Faculty Publications: June, 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:
Updated Kinematic Constraints on a Dark Disk
Authors:
Kramer, Eric David; Randall, Lisa
Publication:
The Astrophysical Journal, Volume 824, Issue 2, article id. 116, pp. (2016). (ApJ Homepage)
Publication Date:
06/2016
Origin:
IOP
Astronomy Keywords:
dark matter, Galaxy: disk, Galaxy: kinematics and dynamics, local interstellar matter, solar neighborhood
DOI:
10.3847/0004-637X/824/2/116
Bibliographic Code:
2016ApJ...824..116K

Abstract

We update the method of the Holmberg & Flynn 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, using the 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}ȯ {{{pc}}}-2 (and as small as 0 {M}ȯ {{{pc}}}-2), 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:
Physics at a 100 TeV pp collider: beyond the Standard Model phenomena
Authors:
Golling, T.; Hance, M.; Harris, P.;... Reece, M.;... and 110 coauthors
Publication:
eprint arXiv:1606.00947
Publication Date:
06/2016
Origin:
ARXIV
Keywords:
High Energy Physics - Phenomenology, High Energy Physics - Experiment
Comment:
196 pages, 114 figures. Chapter 3 of the "Physics at the FCC-hh" Report
Bibliographic Code:
2016arXiv160600947G

Abstract

This report summarises the physics opportunities in the search and study of physics beyond the Standard Model at a 100 TeV pp collider.

 

Title:
Gravitational wave detection with optical lattice atomic clocks
Authors:
Kolkowitz, Shimon; Pikovski, Igor; Langellier, Nicholas; Lukin, Mikhail D.; Walsworth, Ronald L.; Ye, Jun
Publication:
eprint arXiv:1606.01859
Publication Date:
06/2016
Origin:
ARXIV
Keywords:
Physics - Atomic Physics, Astrophysics - Instrumentation and Methods for Astrophysics, General Relativity and Quantum Cosmology, Physics - Optics, Quantum Physics
Comment:
8 pages, 2 figures, and supplemental material
Bibliographic Code:
2016arXiv160601859K

Abstract

We propose a space-based gravitational wave detector consisting of two spatially separated, drag-free satellites sharing ultra-stable optical laser light over a single baseline. Each satellite contains an optical lattice atomic clock, which serves as a sensitive, narrowband detector of the local frequency of the shared laser light. A synchronized two-clock comparison between the satellites will be sensitive to the effective Doppler shifts induced by incident gravitational waves (GWs) at a level competitive with other proposed space-based GW detectors, while providing complementary features. The detected signal is a differential frequency shift of the shared laser light due to the relative velocity of the satellites, rather than a phase shift arising from the relative satellite positions, and the detection window can be tuned through the control sequence applied to the atoms' internal states. This scheme enables the detection of GWs from continuous, spectrally narrow sources, such as compact binary inspirals, with frequencies ranging from ~3 mHz - 10 Hz without loss of sensitivity, thereby bridging the detection gap between space-based and terrestrial GW detectors. Our proposed GW detector employs just two satellites, is compatible with integration with an optical interferometric detector, and requires only realistic improvements to existing ground-based clock and laser technologies.

 

Title:
Adiabatic Quantum Search in Open Systems
Authors:
Wild, Dominik S.; Gopalakrishnan, Sarang; Knap, Michael; Yao, Norman Y.; Lukin, Mikhail D.
Publication:
eprint arXiv:1606.01898
Publication Date:
06/2016
Origin:
ARXIV
Keywords:
Quantum Physics, Condensed Matter - Statistical Mechanics
Comment:
5 pages, 2 figures, 10 pages supplemental materials
Bibliographic Code:
2016arXiv160601898W

Abstract

Adiabatic quantum algorithms represent a promising approach to universal quantum computation. Whilst in a closed system these algorithms are limited by avoided level crossings, where the gap becomes exponentially small in the system size, their robustness in open systems remains unresolved. We study the dynamics in the proximity of such an avoided level crossing associated with the adiabatic quantum search algorithm in a quantum system that is coupled to a generic environment. At zero temperature, we find that the algorithm remains scalable provided the noise spectral density of the environment decays sufficiently fast at low frequencies. At finite temperature, however, scattering processes render the algorithm inefficient and no quantum speedup can be achieved. Owing to the generic nature of our model, we expect our results to be widely applicable to other adiabatic quantum algorithms.

 

Title:
BICEP2 / Keck Array VIII: Measurement of gravitational lensing from large-scale B-mode polarization
Authors:
Keck Array, The; BICEP2 Collaborations;Ade, P. A. R.; Ahmed, Z.; Aikin, R. W.;... Dvorkin, C.;... Kovac, J. M.; ... .; and 58 coauthors
Publication:
eprint arXiv:1606.01968
Publication Date:
06/2016
Origin:
ARXIV
Keywords:
Astrophysics - Cosmology and Nongalactic Astrophysics
Comment:
12 pages, 8 figures
Bibliographic Code:
2016arXiv160601968K

Abstract

We present measurements of polarization lensing using the 150 GHz maps which include all data taken by the BICEP2 & Keck Array CMB polarization experiments up to and including the 2014 observing season (BK14). Despite their modest angular resolution ($\sim 0.5^\circ$), the excellent sensitivity ($\sim 3\mu$K-arcmin) of these maps makes it possible to directly reconstruct the lensing potential using only information at larger angular scales ($\ell\leq 700$). From the auto-spectrum of the reconstructed potential we measure an amplitude of the spectrum to be $A^{\phi\phi}_{\rm L}=1.15\pm 0.36$ (Planck $\Lambda$CDM prediction corresponds to $A^{\phi\phi}_{\rm L}=1$), and reject the no-lensing hypothesis at 5.8$\sigma$, which is the highest significance achieved to date using an EB lensing estimator. Taking the cross-spectrum of the reconstructed potential with the Planck 2015 lensing map yields $A^{\phi\phi}_{\rm L}=1.13\pm 0.20$. These direct measurements of $A^{\phi\phi}_{\rm L}$ are consistent with the $\Lambda$CDM cosmology, and with that derived from the previously reported BK14 B-mode auto-spectrum ($A^{\rm BB}_{\rm L}=1.20\pm 0.17$). We perform a series of null tests and consistency checks to show that these results are robust against systematics and are insensitive to analysis choices. These results unambiguously demonstrate that the B-modes previously reported by BICEP / Keck at intermediate angular scales ($150\lesssim\ell\lesssim 350$) are dominated by gravitational lensing. The good agreement between the lensing amplitudes obtained from the lensing reconstruction and B-mode spectrum starts to place constraints on any alternative cosmological sources of B-modes at these angular scales.

 

Title:
Precision direct photon spectra at high energy and comparison to the 8 TeV ATLAS data
Authors:
Schwartz, Matthew D.
Publication:
eprint arXiv:1606.02313
Publication Date:
06/2016
Origin:
ARXIV
Keywords:
High Energy Physics - Phenomenology
Comment:
18 pages, 22 plots, 4 tables
Bibliographic Code:
2016arXiv160602313S

Abstract

The direct photon spectrum is computed to the highest currently available precision and compared to ATLAS data from 8 TeV collisions at the LHC. The prediction includes threshold resummation at next-to-next-to-next-to-leading logarithmic order through the program PeTeR, matched to next-to-leading fixed order with fragmentation effects using JetPhox and includes the resummation of leading-logarithmic electroweak Sudakov effects. Remarkably, improved agreement with data can be seen when each component of the calculation is added successively. This comparison demonstrates the importance of both threshold logs and electroweak Sudakov effects. Numerical values for the predictions are included.

 

Title:
Physics Fun with Discrete Scale Invariance
Authors:
Georgi, Howard
Publication:
eprint arXiv:1606.03405
Publication Date:
06/2016
Origin:
ARXIV
Keywords:
High Energy Physics - Phenomenology, High Energy Physics - Theory
Comment:
18 pages, 24 figures
Bibliographic Code:
2016arXiv160603405G

Abstract

I construct a quantum field theory model with discrete scale invariance at tree level. The model has some unusual mathematical properties (such as the appearance of $q$-hypergeometric series) and may possibly have some interesting physical properties as well. In this note, I explore some possible physics that could be regarded as a violation of standard effective field theory ideas.

 

Title:
Sidney Coleman's Harvard
Authors:
Georgi, Howard
Publication:
eprint arXiv:1606.03738
Publication Date:
06/2016
Origin:
ARXIV
Keywords:
Physics - History and Philosophy of Physics, High Energy Physics - Phenomenology
Comment:
21 pages
Bibliographic Code:
2016arXiv160603738G

Abstract

A talk presented at the April 2016 APS meeting in Salt Lake City: The speaker had the great good fortune to take an undergraduate course in group theory from Sidney Coleman, and (after graduate school away) was hired by Coleman to a postdoctoral position and eventually became a faculty colleague. He will share some still vivid memories of this remarkable character.

 

Title:
Electronic quasiparticles in the quantum dimer model: density matrix renormalization group results
Authors:
Lee, Junhyun; Sachdev, Subir; White, Steven R.
Publication:
eprint arXiv:1606.04105
Publication Date:
06/2016
Origin:
ARXIV
Keywords:
Condensed Matter - Strongly Correlated Electrons
Comment:
14 pages, 7 figures
Bibliographic Code:
2016arXiv160604105L

Abstract

We study a recently proposed quantum dimer model for the pseudogap metal state of the cuprates. The model contains bosonic dimers, representing a spin-singlet valence bond between a pair of electrons, and fermionic dimers, representing a quasiparticle with spin-$1/2$ and charge $+e$. By density matrix renormalization group calculations on a long but finite cylinder, we obtain the ground state density distribution of the fermionic dimers for a number of different total densities. From the Friedel oscillations at open boundaries, we deduce that the Fermi surface consists of small hole pockets near $(\pi/2, \pi/2)$, and this feature persists up to doping density $1/16$. We also compute the entanglement entropy and find that it closely matches the sum of the entanglement entropies of a critical boson and a low density of free fermions. Our results support the existence of a fractionalized Fermi liquid (FL*) in this model.

 

Title:
Diboson Excess from a New Strong Force
Authors:
Georgi, Howard; Nakai, Yuichiro
Publication:
eprint arXiv:1606.05865
Publication Date:
06/2016
Origin:
ARXIV
Keywords:
High Energy Physics - Phenomenology
Comment:
33 pages, 4 figures, 7 tables
Bibliographic Code:
2016arXiv160605865G

Abstract

We explore a "partial unification" model that could explain the diphoton event excess around $750 \, \rm GeV$ recently reported by the LHC experiments. A new strong gauge group is combined with the ordinary color and hypercharge gauge groups. The VEV responsible for the combination is of the order of the $SU(2)\times U(1)$ breaking scale, but the coupling of the new physics to standard model particles is suppressed by the strong interaction of the new gauge group. This simple extension of the standard model has a rich phenomenology, including composite particles of the new confining gauge interaction, a coloron and a $Z'$ which are rather weakly coupled to standard model particles, and massive vector bosons charged under both the ordinary color and hypercharge gauge groups and the new strong gauge group. The new scalar glueball could have mass of around $750 \, \rm GeV$, be produced by gluon fusion and decay into two photons, both through loops of the new massive vector bosons. The simplest version of the model has some issues: the massive vector bosons are stable and the coloron and the $Z'$ are strongly constrained by search data. An extension of the model to include additional fermions with the new gauge coupling, though not as simple and elegant, can address both issues and more. It allows the massive vector boson to decay into a colorless, neutral state that could be a candidate of the dark matter. And the coloron and $Z'$ can decay dominantly into the new fermions, completely changing the search bounds. In addition, $SU(N)$ fermions below the symmetry breaking scale make it more plausible that the lightest glueball is at $750$~GeV. Whatever becomes of the $750$~GeV diphoton excess, the model is an unusual example of how new physics at small scales could be hidden by strong interactions.

 

Title:
4d N=2 SCFT from Complete Intersection Singularity
Authors:
Wang, Yifan; Xie, Dan; Yau, Stephen S.-T.; Yau, Shing-Tung
Publication:
eprint arXiv:1606.06306
Publication Date:
06/2016
Origin:
ARXIV
Keywords:
High Energy Physics - Theory
Comment:
46 pages, 85 figures
Bibliographic Code:
2016arXiv160606306W

Abstract

Detailed studies of four dimensional N=2 superconformal field theories (SCFT) defined by isolated complete intersection singularities are performed: we compute the Coulomb branch spectrum, Seiberg-Witten solutions and central charges. Most of our theories have exactly marginal deformations and we identify the weakly coupled gauge theory descriptions for many of them, which involve (affine) D and E shaped quiver gauge theories and theories formed from Argyres-Douglas matters. These investigations provide strong evidence for the singularity approach in classifying 4d N=2 SCFTs.

 

Title:
Designing steep, sharp patterns on uniformly ion-bombarded surfaces
Authors:
Perkinson, Joy C.; Aziz, Michael J.; Brenner, Michael P.; Holmes-Cerfon, Miranda
Publication:
eprint arXiv:1606.06675
Publication Date:
06/2016
Origin:
ARXIV
Keywords:
Condensed Matter - Materials Science, Mathematics - Analysis of PDEs, Nonlinear Sciences - Pattern Formation and Solitons
Bibliographic Code:
2016arXiv160606675P

Abstract

We propose and experimentally test a method to fabricate patterns of steep, sharp features on surfaces, by exploiting the nonlinear dynamics of uniformly ion bombarded surfaces. We show via theory, simulation, and experiment, that the steepest parts of the surface evolve as one-dimensional curves which move in the normal direction at constant velocity. The curves are a special solution to the nonlinear equations that arises spontaneously whenever the initial patterning on the surface contains slopes larger than a critical value; mathematically they are traveling waves (shocks) that have the special property of being undercompressive. We derive the evolution equation for the curves by considering long-wavelength perturbations to the one-dimensional traveling wave, using the unusual boundary conditions required for an undercompressive shock, and we show this equation accurately describes the evolution of shapes on surfaces, both in simulations and in experiments. Because evolving a collection of one-dimensional curves is fast, this equation gives a computationally efficient and intuitive method for solving the inverse problem of finding the initial surface so the evolution leads to a desired target pattern. We illustrate this method by solving for the initial surface that will produce a lattice of diamonds connected by steep, sharp ridges, and experimentally demonstrating the evolution of the initial surface into the target pattern.

 

Title:
Statistical mechanics of thin spherical shells
Authors:
Kosmrlj, Andrej; Nelson, David R.
Publication:
eprint arXiv:1606.06750
Publication Date:
06/2016
Origin:
ARXIV
Keywords:
Condensed Matter - Soft Condensed Matter, Condensed Matter - Statistical Mechanics, Physics - Biological Physics
Comment:
16 pages, 6 figures
Bibliographic Code:
2016arXiv160606750K

Abstract

We explore how thermal fluctuations affect the mechanics of thin amorphous spherical shells. In flat membranes with a shear modulus, thermal fluctuations increase the bending rigidity and reduce the in-plane elastic moduli in a scale-dependent fashion. This is still true for spherical shells. However, the additional coupling between the shell curvature, the local in-plane stretching modes and the local out-of-plane undulations, leads to novel phenomena. In spherical shells thermal fluctuations produce a radius-dependent negative effective surface tension, equivalent to applying an inward external pressure. By adapting renormalization group calculations to allow for a spherical background curvature, we show that while small spherical shells are stable, sufficiently large shells are crushed by this thermally generated "pressure". Such shells can be stabilized by an outward osmotic pressure, but the effective shell size grows non-linearly with increasing outward pressure, with the same universal power law exponent that characterizes the response of fluctuating flat membranes to a uniform tension.

 

Title:
Measurement of the $WW$ and $WZ$ production cross section using final states with a charged lepton and heavy-flavor jets in the full CDF Run II data set
Authors:
CDF Collaboration; Aaltonen, T.; Amerio, S.; Amidei, D.;... Franklin, M.; ... ; and 394 coauthors
Publication:
eprint arXiv:1606.06823
Publication Date:
06/2016
Origin:
ARXIV
Keywords:
High Energy Physics - Experiment
Comment:
19 pages, 11 figures, submitted to Physical Review D
Bibliographic Code:
2016arXiv160606823C

Abstract

We present a measurement of the $WW$ and $WZ$ diboson production cross-sections in a final state consistent with leptonic $W$ boson decay and jets originating from heavy-flavor quarks from either a $W$ or a $Z$ boson decay. This analysis uses the full data set collected with the CDF II detector during Run II of the Tevatron proton-antiproton collider, corresponding to an integrated luminosity of 9.4 fb$^{-1}$ at $\sqrt{s}=1.96$ TeV. An analysis of the dijet mass spectrum provides $3.7\sigma$ evidence of the summed production processes of either $WW$ or $WZ$ bosons with a measured cross section of $\sigma_{WW+WZ} = 13.7\pm 3.9$ pb. Independent measurements of the $WW$ and $WZ$ production cross-sections are allowed by the different heavy-flavor decay-patterns of the $W$ and $Z$ bosons and by the analysis of secondary-decay vertices reconstructed within heavy-flavor jets. The productions of $WW$ and of $WZ$ dibosons are independently seen with significances of $2.9\sigma$ and $2.1\sigma$, respectively, with cross sections of $\sigma_{WW}= 9.4\pm 4.2$ pb and $\sigma_{WZ}=3.7^{+2.5}_{-2.2}$ pb. The measurements are consistent with standard-model predictions.

 

Title:
Science Impacts of the SPHEREx All-Sky Optical to Near-Infrared Spectral Survey: Report of a Community Workshop Examining Extragalactic, Galactic, Stellar and Planetary Science
Authors:
Doré, Olivier; Werner, Michael W.; Ashby, Matt;... Finkbeiner, Douglas;... ; and 64 coauthors
Publication:
eprint arXiv:1606.07039
Publication Date:
06/2016
Origin:
ARXIV
Keywords:
Astrophysics - Cosmology and Nongalactic Astrophysics, Astrophysics - Astrophysics of Galaxies
Comment:
Report of the First SPHEREx Community Workshop, http://spherex.caltech.edu/Workshop.html , 84 pages, 28 figures
Bibliographic Code:
2016arXiv160607039D

Abstract

SPHEREx is a proposed SMEX mission selected for Phase A. SPHEREx will carry out the first all-sky spectral survey and provide for every 6.2" pixel a spectra between 0.75 and 4.18 $\mu$m [with R$\sim$41.4] and 4.18 and 5.00 $\mu$m [with R$\sim$135]. The SPHEREx team has proposed three specific science investigations to be carried out with this unique data set: cosmic inflation, interstellar and circumstellar ices, and the extra-galactic background light. It is readily apparent, however, that many other questions in astrophysics and planetary sciences could be addressed with the SPHEREx data. The SPHEREx team convened a community workshop in February 2016, with the intent of enlisting the aid of a larger group of scientists in defining these questions. This paper summarizes the rich and varied menu of investigations that was laid out. It includes studies of the composition of main belt and Trojan/Greek asteroids; mapping the zodiacal light with unprecedented spatial and spectral resolution; identifying and studying very low-metallicity stars; improving stellar parameters in order to better characterize transiting exoplanets; studying aliphatic and aromatic carbon-bearing molecules in the interstellar medium; mapping star formation rates in nearby galaxies; determining the redshift of clusters of galaxies; identifying high redshift quasars over the full sky; and providing a NIR spectrum for most eROSITA X-ray sources. All of these investigations, and others not listed here, can be carried out with the nominal all-sky spectra to be produced by SPHEREx. In addition, the workshop defined enhanced data products and user tools which would facilitate some of these scientific studies. Finally, the workshop noted the high degrees of synergy between SPHEREx and a number of other current or forthcoming programs, including JWST, WFIRST, Euclid, GAIA, K2/Kepler, TESS, eROSITA and LSST.

 

Title:
Dumbbell Defects in FeSe Films: A Scanning Tunneling Microscopy and First-Principles Investigation
Authors:
Huang, Dennis; Webb, Tatiana A.; Song, Can-Li; Chang, Cui-Zu; Moodera, Jagadeesh S.; Kaxiras, Efthimios; Hoffman, Jennifer E.
Publication:
eprint arXiv:1606.07057
Publication Date:
06/2016
Origin:
ARXIV
Keywords:
Condensed Matter - Superconductivity, Condensed Matter - Strongly Correlated Electrons
Comment:
7 pages, 5 figures; Nano Lett. 2016; doi:10.1021/acs.nanolett.6b01163
Bibliographic Code:
2016arXiv160607057H

Abstract

The properties of iron-based superconductors (Fe-SCs) can be varied dramatically with the introduction of dopants and atomic defects. As a pressing example, FeSe, parent phase of the highest-$T_c$ Fe-SC, exhibits prevalent defects with atomic-scale "dumbbell" signatures as imaged by scanning tunneling microscopy (STM). These defects spoil superconductivity when their concentration exceeds 2.5%. Resolving their chemical identity is prerequisite to applications such as nanoscale patterning of superconducting/nonsuperconducting regions in FeSe, as well as fundamental questions such as the mechanism of superconductivity and the path by which the defects destroy it. We use STM and density functional theory to characterize and identify the dumbbell defects. In contrast to previous speculations about Se adsorbates or substitutions, we find that an Fe-site vacancy is the most energetically favorable defect in Se-rich conditions, and reproduces our observed STM signature. Our calculations shed light more generally on the nature of Se capping, the removal of Fe vacancies via annealing, and their ordering into a $\sqrt{5}$$\times$$\sqrt{5}$ superstructure in FeSe and related alkali-doped compounds.

 

Title:
Spin density wave order, topological order, and Fermi surface reconstruction
Authors:
Sachdev, Subir; Berg, Erez; Chatterjee, Shubhayu; Schattner, Yoni
Publication:
eprint arXiv:1606.07813
Publication Date:
06/2016
Origin:
ARXIV
Keywords:
Condensed Matter - Strongly Correlated Electrons, High Energy Physics - Theory
Comment:
32 pages, 3 figures; (v2) 33 pages, 4 figures, added figure, clarifications and references
Bibliographic Code:
2016arXiv160607813S

Abstract

In the conventional theory of density wave ordering in metals, the onset of spin density wave (SDW) order co-incides with the reconstruction of the Fermi surfaces into small 'pockets'. We present models which display this transition, while also displaying an alternative route between these phases via an intermediate phase with topological order, no broken symmetry, and pocket Fermi surfaces. The models involve coupling emergent gauge fields to a fractionalized SDW order, but retain the canonical electron operator in the underlying Hamiltonian. We establish an intimate connection between the suppression of certain defects in the SDW order, and the presence of Fermi surface sizes distinct from the Luttinger value in Fermi liquids. We discuss the relevance of such models to the physics of the hole-doped cuprates near optimal doping.

 

Title:
Evidence for a Lattice Weak Gravity Conjecture
Authors:
Heidenreich, Ben; Reece, Matthew; Rudelius, Tom
Publication:
eprint arXiv:1606.08437
Publication Date:
06/2016
Origin:
ARXIV
Keywords:
High Energy Physics - Theory, General Relativity and Quantum Cosmology, High Energy Physics - Phenomenology
Comment:
36 pages
Bibliographic Code:
2016arXiv160608437H

Abstract

The Weak Gravity Conjecture postulates the existence of superextremal charged particles, i.e. those with mass smaller than or equal to their charge in Planck units. We present further evidence for our recent observation that in known examples a much stronger statement is true: an infinite tower of superextremal particles of different charges exists. We show that effective Kaluza-Klein field theories and perturbative string vacua respect the Sublattice Weak Gravity Conjecture, namely that a finite index sublattice of the full charge lattice exists with a superextremal particle at each site. In perturbative string theory we show that this follows from modular invariance. However, we present counterexamples to the stronger possibility that a superextremal state exists at every lattice site, including an example in which the lightest charged state is subextremal. The Sublattice Weak Gravity Conjecture has many implications both for abstract theories of quantum gravity and for real-world physics. For instance, it implies that if a gauge group with very small coupling $e$ exists, then scattering at energies above $\sim e^{1/3} M_{\rm Pl}$ generically produces black holes.

 

Title:
Dynamics of D-branes I. The non-Abelian Dirac-Born-Infeld action, its first variation, and the equations of motion for D-branes --- with remarks on the non-Abelian Chern-Simons/Wess-Zumino term
Authors:
Liu, Chien-Hao; Yau, Shing-Tung
Publication:
eprint arXiv:1606.08529
Publication Date:
06/2016
Origin:
ARXIV
Keywords:
High Energy Physics - Theory, Mathematics - Algebraic Geometry, Mathematics - Differential Geometry, Mathematics - Symplectic Geometry, 81T30, 35J20, 16S50, 14A22, 35R01
Comment:
73+2 pages, 8 figures
Bibliographic Code:
2016arXiv160608529L

Abstract

In earlier works, D(1) (arXiv:0709.1515 [math.AG]), D(11.1) (arXiv:1406.0929 [math.DG]), D(11.2) (arXiv:1412.0771 [hep-th]), and D(11.3.1) (arXiv:1508.02347 [math.DG]), we have explained why a D-brane in string theory, when treated as a fundamental dynamical object, can be described by a map $\varphi$ from an Azumaya/matrix manifold $X^{Az}$ (cf. D-brane world-volume) with a fundamental module with a connection $(E,\nabla)$ (cf. Chan-Paton bundle) to the target space-time $Y$. In this sequel, we construct a non-Abelian Dirac-Born-Infeld action functional $S_{DBI}^{(\Phi, g, B)}(\varphi,\nabla)$ for such pairs $(\varphi,\nabla)$. We next develop a technical tool needed to study variations of this action and apply it to derive the first variation $\delta S_{DBI}^{(\Phi,g,B)}/\delta(\varphi,\nabla)$ of $S_{DBI}^{(\Phi,g,B)}$ with respect to $(\varphi,\nabla)$. The equations of motion that govern the dynamics of D-branes then follow. A complete action for a D-brane world-volume must include also the Chern-Simons/Wess-Zumino term $S_{CS/WZ}^{(C)}(\varphi,\nabla)$ that governs how the D-brane world-volume couples with the Ramond-Ramond fields $C$ on $Y$. In the current notes, a version $S^{(C,B)}_{CS/WZ}(\varphi,\nabla)$ of non-Abelian Chern-Simons/Wess-Zumino action functional for $(\varphi,\nabla)$ that follows the same guide with which we construct $S^{(\Phi,g,B)}_{DBI}(\varphi,\nabla)$ is constructed for lower-dimensional D-branes (i.e. D(-1)-, D0-, D1-, D2-branes). Its first variation $\delta S^{(C,B)}_{CS/WZ}(\varphi,\nabla)/\delta(\varphi,\nabla)$ is derived and its contribution to the equations of motion for $(\varphi, \nabla)$ follows. The current notes lay down a foundation toward the dynamics of D-branes along the line of this D-project.

 

Title:
K stability and stability of chiral ring
Authors:
Collins, Tristan C.; Xie, Dan; Yau, Shing-Tung
Publication:
eprint arXiv:1606.09260
Publication Date:
06/2016
Origin:
ARXIV
Keywords:
High Energy Physics - Theory, Mathematics - Differential Geometry
Comment:
22 pages, 4 figures
Bibliographic Code:
2016arXiv160609260C

Abstract

We define a notion of stability for chiral ring of four dimensional N=1 theory by introducing test chiral rings and generalized a maximization. We conjecture that a chiral ring is the chiral ring of a superconformal field theory if and only if it is stable. We then study N=1 field theory derived from D3 branes probing a three-fold singularity X, and show that the K stability which implies the existence of Ricci-flat conic metric on X is equivalent to the stability of chiral ring of the corresponding field theory.

 

Title:
Gauss-Manin Connection in Disguise: Calabi-Yau Threefolds
Authors:
Alim, Murad; Movasati, Hossein; Scheidegger, Emanuel; Yau, Shing-Tung
Publication:
Communications in Mathematical Physics, Volume 344, Issue 3, pp.889-914
Publication Date:
06/2016
Origin:
SPRINGER
Abstract Copyright:
(c) 2016: Springer-Verlag Berlin Heidelberg
DOI:
10.1007/s00220-016-2640-9
Bibliographic Code:
2016CMaPh.344..889A

Abstract

We describe a Lie Algebra on the moduli space of non-rigid compact Calabi-Yau threefolds enhanced with differential forms and its relation to the Bershadsky-Cecotti-Ooguri-Vafa holomorphic anomaly equation. In particular, we describe algebraic topological string partition functions {{F}g^alg, g ≥ 1}, which encode the polynomial structure of holomorphic and non-holomorphic topological string partition functions. Our approach is based on Grothendieck's algebraic de Rham cohomology and on the algebraic Gauss-Manin connection. In this way, we recover a result of Yamaguchi-Yau and Alim-Länge in an algebraic context. Our proofs use the fact that the special polynomial generators defined using the special geometry of deformation spaces of Calabi-Yau threefolds correspond to coordinates on such a moduli space. We discuss the mirror quintic as an example.

 

Title:
Measurement of the charged-particle multiplicity inside jets from √{s}=8 {TeV} pp collisions with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... ; Huth, J.;... Morii, M.;... and 2864 coauthors
Publication:
The European Physical Journal C, Volume 76, Issue 6, article id. #322, 23 pp. (EPJC Homepage)
Publication Date:
06/2016
Origin:
SPRINGER
Abstract Copyright:
(c) 2016: CERN for the benefit of the ATLAS collaboration
DOI:
10.1140/epjc/s10052-016-4126-5
Bibliographic Code:
2016EPJC...76..322A

Abstract

The number of charged particles inside jets is a widely used discriminant for identifying the quark or gluon nature of the initiating parton and is sensitive to both the perturbative and non-perturbative components of fragmentation. This paper presents a measurement of the average number of charged particles with p_ {T}>500 {MeV} inside high-momentum jets in dijet events using 20.3 fb^{-1} of data recorded with the ATLAS detector in pp collisions at √{s}=8 {TeV} collisions at the LHC. The jets considered have transverse momenta from 50 {GeV} up to and beyond 1.5 {TeV}. The reconstructed charged-particle track multiplicity distribution is unfolded to remove distortions from detector effects and the resulting charged-particle multiplicity is compared to several models. Furthermore, quark and gluon jet fractions are used to extract the average charged-particle multiplicity for quark and gluon jets separately.

 

Title:
Electric field effect thermoelectric transport in individual silicon and germanium/silicon nanowires
Authors:
Brovman, Yuri M.; Small, Joshua P.; Hu, Yongjie; Fang, Ying; Lieber, Charles M.; Kim, Philip
Publication:
Journal of Applied Physics, Volume 119, Issue 23, id.234304 (JAP Homepage)
Publication Date:
06/2016
Origin:
AIP
Abstract Copyright:
2016: Author(s)
DOI:
10.1063/1.4953818
Bibliographic Code:
2016JAP...119w4304B

Abstract

We have simultaneously measured conductance and thermoelectric power (TEP) of individual silicon and germanium/silicon core/shell nanowires in the field effect transistor device configuration. As the applied gate voltage changes, the TEP shows distinctly different behaviors while the electrical conductance exhibits the turn-off, subthreshold, and saturation regimes, respectively. At room temperature, peak TEP value of ˜300 μ V/K is observed in the subthreshold regime of the Si devices. The temperature dependence of the saturated TEP values is used to estimate the carrier doping of Si nanowires.

 

Title:
Relative entropy equals bulk relative entropy
Authors:
Jafferis, Daniel L.; Lewkowycz, Aitor; Maldacena, Juan; Suh, S. Josephine
Affiliation:
AA(Center for Fundamental Laws of Nature, Harvard University), AB(Jadwin Hall, Princeton University), AC(Institute for Advanced Study), AD(Kavli Institute for Theoretical Physics; Department of Physics and Astronomy, University of British Columbia)
Publication:
Journal of High Energy Physics, Volume 2016, Issue 6, article id. #4, 20 pp.
Publication Date:
06/2016
Origin:
SPRINGER
Keywords:
AdS-CFT Correspondence, 1/N Expansion, Models of Quantum Gravity, Field Theories in Higher Dimensions
Abstract Copyright:
(c) 2016: The Author(s)
DOI:
10.1007/JHEP06(2016)004
Bibliographic Code:
2016JHEP...06..004J

Abstract

We consider the gravity dual of the modular Hamiltonian associated to a general subregion of a boundary theory. We use it to argue that the relative entropy of nearby states is given by the relative entropy in the bulk, to leading order in the bulk gravitational coupling. We also argue that the boundary modular flow is dual to the bulk modular flow in the entanglement wedge, with implications for entanglement wedge reconstruction.

 

Title:
Search for new phenomena in events with a photon and missing transverse momentum in pp collisions at √{s}=13 TeV with the ATLAS detector
Authors:
Aaboud, M.; Aad, G.; Abbott, B.; Abdallah, J.;... ; Franklin, M.;... ; Huth, J.;... Morii, M.;... and 2848 coauthors
Publication:
Journal of High Energy Physics, Volume 2016, Issue 6, article id. #59, 41 pp.
Publication Date:
06/2016
Origin:
SPRINGER
Keywords:
Hadron-Hadron scattering (experiments)
Abstract Copyright:
(c) 2016: The Author(s)
DOI:
10.1007/JHEP06(2016)059
Bibliographic Code:
2016JHEP...06..059A

Abstract

Results of a search for new phenomena in events with an energetic photon and large missing transverse momentum with the ATLAS experiment at the Large Hadron Collider are reported. The data were collected in proton-proton collisions at a centre-of-mass energy of 13 TeV and correspond to an integrated luminosity of 3.2 fb-1. The observed data are in agreement with the Standard Model expectations. Exclusion limits are presented in models of new phenomena including pair production of dark matter candidates or large extra spatial dimensions. In a simplified model of dark matter and an axial-vector mediator, the search excludes mediator masses below 710 GeV for dark matter candidate masses below 150 GeV. In an effective theory of dark matter production, values of the suppression scale M ∗ up to 570 GeV are excluded and the effect of truncation for various coupling values is reported. For the ADD large extra spatial dimension model the search places more stringent limits than earlier searches in the same event topology, excluding M D up to about 2.3 (2.8) TeV for two (six) additional spatial dimensions; the limits are reduced by 20-40% depending on the number of additional spatial dimensions when applying a truncation procedure. [Figure not available: see fulltext.]

 

Title:
A search for top squarks with R-parity-violating decays to all-hadronic final states with the ATLAS detector in √{s}=8 TeV proton-proton collisions
Authors:
Aad, G.; Abbott, B.; Abdallah, J.; Abdinov, O.;... Franklin, M.;... ; Huth, J.;... Morii, M.;... and 2822 coauthors
Publication:
Journal of High Energy Physics, Volume 2016, Issue 6, article id. #67, 49 pp.
Publication Date:
06/2016
Origin:
SPRINGER
Keywords:
Hadron-Hadron scattering (experiments)
Abstract Copyright:
(c) 2016: The Author(s)
DOI:
10.1007/JHEP06(2016)067
Bibliographic Code:
2016JHEP...06..067A

Abstract

A search for the pair production of top squarks, each with R-parity-violating decays into two Standard Model quarks, is performed using 17.4 fb-1 of √{s}=8 TeV proton-proton collision data recorded by the ATLAS experiment at the LHC. Each top squark is assumed to decay to a b- and an s-quark, leading to four quarks in the final state. Background discrimination is achieved with the use of b-tagging and selections on the mass and substructure of large-radius jets, providing sensitivity to top squark masses as low as 100 GeV. No evidence of an excess beyond the Standard Model background prediction is observed and top squarks decaying to overline{b}overline{s} are excluded for top squark masses in the range 100 le {m}_{overline{t}}le 315 GeV at 95% confidence level. [Figure not available: see fulltext.]

 

Title:
Measurement of the relative width difference of the {B}^0-{overline{B}}^0 system with the ATLAS detector
Authors:
Aaboud, M.; Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... ; Huth, J.;... Morii, M.;... and 2848 coauthors
Publication:
Journal of High Energy Physics, Volume 2016, Issue 6, article id. #81, 39 pp.
Publication Date:
06/2016
Origin:
SPRINGER
Keywords:
B physics, Hadron-Hadron scattering (experiments)
Abstract Copyright:
(c) 2016: The Author(s)
DOI:
10.1007/JHEP06(2016)081
Bibliographic Code:
2016JHEP...06..081A

Abstract

xperiment at the LHC in pp collisions at √{s}=7 TeV and √{s}=8 TeV and corresponding to an integrated luminosity of 25.2 fb-1. The value of ΔΓ d d is obtained by comparing the decay-time distributions of B 0 → J/ ψK S and B 0 → J/ ψK *0(892) decays. The result is ΔΓ d d = (-0.1±1.1 (stat.)± 0.9 (syst.)) × 10-2. Currently, this is the most precise single measurement of ΔΓ d d . It agrees with the Standard Model prediction and the measurements by other experiments. [Figure not available: see fulltext.]

 

Title:
Identification of high transverse momentum top quarks 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 2863 coauthors
Publication:
Journal of High Energy Physics, Volume 2016, Issue 6, article id. #93, 81 pp.
Publication Date:
06/2016
Origin:
SPRINGER
Keywords:
Hadron-Hadron scattering (experiments)
Abstract Copyright:
(c) 2016: The Author(s)
DOI:
10.1007/JHEP06(2016)093
Bibliographic Code:
2016JHEP...06..093A

Abstract

This paper presents studies of the performance of several jet-substructure techniques, which are used to identify hadronically decaying top quarks with high transverse momentum contained in large-radius jets. The efficiency of identifying top quarks is measured using a sample of top-quark pairs and the rate of wrongly identifying jets from other quarks or gluons as top quarks is measured using multijet events collected with the ATLAS experiment in 20.3 fb-1 of 8 TeV proton-proton collisions at the Large Hadron Collider. Predictions from Monte Carlo simulations are found to provide an accurate description of the performance. The techniques are compared in terms of signal efficiency and background rejection using simulations, covering a larger range in jet transverse momenta than accessible in the dataset. Additionally, a novel technique is developed that is optimized to reconstruct top quarks in events with many jets. [Figure not available: see fulltext.]

 

Title:
Airy Equation for the Topological String Partition Function in a Scaling Limit
Authors:
Alim, Murad; Yau, Shing-Tung; Zhou, Jie
Publication:
Letters in Mathematical Physics, Volume 106, Issue 6, pp.719-729
Publication Date:
06/2016
Origin:
SPRINGER
Abstract Copyright:
(c) 2016: Springer Science+Business Media Dordrecht
DOI:
10.1007/s11005-016-0840-z
Bibliographic Code:
2016LMaPh.106..719A

Abstract

We use the polynomial formulation of the holomorphic anomaly equations governing perturbative topological string theory to derive the free energies in a scaling limit to all orders in perturbation theory for any Calabi-Yau threefold. The partition function in this limit satisfies an Airy differential equation in a rescaled topological string coupling. One of the two solutions of this equation gives the perturbative expansion and the other solution provides geometric hints of the non-perturbative structure of topological string theory. Both solutions can be expanded naturally around strong coupling.

 

Title:
On the growth and form of cortical convolutions
Authors:
Tallinen, Tuomas; Chung, Jun Young; Rousseau, François; Girard, Nadine; Lefèvre, Julien; Mahadevan, L.
Publication:
Nature Physics, Volume 12, Issue 6, pp. 588-593 (2016).
Publication Date:
06/2016
Origin:
NATURE
Abstract Copyright:
(c) 2016: Nature Publishing Group
DOI:
10.1038/nphys3632
Bibliographic Code:
2016NatPh..12..588T

Abstract

The rapid growth of the human cortex during development is accompanied by the folding of the brain into a highly convoluted structure. Recent studies have focused on the genetic and cellular regulation of cortical growth, but understanding the formation of the gyral and sulcal convolutions also requires consideration of the geometry and physical shaping of the growing brain. To study this, we use magnetic resonance images to build a 3D-printed layered gel mimic of the developing smooth fetal brain; when immersed in a solvent, the outer layer swells relative to the core, mimicking cortical growth. This relative growth puts the outer layer into mechanical compression and leads to sulci and gyri similar to those in fetal brains. Starting with the same initial geometry, we also build numerical simulations of the brain modelled as a soft tissue with a growing cortex, and show that this also produces the characteristic patterns of convolutions over a realistic developmental course. All together, our results show that although many molecular determinants control the tangential expansion of the cortex, the size, shape, placement and orientation of the folds arise through iterations and variations of an elementary mechanical instability modulated by early fetal brain geometry.

 

Title:
Measurement of D, D± and Ds± meson production cross sections in pp collisions at √{ s} = 7 TeV with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.; Abdinov, O.;... Franklin, M.;... ; Huth, J.;... Morii, M.;... and 2831 coauthors
Publication:
Nuclear Physics, Section B, Volume 907, p. 717-763.
Publication Date:
06/2016
Origin:
ELSEVIER
Abstract Copyright:
(c) 2016 The Authors
DOI:
10.1016/j.nuclphysb.2016.04.032
Bibliographic Code:
2016NuPhB.907..717A

Abstract

The production of D, D± and Ds± charmed mesons has been measured with the ATLAS detector in pp collisions at √{ s} = 7 TeV at the LHC, using data corresponding to an integrated luminosity of 280 nb-1. The charmed mesons have been reconstructed in the range of transverse momentum 3.5 <pT (D) < 100 GeV and pseudorapidity | η (D) | < 2.1. The differential cross sections as a function of transverse momentum and pseudorapidity were measured for D and D± production. The next-to-leading-order QCD predictions are consistent with the data in the visible kinematic region within the large theoretical uncertainties. Using the visible D cross sections and an extrapolation to the full kinematic phase space, the strangeness-suppression factor in charm fragmentation, the fraction of charged non-strange D mesons produced in a vector state, and the total cross section of charm production at √{ s} = 7 TeV were derived.

 

Title:
Ultra-precise holographic beam shaping for microscopic quantum control
Authors:
Zupancic, Philip; Preiss, Philipp M.; Ma, Ruichao; Lukin, Alexander; Eric Tai, M.; Rispoli, Matthew; Islam, Rajibul; Greiner, Markus
Publication:
Optics Express, vol. 24, issue 13, p. 13881
Publication Date:
06/2016
Origin:
CROSSREF
DOI:
10.1364/OE.24.013881
Bibliographic Code:
2016OExpr..2413881Z

Abstract

High-resolution addressing of individual 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:
The characterization of the gamma-ray signal from the central Milky Way: A case for annihilating dark matter
Authors:
Daylan, Tansu; Finkbeiner, Douglas P.; Hooper, Dan; Linden, Tim; Portillo, Stephen K. N.; Rodd, Nicholas L.; Slatyer, Tracy R.
Publication:
Physics of the Dark Universe, Volume 12, p. 1-23.
Publication Date:
06/2016
Origin:
ELSEVIER
Keywords:
Dark matter, Indirect detection, Gamma-rays
Abstract Copyright:
(c) 2016 Elsevier B.V.
DOI:
10.1016/j.dark.2015.12.005
Bibliographic Code:
2016PDU....12....1D

Abstract

Past studies have identified a spatially extended excess of ˜1-3 GeV gamma rays from the region surrounding the Galactic Center, consistent with the emission expected from annihilating dark matter. We revisit and scrutinize this signal with the intention of further constraining its characteristics and origin. By applying cuts to the Fermi event parameter CTBCORE, we suppress the tails of the point spread function and generate high resolution gamma-ray maps, enabling us to more easily separate the various gamma-ray components. Within these maps, we find the GeV excess to be robust and highly statistically significant, with a spectrum, angular distribution, and overall normalization that is in good agreement with that predicted by simple annihilating dark matter models. For example, the signal is very well fit by a 36-51 GeV dark matter particle annihilating to b b ¯ with an annihilation cross section of σv =(1 - 3) × 10-26cm3 / s (normalized to a local dark matter density of 0.4 GeV /cm3). Furthermore, we confirm that the angular distribution of the excess is approximately spherically symmetric and centered around the dynamical center of the Milky Way (within ˜ 0.05∘ of Sgr A∗), showing no sign of elongation along the Galactic Plane. The signal is observed to extend to at least ≃ 10∘ from the Galactic Center, which together with its other morphological traits disfavors the possibility that this emission originates from previously known or modeled pulsar populations.

 

Title:
Continuum-mediated dark matter-baryon scattering
Authors:
Katz, Andrey; Reece, Matthew; Sajjad, Aqil
Publication:
Physics of the Dark Universe, Volume 12, p. 24-36.
Publication Date:
06/2016
Origin:
ELSEVIER
Keywords:
Dark matter direct detection, Dark matter models, Light dark matter mediators
Abstract Copyright:
(c) 2016 The Authors
DOI:
10.1016/j.dark.2016.01.002
Bibliographic Code:
2016PDU....12...24K

Abstract

Many models of dark matter scattering with baryons may be treated either as a simple contact interaction or as the exchange of a light mediator particle. We study an alternative, in which a continuum of light mediator states may be exchanged. This could arise, for instance, from coupling to a sector which is approximately conformal at the relevant momentum transfer scale. In the non-relativistic effective theory of dark matter-baryon scattering, which is useful for parametrizing direct detection signals, the effect of such continuum mediators is to multiply the amplitude by a function of the momentum transfer q, which in the simplest case is just a power law. We develop the basic framework and study two examples: the case where the mediator is a scalar operator coupling to the Higgs portal (which turns out to be highly constrained) and the case of an antisymmetric tensor operator Oμν that mixes with the hypercharge field strength and couples to dark matter tensor currents, which has an interesting viable parameter space. We describe the effect of such mediators on the cross sections and recoil energy spectra that could be observed in direct detection.

 

Title:
Search for new phenomena in final states with large jet multiplicities and missing transverse momentum with ATLAS using √{ s} = 13 TeV proton-proton collisions
Authors:
Aad, G.; Abbott, B.; Abdallah, J.; Abdinov, O.;... Franklin, M.;... ; Huth, J.;... Morii, M.;... and 2849 coauthors
Publication:
Physics Letters B, Volume 757, p. 334-355.
Publication Date:
06/2016
Origin:
ELSEVIER
Abstract Copyright:
(c) 2016 CERN for the benefit of the ATLAS Collaboration
DOI:
10.1016/j.physletb.2016.04.005
Bibliographic Code:
2016PhLB..757..334A

Abstract

Results are reported of a search for new phenomena, such as supersymmetric particle production, that could be observed in high-energy proton-proton collisions. Events with large numbers of jets, together with missing transverse momentum from unobserved particles, are selected. The data analysed were recorded by the ATLAS experiment during 2015 using the 13 TeV centre-of-mass proton-proton collisions at the Large Hadron Collider, and correspond to an integrated luminosity of 3.2 fb-1. The search selected events with various jet multiplicities from ≥7 to ≥10 jets, and with various b-jet multiplicity requirements to enhance sensitivity. No excess above Standard Model expectations is observed. The results are interpreted within two supersymmetry models, where gluino masses up to 1400 GeV are excluded at 95% confidence level, significantly extending previous limits.

 

Title:
Weak crystallization theory of metallic alloys
Authors:
Martin, Ivar; Gopalakrishnan, Sarang; Demler, Eugene A.
Publication:
Physical Review B, Volume 93, Issue 23, id.235140 (PhRvB Homepage)
Publication Date:
06/2016
Origin:
APS
Abstract Copyright:
2016: American Physical Society
DOI:
10.1103/PhysRevB.93.235140
Bibliographic Code:
2016PhRvB..93w5140M

Abstract

Crystallization is one of the most familiar, but hardest to analyze, phase transitions. The principal reason is that crystallization typically occurs via a strongly first-order phase transition, and thus rigorous treatment would require comparing energies of an infinite number of possible crystalline states with the energy of liquid. A great simplification occurs when crystallization transition happens to be weakly first order. In this case, weak crystallization theory, based on unbiased Ginzburg-Landau expansion, can be applied. Even beyond its strict range of validity, it has been a useful qualitative tool for understanding crystallization. In its standard form, however, weak crystallization theory cannot explain the existence of a majority of observed crystalline and quasicrystalline states. Here we extend the weak crystallization theory to the case of metallic alloys. We identify a singular effect of itinerant electrons on the form of weak crystallization free energy. It is geometric in nature, generating strong dependence of free energy on the angles between ordering wave vectors of ionic density. That leads to stabilization of fcc, rhombohedral, and icosahedral quasicrystalline (iQC) phases, which are absent in the generic theory with only local interactions. As an application, we find the condition for stability of iQC that is consistent with the Hume-Rothery rules known empirically for the majority of stable iQC; namely, the length of the primary Bragg-peak wave vector is approximately equal to the diameter of the Fermi sphere.

 

Title:
Electronic structure theory of weakly interacting bilayers
Authors:
Fang, Shiang; Kaxiras, Efthimios
Publication:
Physical Review B, Volume 93, Issue 23, id.235153 (PhRvB Homepage)
Publication Date:
06/2016
Origin:
APS
Abstract Copyright:
2016: American Physical Society
DOI:
10.1103/PhysRevB.93.235153
Bibliographic Code:
2016PhRvB..93w5153F

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 pz 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 moiré 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:
Measurements of Z γ and Z γ γ production 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 2855 coauthors
Publication:
Physical Review D, Volume 93, Issue 11, id.112002 (PhRvD Homepage)
Publication Date:
06/2016
Origin:
APS
Abstract Copyright:
2016: CERN
DOI:
10.1103/PhysRevD.93.112002
Bibliographic Code:
2016PhRvD..93k2002A

Abstract

The production of Z bosons with one or two isolated high-energy photons is studied using p p collisions at √{s }=8 TeV . The analyses use a data sample with an integrated luminosity of 20.3 fb-1 collected by the ATLAS detector during the 2012 LHC data taking. The Z γ and Z γ γ production cross sections are measured with leptonic (e+e-, μ+μ-, ν ν ¯) decays of the Z boson, in extended fiducial regions defined in terms of the lepton and photon acceptance. They are then compared to cross-section predictions from the Standard Model, where the sources of the photons are radiation off initial-state quarks and radiative Z -boson decay to charged leptons, and from fragmentation of final-state quarks and gluons into photons. The yields of events with photon transverse energy ET>250 GeV from ℓ+-γ events and with ET>400 GeV from ν ν ¯ γ events are used to search for anomalous triple gauge-boson couplings Z Z γ and Z γ γ . The yields of events with diphoton invariant mass mγ γ>200 GeV from ℓ+- γ γ events and with mγ γ>300 GeV from ν ν ¯ γ γ events are used to search for anomalous quartic gauge-boson couplings Z Z γ γ and Z γ γ γ. No deviations from Standard Model predictions are observed and limits are placed on parameters used to describe anomalous triple and quartic gauge-boson couplings.

 

Title:
Measurement of the forward-backward asymmetry in low-mass bottom-quark pairs produced in proton-antiproton collisions
Authors:
Aaltonen, T.; Amerio, S.; Amidei, D.;... Franklin, M.;... and 394 coauthors; CDF Collaboration
Publication:
Physical Review D, Volume 93, Issue 11, id.112003 (PhRvD Homepage)
Publication Date:
06/2016
Origin:
APS
Abstract Copyright:
2016: American Physical Society
DOI:
10.1103/PhysRevD.93.112003
Bibliographic Code:
2016PhRvD..93k2003A

Abstract

We report a measurement of the forward-backward asymmetry, AFB , in b b ¯ pairs produced in proton-antiproton collisions and identified by muons from semileptonic b -hadron decays. The event sample is collected at a center-of-mass energy of √{s }=1.96 TeV with the CDF II detector and corresponds to 6.9 fb-1 of integrated luminosity. We obtain an integrated asymmetry of AFB(b b ¯ ) =(1.2 ±0.7 )% at the particle level for b -quark pairs with invariant mass, mb b ¯ , down to 40 GeV /c2 and measure the dependence of AFB(b b ¯ ) on mb b ¯ . The results are compatible with expectations from the standard model.

 

Title:
Measurement of the forward-backward asymmetry of top-quark and antiquark pairs using the full CDF Run II data set
Authors:
Aaltonen, T.; Amerio, S.; Amidei, D.;... Franklin, M.;... and 393 coauthors; CDF Collaboration
Publication:
Physical Review D, Volume 93, Issue 11, id.112005 (PhRvD Homepage)
Publication Date:
06/2016
Origin:
APS
Abstract Copyright:
2016: American Physical Society
DOI:
10.1103/PhysRevD.93.112005
Bibliographic Code:
2016PhRvD..93k2005A

Abstract

We measure the forward-backward asymmetry of the production of top-quark and antiquark pairs in proton-antiproton collisions at center-of-mass energy √{s }=1.96 TeV using the full data set collected by the Collider Detector at Fermilab (CDF) in Tevatron Run II corresponding to an integrated luminosity of 9.1 fb-1 . The asymmetry is characterized by the rapidity difference between top quarks and antiquarks (Δ y ) and measured in the final state with two charged leptons (electrons and muons). The inclusive asymmetry, corrected to the entire phase space at parton level, is measured to be AFBt t ¯=0.12 ±0.13 , consistent with the expectations from the standard model (SM) and previous CDF results in the final state with a single charged lepton. The combination of the CDF measurements of the inclusive AFBt t ¯ in both final states yields AFBt t ¯=0.160 ±0.045 , which is consistent with the SM predictions. We also measure the differential asymmetry as a function of Δ y . A linear fit to AFBt t ¯(|Δ y |), assuming zero asymmetry at Δ y =0 , yields a slope of α =0.14 ±0.15 , consistent with the SM prediction and the previous CDF determination in the final state with a single charged lepton. The combined slope of AFBt t ¯(|Δ y |) in the two final states is α =0.227 ±0.057 , which is 2.0 σ larger than the SM prediction.

 

Title:
Search for a low-mass neutral Higgs boson with suppressed couplings to fermions using events with multiphoton final states
Authors:
Aaltonen, T.; Amerio, S.; Amidei, D.;... Franklin, M.;... and 394 coauthors; CDF Collaboration
Publication:
Physical Review D, Volume 93, Issue 11, id.112010 (PhRvD Homepage)
Publication Date:
06/2016
Origin:
APS
Abstract Copyright:
2016: American Physical Society
DOI:
10.1103/PhysRevD.93.112010
Bibliographic Code:
2016PhRvD..93k2010A

Abstract

A search for a Higgs boson with suppressed couplings to fermions, hf, assumed to be the neutral, lower-mass partner of the Higgs boson discovered at the Large Hadron Collider, is reported. Such a Higgs boson could exist in extensions of the standard model with two Higgs doublets, and could be produced via p p ¯→H±hf→W*hfhf→4 γ +X , where H± is a charged Higgs boson. This analysis uses all events with at least three photons in the final state from proton-antiproton collisions at a center-of-mass energy of 1.96 TeV collected by the Collider Detector at Fermilab, corresponding to an integrated luminosity of 9.2 fb-1. No evidence of a signal is observed in the data. Values of Higgs-boson masses between 10 and 100 GeV /c2 are excluded at 95% Bayesian credibility.

 

Title:
Binding energies of nucleobase complexes: Relevance to homology recognition of DNA
Authors:
León, Sergio Cruz; Prentiss, Mara; Fyta, Maria
Publication:
Physical Review E, Volume 93, Issue 6, id.062410 (PhRvE Homepage)
Publication Date:
06/2016
Origin:
APS
Abstract Copyright:
2016: American Physical Society
DOI:
10.1103/PhysRevE.93.062410
Bibliographic Code:
2016PhRvE..93f2410L

Abstract

The binding energies of complexes of DNA nucleobase pairs are evaluated using quantum mechanical calculations at the level of dispersion corrected density functional theory. We begin with Watson-Crick base pairs of singlets, duplets, and triplets and calculate their binding energies. At a second step, mismatches are incorporated into the Watson-Crick complexes in order to evaluate the variation in the binding energy with respect to the canonical Watson-Crick pairs. A linear variation of this binding energy with the degree of mismatching is observed. The binding energies for the duplets and triplets containing mismatches are further compared to the energies of the respective singlets in order to assess the degree of collectivity in these complexes. This study also suggests that mismatches do not considerably affect the energetics of canonical base pairs. Our work is highly relevant to the recognition process in DNA promoted through the RecA protein and suggests a clear distinction between recognition in singlets, and recognition in duplets or triplets. Our work assesses the importance of collectivity in the homology recognition of DNA.

 

Title:
Quantum Metrology Enhanced by Repetitive Quantum Error Correction
Authors:
Unden, Thomas; Balasubramanian, Priya; Louzon, Daniel; Vinkler, Yuval; Plenio, Martin B.; Markham, Matthew; Twitchen, Daniel; Stacey, Alastair; Lovchinsky, Igor; Sushkov, Alexander O.; Lukin, Mikhail D.; Retzker, Alex; Naydenov, Boris; McGuinness, Liam P.; Jelezko, Fedor
Publication:
Physical Review Letters, Volume 116, Issue 23, id.230502 (PhRvL Homepage)
Publication Date:
06/2016
Origin:
APS
Abstract Copyright:
2016: American Physical Society
DOI:
10.1103/PhysRevLett.116.230502
Bibliographic Code:
2016PhRvL.116w0502U

Abstract

We experimentally demonstrate the protection of a room-temperature hybrid spin register against environmental decoherence by performing repeated quantum error correction whilst maintaining sensitivity to signal fields. We use a long-lived nuclear spin to correct multiple phase errors on a sensitive electron spin in diamond and realize magnetic field sensing beyond the time scales set by natural decoherence. The universal extension of sensing time, robust to noise at any frequency, demonstrates the definitive advantage entangled multiqubit systems provide for quantum sensing and offers an important complement to quantum control techniques.

 

Title:
Soft Hair on Black Holes
Authors:
Hawking, Stephen W.; Perry, Malcolm J.; Strominger, Andrew
Publication:
Physical Review Letters, Volume 116, Issue 23, id.231301 (PhRvL Homepage)
Publication Date:
06/2016
Origin:
APS
Abstract Copyright:
2016: American Physical Society
DOI:
10.1103/PhysRevLett.116.231301
Bibliographic Code:
2016PhRvL.116w1301H

Abstract

It has recently been shown that Bondi-van der Burg-Metzner-Sachs supertranslation symmetries imply an infinite number of conservation laws for all gravitational theories in asymptotically Minkowskian spacetimes. These laws require black holes to carry a large amount of soft (i.e., zero-energy) supertranslation hair. The presence of a Maxwell field similarly implies soft electric hair. This Letter gives an explicit description of soft hair in terms of soft gravitons or photons on the black hole horizon, and shows that complete information about their quantum state is stored on a holographic plate at the future boundary of the horizon. Charge conservation is used to give an infinite number of exact relations between the evaporation products of black holes which have different soft hair but are otherwise identical. It is further argued that soft hair which is spatially localized to much less than a Planck length cannot be excited in a physically realizable process, giving an effective number of soft degrees of freedom proportional to the horizon area in Planck units.

 

Title:
Fluctuations in the Kinetics of Linear Protein Self-Assembly
Authors:
Michaels, Thomas C. T.; Dear, Alexander J.; Kirkegaard, Julius B.; Saar, Kadi L.; Weitz, David A.; Knowles, Tuomas P. J.
Publication:
Physical Review Letters, Volume 116, Issue 25, id.258103 (PhRvL Homepage)
Publication Date:
06/2016
Origin:
APS
Abstract Copyright:
2016: American Physical Society
DOI:
10.1103/PhysRevLett.116.258103
Bibliographic Code:
2016PhRvL.116y8103M

Abstract

Biological systems are characterized by compartmentalization from the subcellular to the tissue level, and thus reactions in small volumes are ubiquitous in living systems. Under such conditions, statistical number fluctuations, which are commonly negligible in bulk reactions, can become dominant and lead to stochastic behavior. We present here a stochastic model of protein filament formation in small volumes. We show that two principal regimes emerge for the system behavior, a small fluctuation regime close to bulk behavior and a large fluctuation regime characterized by single rare events. Our analysis shows that in both regimes the reaction lag-time scales inversely with the system volume, unlike in bulk. Finally, we use our stochastic model to connect data from small-volume microdroplet experiments of amyloid formation to bulk aggregation rates, and show that digital analysis of an ensemble of protein aggregation reactions taking place under microconfinement provides an accurate measure of the rate of primary nucleation of protein aggregates, a process that has been challenging to quantify from conventional bulk experiments.

 

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