Faculty Publications: March, 2014
Query Results from the Smithsonian/NASA Astrophysics Data System (ADS)
The following are Harvard Physics faculty members' publications, added to the ADS database last month. Please note that some publications which appeared in print last month may not be included in the database (and therefore may not appear on this list) until the following month.
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2014
Title: | Degree-scale Cosmic Microwave Background Polarization Measurements from Three Years of BICEP1 Data | |
Authors: | Barkats, D.; Aikin, R.; Bischoff, C.; Buder, I.; Kaufman, J. P.; Keating, B. G.; Kovac, J. M.;... and 27 coauthors | |
Publication: | The Astrophysical Journal, Volume 783, Issue 2, article id. 67, 18 pp. (2014). (ApJ Homepage) | |
Publication Date: | 03/2014 | |
Origin: | IOP | |
Astronomy Keywords: | cosmic background radiation, cosmology: observations, gravitational waves, inflation, polarization | |
DOI: | 10.1088/0004-637X/783/2/67 | |
Bibliographic Code: | 2014ApJ...783...67B |
Abstract
BICEP1 is a millimeter-wavelength telescope designed specifically to measure the inflationary B-mode polarization of the cosmic microwave background at degree angular scales. We present results from an analysis of the data acquired during three seasons of observations at the South Pole (2006-2008). This work extends the two-year result published in Chiang et al., with additional data from the third season and relaxed detector-selection criteria. This analysis also introduces a more comprehensive estimation of band power window functions, improved likelihood estimation methods, and a new technique for deprojecting monopole temperature-to-polarization leakage that reduces this class of systematic uncertainty to a negligible level. We present maps of temperature, E- and B-mode polarization, and their associated angular power spectra. The improvement in the map noise level and polarization spectra error bars are consistent with the 52% increase in integration time relative to Chiang et al. We confirm both self-consistency of the polarization data and consistency with the two-year results. We measure the angular power spectra at 21 <= l <= 335 and find that the EE spectrum is consistent with Lambda cold dark matter cosmology, with the first acoustic peak of the EE spectrum now detected at 15σ. The BB spectrum remains consistent with zero. From B-modes only, we constrain the tensor-to-scalar ratio to r = 0.03^{+0.27}_{-0.23}, or r < 0.70 at 95% confidence level.
Title: | Measuring Distances and Reddenings for a Billion Stars: Toward a 3D Dust Map from Pan-STARRS 1 | |
Authors: | Green, Gregory Maurice; Schlafly, Edward F.; Finkbeiner, Douglas P.; Jurić, Mario; Rix, Hans-Walter; Burgett, Will; Chambers, Kenneth C.; Draper, Peter W.; Flewelling, Heather; Kudritzki, Rolf Peter; Magnier, Eugene; Martin, Nicolas; Metcalfe, Nigel; Tonry, John; Wainscoat, Richard; Waters, Christopher | |
Publication: | The Astrophysical Journal, Volume 783, Issue 2, article id. 114, 16 pp. (2014). (ApJ Homepage) | |
Publication Date: | 03/2014 | |
Origin: | IOP | |
Astronomy Keywords: | dust, extinction, Galaxy: structure, ISM: structure, methods: statistical, stars: distances | |
DOI: | 10.1088/0004-637X/783/2/114 | |
Bibliographic Code: | 2014ApJ...783..114G |
Abstract
We present a method to infer reddenings and distances to stars based only on their broad-band photometry, and show how this method can be used to produce a three-dimensional (3D) dust map of the Galaxy. Our method samples from the full probability density function of distance, reddening, and stellar type for individual stars, as well as the full uncertainty in reddening as a function of distance in the 3D dust map. We incorporate prior knowledge of the distribution of stars in the Galaxy and the detection limits of the survey. For stars in the Pan-STARRS 1 (PS1) 3π survey, we demonstrate that our reddening estimates are unbiased and accurate to ~0.13 mag in E(B - V) for the typical star. Based on comparisons with mock catalogs, we expect distances for main-sequence stars to be constrained to within ~20%-60%, although this range can vary, depending on the reddening of the star, the precise stellar type, and its position on the sky. A later paper will present a 3D map of dust over the three quarters of the sky surveyed by PS1. Both the individual stellar inferences and the 3D dust map will enable a wealth of Galactic science in the plane. The method we present is not limited to the passbands of the PS1 survey but may be extended to incorporate photometry from other surveys, such as the Two Micron All Sky Survey, the Sloan Digital Sky Survey (where available), and in the future, LSST and Gaia.
Title: | Charge-exchange Coupling between Pickup Ions across the Heliopause and its Effect on Energetic Neutral Hydrogen Flux | |
Authors: | Zirnstein, E. J.; Heerikhuisen, J.; Zank, G. P.; Pogorelov, N. V.; McComas, D. J.; Desai, M. I. | |
Publication: | The Astrophysical Journal, Volume 783, Issue 2, article id. 129, 8 pp. (2014). (ApJ Homepage) | |
Publication Date: | 03/2014 | |
Origin: | IOP | |
Astronomy Keywords: | ISM: atoms, ISM: bubbles, methods: numerical, solar wind, Sun: heliosphere | |
DOI: | 10.1088/0004-637X/783/2/129 | |
Bibliographic Code: | 2014ApJ...783..129Z |
Abstract
Pickup ions (PUIs) appear to play an integral role in the multi-component nature of the plasma in the interaction between the solar wind (SW) and local interstellar medium (LISM). Three-dimensional (3D) MHD simulations with a kinetic treatment for neutrals and PUIs are currently still not viable. In light of recent energetic neutral atom (ENA) observations by the Interstellar Boundary EXplorer, the purpose of this paper is to illustrate the complex coupling between PUIs across the heliopause (HP) as facilitated by ENAs using estimates of PUI properties extracted from a 3D MHD simulation of the SW-LISM interaction with kinetic neutrals. First, we improve upon the multi-component treatment of the inner heliosheath (IHS) plasma from Zank et al. by including the extinction of PUIs through charge-exchange. We find a significant amount of energy is transferred away from hot, termination shock-processed PUIs into a colder, "freshly injected" PUI population. Second, we extend the multi-component approach to estimate ENA flux from the outer heliosheath (OHS), formed from charge-exchange between interstellar hydrogen atoms and energetic PUIs. These PUIs are formed from ENAs in the IHS that crossed the HP and experienced charge-exchange. Our estimates, based on plasma-neutral simulations of the SW-LISM interaction and a post-processing analysis of ENAs and PUIs, suggest the majority of flux visible at 1 AU from the front of the heliosphere, between ~0.02 and 10 keV, originates from OHS PUIs, indicating strong coupling between the IHS and OHS plasmas through charge-exchange.
Title: | Improving dopant incorporation during femtosecond-laser doping of Si with a Se thin-film dopant precursor | |
Authors: | Smith, Matthew J.; Sher, Meng-Ju; Franta, Benjamin; Lin, Yu-Ting; Mazur, Eric; Gradečak, Silvija | |
Publication: | Applied Physics A, Volume 114, Issue 4, pp.1009-1016 (ApPhA Homepage) | |
Publication Date: | 03/2014 | |
Origin: | SPRINGER | |
Abstract Copyright: | (c) 2014: Springer-Verlag Berlin Heidelberg | |
DOI: | 10.1007/s00339-013-7673-8 | |
Bibliographic Code: | 2014ApPhA.114.1009S |
Abstract
We study the dopant incorporation processes during thin-film fs-laser doping of Si and tailor the dopant distribution through optimization of the fs-laser irradiation conditions. Scanning electron microscopy, transmission electron microscopy, and profilometry are used to study the interrelated dopant incorporation and surface texturing mechanisms during fs-laser irradiation of Si coated with a Se thin-film dopant precursor. We show that the crystallization of Se-doped Si and micrometer-scale surface texturing are closely coupled and produce a doped surface that is not conducive to device fabrication. Next, we use this understanding of the dopant incorporation process to decouple dopant crystallization from surface texturing by tailoring the irradiation conditions. A low-fluence regime is identified in which a continuous surface layer of doped crystalline material forms in parallel with laser-induced periodic surface structures over many laser pulses. This investigation demonstrates the ability to tailor the dopant distribution through a systematic investigation of the relationship between fs-laser irradiation conditions, microstructure, and dopant distribution.
Title: | Deformations with Maximal Supersymmetries Part 1: On-shell Formulation | |
Authors: | Chang, Chi-Ming; Lin, Ying-Hsuan; Wang, Yifan; Yin, Xi | |
Publication: | eprint arXiv:1403.0545 | |
Publication Date: | 03/2014 | |
Origin: | ARXIV | |
Keywords: | High Energy Physics - Theory, Mathematical Physics | |
Comment: | 58 pages, new references are added | |
Bibliographic Code: | 2014arXiv1403.0545C |
Abstract
We study deformations of maximally supersymmetric gauge theories by higher dimensional operators in various spacetime dimensions. We classify infinitesimal deformations that preserve all 16 supersymmetries, while allowing the possibility of breaking either Lorentz or R-symmetry, using an on-shell algebraic method developed by Movshev and Schwarz. We also consider the problem of extending the deformation beyond the first order.
Title: | Dark Matter as a Trigger for Periodic Comet Impacts | |
Authors: | Randall, Lisa; Reece, Matthew | |
Publication: | eprint arXiv:1403.0576 | |
Publication Date: | 03/2014 | |
Origin: | ARXIV | |
Keywords: | Astrophysics - Galaxy Astrophysics, Astrophysics - Earth and Planetary Astrophysics | |
Comment: | Accepted by Physical Review Letters. 4 figures, no dinosaurs | |
Bibliographic Code: | 2014arXiv1403.0576R |
Abstract
Although statistical evidence is not overwhelming, possible support for an approximately 35 million year periodicity in the crater record on Earth could indicate a nonrandom underlying enhancement of meteorite impacts at regular intervals. A proposed explanation in terms of tidal effects on Oort cloud comet perturbations as the Solar System passes through the galactic midplane is hampered by lack of an underlying cause for sufficiently enhanced gravitational effects over a sufficiently short time interval and by the time frame between such possible enhancements. We show that a smooth dark disk in the galactic midplane would address both these issues and create a periodic enhancement of the sort that has potentially been observed. Such a disk is motivated by a novel dark matter component with dissipative cooling that we considered in earlier work. We show how to evaluate the statistical evidence for periodicity by input of appropriate measured priors from the galactic model, justifying or ruling out periodic cratering with more confidence than by evaluating the data without an underlying model. We find that, marginalizing over astrophysical uncertainties, the likelihood ratio for such a model relative to one with a constant cratering rate is 3.0, which moderately favors the dark disk model. Our analysis furthermore yields a posterior distribution that, based on current crater data, singles out a dark matter disk surface density of approximately 10 solar masses per square parsec. The geological record thereby motivates a particular model of dark matter that will be probed in the near future.
Title: | Interferometric probes of many-body localization | |
Authors: | Serbyn, M.; Knap, M.; Gopalakrishnan, S.; Papić, Z.; Yao, N. Y.; Laumann, C. R.; Abanin, D. A.; Lukin, M. D.; Demler, E. A. | |
Publication: | eprint arXiv:1403.0693 | |
Publication Date: | 03/2014 | |
Origin: | ARXIV | |
Keywords: | Condensed Matter - Disordered Systems and Neural Networks, Condensed Matter - Quantum Gases, Condensed Matter - Statistical Mechanics | |
Comment: | 5 pages, 4 figures | |
Bibliographic Code: | 2014arXiv1403.0693S |
Abstract
We propose a method for detecting many-body localization (MBL) in disordered spin systems. The method involves pulsed, coherent spin manipulations that probe the dephasing of a given spin due to its entanglement with a set of distant spins. It allows one to distinguish the MBL phase from a non-interacting localized phase and a delocalized phase. In particular, we show that for a properly chosen pulse sequence the MBL phase exhibits a characteristic power-law decay reflecting its slow growth of entanglement. We find that this power-law decay is robust with respect to thermal and disorder averaging, provide numerical simulations supporting our results, and discuss possible experimental realizations in solid-state and cold atom systems.
Title: | Deformations with Maximal Supersymmetries Part 2: Off-shell Formulation | |
Authors: | Chang, Chi-Ming; Lin, Ying-Hsuan; Wang, Yifan; Yin, Xi | |
Publication: | eprint arXiv:1403.0709 | |
Publication Date: | 03/2014 | |
Origin: | ARXIV | |
Keywords: | High Energy Physics - Theory | |
Comment: | 36 pages, new references are added | |
Bibliographic Code: | 2014arXiv1403.0709C |
Abstract
Continuing our exploration of maximally supersymmetric gauge theories (MSYM) deformed by higher dimensional operators, in this paper we consider an off-shell approach based on pure spinor superspace and focus on constructing supersymmetric deformations beyond the first order. In particular, we give a construction of the Batalin-Vilkovisky action of an all-order non-Abelian Born-Infeld deformation of MSYM in the non-minimal pure spinor formalism. We also discuss subtleties in the integration over the pure spinor superspace and the relevance of Berkovits-Nekrasov regularization.
Title: | Combined analysis of $\nu_{\mu}$ disappearance and $\nu_{\mu} \rightarrow \nu_{e}$ appearance in MINOS using accelerator and atmospheric neutrinos | |
Authors: | MINOS Collaboration; Adamson, P.; Anghel, I.; Aurisano, A.;... Feldman, G. J.;... ; and 109 coauthors | |
Publication: | eprint arXiv:1403.0867 | |
Publication Date: | 03/2014 | |
Origin: | ARXIV | |
Keywords: | High Energy Physics - Experiment, High Energy Physics - Phenomenology | |
Comment: | 6 pages, 2 figures | |
Bibliographic Code: | 2014arXiv1403.0867M |
Abstract
We report on a new analysis of neutrino oscillations in MINOS using the complete set of accelerator and atmospheric data. The analysis combines the $\nu_{\mu}$ disappearance and $\nu_{e}$ appearance data using the three-flavor formalism. We measure $|\Delta m^{2}_{32}|=[2.28-2.46]\times10^{-3}\mbox{\,eV}^{2}$ (68% C.L.) and $\sin^{2}\theta_{23}=0.35-0.65$ (90% C.L.) in the normal hierarchy, and $|\Delta m^{2}_{32}|=[2.32-2.53]\times10^{-3}\mbox{\,eV}^{2}$ (68% C.L.) and $\sin^{2}\theta_{23}=0.34-0.67$ (90% C.L.) in the inverted hierarchy. The data also constrain $\delta_{CP}$, the $\theta_{23}$ octant degeneracy and the mass hierarchy; we disfavor 36% (11%) of this three-parameter space at 68% (90%) C.L.
Title: | Effective field theory and keV lines from dark matter | |
Authors: | Krall, Rebecca; Reece, Matthew; Roxlo, Thomas | |
Publication: | eprint arXiv:1403.1240 | |
Publication Date: | 03/2014 | |
Origin: | ARXIV | |
Keywords: | High Energy Physics - Phenomenology | |
Bibliographic Code: | 2014arXiv1403.1240K |
Abstract
We survey operators that can lead to a keV photon line from dark matter decay or annihilation. We are motivated in part by recent claims of an unexplained 3.5 keV line in galaxy clusters and in Andromeda, but our results could apply to any hypothetical line observed in this energy range. We find that given the amount of flux that is observable, explanations in terms of decay are more plausible than annihilation, at least if the annihilation is directly to Standard Model states rather than intermediate particles. The decay case can be explained by a scalar or pseudoscalar field coupling to photons suppressed by a scale not far below the reduced Planck mass, which can be taken as a tantalizing hint of high-scale physics. The scalar case is particularly interesting from the effective field theory viewpoint, and we discuss it at some length. Because of a quartically divergent mass correction, naturalness strongly suggests the theory should be cut off at or below the 1000 TeV scale. The most plausible such natural UV completion would involve supersymmetry. These bottom-up arguments reproduce expectations from top-down considerations of the physics of moduli. A keV line could also arise from the decay of a sterile neutrino, in which case a renormalizable UV completion exists and no direct inference about high-scale physics is possible.
Title: | Extremal Bundles on Calabi-Yau Threefolds | |
Authors: | Gao, Peng; He, Yang-Hui; Yau, Shing-Tung | |
Publication: | eprint arXiv:1403.1268 | |
Publication Date: | 03/2014 | |
Origin: | ARXIV | |
Keywords: | High Energy Physics - Theory, Mathematics - Algebraic Geometry | |
Comment: | 49 pages, 24 figures; minor errors corrected | |
Bibliographic Code: | 2014arXiv1403.1268G |
Abstract
We study constructions of stable holomorphic vector bundles on Calabi-Yau threefolds, especially those with exact anomaly cancellation which we call extremal. By going through the known databases we find that such examples are rare in general and can be ruled out for the spectral cover construction for all elliptic threefolds. We then introduce a generalized version of Hartshorne-Serre construction and use it to yield extremal bundles of general ranks and study their geometry. In light of this probing the geometry of the space of stable vector bundles, we revisit the DRY conjecture on stable reflexive sheaves while focusing on the distribution of Chern numbers to use both theoretical and statistical ideas to provide evidence for DRY.
Title: | Tunable Fractional Quantum Hall Phases in Bilayer Graphene | |
Authors: | Maher, Patrick; Wang, Lei; Gao, Yuanda; Forsythe, Carlos; Taniguchi, Takashi; Watanabe, Kenji; Abanin, Dmitry; Papić, Zlatko; Cadden-Zimansky, Paul; Hone, James; Kim, Philip; Dean, Cory R. | |
Publication: | eprint arXiv:1403.2112 | |
Publication Date: | 03/2014 | |
Origin: | ARXIV | |
Keywords: | Condensed Matter - Mesoscale and Nanoscale Physics | |
Bibliographic Code: | 2014arXiv1403.2112M |
Abstract
Symmetry breaking in a quantum system often leads to complex emergent behavior. In bilayer graphene (BLG), an electric field applied perpendicular to the basal plane breaks the inversion symmetry of the lattice, opening a band gap at the charge neutrality point. In a quantizing magnetic field electron interactions can cause spontaneous symmetry breaking within the spin and valley degrees of freedom, resulting in quantum Hall states (QHS) with complex order. Here we report fractional quantum Hall states (FQHS) in bilayer graphene which show phase transitions that can be tuned by a transverse electric field. This result provides a model platform to study the role of symmetry breaking in emergent states with distinct topological order.
Title: | Measurement of the ZZ production cross section using the full CDF II data set | |
Authors: | CDF Collaboration; Aaltonen, T.; Amerio, S.; Amidei, D.;... Franklin, M.;... Guimaraes da Costa, J.;... and 402 coauthors | |
Publication: | eprint arXiv:1403.2300 | |
Publication Date: | 03/2014 | |
Origin: | ARXIV | |
Keywords: | High Energy Physics - Experiment | |
Comment: | 13 pages, 7 figures. To be submitted to Phys. Rev. D | |
Bibliographic Code: | 2014arXiv1403.2300C |
Abstract
We present a measurement of the ZZ boson-pair production cross section in 1.96 TeV center-of-mass energy ppbar collisions. We reconstruct final states incorporating four charged leptons or two charged leptons and two neutrinos from the full data set collected by the Collider Detector experiment at the Fermilab Tevatron, corresponding to 9.7 fb-1 of integrated luminosity. Combining the results obtained from each final state, we measure a cross section of 1.04(+0.32)(-0.25) pb, in good agreement with the standard model prediction at next-to-leading order in the strong-interaction coupling.
Title: | Revealing topological superconductivity in extended quantum spin Hall Josephson junctions | |
Authors: | Lee, Shu-Ping; Michaeli, Karen; Alicea, Jason; Yacoby, Amir | |
Publication: | eprint arXiv:1403.2747 | |
Publication Date: | 03/2014 | |
Origin: | ARXIV | |
Keywords: | Condensed Matter - Superconductivity, Condensed Matter - Mesoscale and Nanoscale Physics | |
Comment: | 8 pages, 6 figures | |
Bibliographic Code: | 2014arXiv1403.2747L |
Abstract
Quantum spin Hall-superconductor hybrids are promising sources of topological superconductivity and Majorana modes, particularly given recent progress on HgTe and InAs/GaSb. We propose a new method of revealing topological superconductivity in extended quantum spin Hall Josephson junctions supporting `fractional Josephson currents'. Specifically, we show that as one threads magnetic flux between the superconductors, the critical current traces an interference pattern featuring sharp fingerprints of topological superconductivity---even when noise spoils parity conservation.
Title: | Gravity Waves from Extreme-Mass-Ratio Plunges into Kerr Black Holes | |
Authors: | Hadar, Shahar; Porfyriadis, Achilleas P.; Strominger, Andrew | |
Publication: | eprint arXiv:1403.2797 | |
Publication Date: | 03/2014 | |
Origin: | ARXIV | |
Keywords: | High Energy Physics - Theory, General Relativity and Quantum Cosmology | |
Comment: | 20 pages, 1 figure | |
Bibliographic Code: | 2014arXiv1403.2797H |
Abstract
Massive objects orbiting a near-extreme Kerr black hole quickly plunge into the horizon after passing the innermost stable circular orbit. The plunge trajectory is shown to be related by a conformal map to a circular orbit. Conformal symmetry of the near-horizon region is then used to compute the gravitational radiation produced during the plunge phase.
Title: | Atomically thin p-n junctions with van der Waals heterointerfaces | |
Authors: | Lee, Chul-Ho; Lee, Gwan-Hyoung; van der Zande, Arend M.; Chen, Wenchao; Li, Yilei; Han, Minyong; Cui, Xu; Arefe, Ghidewon; Nuckolls, Colin; Heinz, Tony F.; Guo, Jing; Hone, James; Kim, Philip | |
Publication: | eprint arXiv:1403.3062 | |
Publication Date: | 03/2014 | |
Origin: | ARXIV | |
Keywords: | Condensed Matter - Mesoscale and Nanoscale Physics | |
Comment: | 29 pages, 3 figures in main & 10 figures in supplementary information | |
Bibliographic Code: | 2014arXiv1403.3062L |
Abstract
Semiconductor p-n junctions are essential building blocks for modern electronics and optoelectronics. In conventional semiconductors, a p-n junction produces depletion regions of free charge carriers at equilibrium and built-in potentials associated with uncompensated dopant atoms. Carrier transport across the junction occurs by diffusion and drift processes defined by the spatial extent of this region. With the advent of atomically thin van der Waals (vdW) materials and their heterostructures, we are now able to realize a p-n junction at the ultimate quantum limit. In particular, vdW junctions composed of p- and n-type semiconductors each just one unit cell thick are predicted to exhibit completely different charge transport characteristics than bulk junctions. Here we report the electronic and optoelectronic characterization of atomically thin p-n heterojunctions fabricated using vdW assembly of transition metal dichalcogenides (TMDCs). Across the p-n interface, we observe gate-tuneable diode-like current rectification and photovoltaic response. We find that the tunnelling-assisted interlayer recombination of the majority carriers is responsible for the tunability of the electronic and optoelectronic processes. Sandwiching an atomic p-n junction between graphene layers enhances collection of the photoexcited carriers. The atomically scaled vdW p-n heterostructures presented here constitute the ultimate quantum limit for functional electronic and optoelectronic components.
Title: | A Large Catalog of Accurate Distances to Molecular Clouds from PS1 Photometry | |
Authors: | Schlafly, E. F.; Green, G.; Finkbeiner, D. P.; Rix, H.-W.; Bell, E. F.; Burgett, W. S.; Chambers, K. C.; Draper, P. W.; Hodapp, K. W.; Kaiser, N.; Magnier, E. A.; Martin, N. F.; Metcalfe, N.; Price, P. A.; Tonry, J. L. | |
Publication: | eprint arXiv:1403.3393 | |
Publication Date: | 03/2014 | |
Origin: | ARXIV | |
Keywords: | Astrophysics - Galaxy Astrophysics | |
Comment: | 16 pages, 4 figures | |
Bibliographic Code: | 2014arXiv1403.3393S |
Abstract
Distance measurements to molecular clouds are important, but are often made separately for each cloud of interest, employing very different different data and techniques. We present a large, homogeneous catalog of distances to molecular clouds, most of which are of unprecedented accuracy. We determine distances using optical photometry of stars along lines of sight toward these clouds, obtained from PanSTARRS-1. We simultaneously infer the reddenings and distances to these stars, tracking the full probability distribution function using a technique presented in Green et al. (2014). We fit these star-by-star measurements using a simple dust screen model to find the distance to each cloud. We thus estimate the distances to almost all of the clouds in the Magnani et al. (1985) catalog, as well as many other well-studied clouds, including Orion, Perseus, Taurus, Cepheus, Polaris, California, and Monoceros R2, avoiding only the inner Galaxy. Typical statistical uncertainties in the distances are 5%, though the systematic uncertainty stemming from the quality of our stellar models is about 10%. The resulting catalog is the largest catalog of accurate, directly-measured distances to molecular clouds. Our distance estimates are generally consistent with available distance estimates from the literature, though in some cases the literature estimates are off by a factor of more than two.
Title: | Are non-Fermi-liquids stable to Cooper pairing? | |
Authors: | Metlitski, Max A.; Mross, David F.; Sachdev, Subir; Senthil, T. | |
Publication: | eprint arXiv:1403.3694 | |
Publication Date: | 03/2014 | |
Origin: | ARXIV | |
Keywords: | Condensed Matter - Strongly Correlated Electrons | |
Comment: | 16 pages, 7 figures | |
Bibliographic Code: | 2014arXiv1403.3694M |
Abstract
States of matter with a sharp Fermi-surface but no well-defined Landau quasiparticles arise in a number of physical systems. Examples include: ${\it (i)}$ quantum critical points associated with the onset of order in metals; ${\it (ii)}$ spinon Fermi-surface (U(1) spin-liquid) state of a Mott insulator; ${\it (iii)}$ Halperin-Lee-Read composite fermion charge liquid state of a half-filled Landau level. In this work, we use renormalization group techniques to investigate possible instabilities of such non-Fermi-liquids in two spatial dimensions to Cooper pairing. We consider the Ising-nematic quantum critical point as an example of a phase transition in a metal, and demonstrate that the attractive interaction mediated by the order parameter fluctuations always leads to a superconducting instability. Moreover, in the regime where our calculation is controlled, superconductivity preempts the destruction of electronic quasiparticles. On the other hand, the spinon Fermi-surface and the Halperin-Lee-Read states are stable against Cooper pairing for a sufficiently weak attractive short-range interaction; however, once the strength of attraction exceeds a critical value, pairing sets in. We describe the ensuing quantum phase transition between ${\it (i)}$ $U(1)$ and $Z_2$ spin-liquid states; ${\it (ii)}$ Halperin-Lee-Read and Moore-Read states.
Title: | BICEP2 I: Detection Of B-mode Polarization at Degree Angular Scales | |
Authors: | BICEP2 Collaboration; Ade, P. A. R; Aikin, R. W.; Barkats, D.; Benton, S. J.;... Kovac, J. M.;... and 43 coauthors | |
Publication: | eprint arXiv:1403.3985 | |
Publication Date: | 03/2014 | |
Origin: | ARXIV | |
Keywords: | Astrophysics - Cosmology and Extragalactic Astrophysics, General Relativity and Quantum Cosmology, High Energy Physics - Phenomenology, High Energy Physics - Theory | |
Comment: | 19 pages, 14 figures | |
Bibliographic Code: | 2014arXiv1403.3985B |
Abstract
We report results from the BICEP2 experiment, a Cosmic Microwave Background (CMB) polarimeter specifically designed to search for the signal of inflationary gravitational waves in the B-mode power spectrum around l=80. The telescope comprised a 26 cm aperture all-cold refracting optical system equipped with a focal plane of 512 antenna coupled transition edge sensor (TES) 150 GHz bolometers each with temperature sensitivity of approx. 300 uk.sqrt(s). BICEP2 observed from the South Pole for three seasons from 2010 to 2012. A low-foreground region of sky with an effective area of 380 square degrees was observed to a depth of 87 nK-degrees in Stokes Q and U. In this paper we describe the observations, data reduction, maps, simulations and results. We find an excess of B-mode power over the base lensed-LCDM expectation in the range 30<l<150, inconsistent with the null hypothesis at a significance of $>5\sigma$. Through jackknife tests and simulations based on detailed calibration measurements we show that systematic contamination is much smaller than the observed excess. We also estimate potential foreground signals and find that available models predict these to be considerably smaller than the observed signal. These foreground models possess no significant cross-correlation with our maps. Additionally, cross-correlating BICEP2 against 100 GHz maps from the BICEP1 experiment, the excess signal is confirmed with $3\sigma$ significance and its spectral index is found to be consistent with that of the CMB, disfavoring synchrotron or dust at $2.3\sigma$ and $2.2\sigma$, respectively. The observed B-mode power spectrum is well-fit by a lensed-LCDM + tensor theoretical model with tensor/scalar ratio $r=0.20^{+0.07}_{-0.05}$, with r=0 disfavored at $7.0\sigma$. Subtracting the best available estimate for foreground dust modifies the likelihood slightly so that r=0 is disfavored at $5.9\sigma$.
Title: | Kramers Pairs of Majorana Fermions and Parafermions in Fractional Topological Insulators | |
Authors: | Klinovaja, Jelena; Yacoby, Amir; Loss, Daniel | |
Publication: | eprint arXiv:1403.4125 | |
Publication Date: | 03/2014 | |
Origin: | ARXIV | |
Keywords: | Condensed Matter - Mesoscale and Nanoscale Physics | |
Bibliographic Code: | 2014arXiv1403.4125K |
Abstract
We propose a scheme based on topological insulators to generate Kramers pairs of Majorana fermions or parafermions in the complete absence of magnetic fields. Our setup consists of two topological insulators whose edge states are brought close to an s-wave superconductor. The resulting proximity effect leads to an interplay between a non-local crossed Andreev pairing, which is dominant in the strong electron-electron interaction regime, and usual superconducting pairing, which is dominant at large separation between the two topological insulator edges. As a result, there are zero-energy bound states localized at interfaces between spatial regions dominated by the two different types of pairing. Due to the preserved time-reversal symmetry, the bound states come in Kramers pairs. If the topological insulators carry fractional edge states, the zero-energy bound states are parafermions, otherwise, they are Majorana fermions.
Title: | Multi-epoch spectropolarimetry of SN 2009ip: direct evidence for aspherical circumstellar material | |
Authors: | Mauerhan, Jon C.; Williams, G. Grant; Smith, Nathan; Smith, Paul S.; Filippenko, Alexei V.; Hoffman, Jennifer L.; Leonard, Douglas C.; Milne, Peter; Clubb, Kelsey I.; Fox, Ori D.; Kelly, Patrick L. | |
Publication: | eprint arXiv:1403.4240 | |
Publication Date: | 03/2014 | |
Origin: | ARXIV | |
Keywords: | Astrophysics - Solar and Stellar Astrophysics, Astrophysics - Galaxy Astrophysics | |
Comment: | submitted to MNRAS 2014 March 16. 15 pages, 10 figures | |
Bibliographic Code: | 2014arXiv1403.4240M |
Abstract
We present spectropolarimetry of SN 2009ip throughout the evolution of its 2012 explosion. During the initial 2012a phase, when the source spectrum exhibits broad P-Cygni lines, we measure a V-band polarization of P~0.9% at a position angle of ~166 deg, indicating substantial asphericity for the 2012a outflow. Near the subsequent peak of the 2012b phase, when the spectrum shows signs of intense interaction with circumstellar material (CSM), we measure P~1.7% at a position angle of 72 deg, indicating a separate physical component of polarization, which has a higher degree of asphericity than the 2012a outflow and an orthogonal axis of symmetry on the sky. Around 30 days past peak, which is coincident with a bump in the declining light curve, we measure P~0.7% and significant variations in P across some broad lines, particularly HeI/NaI. By 60 days past peak the source appears to be approaching a low value of interstellar polarization (P<0.2%). The results are consistent with a scenario in which a potentially bipolar explosion during 2012a impacts a toroidal distribution of CSM, thereby causing the 2012b brightening. Orthogonality between the 2012a and 2012b geometries is inconsistent with the hypothesis that the 2012a event launched the CSM that was hit 40 days later by material from the 2012b event. Rather, the aspherical CSM probably has a separate origin associated with the outbursts of the stellar progenitor during prior years. Previous calculations that assumed spherical symmetry for the CSM have underestimated the required explosion energy, as the results suggest that <10% of the fast SN ejecta participated in strong CSM interaction during the 2012b phase. In light of the spectropolarimetric results, a kinetic energy of 1e51 erg for the ejecta is difficult to avoid, supporting the interpretation that the 2012 outburst was the result of a core-collapse supernova explosion (abridged).
Title: | Stabilizing the false vacuum: Mott skyrmions | |
Authors: | Kanász-Nagy, Márton; Dóra, Balázs; Demler, Eugene A.; Zaránd, Gergely | |
Publication: | eprint arXiv:1403.4242 | |
Publication Date: | 03/2014 | |
Origin: | ARXIV | |
Keywords: | Condensed Matter - Quantum Gases, Physics - Atomic Physics, Quantum Physics | |
Comment: | 11 pages, 6 figures | |
Bibliographic Code: | 2014arXiv1403.4242K |
Abstract
Topological excitations keep fascinating physicists since many decades. While individual vortices and solitons emerge and have been observed in many areas of physics, their most intriguing higher dimensional topological relatives, skyrmions (smooth, topologically stable textures) and magnetic monopoles -- emerging almost necessarily in any grand unified theory and responsible for charge quantization -- remained mostly elusive. Here we propose that loading a three-component nematic superfluid such as $^{23}$Na into a deep optical lattice and thereby creating an insulating core, one can create topologically stable skyrmion textures and investigate their properties in detail. We show furthermore that the spectrum of the excitations of the superfluid and their quantum numbers change dramatically in the presence of the skyrmion, and they reflect the presence of a trapped monopole, as imposed by the skyrmion's topology.
Title: | BICEP2 II: Experiment and Three-Year Data Set | |
Authors: | BICEP2 Collaboration; Ade, P. A. R; Aikin, R. W.; Amiri, M.;... Kovac, J. M.;... and 47 coauthors | |
Publication: | eprint arXiv:1403.4302 | |
Publication Date: | 03/2014 | |
Origin: | ARXIV | |
Keywords: | Astrophysics - Cosmology and Nongalactic Astrophysics, Astrophysics - Instrumentation and Methods for Astrophysics | |
Comment: | 29 pages, 24 figures | |
Bibliographic Code: | 2014arXiv1403.4302B |
Abstract
The BICEP2 instrument was designed to measure the polarization of the cosmic microwave background (CMB) on angular scales of 1 to 5 degrees ($\ell$=40-200), near the expected peak of the B-mode polarization signature of primordial gravitational waves from cosmic inflation. Measuring B-modes requires dramatic improvement in sensitivity combined with exquisite control of systematics. We have built on the successful strategy of BICEP1, which achieved the most sensitive limit on B-modes at these scales. The telescope had a 26 cm aperture and cold, on-axis, refractive optics, and it observed from a three-axis mount at the South Pole. BICEP2 adopted a new detector design in which beam-defining slot antenna arrays couple to transition-edge sensor (TES) bolometers, all fabricated monolithically on a common substrate. BICEP2 took advantage of this design's scalable fabrication and multiplexed SQUID readout to field more detectors than BICEP1, improving mapping speed by more than a factor of ten. In this paper we report on the design and performance of the instrument and on the three-year data set. BICEP2 completed three years of observation with 500 detectors at 150 GHz. After optimization of detector and readout parameters BICEP2 achieved an instrument noise equivalent temperature of 15.8 $\mu$K sqrt(s) and the full data set reached Stokes Q and U map depths of 87.8 nK in square-degree pixels (5.3 $\mu$K arcmin) over an effective area of 390.3 square degrees within a 1000 square degree field. These are the deepest CMB polarization maps at degree angular scales.
Title: | Multiple Scattering and Plasmon Resonance in the Intermediate Regime | |
Authors: | Liu, Bo; Heller, Eric J. | |
Publication: | eprint arXiv:1403.4310 | |
Publication Date: | 03/2014 | |
Origin: | ARXIV | |
Keywords: | Condensed Matter - Mesoscale and Nanoscale Physics, Physics - Optics | |
Bibliographic Code: | 2014arXiv1403.4310L |
Abstract
The collective excitation of the conduction electrons in subwavelength structures gives rise to the Localized Surface Plasmon(LSP). The system consisting of two such LSPs, known as the dimer system,is of fundamental interest and is being actively investigated in the literature. Three regimes have been previously identified and they are the photonic regime, the strong coupling regime and the quantum tunneling regime. In this Letter, we propose a new regime for this intriguing systems, the intermediate regime. In this new regime, the quasistatic approximation, which is widely used to study such LSP systems, fails to capture the main physics: the multiple scattering of the electromagnetic waves between the two LSPs, which significantly modifies the properties of the resonant modes in the system. This intermediate regime provides a new route to explore in plasmonics, where controlling both the excited plasmon modes and the damping rates are of paramount significance.
Title: | Phase diagram and excitations of a Shiba molecule | |
Authors: | Yao, N. Y.; Moca, C. P.; Weymann, I.; Sau, J. D.; Lukin, M. D.; Demler, E. A.; Zaránd, G. | |
Publication: | eprint arXiv:1403.4611 | |
Publication Date: | 03/2014 | |
Origin: | ARXIV | |
Keywords: | Condensed Matter - Superconductivity, Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Strongly Correlated Electrons | |
Comment: | 13 pages, 7 figures | |
Bibliographic Code: | 2014arXiv1403.4611Y |
Abstract
We analyze the phase diagram associated with a pair of magnetic impurities trapped in a superconducting host. The natural interplay between Kondo screening, superconductivity and exchange interactions leads to a rich array of competing phases, whose transitions are characterized by discontinuous changes of the total spin. Our analysis is based on a combination of numerical renormalization group techniques as well as semi-classical analytics. In addition to the expected screened and unscreened phases, we observe a new molecular doublet phase where the impurity spins are only partially screened by a single extended quasiparticle. Direct signatures of the various Shiba molecule states can be observed via RF spectroscopy.
Title: | Bright and fast voltage reporters across the visible spectrum via electrochromic FRET (eFRET) | |
Authors: | Zou, Peng; Zhao, Yongxin; Douglass, Adam D.; Hochbaum, Daniel R.; Brinks, Daan; Werley, Christopher A.; Jed Harrison, D.; Campbell, Robert E.; Cohen, Adam E. | |
Publication: | eprint arXiv:1403.4636 | |
Publication Date: | 03/2014 | |
Origin: | ARXIV | |
Keywords: | Quantitative Biology - Biomolecules, Physics - Biological Physics, Quantitative Biology - Neurons and Cognition | |
Comment: | * Denotes equal contribution. For correspondence regarding the library screen: robert.e.campbell@ualberta.ca; For other correspondence: cohen@chemistry.harvard.edu | |
Bibliographic Code: | 2014arXiv1403.4636Z |
Abstract
We present a palette of brightly fluorescent genetically encoded voltage indicators (GEVIs) with excitation and emission peaks spanning the visible spectrum, sensitivities from 6 - 10% Delta F/F per 100 mV, and half-maximal response times from 1 - 7 ms. A fluorescent protein is fused to an Archaerhodopsin-derived voltage sensor. Voltage-induced shifts in the absorption spectrum of the rhodopsin lead to voltage-dependent nonradiative quenching of the appended fluorescent protein. Through a library screen, we identified linkers and fluorescent protein combinations which reported neuronal action potentials in cultured rat hippocampal neurons with a single-trial signal-to-noise ratio from 6.6 to 11.6 in a 1 kHz imaging bandwidth at modest illumination intensity. The freedom to choose a voltage indicator from an array of colors facilitates multicolor voltage imaging, as well as combination with other optical reporters and optogenetic actuators.
Title: | Non-global Logarithms at 3 Loops, 4 Loops, 5 Loops and Beyond | |
Authors: | Schwartz, Matthew D.; Zhu, Hua Xing | |
Publication: | eprint arXiv:1403.4949 | |
Publication Date: | 03/2014 | |
Origin: | ARXIV | |
Keywords: | High Energy Physics - Phenomenology, High Energy Physics - Theory | |
Comment: | 42 pages, 6 figures | |
Bibliographic Code: | 2014arXiv1403.4949S |
Abstract
We calculate the coefficients of the leading non-global logarithms for the hemisphere mass distribution analytically at 3, 4, and 5 loops at large Nc . We confirm that the integrand derived with the strong-energy-ordering approximation and fixed-order iteration of the Banfi-Marchesini-Syme (BMS) equation agree. Our calculation exploits a hidden PSL(2,R) symmetry associated with the jet directions, apparent in the BMS equation after a stereographic projection to the Poincare disk. The required integrals have an iterated form, leading to functions of uniform transcendentality. This allows us to extract the coefficients, and some functional dependence on the jet directions, by computing the symbols and coproducts of appropriate expressions involving classical and Goncharov polylogarithms. Convergence of the series to a numerical solution of the BMS equation is also discussed.
Title: | Measurements of Direct CP-Violating Asymmetries in Charmless Decays of Bottom Baryons | |
Authors: | CDF Collaboration; Aaltonen, T.; Amerio, S.; Amidei, D.;... Franklin, M.;... Guimaraes da Costa, J.;... and 402 coauthors | |
Publication: | eprint arXiv:1403.5586 | |
Publication Date: | 03/2014 | |
Origin: | ARXIV | |
Keywords: | High Energy Physics - Experiment | |
Comment: | 8 pages, 2 figures, 1 table. Submitted to Phys.Rev.Lett | |
Bibliographic Code: | 2014arXiv1403.5586C |
Abstract
We report final measurements of direct $\mathit{CP}$--violating asymmetries in charmless decays of neutral bottom hadrons to pairs of charged hadrons with the upgraded Collider Detector at the Fermilab Tevatron. Using the complete $\sqrt{s}=1.96$ TeV proton-antiproton collisions data set, corresponding to \mbox{9.3 fb$^{-1}$} of integrated luminosity, we measure $\mathcal{A}(\Lambda^0_b \rightarrow p\pi^{-}) = +0.06 \pm 0.07\mathrm{(stat)} \pm 0.03\mathrm{(syst)}$ and $\mathcal{A}(\Lambda^0_b \rightarrow pK^{-}) = -0.10 \pm 0.08\mathrm{(stat)} \pm 0.04\mathrm{(syst)}$, compatible with no asymmetry. In addition we measure the $\mathit{CP}$--violating asymmetries in $B^0_s \rightarrow K^{-}\pi^{+}$ and $B^0 \rightarrow K^{+}\pi^{-}$ decays to be $\mathcal{A}(B^0_s \rightarrow K^{-}\pi^{+}) = +0.22 \pm 0.07\mathrm{stat)} \pm 0.02\mathrm{(syst)}$ and $\mathcal{A}(B^0 \rightarrow K^{+}\pi^{-}) = -0.083\pm 0.013 \mathrm{(stat)} \pm 0.004\mathrm{(syst)}$, respectively, which are significantly different from zero and consistent with current world averages.
Title: | Hard-Soft-Collinear Factorization to All Orders | |
Authors: | Feige, Ilya; Schwartz, Matthew D. | |
Publication: | eprint arXiv:1403.6472 | |
Publication Date: | 03/2014 | |
Origin: | ARXIV | |
Keywords: | High Energy Physics - Phenomenology | |
Bibliographic Code: | 2014arXiv1403.6472F |
Abstract
We provide a precise statement of hard-soft-collinear factorization of scattering amplitudes and prove it to all orders in perturbation theory. Factorization is formulated as the equality at leading power of scattering amplitudes in QCD with other amplitudes in QCD computed from a product of operator matrix elements. The equivalence is regulator independent and gauge independent. As the formulation relates amplitudes to the same amplitudes with additional soft or collinear particles, it includes as special cases the factorization of soft currents and collinear splitting functions from generic matrix elements, both of which are shown to be process independent to all orders. We show that the overlapping soft-collinear region is naturally accounted for by vacuum matrix elements of kinked Wilson lines. Although the proof is self-contained, it combines techniques developed for the study of pinch surfaces, scattering amplitudes, and effective field theory.
Title: | Poisson metrics on flat vector bundles over non-compact curves | |
Authors: | Collins, Tristan C.; Jacob, Adam; Yau, Shing-Tung | |
Publication: | eprint arXiv:1403.7825 | |
Publication Date: | 03/2014 | |
Origin: | ARXIV | |
Keywords: | Mathematics - Differential Geometry | |
Comment: | 55 pages | |
Bibliographic Code: | 2014arXiv1403.7825C |
Abstract
Let (E,D,P) be a flat vector bundle with a parabolic structure over a punctured Riemann surface, (M,g). We consider a deformation of the harmonic metric equation which we call the Poisson metric equation. This equation arises naturally as the dimension reduction of the Hermitian-Yang-Mills equation for holomorphic vector bundles on K3 surfaces in the large complex structure limit. We define a notion of slope stability, and show that if the flat connection D has regular singularities, and the Riemannian metric g has finite volume then E admits a Poisson metric with asymptotics determined by the parabolic structure if and only if (E,D,P) is slope polystable.
Title: | Mass and lifetime measurements of bottom and charm baryons in $p\bar p$ collisions at $\sqrt{s}= 1.96 TeV | |
Authors: | CDF Collaboration; Aaltonen, T.; Amerio, S.; Amidei, D.;... Franklin, M.;... Guimaraes da Costa, J.;... and 402 coauthors | |
Publication: | eprint arXiv:1403.8126 | |
Publication Date: | 03/2014 | |
Origin: | ARXIV | |
Keywords: | High Energy Physics - Experiment | |
Bibliographic Code: | 2014arXiv1403.8126C |
Abstract
We report on mass and lifetime measurements of several ground state charmed and bottom baryons, using a data sample corresponding to 9.6 $\textrm{fb}^{-1}$ from $p\bar p$ collisions at $\sqrt{s}=1.96$ TeV, and recorded with the Collider Detector at Fermilab. Baryon candidates are reconstructed from data collected with an online event selection designed for the collection of long-lifetime heavy-flavor decay products and a second event selection designed to collect $J/\psi \rightarrow \mu^+ \, \mu^-$ candidates. First evidence for the process $\Omega_b^- \rightarrow \Omega_c^0 \, \pi^-$ is presented with a significance of $3.3\sigma$. We measure the following baryon masses: \begin{eqnarray} M(\Xi_c^{0}) = 2470.85\pm0.24(stat)\pm0.55(syst) \, MeV/c^2, \nonumber M(\Xi_c^{+}) = 2468.00\pm0.18(stat)\pm0.51(syst) \, MeV/c^2, \nonumber \\ M(\Lambda_b) = 5620.15\pm0.31(stat)\pm0.47(syst) \, MeV/c^2, \nonumber \\ M(\Xi_b^-) = 5793.4\pm1.8(stat)\pm0.7(syst) \, MeV/c^2, \nonumber \\ M(\Xi_b^0) = 5788.7\pm4.3(stat)\pm1.4(syst) \, MeV/c^2, \, and \nonumber \\ M(\Omega_b^-) = 6047.5\pm3.8(stat)\pm0.6(syst) \, MeV/c^2. \nonumber \end{eqnarray} The isospin splitting of the $\Xi_b^{-,0}$ states is found to be $M(\Xi_b^-)-M(\Xi_b^0)=4.7\pm4.7(stat)\pm0.7(syst)$ MeV/$c^2$. The isospin splitting of the $\Xi_c^{0,+}$ states is found to be $M(\Xi_c^0)-M(\Xi_c^+)$ = $2.85\pm0.30(stat)\pm0.04(syst)$ MeV/$c^2$. The following lifetime measurements are made: \begin{eqnarray} \tau(\Lambda_b) = 1.565\pm0.035(stat)\pm0.020(syst) \, ps, \nonumber \\ \tau(\Xi_b^-) = 1.32\pm0.14(stat)\pm0.02(syst) \, ps, \nonumber \\ \tau(\Omega_b^-) = 1.66^{+0.53}_{-0.40}(stat)\pm0.02(syst) \, ps. \nonumber \end{eqnarray}.
Title: | Generalized Cohomologies and Supersymmetry | |
Authors: | Tseng, Li-Sheng; Yau, Shing-Tung | |
Publication: | Communications in Mathematical Physics, Volume 326, Issue 3, pp.875-885 | |
Publication Date: | 03/2014 | |
Origin: | SPRINGER | |
Abstract Copyright: | (c) 2014: Springer-Verlag Berlin Heidelberg | |
DOI: | 10.1007/s00220-014-1895-2 | |
Bibliographic Code: | 2014CMaPh.326..875T |
Abstract
We show that the complex cohomologies of Bott, Chern, and Aeppli and the symplectic cohomologies of Tseng and Yau arise in the context of type II string theory. Specifically, they can be used to count a subset of scalar moduli fields in Minkowski compactification with RR fluxes in the presence of either O5/ D5 or O6/ D6 brane sources, respectively. Further, we introduce a new set of cohomologies within the generalized complex geometry framework which interpolate between these known complex and symplectic cohomologies. The generalized complex cohomologies play the analogous role for counting massless fields for a general supersymmetric Minkowski type II compactification with Ramond-Ramond flux.
Title: | Harmonically trapped two-atom systems: Interplay of short-range s-wave interaction and spin-orbit coupling | |
Authors: | Yin, X. Y.; Gopalakrishnan, S.; Blume, D. | |
Publication: | Physical Review A, Volume 89, Issue 3, id.033606 (PhRvA Homepage) | |
Publication Date: | 03/2014 | |
Origin: | APS | |
PACS Keywords: | Multicomponent condensates, spinor condensates, Fermion systems and electron gas, Boson systems, Multicomponent condensates, spinor condensates | |
Abstract Copyright: | 2014: American Physical Society | |
DOI: | 10.1103/PhysRevA.89.033606 | |
Bibliographic Code: | 2014PhRvA..89c3606Y |
Abstract
The coupling between the spin degrees of freedom and the orbital angular momentum has a profound effect on the properties of nuclei, atoms, and condensed-matter systems. Recently, synthetic gauge fields have been realized experimentally in neutral cold-atom systems, giving rise to a spin-orbit coupling term with "strength" kso. This paper investigates the interplay between the single-particle spin-orbit coupling term of Rashba type and the short-range two-body s-wave interaction for cold atoms under external confinement. Specifically, we consider two different harmonically trapped two-atom systems. The first system consists of an atom with spin-orbit coupling that interacts with a structureless particle through a short-range two-body potential. The second system consists of two atoms that both feel the spin-orbit coupling term and that interact through a short-range two-body potential. Treating the spin-orbit term perturbatively, we determine the correction to the ground-state energy for various generic parameter combinations. Selected excited states are also treated. An important aspect of our study is that the perturbative treatment is not limited to small s-wave scattering lengths but provides insights into the system behavior over a wide range of scattering lengths, including the strongly interacting unitary regime. We find that the interplay between the spin-orbit coupling term and the s-wave interaction generically enters, depending on the exact parameter combinations of the s-wave scattering lengths, at order kso2 or kso4 for the ground state and leads to a shift of the energy of either sign. While the absence of a term proportional to kso follows straightforwardly from the functional form of the spin-orbit coupling term, the absence of a term proportional to kso2 for certain parameter combinations is unexpected. The well-known fact that the spin-orbit coupling term couples the relative and center-of-mass degrees of freedom has interesting consequences for the trapped two-particle systems. For example, we find that, for certain parameter combinations, the spin-orbit coupling term turns sharp crossings into avoided crossings with an energy splitting proportional to kso. Our perturbative results are confirmed by numerical calculations that expand the eigenfunctions of the two-particle Hamiltonian in terms of basis functions that contain explicitly correlated Gaussians.
Title: | Variational polaron method for Bose-Bose mixtures | |
Authors: | Benjamin, David; Demler, Eugene | |
Publication: | Physical Review A, Volume 89, Issue 3, id.033615 (PhRvA Homepage) | |
Publication Date: | 03/2014 | |
Origin: | APS | |
PACS Keywords: | Multicomponent condensates, spinor condensates, Atoms in optical lattices, Polarons and electron-phonon interactions | |
Abstract Copyright: | 2014: American Physical Society | |
DOI: | 10.1103/PhysRevA.89.033615 | |
Bibliographic Code: | 2014PhRvA..89c3615B |
Abstract
We study degenerate mixtures of heavy bosons and light superfluid bosons using a variational polaron transformation. We consider the Mott-insulator-superfluid transition of the heavy species and find that at T =0 interaction favors the superfluid phase of the heavy species. Our analytic results agree well with numerically exact quantum Monte Carlo simulations in two dimensions. We then show that in three dimensions the variational polaron transformation can be combined with a Gutzwiller approximation to give good results.
Title: | Evidence for the decay B0→ωω and search for B0→ωϕ | |
Authors: | Lees, J. P.; Poireau, V.; Tisserand, V.;... Morii, M.;... and 327 coauthors (Babar Collaboration) | |
Publication: | Physical Review D, Volume 89, Issue 5, id.051101 (PhRvD Homepage) | |
Publication Date: | 03/2014 | |
Origin: | APS | |
PACS Keywords: | Decays of bottom mesons, Charge conjugation parity time reversal and other discrete symmetries, Determination of Kobayashi-Maskawa matrix elements | |
Abstract Copyright: | 2014: American Physical Society | |
DOI: | 10.1103/PhysRevD.89.051101 | |
Bibliographic Code: | 2014PhRvD..89e1101L |
Abstract
We describe searches for B meson decays to the charmless vector-vector final states ωω and ωϕ with 471×106BB stretchy="false">¯ pairs produced in e+e- annihilation at √s =10.58 GeV using the BABAR detector at the PEP-II collider at the SLAC National Accelerator Laboratory. We measure the branching fraction B(B0→ωω)=(1.2±0.3-0.2+0.3)×10-6, where the first uncertainty is statistical and the second is systematic, corresponding to a significance of 4.4 standard deviations. We also determine the upper limit B(B0→ωϕ)<0.7×10-6 at 90% confidence level. These measurements provide the first evidence for the decay B0→ωω, and an improvement of the upper limit for the decay B0→ωϕ.
Title: | Measurement of the inclusive isolated prompt photons cross section in pp collisions at √s =7 TeV with the ATLAS detector using 4.6 fb-1 | |
Authors: | Aad, G.; Abajyan, T.; Abbott, B.;... ; Franklin, M.;... Guimarães da Costa, J.;... Huth, J.;...; Morii, M.; and 2910 coauthors | |
Publication: | Physical Review D, Volume 89, Issue 5, id.052004 (PhRvD Homepage) | |
Publication Date: | 03/2014 | |
Origin: | APS | |
PACS Keywords: | Inclusive production with identified leptons photons or other nonhadronic particles, Experimental tests | |
Abstract Copyright: | 2014: CERN | |
DOI: | 10.1103/PhysRevD.89.052004 | |
Bibliographic Code: | 2014PhRvD..89e2004A |
Abstract
A measurement of the cross section for the production of isolated prompt photons in pp collisions at a center-of-mass energy √s =7 TeV is presented. The results are based on an integrated luminosity of 4.6 fb-1 collected with the ATLAS detector at the LHC. The cross section is measured as a function of photon pseudorapidity ηγ and transverse energy ETγ in the kinematic range 100≤ETγ<1000 GeV and in the regions |ηγ|<1.37 and 1.52≤|ηγ|<2.37. The results are compared to leading-order parton-shower Monte Carlo models and next-to-leading-order perturbative QCD calculations. Next-to-leading-order perturbative QCD calculations agree well with the measured cross sections as a function of ETγ and ηγ.
Title: | Self-calibration of BICEP1 three-year data and constraints on astrophysical polarization rotation | |
Authors: | Kaufman, J. P.; Miller, N. J.; Shimon, M.; Barkats, D.; Bischoff, C.; Buder, I.; Keating, B. G.; Kovac, J. M.;... and 28 coauthors | |
Publication: | Physical Review D, Volume 89, Issue 6, id.062006 (PhRvD Homepage) | |
Publication Date: | 03/2014 | |
Origin: | APS | |
PACS Keywords: | Background radiations | |
Abstract Copyright: | 2014: American Physical Society | |
DOI: | 10.1103/PhysRevD.89.062006 | |
Bibliographic Code: | 2014PhRvD..89f2006K |
Abstract
Cosmic microwave background (CMB) polarimeters aspire to measure the faint B-mode signature predicted to arise from inflationary gravitational waves. They also have the potential to constrain cosmic birefringence, rotation of the polarization of the CMB arising from parity-violating physics, which would produce nonzero expectation values for the CMB's temperature to B-mode correlation (TB) and E-mode to B-mode correlation (EB) spectra. However, instrumental systematic effects can also cause these TB and EB correlations to be nonzero. In particular, an overall miscalibration of the polarization orientation of the detectors produces TB and EB spectra which are degenerate with isotropic cosmological birefringence, while also introducing a small but predictable bias on the BB spectrum. We find that Bicep1 three-year spectra, which use our standard calibration of detector polarization angles from a dielectric sheet, are consistent with a polarization rotation of α =-2.77°±0.86°(statistical)±1.3°(systematic). We have revised the estimate of systematic error on the polarization rotation angle from the two-year analysis by comparing multiple calibration methods. We also account for the (negligible) impact of measured beam systematic effects. We investigate the polarization rotation for the Bicep1 100 GHz and 150 GHz bands separately to investigate theoretical models that produce frequency-dependent cosmic birefringence. We find no evidence in the data supporting either of these models or Faraday rotation of the CMB polarization by the Milky Way galaxy's magnetic field. If we assume that there is no cosmic birefringence, we can use the TB and EB spectra to calibrate detector polarization orientations, thus reducing bias of the cosmological B-mode spectrum from leaked E-modes due to possible polarization orientation miscalibration. After applying this "self-calibration" process, we find that the upper limit on the tensor-to-scalar ratio decreases slightly, from r<0.70 to r<0.65 at 95% confidence.
Title: | First Results from the LUX Dark Matter Experiment at the Sanford Underground Research Facility | |
Authors: | Akerib, D. S.; Araújo, H. M.; Bai, X.;... Morii, M.;... and 99 coauthors | |
Publication: | Physical Review Letters, Volume 112, Issue 9, id.091303 (PhRvL Homepage) | |
Publication Date: | 03/2014 | |
Origin: | APS | |
PACS Keywords: | Dark matter, Tracking and position-sensitive detectors, Neutrino muon pion and other elementary particle detectors, cosmic ray detectors | |
Abstract Copyright: | 2014: American Physical Society | |
DOI: | 10.1103/PhysRevLett.112.091303 | |
Bibliographic Code: | 2014PhRvL.112i1303A |
Abstract
The Large Underground Xenon (LUX) experiment is a dual-phase xenon time-projection chamber operating at the Sanford Underground Research Facility (Lead, South Dakota). The LUX cryostat was filled for the first time in the underground laboratory in February 2013. We report results of the first WIMP search data set, taken during the period from April to August 2013, presenting the analysis of 85.3 live days of data with a fiducial volume of 118 kg. A profile-likelihood analysis technique shows our data to be consistent with the background-only hypothesis, allowing 90% confidence limits to be set on spin-independent WIMP-nucleon elastic scattering with a minimum upper limit on the cross section of 7.6×10-46 cm2 at a WIMP mass of 33 GeV/c2. We find that the LUX data are in disagreement with low-mass WIMP signal interpretations of the results from several recent direct detection experiments.
Title: | Search for Quantum Black Hole Production in High-Invariant-Mass Lepton+Jet Final States Using pp Collisions at √s =8 TeV and the ATLAS Detector | |
Authors: | Aad, G.; Abajyan, T.; Abbott, B.;... ; Franklin, M.;... Guimarães da Costa, J.;... Huth, J.;...; Morii, M.; and 2903 coauthors | |
Publication: | Physical Review Letters, Volume 112, Issue 9, id.091804 (PhRvL Homepage) | |
Publication Date: | 03/2014 | |
Origin: | APS | |
PACS Keywords: | Inclusive production with identified leptons photons or other nonhadronic particles, Kaluza-Klein theories, Higher-dimensional black holes black strings and related objects | |
Abstract Copyright: | 2014: CERN | |
DOI: | 10.1103/PhysRevLett.112.091804 | |
Bibliographic Code: | 2014PhRvL.112i1804A |
Abstract
This Letter presents a search for quantum black-hole production using 20.3 fb-1 of data collected with the ATLAS detector in pp collisions at the LHC at √s =8 TeV. The quantum black holes are assumed to decay into a final state characterized by a lepton (electron or muon) and a jet. In either channel, no event with a lepton-jet invariant mass of 3.5 TeV or more is observed, consistent with the expected background. Limits are set on the product of cross sections and branching fractions for the lepton+jet final states of quantum black holes produced in a search region for invariant masses above 1 TeV. The combined 95% confidence level upper limit on this product for quantum black holes with threshold mass above 3.5 TeV is 0.18 fb. This limit constrains the threshold quantum black-hole mass to be above 5.3 TeV in the model considered.
Title: | Spatial Propagation of Protein Polymerization | |
Authors: | Cohen, S. I. A.; Rajah, L.; Yoon, C. H.; Buell, A. K.; White, D. A.; Sperling, R. A.; Vendruscolo, M.; Terentjev, E. M.; Dobson, C. M.; Weitz, D. A.; Knowles, T. P. J. | |
Publication: | Physical Review Letters, vol. 112, Issue 9, id. 098101 (PhRvL Homepage) | |
Publication Date: | 03/2014 | |
Origin: | APS | |
PACS Keywords: | Fibrils, Aggregation, Polymerization, Diffusion | |
DOI: | 10.1103/PhysRevLett.112.098101 | |
Bibliographic Code: | 2014PhRvL.112i8101C |
Abstract
We consider the spatial dependence of filamentous protein self-assembly. Through studying the cases where the spreading of aggregated material is dominated either by diffusion or by growth, we derive analytical results for the spatial evolution of filamentous protein aggregation, which we validate against Monte Carlo simulations. Moreover, we compare the predictions of our theory with experimental measurements of two systems for which we identify the propagation as either growth or diffusion controlled. Our results connect the macroscopic observables that characterize the spatial propagation of protein self-assembly with the underlying microscopic processes and provide physical limits on spatial propagation and prionlike behavior associated with protein aggregation.
Title: | First Search for Exotic Z Boson Decays into Photons and Neutral Pions in Hadron Collisions | |
Authors: | Aaltonen, T.; Amerio, S.; Amidei, D.;... Franklin, M.;... ; Guimaraes da Costa, J.;... and 403 coauthors | |
Publication: | Physical Review Letters, Volume 112, Issue 11, id.111803 (PhRvL Homepage) | |
Publication Date: | 03/2014 | |
Origin: | APS | |
PACS Keywords: | Decays of Z bosons, Models beyond the standard model, Z bosons | |
Abstract Copyright: | 2014: American Physical Society | |
DOI: | 10.1103/PhysRevLett.112.111803 | |
Bibliographic Code: | 2014PhRvL.112k1803A |
Abstract
A search for forbidden and exotic Z boson decays in the diphoton mass spectrum is presented for the first time in hadron collisions, based on data corresponding to 10.0 fb-1 of integrated luminosity from proton-antiproton collisions at √s =1.96 TeV collected by the CDF experiment. No evidence of signal is observed, and 95% credibility level Bayesian upper limits are set on the branching ratios of decays of the Z boson to a photon and neutral pion (which is detected as a photon), a pair of photons, and a pair of neutral pions. The observed branching ratio limits are 2.01×10-5 for Z→π0γ, 1.46×10-5 for Z→γγ, and 1.52×10-5 for Z→π0π0. The Z→π0γ and Z→γγ limits improve the most stringent results from other experiments by factors of 2.6 and 3.6, respectively. The Z→π0π0 branching ratio limit is the first experimental result on this decay.
Title: | Magnetic Trapping of Molecules via Optical Loading and Magnetic Slowing | |
Authors: | Lu, Hsin-I.; Kozyryev, Ivan; Hemmerling, Boerge; Piskorski, Julia; Doyle, John M. | |
Publication: | Physical Review Letters, Volume 112, Issue 11, id.113006 (PhRvL Homepage) | |
Publication Date: | 03/2014 | |
Origin: | APS | |
PACS Keywords: | Slowing and cooling of molecules, Trapping of molecules, Mechanical effects of light on atoms molecules and ions | |
Abstract Copyright: | 2014: American Physical Society | |
DOI: | 10.1103/PhysRevLett.112.113006 | |
Bibliographic Code: | 2014PhRvL.112k3006L |
Abstract
Calcium monofluoride (CaF) is magnetically slowed and trapped using optical pumping. Starting from a collisionally cooled slow beam, CaF with an initial velocity of ˜30 m/s is slowed via magnetic forces as it enters a 800 mK deep magnetic trap. Employing two-stage optical pumping, CaF is irreversibly loaded into the trap via two scattered photons. We observe a trap lifetime exceeding 500 ms limited by background collisions. This method paves the way for cooling and magnetic trapping of chemically diverse molecules without closed cycling transitions.
Title: | Quantum Field Theory and the Standard Model | |
Authors: | Schwartz, Matthew D. | |
Publication: | Quantum Field Theory and the Standard Model, by Matthew D. Schwartz, Cambridge, UK: Cambridge University Press, 2014 | |
Publication Date: | 03/2014 | |
Origin: | CUP | |
Bibliographic Code: | 2014qfts.book.....S |
Abstract
Part I. Field Theory: 1. Microscopic theory of radiation; 2. Lorentz invariance and second quantization; 3. Classical Field Theory; 4. Old-fashioned perturbation theory; 5. Cross sections and decay rates; 6. The S-matrix and time-ordered products; 7. Feynman rules; Part II. Quantum Electrodynamics: 8. Spin 1 and gauge invariance; 9. Scalar QED; 10. Spinors; 11. Spinor solutions and CPT; 12. Spin and statistics; 13. Quantum electrodynamics; 14. Path integrals; Part III. Renormalization: 15. The Casimir effect; 16. Vacuum polarization; 17. The anomalous magnetic moment; 18. Mass renormalization; 19. Renormalized perturbation theory; 20. Infrared divergences; 21. Renormalizability; 22. Non-renormalizable theories; 23. The renormalization group; 24. Implications of Unitarity; Part IV. The Standard Model: 25. Yang–Mills theory; 26. Quantum Yang-Mills theory; 27. Gluon scattering and the spinor-helicity formalism; 28. Spontaneous symmetry breaking; 29. Weak interactions; 30. Anomalies; 31. Precision tests of the standard model; 32. QCD and the parton model; Part V. Advanced Topics: 33. Effective actions and Schwinger proper time; 34. Background fields; 35. Heavy-quark physics; 36. Jets and effective field theory; Appendices; References; Index.
Title: | Teaching and physics education research: bridging the gap | |
Authors: | Fraser, James M.; Timan, Anneke L.; Miller, Kelly; Dowd, Jason E.; Tucker, Laura; Mazur, Eric | |
Publication: | Reports on Progress in Physics, Volume 77, Issue 3, article id. 032401 (2014). | |
Publication Date: | 03/2014 | |
Origin: | IOP | |
DOI: | 10.1088/0034-4885/77/3/032401 | |
Bibliographic Code: | 2014RPPh...77c2401F |
Abstract
Physics faculty, experts in evidence-based research, often rely on anecdotal experience to guide their teaching practices. Adoption of research-based instructional strategies is surprisingly low, despite the large body of physics education research (PER) and strong dissemination effort of PER researchers and innovators. Evidence-based PER has validated specific non-traditional teaching practices, but many faculty raise valuable concerns toward their applicability. We address these concerns and identify future studies required to overcome the gap between research and practice.
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