Recursos de colección

Caltech Authors (147.820 recursos)

Repository of works by Caltech published authors.

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Mostrando recursos 1 - 20 de 1.459

  1. On ground states for the L^2-critical boson star equation

    Frank, Rupert L.; Lenzmann, Enno
    We consider ground state solutions u ⩾ 0 for the L^2-critical boson star equation √−u − (|x|^(−1) ∗ |u|^2)u = −u in R^3. We prove analyticity and radial symmetry of u. In a previous version of this paper, we also stated uniqueness and nondegeneracy of ground states for the L^2-critical boson star equation in R^3, but the arguments given there contained a gap. However, we refer to our recent preprint [FraLe] in arXiv:1009.4042, where we prove a general uniqueness and nondegeneracy result for ground states of nonlinear equations with fractional Laplacians in d = 1 space dimension.

  2. The NuSTAR View of the Seyfert 2 Galaxy NGC 4388

    Kamraj, N.; Rivers, E.; Harrison, F. A.; Brightman, M.; Baloković, M.
    We present analysis of NuSTAR X-ray observations in the 3-79 keV energy band of the Seyfert 2 galaxy NGC 4388, taken in 2013. The broadband sensitivity of NuSTAR, covering the Fe K$\alpha$ line and Compton reflection hump, enables tight constraints to be placed on reflection features in AGN X-ray spectra, thereby providing insight into the geometry of the circumnuclear material. In this observation, we found the X-ray spectrum of NGC 4388 to be well described by a moderately absorbed power law with non-relativistic reflection. We fit the spectrum with phenomenological reflection models and a physical torus model, and find the source to be absorbed by Compton-thin material (N$_{H}...

  3. Uniqueness of ground states for the L^2-critical boson star equation

    Frank, Rupert L.; Lenzmann, Enno
    We establish uniqueness of ground states u(x)≥0 for the L^2-critical boson star equation √−Δu−(|x|^(−1)∗|u|2)u=−u in R^3. The proof blends variational arguments with the harmonic extension to the halfspace R^4_+. Apart from uniqueness, we also show radiality of ground states (up to translations) and the nondegeneracy of the linearization. Our results provide an indispensable basis for the blowup analysis of the time-dependent L^2-critical boson star equation. The uniqueness proof can be generalized to different fractional Laplacians (−Δ)^s and space dimensions.

  4. Remarks on eigenvalue estimates and semigroup domination

    Frank, Rupert L.
    We present an overview over recent results concerning semi-classical spectral estimates for magnetic Schroedinger operators. We discuss how the constants in magnetic and non-magnetic eigenvalue bounds are related and we prove, in an abstract setting, that any non-magnetic Lieb-Thirring-type inequality implies a magnetic Lieb-Thirring-type inequality with possibly a larger constant.

  5. The Complete Calibration of the Color-Redshift Relation (C3R2) Survey: Survey Overview and Data Release 1

    Masters, Daniel; Stern, Daniel; Cohen, Judith G.; Capak, Peter; Rhodes, Jason; Castander, Francisco; Paltani, Stephane
    A key goal of the Stage IV dark energy experiments Euclid, LSST and WFIRST is to measure the growth of structure with cosmic time from weak lensing analysis over large regions of the sky. Weak lensing cosmology will be challenging: in addition to highly accurate galaxy shape measurements, statistically robust and accurate photometric redshift (photo-z) estimates for billions of faint galaxies will be needed in order to reconstruct the three-dimensional matter distribution. Here we present an overview of and initial results from the Complete Calibration of the Color-Redshift Relation (C3R2) survey, designed specifically to calibrate the empirical galaxy color-redshift relation to the Euclid depth. These redshifts will also be...

  6. Symmetry and duality in bosonization of two-dimensional Dirac fermions

    Mross, David F.; Alicea, Jason; Motrunich, Olexei I.
    Recent work on a family of boson-fermion mappings has emphasized the interplay of symmetry and duality: Phases related by a particle-vortex duality of bosons (fermions) are related by time-reversal symmetry in their fermionic (bosonic) formulation. We present exact mappings for a number of concrete models that make this property explicit on the operator level. We illustrate the approach with one- and two-dimensional quantum Ising models, and then similarly explore the duality web of complex bosons and Dirac fermions in (2+1) dimensions.

  7. CO excitation in the Seyfert galaxy NGC7130

    Pozzi, F.; Vallini, L.; Vignali, C.; Talia, M.; Gruppioni, C.; Mingozzi, M.; Massardi, M.; Andreani, P.
    We present a coherent multi-band modelling of the CO Spectral Energy Distribution of the local Seyfert Galaxy NGC7130 to assess the impact of the AGN activity on the molecular gas. We take advantage of all the available data from X-ray to the sub-mm, including ALMA data. The high-resolution (~0.2") ALMA CO(6-5) data constrain the spatial extension of the CO emission down to ~70 pc scale. From the analysis of the archival CHANDRA and NuSTAR data, we infer the presence of a buried, Compton-thick AGN of moderate luminosity, L_2-10keV ~ 1.6x10^{43} ergs-1. We explore photodissociation and X-ray-dominated regions (PDRs and XDRs) models to reproduce the CO emission. We find...

  8. Sagittarius A* High Energy X-ray Flare Properties During NuSTAR Monitoring of the Galactic Center from 2012 to 2015

    Zhang, Shuo; Baganoff, Frederick K.; Ponti, Gabriele; Neilsen, Joseph; Tomsick, John A.; Dexter, Jason; Clavel, Maïca; Markoff, Sera; Hailey, Charles J.; Mori, Kaya; Barrière, Nicolas M.; Nowak, Michael A.; Boggs, Steven E.; Christensen, Finn E.; Craig, William W.; Grefenstette, Brian W.; Harrison, Fiona A.; Madsen, Kristin K.; Stern, Daniel; Zhang, William W.
    Understanding the origin of the flaring activity from the Galactic center supermassive black hole, Sagittarius A^* , is a major scientific goal of the NuSTAR Galactic plane survey campaign. We report on the data obtained between July 2012 and April 2015, including 27 observations on Sgr A^* with a total exposure of = 1 Ms. We found a total of ten X-ray flares detected in the NuSTAR observation window, with luminosities in the range of L_3_(−79 keV) ∼ (0.2–4.0)×10^(35) erg s^−1 . With this largest hard X-ray Sgr A^* flare dataset to date, we studied the flare spectral properties. Seven flares are detected above 5σ significance, showing a...

  9. Reducing Versatile Bat Wing Conformations to a 1-DoF Machine

    Hoff, Jonathan; Ramezani, Alireza; Chung, Soon-Jo; Hutchinson, Seth
    Recent works have shown success in mimicking the flapping flight of bats on the robotic platform Bat Bot (B2). This robot has only five actuators but retains the ability to flap and fold-unfold its wings in flight. However, this bat-like robot has been unable to perform folding-unfolding of its wings within the period of a wingbeat cycle, about 100 ms. The DC motors operating the spindle mechanisms cannot attain this folding speed. Biological bats rely on this periodic folding of their wings during the upstroke of the wingbeat cycle. It reduces the moment of inertia of the wings and limits...

  10. Describing Robotic Bat Flight with Stable Periodic Orbits

    Ramezani, Alireza; Ahmed, Syed Usman; Hoff, Jonathan; Chung, Soon-Jo; Hutchinson, Seth
    From a dynamic system point of view, bat locomotion stands out among other forms of flight. During a large part of bat wingbeat cycle the moving body is not in a static equilibrium. This is in sharp contrast to what we observe in other simpler forms of flight such as insects, which stay at their static equilibrium. Encouraged by biological examinations that have revealed bats exhibit periodic and stable limit cycles, this work demonstrates that one effective approach to stabilize articulated flying robots with bat morphology is locating feasible limit cycles for these robots; then, designing controllers that retain the closed-loop...

  11. Analysis of NuSTAR and Suzaku observations of Cyg X-1 in the hard state: evidence for a truncated disc geometry

    Basak, Rupal; Zdziarski, Andrzej A.; Parker, Michael; Islam, Nazma
    The geometry of the accretion flow in black-hole X-ray binaries in the hard state, in particular the position of the disc inner edge, has been a subject of intense debate in recent years. We address this issue by performing a spectral study of simultaneous observations of Cyg X-1 in the hard state by {\it{NuSTAR}\} and {\it{Suzaku}}. The same data were analysed before, and modelled by a lamppost containing hybrid electrons and located very close to the horizon, which emission was incident on a surrounding disc extending almost to the innermost stable circular orbit. We re-analyse the incident continuum model and show that it suffers from the lack of...

  12. Detection of Cyclotron Resonance Scattering Feature in High Mass X-ray Binary Pulsar SMC X-2

    Jaisawal, Gaurava K.; Naik, Sachindra
    We report broadband spectral properties of the high mass X-ray binary pulsar SMC X-2 by using three simultaneous $NuSTAR$ and $Swift$/XRT observations during its 2015 outburst. The pulsar was significantly bright, reaching a luminosity up to as high as $\sim$5.5$\times$10$^{38}$~ergs~s$^{-1}$ in 1-70 keV range. Spin period of the pulsar was estimated to be 2.37 s. Pulse profiles were found to be strongly luminosity dependent. The 1-70 keV energy spectrum of the pulsar was well described with three different continuum models such as (i) negative and positive power-law with exponential cutoff, (ii) Fermi-Dirac cutoff power-law and (iii) cutoff power-law models. Apart from the presence of an iron line at $\sim$6.4...

  13. No difference in orbital parameters of RV-detected giant planets between 0.1 and 5 au in single vs multi-stellar systems

    Ngo, Henry; Knutson, Heather A.; Bryan, Marta L.; Blunt, Sarah; Nielsen, Eric L.; Batygin, Konstantin; Bowler, Brendan P.; Crepp, Justin R.; Hinkley, Sasha; Howard, Andrew W.; Mawet, Dimitri
    Our Keck/NIRC2 imaging survey searches for stellar companions around 144 systems with radial velocity (RV) detected giant planets to determine whether stellar binaries influence the planets' orbital parameters. This survey, the largest of its kind to date, finds eight confirmed binary systems and three confirmed triple systems. These include three new multi-stellar systems (HD 30856, HD 86081, and HD 207832) and three multi-stellar systems with newly confirmed common proper motion (HD 43691, HD 116029, and HD 164509). We combine these systems with seven RV planet-hosting multi-stellar systems from the literature in order to test for differences in the properties of planets with semimajor axes ranging between 0.1-5 au in...

  14. Photopolarimetric characteristics of brown dwarfs bearing uniform cloud decks

    Sanghavi, Suniti; Millar-Blanchaer, Maxwell A.; Shporer, Avi; Riedel, Adric; Tinyatont, Samaporn; Nilsson, Ricky; Kataria, Tiffany; Mawet, Dimitri
    It has long been known that an envelope of scattering particles like free electrons, atoms and molecules, or particulate aggregates like haze or cloud grains affect the intensity and polarization of radiation emitted by a rotating body (Chandrasekhar 1946; Harrington and Collins 1968, Sengupta and Marley 2010, Marley and Sengupta 2011, de Kok et al. 2011). Due to their high rotation rates, brown dwarfs (BDs) are expected to be considerably oblate. We present a conics-based radiative transfer scheme for computing the disc-resolved and disc-integrated polarized emission of an oblate body. Using this capability, we examine the photopolarimetric signal of BDs as a function of the scattering properties of its...

  15. VIP: Vortex Image Processing package for high-contrast direct imaging

    Gomez Gonzalez, C. A.; Wertz, O.; Absil, O.; Christiaens, V.; Defrere, D.; Mawet, D.; Milli, J.; Absil, P.-A.; Van Droogenbroeck, M.; Cantalloube, F.; Hinz, P. M.; Skemer, A. J.; Karlsson, M.; Surdej, J.
    We present the Vortex Image Processing (VIP) library, a python package dedicated to astronomical high-contrast imaging. Our package relies on the extensive python stack of scientific libraries and aims to provide a flexible framework for high-contrast data and image processing. In this paper, we describe the capabilities of VIP related to processing image sequences acquired using the angular differential imaging (ADI) observing technique. VIP implements functionalities for building high-contrast data processing pipelines, encompass- ing pre- and post-processing algorithms, potential sources position and flux estimation, and sensitivity curves generation. Among the reference point-spread function subtraction techniques for ADI post-processing, VIP includes several flavors of principal component analysis (PCA) based algorithms, such as...

  16. A Note on Inhomogeneous Ground States at Large Global Charge

    Hellerman, Simeon; Kobayashi, Nozomu; Maeda, Shunsuke; Watanabe, Masataka
    In this note we search for the ground state, in infinite volume, of the D = 3 WilsonFisher conformal O(4) model, at nonzero values of the two independent charge densities ρ1,2 . Using an effective theory valid on scales longer than the scale defined by the charge density, we show that the ground-state configuration is inhomogeneous for generic ratios ρ1 /ρ2 . This result confirms, within the context of a well-defined effective theory, a recent no-go result of [2] . We also show that any spatially periodic ground state solutions have an energetic preference towards longer periods, within some range of ρ1/ρ2 containing a neighborhood of zero. This suggests that...

  17. General Bootstrap Equations in 4D CFTs

    Cuomo, Gabriel Francisco; Karateev, Denis; Kravchuk, Petr
    We provide a framework for generic 4D conformal bootstrap computations. It is based on the unification of two independent approaches, the covariant (embedding) formalism and the non-covariant (conformal frame) formalism. We construct their main ingredients (tensor structures and differential operators) and establish a precise connection between them. We supplement the discussion by additional details like classification of tensor structures of n-point functions, normalization of 2-point functions and seed conformal blocks, Casimir differential operators and treatment of conserved operators and permutation symmetries. Finally, we implement our framework in a Mathematica package and make it freely available.

  18. Carving Out the End of the World or (Superconformal Bootstrap in Six Dimensions)

    Chang, Chi-Ming; Lin, Ying-Hsuan
    We bootstrap N = (1, 0) superconformal field theories in six dimensions, by analyzing the four-point function of flavor current multiplets. Assuming E8 flavor group, we present universal bounds on the central charge CT and the flavor central charge CJ . Based on the numerical data, we conjecture that the rank-one E-string theory saturates the universal lower bound on CJ , and numerically determine the spectrum of long multiplets in the rank-one E-string theory. We comment on the possibility of solving the higher-rank E-string theories by bootstrap and thereby probing M-theory on AdS7 × S^4/Z_2.

  19. Unifying Relations for Scattering Amplitudes

    Cheung, Clifford; Shen, Chia-Hsien; Wen, Congkao
    We derive new amplitudes relations revealing a hidden unity among wide-ranging theories in arbitrary spacetime dimensions. Our results rely on a set of Lorentz invariant differential operators which transmute physical tree-level scattering amplitudes into new ones. By transmuting the amplitudes of gravity coupled to a dilaton and two-form, we generate all the amplitudes of Einstein-Yang-Mills theory, Dirac-Born-Infield theory, special Galileon, nonlinear sigma model, and biadjoint scalar theory. Transmutation also relates amplitudes in string theory and its variants. As a corollary, celebrated aspects of gluon and graviton scattering like color-kinematics duality, the KLT relations, and the CHY construction are inherited traits of the transmuted amplitudes. Transmutation recasts the Adler zero as...

  20. The Surface Subgroup and the Ehrenpreis Conjectures

    Kahn, Jeremy; Markovic, Vladimir
    We survey our recent results including the Surface Subgroup Theorem and the Ehrenpreis Conjecture. Applications and future direction are discussed.

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