Faculty Publications: April, 2015

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

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

see also:
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Title:
New Upper Limit on the Electron's Electric Dipole Moment
Authors:
Doyle, John
Affiliation:
AA(Harvard University)
Publication:
APS April Meeting 2015, abstract #B8.003
Publication Date:
04/2015
Origin:
APS
Bibliographic Code:
2015APS..APR.B8003D

Abstract

The ACME collaboration has measured the electron's electric dipole moment (eEDM) to be de =(- 2 . 1 +/- 3 .7stat +/- 2 .5syst) ×10-29 e .cm. This corresponds to an upper limit of | de | < 8 . 7 × 10-29 e .cm with 90 percent confidence, which represents an order of magnitude improvement on the previous best limit. We describe our method of measuring the eEDM using a buffer gas cooled beam of thorium monoxide (ThO) and discuss our approach to finding and quantifying systematic effects. This results constrains T-violating physics at the TeV energy scale.

This project is supported by NSF.

 

Title:
Exact Solutions for Extreme Black Hole Magnetospheres
Authors:
Rodriguez, Maria J.; Lupsasca, Alexandru; Strominger, Andrew
Affiliation:
AA(Harvard University), AB(Harvard University), AC(Harvard University)
Publication:
APS April Meeting 2015, abstract #R7.002
Publication Date:
04/2015
Origin:
APS
Bibliographic Code:
2015APS..APR.R7002R

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 talk I will explain how to analytically obtain several infinite families of exact solutions of the full nonlinear FFE equations very near the horizon of a maximally spinning black hole, where the energy extraction takes place.

 

Title:
Constraints on B Modes from BICEP2, KECK and Planck
Authors:
Kovac, John
Affiliation:
AA(Harvard University)
Publication:
APS April Meeting 2015, abstract #S9.001
Publication Date:
04/2015
Origin:
APS
Bibliographic Code:
2015APS..APR.S9001K

Abstract

No abstract available.

 

Title:
A First-order Phase Transition to Metallic Hydrogen
Authors:
Zaghoo, Mohamed; Salamat, Ashkan; Silvera, Isaac F.
Publication:
eprint arXiv:1504.00259
Publication Date:
04/2015
Origin:
ARXIV
Keywords:
Condensed Matter - Materials Science
Comment:
ten pages plus 5 figures plus Supplementary Information, submitted for publication
Bibliographic Code:
2015arXiv150400259Z

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 T=0 K to very high temperatures. We have conducted measurements of optical properties of hot dense hydrogen in the region of 1.1-1.7 Mbar and up to 2200 K. We observe 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:
Optical properties of inhomogeneous metallic hydrogen plasmas
Authors:
Van den Broeck, N.; Brosens, F.; Tempere, J.; Silvera, I. F.
Publication:
eprint arXiv:1504.00271
Publication Date:
04/2015
Origin:
ARXIV
Keywords:
Condensed Matter - Materials Science, Physics - Optics
Bibliographic Code:
2015arXiv150400271V

Abstract

We investigate the optical properties of hydrogen as it undergoes a transition from the insulating molecular to the metallic atomic phase, when heated by a pulsed laser at megabar pressures in a diamond anvil cell. Most current experiments attempt to observe this transition by detecting a change in the optical reflectance and/or transmittance. Theoretical models for this change are based on the dielectric function calculated for bulk, homogeneous slabs of material. Experimentally, one expects a hydrogen plasma density that varies on a length scale not substantially smaller than the wave length of the probing light. We show that taking this inhomogeneity into account can lead to significant corrections in the reflectance and transmittance. We present a technique to calculate the optical properties of systems with a smoothly varying density of charge carriers, determine the optical response for metallic hydrogen in the diamond anvil cell experiment and contrast this with the standard results. Analyzing recent experimental results we obtain $\sigma^{Drude}_{DC}=(2.1 \pm 1.3) \times 10^3$ ($\Omega$ cm)$^{-1}$ for the conductivity of metallic hydrogen at 170 GPa and 1250 K.

 

Title:
Nano-friction in cavity quantum electrodynamics
Authors:
Fogarty, T.; Cormick, C.; Landa, H.; Stojanovic, Vladimir M.; Demler, E.; Morigi, Giovanna
Publication:
eprint arXiv:1504.00275
Publication Date:
04/2015
Origin:
ARXIV
Keywords:
Quantum Physics, Condensed Matter - Quantum Gases
Comment:
9 pages, 6 figures
Bibliographic Code:
2015arXiv150400275F

Abstract

The Frenkel-Kontorova model reproduces in one dimension the essential features of the stick-slip motion characteristic of friction. We theoretically analyze a realization where the atomic array is an ion chain and the substrate potential is the optical lattice of a high-finesse resonator, to which the ions dipolar transitions strongly couple. In this regime the lattice depth depends on their spatial density and the cavity potential behaves like a dynamically deformable substrate, which mediates infinitely long-ranged interactions between the ions. We characterize the properties of the stationary state, resulting from the balance between a pump driving the resonator and losses due to cavity decay, in a finite chain within a harmonic trap. When the cavity wavelength is incommensurate with the interparticle distance at the chain center, the phase diagram exhibits a sliding-to-pinned transition. The transition point depends on the cavity nonlinearity $C$, and its nature changes from a symmetry-breaking to a first-order transition as $C$ is increased. Its salient features can be explained by the global lattice deformation and can be revealed by monitoring the emitted field, which carries information about the ions structure within the cavity mode. These dynamics represent a paradigm of competing self-organizing mechanisms which can be observed in existing experimental setups.

 

Title:
Scaling dimensions of monopole operators in the $\mathbb{CP}^{N_b - 1}$ theory in $2+1$ dimensions
Authors:
Dyer, Ethan; Mezei, Márk; Pufu, Silviu S.; Sachdev, Subir
Publication:
eprint arXiv:1504.00368
Publication Date:
04/2015
Origin:
ARXIV
Keywords:
High Energy Physics - Theory, Condensed Matter - Strongly Correlated Electrons
Comment:
31 pages + Appendices, 4 figures
Bibliographic Code:
2015arXiv150400368D

Abstract

We study monopole operators at the conformal critical point of the $\mathbb{CP}^{N_b - 1}$ theory in $2+1$ spacetime dimensions. Using the state-operator correspondence and a saddle point approximation, we compute the scaling dimensions of the operators that insert one or two units of magnetic flux to next-to-leading order in $1/N_b$. We compare our results to numerical studies of quantum antiferromagnets on two-dimensional lattices with SU($N_b$) global symmetry, using the mapping of the monopole operators to valence bond solid order parameters of the lattice antiferromagnet. For the monopole operators that insert three or more units of magnetic flux, we find that the rotationally-symmetric saddle point is unstable; in order to obtain the scaling dimensions of these operators, even at leading order in $1/N_b$, one should consider non-spherically-symmetric saddles.

 

Title:
Towards an Understanding of the Correlations in Jet Substructure
Authors:
Adams, D.; Arce, A.; Asquith, L.;... Schwartz, M. D.; ... and 82 coauthors
Publication:
eprint arXiv:1504.00679
Publication Date:
04/2015
Origin:
ARXIV
Keywords:
High Energy Physics - Phenomenology, High Energy Physics - Experiment
Comment:
Report prepared by the participants of the BOOST 2013 workshop, hosted by the University of Arizona at Flagstaff, AZ, 12-16 August 2013. 54 pages, 51 figures. Version submitted to EPJC
Bibliographic Code:
2015arXiv150400679A

Abstract

Over the past decade, a large number of jet substructure observables have been proposed in the literature, and explored at the LHC experiments. Such observables attempt to utilize the internal structure of jets in order to distinguish those initiated by quarks, gluons, or by boosted heavy objects, such as top quarks and W bosons. This report, originating from and motivated by the BOOST2013 workshop, presents original particle-level studies that aim to improve our understanding of the relationships between jet substructure observables, their complementarity, and their dependence on the underlying jet properties, particularly the jet radius and jet transverse momentum. This is explored in the context of quark/gluon discrimination, boosted W boson tagging and boosted top quark tagging.

 

Title:
Search for Resonances Decaying to Top and Bottom Quarks with the CDF Experiment
Authors:
CDF Collaboration; Aaltonen, T.; Amerio, S.; Amidei, D.;... ; Franklin, M.;... Guimaraes da Costa, J.;... and 399 coauthors
Publication:
eprint arXiv:1504.01536
Publication Date:
04/2015
Origin:
ARXIV
Keywords:
High Energy Physics - Experiment, High Energy Physics - Phenomenology
Comment:
submitted to Phys. Rev. Lett
Bibliographic Code:
2015arXiv150401536C

Abstract

We report on a search for charged massive resonances decaying to top ($t$) and bottom ($b$) quarks in the full data set of proton-antiproton collisions at center-of-mass energy of $\sqrt{s} = 1.96$ TeV collected by the CDF~II detector at the Tevatron, corresponding to an integrated luminosity of 9.5 $fb^{-1}$. No significant excess above the standard model (SM) background prediction is observed. We set 95% Bayesian credibility mass-dependent upper limits on the heavy charged particle production cross section times branching ratio to $t b$. Using a SM extension with a $W^{\prime}$ and left-right-symmetric couplings as a benchmark model, we constrain the $W^{\prime}$ mass and couplings in the 300 to 900 GeV/$c^2$ range. The limits presented here are the most stringent for a charged resonance with mass in the range 300 -- 600 GeV/$c^2$ decaying to top and bottom quarks.

 

Title:
D-branes and synthetic/$C^{\infty}$-algebraic symplectic/calibrated geometry, I: Lemma on a finite algebraicness property of smooth maps from Azumaya/matrix manifolds
Authors:
Liu, Chien-Hao; Yau, Shing-Tung
Publication:
eprint arXiv:1504.01841
Publication Date:
04/2015
Origin:
ARXIV
Keywords:
Mathematics - Symplectic Geometry, High Energy Physics - Theory, Mathematics - Algebraic Geometry, Mathematics - Differential Geometry, 51K10, 58A40, 53D12, 14A22, 16S50, 81T30
Comment:
19 pages, 6 figures
Bibliographic Code:
2015arXiv150401841L

Abstract

We lay down an elementary yet fundamental lemma concerning a finite algebraicness property of a smooth map from an Azumaya/matrix manifold with a fundamental module to a smooth manifold. This gives us a starting point to build a synthetic (synonymously, $C^{\infty}$-algebraic) symplectic geometry and calibrated geometry that are both tailored to and guided by D-brane phenomena in string theory and along the line of our previous works D(11.1) (arXiv:1406.0929 [math.DG]) and D(11.2) (arXiv:1412.0771 [hep-th]).

 

Title:
Long-distance entanglement distribution using individual atoms in optical cavities
Authors:
Borregaard, Johannes; Kómár, Peter; Kessler, Eric M.; Lukin, Mikhail D.; Sørensen, Anders S.
Publication:
eprint arXiv:1504.03703
Publication Date:
04/2015
Origin:
ARXIV
Keywords:
Quantum Physics
Comment:
15 pages, 13 figures
Bibliographic Code:
2015arXiv150403703B

Abstract

Individual atoms in optical cavities can provide an efficient interface between stationary qubits and flying qubits (photons), which is an essentiel building block for quantum communication. Furthermore, cavity assisted controlled-not (CNOT) gates can be used for swapping entanglement to long distances in a quantum repeater setup. Nonetheless, dissipation introduced by the cavity during the CNOT may increase the experimental difficulty in obtaining long-distance entanglement distribution using these systems. We analyse and compare a number of cavity-based repeater schemes combining various entanglement generation schemes and cavity assisted CNOT gates. We find that a scheme, where high-fidelity entanglement is first generated in a two-photon detection scheme and then swapped to long distances using a recently proposed heralded CZ-gate exhibits superior performance compared to the other schemes. The heralded gate moves the effect of dissipation from the fidelity to the success probability of the gate thereby enabling high-fidelity entanglement swapping. As a result, high-rate entanglement distribution can be achieved over long distances even for low cooperativities of the atom-cavity systems. This high-fidelity repeater is shown to outperform the other cavity-based schemes by up to two orders of magnitude in the rate for realistic parameters and large distances (1000 km).

 

Title:
Single Vortex Pinning and Penetration Depth in Superconducting NdFeAsO$_{1-x}$F$_x$
Authors:
Zhang, Jessie T.; Kim, Jeehoon; Huefner, Magdalena; Ye, Cun; Kim, Stella; Canfield, Paul C.; Prozorov, Ruslan; Auslaender, Ophir M.; Hoffman, Jennifer E.
Publication:
eprint arXiv:1504.04045
Publication Date:
04/2015
Origin:
ARXIV
Keywords:
Condensed Matter - Superconductivity
Bibliographic Code:
2015arXiv150404045Z

Abstract

We use a magnetic force microscope (MFM) to investigate single vortex pinning and penetration depth in NdFeAsO$_{1-x}$F$_x$, one of the highest-$T_c$ iron-based superconductors. In fields up to 20 Gauss, we observe a disordered vortex arrangement, implying that the pinning forces are stronger than the vortex-vortex interactions. We measure the typical force to depin a single vortex, $F_{\mathrm{depin}} \simeq 4.5$ pN, corresponding to a critical current up to $J_c \simeq 7 \times 10^5$ A/cm$^2$. Furthermore, our MFM measurements allow the first local and absolute determination of the superconducting in-plane penetration depth in NdFeAsO$_{1-x}$F$_x$, $\lambda_{ab}=320 \pm 60$ nm, which is larger than previous bulk measurements.

 

Title:
Site-resolved Imaging of Fermionic Lithium-6 in an Optical Lattice
Authors:
Parsons, Maxwell F.; Huber, Florian; Mazurenko, Anton; Chiu, Christie S.; Setiawan, Widagdo; Wooley-Brown, Katherine; Blatt, Sebastian; Greiner, Markus
Publication:
eprint arXiv:1504.04397
Publication Date:
04/2015
Origin:
ARXIV
Keywords:
Condensed Matter - Quantum Gases, Physics - Atomic Physics
Comment:
5 pages, 4 figures, added references
Bibliographic Code:
2015arXiv150404397P

Abstract

We demonstrate site-resolved imaging of individual fermionic lithium-6 atoms in a 2D optical lattice. To preserve the density distribution during fluorescence imaging, we simultaneously cool the atoms with 3D Raman sideband cooling. This laser cooling technique, demonstrated here for the first time for lithium-6 atoms, also provides a pathway to rapid low-entropy filling of an optical lattice. We are able to determine the occupation of individual lattice sites with a fidelity >95%, enabling direct, local measurement of particle correlations in Fermi lattice systems. This ability will be instrumental for creating and investigating low-temperature phases of the Fermi-Hubbard model, including antiferromagnets and d-wave superfluidity.

 

Title:
6d String Chains
Authors:
Gadde, Abhijit; Haghighat, Babak; Kim, Joonho; Kim, Seok; Lockhart, Guglielmo; Vafa, Cumrun
Publication:
eprint arXiv:1504.04614
Publication Date:
04/2015
Origin:
ARXIV
Keywords:
High Energy Physics - Theory
Comment:
33 pages, 14 figures
Bibliographic Code:
2015arXiv150404614G

Abstract

We consider bound states of strings which arise in 6d (1,0) SCFTs that are realized in F-theory in terms of linear chains of spheres with negative self-intersections 1,2, and 4. These include the strings associated to N small E8 instantons, as well as the ones associated to M5 branes probing A and D type singularities in M-theory or D5 branes probing ADE singularities in Type IIB string theory. We find that these bound states of strings admit (0,4) supersymmetric quiver descriptions and show how one can compute their elliptic genera.

 

Title:
Universal Quantum Transducers based on Surface Acoustic Waves
Authors:
Schuetz, Martin J. A.; Kessler, Eric M.; Giedke, Geza; Vandersypen, Lieven M. K.; Lukin, Mikhail D.; Cirac, J. Ignacio
Publication:
eprint arXiv:1504.05127
Publication Date:
04/2015
Origin:
ARXIV
Keywords:
Quantum Physics, Condensed Matter - Mesoscale and Nanoscale Physics
Comment:
Manuscript: 8 pages, 3 figures. Appendices: 17 pages, 12 figures
Bibliographic Code:
2015arXiv150405127S

Abstract

We propose a universal, on-chip quantum transducer based on surface acoustic waves in piezo-active materials. Because of the intrinsic piezoelectric (and/or magnetostrictive) properties of the material, our approach provides a universal platform capable of coherently linking a broad array of qubits, including quantum dots, trapped ions, nitrogen-vacancy centers or superconducting qubits. The quantized modes of surface acoustic waves lie in the gigahertz range, can be strongly confined close to the surface in phononic cavities and guided in acoustic waveguides. We show that this type of surface acoustic excitations can be utilized efficiently as a quantum bus, serving as an on-chip, mechanical cavity-QED equivalent of microwave photons and enabling long-range coupling of a wide range of qubits.

 

Title:
Far-from-equilibrium field theory of many-body quantum spin systems: Prethermalization and relaxation of spin spiral states in three dimensions
Authors:
Babadi, Mehrtash; Demler, Eugene; Knap, Michael
Publication:
eprint arXiv:1504.05956
Publication Date:
04/2015
Origin:
ARXIV
Keywords:
Condensed Matter - Quantum Gases, Condensed Matter - Strongly Correlated Electrons, Quantum Physics
Bibliographic Code:
2015arXiv150405956B

Abstract

We study theoretically the far-from-equilibrium relaxation dynamics of spin spiral states in the three dimensional isotropic Heisenberg model. The investigated problem serves as an archetype for understanding quantum dynamics of isolated many-body systems in the vicinity of a spontaneously broken continuous symmetry. We present a field-theoretical formalism that systematically improves on mean-field for describing the real-time quantum dynamics of generic spin-1/2 systems. This is achieved by mapping spins to Majorana fermions followed by a 1/N expansion of the resulting two-particle irreducible (2PI) effective action. Our analysis reveals rich fluctuation-induced relaxation dynamics in the unitary evolution of spin spiral states. In particular, we find the sudden appearance of long-lived prethermalized plateaus with diverging lifetimes as the spiral winding is tuned toward the thermodynamically stable ferro- or antiferromagnetic phases. The emerging prethermalized states are characterized by different bosonic modes being thermally populated at different effective temperatures, and by a hierarchical relaxation process reminiscent of glassy systems. Spin-spin correlators found by solving the non-equilibrium Bethe-Salpeter equation provide further insight into the dynamic formation of correlations, the fate of unstable collective modes, and the emergence of fluctuation-dissipation relations. Our predictions can be verified experimentally using recent realizations of spin spiral states [S. Hild, et al. Phys. Rev. Lett. 113, 147205 (2014)].

 

Title:
Quantum optics with nitrogen-vacancy centers in diamond
Authors:
Chu, Yiwen; Lukin, Mikhail D.
Publication:
eprint arXiv:1504.05990
Publication Date:
04/2015
Origin:
ARXIV
Keywords:
Quantum Physics
Bibliographic Code:
2015arXiv150405990C

Abstract

We review the electronic level structure of the nitrogen-vacancy in diamond and some common experimental techniques to study its optical properties at low temperatures. We then summarize several recent experiments and advances in using nitrogen-vacancy centers for quantum optics.

 

Title:
First measurement of the forward-backward asymmetry in bottom-quark pair production at high mass
Authors:
CDF Collaboration; Aaltonen, T.; Amerio, S.; Amidei, D.; Franklin, M.;... Guimaraes da Costa, J.;... and 398 coauthors
Publication:
eprint arXiv:1504.06888
Publication Date:
04/2015
Origin:
ARXIV
Keywords:
High Energy Physics - Experiment
Comment:
11 pages, for submission to Physical Review D
Bibliographic Code:
2015arXiv150406888C

Abstract

We measure the particle-level forward-backward production asymmetry in $b\bar{b}$ pairs with masses $m(b\bar{b})$ larger than 150 GeV/$c^2$, using events with hadronic jets and employing jet charge to distinguish $b$ from $\bar{b}$. The measurement uses 9.5/fb of ppbar collisions at a center of mass energy of 1.96 TeV recorded by the CDF II detector. The asymmetry as a function of $m(b\bar{b})$ is consistent with zero, as well as with the predictions of the standard model. The measurement disfavors a simple model including an axigluon with a mass of 200 GeV/$c^2$ whereas a model containing a heavier 345 GeV/$c^2$ axigluon is not excluded.

 

Title:
Spatially resolved edge currents and guided-wave electronic states in graphene
Authors:
Allen, Monica T.; Shtanko, Oles; Cosma Fulga, Ion; Akhmerov, Anton; Watanabi, Kenji; Taniguchi, Takashi; Jarillo-Herrero, Pablo; Levitov, Leonid S.; Yacoby, Amir
Publication:
eprint arXiv:1504.07630
Publication Date:
04/2015
Origin:
ARXIV
Keywords:
Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Superconductivity
Comment:
31 pages, including supplementary materials
Bibliographic Code:
2015arXiv150407630A

Abstract

A far-reaching goal of graphene research is exploiting the unique properties of carriers to realize extreme nonclassical electronic transport. Of particular interest is harnessing wavelike carriers to guide and direct them on submicron scales, similar to light in optical fibers. Such modes, while long anticipated, have never been demonstrated experimentally. In order to explore this behavior, we employ superconducting interferometry in a graphene Josephson junction to reconstruct the real-space supercurrent density using Fourier methods. Our measurements reveal charge flow guided along crystal boundaries close to charge neutrality. We interpret the observed edge currents in terms of guided-wave states, confined to the edge by band bending and transmitted as plane waves. As a direct analog of refraction-based confinement of light in optical fibers, such nonclassical states afford new means for information transduction and processing at the nanoscale.

 

Title:
Fast plunges into Kerr black holes
Authors:
Hadar, Shahar; Porfyriadis, Achilleas P.; Strominger, Andrew
Publication:
eprint arXiv:1504.07650
Publication Date:
04/2015
Origin:
ARXIV
Keywords:
High Energy Physics - Theory, Astrophysics - High Energy Astrophysical Phenomena, General Relativity and Quantum Cosmology
Comment:
16 pages, 2 figures
Bibliographic Code:
2015arXiv150407650H

Abstract

Most extreme-mass-ratio-inspirals of small compact objects into supermassive black holes end with a fast plunge from an eccentric last stable orbit. For rapidly rotating black holes such fast plunges may be studied in the context of the Kerr/CFT correspondence because they occur in the near-horizon region where dynamics are governed by the infinite dimensional conformal symmetry. In this paper we use conformal transformations to analytically solve for the radiation emitted from fast plunges into near-extreme Kerr black holes. We find perfect agreement between the gravity and CFT computations.

 

Title:
The string origin of dyonic N=8 supergravity and its simple Chern-Simons duals
Authors:
Guarino, Adolfo; Jafferis, Daniel L.; Varela, Oscar
Publication:
eprint arXiv:1504.08009
Publication Date:
04/2015
Origin:
ARXIV
Keywords:
High Energy Physics - Theory
Comment:
4 pages + references, two columns
Bibliographic Code:
2015arXiv150408009G

Abstract

We clarify the higher-dimensional origin of a class of dyonic gaugings of D=4 N=8 supergravity recently discovered, when the gauge group is chosen to be ISO(7). This dyonically-gauged maximal supergravity arises from consistent truncation of massive IIA supergravity on $S^6$, and its magnetic coupling constant descends directly from the Romans mass. The critical points of the supergravity uplift to new AdS4 massive type IIA vacua. We identify the corresponding CFT3 duals as super-Chern-Simons-matter theories with simple gauge group SU(N), with level k given by the Romans mass. In particular, we find a critical point that uplifts to the first explicit N=2 AdS4 massive IIA background. We compute its free energy and that of the candidate dual Chern-Simons theory by localisation to a solvable matrix model, and find perfect agreement. This provides the first AdS/CFT precision match in massive type IIA string theory.

 

Title:
Geometric Engineering, Mirror Symmetry and 6d (1,0) -> 4d, N=2
Authors:
Del Zotto, Michele; Vafa, Cumrun; Xie, Dan
Publication:
eprint arXiv:1504.08348
Publication Date:
04/2015
Origin:
ARXIV
Keywords:
High Energy Physics - Theory
Comment:
58 pages, 8 figures
Bibliographic Code:
2015arXiv150408348D

Abstract

We study compactification of 6 dimensional (1,0) theories on T^2. We use geometric engineering of these theories via F-theory and employ mirror symmetry technology to solve for the effective 4d N=2 geometry for a large number of the (1,0) theories including those associated with conformal matter. Using this we show that for a given 6d theory we can obtain many inequivalent 4d N=2 SCFTs. Some of these respect the global symmetries of the 6d theory while others exhibit SL(2,Z) duality symmetry inherited from global diffeomorphisms of the T^2. This construction also explains the 6d origin of moduli space of 4d affine ADE quiver theories as flat ADE connections on T^2. Among the resulting 4d N=2 CFTs we find theories whose vacuum geometry is captured by an LG theory (as opposed to a curve or a local CY geometry). We obtain arbitrary genus curves of class S with punctures from toroidal compactification of (1,0) SCFT's where the curve of the class S theory emerges through mirror symmetry. We also show that toroidal compactification of the little string version of these theories can lead to class S theories with no punctures on arbitrary genus Riemann surface.

 

Title:
Geometry of 6D RG Flows
Authors:
Heckman, Jonathan J.; Morrison, David R.; Rudelius, Tom; Vafa, Cumrun
Publication:
eprint arXiv:1505.00009
Publication Date:
04/2015
Origin:
ARXIV
Keywords:
High Energy Physics - Theory
Comment:
34 pages, 5 figures
Bibliographic Code:
2015arXiv150500009H

Abstract

We study renormalization group flows between six-dimensional superconformal field theories (SCFTs) using their geometric realizations as singular limits of F-theory compactified on elliptically fibered Calabi-Yau threefolds. There are two general types of flows: One corresponds to giving expectation values to scalars in the tensor multiplets (tensor branch flow) realized as resolving the base of the geometry. The other corresponds to giving expectation values to hypermultiplets (Higgs branch flow) realized as complex structure deformations of the geometry. To corroborate this physical picture we calculate the change in the anomaly polynomial for these theories, finding strong evidence for a flow from a UV fixed point to an IR fixed point. Moreover, we find evidence against non-trivial dualities for 6D SCFTs. In addition we find non-trivial RG flows for theories realizing small E8 instantons on ALE spaces.

 

Title:
Measurement of the top-quark mass in the fully hadronic decay channel from ATLAS data at sqrt(s)=7 TeV
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Barreiro Guimarães da Costa, J.;... Franklin, M.;... ; Huth, J.;... Morii, M.;... and 2884 coauthors
Publication:
The European Physical Journal C, Volume 75, article id. #158, 26 pp. (EPJC Homepage)
Publication Date:
04/2015
Origin:
SPRINGER
Keywords:
ATLAS, LHC, Proton-proton collisions, Top quark, Top-quark mass, Fully hadronic
Abstract Copyright:
(c) 2015: CERN for the benefit of the ATLAS Collaboration
DOI:
10.1140/epjc/s10052-015-3373-1
Bibliographic Code:
2015EPJC...75..158A

Abstract

The mass of the top quark is measured in a data set corresponding to 4.6 of proton-proton collisions with centre-of-mass energy TeV collected by the ATLAS detector at the LHC. Events consistent with hadronic decays of top-antitop quark pairs with at least six jets in the final state are selected. The substantial background from multijet production is modelled with data-driven methods that utilise the number of identified -quark jets and the transverse momentum of the sixth leading jet, which have minimal correlation. The top-quark mass is obtained from template fits to the ratio of three-jet to dijet mass. The three-jet mass is calculated from the three jets produced in a top-quark decay. Using these three jets the dijet mass is obtained from the two jets produced in the boson decay. The top-quark mass obtained from this fit is thus less sensitive to the uncertainty in the energy measurement of the jets. A binned likelihood fit yields a top-quark mass of
m t=175.1±1.4 (stat.) ±1.2 (syst.)  GeV.

 

Title:
Search for decays in collisions at = 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 2884 coauthors
Publication:
The European Physical Journal C, Volume 75, article id. #165, 23 pp. (EPJC Homepage)
Publication Date:
04/2015
Origin:
SPRINGER
Abstract Copyright:
(c) 2015: CERN for the benefit of the ATLAS collaboration
DOI:
10.1140/epjc/s10052-015-3372-2
Bibliographic Code:
2015EPJC...75..165A

Abstract

A search for a massive gauge boson decaying to a top quark and a bottom quark is performed with the ATLAS detector in collisions at the LHC. The dataset was taken at a centre-of-mass energy of and corresponds to of integrated luminosity. This analysis is done in the hadronic decay mode of the top quark, where novel jet substructure techniques are used to identify jets from high-momentum top quarks. This allows for a search for high-mass bosons in the range 1.5-3.0 . -tagging is used to identify jets originating from -quarks. The data are consistent with Standard Model background-only expectations, and upper limits at 95 % confidence level are set on the cross section times branching ratio ranging from to for left-handed bosons, and ranging from to for bosons with purely right-handed couplings. Upper limits at 95 % confidence level are set on the -boson coupling to as a function of the mass using an effective field theory approach, which is independent of details of particular models predicting a boson.

 

Title:
Search for squarks and gluinos in events with isolated leptons, jets and missing transverse momentum 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 2869 coauthors
Publication:
Journal of High Energy Physics, Volume 2015, article id. #116, 75 pp.
Publication Date:
04/2015
Origin:
SPRINGER
Keywords:
Hadron-Hadron Scattering
Abstract Copyright:
(c) 2015: The Author(s)
DOI:
10.1007/JHEP04(2015)116
Bibliographic Code:
2015JHEP...04..116A

Abstract

The results of a search for supersymmetry in final states containing at least one isolated lepton (electron or muon), jets and large missing transverse momentum with the ATLAS detector at the Large Hadron Collider are reported. The search is based on proton-proton collision data at a centre-of-mass energy TeV collected in 2012, corresponding to an integrated luminosity of 20 fb-1. No significant excess above the Standard Model expectation is observed. Limits are set on supersymmetric particle masses for various supersymmetric models. Depending on the model, the search excludes gluino masses up to 1.32 TeV and squark masses up to 840 GeV. Limits are also set on the parameters of a minimal universal extra dimension model, excluding a compactification radius of 1 /Rc = 950 GeV for a cut-off scale times radius (Lambda Rc) of approximately 30. [Figure not available: see fulltext.]

 

Title:
Evidence for the Higgs-boson Yukawa coupling to tau leptons with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Barreiro Guimarães da Costa, J.;... Franklin, M.;... ; Huth, J.;... Morii, M.;... and 2878 coauthors
Publication:
Journal of High Energy Physics, Volume 2015, article id. #117, 74 pp.
Publication Date:
04/2015
Origin:
SPRINGER
Keywords:
Hadron-Hadron Scattering
Abstract Copyright:
(c) 2015: The Author(s)
DOI:
10.1007/JHEP04(2015)117
Bibliographic Code:
2015JHEP...04..117A

Abstract

Results of a search for H --> tautau decays are presented, based on the full set of proton-proton collision data recorded by the ATLAS experiment at the LHC during 2011 and 2012. The data correspond to integrated luminosities of 4.5 fb-1 and 20.3 fb-1 at centre-of-mass energies of TeV and TeV respectively. All combinations of leptonic ( with l = e, mu) and hadronic ( tau --> hadrons nu) tau decays are considered. An excess of events over the expected background from other Standard Model processes is found with an observed (expected) significance of 4.5 (3.4) standard deviations. This excess provides evidence for the direct coupling of the recently discovered Higgs boson to fermions. The measured signal strength, normalised to the Standard Model expectation, of mu = 1. 43{-/0.37 +0.43} is consistent with the predicted Yukawa coupling strength in the Standard Model. [Figure not available: see fulltext.]

 

Title:
Electron--phonon processes of the silicon-vacancy centre in diamond
Authors:
Jahnke, Kay D.; Sipahigil, Alp; Binder, Jan M.; Doherty, Marcus W.; Metsch, Mathias; Rogers, Lachlan J.; Manson, Neil B.; Lukin, Mikhail D.; Jelezko, Fedor
Publication:
New Journal of Physics, Volume 17, Issue 4, article id. 043011 (2015).
Publication Date:
04/2015
Origin:
IOP
DOI:
10.1088/1367-2630/17/4/043011
Bibliographic Code:
2015NJPh...17d3011J

Abstract

We investigate phonon induced electronic dynamics in the ground and excited states of the negatively charged silicon-vacancy (Si{{V}-}) centre in diamond. Optical transition line widths, transition wavelength and excited state lifetimes are measured for the temperature range 4 K--350 K. The ground state orbital relaxation rates are measured using time-resolved fluorescence techniques. A microscopic model of the thermal broadening in the excited and ground states of the Si{{V}-} centre is developed. A vibronic process involving single-phonon transitions is found to determine orbital relaxation rates for both the ground and the excited states at cryogenic temperatures. We discuss the implications of our findings for coherence of qubits in the ground states and propose methods to extend coherence times of Si{{V}-} qubits.

 

Title:
Collisional relaxation of vibrational states of SrOH with He at 2 K
Authors:
Kozyryev, Ivan; Baum, Louis; Matsuda, Kyle; Olson, Peter; Hemmerling, Boerge; Doyle, John M.
Publication:
New Journal of Physics, Volume 17, Issue 4, article id. 045003 (2015).
Publication Date:
04/2015
Origin:
IOP
DOI:
10.1088/1367-2630/17/4/045003
Bibliographic Code:
2015NJPh...17d5003K

Abstract

Vibrational relaxation of strontium monohydroxide (SrOH) molecules in collisions with helium (He) at 2 K is studied. We find the diffusion cross section of SrOH at 2.2 K to be {{sigma }d}=(5+/-2)× {{10}-14} c{{m}2} and the vibrational quenching cross section for the (100) Sr--O stretching mode to be {{sigma }q} \=\(7+/- 2)× {{10}-17}c{{m}2}. The resulting ratio {{gamma }100} = {{sigma }d}/{{sigma }q}~ 700 is more than an order of magnitude smaller than for previously studied few-atom radicals (Au et al 2014 Phys. Rev. A 90 032703 ). We also determine the Franck--Condon factor for SrOH ({{\tilde{A}}2}{{\Pi }1/2}(100)<=ftarrow {{\tilde{X}}2}{{Sigma }+}(000)) to be (4.8+/-0.8)× {{10}-2}.

 

Title:
Search for pair-produced long-lived neutral particles decaying to jets in the ATLAS hadronic calorimeter in pp collisions at &surd;{ s} = 8 TeV
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Barreiro Guimarães da Costa, J.;... Franklin, M.;... ; Huth, J.;... Morii, M.;... and 2891 coauthors
Publication:
Physics Letters B, Volume 743, p. 15-34.
Publication Date:
04/2015
Origin:
ELSEVIER
Keywords:
High-energy collider experiment, Long-lived neutral particle, New physics
Abstract Copyright:
(c) 2015 Elsevier Science B.V. All rights reserved.
DOI:
10.1016/j.physletb.2015.02.015
Bibliographic Code:
2015PhLB..743...15A

Abstract

The ATLAS detector at the Large Hadron Collider at CERN is used to search for the decay of a scalar boson to a pair of long-lived particles, neutral under the Standard Model gauge group, in 20.3 fb-1 of data collected in proton-proton collisions at &surd;{ s} = 8 TeV. This search is sensitive to long-lived particles that decay to Standard Model particles producing jets at the outer edge of the ATLAS electromagnetic calorimeter or inside the hadronic calorimeter. No significant excess of events is observed. Limits are reported on the product of the scalar boson production cross section times branching ratio into long-lived neutral particles as a function of the proper lifetime of the particles. Limits are reported for boson masses from 100 GeV to 900 GeV, and a long-lived neutral particle mass from 10 GeV to 150 GeV.

 

Title:
Search for W' --> t b bar in the lepton plus jets final state in proton-proton collisions at a centre-of-mass energy of &surd;{ s} = 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 2878 coauthors
Publication:
Physics Letters B, Volume 743, p. 235-255.
Publication Date:
04/2015
Origin:
ELSEVIER
Abstract Copyright:
(c) 2015 Elsevier Science B.V. All rights reserved.
DOI:
10.1016/j.physletb.2015.02.051
Bibliographic Code:
2015PhLB..743..235A

Abstract

A search for new charged massive gauge bosons, called W', is performed with the ATLAS detector at the LHC, in proton-proton collisions at a centre-of-mass energy of &surd;{ s} = 8 TeV, using a dataset corresponding to an integrated luminosity of 20.3fb-1. This analysis searches for W' bosons in the W' --> t b bar decay channel in final states with electrons or muons, using a multivariate method based on boosted decision trees. The search covers masses between 0.5 and 3.0 TeV, for right-handed or left-handed W' bosons. No significant deviation from the Standard Model expectation is observed and limits are set on the W' --> t b bar cross-section times branching ratio and on the W'-boson effective couplings as a function of the W'-boson mass using the CLs procedure. For a left-handed (right-handed) W' boson, masses below 1.70 (1.92) TeV are excluded at 95% confidence level.

 

Title:
Quantum gas microscopy with spin, atom-number, and multilayer readout
Authors:
Preiss, Philipp M.; Ma, Ruichao; Tai, M. Eric; Simon, Jonathan; Greiner, Markus
Publication:
Physical Review A, Volume 91, Issue 4, id.041602 (PhRvA Homepage)
Publication Date:
04/2015
Origin:
APS
PACS Keywords:
Tunneling Josephson effect Bose-Einstein condensates in periodic potentials solitons vortices and topological excitations, Atoms in optical lattices, Atom traps and guides
Abstract Copyright:
2015: American Physical Society
DOI:
10.1103/PhysRevA.91.041602
Bibliographic Code:
2015PhRvA..91d1602P

Abstract

Atom- and site-resolved experiments with ultracold atoms in optical lattices provide a powerful platform for the simulation of strongly correlated materials. In this Rapid Communication, we present a toolbox for the preparation, control, and site-resolved detection of a tunnel-coupled bilayer degenerate quantum gas. Using a collisional blockade, we engineer occupation-dependent interplane transport which enables us to circumvent light-assisted pair loss during imaging and count n =0 to n =3 atoms per site. We obtain the first number- and site-resolved images of the Mott insulator "wedding cake" structure and observe the emergence of antiferromagnetic ordering across a magnetic quantum phase transition. We are further able to employ the bilayer system for spin-resolved readout of a mixture of two hyperfine states. This work opens the door to direct detection of entanglement and Kosterlitz-Thouless-type phase dynamics, as well as studies of coupled planar quantum materials.

 

Title:
Spin-polarized quantum well states on Bi2-xFexSe3
Authors:
Yee, Michael M.; Zhu, Z.-H.; Soumyanarayanan, Anjan; He, Yang; Song, Can-Li; Pomjakushina, Ekaterina; Salman, Zaher; Kanigel, Amit; Segawa, Kouji; Ando, Yoichi; Hoffman, Jennifer E.
Publication:
Physical Review B, Volume 91, Issue 16, id.161306 (PhRvB Homepage)
Publication Date:
04/2015
Origin:
APS
PACS Keywords:
Electron density of states and band structure of crystalline solids, Scanning tunneling microscopy, Density functional theory local density approximation gradient and other corrections, Surface states band structure electron density of states
Abstract Copyright:
2015: American Physical Society
DOI:
10.1103/PhysRevB.91.161306
Bibliographic Code:
2015PhRvB..91p1306Y

Abstract

Low temperature scanning tunneling microscopy is used to image the doped topological insulator Bi2-xFexSe3 . Interstitial Fe defects allow the detection of quasiparticle interference, and the reconstruction of the empty state band structure. Quantitative comparison between measured data and density functional theory calculations reveals the unexpected coexistence of quantum well states (QWSs) with topological surface states (TSSs) on the atomically clean surface of Bi2-xFexSe3 . Spectroscopic measurements quantify the breakdown of linear dispersion due to hexagonal warping. Nonetheless, both QWSs and TSSs remain spin polarized and protected from backscattering to almost 1 eV above the Dirac point, suggesting their utility for spin-based applications.

 

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:
Physical Review B, Volume 91, Issue 16, id.165201 (PhRvB Homepage)
Publication Date:
04/2015
Origin:
APS
PACS Keywords:
Phonon-electron interactions, Phonon-defect interactions, Spectroscopy of solid state dynamics, Optical transient phenomena: quantum beats photon echo free-induction decay dephasings and revivals optical nutation and self-induced transparency
Abstract Copyright:
2015: American Physical Society
DOI:
10.1103/PhysRevB.91.165201
Bibliographic Code:
2015PhRvB..91p5201G

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:
Revealing the flux: Using processed Husimi maps to visualize dynamics of bound systems and mesoscopic transport
Authors:
Mason, Douglas J.; Borunda, Mario F.; Heller, Eric J.
Publication:
Physical Review B, Volume 91, Issue 16, id.165405 (PhRvB Homepage)
Publication Date:
04/2015
Origin:
APS
PACS Keywords:
Semiclassical theories and applications, Foundations of quantum mechanics, measurement theory, Data presentation and visualization: algorithms and implementation
Abstract Copyright:
2015: American Physical Society
DOI:
10.1103/PhysRevB.91.165405
Bibliographic Code:
2015PhRvB..91p5405M

Abstract

We elaborate upon the "processed Husimi map" representation for visualizing quantum wave functions using coherent states as a measurement of the local phase space to produce a vector field related to the probability flux. Adapted from the Husimi projection, the processed Husimi map is mathematically related to the flux operator under certain limits but offers a robust and flexible alternative since it can operate away from these limits and in systems that exhibit zero flux. The processed Husimi map is further capable of revealing the full classical dynamics underlying a quantum wave function since it reverse engineers the wave function to yield the underlying classical ray structure. We demonstrate the capabilities of processed Husimi maps on bound systems with and without electromagnetic fields, as well as on open systems on and off resonance, to examine the relationship between closed system eigenstates and mesoscopic transport.

 

Title:
Observation of top-quark pair production in association with a photon and measurement of the t t ¯ gamma production cross section in p p 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 2876 coauthors
Publication:
Physical Review D, Volume 91, Issue 7, id.072007 (PhRvD Homepage)
Publication Date:
04/2015
Origin:
APS
PACS Keywords:
Top quarks, Supersymmetric models, Inclusive production with identified leptons photons or other nonhadronic particles, Supersymmetric partners of known particles
Abstract Copyright:
2015: CERN
DOI:
10.1103/PhysRevD.91.072007
Bibliographic Code:
2015PhRvD..91g2007A

Abstract

A search is performed for top-quark pairs (t t ¯) produced together with a photon (gamma ) with transverse energy greater than 20 GeV using a sample of t t ¯ candidate events in final states with jets, missing transverse momentum, and one isolated electron or muon. The data set used corresponds to an integrated luminosity of 4.59 fb-1 of proton-proton collisions at a center-of-mass energy of 7 TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. In total, 140 and 222 t t ¯gamma candidate events are observed in the electron and muon channels, to be compared to the expectation of 79 ±26 and 120 ±39 non-t t ¯gamma background events, respectively. The production of t t ¯gamma events is observed with a significance of 5.3 standard deviations away from the null hypothesis. The t t ¯gamma production cross section times the branching ratio (BR) of the single-lepton decay channel is measured in a fiducial kinematic region within the ATLAS acceptance. The measured value is sigmatt ¯ gamma fid×BR =63 ±8 (stat)-13+17(syst)±1 (lumi) fb per lepton flavor, in good agreement with the leading-order theoretical calculation normalized to the next-to-leading-order theoretical prediction of 48 ±10 fb.

 

Authors:
Ocko, Samuel A.; Mahadevan, L.
Publication:
Physical Review Letters, Volume 114, Issue 13, id.134501 (PhRvL Homepage)
Publication Date:
04/2015
Origin:
APS
PACS Keywords:
Flows through porous media, Networks, Patterns
Abstract Copyright:
2015: American Physical Society
DOI:
10.1103/PhysRevLett.114.134501
Bibliographic Code:
2015PhRvL.114m4501O

Abstract

An active conducting medium is one where the resistance (conductance) of the medium is modified by the current (flow) and in turn modifies the flow, so that the classical linear laws relating current and resistance, e.g., Ohm's law or Darcy's law, are modified over time as the system itself evolves. We consider a minimal model for this feedback coupling in terms of two parameters that characterize the way in which addition or removal of matter follows a simple local (or nonlocal) feedback rule corresponding to either flow-seeking or flow-avoiding behavior. Using numerical simulations and a continuum mean field theory, we show that flow-avoiding feedback causes an initially uniform system to become strongly heterogeneous via a tunneling (channel-building) phase separation; flow-seeking feedback leads to an immuring (wall-building) phase separation. Our results provide a qualitative explanation for the patterning of active conducting media in natural systems, while suggesting ways to realize complex architectures using simple rules in engineered systems.

 

Title:
Efficient Readout of a Single Spin State in Diamond via Spin-to-Charge Conversion
Authors:
Shields, B. J.; Unterreithmeier, Q. P.; de Leon, N. P.; Park, H.; Lukin, M. D.
Publication:
Physical Review Letters, Volume 114, Issue 13, id.136402 (PhRvL Homepage)
Publication Date:
04/2015
Origin:
APS
PACS Keywords:
Elemental semiconductors, Quantum information, Magnetometers for magnetic field measurements
Abstract Copyright:
2015: American Physical Society
DOI:
10.1103/PhysRevLett.114.136402
Bibliographic Code:
2015PhRvL.114m6402S

Abstract

Efficient readout of individual electronic spins associated with atomlike impurities in the solid state is essential for applications in quantum information processing and quantum metrology. We demonstrate a new method for efficient spin readout of nitrogen-vacancy (NV) centers in diamond. The method is based on conversion of the electronic spin state of the NV to a charge-state distribution, followed by single-shot readout of the charge state. Conversion is achieved through a spin-dependent photoionization process in diamond at room temperature. Using NVs in nanofabricated diamond beams, we demonstrate that the resulting spin readout noise is within a factor of 3 of the spin projection noise level. Applications of this technique for nanoscale magnetic sensing are discussed.

 

Title:
Constraints on Models of the Higgs Boson with Exotic Spin and Parity using Decays to Bottom-Antibottom Quarks in the Full CDF Data Set
Authors:
Aaltonen, T.; Amerio, S.; Amidei, D.;... Franklin, M.;... Guimaraes da Costa, J.;...; and 398 coauthors
Publication:
Physical Review Letters, Volume 114, Issue 14, id.141802 (PhRvL Homepage)
Publication Date:
04/2015
Origin:
APS
PACS Keywords:
Limits on production of particles, Standard-model Higgs bosons
Abstract Copyright:
2015: American Physical Society
DOI:
10.1103/PhysRevLett.114.141802
Bibliographic Code:
2015PhRvL.114n1802A

Abstract

A search for particles with the same mass and couplings as those of the standard model Higgs boson but different spin and parity quantum numbers is presented. We test two specific alternative Higgs boson hypotheses: a pseudoscalar Higgs boson with spin-parity JP=0- and a gravitonlike Higgs boson with JP=2+, assuming for both a mass of 125 GeV /c2. We search for these exotic states produced in association with a vector boson and decaying into a bottom-antibottom quark pair. The vector boson is reconstructed through its decay into an electron or muon pair, or an electron or muon and a neutrino, or it is inferred from an imbalance in total transverse momentum. We use expected kinematic differences between events containing exotic Higgs bosons and those containing standard model Higgs bosons. The data were collected by the CDF experiment at the Tevatron proton-antiproton collider, operating at a center-of-mass energy of &surd;{s }=1.96 TeV , and correspond to an integrated luminosity of 9.45 fb-1. We exclude deviations from the predictions of the standard model with a Higgs boson of mass 125 GeV /c2 at the level of 5 standard deviations, assuming signal strengths for exotic boson production equal to the prediction for the standard model Higgs boson, and set upper limits of approximately 30% relative to the standard model rate on the possible rate of production of each exotic state.

 

Title:
Measurement of Spin Correlation in Top-Antitop Quark Events and Search for Top Squark Pair Production in p p Collisions at &surd;{s }=8 TeV Using the ATLAS Detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Barreiro Guimarães da Costa, J.;... Franklin, M.;... ; Huth, J.;... Morii, M.;... and 2872 coauthors
Publication:
Physical Review Letters, Volume 114, Issue 14, id.142001 (PhRvL Homepage)
Publication Date:
04/2015
Origin:
APS
PACS Keywords:
Top quarks, Experimental tests, Inclusive production with identified leptons photons or other nonhadronic particles, Supersymmetric partners of known particles
Abstract Copyright:
2015: CERN
DOI:
10.1103/PhysRevLett.114.142001
Bibliographic Code:
2015PhRvL.114n2001A

Abstract

A measurement of spin correlation in t t ¯ production is presented using data collected with the ATLAS detector at the Large Hadron Collider in proton-proton collisions at a center-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 20.3 fb-1 . The correlation between the top and antitop quark spins is extracted from dilepton t t ¯ events by using the difference in the azimuthal angle between the two charged leptons in the laboratory frame. In the helicity basis the measured degree of correlation corresponds to Ahelicity=0.38 ±0.04 , in agreement with the standard model prediction. A search is performed for pair production of top squarks with masses close to the top quark mass decaying to predominantly right-handed top quarks and a light neutralino, the lightest supersymmetric particle. Top squarks with masses between the top quark mass and 191 GeV are excluded at the 95% confidence level.

 

Title:
Phonon-Induced Population Dynamics and Intersystem Crossing in Nitrogen-Vacancy Centers
Authors:
Goldman, M. L.; Sipahigil, A.; Doherty, M. W.; Yao, N. Y.; Bennett, S. D.; Markham, M.; Twitchen, D. J.; Manson, N. B.; Kubanek, A.; Lukin, M. D.
Publication:
Physical Review Letters, Volume 114, Issue 14, id.145502 (PhRvL Homepage)
Publication Date:
04/2015
Origin:
APS
PACS Keywords:
Phonon-electron interactions, Optical transient phenomena: quantum beats photon echo free-induction decay dephasings and revivals optical nutation and self-induced transparency, Phonon-defect interactions, Spectroscopy of solid state dynamics
Abstract Copyright:
2015: American Physical Society
DOI:
10.1103/PhysRevLett.114.145502
Bibliographic Code:
2015PhRvL.114n5502G

Abstract

We report direct measurement of population dynamics in the excited state manifold of a nitrogen-vacancy (NV) center in diamond. We quantify the phonon-induced mixing rate and demonstrate that it can be completely suppressed at low temperatures. Further, we measure the intersystem crossing (ISC) rate for different excited states and develop a theoretical model that unifies the phonon-induced mixing and ISC mechanisms. We find that our model is in excellent agreement with experiment and that it can be used to predict unknown elements of the NV center's electronic structure. We discuss the model's implications for enhancing the NV center's performance as a room-temperature sensor.

 

Title:
Tevatron Constraints on Models of the Higgs Boson with Exotic Spin and Parity Using Decays to Bottom-Antibottom Quark Pairs
Authors:
Aaltonen, T.; Abazov, V. M.; Abbott, B.;... Franklin, M.;... Guimaraes da Costa, J.;... and 762 coauthors
Publication:
Physical Review Letters, Volume 114, Issue 15, id.151802 (PhRvL Homepage)
Publication Date:
04/2015
Origin:
APS
PACS Keywords:
Limits on production of particles, Standard-model Higgs bosons
Abstract Copyright:
2015: American Physical Society
DOI:
10.1103/PhysRevLett.114.151802
Bibliographic Code:
2015PhRvL.114o1802A

Abstract

Combined constraints from the CDF and D0 Collaborations on models of the Higgs boson with exotic spin J and parity P are presented and compared with results obtained assuming the standard model value JP=0+. Both collaborations analyzed approximately 10 fb-1 of proton-antiproton collisions with a center-of-mass energy of 1.96 TeV collected at the Fermilab Tevatron. Two models predicting exotic Higgs bosons with JP=0- and JP=2+ are tested. The kinematic properties of exotic Higgs boson production in association with a vector boson differ from those predicted for the standard model Higgs boson. Upper limits at the 95% credibility level on the production rates of the exotic Higgs bosons, expressed as fractions of the standard model Higgs boson production rate, are set at 0.36 for both the JP=0- hypothesis and the JP=2+ hypothesis. If the production rate times the branching ratio to a bottom-antibottom pair is the same as that predicted for the standard model Higgs boson, then the exotic bosons are excluded with significances of 5.0 standard deviations and 4.9 standard deviations for the JP=0- and JP=2+ hypotheses, respectively.

 

Title:
Anomalous Diffusion and Griffiths Effects Near the Many-Body Localization Transition
Authors:
Agarwal, Kartiek; Gopalakrishnan, Sarang; Knap, Michael; Müller, Markus; Demler, Eugene
Publication:
Physical Review Letters, Volume 114, Issue 16, id.160401 (PhRvL Homepage)
Publication Date:
04/2015
Origin:
APS
PACS Keywords:
Spin chain models, Quantum transport, Localization effects
Abstract Copyright:
2015: American Physical Society
DOI:
10.1103/PhysRevLett.114.160401
Bibliographic Code:
2015PhRvL.114p0401A

Abstract

We explore the high-temperature dynamics of the disordered, one-dimensional X X Z 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 ac conductivity vanishes near zero frequency as a power law; and (iii) the distribution of resistivities 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 quantum Griffiths phase. We establish scaling relations between the associated exponents, assuming a scaling form of the spin-diffusion propagator. A phenomenological classical resistor-capacitor model captures all the essential features.

 

Title:
Search for Scalar Charm Quark Pair Production in p p Collisions at &surd;{s }=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 2818 coauthors
Publication:
Physical Review Letters, Volume 114, Issue 16, id.161801 (PhRvL Homepage)
Publication Date:
04/2015
Origin:
APS
PACS Keywords:
Supersymmetric partners of known particles, Supersymmetric models, Limits on production of particles
Abstract Copyright:
2015: CERN
DOI:
10.1103/PhysRevLett.114.161801
Bibliographic Code:
2015PhRvL.114p1801A

Abstract

The results of a dedicated search for pair production of scalar partners of charm quarks are reported. The search is based on an integrated luminosity of 20.3 fb-1 of p p collisions at &surd;{s }=8 TeV recorded with the ATLAS detector at the LHC. The search is performed using events with large missing transverse momentum and at least two jets, where the two leading jets are each tagged as originating from c quarks. Events containing isolated electrons or muons are vetoed. In an R -parity-conserving minimal supersymmetric scenario in which a single scalar-charm state is kinematically accessible, and where it decays exclusively into a charm quark and a neutralino, 95% confidence-level upper limits are obtained in the scalar-charm-neutralino mass plane such that, for neutralino masses below 200 GeV, scalar-charm masses up to 490 GeV are excluded.

 

 


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The raw results file is generated automatically and provides up-to-date listings of all faculty publications added to the database during the 30 last days. However, it is likely to include irrelevant results: i.e., authors who are not affiliated with Harvard Physics Department, but whose names happen to be identical to those of our faculty members, as well as all publications which were added to the database in the last 30 days, but may have been published months or even years ago.

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