXIV
Keywords:
Astrophysics - Astrophysics of Galaxies
Comment:
Accepted for publication in ApJ
Bibliographic Code:
2016arXiv160401407K

Abstract

We update the method of the Holmberg & Flynn (2000) study, including an updated model of the Milky Way's interstellar gas, radial velocities, an updated reddening map, and a careful statistical analysis, to bound the allowed surface density and scale height of a dark disk. We pay careful attention to the self-consistency of the model, including the gravitational influence of the dark disk on other disk components, and to the net velocity of the tracer stars. We find that the data set exhibits a non-zero bulk velocity in the vertical direction as well as a displacement from the expected location at the Galactic midplane. If not properly accounted for, these features would bias the bound toward low dark disk mass. We therefore perform our analysis two ways. In the first, traditional method, we subtract the mean velocity and displacement from the tracers' phase space distributions. In the second method, we perform a non-equilibrium version of the HF method to derive a bound on the dark disk parameters for an oscillating tracer distribution. Despite updates in the mass model and reddening map, the traditional method results remain consistent with those of HF2000. The second, non-equilibrium technique, however, allows a surface density as large as $14\, M_\odot\,{\rm pc}^{-2}$ (and as small as 0), demonstrating much weaker constraints. For both techniques, the bound on surface density is weaker for larger scale height. In future analyses of Gaia data, it will be important to verify whether the tracer populations are in equilibrium.

 

Title:
Sharp Davies-Gaffney-Grigor'yan Lemma on Graphs
Authors:
Bauer, Frank; Hua, Bobo; Yau, Shing-Tung
Publication:
eprint arXiv:1604.01911
Publication Date:
04/2016
Origin:
ARXIV
Keywords:
Mathematics - Differential Geometry, Mathematics - Metric Geometry, Mathematics - Spectral Theory
Bibliographic Code:
2016arXiv160401911B

Abstract

In this note, we prove the sharp Davies-Gaffney-Grigor'yan lemma for minimal heat kernels on graphs.

 

Title:
Chiral algebra of Argyres-Douglas theory from M5 brane
Authors:
Xie, Dan; Yan, Wenbin; Yau, Shing-Tung
Publication:
eprint arXiv:1604.02155
Publication Date:
04/2016
Origin:
ARXIV
Keywords:
High Energy Physics - Theory, Mathematics - Quantum Algebra, Mathematics - Representation Theory
Comment:
5 pages, 1 figure
Bibliographic Code:
2016arXiv160402155X

Abstract

We study chiral algebras associated with Argyres-Douglas theories engineered from M5 brane. For the theory engineered using 6d $(2,0)$ type $J$ theory on a sphere with a single irregular singularity (without mass parameter), its chiral algebra is the minimal model of W algebra of $J$ type. For the theory engineered using an irregular singularity and a regular full singularity, its chiral algebra is the affine Kac-Moody algebra of $J$ type. We can obtain the Schur index of these theories by computing the vacua character of the corresponding chiral algebra.

 

Title:
Quasi-local energy with respect to a static spacetime
Authors:
Chen, Po-Ning; Wang, Mu-Tao; Wang, Ye-Kai; Yau, Shing-Tung
Publication:
eprint arXiv:1604.02983
Publication Date:
04/2016
Origin:
ARXIV
Keywords:
Mathematics - Differential Geometry, General Relativity and Quantum Cosmology
Comment:
16 pages. arXiv admin note: text overlap with arXiv:1603.02975
Bibliographic Code:
2016arXiv160402983C

Abstract

This article considers the quasi-local energy in reference to a general static spacetime. We follow the approach developed by the authors in [19, 20, 7, 9] and define the quasi-local energy as a difference of surface Hamiltonians, which are derived from the Einstein-Hilbert action. The new quasi-local energy provides an effective gauge independent measurement of how far a spacetime deviates away from the reference static spacetime on a finitely extended region.

 

Title:
Direct single-shot observation of millimeter wave superradiance in Rydberg-Rydberg transitions
Authors:
Grimes, David D.; Coy, Stephen L.; Barnum, Timothy J.; Zhou, Yan; Yelin, Susanne F.; Field, Robert W.
Publication:
eprint arXiv:1604.03005
Publication Date:
04/2016
Origin:
ARXIV
Keywords:
Physics - Atomic Physics
Comment:
5 pages, 4 figures
Bibliographic Code:
2016arXiv160403005G

Abstract

We have directly detected millimeter wave (mm-wave) free space superradiant emission from Rydberg states ($n \sim 30$) of barium atoms in a single shot. We trigger the cooperative effects with a weak initial pulse and detect with single-shot sensitivity and 20 ps time resolution, which allows measurement and shot-by-shot analysis of the distribution of decay rates, time delays, and time-dependent frequency shifts. Cooperative line shifts and decay rates are observed that exceed values that would correspond to the Doppler width of 250 kHz by a factor of 20 and the spontaneous emission rate of 50 Hz by a factor of $10^5$. The initial superradiant output pulse is followed by evolution of the radiation-coupled many-body system toward complex long-lasting emission modes. A comparison to a mean-field theory is presented which reproduces the quantitative time-domain results, but fails to account for either the frequency-domain observations or the long-lived features.

 

Title:
F-Theory and N=1 SCFTs in Four Dimensions
Authors:
Morrison, David R.; Vafa, Cumrun
Publication:
eprint arXiv:1604.03560
Publication Date:
04/2016
Origin:
ARXIV
Keywords:
High Energy Physics - Theory
Bibliographic Code:
2016arXiv160403560M

Abstract

Using the F-theory realization, we identify a subclass of 6d (1,0) SCFTs whose compactification on a Riemann surface leads to N = 1 4d SCFTs where the moduli space of the Riemann surface is part of the moduli space of the theory. In particular we argue that for a special case of these theories (dual to M5 branes probing ADE singularities), we obtain 4d N = 1 theories whose space of marginal deformations is given by the moduli space of flat ADE connections on a Riemann surface.

 

Title:
Electronic Structure Theory of Weakly Interacting Bilayers
Authors:
Fang, Shiang; Kaxiras, Efthimios
Publication:
eprint arXiv:1604.05371
Publication Date:
04/2016
Origin:
ARXIV
Keywords:
Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Materials Science
Comment:
7 pages, 4 figures
Bibliographic Code:
2016arXiv160405371F

Abstract

We derive electronic structure models for weakly interacting bilayers such as graphene-graphene and graphene-hexagonal boron nitride, based on density functional theory calculations followed by Wannier transformation of electronic states. These transferable interlayer coupling models can be applied to investigate the physics of bilayers with arbitrary translations and twists. The functional form, in addition to the dependence on the distance, includes the angular dependence that results from higher angular momentum components in the Wannier $p_z$ orbitals. We demonstrate the capabilities of the method by applying it to a rotated graphene bilayer, which produces the analytically predicted renormalization of the Fermi velocity, van Hove singularities in the density of states, and Moir\'{e} pattern of the electronic localization at small twist angles. We further extend the theory to obtain the effective couplings by integrating out neighboring layers. This approach is instrumental for the design of van der Walls heterostructures with desirable electronic features and transport properties and for the derivation of low-energy theories for graphene stacks, including proximity effects from other layers.

 

Title:
Precision decay rate calculations in quantum field theory
Authors:
Andreassen, Anders; Farhi, David; Frost, William; Schwartz, Matthew D.
Publication:
eprint arXiv:1604.06090
Publication Date:
04/2016
Origin:
ARXIV
Keywords:
High Energy Physics - Theory, High Energy Physics - Phenomenology
Comment:
88 pages, 18 figures
Bibliographic Code:
2016arXiv160406090A

Abstract

Tunneling in quantum field theory is worth understanding properly, not least because it controls the long term fate of our universe. There are however, a number of features of tunneling rate calculations which lack a desirable transparency, such as the necessity of analytic continuation, the appropriateness of using an effective instead of classical potential, and the sensitivity to short-distance physics. This paper attempts to review in pedagogical detail the physical origin of tunneling and its connection to the path integral. Both the traditional potential-deformation method and a recent more direct propagator-based method are discussed. Some new insights from using approximate semi-classical solutions are presented. In addition, we explore the sensitivity of the lifetime of our universe to short distance physics, such as quantum gravity, emphasizing a number of important subtleties.

 

Title:
Quantum dynamics of ultracold Bose polarons
Authors:
Shchadilova, Yulia E.; Schmidt, Richard; Grusdt, Fabian; Demler, Eugene
Publication:
eprint arXiv:1604.06469
Publication Date:
04/2016
Origin:
ARXIV
Keywords:
Condensed Matter - Quantum Gases, Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Other Condensed Matter, Condensed Matter - Strongly Correlated Electrons, Quantum Physics
Comment:
9 pages, 4 figures
Bibliographic Code:
2016arXiv160406469S

Abstract

We analyze the dynamics of Bose polarons in the vicinity of a Feshbach resonance between the impurity and host atoms. We compute the radio-frequency absorption spectra for the case when the initial state of the impurity is non-interacting and the final state is strongly interacting. We compare results of different theoretical approaches including a single excitation expansion, a self-consistent T-matrix method, and a time-dependent coherent state approach. Our analysis reveals sharp spectral features arising from metastable states with several Bogoliubov excitations bound to the impurity atom. This surprising result of the interplay of many-body and few-body Efimov type bound state physics can only be obtained by going beyond the commonly used Fr\"ohlich model and including quasiparticle scattering processes. Close to the resonance we find that strong fluctuations lead to a broad, incoherent absorption spectrum where no quasi-particle peak can be assigned.

 

Title:
Colloidal particle adsorption at liquid interfaces: Capillary driven dynamics and thermally activated kinetics
Authors:
Rahmani, Amir M.; Wang, Anna; Manoharan, Vinothan N.; Colosqui, Carlos E.
Publication:
eprint arXiv:1604.06836
Publication Date:
04/2016
Origin:
ARXIV
Keywords:
Condensed Matter - Soft Condensed Matter
Comment:
8 pages, 4 figures
Bibliographic Code:
2016arXiv160406836R

Abstract

The adsorption of single colloidal microparticles (0.5--1 $\mu$m radius) at a water-oil interface has been recently studied experimentally using digital holographic microscopy [Kaz \textit{et al., Nat. Mater.}, 2012, \textbf{11}, 138--142]. An initially fast adsorption dynamics driven by capillary forces is followed by an unexpectedly slow relaxation to equilibrium that is logarithmic in time and can span hours or days. The slow relaxation kinetics has been attributed to the presence of surface "defects" with nanoscale dimensions (1--5\,nm) that induce multiple metastable configurations of the contact line perimeter. A kinetic model considering thermally activated transitions between such metastable configurations has been proposed [Colosqui \textit{et al., Phys. Rev. Lett.}, 2013, \textbf{111}, 028302] to predict both the relaxation rate and the crossover point to the slow logarithmic regime. However, the adsorption dynamics observed experimentally before the crossover point has remained unstudied. In this work, we propose a Langevin model that is able to describe the entire adsorption process of single colloidal particles by considering metastable states produced by surface defects and thermal motion of the particle and liquid interface. Invoking the fluctuation dissipation theorem, we introduce a drag term that considers significant dissipative forces induced by thermal fluctuations of the liquid interface. Langevin dynamics simulations based on the proposed adsorption model yield close agreement with experimental observations for different microparticles, capturing the crossover from (fast) capillary driven dynamics to (slow) thermally activated kinetics.

 

Title:
Ultrafast many-body interferometry of impurities coupled to a Fermi sea
Authors:
Cetina, M.; Jag, M.; Lous, R. S.; Fritsche, I.; Walraven, J. T. M.; Grimm, R.; Levinsen, J.; Parish, M. M.; Schmidt, R.; Knap, M.; Demler, E.
Publication:
eprint arXiv:1604.07423
Publication Date:
04/2016
Origin:
ARXIV
Keywords:
Condensed Matter - Quantum Gases
Comment:
21 pages, 14 figures
Bibliographic Code:
2016arXiv160407423C

Abstract

The fastest possible collective response of a quantum many-body system is related to its excitations at the highest possible energy. In condensed-matter systems, the corresponding timescale is typically set by the Fermi energy. Taking advantage of fast and precise control of interactions between ultracold atoms, we report on the observation of ultrafast dynamics of impurities coupled to an atomic Fermi sea. Our interferometric measurements track the non-perturbative quantum evolution of a fermionic many-body system, revealing in real time the formation dynamics of quasiparticles and the quantum interference between attractive and repulsive states throughout the full depth of the Fermi sea. Ultrafast time-domain methods to manipulate and investigate strongly interacting quantum gases open up new windows on the dynamics of quantum matter under extreme non-equilibrium conditions.

 

Title:
Ultra-precise holographic beam shaping for microscopic quantum control
Authors:
Zupancic, Philip; Preiss, Philipp M.; Ma, Ruichao; Lukin, Alexander; Tai, M. Eric; Rispoli, Matthew; Islam, Rajibul; Greiner, Markus
Publication:
eprint arXiv:1604.07653
Publication Date:
04/2016
Origin:
ARXIV
Keywords:
Condensed Matter - Quantum Gases, Physics - Optics, Quantum Physics
Comment:
12 pages, 7 figures
Bibliographic Code:
2016arXiv160407653Z

Abstract

High-resolution addressing of single ultracold atoms, trapped ions or solid state emitters allows for exquisite control in quantum optics experiments. This becomes possible through large aperture magnifying optics that project microscopic light patterns with diffraction limited performance. We use programmable amplitude holograms generated on a digital micromirror device to create arbitrary microscopic beam shapes with full phase and amplitude control. The system self-corrects for aberrations of up to several $\lambda$ and reduces them to $\lambda/50$, leading to light patterns with a precision on the $10^{-4}$ level. We demonstrate aberration-compensated beam shaping in an optical lattice experiment and perform single-site addressing in a quantum gas microscope for $^{87}$Rb.

 

Title:
4d N=2 SCFT and singularity theory Part II: Complete intersection
Authors:
Chen, Bingyi; Xie, Dan; Yau, Shing-Tung; Yau, Stephen S.-T.; Zuo, Huaiqing
Publication:
eprint arXiv:1604.07843
Publication Date:
04/2016
Origin:
ARXIV
Keywords:
High Energy Physics - Theory, Mathematics - Algebraic Geometry
Comment:
64 pages, 1 figure
Bibliographic Code:
2016arXiv160407843C

Abstract

We classify three dimensional isolated weighted homogeneous rational complete intersection singularities, which define many new four dimensional N=2 superconformal field theories. We also determine the mini-versal deformation of these singularities, and therefore solve the Coulomb branch spectrum and Seiberg-Witten solution.

 

Title:
Supplement: Localization and broadband follow-up of the gravitational-wave transient GW150914
Authors:
Abbott, B. P.; Abbott, R.; Abbott, T. D.; ... Stubbs, C. W.; ... and 1581 coauthors (for the VISTA Collaboration)
Publication:
eprint arXiv:1604.07864
Publication Date:
04/2016
Origin:
ARXIV
Keywords:
Astrophysics - High Energy Astrophysical Phenomena, General Relativity and Quantum Cosmology
Comment:
19 pages, 1 table, submitted to ApJS
Bibliographic Code:
2016arXiv160407864A

Abstract

This Supplement provides supporting material for arXiv:1602.08492 . We briefly summarize past electromagnetic follow-up efforts as well as the organization and policy of the current electromagnetic follow-up program. We compare the four probability sky maps produced for the gravitational-wave transient GW150914, and provide additional details of the electromagnetic follow-up observations that were performed in the different bands.

 

Title:
Rydberg atom mediated non-destructive readout of collective rotational states in polar molecule arrays
Authors:
Kuznetsova, Elena; Rittenhouse, Seth T.; Sadeghpour, H. R.; Yelin, Susanne F.
Publication:
eprint arXiv:1604.08535
Publication Date:
04/2016
Origin:
ARXIV
Keywords:
Quantum Physics, Physics - Atomic Physics
Bibliographic Code:
2016arXiv160408535K

Abstract

We analyze in detail the possibility to use charge-dipole interaction between a single polar molecule or a 1D molecular array and a single Rydberg atom to read out rotational populations. The change in the Rydberg electron energy is conditioned on the rotational state of the polar molecules, allowing for realization of a CNOT quantum gate between the molecules and the atom. Subsequent readout of the atomic fluorescence results in a non-destructive measurement of the rotational state. We study the interaction between a 1D array of polar molecules and an array or a cloud of atoms in a Rydberg superatom (blockaded) state and calculate the resolved energy shifts of Rb(60s) with KRb and RbYb molecules, with N=1, 3, 5 molecules. We show that collective molecular rotational states can be read out using the conditioned Rydberg energy shifts.

 

Title:
Hydrodynamic theory of thermoelectric transport and negative magnetoresistance in Weyl semimetals
Authors:
Lucas, Andrew; Davison, Richard A.; Sachdev, Subir
Publication:
eprint arXiv:1604.08598
Publication Date:
04/2016
Origin:
ARXIV
Keywords:
Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Mesoscale and Nanoscale Physics, High Energy Physics - Theory
Comment:
23 pages
Bibliographic Code:
2016arXiv160408598L

Abstract

We present a minimal hydrodynamic formalism for thermoelectric transport in Weyl semimetals where the electron-electron scattering time is faster than the electron-impurity scattering time. Our model consists of relativistic fluids at each Weyl node, coupled together by perturbatively small inter-valley scattering, and long-range Coulomb interactions. We analytically compute all thermoelectric transport coefficients in the limit of perturbatively weak disorder and magnetic field, and confirm Onsager reciprocity and positive-definiteness of the conductivity matrix. Three distinct anomalous relaxation times govern negative magnetoresistance in the thermoelectric transport coefficients: while negative electrical magnetoresistance is governed by the standard chiral anomaly, negative thermal magnetoresistance is governed by a distinct gauge-gravitational anomaly. All of the hydrodynamic coefficients in our formalism may be computed for a given microscopic model of a Weyl semimetal via memory matrix techniques.

 

Title:
Plastic deformation of tubular crystals by dislocation glide
Authors:
Beller, Daniel A.; Nelson, David R.
Publication:
eprint arXiv:1605.00114
Publication Date:
04/2016
Origin:
ARXIV
Keywords:
Condensed Matter - Soft Condensed Matter
Comment:
17 pages, 11 figures
Bibliographic Code:
2016arXiv160500114B

Abstract

Tubular crystals, two-dimensional lattices wrapped into cylindrical topologies, arise in many contexts, including botany and biofilaments, and in physical systems such as carbon nanotubes. The geometrical principles of botanical phyllotaxis, describing the spiral packings on cylinders commonly found in nature, have found application in all these systems. Several recent studies have examined defects in tubular crystals associated with crystalline packings that must accommodate a fixed tube radius. Here, we study the mechanics of tubular crystals with variable tube radius, with dislocations interposed between regions of different phyllotactic packings. Unbinding and separation of dislocation pairs with equal and opposite Burgers vectors allow the growth of one phyllotactic domain at the expense of another. In particular, glide separation of dislocations offers a low-energy mode for plastic deformations of solid tubes in response to external stresses, reconfiguring the lattice step by step. Through theory and simulation, we examine how the tube's radius and helicity affects, and is in turn altered by, the mechanics of dislocation glide. We also discuss how a sufficiently strong bending rigidity can alter or arrest the deformations of tubes with small radii.

 

Title:
Measurement of the centrality dependence of the charged-particle pseudorapidity distribution in proton-lead collisions at √{s_{_ {NN}}} = 5.02 TeV with the ATLAS detector
Authors:
Aad, G.; Abajyan, T.; Abbott, B.; Abdallah, J.; ... Franklin, M.; ... Huth, J.; ... Morii, M.; ... ; and 2836 coauthors
Publication:
The European Physical Journal C, Volume 76, Issue 4, article id. #199, 30 pp. (EPJC Homepage)
Publication Date:
04/2016
Origin:
SPRINGER
Abstract Copyright:
(c) 2016: The Author(s)
DOI:
10.1140/epjc/s10052-016-4002-3
Bibliographic Code:
2016EPJC...76..199A

Abstract

The centrality dependence of the mean charged-particle multiplicity as a function of pseudorapidity is measured in approximately 1 μ b^{-1} of proton-lead collisions at a nucleon-nucleon centre-of-mass energy of √{s_{_ {NN}}} = 5.02 {TeV} using the ATLAS detector at the Large Hadron Collider. Charged particles with absolute pseudorapidity less than 2.7 are reconstructed using the ATLAS pixel detector. The [InlineEquation not available: see fulltext.] collision centrality is characterised by the total transverse energy measured in the Pb-going direction of the forward calorimeter. The charged-particle pseudorapidity distributions are found to vary strongly with centrality, with an increasing asymmetry between the proton-going and Pb-going directions as the collisions become more central. Three different estimations of the number of nucleons participating in the [InlineEquation not available: see fulltext.] collision have been carried out using the Glauber model as well as two Glauber-Gribov inspired extensions to the Glauber model. Charged-particle multiplicities per participant pair are found to vary differently for these three models, highlighting the importance of including colour fluctuations in nucleon-nucleon collisions in the modelling of the initial state of [InlineEquation not available: see fulltext.] collisions.

 

Title:
Search for new phenomena in events with at least three photons collected in pp collisions at √{s} = 8 TeV with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.; Abdinov, O.; ... Franklin, M.; ... Huth, J.; ... Morii, M.; ... ; and 2858 coauthors
Publication:
The European Physical Journal C, Volume 76, Issue 4, article id. #210, 26 pp. (EPJC Homepage)
Publication Date:
04/2016
Origin:
SPRINGER
Abstract Copyright:
(c) 2016: CERN for the benefit of the ATLAS collaboration
DOI:
10.1140/epjc/s10052-016-4034-8
Bibliographic Code:
2016EPJC...76..210A

Abstract

Results of a search for new phenomena in events with at least three photons are reported. Data from proton-proton collisions at a centre-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 20.3 fb^{-1}, were collected with the ATLAS detector at the LHC. The observed data are well described by the Standard Model. Limits at the 95 % confidence level on new phenomena are presented based on the rate of events in an inclusive signal region and a restricted signal region targeting the rare decay Z→ 3γ , as well as di-photon and tri-photon resonance searches. For a Standard Model Higgs boson decaying to four photons via a pair of intermediate pseudoscalar particles ( a), limits are found to be σ × {{ BR }}(h → aa) × {{ BR }}(a → γ γ )2 < 10^{-3} σ _{ {SM}} for 10 GeV < ma < 62 GeV. Limits are also presented for Higgs boson-like scalars ( H) for mH > 125 GeV, and for a Z' decaying to three photons via Z' → a+γ → 3γ . Additionally, the observed limit on the branching ratio of the Z boson decay to three photons is found to be BR(Z → 3γ ) < 2.2 × 10^{-6}, a result five times stronger than the previous result from LEP.

 

Title:
Search for anomalous couplings in the W tb vertex from the measurement of double differential angular decay rates of single top quarks produced in the t-channel with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.; Abdinov, O.; ... Franklin, M.; ... Huth, J.; ... Morii, M.; ... ; and 2859 coauthors
Publication:
The European Physical Journal C, Volume 76, Issue 4, article id. #210, 26 pp. (EPJC Homepage)
Publication Date:
04/2016
Origin:
SPRINGER
Abstract Copyright:
(c) 2016: CERN for the benefit of the ATLAS collaboration
DOI:
10.1140/epjc/s10052-016-4034-8
Bibliographic Code:
2016EPJC...76..210A

Abstract

Results of a search for new phenomena in events with at least three photons are reported. Data from proton-proton collisions at a centre-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 20.3 fb^{-1}, were collected with the ATLAS detector at the LHC. The observed data are well described by the Standard Model. Limits at the 95 % confidence level on new phenomena are presented based on the rate of events in an inclusive signal region and a restricted signal region targeting the rare decay Z→ 3γ , as well as di-photon and tri-photon resonance searches. For a Standard Model Higgs boson decaying to four photons via a pair of intermediate pseudoscalar particles ( a), limits are found to be σ × {{ BR }}(h → aa) × {{ BR }}(a → γ γ )2 &lt; 10^{-3} σ _{ {SM}} for 10 GeV < ma < 62 GeV. Limits are also presented for Higgs boson-like scalars ( H) for mH > 125 GeV, and for a Z' decaying to three photons via Z' → a+γ → 3γ . Additionally, the observed limit on the branching ratio of the Z boson decay to three photons is found to be BR(Z → 3γ ) < 2.2 × 10^{-6}, a result five times stronger than the previous result from LEP.

 

Title:
SUSY's Ladder: reframing sequestering at Large Volume
Authors:
Reece, Matthew; Xue, Wei
Affiliation:
AA(Department of Physics, Harvard University), AB(Center for Theoretical Physics, Massachusetts Institute of Technology)
Publication:
Journal of High Energy Physics, Volume 2016, Issue 4, article id. #45, 41 pp.
Publication Date:
04/2016
Origin:
SPRINGER
Keywords:
Effective field theories, Supergravity Models, Supersymmetric Effective Theories, Field Theories in Higher Dimensions
Abstract Copyright:
(c) 2016: The Author(s)
DOI:
10.1007/JHEP04(2016)045
Bibliographic Code:
2016JHEP...04..045R

Abstract

Theories with approximate no-scale structure, such as the Large Volume Scenario, have a distinctive hierarchy of multiple mass scales in between TeV gaugino masses and the Planck scale, which we call SUSY's Ladder. This is a particular realization of Split Supersymmetry in which the same small parameter suppresses gaugino masses relative to scalar soft masses, scalar soft masses relative to the gravitino mass, and the UV cutoff or string scale relative to the Planck scale. This scenario has many phenomenologically interesting properties, and can avoid dangers including the gravitino problem, flavor problems, and the moduli-induced LSP problem that plague other supersymmetric theories. We study SUSY's Ladder using a superspace formalism that makes the mysterious cancelations in previous computations manifest. This opens the possibility of a consistent effective field theory understanding of the phenomenology of these scenarios, based on power-counting in the small ratio of string to Planck scales. We also show that four-dimensional theories with approximate no-scale structure enforced by a single volume modulus arise only from two special higher-dimensional theories: five-dimensional supergravity and ten-dimensional type IIB supergravity. This gives a phenomenological argument in favor of ten dimensional ultraviolet physics which is different from standard arguments based on the consistency of superstring theory.

 

Title:
Perturbation theory for weakly coupled two-dimensional layers
Authors:
Tritsaris, Georgios A.; Shirodkar, Sharmila N.; Kaxiras, Efthimios; Cazeaux, Paul; Luskin, Mitchell; Plecháč, Petr; Cancès, Eric
Publication:
Journal of Materials Research, vol. 31, issue 07, pp. 959-966
Publication Date:
04/2016
Origin:
CROSSREF
DOI:
10.1557/jmr.2016.99
Bibliographic Code:
2016JMatR..31..959T

Abstract

Not Available

 

Title:
Biomimetic 4D printing
Authors:
Sydney Gladman, A.; Matsumoto, Elisabetta A.; Nuzzo, Ralph G.; Mahadevan, L.; Lewis, Jennifer A.
Publication:
Nature Materials, Volume 15, Issue 4, pp. 413-418 (2016).
Publication Date:
04/2016
Origin:
NATURE
Abstract Copyright:
(c) 2016: Nature Publishing Group
DOI:
10.1038/nmat4544
Bibliographic Code:
2016NatMa..15..413S

Abstract

Shape-morphing systems can be found in many areas, including smart textiles, autonomous robotics, biomedical devices, drug delivery and tissue engineering. The natural analogues of such systems are exemplified by nastic plant motions, where a variety of organs such as tendrils, bracts, leaves and flowers respond to environmental stimuli (such as humidity, light or touch) by varying internal turgor, which leads to dynamic conformations governed by the tissue composition and microstructural anisotropy of cell walls. Inspired by these botanical systems, we printed composite hydrogel architectures that are encoded with localized, anisotropic swelling behaviour controlled by the alignment of cellulose fibrils along prescribed four-dimensional printing pathways. When combined with a minimal theoretical framework that allows us to solve the inverse problem of designing the alignment patterns for prescribed target shapes, we can programmably fabricate plant-inspired architectures that change shape on immersion in water, yielding complex three-dimensional morphologies.

 

Title:
Bending and buckling of wet paper
Authors:
Lee, Minhee; Kim, Seungho; Kim, Ho-Young; Mahadevan, L.
Publication:
Physics of Fluids, Volume 28, Issue 4, id.042101 (PhFl Homepage)
Publication Date:
04/2016
Origin:
AIP
Abstract Copyright:
2016: AIP Publishing LLC
DOI:
10.1063/1.4944659
Bibliographic Code:
2016PhFl...28d2101L

Abstract

Flat paper stained with water buckles and wrinkles as it swells and deforms out of the original plane. Here we quantify the geometry and mechanics of a strip of paper that swells when it imbibes water from a narrow capillary. Characterizing the hygroexpansive nature of paper shows that thickness-wise swelling is much faster than in-plane water imbibition, leading to a simple picture for the process by which the strip of paper bends out of the plane. We model the out-of-plane deformation using a quasi-static theory and show that our results are consistent with quantitative experiments.

 

Title:
Combination of searches for WW, WZ, and ZZ resonances in pp collisions at √{ s} = 8 TeV with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.; Abdinov, O.; ... Franklin, M.; ... Huth, J.; ... Morii, M.; ... ; and 2864 coauthors
Publication:
Physics Letters B, Volume 755, p. 285-305.
Publication Date:
04/2016
Origin:
ELSEVIER
Abstract Copyright:
(c) 2016 CERN for the benefit of the ATLAS Collaboration
DOI:
10.1016/j.physletb.2016.02.015
Bibliographic Code:
2016PhLB..755..285A

Abstract

The ATLAS experiment at the CERN Large Hadron Collider has performed searches for new, heavy bosons decaying to WW, WZ and ZZ final states in multiple decay channels using 20.3 fb-1 of pp collision data at √{ s} = 8 TeV. In the current study, the results of these searches are combined to provide a more stringent test of models predicting heavy resonances with couplings to vector bosons. Direct searches for a charged diboson resonance decaying to WZ in the ℓνℓ‧ℓ‧ (ℓ = μ , e), ℓℓq q bar , ℓνq q bar and fully hadronic final states are combined and upper limits on the rate of production times branching ratio to the WZ bosons are compared with predictions of an extended gauge model with a heavy W‧ boson. In addition, direct searches for a neutral diboson resonance decaying to WW and ZZ in the ℓℓq q bar , ℓνq q bar , and fully hadronic final states are combined and upper limits on the rate of production times branching ratio to the WW and ZZ bosons are compared with predictions for a heavy, spin-2 graviton in an extended Randall-Sundrum model where the Standard Model fields are allowed to propagate in the bulk of the extra dimension.

 

Title:
Polaronic mass renormalization of impurities in Bose-Einstein condensates: Correlated Gaussian-wave-function approach
Authors:
Shchadilova, Yulia E.; Grusdt, Fabian; Rubtsov, Alexey N.; Demler, Eugene
Publication:
Physical Review A, Volume 93, Issue 4, id.043606 (PhRvA Homepage)
Publication Date:
04/2016
Origin:
APS
Abstract Copyright:
2016: American Physical Society
DOI:
10.1103/PhysRevA.93.043606
Bibliographic Code:
2016PhRvA..93d3606S

Abstract

We propose a class of variational Gaussian wave functions to describe Fröhlich polarons at finite momenta. Our wave functions give polaron energies that are in excellent agreement with the existing Monte Carlo results for a broad range of interactions. We calculate the effective mass of polarons and find smooth crossover between weak- and intermediate-coupling strength. Effective masses that we obtain are considerably larger than those predicted by the mean-field method. A prediction based on our variational wave functions is a special pattern of correlations between host atoms that can be measured in time-of-flight experiments.

 

Title:
Griffiths effects and slow dynamics in nearly many-body localized systems
Authors:
Gopalakrishnan, Sarang; Agarwal, Kartiek; Demler, Eugene A.; Huse, David A.; Knap, Michael
Publication:
Physical Review B, Volume 93, Issue 13, id.134206 (PhRvB Homepage)
Publication Date:
04/2016
Origin:
APS
Abstract Copyright:
2016: American Physical Society
DOI:
10.1103/PhysRevB.93.134206
Bibliographic Code:
2016PhRvB..93m4206G

Abstract

The low-frequency response of systems near a many-body localization transition can be dominated by rare regions that are locally critical or "in the other phase." It is known that in one dimension, these rare regions can cause the dc conductivity and diffusion constant to vanish even inside the delocalized thermal phase. Here, we present a general analysis of such Griffiths effects in the thermal phase near the many-body localization transition: we consider both one-dimensional and higher-dimensional systems, subject to quenched randomness, and discuss both linear response (including the frequency- and wave-vector-dependent conductivity) and more general dynamics. In all the regimes we consider, we identify observables that are dominated by rare-region effects. In some cases (one-dimensional systems and Floquet systems with no extensive conserved quantities), essentially all long-time local observables are dominated by rare-region effects; in others, generic observables are instead dominated by hydrodynamic long-time tails throughout the thermal phase, and one must look at specific probes, such as spin echo, to see Griffiths behavior.

 

Title:
Evidence of a first-order phase transition to metallic hydrogen
Authors:
Zaghoo, Mohamed; Salamat, Ashkan; Silvera, Isaac F.
Publication:
Physical Review B, Volume 93, Issue 15, id.155128 (PhRvB Homepage)
Publication Date:
04/2016
Origin:
APS
Abstract Copyright:
2016: American Physical Society
DOI:
10.1103/PhysRevB.93.155128
Bibliographic Code:
2016PhRvB..93o5128Z

Abstract

The insulator-metal transition in hydrogen is one of the most outstanding problems in condensed-matter physics. The high-pressure metallic phase is now predicted to be liquid atomic from the low-temperature limit with the system in the ground state to very high temperatures. We have conducted measurements of optical properties of hot dense hydrogen in the region of 1.1-1.7 Mbars and up to 2200 K. We present evidence supportive of a first-order phase transition accompanied by changes in transmittance and reflectance, characteristic of a metal. The phase line of this transition has a negative slope in agreement with theories of the so-called plasma phase transition.

 

Title:
Light propagation in stratified media with soft interfaces
Authors:
Van den Broeck, N.; Brosens, F.; Tempere, J.; Silvera, I. F.
Publication:
Physical Review B, Volume 93, Issue 15, id.155129 (PhRvB Homepage)
Publication Date:
04/2016
Origin:
APS
Abstract Copyright:
2016: American Physical Society
DOI:
10.1103/PhysRevB.93.155129
Bibliographic Code:
2016PhRvB..93o5129V

Abstract

The propagation of light through materials in which the density of charge carriers varies smoothly on a scale smaller than or comparable to the wavelength requires a description that goes beyond the commonly used Fresnel equations. We propose a method to solve Maxwell's equations in such a way that any linear response theory for the bulk material can be combined with a given smooth density profile for the (free or bound) charge carriers. This method is implemented for linearly polarized monochromatic light impinging on inhomogeneous multilayer systems, leading to a fast algorithm that yields reflectance and transmittance for such systems. We apply our algorithm to investigate the difference in optical response between smooth interfaces and abrupt interfaces in stratified systems where the materials can have complex bulk permittivities, and find that the smoothening of the interface on a wavelength scale significantly reduces reflection in favor of absorption. This result is of importance to current experiments that aim to detect metallic hydrogen and deuterium films using their optical response. Our results show that for a correct interpretation of these experiments it is important to consider the smoothness of the density profile of the metallic layer. Also, for nonabsorbing layers, a smooth, rather than abrupt transition, can have an important impact on the design of optical filters.

 

Title:
Search for dark matter produced in association with a Higgs boson decaying to two bottom quarks in p p collisions at √{s }=8 TeV with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.; Abdinov, O.; ... Franklin, M.; ... Huth, J.; ... Morii, M.; ... ; and 2867 coauthors
Publication:
Physical Review D, Volume 93, Issue 7, id.072007 (PhRvD Homepage)
Publication Date:
04/2016
Origin:
APS
Abstract Copyright:
2016: CERN
DOI:
10.1103/PhysRevD.93.072007
Bibliographic Code:
2016PhRvD..93g2007A

Abstract

This article reports on a search for dark matter pair production in association with a Higgs boson decaying to a pair of bottom quarks, using data from 20.3 fb-1 of p p collisions at a center-of-mass energy of 8 TeV collected by the ATLAS detector at the LHC. The decay of the Higgs boson is reconstructed as a high-momentum b b ¯ system with either a pair of small-radius jets, or a single large-radius jet with substructure. The observed data are found to be consistent with the expected Standard Model backgrounds. Model-independent upper limits are placed on the visible cross sections for events with a Higgs boson decaying into b b ¯ and large missing transverse momentum with thresholds ranging from 150 to 400 GeV. Results are interpreted using a simplified model with a Z' gauge boson decaying into different Higgs bosons predicted in a two-Higgs-doublet model, of which the heavy pseudoscalar Higgs decays into a pair of dark matter particles. Exclusion limits are also presented for the mass scales of various effective field theory operators that describe the interaction between dark matter particles and the Higgs boson.

 

Title:
F-theory and the classification of little strings
Authors:
Bhardwaj, Lakshya; Del Zotto, Michele; Heckman, Jonathan J.; Morrison, David R.; Rudelius, Tom; Vafa, Cumrun
Publication:
Physical Review D, Volume 93, Issue 8, id.086002 (PhRvD Homepage)
Publication Date:
04/2016
Origin:
APS
Abstract Copyright:
2016: American Physical Society
DOI:
10.1103/PhysRevD.93.086002
Bibliographic Code:
2016PhRvD..93h6002B

Abstract

Little string theories (LSTs) are UV complete nonlocal six-dimensional (6D) theories decoupled from gravity in which there is an intrinsic string scale. In this paper, we present a systematic approach to the construction of supersymmetric LSTs via the geometric phases of F-theory. Our central result is that all LSTs with more than one tensor multiplet are obtained by a mild extension of 6D superconformal field theories in which the theory is supplemented by an additional, nondynamical tensor multiplet, analogous to adding an affine node to an ADE quiver, resulting in a negative semidefinite Dirac pairing. We also show that all 6D superconformal field theories naturally embed in a LST. Motivated by physical considerations, we show that in geometries where we can verify the presence of two elliptic fibrations, exchanging the roles of these fibrations amounts to T-duality in the 6D theory compactified on a circle.

 

Title:
Non-Hermitian localization in biological networks
Authors:
Amir, Ariel; Hatano, Naomichi; Nelson, David R.
Publication:
Physical Review E, Volume 93, Issue 4, id.042310 (PhRvE Homepage)
Publication Date:
04/2016
Origin:
APS
Abstract Copyright:
2016: American Physical Society
DOI:
10.1103/PhysRevE.93.042310
Bibliographic Code:
2016PhRvE..93d2310A

Abstract

We explore the spectra and localization properties of the N -site banded one-dimensional non-Hermitian random matrices that arise naturally in sparse neural networks. Approximately equal numbers of random excitatory and inhibitory connections lead to spatially localized eigenfunctions and an intricate eigenvalue spectrum in the complex plane that controls the spontaneous activity and induced response. A finite fraction of the eigenvalues condense onto the real or imaginary axes. For large N , the spectrum has remarkable symmetries not only with respect to reflections across the real and imaginary axes but also with respect to 90∘ rotations, with an unusual anisotropic divergence in the localization length near the origin. When chains with periodic boundary conditions become directed, with a systematic directional bias superimposed on the randomness, a hole centered on the origin opens up in the density-of-states in the complex plane. All states are extended on the rim of this hole, while the localized eigenvalues outside the hole are unchanged. The bias-dependent shape of this hole tracks the bias-independent contours of constant localization length. We treat the large-N limit by a combination of direct numerical diagonalization and using transfer matrices, an approach that allows us to exploit an electrostatic analogy connecting the "charges" embodied in the eigenvalue distribution with the contours of constant localization length. We show that similar results are obtained for more realistic neural networks that obey "Dale's law" (each site is purely excitatory or inhibitory) and conclude with perturbation theory results that describe the limit of large directional bias, when all states are extended. Related problems arise in random ecological networks and in chains of artificial cells with randomly coupled gene expression patterns.

 

Title:
Enhanced Thermoelectric Power in Graphene: Violation of the Mott Relation by Inelastic Scattering
Authors:
Ghahari, Fereshte; Xie, Hong-Yi; Taniguchi, Takashi; Watanabe, Kenji; Foster, Matthew S.; Kim, Philip
Publication:
Physical Review Letters, Volume 116, Issue 13, id.136802 (PhRvL Homepage)
Publication Date:
04/2016
Origin:
APS
Abstract Copyright:
2016: American Physical Society
DOI:
10.1103/PhysRevLett.116.136802
Bibliographic Code:
2016PhRvL.116m6802G

Abstract

We report the enhancement of the thermoelectric power (TEP) in graphene with extremely low disorder. At high temperature we observe that the TEP is substantially larger than the prediction of the Mott relation, approaching to the hydrodynamic limit due to strong inelastic scattering among the charge carriers. However, closer to room temperature the inelastic carrier-optical-phonon scattering becomes more significant and limits the TEP below the hydrodynamic prediction. We support our observation by employing a Boltzmann theory incorporating disorder, electron interactions, and optical phonons.

 

Title:
New Phases and Dissociation-Recombination of Hydrogen Deuteride to 3.4 Mbar
Authors:
Dias, Ranga P.; Noked, Ori; Silvera, Isaac F.
Publication:
Physical Review Letters, Volume 116, Issue 14, id.145501 (PhRvL Homepage)
Publication Date:
04/2016
Origin:
APS
Abstract Copyright:
2016: American Physical Society
DOI:
10.1103/PhysRevLett.116.145501
Bibliographic Code:
2016PhRvL.116n5501D

Abstract

We present infrared absorption studies of solid hydrogen deuteride to pressures as high as 340 GPa (100 GPa =1 Mbar ) in a diamond anvil cell and temperatures in the range 5-295 K. Above 198 GPa the HD sample transforms to a mixture of HD, H2 , and D2 , interpreted as a process of dissociation and recombination. Three new phase lines are observed, two of which differ remarkably from those of the high-pressure homonuclear species, but none are metallic. The time-dependent spectral changes are analyzed to determine the molecular concentrations as a function of time; the nucleon exchange achieves steady state concentrations in ˜20 h at ˜200 GPa .

 

Title:
First Measurement of Electron Neutrino Appearance in NOvA
Authors:
Adamson, P.; Ader, C.; Andrews, M.; ... Feldman, G. J.; ... and 257 coauthors
Publication:
Physical Review Letters, Volume 116, Issue 15, id.151806 (PhRvL Homepage)
Publication Date:
04/2016
Origin:
APS
Abstract Copyright:
2016: American Physical Society
DOI:
10.1103/PhysRevLett.116.151806
Bibliographic Code:
2016PhRvL.116o1806A

Abstract

We report results from the first search for νμ→νe transitions by the NOvA experiment. In an exposure equivalent to 2.74 ×1020 protons on target in the upgraded NuMI beam at Fermilab, we observe 6 events in the Far Detector, compared to a background expectation of 0.99 ±0.11 (syst) events based on the Near Detector measurement. A secondary analysis observes 11 events with a background of 1.07 ±0.14 (syst) . The 3.3 σ excess of events observed in the primary analysis disfavors 0.1 π <δC P<0.5 π in the inverted mass hierarchy at the 90% C.L.

 

Title:
Current Correlations from a Mesoscopic Anyon Collider
Authors:
Rosenow, Bernd; Levkivskyi, Ivan P.; Halperin, Bertrand I.
Publication:
Physical Review Letters, Volume 116, Issue 15, id.156802 (PhRvL Homepage)
Publication Date:
04/2016
Origin:
APS
Abstract Copyright:
2016: American Physical Society
DOI:
10.1103/PhysRevLett.116.156802
Bibliographic Code:
2016PhRvL.116o6802R

Abstract

Fermions and bosons are fundamental realizations of exchange statistics, which governs the probability for two particles being close to each other spatially. Anyons in the fractional quantum Hall effect are an example for exchange statistics intermediate between bosons and fermions. We analyze a mesoscopic setup in which two dilute beams of anyons collide with each other, and relate the correlations of current fluctuations to the probability of particles excluding each other spatially. While current correlations for fermions vanish, negative correlations for anyons are a clear signature of a reduced spatial exclusion as compared to fermions.

 

Title:
Narrow-Linewidth Homogeneous Optical Emitters in Diamond Nanostructures via Silicon Ion Implantation
Authors:
Evans, Ruffin E.; Sipahigil, Alp; Sukachev, Denis D.; Zibrov, Alexander S.; Lukin, Mikhail D.
Publication:
Physical Review Applied, Volume 5, Issue 4, id.044010
Publication Date:
04/2016
Origin:
APS
Abstract Copyright:
2016: American Physical Society
DOI:
10.1103/PhysRevApplied.5.044010
Bibliographic Code:
2016PhRvP...5d4010E

Abstract

The negatively charged silicon-vacancy (SiV-) center in diamond is a bright source of indistinguishable single photons and a useful resource in quantum-information protocols. Until now, SiV- centers with narrow optical linewidths and small inhomogeneous distributions of SiV- transition frequencies have only been reported in samples doped with silicon during diamond growth. We present a technique for producing implanted SiV- centers with nearly lifetime-limited optical linewidths and a small inhomogeneous distribution. These properties persist after nanofabrication, paving the way for the incorporation of high-quality SiV- centers into nanophotonic devices.

 

Title:
Leo Philip Kadanoff
Authors:
Brenner, Michael P.; Nagel, Sidney R.
Publication:
Physics Today, vol. 69, issue 4, pp. 69-70
Publication Date:
04/2016
Origin:
CROSSREF
DOI:
10.1063/PT.3.3146
Bibliographic Code:
2016PhT....69d..69B

Abstract

Not Available

 

Title:
A Tale of Two Domes
Authors:
Huang, Dennis; Hoffman, Jennifer E.
Publication:
Physics, Volume 9, id.38
Publication Date:
04/2016
Origin:
APS
DOI:
10.1103/Physics.9.38
Bibliographic Code:
2016PhyOJ...9...38H

Abstract

Not Available

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