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rss_1.0 Recursos de colección

Caltech Authors (97,430 recursos)
Repository of works by Caltech published authors.

Type = Report or Paper

Mostrando recursos 1 - 20 de 2,687

1. Classification of spin liquids on the square lattice with strong spin-orbit coupling - Reuther, Johannes; Lee, Shu-Ping; Alicea, Jason
Spin liquids represent exotic types of quantum matter that evade conventional symmetry-breaking order even at zero temperature. Exhaustive classifications of spin liquids have been carried out in several systems, particularly in the presence of full SU(2) spin-rotation symmetry. Real magnetic compounds, however, generically break SU(2) spin symmetry as a result of spin-orbit coupling - which in many materials provides an 'order one' effect. We generalize previous works by using the projective symmetry group method to classify Z_2 spin liquids on the square lattice when SU(2) spin symmetry is maximally lifted. We find that, counterintuitively, the lifting of spin symmetry actually results in vastly more spin liquid phases compared to SU(2)-invariant...

2. On the Nature of Type Ia-CSM Supernovae: Optical and Near-Infrared Spectra of SN 2012ca and SN 2013dn - Fox, Ori D.; Silverman, Jeffrey M.; Filippenko, Alexei V.; Mauerhan, Jon; Becker, Juliette; Borish, H. Jacob; Cenko, S. Bradley; Clubb, Kelsey I.; Graham, Melissa; Hsiao, Eric; Kelly, Patrick L.; Lee, William H.; Marion, G. H.; Milisavljevic, Dan; Parrent, Jerod; Shivvers, Isaac; Skrutskie, Michael; Smith, Nathan; Wilson, John; Zheng, Weikang
A growing subset of Type Ia supernovae (SNe Ia) show evidence for unexpected interaction with a dense circumstellar medium (SNe Ia-CSM). The precise nature of the progenitor, however, remains debated owing to spectral ambiguities arising from a strong contribution from the CSM interaction. Late-time spectra offer potential insight if the post-shock cold, dense shell becomes sufficiently thin and/or the ejecta begin to cross the reverse shock. To date, few high-quality spectra of this kind exist. Here we report on the late-time optical and infrared spectra of the SNe Ia-CSM 2012ca and 2013dn. These SNe Ia-CSM spectra exhibit low [Fe III]/[Fe II] ratios and...

3. Probing the very-high-energy γ-ray spectral curvature in the blazar PG 1553+113 with the MAGIC telescopes - Aleksić, J.; Hovatta, T.; Max-Moerbeck, W.
PG 1553+113 is a very-high-energy (VHE, E > 100 GeV) γ-ray emitter classified as a BL Lac object. Its redshift is constrained by intergalactic absorption lines in the range 0.4 < z < 0.58. The MAGIC telescopes have monitored the source’s activity since 2005. In early 2012, PG 1553+113 was found in a high-state, and later, in April of the same year, the source reached the highest VHE flux state detected so far. Simultaneous observations carried out in X-rays during 2012 April show similar flaring behaviour. In contrast, the γ-ray flux at E < 100 GeV observed by Fermi-LAT is compatible...

4. Imaginary supergravity or Virial supergravity? - Nakayama, Yu
When a globally supersymmetric theory is scale invariant, it must possess a Virial supercurrent supermultiplet. The multiplet structure is analogous to the R-current supermultiplet in globally R-symmetric theories but we put extra "i"s in various formulae. We construct a novel type of supergravity from gauging the Virial supercurrent supermultiplet in d=1+3 dimensions. We give the full non-linear superspace action with the help of a covariantly linear unitary superconformal compensator. The resulting supergravity is peculiar: (1) no Einstein-like second order kinetic term is allowed without matter (2) there exists a dynamical non-geometrical connection (3) the metric is unimodular in the Wess-Zumino...

5. CARMA observations of massive Planck-discovered cluster candidates at z ≳ 0.5 associated with WISE overdensities: strategy, observations and validation - Rodríguez-Gonzálvez, Carmen; Muchovej, Stephen; Chary, Ranga-Ram
We present 1 − 2′ spatial resolution CARMA-8 31-GHz observations towards 19 unconfirmed Planck cluster candidates, selected to have significant galaxy overdensities from the WISE early data release and thought to be at z ≳ 1 from the WISE colors of the putative brightest cluster galaxy (BCG). We find a Sunyaev-Zeldovich (SZ) detection in the CARMA-8 data towards 9 candidate clusters, where one detection is considered tentative. For each cluster candidate we present CARMA-8 maps, a study of their radio-source environment and we assess the reliability of the SZ detection. The CARMA SZ detections appear to be SZ-bright, with the mean,...

6. Probing large-scale wind structures in Vela X–1 using off-states with INTEGRAL - Sidoli, L.; Paizis, A.; Fürst, F.; Torrejón, J. M.; Kretschmar, P.; Bozzo, E.; Pottschmidt, K.
Vela X–1 is the prototype of the class of wind-fed accreting pulsars in high mass X–ray binaries hosting a supergiant donor. We have analyzed in a systematic way ten years of INTEGRAL data of VelaX–1 (22–50 keV) and we found that when outside the X–ray eclipse, the source undergoes several luminosity drops where the hard X–rays luminosity goes below ~5×10^(34) erg s^(−1), becoming undetected by INTEGRAL. These drops in the X–ray flux are usually referred to as “off-states” in the literature. We have investigated the distribution of these off-states along the VelaX–1 ~8.9 day orbit, finding that their orbital occurrence...

7. Multiple Images of a Highly Magnified Supernova Formed by an Early-Type Cluster Galaxy Lens - Kelly, Patrick L.; Zitrin, Adi; Merten, Julian
We report the discovery of the first multiply-imaged gravitationally lensed supernova. The four images form an Einstein cross with over 200 diameter around a z = 0.544 elliptical galaxy that is a member of the cluster MACS J1149.6+2223. The supernova appeared in Hubble Space Telescope near-infrared exposures taken on 3-20 November 2014 UT, as part of the Grism Lens-Amplified Survey from Space. The images of the supernova coincide with the strongly lensed arm of a spiral galaxy at z = 1.491, which is itself multiply imaged by the cluster potential. A measurement of the time delays between the multiple images...

8. Legacy ExtraGalactic UV Survey (LEGUS) with The Hubble Space Telescope. I. Survey Description - Calzetti, D.; Lee, J. C.; de Mink, S. E.; Martin, C.; van Dyk, S. D.
The Legacy ExtraGalactic UV Survey (LEGUS) is a Cycle 21 Treasury program on the Hubble Space Telescope, aimed at the investigation of star formation and its relation with galactic environment in nearby galaxies, from the scales of individual stars to those of ~kpc–size clustered structures. Five–band imaging, from the near–ultraviolet to the I–band, with the Wide Field Camera 3, plus parallel optical imaging with the Advanced Camera for Surveys, is being collected for selected pointings of 50 galaxies within the local 12 Mpc. The filters used for the Observations with the Wide Field Camera 3 are: F275W(λ2,704Å), F336W(λ3,355Å), F438W(λ4,325Å), F555W(λ5,308Å), and...

9. Optimization of spectroscopic surveys for testing non-Gaussianity - Raccanelli, Alvise; Doré, Olivier; Dalal, Neal
We investigate optimization strategies to measure primordial non-Gaussianity with future spectroscopic surveys. We forecast measurements coming from the 3D galaxy power spectrum and compute constraints on primordial non-Gaussianity parameters f_(NL) and n_(NG). After studying the dependence on those parameters upon survey specifications such as redshift range, area, number density, we assume a reference mock survey and investigate the trade-off between number density and area surveyed. We then define the observational requirements to reach the detection of f_(NL) of order 1. Our results show that while power spectrum constraints on non-Gaussianity from future spectroscopic surveys can be competitive with current CMB...

10. Automated Real-Time Classification and Decision Making in Massive Data Streams from Synoptic Sky Surveys - Djorgovski, S. G.; Mahabal, A. A.; Donalek, C.; Graham, M. J.; Drake, A. J.; Turmon, M.; Fuchs, T.
The nature of scientific and technological data collection is evolving rapidly: data volumes and rates grow exponentially, with increasing complexity and information content, and there has been a transition from static data sets to data streams that must be analyzed in real time. Interesting or anomalous phenomena must be quickly characterized and followed up with additional measurements via optimal deployment of limited assets. Modern astronomy presents a variety of such phenomena in the form of transient events in digital synoptic sky surveys, including cosmic explosions (supernovae, gamma ray bursts), relativistic phenomena (black hole formation, jets), potentially hazardous asteroids, etc. We...

11. Accounting for Cosmic Variance in Studies of Gravitationally-Lensed High-Redshift Galaxies in the Hubble Frontier Field Clusters - Robertson, Brant E.; Ellis, Richard S.; Dunlop, James S.; McLure, Ross J.; Stark, Dan P.; McLeod, Derek
Strong gravitational lensing provides a powerful means for studying faint galaxies in the distant universe. By magnifying the apparent brightness of background sources, massive clusters enable the detection of galaxies fainter than the usual sensitivity limit for blank fields. However, this gain in effective sensitivity comes at the cost of a reduced survey volume and, in this Letter, we demonstrate there is an associated increase in the cosmic variance uncertainty. As an example, we show that the cosmic variance uncertainty of the high redshift population viewed through the Hubble Space Telescope Frontier Field cluster Abell 2744 increases from ~ 35% at redshift z ~ 7 to...

12. Multivariate Regression Analysis of Gravitational Waves from Rotating Core Collapse - Engels, William J.; Frey, Raymond; Ott, Christian D.
We present a new multivariate regression model for analysis and parameter estimation of gravitational waves observed from well but not perfectly modeled sources such as core-collapse supernovae. Our approach is based on a principal component decomposition of simulated waveform catalogs. Instead of reconstructing waveforms by direct linear combination of physically meaningless principal components, we solve via least squares for the relationship that encodes the connection between chosen physical parameters and the principal component basis. Although our approach is linear, the waveforms' parameter dependence may be non-linear. For the case of gravitational waves from rotating core collapse, we show, using statistical hypothesis testing, that our method is capable of identifying the...

13. Low EUV Luminosities Impinging on Protoplanetary Disks - Pascucci, I.; Ricci, L.; Gorti, U.; Hollenbach, D.; Hendler, N. P.; Brooks, K. J.; Contreras, Y.
The amount of high-energy stellar radiation reaching the surface of protoplanetary disks is essential to determine their chemistry and physical evolution. Here, we use millimetric and centimetric radio data to constrain the EUV luminosity impinging on 14 disks around young (~2-10Myr) sun-like stars. For each object we identify the long-wavelength emission in excess to the dust thermal emission, attribute that to free-free disk emission, and thereby compute an upper limit to the EUV reaching the disk. We find upper limits lower than 10^(42) photons/s for all sources without jets and lower than 5×10^(40) photons/s for the three older sources in...

14. The Illustris simulation: Evolving population of black holes across cosmic time - Sijacki, Debora; Vogelsberger, Mark; Genel, Shy; Springel, Volker; Torrey, Paul; Snyder, Gregory A.; Nelson, Dylan; Hernquist, Lars
We study the properties of black holes and their host galaxies across cosmic time in the Illustris simulation. Illustris is a large scale cosmological hydrodynamical simulation which resolves a (106.5 Mpc)^3 volume with more than 12 billion resolution elements and includes state-of-the-art physical models relevant for galaxy formation. We find that the black hole mass density for redshifts z = 0 - 5 and the black hole mass function at z = 0 predicted by Illustris are in excellent agreement with the most recent observational constraints. We show that the bolometric and hard X-ray luminosity functions of AGN at z = 0 reproduce observational data very well over...

15. Neutral hydrogen in galaxy halos at the peak of the cosmic star formation history - Faucher-Giguere, C.-A.; Hopkins, P. F.; Keres, D.; Muratov, A. L.; Quataert, E.; Murray, N.
Gas inflows and outflows regulate star formation in galaxies. Probing these processes is one of the central motivations for spectroscopic measurements of the circum-galactic medium. We use high-resolution cosmological zoom-in simulations from the FIRE project to make predictions for the covering fractions of neutral hydrogen around galaxies at z=2-4. These simulations resolve the interstellar medium of galaxies and explicitly implement a comprehensive set of stellar feedback mechanisms. Our simulation sample consists of 16 main halos covering the mass range M_h~2x10^9-8x10^12 Msun at z=2, including 12 halos in the mass range M_h~10^11-10^12 Msun corresponding to Lyman break galaxies (LBGs). We process our simulations with a ray tracing method to compute the...

16. Neutrino-driven Turbulent Convection and Standing Accretion Shock Instability in Three-Dimensional Core-Collapse Supernovae - Abdikamalov, E.; Ott, C. D.; Radice, D.; Roberts, L. F.; Haas, R.; Reisswig, C.; Moesta, P.; Klion, H.; Schnetter, E.
We conduct a series of numerical experiments into the nature of three-dimensional (3D) hydrodynamics in the postbounce stalled-shock phase of core-collapse supernovae using 3D general-relativistic hydrodynamic simulations of a 27-M⊙ progenitor star with a neutrino leakage/heating scheme. We vary the strength of neutrino heating and find three cases of 3D dynamics: (1) neutrino-driven convection, (2) initially neutrino-driven convection and subsequent development of the standing accretion shock instability (SASI), (3) SASI dominated evolution. This confirms previous 3D results of Hanke et al. 2013, ApJ 770, 66 and Couch & Connor 2014, ApJ 785, 123. We carry out simulations with resolutions differing...

17. WISE J072003.20-084651.2: An Old and Active M9.5 + T5 Spectral Binary 6 PC from the Sun - Burgasser, Adam J.; Gillon, Michael; Melis, Carl; Bowler, Brendan P.; Michelsen, Eric L.; Gagliuffi, Daniella Bardalez; Gelino, Christopher R.; Jehin, E.; Delrez, L.; Manfroid, J.; Blake, Cullen H.
[Abridged] We report observations of the recently discovered, nearby late-M dwarf WISE J072003.20-084651.2. Astrometric measurements obtained with TRAPPIST improve the distance measurement to 6.0±1.0 pc and confirm the low tangential velocity (3.5±0.6 km/s) reported by Scholz. Low-resolution optical spectroscopy indicates a spectral type of M9.5 and prominent Hα emission ( = -4.68±0.06), but no evidence of subsolar metallicity or Li I absorption. Near-infrared spectroscopy reveals subtle peculiarities indicating the presence of a T5 binary companion, and high-resolution laser guide star adaptive optics imaging reveals a faint (ΔH = 4.1) candidate source 0"14 (0.8 AU) from the primary. We measure a...

18. Is cosmological constant screened in Liouville gravity with matter? - Inami, Takeo; Koyama, Yoji; Nakayama, Yu; Suzuki, Mariko
There has been a proposal that infrared quantum effects of massless interacting field theories in de-Sitter space may provide time-dependent screening of the cosmological constant. As a concrete model of the proposal, we study the three loop corrections to the energy-momentum tensor of massless λϕ4 theory in the background of classical Liouville gravity in D=2 dimensional de-Sitter space. We find that the cosmological constant is screened in sharp contrast to the massless λϕ4 theory in D=4 dimensions due to the sign difference between the cosmological constant of the Liouville gravity and that of the Einstein gravity. We also propose an...

19. Asymptotic Symmetries of Massless QED in Even Dimensions - Kapec, Daniel; Lysov, Vyacheslav; Strominger, Andrew
We consider the scattering of massless particles coupled to an abelian gauge field in 2n-dimensional Minkowski spacetime. Weinberg's soft photon theorem is recast as Ward identities for infinitely many new nontrivial symmetries of the massless QED S-matrix, with one such identity arising for each propagation direction of the soft photon. These symmetries are identified as large gauge transformations with angle-dependent gauge parameters that are constant along the null generators of null infinity. Almost all of the symmetries are spontaneously broken in the standard vacuum and the soft photons are the corresponding Goldstone bosons. Our result establishes a relationship between soft theorems and asymptotic symmetry groups in any even dimension.

20. Tomography from Entanglement - Lin, Jennifer; Marcolli, Matilde; Ooguri, Hirosi; Stoica, Bogdan
The Ryu-Takayanagi formula relates the entanglement entropy in a conformal field theory to the area of a minimal surface in its holographic dual. We show that this relation can be inverted for any state in the conformal field theory to compute the bulk stress-energy tensor near the boundary of the bulk spacetime, reconstructing the local data in the bulk from the entanglement on the boundary. We also show that positivity, monotonicity, and convexity of the relative entropy for small spherical domains between the reduced density matrices of any state and of the ground state of the conformal field theory, follow from positivity conditions on the bulk matter energy...

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