# Faculty Publications: March, 2016

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

 Title: Excitation intensity dependence of photoluminescence from monolayers of MoS2 and WS2/MoS2 heterostructures Authors: Kaplan, D.; Gong, Y.; Mills, K.; Swaminathan, V.; Ajayan, P. M.; Shirodkar, S.; Kaxiras, E. Publication: 2D Materials, Volume 3, Issue 1, article id. 015005 (2016). (IOP Homepage) Publication Date: 03/2016 Origin: IOP DOI: 10.1088/2053-1583/3/1/015005 Bibliographic Code: 2016TDM.....3a5005K

### Abstract

A detailed study of the excitation dependence of the photoluminescence (PL) from monolayers of MoS2 and WS2/MoS2 heterostructures grown by chemical vapor deposition on Si substrates has revealed that the luminescence from band edge excitons from MoS2 monolayers shows a linear dependence on excitation intensity for both above band gap and resonant excitation conditions. In particular, a band separated by ∼55 meV from the A exciton, referred to as the C band, shows the same linear dependence on excitation intensity as the band edge excitons. A band similar to the C band has been previously ascribed to a trion, a charged, three-particle exciton. However, in our study the C band does not show the 3/2 power dependence on excitation intensity as would be expected for a three-particle exciton. Further, the PL from the MoS2 monolayer in a bilayer WS2/MoS2 heterostructure, under resonant excitation conditions where only the MoS2 absorbs the laser energy, also revealed a linear dependence on excitation intensity for the C band, confirming that its origin is not due to a trion but instead a bound exciton, presumably of an unintentional impurity or a native point defect such as a sulfur vacancy. The PL from the WS2/MoS2 heterostructure, under resonant excitation conditions also showed additional features which are suggested to arise from the interface states at the heteroboundary. Further studies are required to clearly identify the origin of these features.

 Title: Mesoscopic Rydberg Impurity in an Atomic Quantum Gas Authors: Schmidt, Richard; Sadeghpour, H. R.; Demler, E. Publication: Physical Review Letters, Volume 116, Issue 10, id.105302 (PhRvL Homepage) Publication Date: 03/2016 Origin: APS Abstract Copyright: 2016: American Physical Society DOI: 10.1103/PhysRevLett.116.105302 Bibliographic Code: 2016PhRvL.116j5302S

### Abstract

Giant impurity excitations are powerful probes for exploring new regimes of far out of equilibrium dynamics in few- and many-body quantum systems, and in situ observations of correlations. Motivated by recent experimental progress in spectroscopic studies of Rydberg excitations in ultracold atoms, we develop a new theoretical approach for describing multiscale dynamics of Rydberg excitations in quantum Bose gases. We find that the crossover from few- to many-body dynamics manifests in a dramatic change in spectral profile from resolved molecular lines to broad Gaussian distributions representing a superpolaronic state in which many atoms bind to the Rydberg impurity. We discuss signatures of this crossover in the temperature and density dependence of the spectra.

 Title: Measurement of the Z Z Production Cross Section in p p Collisions at √{s }=13 TeV with the ATLAS Detector Authors: Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2845 coauthors Publication: Physical Review Letters, Volume 116, Issue 10, id.101801 (PhRvL Homepage) Publication Date: 03/2016 Origin: APS Abstract Copyright: 2016: CERN DOI: 10.1103/PhysRevLett.116.101801 Bibliographic Code: 2016PhRvL.116j1801A

### Abstract

The Z Z production cross section in proton-proton collisions at 13 TeV center-of-mass energy is measured using 3.2 fb-1 of data recorded with the ATLAS detector at the Large Hadron Collider. The considered Z boson candidates decay to an electron or muon pair of mass 66-116 GeV. The cross section is measured in a fiducial phase space reflecting the detector acceptance. It is also extrapolated to a total phase space for Z bosons in the same mass range and of all decay modes, giving 16. 7-2.0+2.2(stat )+0.9/-0.7 (syst )+1.0/-0.7 (lumi ) pb . The results agree with standard model predictions.

 Title: Measurement of jet charge in dijet events from √{s }=8 TeV p p collisions with the ATLAS detector Authors: Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2859 coauthors Publication: Physical Review D, Volume 93, Issue 5, id.052003 (PhRvD Homepage) Publication Date: 03/2016 Origin: APS Abstract Copyright: 2016: CERN DOI: 10.1103/PhysRevD.93.052003 Bibliographic Code: 2016PhRvD..93e2003A

### Abstract

The momentum-weighted sum of the charges of tracks associated to a jet is sensitive to the charge of the initiating quark or gluon. This paper presents a measurement of the distribution of momentum-weighted sums, called jet charge, in dijet events using 20.3 fb-1 of data recorded with the ATLAS detector at √{s }=8 TeV in p p collisions at the LHC. The jet charge distribution is unfolded to remove distortions from detector effects and the resulting particle-level distribution is compared with several models. The pT dependence of the jet charge distribution average and standard deviation are compared to predictions obtained with several leading-order and next-to-leading-order parton distribution functions. The data are also compared to different Monte Carlo simulations of QCD dijet production using various settings of the free parameters within these models. The chosen value of the strong coupling constant used to calculate gluon radiation is found to have a significant impact on the predicted jet charge. There is evidence for a pT dependence of the jet charge distribution for a given jet flavor. In agreement with perturbative QCD predictions, the data show that the average jet charge of quark-initiated jets decreases in magnitude as the energy of the jet increases.

 Title: Search for the electroweak production of supersymmetric particles in √{s }=8 TeV p p collisions with the ATLAS detector Authors: Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2862 coauthors
 ublication: Physical Review D, Volume 93, Issue 5, id.052002 (PhRvD Homepage) Publication Date: 03/2016 Origin: APS Abstract Copyright: 2016: CERN DOI: 10.1103/PhysRevD.93.052002 Bibliographic Code: 2016PhRvD..93e2002A

### Abstract

The ATLAS experiment has performed extensive searches for the electroweak production of charginos, neutralinos, and staus. This article summarizes and extends the search for electroweak supersymmetry with new analyses targeting scenarios not covered by previously published searches. New searches use vector-boson fusion production, initial-state radiation jets, and low-momentum lepton final states, as well as multivariate analysis techniques to improve the sensitivity to scenarios with small mass splittings and low-production cross sections. Results are based on 20 fb-1 of proton-proton collision data at √{s }=8 TeV recorded with the ATLAS experiment at the Large Hadron Collider. No significant excess beyond Standard Model expectations is observed. The new and existing searches are combined and interpreted in terms of 95% confidence-level exclusion limits in simplified models, where a single production process and decay mode is assumed, as well as within phenomenological supersymmetric models.

 Title: Measurement of the Bc± production cross section in p p ¯ collisions at √{s }=1.96 TeV Authors: Aaltonen, T.; Amerio, S.; Amidei, D.;... Franklin, M.;... and 395 coauthors Publication: Physical Review D, Volume 93, Issue 5, id.052001 (PhRvD Homepage) Publication Date: 03/2016 Origin: APS Abstract Copyright: 2016: American Physical Society DOI: 10.1103/PhysRevD.93.052001 Bibliographic Code: 2016PhRvD..93e2001A

### Abstract

We describe a measurement of the ratio of the cross sections times branching fractions of the Bc+ meson in the decay mode Bc+→J /ψ μ+ν to the B+ meson in the decay mode B+→J /ψ K+ in proton-antiproton collisions at center-of-mass energy √{s }=1.96 TeV . The measurement is based on the complete CDF Run II data set, which comes from an integrated luminosity of 8.7 fb-1. The ratio of the production cross sections times branching fractions for Bc+ and B+ mesons with momentum transverse to the beam greater than 6 GeV /c and rapidity magnitude smaller than 0.6 is 0.211 ±0.012 (stat)-0.020 +0.021(syst ) . Using the known B+→J /ψ K+ branching fraction, the known B+ production cross section, and a selection of the predicted Bc+→J /ψ μ+ν branching fractions, the range for the total Bc+ production cross section is estimated.

 Title: Fractionalized Fermi liquid on the surface of a topological Kondo insulator Authors: Thomson, Alex; Sachdev, Subir Publication: Physical Review B, Volume 93, Issue 12, id.125103 (PhRvB Homepage) Publication Date: 03/2016 Origin: APS Abstract Copyright: 2016: American Physical Society DOI: 10.1103/PhysRevB.93.125103 Bibliographic Code: 2016PhRvB..93l5103T

### Abstract

We argue that topological Kondo insulators can also have "intrinsic" topological order associated with fractionalized excitations on their surfaces. The hybridization between the local moments and conduction electrons can weaken near the surface, and this enables the local moments to form spin liquids. This coexists with the conduction electron surface states, realizing a surface fractionalized Fermi liquid. We present mean-field solutions of a Kondo-Heisenberg model in two spatial dimensions which display such surfaces.

 Title: Search for new phenomena in dijet mass and angular distributions from pp collisions at √{ s} = 13 TeV with the ATLAS detector Authors: Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2830 coauthors Publication: Physics Letters B, Volume 754, p. 302-322. Publication Date: 03/2016 Origin: ELSEVIER Abstract Copyright: (c) 2016 CERN for the benefit of the ATLAS Collaboration DOI: 10.1016/j.physletb.2016.01.032 Bibliographic Code: 2016PhLB..754..302A

### Abstract

This Letter describes a model-agnostic search for pairs of jets (dijets) produced by resonant and non-resonant phenomena beyond the Standard Model in 3.6 fb-1 of proton-proton collisions with a centre-of-mass energy of √{ s} = 13 TeV recorded by the ATLAS detector at the Large Hadron Collider. The distribution of the invariant mass of the two leading jets is examined for local excesses above a data-derived estimate of the smoothly falling prediction of the Standard Model. The data are also compared to a Monte Carlo simulation of Standard Model angular distributions derived from the rapidity of the two jets. No evidence of anomalous phenomena is observed in the data, which are used to exclude, at 95% CL, quantum black holes with threshold masses below 8.3 TeV, 8.1 TeV, or 5.1 TeV in three different benchmark scenarios; resonance masses below 5.2 TeV for excited quarks, 2.6 TeV in a W model, a range of masses starting from mZ = 1.5 TeV and couplings from gq = 0.2 in a Z model; and contact interactions with a compositeness scale below 12.0 TeV and 17.5 TeV respectively for destructive and constructive interference between the new interaction and QCD processes. These results significantly extend the ATLAS limits obtained from 8 TeV data. Gaussian-shaped contributions to the mass distribution are also excluded if the effective cross-section exceeds values ranging from approximately 50-300 fb for masses below 2 TeV to 2-20 fb for masses above 4 TeV.

 Title: Dijet production in √{ s} = 7 TeVpp collisions with large rapidity gaps at the ATLAS experiment Authors: Aad, G.; Abbott, B.; Abdallah, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2862 coauthors Publication: Physics Letters B, Volume 754, p. 214-234. Publication Date: 03/2016 Origin: ELSEVIER Abstract Copyright: (c) 2016 CERN for the benefit of the ATLAS Collaboration DOI: 10.1016/j.physletb.2016.01.028 Bibliographic Code: 2016PhLB..754..214A

### Abstract

A 6.8 nb-1 sample of pp collision data collected under low-luminosity conditions at √{ s} = 7TeV by the ATLAS detector at the Large Hadron Collider is used to study diffractive dijet production. Events containing at least two jets with pT > 20GeV are selected and analysed in terms of variables which discriminate between diffractive and non-diffractive processes. Cross sections are measured differentially in ΔηF, the size of the observable forward region of pseudorapidity which is devoid of hadronic activity, and in an estimator, ξ ˜ , of the fractional momentum loss of the proton assuming single diffractive dissociation (pp → pX). Model comparisons indicate a dominant non-diffractive contribution up to moderately large ΔηF and small ξ ˜ , with a diffractive contribution which is significant at the highest ΔηF and the lowest ξ ˜ . The rapidity-gap survival probability is estimated from comparisons of the data in this latter region with predictions based on diffractive parton distribution functions.

 Title: Using DNA to program the self-assembly of colloidal nanoparticles and microparticles Authors: Rogers, W. Benjamin; Shih, William M.; Manoharan, Vinothan N. Publication: Nature Reviews Materials, Volume 1, Issue 3, pp. 16008 (2016). Publication Date: 03/2016 Origin: NATURE Abstract Copyright: (c) 2016: Macmillan Publishers Limited DOI: 10.1038/natrevmats.2016.8 Bibliographic Code: 2016NatRM...116008R

### Abstract

DNA is not just the stuff of our genetic code; it is also a means to design self-assembling materials. Grafting DNA onto nano- and microparticles can, in principle, ‘program’ them with information that tells them exactly how to self-assemble. Although fully programmable assembly has not yet been realized, the groundwork has been laid: with an understanding of how specific interparticle attractions arise from DNA hybridization, we can now make systems that reliably assemble in and out of equilibrium. We discuss these advances, and the design rules that will allow us to control — and ultimately program — the assembly of new materials.

 Title: Modulation of mechanical resonance by chemical potential oscillation in graphene Authors: Chen, Changyao; Deshpande, Vikram V.; Koshino, Mikito; Lee, Sunwoo; Gondarenko, Alexander; MacDonald, Allan H.; Kim, Philip; Hone, James Publication: Nature Physics, Volume 12, Issue 3, pp. 240-244 (2016). Publication Date: 03/2016 Origin: NATURE Abstract Copyright: (c) 2016: Nature Publishing Group DOI: 10.1038/nphys3576 Bibliographic Code: 2016NatPh..12..240C

### Abstract

The classical picture of the force on a capacitor assumes a large density of electronic states, such that the electrochemical potential of charges added to the capacitor is given by the external electrostatic potential and the capacitance is determined purely by geometry. Here we consider capacitively driven motion of a nano-mechanical resonator with a low density of states, in which these assumptions can break down. We find three leading-order corrections to the classical picture: the first of which is a modulation in the static force due to variation in the internal chemical potential; the second and third are changes in the static force and dynamic spring constant due to the rate of change of chemical potential, expressed as the quantum (density of states) capacitance. As a demonstration, we study capacitively driven graphene mechanical resonators, where the chemical potential is modulated independently of the gate voltage using an applied magnetic field to manipulate the energy of electrons residing in discrete Landau levels. In these devices, we observe large periodic frequency shifts consistent with the three corrections to the classical picture. In devices with extremely low strain and disorder, the first correction term dominates and the resonant frequency closely follows the chemical potential. The theoretical model fits the data with only one adjustable parameter representing disorder-broadening of the Landau levels. The underlying electromechanical coupling mechanism is not limited by the particular choice of material, geometry, or mechanism for variation in the chemical potential, and can thus be extended to other low-dimensional systems.

 Title: Nature of the quantum metal in a two-dimensional crystalline superconductor Authors: Tsen, A. W.; Hunt, B.; Kim, Y. D.; Yuan, Z. J.; Jia, S.; Cava, R. J.; Hone, J.; Kim, P.; Dean, C. R.; Pasupathy, A. N. Publication: Nature Physics, Volume 12, Issue 3, pp. 208-212 (2016). Publication Date: 03/2016 Origin: NATURE Abstract Copyright: (c) 2016: Nature Publishing Group DOI: 10.1038/nphys3579 Bibliographic Code: 2016NatPh..12..208T

### Abstract

Two-dimensional (2D) materials are not expected to be metals at low temperature owing to electron localization. Consistent with this, pioneering studies on thin films reported only superconducting and insulating ground states, with a direct transition between the two as a function of disorder or magnetic field. However, more recent works have revealed the presence of an intermediate quantum metallic state occupying a substantial region of the phase diagram, whose nature is intensely debated. Here, we observe such a state in the disorder-free limit of a crystalline 2D superconductor, produced by mechanical co-lamination of NbSe2 in an inert atmosphere. Under a small perpendicular magnetic field, we induce a transition from superconductor to the quantum metal. We find a unique power-law scaling with field in this phase, which is consistent with the Bose-metal model where metallic behaviour arises from strong phase fluctuations caused by the magnetic field.

 Title: Large numbers of cold positronium atoms created in laser-selected Rydberg states using resonant charge exchange Authors: McConnell, R.; Gabrielse, G.; Kolthammer, W. S.; Richerme, P.; Müllers, A.; Walz, J.; Grzonka, D.; Zielinski, M.; Fitzakerley, D.; George, M. C.; Hessels, E. A.; Storry, C. H.; Weel, M.; ATRAP Collaboration Publication: Journal of Physics B: Atomic, Molecular, and Optical Physics, Volume 49, Issue 6, article id. 064002 (2016). Publication Date: 03/2016 Origin: IOP DOI: 10.1088/0953-4075/49/6/064002 Bibliographic Code: 2016JPhB...49f4002M

### Abstract

Lasers are used to control the production of highly excited positronium atoms (Ps*). The laser light excites Cs atoms to Rydberg states that have a large cross section for resonant charge-exchange collisions with cold trapped positrons. For each trial with 30 million trapped positrons, more than 700 000 of the created Ps* have trajectories near the axis of the apparatus, and are detected using Stark ionization. This number of Ps* is 500 times higher than realized in an earlier proof-of-principle demonstration (2004 Phys. Lett. B 597 257). A second charge exchange of these near-axis Ps* with trapped antiprotons could be used to produce cold antihydrogen, and this antihydrogen production is expected to be increased by a similar factor.

 Title: Electron-cooled accumulation of 4 × 109 positrons for production and storage of antihydrogen atoms Authors: Fitzakerley, D. W.; George, M. C.; Hessels, E. A.; Skinner, T. D. G.; Storry, C. H.; Weel, M.; Gabrielse, G.; Hamley, C. D.; Jones, N.; Marable, K.; Tardiff, E.; Grzonka, D.; Oelert, W.; Zielinski, M.; ATRAP Collaboration Publication: Journal of Physics B: Atomic, Molecular, and Optical Physics, Volume 49, Issue 6, article id. 064001 (2016). Publication Date: 03/2016 Origin: IOP DOI: 10.1088/0953-4075/49/6/064001 Bibliographic Code: 2016JPhB...49f4001F

### Abstract

Four billion positrons (e+) are accumulated in a Penning–Ioffe trap apparatus at 1.2 K and <6 × 10‑17 Torr. This is the largest number of positrons ever held in a Penning trap. The e+ are cooled by collisions with trapped electrons (e) in this first demonstration of using e for efficient loading of e+ into a Penning trap. The combined low temperature and vacuum pressure provide an environment suitable for antihydrogen (\bar{{{H}}}) production, and long antimatter storage times, sufficient for high-precision tests of antimatter gravity and of CPT.

 Title: Flooded Dark Matter and S level rise Authors: Randall, Lisa; Scholtz, Jakub; Unwin, James Publication: Journal of High Energy Physics, Volume 2016, article id. #11, 26 pp. Publication Date: 03/2016 Origin: SPRINGER Keywords: Beyond Standard Model, Cosmology of Theories beyond the SM Abstract Copyright: (c) 2016: The Author(s) DOI: 10.1007/JHEP03(2016)011 Bibliographic Code: 2016JHEP...03..011R

### Abstract

Most dark matter models set the dark matter relic density by some interaction with Standard Model particles. Such models generally assume the existence of Standard Model particles early on, with the dark matter relic density a later consequence of those interactions. Perhaps a more compelling assumption is that dark matter is not part of the Standard Model sector and a population of dark matter too is generated at the end of inflation. This democratic assumption about initial conditions does not necessarily provide a natural value for the dark matter relic density, and furthermore superficially leads to too much entropy in the dark sector relative to ordinary matter. We address the latter issue by the late decay of heavy particles produced at early times, thereby associating the dark matter relic density with the lifetime of a long-lived state. This paper investigates what it would take for this scenario to be compatible with observations in what we call Flooded Dark Matter (FDM) models and discusses several interesting consequences. One is that dark matter can be very light and furthermore, light dark matter is in some sense the most natural scenario in FDM as it is compatible with larger couplings of the decaying particle. A related consequence is that the decay of the field with the smallest coupling and hence the longest lifetime dominates the entropy and possibly the matter content of the Universe, a principle we refer to as "Maximum Baroqueness". We also demonstrate that the dark sector should be colder than the ordinary sector, relaxing the most stringent free-streaming constraints on light dark matter candidates. We will discuss the potential implications for the core-cusp problem in a follow-up paper. The FDM framework will furthermore have interesting baryogenesis implications. One possibility is that dark matter is like the baryon asymmetry and both are simultaneously diluted by a late entropy dump. Alternatively, FDM is compatible with an elegant non-thermal leptogenesis implementation in which decays of a heavy right-handed neutrino lead to late time reheating of the Standard Model degrees of freedom and provide suitable conditions for creation of a lepton asymmetry.

 Title: Factorization for groomed jet substructure beyond the next-to-leading logarithm Authors: Frye, Christopher; Larkoski, Andrew J.; Schwartz, Matthew D.; Yan, Kai Publication: eprint arXiv:1603.09338 Publication Date: 03/2016 Origin: ARXIV Keywords: High Energy Physics - Phenomenology Comment: 43 pages + appendices, 13 figures Bibliographic Code: 2016arXiv160309338F

### Abstract

Jet grooming algorithms are widely used in experimental analyses at hadron colliders to remove contaminating radiation from within jets. While the algorithms perform a great service to the experiments, their intricate algorithmic structure and multiple parameters has frustrated precision theoretic understanding. In this paper, we demonstrate that one particular groomer called soft drop actually makes precision jet substructure easier. In particular, we derive a factorization formula for a large class of soft drop jet substructure observables, including jet mass. The essential observation that allows for this factorization is that, without the soft wide-angle radiation groomed by soft drop, all singular contributions are collinear. The simplicity and universality of the collinear limit in QCD allows us to show that to all orders, the normalized differential cross section has no contributions from non-global logarithms. It is also independent of process, up to the relative fraction of quark and gluon jets. In fact, soft drop allows us to define this fraction precisely. The factorization theorem also explains why soft drop observables are less sensitive to hadronization than their ungroomed counterparts. Using the factorization theorem, we resum the soft drop jet mass to next-to-next-to-leading logarithmic accuracy. This requires calculating some clustering effects that are closely related to corresponding effects found in jet veto calculations. We match our resummed calculation to fixed order results for both $e^+e^-\to$ dijets and $pp\to Z+j$ events, producing the first jet substructure predictions (groomed or ungroomed) to this accuracy for the LHC.

 Title: Fermi polaron-polaritons in charge-tunable atomically thin semiconductors Authors: Sidler, Meinrad; Back, Patrick; Cotlet, Ovidiu; Srivastava, Ajit; Fink, Thomas; Kroner, Martin; Demler, Eugene; Imamoglu, Atac Publication: eprint arXiv:1603.09215 Publication Date: 03/2016 Origin: ARXIV Keywords: Condensed Matter - Mesoscale and Nanoscale Physics Bibliographic Code: 2016arXiv160309215S

### Abstract

The dynamics of a mobile quantum impurity in a degenerate Fermi system is a fundamental problem in many-body physics. The interest in this field has been renewed due to recent ground-breaking experiments with ultra-cold Fermi gases. Optical creation of an exciton or a polariton in a two-dimensional electron system embedded in a microcavity constitutes a new frontier for this field due to an interplay between cavity-coupling favoring ultra-low mass polariton formation and exciton-electron interactions leading to polaron or trion formation. Here, we present cavity spectroscopy of gate-tunable monolayer MoSe$_2$ exhibiting strongly bound trion and polaron resonances, as well as non-perturbative coupling to a single microcavity mode. As the electron density is increased, the oscillator strength determined from the polariton splitting is gradually transferred from the higher-energy repulsive-exciton-polaron resonance to the lower-energy attractive-polaron manifold. Simultaneous observation of polariton formation in both attractive and repulsive branches indicate a new regime of polaron physics where the polariton impurity mass is much smaller than that of the electrons. Our findings shed new light on optical response of semiconductors in the presence of free carriers by identifying the Fermi polaron nature of excitonic resonances and constitute a first step in investigation of a new class of degenerate Bose-Fermi mixtures.

 Title: Nonexistence for complete K\"ahler Einstein metrics on some noncompact manifolds Authors: Gao, Peng; Yau, Shing-Tung; Zhou, Wubin Publication: eprint arXiv:1603.09135 Publication Date: 03/2016 Origin: ARXIV Keywords: Mathematics - Differential Geometry Bibliographic Code: 2016arXiv160309135G

### Abstract

Let $M$ be a compact K\"ahler manifold and $N$ be a subvariety with codimension greater than or equal to 2. We show that there are no complete K\"ahler--Einstein metrics on $M-N$. As an application, let $E$ be an exceptional divisor of $M$. Then $M-E$ cannot admit any complete K\"ahler--Einstein metric if blow-down of $E$ is a complex variety with only canonical or terminal singularities. A similar result is shown for pairs.

 Title: On complete constant scalar curvature K\"ahler metrics with Poincar\'e-Mok-Yau asymptotic property Authors: Fu, Jixiang; Yau, Shing-Tung; Zhou, Wubin Publication: eprint arXiv:1603.09131 Publication Date: 03/2016 Origin: ARXIV Keywords: Mathematics - Differential Geometry Bibliographic Code: 2016arXiv160309131F

### Abstract

Let $X$ be a compact K\"ahler manifold and $S$ a subvariety of $X$ with higher co-dimension. The aim is to study complete constant scalar curvature K\"ahler metrics on non-compact K\"ahler manifold $X-S$ with Poincar\'e--Mok--Yau asymptotic property (see Definition \ref{def}). In this paper, the methods of Calabi's ansatz and the moment construction are used to provide some special examples of such metrics.

 Title: Quasi-local energy in presence of gravitational radiation Authors: Chen, Po-Ning; Wang, Mu-Tao; Yau, Shing-Tung Publication: eprint arXiv:1603.08860 Publication Date: 03/2016 Origin: ARXIV Keywords: Mathematics - Differential Geometry, General Relativity and Quantum Cosmology Comment: 5 pages and 2 figures Bibliographic Code: 2016arXiv160308860C

### Abstract

We discuss our recent work [4] in which gravitational radiation was studied by evaluating the Wang-Yau quasi-local mass of surfaces of fixed size at the infinity of both axial and polar perturbations of the Schwarzschild spacetime, \`{a} la Chandrasekhar [1].

 Title: Striated Populations in Disordered Environments with Advection Authors: Chotibut, Thiparat; Nelson, David R.; Succi, Sauro Publication: eprint arXiv:1603.08646 Publication Date: 03/2016 Origin: ARXIV Keywords: Quantitative Biology - Populations and Evolution, Condensed Matter - Disordered Systems and Neural Networks, Condensed Matter - Statistical Mechanics Comment: 30 pages, 8 figures Bibliographic Code: 2016arXiv160308646C

### Abstract

Growth in static and controlled environments such as a Petri dish can be used to study the spatial population dynamics of microorganisms. However, natural populations such as marine microbes experience fluid advection and often grow up in heterogeneous environments. We investigate a generalized Fisher-Kolmogorov-Petrovsky-Piscounov (FKPP) equation describing single species population subject to a constant flow field and quenched random spatially inhomogeneous growth rates with a fertile overall growth condition. We analytically and numerically demonstrate that the non-equilibrium steady-state population density develops a flow-driven striation pattern. The striations are highly asymmetric with a longitudinal correlation length that diverges linearly with the flow speed and a transverse correlation length that approaches a finite velocity-independent value. Linear response theory is developed to study the statistics of the steady states. Theoretical predictions show excellent agreement with the numerical steady states of the generalized FKPP equation obtained from Lattice Boltzmann simulations. These findings suggest that, although the growth disorder can be spatially uncorrelated, correlated population structures with striations emerge naturally at sufficiently strong advection.

 Title: STIRAP preparation of a coherent superposition of ThO $H^3\Delta_1$ states for an improved electron EDM measurement Authors: Panda, C. D.; O'Leary, B. R.; West, A. D.; Baron, J.; Hess, P. W.; Hoffman, C.; Kirilov, E.; Overstreet, C. B.; West, E. P.; DeMille, D.; Doyle, J. M.; Gabrielse, G. Publication: eprint arXiv:1603.07707 Publication Date: 03/2016 Origin: ARXIV Keywords: Physics - Atomic Physics, High Energy Physics - Experiment Bibliographic Code: 2016arXiv160307707P

### Abstract

Experimental searches for the electron electric dipole moment (EDM) probe new physics beyond the Standard Model. The current best EDM limit was set by the ACME Collaboration [Science \textbf{343}, 269 (2014)], constraining time reversal symmetry ($T$) violating physics at the TeV energy scale. ACME used optical pumping to prepare a coherent superposition of ThO $H^3\Delta_1$ states that have aligned electron spins. Spin precession due to the molecule's internal electric field was measured to extract the EDM. We report here on an improved method for preparing this spin-aligned state of the electron by using STIRAP. We demonstrate a transfer efficiency of $75\pm5\%$, representing a significant gain in signal for a next generation EDM experiment. We discuss the particularities of implementing STIRAP in systems such as ours, where molecular ensembles with large phase-space distributions are transfered via weak molecular transitions with limited laser power and limited optical access.

 Title: Area, Entanglement Entropy and Supertranslations at Null Infinity Authors: Kapec, Daniel; Raclariu, Ana-Maria; Strominger, Andrew Publication: eprint arXiv:1603.07706 Publication Date: 03/2016 Origin: ARXIV Keywords: High Energy Physics - Theory, General Relativity and Quantum Cosmology Comment: 14 pages Bibliographic Code: 2016arXiv160307706K

### Abstract

The area of a cross-sectional cut $\Sigma$ of future null infinity ($\mathcal{I}^+$) is infinite. We define a finite, renormalized area by subtracting the area of the same cut in any one of the infinite number of BMS-degenerate classical vacua. The renormalized area acquires an anomalous dependence on the choice of vacuum. We relate it to the modular energy, including a soft graviton contribution, of the region of $\mathcal{I}^+$ to the future of $\Sigma$. Under supertranslations, the renormalized area shifts by the supertranslation charge of $\Sigma$. In quantum gravity, we conjecture a bound relating the renormalized area to the entanglement entropy across $\Sigma$ of the outgoing quantum state on $\mathcal{I}^+$.

 Title: A Diphoton Resonance from Bulk RS Authors: Csaki, Csaba; Randall, Lisa Publication: eprint arXiv:1603.07303 Publication Date: 03/2016 Origin: ARXIV Keywords: High Energy Physics - Phenomenology, High Energy Physics - Experiment, High Energy Physics - Theory Comment: 14 pages, LaTeX, 7 figures Bibliographic Code: 2016arXiv160307303C

### Abstract

Recent LHC data hints at a 750 GeV mass resonance that decays into two photons. A significant feature of this resonance is that its decays to Higges and to any other Standard Model particles are so far too low to be detected. Such a state has a compelling explanation in terms of a scalar or a pseudoscalar that is strongly coupled to vector states charged under the Standard Model gauge groups. We argue that if the state is a scalar, some form of sequestering is likely to be necessary to naturally explain the suppressed scalar-Higgs interactions. Such a scenario is readily accommodated in bulk RS with a scalar localized in the bulk away from the Higgs. Turning this around, we argue that a good way to find the elusive bulk RS model might be the search for a resonance with prominent couplings to gauge bosons.

 Title: Precision physics with pile-up insensitive observables Authors: Frye, Christopher; Larkoski, Andrew J.; Schwartz, Matthew D.; Yan, Kai Publication: eprint arXiv:1603.06375 Publication Date: 03/2016 Origin: ARXIV Keywords: High Energy Physics - Phenomenology, High Energy Physics - Experiment Comment: 5 pages, 6 figures; v2 added references to SCET, FastJet, and mMDT Bibliographic Code: 2016arXiv160306375F

### Abstract

To deepen the search for beyond the Standard Model physics, the Large Hadron Collider is pushing to higher and higher luminosity. At high luminosity, precision physics becomes increasingly difficult due to contamination from additional proton collisions per bunch crossing called pile-up. In recent years, many methods have been developed to cull this excess mostly low-energy radiation away from important signal regions, but it has been unclear if these methods were amenable to systematically-improvable theoretical understanding. In this paper, it is shown that one such method, soft drop jet grooming, has excellent theoretical properties: it is ultra-local, depending on only radiation within a jet, and it is free of non-global logarithms. Calculations of the soft drop jet mass and related observables are presented at next-to-next-to-leading logarithmic accuracy matched to next-to-next-to-leading fixed-order in perturbative Quantum Chromodynamics. Once measured at the Large Hadron Collider, precision comparisons between theory and data can be made, essentially independent of the amount of pile-up contamination.

 Title: Quantum network of neutral atom clocks Authors: Kómár, P.; Topcu, T.; Kessler, E. M.; Derevianko, A.; Vuletić, V.; Ye, J.; Lukin, M. D. Publication: eprint arXiv:1603.06258 Publication Date: 03/2016 Origin: ARXIV Keywords: Quantum Physics Comment: 13 pages, 11 figures Bibliographic Code: 2016arXiv160306258K

### Abstract

We propose a protocol for creating a fully entangled GHZ-type state of neutral atoms in spatially separated optical atomic clocks. In our scheme, local operations make use of the strong dipole-dipole interaction between Rydberg excitations, which give rise to fast and reliable quantum operations involving all atoms in the ensemble. The necessary entanglement between distant ensembles is mediated by single-photon quantum channels and collectively enhanced light-matter couplings. These techniques can be used to create the recently proposed quantum clock network based on neutral atom optical clocks. We specifically analyze a possible realization of this scheme using neutral Yb ensembles.

 Title: BICEP2 / Keck Array VII: Matrix based E/B Separation applied to BICEP2 and the Keck Array Authors: Array, Keck; BICEP2 Collaborations; :; Ade, P.; Ahmed, Z.; Aikin, R. W.; Alexander, K. D.; Barkats, D.; Benton, S. J.; Bischoff, C. A.; Bock, J. J.; Bowens-Rubin, R.; Brevik, J. A.; Buder, I.; Bullock, E.; Buza, V.; Connors, J.; Crill, B. P.; Duband, L.; Dvorkin, C.; Filippini, J. P.; Fliescher, S.; Grayson, J.; Halpern, M.; Harrison, S.; Hildebrandt, S. R.; Hilton, G. C.; Hui, H.; Irwin, K. D.; Kang, J.; Karkare, K. S.; Karpel, E.; Kaufman, J. P.; Keating, B. G.; Kefeli, S.; Kernasovskiy, S. A.; Kovac, J.; Kuo, C. L.; Leitch, E. M.; Lueker, M.; Megerian, K. G.; Namikawa, T.; Netterfield, C. B.; Nguyen, H. T.; O'Brient, R.; W., R., IV; Orlando, A.; Pryke, C.; Richter, S.; Schwarz, R.; Sheehy, C. D.; Staniszewski, Z. K.; Steinbach, B.; Sudiwala, R. V.; Teply, G. P.; Thompson, K. L.; Tolan, J. E.; Tucker, C.; Turner, A. D.; Vieregg, A. G.; Weber, A. C.; Wiebe, D. V.; Willmert, J.; Wong, C. L.; Wu, W. L.; Yoon, K. W. Publication: eprint arXiv:1603.05976 Publication Date: 03/2016 Origin: ARXIV Keywords: Astrophysics - Instrumentation and Methods for Astrophysics, Astrophysics - Cosmology and Nongalactic Astrophysics Bibliographic Code: 2016arXiv160305976A

### Abstract

A linear polarization field on the sphere can be uniquely decomposed into an E-mode and a B-mode component. These two components are analytically defined in terms of spin-2 spherical harmonics. Maps that contain filtered modes on a partial sky can also be decomposed into E-mode and B-mode components. However, the lack of full sky information prevents orthogonally separating these components using spherical harmonics. In this paper, we present a technique for decomposing an incomplete map into E and B-mode components using E and B eigenmodes of the pixel covariance in the observed map. This method is found to orthogonally define E and B in the presence of both partial sky coverage and spatial filtering. This method has been applied to the BICEP2 and the Keck Array maps and results in reducing E to B leakage from LCDM E-modes to a level corresponding to a tensor-to-scalar ratio of $r<1\times10^{-4}$.

 Title: Negative Branes, Supergroups and the Signature of Spacetime Authors: Dijkgraaf, Robbert; Heidenreich, Ben; Jefferson, Patrick; Vafa, Cumrun Publication: eprint arXiv:1603.05665 Publication Date: 03/2016 Origin: ARXIV Keywords: High Energy Physics - Theory Comment: 66 pages, 12 figures Bibliographic Code: 2016arXiv160305665D

### Abstract

We study the realization of supergroup gauge theories using negative branes in string theory. We show that negative branes are intimately connected with the possibility of timelike compactification and exotic spacetime signatures previously studied by Hull. Isolated negative branes dynamically generate a change in spacetime signature near their worldvolumes, and are related by string dualities to a smooth M-theory geometry with closed timelike curves. Using negative D3 branes, we show that $SU(0|N)$ supergroup theories are holographically dual to an exotic variant of type IIB string theory on $dS_{3,2} \times \bar S^5$, for which the emergent dimensions are timelike. Using branes, mirror symmetry and Nekrasov's instanton calculus, all of which agree, we derive the Seiberg-Witten curve for $\mathcal N=2 ~SU(N|M)$ gauge theories. Together with our exploration of holography and string dualities for negative branes, this suggests that supergroup gauge theories may be non-perturbatively well-defined objects, though several puzzles remain.

 Title: Transition from the $\mathbb{Z}_2$ spin liquid to antiferromagnetic order: spectrum on the torus Authors: Whitsitt, Seth; Sachdev, Subir Publication: eprint arXiv:1603.05652 Publication Date: 03/2016 Origin: ARXIV Keywords: Condensed Matter - Strongly Correlated Electrons Bibliographic Code: 2016arXiv160305652W

### Abstract

We describe the finite-size spectrum in the vicinity of the quantum critical point between a $\mathbb{Z}_2$ spin liquid and a coplanar antiferromagnet on the torus. We obtain the universal evolution of all low-lying states in an antiferromagnet with global SU(2) spin rotation symmetry, as it moves from the 4-fold topological degeneracy in a gapped $\mathbb{Z}_2$ spin liquid to the Anderson "tower-of-states" in the ordered antiferromagnet. Due to the existence of nontrivial order on either side of this transition, this critical point cannot be described in a conventional Landau-Ginzburg-Wilson framework. Instead it is described by a theory involving fractionalized degrees of freedom known as the O$(4)^\ast$ model, whose spectrum is altered in a significant way by its proximity to a topologically ordered phase. We compute the spectrum by relating it to the spectrum of the O$(4)$ Wilson-Fisher fixed point on the torus, modified with a selection rule on the states, and with nontrivial boundary conditions corresponding to topological sectors in the spin liquid. The spectrum of the critical O($2N$) model is calculated directly at $N=\infty$, which then allows a reconstruction of the full spectrum of the O($2N)^\ast$ model at leading order in $1/N$. This spectrum is a unique characteristic of the vicinity of a fractionalized quantum critical point, as well as a universal signature of the existence of proximate $\mathbb{Z}_2$ topological and antiferromagnetically-ordered phases, and can be compared with numerical computations on quantum antiferromagnets on two dimensional lattices.

 Title: Numerical study of fermion and boson models with infinite-range random interactions Authors: Fu, Wenbo; Sachdev, Subir Publication: eprint arXiv:1603.05246 Publication Date: 03/2016 Origin: ARXIV Keywords: Condensed Matter - Strongly Correlated Electrons, High Energy Physics - Theory Comment: 20 pages, 10 figures Bibliographic Code: 2016arXiv160305246F

### Abstract

We present numerical studies of fermion and boson models with random all-to-all interactions (the SYK models). The high temperature expansion and exact diagonalization of the $N$-site fermion model are used to compute the entropy density: our results are consistent with the numerical solution of $N=\infty$ saddle point equations, and the presence of a non-zero entropy density in the limit of vanishing temperature. The exact diagonalization results for the fermion Green's function also appear to converge well to the $N=\infty$ solution. For the hard-core boson model, the exact diagonalization study indicates spin glass order. Some results on the entanglement entropy and the out-of-time-order correlators are also presented.

 Title: Regimes of heating and dynamical response in driven many-body localized systems Authors: Gopalakrishnan, Sarang; Knap, Michael; Demler, Eugene Publication: eprint arXiv:1603.04448 Publication Date: 03/2016 Origin: ARXIV Keywords: Condensed Matter - Disordered Systems and Neural Networks, Condensed Matter - Statistical Mechanics, Condensed Matter - Strongly Correlated Electrons Comment: 16 pages, 9 figures Bibliographic Code: 2016arXiv160304448G

### Abstract

We explore the response of many-body localized (MBL) systems to periodic driving of arbitrary amplitude, focusing on the rate at which they exchange energy with the drive. To this end, we introduce an infinite-temperature generalization of the effective "heating rate" in terms of the spread of a random walk in energy space. We compute this heating rate numerically and estimate it analytically in various regimes. When the drive amplitude is much smaller than the frequency, this effective heating rate is given by linear response theory with a coefficient that is proportional to the optical conductivity; in the opposite limit, the response is nonlinear and the heating rate is a nontrivial power-law of time. We discuss the mechanisms underlying this crossover in the MBL phase, and comment on its implications for the subdiffusive thermal phase near the MBL transition.

 Title: Quantum thermalization through entanglement in an isolated many-body system Authors: Kaufman, Adam M.; Tai, M. Eric; Lukin, Alexander; Rispoli, Matthew; Schittko, Robert; Preiss, Philipp M.; Greiner, Markus Publication: eprint arXiv:1603.04409 Publication Date: 03/2016 Origin: ARXIV Keywords: Quantum Physics, Condensed Matter - Quantum Gases, Physics - Atomic Physics Bibliographic Code: 2016arXiv160304409K

### Abstract

The concept of entropy is fundamental to thermalization, yet appears at odds with basic principles in quantum mechanics. While statistical mechanics relies on the maximization of entropy for a system at thermal equilibrium, an isolated many-body system undergoing Schr\"odinger dynamics has zero entropy because, at any given time, it is described by a single quantum state. The underlying role of quantum mechanics in many-body physics is then seemingly antithetical to the success of statistical mechanics in a large variety of systems. Here we observe experimentally how this conflict is resolved: we perform microscopy on an evolving quantum state, and we see thermalization occur on a local scale, while we measure that the full quantum state remains pure. We directly measure entanglement entropy and observe how it assumes the role of the thermal entropy in thermalization. Although the full state has zero entropy, entanglement creates local entropy that validates the use of statistical physics for local observables. In combination with number-resolved, single-site imaging, we demonstrate how our measurements of a pure quantum state agree with the Eigenstate Thermalization Hypothesis and thermal ensembles in the presence of a near-volume law in the entanglement entropy.

 Title: Radiation Pressure Force from Optical Cycling on a Polyatomic Molecule Authors: Kozyryev, Ivan; Baum, Louis; Matsuda, Kyle; Hemmerling, Boerge; Doyle, John M. Publication: eprint arXiv:1603.04089 Publication Date: 03/2016 Origin: ARXIV Keywords: Physics - Atomic Physics Bibliographic Code: 2016arXiv160304089K

### Abstract

We demonstrate multiple photon cycling and radiative force deflection on the triatomic free radical strontium monohydroxide (SrOH). Optical cycling is achieved on SrOH in a cryogenic buffer-gas beam by employing the rotationally closed $P\left(N''=1\right)$ branch of the vibronic transition $\tilde{X}^{2}\Sigma^{+}\left(000\right)\leftrightarrow\tilde{A}^{2}\Pi_{1/2}\left(000\right)$. A single repumping laser excites the Sr-O stretching vibrational mode, and photon cycling of the molecule deflects the SrOH beam by an angle of $0.2^{\circ}$ via scattering of $\sim100$ photons per molecule. This approach can be used for direct laser cooling of SrOH and more complex, isoelectronic species.

 Title: Interstellar Gas and a Dark Disk Authors: Kramer, Eric David; Randall, Lisa Publication: eprint arXiv:1603.03058 Publication Date: 03/2016 Origin: ARXIV Keywords: Astrophysics - Astrophysics of Galaxies Bibliographic Code: 2016arXiv160303058K

### 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. Although a small dark disk is slightly favored, the current data is inadequate to establish its existence.

 Title: Universal Signatures of Quantum Critical Points from Finite-Size Torus Spectra: A Window into the Operator Content of Higher-Dimensional Conformal Field Theories Authors: Schuler, Michael; Whitsitt, Seth; Henry, Louis-Paul; Sachdev, Subir; Läuchli, Andreas M. Publication: eprint arXiv:1603.03042 Publication Date: 03/2016 Origin: ARXIV Keywords: Condensed Matter - Strongly Correlated Electrons Comment: 5 pages, 4 figures (+Supplemental Material) Bibliographic Code: 2016arXiv160303042S

### Abstract

The low-energy spectra of many body systems on a torus, of finite size $L$, are well understood in magnetically ordered and gapped topological phases. However, the spectra at quantum critical points separating such phases are largely unexplored for 2+1D systems. Using a combination of analytical and numerical techniques, we show that the low-energy torus spectrum at criticality provides a universal fingerprint of the underlying quantum field theory, with the energy levels given by universal numbers times $1/L$. We highlight the implications of a neighboring topological phase on the spectrum by studying the Ising* transition, in the example of the toric code in a longitudinal field, and advocate a phenomenological picture that provides insight into the operator content of the critical field theory.

 Title: Superconductivity from a confinement transition out of a FL* metal with $\mathbb{Z}_2$ topological and Ising-nematic orders Authors: Chatterjee, Shubhayu; Qi, Yang; Sachdev, Subir; Steinberg, Julia Publication: eprint arXiv:1603.03041 Publication Date: 03/2016 Origin: ARXIV Keywords: Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Superconductivity Comment: 26+21 pages, 5 figures, 3 tables Bibliographic Code: 2016arXiv160303041C

### Abstract

The Schwinger-boson theory of the frustrated square lattice antiferromagnet yields a stable, gapped $\mathbb{Z}_2$ spin liquid ground state with time-reversal symmetry, incommensurate spin correlations and long-range Ising-nematic order. We obtain an equivalent description of this state using fermionic spinons (the fermionic spinons can be considered to be bound states of the bosonic spinons and the visons). Upon doping, the $\mathbb{Z}_2$ spin liquid can lead to a FL* metal with small Fermi pockets of electron-like quasiparticles, while preserving the $\mathbb{Z}_2$ topological and Ising-nematic orders. We describe a Higgs transition out of this deconfined metallic state into a confining superconducting state which is usually of the Fulde-Ferrell-Larkin-Ovchinnikov type, with spatial modulation of the superconducting order.

 Title: Quasi-local energy with respect to de Sitter/anti-de Sitter reference Authors: Chen, Po-Ning; Wang, Mu-Tao; Yau, Shing-Tung Publication: eprint arXiv:1603.02975 Publication Date: 03/2016 Origin: ARXIV Keywords: Mathematics - Differential Geometry, General Relativity and Quantum Cosmology Comment: 31 pages Bibliographic Code: 2016arXiv160302975C

### Abstract

This article considers the quasi-local conserved quantities with respect to a reference spacetime with a cosmological constant. We follow the approach developed by the authors in [25,26,7] and define the quasi-local energy as differences of surface Hamiltonians. The ground state for the gravitational energy is taken to be a reference configuration in the de Sitter (dS) or Anti-de Sitter (AdS) spacetime. This defines the quasi-local energy with respect to the reference spacetime and generalizes our previous definition with respect to the Minkowski spacetime. Through an optimal isometric embedding into the reference spacetime, the Killing fields of the reference spacetime are transplanted back to the surface in the physical spacetime to complete the definitions of quasi-local conserved quantities. We also compute how the corresponding total conserved quantities evolve under the Einstein equation with a cosmological constant.

 Title: Laser slowing of CaF molecules to near the capture velocity of a molecular MOT Authors: Hemmerling, Boerge; Chae, Eunmi; Ravi, Aakash; Anderegg, Loic; Drayna, Garrett K.; Hutzler, Nicholas R.; Collopy, Alejandra L.; Ye, Jun; Ketterle, Wolfgang; Doyle, John M. Publication: eprint arXiv:1603.02787 Publication Date: 03/2016 Origin: ARXIV Keywords: Physics - Atomic Physics Bibliographic Code: 2016arXiv160302787H

### Abstract

Laser slowing of CaF molecules down to the capture velocity of a magneto-optical trap (MOT) for molecules is achieved. Starting from a two-stage buffer gas beam source, we apply frequency-broadened "white-light" slowing and observe approximately 6x10^4 CaF molecules with velocities near 10\,m/s. CaF is a candidate for collisional studies in the mK regime. This work represents a significant step towards magneto-optical trapping of CaF.

 Title: New insulating low temperature phase in dense hydrogen: The phase diagram to 421 GPa Authors: Dias, Ranga; Noked, Ori; Silvera, Isaac F. Publication: eprint arXiv:1603.02162 Publication Date: 03/2016 Origin: ARXIV Keywords: Condensed Matter - Other Condensed Matter Bibliographic Code: 2016arXiv160302162D

### Abstract

In the quest to make metallic hydrogen at low temperatures a rich number of new phases have been found and the highest pressure ones have somewhat flat phase lines, around room temperature. We have studied hydrogen to static pressures of GPa in a diamond anvil cell and down to liquid helium temperatures, using infrared spectroscopy. We report a new phase at a pressure of GPa and T=5 K. Although we observe strong darkening of the sample in the visible, we have no evidence that this phase is metallic hydrogen.

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