Recursos de colección
Caltech Authors (147.820 recursos)
Repository of works by Caltech published authors.
Status = Submitted
Repository of works by Caltech published authors.
Status = Submitted
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.
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}...
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.
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.
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...
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.
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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.
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.
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...
Kahn, Jeremy; Markovic, Vladimir
We survey our recent results including the Surface
Subgroup Theorem and the Ehrenpreis Conjecture. Applications
and future direction are discussed.