# Faculty Publications: October, 2016

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

 Title: Interstellar Gas and a Dark Disk Authors: Kramer, Eric David; Randall, Lisa Publication: The Astrophysical Journal, Volume 829, Issue 2, article id. 126, 13 pp. (2016). (ApJ Homepage) Publication Date: 10/2016 Origin: IOP Astronomy Keywords: dark matter, Galaxy: disk, ISM: abundances, ISM: magnetic fields, ISM: structure, local interstellar matter DOI: 10.3847/0004-637X/829/2/126 Bibliographic Code: 2016ApJ...829..126K

### Abstract

We introduce a potentially powerful method for constraining or discovering a thin dark matter disk in the Milky Way. The method relies on the relationship between the midplane densities and scale heights of interstellar gas being determined by the gravitational potential, which is sensitive to the presence of a dark disk. We show how to use the interstellar gas parameters to set a bound on a dark disk and discuss the constraints suggested by the current data. However, current measurements for these parameters are discordant, with the uncertainty in the constraint being dominated by the molecular hydrogen midplane density measurement, as well as by the atomic hydrogen velocity dispersion measurement. Magnetic fields and cosmic ray pressure, which are expected to play a role, are uncertain as well. The current models and data are inadequate to determine the disk's existence, but taken at face value, may favor its existence depending on the gas parameters used.

 Title: Cooperative resonances in light scattering from two-dimensional atomic arrays Authors: Shahmoon, Ephraim; Wild, Dominik S.; Lukin, Mikhail D.; Yelin, Susanne F. Publication: eprint arXiv:1610.00138 Publication Date: 10/2016 Origin: ARXIV Keywords: Quantum Physics, Physics - Atomic Physics, Physics - Optics Comment: 5 pages, 4 figures + Supplemental Document Bibliographic Code: 2016arXiv161000138S

### Abstract

We consider light scattering off a two-dimensional (2D) dipolar array and show how it can be tailored by properly choosing the lattice constant of the order of the incident wavelength. In particular, we demonstrate that such arrays can operate as nearly perfect mirrors for a wide range of incident angles and frequencies close to the individual atomic resonance. These results can be understood in terms of the cooperative resonances of the surface modes supported by the 2D array. Experimental realizations are discussed, using ultracold arrays of trapped atoms and excitons in 2D semiconductor materials, as well as potential applications ranging from atomically thin metasurfaces to single photon nonlinear optics and nanomechanics.

 Title: Superrotations and Black Hole Pair Creation Authors: Strominger, Andrew; Zhiboedov, Alexander Publication: eprint arXiv:1610.00639 Publication Date: 10/2016 Origin: ARXIV Keywords: High Energy Physics - Theory, General Relativity and Quantum Cosmology Comment: 18 pages Bibliographic Code: 2016arXiv161000639S

### Abstract

Recent work has shown that the symmetries of classical gravitational scattering in asymptotically flat spacetimes include, at the linearized level, infinitesimal superrotations. These act like Virasoro generators on the celestial sphere at null infinity. However, due to the singularities in these generators, the physical status of finite superrotations has remained unclear. Here we address this issue in the context of the breaking of a cosmic string via quantum black hole pair nucleation. This process is described by a gravitational instanton known as the $C$-metric. After pair production, the black holes are pulled by the string to null infinity with a constant acceleration. At late times the string decays and the spacetime settles into a vacuum state. We show that the early and late spacetimes before and after string decay differ by a finite superrotation. This provides a physical interpretation of superrotations. They act on spacetimes which are asymptotically flat everywhere except at isolated singularities with cosmic string defects.

 Title: Non-supersymmetric AdS and the Swampland Authors: Ooguri, Hirosi; Vafa, Cumrun Publication: eprint arXiv:1610.01533 Publication Date: 10/2016 Origin: ARXIV Keywords: High Energy Physics - Theory, High Energy Physics - Phenomenology Comment: 14 pages. References added Bibliographic Code: 2016arXiv161001533O

### Abstract

We propose to sharpen the weak gravity conjecture by the statement that, except for BPS states in a supersymmetric theory, the gravitational force is strictly weaker than any electric force and provide a number of evidences for this statement. Our conjecture implies that any non-supersymmetric anti-de Sitter vacuum supported by fluxes must be unstable, as is the case for all known attempts at such holographic constructions.

 Title: Observation of the Wigner-Huntington Transition to Solid Metallic Hydrogen Authors: Dias, Ranga; Silvera, Isaac F. Publication: eprint arXiv:1610.01634 Publication Date: 10/2016 Origin: ARXIV Keywords: Condensed Matter - Materials Science, Condensed Matter - Other Condensed Matter Comment: 11 pages plus supplementary information Bibliographic Code: 2016arXiv161001634D

### Abstract

We have studied solid hydrogen under pressure at low temperatures. With increasing pressure we observe changes in the sample, going from transparent, to black, to a reflective metal, the latter studied at a pressure of 495 GPa. We have measured the reflectance as a function of wavelength in the visible spectrum finding values as high as 0.90 from the metallic hydrogen. We have fit the reflectance using a Drude free electron model to determine the plasma frequency of 30.1 eV at T= 5.5 K, with a corresponding electron carrier density of 6.7x1023 particles/cm3, consistent with theoretical estimates. The properties are those of a metal. Solid metallic hydrogen has been produced in the laboratory.

 Title: Maximizing Science in the Era of LSST: A Community-Based Study of Needed US Capabilities Authors: Najita, Joan; Willman, Beth; Finkbeiner, Douglas P.;... and 48 coauthors Publication: eprint arXiv:1610.01661 Publication Date: 10/2016 Origin: ARXIV Keywords: Astrophysics - Instrumentation and Methods for Astrophysics Comment: 174 pages; one chapter of this report was previously published as arXiv:1607.04302 Bibliographic Code: 2016arXiv161001661N

### Abstract

The Large Synoptic Survey Telescope (LSST) will be a discovery machine for the astronomy and physics communities, revealing astrophysical phenomena from the Solar System to the outer reaches of the observable Universe. While many discoveries will be made using LSST data alone, taking full scientific advantage of LSST will require ground-based optical-infrared (OIR) supporting capabilities, e.g., observing time on telescopes, instrumentation, computing resources, and other infrastructure. This community-based study identifies, from a science-driven perspective, capabilities that are needed to maximize LSST science. Expanding on the initial steps taken in the 2015 OIR System Report, the study takes a detailed, quantitative look at the capabilities needed to accomplish six representative LSST-enabled science programs that connect closely with scientific priorities from the 2010 decadal surveys. The study prioritizes the resources needed to accomplish the science programs and highlights ways that existing, planned, and future resources could be positioned to accomplish the science goals.

 Title: Mapping the Microscale Origins of MRI Contrast with Subcellular NV Diamond Magnetometry Authors: Davis, Hunter C.; Ramesh, Pradeep; Bhatnagar, Aadyot; Lee-Gosselin, Audrey; Barry, John F.; Glenn, David R.; Walsworth, Ronald L.; Shapiro, Mikhail G. Publication: eprint arXiv:1610.01924 Publication Date: 10/2016 Origin: ARXIV Keywords: Physics - Medical Physics, Physics - Biological Physics, Quantum Physics Bibliographic Code: 2016arXiv161001924D

### Abstract

Magnetic resonance imaging (MRI) is a widely used biomedical imaging modality that derives much of its contrast from microscale magnetic field gradients in biological tissues. However, the connection between these sub-voxel field patterns and MRI contrast has not been studied experimentally. Here, we describe a new method to map subcellular magnetic fields in mammalian cells and tissues using nitrogen vacancy diamond magnetometry and connect these maps to voxel-scale MRI contrast, providing insights for in vivo imaging and contrast agent design.

 Title: Superresolution optical magnetic imaging and spectroscopy using individual electronic spins in diamond Authors: Jaskula, Jean-Christophe; Bauch, Erik; Arroyo-Camejo, Silvia; Lukin, Mikhail D.; Hell, Stefan W.; Trifonov, Alexei S.; Walsworth, Ronald L. Publication: eprint arXiv:1610.02097 Publication Date: 10/2016 Origin: ARXIV Keywords: Quantum Physics, Condensed Matter - Mesoscale and Nanoscale Physics Comment: main text: 5 pages, 4 figures. Supplementary Material: 5 pages, 8 figures Bibliographic Code: 2016arXiv161002097J

### Abstract

Nitrogen vacancy (NV) color centers in diamond are a leading modality for both superresolution optical imaging and nanoscale magnetic field sensing. In this work, we solve the remaining key challenge of performing optical magnetic imaging and spectroscopy selectively on multiple NV centers that are located within a diffraction-limited field-of-view. We use spin-RESOLFT microscopy to enable precision nanoscale mapping of magnetic field patterns with resolution down to ~20 nm, while employing a low power optical depletion beam. Moreover, we use a shallow NV to demonstrate the detection of proton nuclear magnetic resonance (NMR) signals exterior to the diamond, with 50 nm lateral imaging resolution and without degrading the proton NMR linewidth.

 Title: CMB-S4 Science Book, First Edition Authors: Abazajian, Kevork N.; Adshead, Peter; Ahmed, Zeeshan;... Dvorkin, Cora;... Kovac, John;... and 81 coauthors Publication: eprint arXiv:1610.02743 Publication Date: 10/2016 Origin: ARXIV Keywords: Astrophysics - Cosmology and Nongalactic Astrophysics, General Relativity and Quantum Cosmology, High Energy Physics - Phenomenology, High Energy Physics - Theory Bibliographic Code: 2016arXiv161002743A

### Abstract

This book lays out the scientific goals to be addressed by the next-generation ground-based cosmic microwave background experiment, CMB-S4, envisioned to consist of dedicated telescopes at the South Pole, the high Chilean Atacama plateau and possibly a northern hemisphere site, all equipped with new superconducting cameras. CMB-S4 will dramatically advance cosmological studies by crossing critical thresholds in the search for the B-mode polarization signature of primordial gravitational waves, in the determination of the number and masses of the neutrinos, in the search for evidence of new light relics, in constraining the nature of dark energy, and in testing general relativity on large scales.

 Title: Engineering Quantum Confinement in Semiconducting van der Waals Heterostructure Authors: Wang, Ke; Taniguchi, Takashi; Watanabe, Kenji; Kim, Philip Publication: eprint arXiv:1610.02929 Publication Date: 10/2016 Origin: ARXIV Keywords: Condensed Matter - Mesoscale and Nanoscale Physics Comment: 12 pages Bibliographic Code: 2016arXiv161002929W

### Abstract

Spatial confinement and manipulation of charged carriers in semiconducting nanostructures are essential for realizing quantum electronic devices. Gate-defined nanostructures made of two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDCs) have the potential to add a unique additional control of quantum degrees of freedom owing to valley-spin locking of confined carriers near the band edges. However, due to prevailing inhomogeneities in the conducting channels, it has been difficult to realize quantum confinement in 2D TMDCs with well-controlled tunnel-coupling strength. Here we demonstrate quantum transport in lateral gate-defined 2D electron quantum dots formed in atomically thin TMDC heterostructures. Utilizing micro-fabricated local contact gates, encapsulation in 2D dielectrics and light illumination at low temperatures, we show that the quality of TMDC 2D electron gases (2DEGs) can be improved, rendering them suitable for mesoscopic quantum transport measurements. We observe quantized conductance in quantum point contact (QPC) channels controlled by gate-tunable confinement. We also demonstrate single electron transport in TMDC quantum dots (QD) with tunable tunnel-coupling. Our observation holds promise for the quantum manipulation of spin and valley degrees of freedom in engineered TMDC nanostructures, enabling versatile 2D quantum electronic devices.

 Title: Parametric Instability Rates in Periodically-Driven Band Systems Authors: Lellouch, S.; Bukov, M.; Demler, E.; Goldman, N. Publication: eprint arXiv:1610.02972 Publication Date: 10/2016 Origin: ARXIV Keywords: Condensed Matter - Quantum Gases Comment: 27 pages, 21 figures, including three appendices Bibliographic Code: 2016arXiv161002972L

### Abstract

This work analyses the dynamical properties of periodically-driven band models. Focusing on the case of Bose-Einstein condensates, and using a meanfield approach to treat inter-particle collisions, we identify the origin of dynamical instabilities arising due to the interplay between the external drive and interactions. We present a widely-applicable generic numerical method to extract instability rates, and link parametric instabilities to uncontrolled energy absorption at short times. Based on the existence of parametric resonances, we then develop an analytical approach within Bogoliubov theory, which quantitatively captures the instability rates of the system, and provides an intuitive picture of the relevant physical processes, including an understanding of how transverse modes affect the formation of parametric instabilities. Importantly, our calculations demonstrate an agreement between the instability rates determined from numerical simulations, and those predicted by theory. To determine the validity regime of the meanfield analysis, we compare the latter to the weakly-coupled conserving approximation. The tools developed and the results obtained in this work are directly relevant to present-day ultracold-atom experiments based on shaken optical lattices, and are expected to provide an insightful guidance in the quest for Floquet engineering.

 Title: Epsilon-Near-Zero behavior from plasmonic Dirac point: theory and realization using two-dimensional materials Authors: Mattheakis, Marios; Valagiannopoulos, Constantinos A.; Kaxiras, Efthimios Publication: eprint arXiv:1610.03439 Publication Date: 10/2016 Origin: ARXIV Keywords: Physics - Optics Comment: Phys. Rev. B 94, 201404 (2016); doi:10.1103/PhysRevB.94.201404 Bibliographic Code: 2016arXiv161003439M

### Abstract

The electromagnetic response of a two-dimensional metal embedded in a periodic array of a dielectric host can give rise to a plasmonic Dirac point that emulates Epsilon-Near-Zero (ENZ) behavior. This theoretical result is extremely sensitive to tructural features like periodicity of the dielectric medium and thickness imperfections. We propose that such a device can actually be realized by using graphene as the 2D metal and materials like the layered semiconducting transition-metal dichalcogenides or hexagonal boron nitride as the dielectric host. We propose a systematic approach, in terms of design characteristics, for constructing metamaterials with linear, elliptical and hyperbolic dispersion relations which produce ENZ behavior, normal or negative diffraction.

 Title: Make Dark Matter Charged Again Authors: Agrawal, Prateek; Cyr-Racine, Francis-Yan; Randall, Lisa; Scholtz, Jakub Publication: eprint arXiv:1610.04611 Publication Date: 10/2016 Origin: ARXIV Keywords: High Energy Physics - Phenomenology, Astrophysics - Cosmology and Nongalactic Astrophysics Comment: 17 pages, 4 figures Bibliographic Code: 2016arXiv161004611A

### Abstract

We revisit constraints on dark matter that is charged under a $U(1)$ gauge group in the dark sector, decoupled from Standard Model forces. We find that the strongest constraints in the literature are subject to a number of mitigating factors. For instance, the naive dark matter thermalization timescale in halos is corrected by saturation effects that slow down isotropization for modest ellipticities. The weakened bounds uncover interesting parameter space, making models with weak-scale charged dark matter viable, even with electromagnetic strength interaction. This also leads to the intriguing possibility that dark matter self-interactions within small dwarf galaxies are extremely large, a relatively unexplored regime in current simulations. Such strong interactions suppress heat transfer over scales larger than the dark matter mean free path, inducing a dynamical cutoff length scale above which the system appears to have only feeble interactions. These effects must be taken into account to assess the viability of darkly-charged dark matter. Future analyses and measurements should probe a promising region of parameter space for this model.

 Title: Monolithic CMOS-compatible zero-index metamaterials Authors: Vulis, Daryl I.; Li, Yang; Reshef, Orad; Camayd-Muñoz, Philip; Yin, Mei; Kita, Shota; Lončar, Marko; Mazur, Eric Publication: eprint arXiv:1610.05368 Publication Date: 10/2016 Origin: ARXIV Keywords: Physics - Optics Comment: 18 pages, 4 figures Bibliographic Code: 2016arXiv161005368V

### Abstract

Zero-index materials exhibit exotic optical properties that can be utilized for integrated-optics applications. However, practical implementation requires compatibility with complementary metallic-oxide-semiconductor (CMOS) technologies. We demonstrate a CMOS-compatible zero-index metamaterial consisting of a square array of air holes in a 220-nm-thick silicon-on-insulator (SOI) wafer. This design is achieved through a Dirac-cone dispersion. The metamaterial is entirely composed of silicon and offers compatibility through low-aspect-ratio structures that can be simply fabricated in a standard device layer. This platform enables mass adoption and exploration of zero-index-based photonic devices at low cost and high fidelity.

 Title: (2,2) Superconformal Bootstrap in Two Dimensions Authors: Lin, Ying-Hsuan; Shao, Shu-Heng; Wang, Yifan; Yin, Xi Publication: eprint arXiv:1610.05371 Publication Date: 10/2016 Origin: ARXIV Keywords: High Energy Physics - Theory Comment: 56 pages, 14 figures Bibliographic Code: 2016arXiv161005371L

### Abstract

We find a simple relation between two-dimensional BPS N=2 superconformal blocks and bosonic Virasoro conformal blocks, which allows us to analyze the crossing equations for BPS 4-point functions in unitary (2,2) superconformal theories numerically with semidefinite programming. We constrain gaps in the non-BPS spectrum through the operator product expansion of BPS operators, in ways that depend on the moduli of exactly marginal deformations through chiral ring coefficients. In some cases, our bounds on the spectral gaps are observed to be saturated by free theories, by N=2 Liouville theory, and by certain Landau-Ginzburg models.

 Title: Dynamical Chern-Simons Theory in the Brillouin Zone Authors: Lian, Biao; Vafa, Cumrun; Vafa, Farzan; Zhang, Shou-Cheng Publication: eprint arXiv:1610.05810 Publication Date: 10/2016 Origin: ARXIV Keywords: Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Superconductivity, High Energy Physics - Theory Comment: 13 pages, 2 figures Bibliographic Code: 2016arXiv161005810L

### Abstract

Berry connection is conventionally defined as a static gauge field in the Brillouin zone. Here we show that for three-dimensional (3d) time-reversal invariant superconductors, a generalized Berry gauge field behaves as a dynamical fluctuating field of a Chern-Simons gauge theory. The gapless nodal lines in the momentum space play the role of Wilson loop observables, while their linking and knot invariants modify the gravitational theta angle. This angle induces a topological gravitomagnetoelectric effect where a temperature gradient induces a rotational energy flow. We also show how topological strings may be realized in the 6 dimensional phase space, where the physical space defects play the role of topological D-branes.

 Title: Entanglement entropy of the large $N$ Wilson-Fisher conformal field theory Authors: Whitsitt, Seth; Witczak-Krempa, William; Sachdev, Subir Publication: eprint arXiv:1610.06568 Publication Date: 10/2016 Origin: ARXIV Keywords: Condensed Matter - Strongly Correlated Electrons, High Energy Physics - Theory Comment: (v2) 23 pages, 3 figures. Added references, minor corrections and clarifications Bibliographic Code: 2016arXiv161006568W

### Abstract

We compute the entanglement entropy of the Wilson-Fisher conformal field theory (CFT) in 2+1 dimensions with O($N$) symmetry in the limit of large $N$ for general entanglement geometries. We show that the leading large $N$ result can be obtained from the entanglement entropy of $N$ Gaussian scalar fields with their mass determined by the geometry. For a few geometries, the universal part of the entanglement entropy of the Wilson-Fisher CFT equals that of a CFT of $N$ massless scalar fields. However, in most cases, these CFTs have a distinct universal entanglement entropy even at $N=\infty$. Notably, for a semi-infinite cylindrical region it scales as $N^0$, in stark contrast to the $N$-linear result of the Gaussian fixed point.

 Title: Selective addressing of solid-state spins at the nanoscale via magnetic resonance frequency encoding Authors: Zhang, Huiliang; Arai, Keigo; Belthangady, Chinmay; Jaskula, Jean-Christophe; Walsworth, Ronald L. Publication: eprint arXiv:1610.06630 Publication Date: 10/2016 Origin: ARXIV Keywords: Quantum Physics, Condensed Matter - Mesoscale and Nanoscale Physics Bibliographic Code: 2016arXiv161006630Z

### Abstract

The nitrogen-vacancy (NV) centre in diamond is a leading platform for nanoscale sensing and imaging, as well as quantum information processing in the solid state. To date, individual control of two NV electronic spins at the nanoscale has been demonstrated. However, a key challenge is to scale up such control to arrays of NV spins. Here we apply nanoscale magnetic resonance frequency encoding to realize site-selective addressing and coherent control of a four-site array of NV spins. Sites in the array are separated by 100 nm, with each site containing multiple NVs separated by ~15 nm. Microcoils fabricated on the diamond chip provide electrically tuneable magnetic-field gradients ~0.1 G/nm. Tailored application of gradient fields and resonant microwaves allow site-selective NV spin manipulation and sensing applications, including Rabi oscillations, imaging, and nuclear magnetic resonance (NMR) spectroscopy with nanoscale resolution. Microcoil-based magnetic resonance of solid-state spins provides a practical platform for quantum-assisted sensing, quantum information processing, and the study of nanoscale spin networks.

 Title: Hamiltonian Truncation Study of Supersymmetric Quantum Mechanics: S-Matrix and Metastable States Authors: Balthazar, Bruno; Rodriguez, Victor A.; Yin, Xi Publication: eprint arXiv:1610.07275 Publication Date: 10/2016 Origin: ARXIV Keywords: High Energy Physics - Theory Comment: 26 pages, 15 figures Bibliographic Code: 2016arXiv161007275B

### Abstract

We implement the Rayleigh-Ritz method in supersymmetric quantum mechanics with flat directions, and extract the S-matrix and metastable resonances. The effectiveness of the method is demonstrated in two strongly coupled systems: an N=1 toy supermembrane model, and an N=4 model with a U(1) gauge multiplet and a charged chiral multiplet.

 Title: Floquet symmetry-protected topological phases in cold atomic systems Authors: Potirniche, Ionut-Dragos; Potter, Andrew C.; Schleier-Smith, Monika; Vishwanath, Ashvin; Yao, Norman Y. Publication: eprint arXiv:1610.07611 Publication Date: 10/2016 Origin: ARXIV Keywords: Condensed Matter - Quantum Gases, Condensed Matter - Disordered Systems and Neural Networks, Condensed Matter - Strongly Correlated Electrons, Quantum Physics Comment: Updated references Bibliographic Code: 2016arXiv161007611P

### Abstract

We propose and analyze two distinct routes toward realizing interacting symmetry-protected topological (SPT) phases via periodic driving. First, we demonstrate that a driven transverse-field Ising model can be used to engineer complex interactions which enable the emulation of an equilibrium SPT. This phase remains stable only within a parametric time scale controlled by the driving frequency, beyond which its topological features break down. To overcome this issue, we consider an alternate route based upon realizing an intrinsically Floquet SPT phase that does not have any equilibrium analogue. In both cases, we show that disorder, leading to many-body localization, prevents runaway heating and enables the observation of coherent quantum dynamics at high energy densities. Furthermore, we clarify the distinction between the equilibrium and Floquet SPT phases by identifying a unique micro-motion-based entanglement spectrum signature of the latter. Finally, we propose a unifying implementation in a one dimensional chain of Rydberg-dressed atoms and show that protected edge modes are observable on realistic experimental time-scales.

 Title: Observation of discrete time-crystalline order in a disordered dipolar many-body system Authors: Choi, Soonwon; Choi, Joonhee; Landig, Renate; Kucsko, Georg; Zhou, Hengyun; Isoya, Junichi; Jelezko, Fedor; Onoda, Shinobu; Sumiya, Hitoshi; Khemani, Vedika; von Keyserlingk, Curt; Yao, Norman Y.; Demler, Eugene; Lukin, Mikhail D. Publication: eprint arXiv:1610.08057 Publication Date: 10/2016 Origin: ARXIV Keywords: Quantum Physics, Condensed Matter - Disordered Systems and Neural Networks, Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Strongly Correlated Electrons, Physics - Atomic Physics Comment: 6 + 3 pages, 4 figures Bibliographic Code: 2016arXiv161008057C

### Abstract

Understanding quantum dynamics away from equilibrium is an outstanding challenge in the modern physical sciences. It is well known that out-of-equilibrium systems can display a rich array of phenomena, ranging from self-organized synchronization to dynamical phase transitions. More recently, advances in the controlled manipulation of isolated many-body systems have enabled detailed studies of non-equilibrium phases in strongly interacting quantum matter. As a particularly striking example, the interplay of periodic driving, disorder, and strong interactions has recently been predicted to result in exotic "time-crystalline" phases, which spontaneously break the discrete time-translation symmetry of the underlying drive. Here, we report the experimental observation of such discrete time-crystalline order in a driven, disordered ensemble of $\sim 10^6$ dipolar spin impurities in diamond at room-temperature. We observe long-lived temporal correlations at integer multiples of the fundamental driving period, experimentally identify the phase boundary and find that the temporal order is protected by strong interactions; this order is remarkably stable against perturbations, even in the presence of slow thermalization. Our work opens the door to exploring dynamical phases of matter and controlling interacting, disordered many-body systems.

 Title: Supersymmetric SYK models Authors: Fu, Wenbo; Gaiotto, Davide; Maldacena, Juan; Sachdev, Subir Publication: eprint arXiv:1610.08917 Publication Date: 10/2016 Origin: ARXIV Keywords: High Energy Physics - Theory, Condensed Matter - Strongly Correlated Electrons Comment: 36 pages, 6 figures Bibliographic Code: 2016arXiv161008917F

### Abstract

We discuss a supersymmetric generalization of the Sachdev-Ye-Kitaev model. These are quantum mechanical models involving $N$ Majorana fermions. The supercharge is given by a polynomial expression in terms of the Majorana fermions with random coefficients. The Hamiltonian is the square of the supercharge. The ${\cal N}=1$ model with a single supercharge has unbroken supersymmetry at large $N$, but non-perturbatively spontaneously broken supersymmetry in the exact theory. We analyze the model by looking at the large $N$ equation, and also by performing numerical computations for small values of $N$. We also compute the large $N$ spectrum of "singlet" operators, where we find a structure qualitatively similar to the ordinary SYK model. We also discuss an ${\cal N}=2$ version. In this case, the model preserves supersymmetry in the exact theory and we can compute a suitably weighted Witten index to count the number of ground states, which agrees with the large $N$ computation of the entropy. In both cases, we discuss the supersymmetric generalizations of the Schwarzian action which give the dominant effects at low energies.

 Title: Measurement of the $D^+$-meson production cross section at low transverse momentum in $p\bar{p}$ collisions at $\sqrt{s}=1.96$ TeV Authors: CDF Collaboration; Aaltonen, T.; Amerio, S.; Amidei, D.;... Franklin, M.;... and 391 coauthors Publication: eprint arXiv:1610.08989 Publication Date: 10/2016 Origin: ARXIV Keywords: High Energy Physics - Experiment Comment: 8 pages, 3 figures Bibliographic Code: 2016arXiv161008989C

### Abstract

We report on a measurement of the $D^{+}$-meson production cross section as a function of transverse momentum ($p_T$) in proton-antiproton ($p\bar{p}$) collisions at 1.96 TeV center-of-mass energy, using the full data set collected by the Collider Detector at Fermilab in Tevatron Run II and corresponding to 10 fb$^{-1}$ of integrated luminosity. We use $D^{+} \to K^-\pi^+\pi^+$ decays fully reconstructed in the central rapidity region $|y|<1$ with transverse momentum down to 1.5 GeV/$c$, a range previously unexplored in $p\bar{p}$ collisions. Inelastic $p\bar{p}$-scattering events are selected online using minimally-biasing requirements followed by an optimized offline selection. The $K^-\pi^+\pi^+$ mass distribution is used to identify the $D^+$ signal, and the $D^+$ transverse impact-parameter distribution is used to separate prompt production, occurring directly in the hard scattering process, from secondary production from $b$-hadron decays. We obtain a prompt $D^+$ signal of 2950 candidates corresponding to a total cross section $\sigma(D^+, 1.5 < p_T < 14.5~\mbox{GeV/}c, |y|<1) = 71.9 \pm 6.8 (\mbox{stat}) \pm 9.3 (\mbox{syst})~\mu$b. While the measured cross sections are consistent with theoretical estimates in each $p_T$ bin, the shape of the observed $p_T$ spectrum is softer than the expectation from quantum chromodynamics. The results are unique in $p\bar{p}$ collisions and can improve the shape and uncertainties of future predictions.

 Title: 4d N=1 from 6d (1,0) Authors: Razamat, Shlomo S.; Vafa, Cumrun; Zafrir, Gabi Publication: eprint arXiv:1610.09178 Publication Date: 10/2016 Origin: ARXIV Keywords: High Energy Physics - Theory Comment: 101 pages, 14 figures Bibliographic Code: 2016arXiv161009178R

### Abstract

We study the geometry of 4d N=1 SCFT's arising from compactification of 6d (1,0) SCFT's on a Riemann surface. We show that the conformal manifold of the resulting theory is characterized, in addition to moduli of complex structure of the Riemann surface, by the choice of a connection for a vector bundle on the surface arising from flavor symmetries in 6d. We exemplify this by considering the case of 4d N=1 SCFT's arising from M5 branes probing Z_k singularity compactified on a Riemann surface. In particular, we study in detail the four dimensional theories arising in the case of two M5 branes on Z_2 singularity. We compute the conformal anomalies and indices of such theories in 4d and find that they are consistent with expectations based on anomaly and the moduli structure derived from the 6 dimensional perspective.

 Title: Scalable Focused Ion Beam Creation of Nearly Lifetime-Limited Single Quantum Emitters in Diamond Nanostructures Authors: Schröder, Tim; Trusheim, Matthew E.; Walsh, Michael; Li, Luozhou; Zheng, Jiabao; Schukraft, Marco; Pacheco, Jose L.; Camacho, Ryan M.; Bielejec, Edward S.; Sipahigil, Alp; Evans, Ruffin E.; Sukachev, Denis D.; Nguyen, Christian T.; Lukin, Mikhail D.; Englund, Dirk Publication: eprint arXiv:1610.09492 Publication Date: 10/2016 Origin: ARXIV Keywords: Quantum Physics, Condensed Matter - Mesoscale and Nanoscale Physics, Physics - Optics Bibliographic Code: 2016arXiv161009492S

### Abstract

The controlled creation of defect center---nanocavity systems is one of the outstanding challenges for efficiently interfacing spin quantum memories with photons for photon-based entanglement operations in a quantum network. Here, we demonstrate direct, maskless creation of atom-like single silicon-vacancy (SiV) centers in diamond nanostructures via focused ion beam implantation with $\sim 32$ nm lateral precision and $< 50$ nm positioning accuracy relative to a nanocavity. Moreover, we determine the Si+ ion to SiV center conversion yield to $\sim 2.5\%$ and observe a 10-fold conversion yield increase by additional electron irradiation. We extract inhomogeneously broadened ensemble emission linewidths of $\sim 51$ GHz, and close to lifetime-limited single-emitter transition linewidths down to $126 \pm13$ MHz corresponding to $\sim 1.4$-times the natural linewidth. This demonstration of deterministic creation of optically coherent solid-state single quantum systems is an important step towards development of scalable quantum optical devices.

 Title: Quantum chaos on a critical Fermi surface Authors: Patel, Aavishkar A.; Sachdev, Subir Publication: eprint arXiv:1611.00003 Publication Date: 10/2016 Origin: ARXIV Keywords: Condensed Matter - Strongly Correlated Electrons, High Energy Physics - Theory, Quantum Physics Comment: 21 pages, 5 figures Bibliographic Code: 2016arXiv161100003P

### Abstract

We compute parameters characterizing many-body quantum chaos for a critical Fermi surface without quasiparticle excitations. We examine a theory of $N$ species of fermions at non-zero density coupled to a $U(1)$ gauge field in two spatial dimensions, and determine the Lyapunov rate and the butterfly vel

 Title: The DESI Experiment Part I: Science,Targeting, and Survey Design Authors: DESI Collaboration; Aghamousa, Amir; Aguilar, Jessica; Ahlen, Steve;... Finkbeiner, Douglas P.;... and 258 coauthors Publication: eprint arXiv:1611.00036 Publication Date: 10/2016 Origin: ARXIV Keywords: Astrophysics - Instrumentation and Methods for Astrophysics, Astrophysics - Cosmology and Nongalactic Astrophysics Bibliographic Code: 2016arXiv161100036D

### Abstract

DESI (Dark Energy Spectroscopic Instrument) is a Stage IV ground-based dark energy experiment that will study baryon acoustic oscillations (BAO) and the growth of structure through redshift-space distortions with a wide-area galaxy and quasar redshift survey. To trace the underlying dark matter distribution, spectroscopic targets will be selected in four classes from imaging data. We will measure luminous red galaxies up to $z=1.0$. To probe the Universe out to even higher redshift, DESI will target bright [O II] emission line galaxies up to $z=1.7$. Quasars will be targeted both as direct tracers of the underlying dark matter distribution and, at higher redshifts ($2.1 < z < 3.5$), for the Ly-$\alpha$ forest absorption features in their spectra, which will be used to trace the distribution of neutral hydrogen. When moonlight prevents efficient observations of the faint targets of the baseline survey, DESI will conduct a magnitude-limited Bright Galaxy Survey comprising approximately 10 million galaxies with a median $z\approx 0.2$. In total, more than 30 million galaxy and quasar redshifts will be obtained to measure the BAO feature and determine the matter power spectrum, including redshift space distortions.

 Title: The DESI Experiment Part II: Instrument Design Authors: DESI Collaboration; Aghamousa, Amir; Aguilar, Jessica; Ahlen, Steve;... Finkbeiner, Douglas P.;... and 258 coauthors Publication: eprint arXiv:1611.00037 Publication Date: 10/2016 Origin: ARXIV Keywords: Astrophysics - Instrumentation and Methods for Astrophysics, Astrophysics - Cosmology and Nongalactic Astrophysics Bibliographic Code: 2016arXiv161100037D

### Abstract

DESI (Dark Energy Spectropic Instrument) is a Stage IV ground-based dark energy experiment that will study baryon acoustic oscillations and the growth of structure through redshift-space distortions with a wide-area galaxy and quasar redshift survey. The DESI instrument is a robotically-actuated, fiber-fed spectrograph capable of taking up to 5,000 simultaneous spectra over a wavelength range from 360 nm to 980 nm. The fibers feed ten three-arm spectrographs with resolution $R= \lambda/\Delta\lambda$ between 2000 and 5500, depending on wavelength. The DESI instrument will be used to conduct a five-year survey designed to cover 14,000 deg$^2$. This powerful instrument will be installed at prime focus on the 4-m Mayall telescope in Kitt Peak, Arizona, along with a new optical corrector, which will provide a three-degree diameter field of view. The DESI collaboration will also deliver a spectroscopic pipeline and data management system to reduce and archive all data for eventual public use.

 Title: The performance of the jet trigger for the ATLAS detector during 2011 data taking Authors: Aad, G.; Abbott, B.; Abdallah, J.; Abdinov, O.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2854 coauthors Publication: The European Physical Journal C, Volume 76, Issue 10, article id. #526, 47 pp. (EPJC Homepage) Publication Date: 10/2016 Origin: SPRINGER Abstract Copyright: (c) 2016: CERN for the benefit of the ATLAS collaboration DOI: 10.1140/epjc/s10052-016-4325-0 Bibliographic Code: 2016EPJC...76..526A

### Abstract

The performance of the jet trigger for the ATLAS detector at the LHC during the 2011 data taking period is described. During 2011 the LHC provided proton-proton collisions with a centre-of-mass energy of 7 TeV and heavy ion collisions with a 2.76 TeV per nucleon-nucleon collision energy. The ATLAS trigger is a three level system designed to reduce the rate of events from the 40 MHz nominal maximum bunch crossing rate to the approximate 400 Hz which can be written to offline storage. The ATLAS jet trigger is the primary means for the online selection of events containing jets. Events are accepted by the trigger if they contain one or more jets above some transverse energy threshold. During 2011 data taking the jet trigger was fully efficient for jets with transverse energy above 25 GeV for triggers seeded randomly at Level 1. For triggers which require a jet to be identified at each of the three trigger levels, full efficiency is reached for offline jets with transverse energy above 60 GeV. Jets reconstructed in the final trigger level and corresponding to offline jets with transverse energy greater than 60 GeV, are reconstructed with a resolution in transverse energy with respect to offline jets, of better than 4 % in the central region and better than 2.5 % in the forward direction.

 Title: Measurements of top-quark pair differential cross-sections in the lepton+jets channel in pp collisions at √{s}=8 {TeV} using the ATLAS detector Authors: Aad, G.; Abbott, B.; Abdallah, J.; Abdinov, O.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2864 coauthors Publication: The European Physical Journal C, Volume 76, Issue 10, article id. #538, 39 pp. (EPJC Homepage) Publication Date: 10/2016 Origin: SPRINGER Abstract Copyright: (c) 2016: CERN for the benefit of the ATLAS collaboration DOI: 10.1140/epjc/s10052-016-4366-4 Bibliographic Code: 2016EPJC...76..538A

### Abstract

Measurements of normalized differential cross-sections of top-quark pair production are presented as a function of the top-quark, tbar{t} system and event-level kinematic observables in proton-proton collisions at a centre-of-mass energy of √{s}=8 TeV. The observables have been chosen to emphasize the tbar{t} production process and to be sensitive to effects of initial- and final-state radiation, to the different parton distribution functions, and to non-resonant processes and higher-order corrections. The dataset corresponds to an integrated luminosity of 20.3 fb^{-1}, recorded in 2012 with the ATLAS detector at the CERN Large Hadron Collider. Events are selected in the lepton+jets channel, requiring exactly one charged lepton and at least four jets with at least two of the jets tagged as originating from a b-quark. The measured spectra are corrected for detector effects and are compared to several Monte Carlo simulations. The results are in fair agreement with the predictions over a wide kinematic range. Nevertheless, most generators predict a harder top-quark transverse momentum distribution at high values than what is observed in the data. Predictions beyond NLO accuracy improve the agreement with data at high top-quark transverse momenta. Using the current settings and parton distribution functions, the rapidity distributions are not well modelled by any generator under consideration. However, the level of agreement is improved when more recent sets of parton distribution functions are used.

 Title: Search for new phenomena in different-flavour high-mass dilepton final states 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 2854 coauthors Publication: The European Physical Journal C, Volume 76, Issue 10, article id. #541, 28 pp. (EPJC Homepage) Publication Date: 10/2016 Origin: SPRINGER Abstract Copyright: (c) 2016: CERN for the benefit of the ATLAS collaboration DOI: 10.1140/epjc/s10052-016-4385-1 Bibliographic Code: 2016EPJC...76..541A

### Abstract

A search is performed for a heavy particle decaying into different flavour dilepton pairs (eμ , eτ or μ τ ), using 3.2 fb^{-1} of proton-proton collision data at √{s}=13 TeV collected in 2015 by the ATLAS detector at the Large Hadron Collider. No excess over the Standard Model prediction is observed. Limits at the 95 % credibility level are set on the mass of a Z^' boson with lepton-flavour-violating couplings at 3.0, 2.7 and 2.6 TeV, and on the mass of a supersymmetric τ sneutrino with R-parity-violating couplings at 2.3, 2.2 and 1.9 TeV, for eμ , eτ and μ τ final states, respectively. The results are also interpreted as limits on the threshold mass for quantum black hole production.

 Title: Search for bottom squark pair production in proton-proton 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 2852 coauthors Publication: The European Physical Journal C, Volume 76, Issue 10, article id. #547, 25 pp. (EPJC Homepage) Publication Date: 10/2016 Origin: SPRINGER Abstract Copyright: (c) 2016: CERN for the benefit of the ATLAS collaboration DOI: 10.1140/epjc/s10052-016-4382-4 Bibliographic Code: 2016EPJC...76..547A

### Abstract

The result of a search for pair production of the supersymmetric partner of the Standard Model bottom quark (tilde{b}^{}1 ) is reported. The search uses 3.2 fb^{-1} of pp collisions at √{s}=13 TeV collected by the ATLAS experiment at the Large Hadron Collider in 2015. Bottom squarks are searched for in events containing large missing transverse momentum and exactly two jets identified as originating from b-quarks. No excess above the expected Standard Model background yield is observed. Exclusion limits at 95 % confidence level on the mass of the bottom squark are derived in phenomenological supersymmetric R-parity-conserving models in which the tilde{b}^{}1 is the lightest squark and is assumed to decay exclusively via tilde{b}^{}1 → b tilde{χ }01, where tilde{χ }01 is the lightest neutralino. The limits significantly extend previous results; bottom squark masses up to 800 (840) GeV are excluded for the tilde{χ }01 mass below 360 (100) GeV whilst differences in mass above 100 GeV between the tilde{b}^{}1 and the tilde{χ }01 are excluded up to a tilde{b}^{}1 mass of 500 GeV.

 Title: Search for gluinos in events with an isolated lepton, jets and missing transverse momentum at √{s} = 13 Te V with the ATLAS detector Authors: Aad, G.; Abbott, B.; Abdallah, J.; Abdinov, O.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2847 coauthors Publication: The European Physical Journal C, Volume 76, Issue 10, article id. #565, 29 pp. (EPJC Homepage) Publication Date: 10/2016 Origin: SPRINGER Abstract Copyright: (c) 2016: The Author(s) DOI: 10.1140/epjc/s10052-016-4397-x Bibliographic Code: 2016EPJC...76..565A

### Abstract

The results of a search for gluinos in final states with an isolated electron or muon, multiple jets and large missing transverse momentum using proton-proton collision data at a centre-of-mass energy of √{s} = 13 { Te V} are presented. The dataset used was recorded in 2015 by the ATLAS experiment at the Large Hadron Collider and corresponds to an integrated luminosity of 3.2 fb^{-1}. Six signal selections are defined that best exploit the signal characteristics. The data agree with the Standard Model background expectation in all six signal selections, and the largest deviation is a 2.1 standard deviation excess. The results are interpreted in a simplified model where pair-produced gluinos decay via the lightest chargino to the lightest neutralino. In this model, gluinos are excluded up to masses of approximately 1.6 Te V depending on the mass spectrum of the simplified model, thus surpassing the limits of previous searches.

 Title: 2D Kac-Moody symmetry of 4D Yang-Mills theory Authors: He, Temple; Mitra, Prahar; Strominger, Andrew Publication: Journal of High Energy Physics, Volume 2016, Issue 10, article id. #137, 19 pp. Publication Date: 10/2016 Origin: SPRINGER Keywords: Gauge Symmetry, Scattering Amplitudes, Spontaneous Symmetry Breaking Abstract Copyright: (c) 2016: The Author(s) DOI: 10.1007/JHEP10(2016)137 Bibliographic Code: 2016JHEP...10..137H

### Abstract

Scattering amplitudes of any four-dimensional theory with nonabelian gauge group G may be recast as two-dimensional correlation functions on the asymptotic twosphere at null infinity. The soft gluon theorem is shown, for massless theories at the semiclassical level, to be the Ward identity of a holomorphic two-dimensional G -Kac-Moody symmetry acting on these correlation functions. Holomorphic Kac-Moody current insertions are positive helicity soft gluon insertions. The Kac-Moody transformations are a CPT invariant subgroup of gauge transformations which act nontrivially at null infinity and comprise the four-dimensional asymptotic symmetry group.

 Title: Self-assembly of acetate adsorbates drives atomic rearrangement on the Au(110) surface Authors: Hiebel, Fanny; Shong, Bonggeun; Chen, Wei; Madix, Robert J.; Kaxiras, Efthimios; Friend, Cynthia M. Publication: Nature Communications, Volume 7, id. 13139 (2016). Publication Date: 10/2016 Origin: NATURE Abstract Copyright: (c) 2016: The Author(s) DOI: 10.1038/ncomms13139 Bibliographic Code: 2016NatCo...713139H

### Abstract

Weak inter-adsorbate interactions are shown to play a crucial role in determining surface structure, with major implications for its catalytic reactivity. This is exemplified here in the case of acetate bound to Au(110), where the small extra energy of the van der Waals interactions among the surface-bound groups drives massive restructuring of the underlying Au. Acetate is a key intermediate in electro-oxidation of CO2 and a poison in partial oxidation reactions. Metal atom migration originates at surface defects and is likely facilitated by weakened Au-Au interactions due to bonding with the acetate. Even though the acetate is a relatively small molecule, weak intermolecular interaction provides the energy required for molecular self-assembly and reorganization of the metal surface.

 itle: The pressing energy innovation challenge of the US National Laboratories Authors: Anadon, Laura Diaz; Chan, Gabriel; Bin-Nun, Amitai Y.; Narayanamurti, Venkatesh Publication: Nature Energy, Volume 1, Issue 10, pp. 16117 (2016). Publication Date: 10/2016 Origin: NATURE Abstract Copyright: (c) 2016: Macmillan Publishers Limited DOI: 10.1038/nenergy.2016.117 Bibliographic Code: 2016NatEn...116117A

### Abstract

Accelerating the development and deployment of energy technologies is a pressing challenge. Doing so will require policy reform that improves the efficacy of public research organizations and strengthens the links between public and private innovators. With their US\$14 billion annual budget and unique mandates, the US National Laboratories have the potential to critically advance energy innovation, yet reviews of their performance find several areas of weak organizational design. Here, we discuss the challenges the National Laboratories face in engaging the private sector, increasing their contributions to transformative research, and developing culture and management practices to better support innovation. We also offer recommendations for how policymakers can address these challenges.

 Title: Elastic instability-mediated actuation by a supra-molecular polymer Authors: Levin, Aviad; Michaels, Thomas C. T.; Adler-Abramovich, Lihi; Mason, Thomas O.; Müller, Thomas; Zhang, Bohan; Mahadevan, L.; Gazit, Ehud; Knowles, Tuomas P. J. Publication: Nature Physics, Volume 12, Issue 10, pp. 926-930 (2016). Publication Date: 10/2016 Origin: NATURE Abstract Copyright: (c) 2016: Nature Publishing Group DOI: 10.1038/nphys3808 Bibliographic Code: 2016NatPh..12..926L

### Abstract

In nature, fast, high-power-density actuation can be achieved through the release of stored elastic energy by exploiting mechanical instabilities in systems including the closure of the Venus flytrap and the dispersal of plant or fungal spores. Here, we use droplet microfluidics to tailor the geometry of a nanoscale self-assembling supra-molecular polymer to create a mechanical instability. We show that this strategy allows the build-up of elastic energy as a result of peptide self-assembly, and its release within milliseconds when the buckled geometry of the nanotube confined within microdroplets becomes unstable with respect to the straight form. These results overcome the inherent limitations of self-assembly for generating large-scale actuation on the sub-second timescale and illuminate the possibilities and performance limits of irreversible actuation by supra-molecular polymers.

 Title: Tracking E coli runs and tumbles with scattering solutions and digital holographic microscopy Authors: Wang, Anna; Garmann, Rees F.; Manoharan, Vinothan N. Publication: Optics Express, vol. 24, issue 21, p. 23719 Publication Date: 10/2016 Origin: CROSSREF DOI: 10.1364/OE.24.023719 Bibliographic Code: 2016OExpr..2423719W

### Abstract

Not Available

 Title: Bayesian approach to analyzing holograms of colloidal particles Authors: Dimiduk, Thomas G.; Manoharan, Vinothan N. Publication: Optics Express, vol. 24, issue 21, p. 24045 Publication Date: 10/2016 Origin: CROSSREF DOI: 10.1364/OE.24.024045 Bibliographic Code: 2016OExpr..2424045D

### Abstract

Not Available

 Title: Measurement of the t t bar production cross-section using eμ events with b-tagged jets in pp collisions at √{ s} = 13TeV with the ATLAS detector Authors: Aaboud, M.; Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2848 coauthors Publication: Physics Letters B, Volume 761, p. 136-157. Publication Date: 10/2016 Origin: ELSEVIER Abstract Copyright: (c) 2016 Elsevier Science B.V. All rights reserved. DOI: 10.1016/j.physletb.2016.08.019 Bibliographic Code: 2016PhLB..761..136A

### Abstract

This paper describes a measurement of the inclusive top quark pair production cross-section (σttbar) with a data sample of 3.2fb-1 of proton-proton collisions at a centre-of-mass energy of √{ s} = 13TeV, collected in 2015 by the ATLAS detector at the LHC. This measurement uses events with an opposite-charge electron-muon pair in the final state. Jets containing b-quarks are tagged using an algorithm based on track impact parameters and reconstructed secondary vertices. The numbers of events with exactly one and exactly two b-tagged jets are counted and used to determine simultaneously σttbar and the efficiency to reconstruct and b-tag a jet from a top quark decay, thereby minimising the associated systematic uncertainties. The cross-section is measured to be...

 Title: Measurement of the total cross section from elastic scattering in pp collisions at √{ s} = 8 TeV with the ATLAS detector Authors: Aaboud, M.; Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2854 coauthors Publication: Physics Letters B, Volume 761, p. 158-178. Publication Date: 10/2016 Origin: ELSEVIER Abstract Copyright: (c) 2016 Elsevier Science B.V. All rights reserved. DOI: 10.1016/j.physletb.2016.08.020 Bibliographic Code: 2016PhLB..761..158A

### Abstract

A measurement of the total pp cross section at the LHC at √{ s} = 8 TeV is presented. An integrated luminosity of 500 μb-1 was accumulated in a special run with high-β beam optics to measure the differential elastic cross section as a function of the Mandelstam momentum transfer variable t. The measurement is performed with the ALFA sub-detector of ATLAS. Using a fit to the differential elastic cross section in the -t range from 0.014 GeV2 to 0.1 GeV2 to extrapolate t → 0, the total cross section, σtot (pp → X), is measured via the optical theorem to be

 Title: Measurement of the top quark mass in the t t bar →dilepton channel from √{ s} = 8 TeV ATLAS data Authors: Aaboud, M.; Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2850 coauthors Publication: Physics Letters B, Volume 761, p. 350-371. Publication Date: 10/2016 Origin: ELSEVIER Abstract Copyright: (c) 2016 Elsevier Science B.V. All rights reserved. DOI: 10.1016/j.physletb.2016.08.042 Bibliographic Code: 2016PhLB..761..350A

### Abstract

The top quark mass is measured in the t t bar →dilepton channel (lepton = e , μ) using ATLAS data recorded in the year 2012 at the LHC. The data were taken at a proton-proton centre-of-mass energy of √{ s} = 8 TeV and correspond to an integrated luminosity of about 20.2 fb-1. Exploiting the template method, and using the distribution of invariant masses of lepton- b-jet pairs, the top quark mass is measured to be mtop = 172.99 ± 0.41 (stat) ± 0.74 (syst) GeV, with a total uncertainty of 0.84 GeV. Finally, a combination with previous ATLAS mtop measurements from √{ s} = 7 TeV data in the t t bar →dilepton and t t bar →lepton +jets channels results in mtop = 172.84 ± 0.34 (stat) ± 0.61 (syst) GeV, with a total uncertainty of 0.70 GeV.

 Title: Search for high-mass new phenomena in the dilepton final state using proton-proton collisions at √{ s} = 13TeV with the ATLAS detector Authors: Aaboud, M.; Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2855 coauthors Publication: Physics Letters B, Volume 761, p. 372-392. Publication Date: 10/2016 Origin: ELSEVIER Abstract Copyright: (c) 2016 Elsevier Science B.V. All rights reserved. DOI: 10.1016/j.physletb.2016.08.055 Bibliographic Code: 2016PhLB..761..372A

### Abstract

A search is conducted for both resonant and non-resonant high-mass new phenomena in dielectron and dimuon final states. The search uses 3.2fb-1 of proton-proton collision data, collected at √{ s} = 13TeV by the ATLAS experiment at the LHC in 2015. The dilepton invariant mass is used as the discriminating variable. No significant deviation from the Standard Model prediction is observed; therefore limits are set on the signal model parameters of interest at 95% credibility level. Upper limits are set on the cross-section times branching ratio for resonances decaying to dileptons, and the limits are converted into lower limits on the resonance mass, ranging between 2.74 TeV and 3.36 TeV, depending on the model. Lower limits on the ℓℓqq contact interaction scale are set between 16.7 TeV and 25.2 TeV, also depending on the model.

 Title: Superconductivity and nematic fluctuations in a model of doped FeSe monolayers: Determinant quantum Monte Carlo study Authors: Dumitrescu, Philipp T.; Serbyn, Maksym; Scalettar, Richard T.; Vishwanath, Ashvin Publication: Physical Review B, Volume 94, Issue 15, id.155127 (PhRvB Homepage) Publication Date: 10/2016 Origin: APS Abstract Copyright: 2016: American Physical Society DOI: 10.1103/PhysRevB.94.155127 Bibliographic Code: 2016PhRvB..94o5127D

### Abstract

In contrast to bulk FeSe, which exhibits nematic order and low temperature superconductivity, highly doped FeSe reverses the situation, having high temperature superconductivity appearing alongside a suppression of nematic order. To investigate this phenomenon, we study a minimal electronic model of FeSe, with interactions that enhance nematic fluctuations. This model is sign problem free, and is simulated using determinant quantum Monte Carlo (DQMC). We developed a DQMC algorithm with parallel tempering, which proves to be an efficient source of global updates and allows us to access the region of strong interactions. Over a wide range of intermediate couplings, we observe superconductivity with an extended s -wave order parameter, along with enhanced, but short-ranged, q =(0 ,0 ) ferro-orbital (nematic) order. These results are consistent with approximate weak-coupling treatments that predict that nematic fluctuations lead to superconducting pairing. Surprisingly, in the parameter range under study, we do not observe nematic long-range order. Instead, at stronger coupling an unusual insulating phase with q =(π ,π ) antiferro-orbital order appears, which is missed by weak-coupling approximations.

 Title: Strain dependence of band gaps and exciton energies in pure and mixed transition-metal dichalcogenides Authors: Defo, Rodrick Kuate; Fang, Shiang; Shirodkar, Sharmila N.; Tritsaris, Georgios A.; Dimoulas, Athanasios; Kaxiras, Efthimios Publication: Physical Review B, Volume 94, Issue 15, id.155310 (PhRvB Homepage) Publication Date: 10/2016 Origin: APS Abstract Copyright: 2016: American Physical Society DOI: 10.1103/PhysRevB.94.155310 Bibliographic Code: 2016PhRvB..94o5310D

### Abstract

The ability to fabricate 2D device architectures with desired properties, based on stacking of weakly (van der Waals) interacting atomically thin layers, is quickly becoming reality. In order to design ever more complex devices of this type, it is crucial to know the precise strain and composition dependence of the layers' electronic and optical properties. Here, we present a theoretical study of these dependences for monolayers with compositions varying from pure MX 2 to the mixed M X Y , where M =Mo , W and X ,Y =S , Se. We employ both density-functional-theory and GW calculations, as well as values of the exciton binding energies based on a self-consistent treatment of dielectric properties, to obtain the band gaps that correspond to optical or transport measurements; we find reasonable agreement with reported experimental values for the unstrained monolayers. Our predictions for the strain-dependent electronic properties should be a useful guide in the effort to design heterostructures composed of these layers on various substrates.

 Title: Resonant inelastic x-ray scattering as a probe of band structure effects in cuprates Authors: Kanász-Nagy, M.; Shi, Y.; Klich, I.; Demler, E. A. Publication: Physical Review B, Volume 94, Issue 16, id.165127 (PhRvB Homepage) Publication Date: 10/2016 Origin: APS Abstract Copyright: 2016: American Physical Society DOI: 10.1103/PhysRevB.94.165127 Bibliographic Code: 2016PhRvB..94p5127K

### Abstract

We analyze within quasiparticle theory a recent resonant inelastic x-ray scattering (RIXS) experiment on YBa2Cu3O6+x with the incoming photon energy detuned at several values from the resonance maximum [Minola et al., Phys. Rev. Lett. 114, 217003 (2015), 10.1103/PhysRevLett.114.217003]. Surprisingly, the data show a much weaker dependence on detuning than expected from recent measurements on a different cuprate superconductor, Bi2Sr2CuO6+x [Guarise et al., Nat. Commun. 5, 5760 (2014), 10.1038/ncomms6760]. We demonstrate here that this discrepancy, originally attributed to collective magnetic excitations, can be understood in terms of the differences between the band structures of these materials. We find good agreement between theory and experiment over a large range of dopings, both in the underdoped and overdoped regimes. Moreover, we demonstrate that the RIXS signal depends sensitively on excitations at energies well above the Fermi surface that are inaccessible to traditionally used band structure probes, such as angle-resolved photoemission spectroscopy. This makes RIXS a powerful probe of band structure, not suffering from surface preparation problems and small sample sizes, making it potentially applicable to a number of cuprate materials.

 Title: Measurement of single π0 production by coherent neutral-current ν Fe interactions in the MINOS Near Detector Authors: Adamson, P.; Anghel, I.; Aurisano, A.;... Feldman, G. J.;... and 113 coauthors; Minos Collaboration Publication: Physical Review D, Volume 94, Issue 7, id.072006 (PhRvD Homepage) Publication Date: 10/2016 Origin: APS Abstract Copyright: 2016: American Physical Society DOI: 10.1103/PhysRevD.94.072006 Bibliographic Code: 2016PhRvD..94g2006A

### Abstract

Forward single π0 production by coherent neutral-current interactions, ν A →ν A π0, is investigated using a 2.8 ×1 020 protons-on-target exposure of the MINOS Near Detector. For single-shower topologies, the event distribution in production angle exhibits a clear excess above the estimated background at very forward angles for visible energy in the range 1-8 GeV. Cross sections are obtained for the detector medium comprised of 80% iron and 20% carbon nuclei with ⟨A ⟩=48, the highest-⟨A ⟩ target used to date in the study of this coherent reaction. The total cross section for coherent neutral-current single π0 production initiated by the νμ flux of the NuMI low-energy beam with mean (mode) Eν of 4.9 GeV (3.0 GeV), is 77.6 ±5.0 (stat)-16.8+15.0(syst )×10-40cm2 per nucleus . The results are in good agreement with predictions of the Berger-Sehgal model.

 Title: Diphoton resonance from a new strong force Authors: Georgi, Howard; Nakai, Yuichiro Publication: Physical Review D, Volume 94, Issue 7, id.075005 (PhRvD Homepage) Publication Date: 10/2016 Origin: APS Abstract Copyright: 2016: American Physical Society DOI: 10.1103/PhysRevD.94.075005 Bibliographic Code: 2016PhRvD..94g5005G

### Abstract

We explore a "partial unification" model that 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 S U (2 )×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 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. If the massive vector bosons are still long lived, they could form new bound states, "vector bosoniums" with additional interesting phenomenology. The model is an explicit example of how new physics at small scales could be hidden by strong interactions.

 Title: X-ray line from exciting dark matter Authors: Finkbeiner, Douglas P.; Weiner, Neal Publication: Physical Review D, Volume 94, Issue 8, id.083002 (PhRvD Homepage) Publication Date: 10/2016 Origin: APS Abstract Copyright: 2016: American Physical Society DOI: 10.1103/PhysRevD.94.083002 Bibliographic Code: 2016PhRvD..94h3002F

### Abstract

The exciting dark matter (XDM) model was proposed as a mechanism to efficiently convert the kinetic energy (in sufficiently hot environments) of dark matter into e +e - pairs. The standard scenario invokes a doublet of nearly degenerate dark matter (DM) states and a dark force to mediate a large upscattering cross section between the two. For heavy (˜TeV ) DM, the kinetic energy of weakly interacting massive particles in large (galaxy-sized or larger) halos is capable of producing low-energy positrons. For lighter dark matter, this is kinematically impossible, and the unique observable signature becomes an x-ray line, arising from χ χ →χ*χ*, followed by χ*→χ γ . This variant of XDM is distinctive from other DM x-ray scenarios in that its signatures tend to be most present in more massive, hotter environments, such as clusters, rather than nearby dwarfs, and has different dependencies from decaying models. We find that it is capable of explaining the recently reported s-ray line at 3.56 keV. For very long lifetimes of the excited state, primordial decays can explain the signal without the presence of upscattering. Thermal models freeze out as in the normal XDM setup, via annihilations to the light boson ϕ . For suitable masses, the annihilation χ χ →ϕ ϕ followed by ϕ →SM can explain the reported gamma-ray signature from the Galactic center. Direct detection is discussed, including the possibility of explaining DAMA via the "luminous" dark matter approach. Quite generally, the proximity of the 3.56 keV line to the energy scale of DAMA motivates a reexamination of electromagnetic explanations. Other signals, including lepton jets and the modification of cores of dwarf galaxies are also considered.

 Title: Imaging grain boundary grooves in hard-sphere colloidal bicrystals Authors: Maire, Eric; Redston, Emily; Persson Gulda, Maria; Weitz, David A.; Spaepen, Frans Publication: Physical Review E, Volume 94, Issue 4, id.042604 (PhRvE Homepage) Publication Date: 10/2016 Origin: APS Abstract Copyright: 2016: American Physical Society DOI: 10.1103/PhysRevE.94.042604 Bibliographic Code: 2016PhRvE..94d2604M

### Abstract

Colloidal particles were sedimented onto patterned glass slides to grow three-dimensional bicrystals with a controlled structure. Three types of symmetric tilt grain boundaries between close-packed face-centered-cubic crystals were produced: Σ 5 (100 ),Σ 17 (100 ) , and Σ 3 (110 ) . The structure of the crystals and their defects were visualized by confocal microscopy, and characterized by simple geometric measurements, including image difference, thresholding, and reprojection. This provided a quick and straightforward way to detect the regions in which the atoms are mobile. This atomic mobility was higher at the grain boundaries and close to the solid-liquid interface. This method was compared to the more conventional analysis based on the calculation of the local order parameter of the individual particles to identify the interface. This was used in turn to identify the presence of grooves at the grain-boundary-liquid triple junction for every type of grain boundary, except for the twin [Σ 3 (110 )] , for which no groove could be detected. Images of these grooves were processed, and the angle linking the grain boundary energy to the solid-liquid interfacial energy was measured. The resulting values of the grain boundary energy were compared to estimates based on the density deficit in the boundary.

 Title: Adiabatic Quantum Search in Open Systems Authors: Wild, Dominik S.; Gopalakrishnan, Sarang; Knap, Michael; Yao, Norman Y.; Lukin, Mikhail D. Publication: Physical Review Letters, Volume 117, Issue 15, id.150501 (PhRvL Homepage) Publication Date: 10/2016 Origin: APS Abstract Copyright: 2016: American Physical Society DOI: 10.1103/PhysRevLett.117.150501 Bibliographic Code: 2016PhRvL.117o0501W

### Abstract

Adiabatic quantum algorithms represent a promising approach to universal quantum computation. In isolated systems, a key limitation to such algorithms is the presence of avoided level crossings, where gaps become extremely small. In open quantum systems, the fundamental robustness of adiabatic algorithms remains unresolved. Here, we study the dynamics near an avoided level crossing associated with the adiabatic quantum search algorithm, when the system 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. By contrast, higher order scattering processes render the algorithm inefficient at any finite temperature regardless of the spectral density, implying that no quantum speedup can be achieved. Extensions and implications for other adiabatic quantum algorithms will be discussed.

 Title: Limits on Active to Sterile Neutrino Oscillations from Disappearance Searches in the MINOS, Daya Bay, and Bugey-3 Experiments Authors: Adamson, P.; An, F. P.; Anghel, I.; ... Feldman, G. J.;... and 117 coauthors Publication: Physical Review Letters, Volume 117, Issue 15, id.151801 (PhRvL Homepage) Publication Date: 10/2016 Origin: APS Abstract Copyright: 2016: American Physical Society DOI: 10.1103/PhysRevLett.117.151801 Bibliographic Code: 2016PhRvL.117o1801A

### Abstract

Searches for a light sterile neutrino have been performed independently by the MINOS and the Daya Bay experiments using the muon (anti)neutrino and electron antineutrino disappearance channels, respectively. In this Letter, results from both experiments are combined with those from the Bugey-3 reactor neutrino experiment to constrain oscillations into light sterile neutrinos. The three experiments are sensitive to complementary regions of parameter space, enabling the combined analysis to probe regions allowed by the Liquid Scintillator Neutrino Detector (LSND) and MiniBooNE experiments in a minimally extended four-neutrino flavor framework. Stringent limits on sin22 θμ e are set over 6 orders of magnitude in the sterile mass-squared splitting Δ m412. The sterile-neutrino mixing phase space allowed by the LSND and MiniBooNE experiments is excluded for Δ m412<0.8 eV2 at 95% CLs.

 Title: Search for Sterile Neutrinos Mixing with Muon Neutrinos in MINOS Authors: Adamson, P.; Anghel, I.; Aurisano, A.; ... Feldman, G. J.;... and 330 coauthors Publication: Physical Review Letters, Volume 117, Issue 15, id.151803 (PhRvL Homepage) Publication Date: 10/2016 Origin: APS Abstract Copyright: 2016: American Physical Society DOI: 10.1103/PhysRevLett.117.151803 Bibliographic Code: 2016PhRvL.117o1803A

### Abstract

We report results of a search for oscillations involving a light sterile neutrino over distances of 1.04 and 735 km in a νμ-dominated beam with a peak energy of 3 GeV. The data, from an exposure of 10.56 ×1 020 protons on target, are analyzed using a phenomenological model with one sterile neutrino. We constrain the mixing parameters θ24 and Δ m412 and set limits on parameters of the four-dimensional Pontecorvo-Maki-Nakagawa-Sakata matrix, |Uμ 4|2 and |Uτ 4|2, under the assumption that mixing between νe and νs is negligible (|Ue 4|2=0 ). No evidence for νμ→νs transitions is found and we set a world-leading limit on θ24 for values of Δ m412 ≲1 eV2.

 Title: Pruning to Increase Taylor Dispersion in Physarum polycephalum Networks Authors: Marbach, Sophie; Alim, Karen; Andrew, Natalie; Pringle, Anne; Brenner, Michael P. Publication: Physical Review Letters, Volume 117, Issue 17, id.178103 (PhRvL Homepage) Publication Date: 10/2016 Origin: APS Abstract Copyright: 2016: American Physical Society DOI: 10.1103/PhysRevLett.117.178103 Bibliographic Code: 2016PhRvL.117q8103M

### Abstract

How do the topology and geometry of a tubular network affect the spread of particles within fluid flows? We investigate patterns of effective dispersion in the hierarchical, biological transport network formed by Physarum polycephalum. We demonstrate that a change in topology—pruning in the foraging state—causes a large increase in effective dispersion throughout the network. By comparison, changes in the hierarchy of tube radii result in smaller and more localized differences. Pruned networks capitalize on Taylor dispersion to increase the dispersion capability.

 Title: Measurement of the Inelastic Proton-Proton Cross Section at √{s }=13 TeV with the ATLAS Detector at the LHC Authors: Aaboud, M.; Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2853 coauthors Publication: Physical Review Letters, Volume 117, Issue 18, id.182002 (PhRvL Homepage) Publication Date: 10/2016 Origin: APS Abstract Copyright: 2016: CERN DOI: 10.1103/PhysRevLett.117.182002 Bibliographic Code: 2016PhRvL.117r2002A

### Abstract

This Letter presents a measurement of the inelastic proton-proton cross section using 60 μb -1 of p p collisions at a center-of-mass energy √{s } of 13 TeV with the ATLAS detector at the LHC. Inelastic interactions are selected using rings of plastic scintillators in the forward region (2.07 <|η |<3.86 ) of the detector. A cross section of 68.1 ±1.4 mb is measured in the fiducial region ξ =MX2/s >10-6, where MX is the larger invariant mass of the two hadronic systems separated by the largest rapidity gap in the event. In this ξ range the scintillators are highly efficient. For diffractive events this corresponds to cases where at least one proton dissociates to a system with MX>13 GeV . The measured cross section is compared with a range of theoretical predictions. When extrapolated to the full phase space, a cross section of 78.1 ±2.9 mb is measured, consistent with the inelastic cross section increasing with center-of-mass energy.

 Title: Fermi Surface Reconstruction and Drop in the Hall Number due to Spiral Antiferromagnetism in High-Tc Cuprates Authors: Eberlein, Andreas; Metzner, Walter; Sachdev, Subir; Yamase, Hiroyuki Publication: Physical Review Letters, Volume 117, Issue 18, id.187001 (PhRvL Homepage) Publication Date: 10/2016 Origin: APS Abstract Copyright: 2016: American Physical Society DOI: 10.1103/PhysRevLett.117.187001 Bibliographic Code: 2016PhRvL.117r7001E

### Abstract

We show that a Fermi surface reconstruction due to spiral antiferromagnetic order may explain the rapid change in the Hall number as recently observed near optimal doping in cuprate superconductors [Badoux et al., Nature (London) 531, 210 (2016)]. The single-particle spectral function in the spiral state exhibits hole pockets which look like Fermi arcs due to a strong momentum dependence of the spectral weight. Adding charge-density wave order further reduces the Fermi surface to a single electron pocket. We propose quantum oscillation measurements to distinguish between commensurate and spiral antiferromagnetic order. Similar results apply to certain metals in which topological order replaces antiferromagnetic order.

 Title: Classification of Interacting Topological Floquet Phases in One Dimension Authors: Potter, Andrew C.; Morimoto, Takahiro; Vishwanath, Ashvin Publication: Physical Review X, Volume 6, Issue 4, id.041001 Publication Date: 10/2016 Origin: APS Abstract Copyright: 2016: authors DOI: 10.1103/PhysRevX.6.041001 Bibliographic Code: 2016PhRvX...6d1001P

### Abstract

Periodic driving of a quantum system can enable new topological phases with no analog in static systems. In this paper, we systematically classify one-dimensional topological and symmetry-protected topological (SPT) phases in interacting fermionic and bosonic quantum systems subject to periodic driving, which we dub Floquet SPTs (FSPTs). For physical realizations of interacting FSPTs, many-body localization by disorder is a crucial ingredient, required to obtain a stable phase that does not catastrophically heat to infinite temperature. We demonstrate that 1D bosonic and fermionic FSPT phases are classified by the same criteria as equilibrium phases but with an enlarged symmetry group G ˜ , which now includes discrete time translation symmetry associated with the Floquet evolution. In particular, 1D bosonic FSPTs are classified by projective representations of the enlarged symmetry group H2(G ˜ ,U (1 )) . We construct explicit lattice models for a variety of systems and then formalize the classification to demonstrate the completeness of this construction. We advocate that a prototypical Z2 bosonic FSPT may be realized by very simple Hamiltonians of the type currently available in existing cold atoms and trapped ion experiments.

 Title: Ultrafast many-body interferometry of impurities coupled to a Fermi sea Authors: Cetina, Marko; Jag, Michael; Lous, Rianne S.; Fritsche, Isabella; Walraven, Jook T. M.; Grimm, Rudolf; Levinsen, Jesper; Parish, Meera M.; Schmidt, Richard; Knap, Michael; Demler, Eugene Publication: Science, Volume 354, Issue 6308, pp. 96-99 (2016). (Sci Homepage) Publication Date: 10/2016 Category: PHYSICS Origin: SCIENCE Abstract Copyright: (c) 2016: Science DOI: 10.1126/science.aaf5134 Bibliographic Code: 2016Sci...354...96C

### Abstract

The fastest possible collective response of a quantum many-body system is related to its excitations at the highest possible energy. In condensed matter systems, the time scale for such “ultrafast” processes is typically set by the Fermi energy. Taking advantage of fast and precise control of interactions between ultracold atoms, we observed nonequilibrium dynamics of impurities coupled to an atomic Fermi sea. Our interferometric measurements track the nonperturbative quantum evolution of a fermionic many-body system, revealing in real time the formation dynamics of quasi-particles and the quantum interference between attractive and repulsive states throughout the full depth of the Fermi sea. Ultrafast time-domain methods applied to strongly interacting quantum gases enable the study of the dynamics of quantum matter under extreme nonequilibrium conditions.

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