4,683 research outputs found
Recent progress on truncated Toeplitz operators
This paper is a survey on the emerging theory of truncated Toeplitz
operators. We begin with a brief introduction to the subject and then highlight
the many recent developments in the field since Sarason's seminal paper in
2007.Comment: 46 page
Model spaces: a survey
This is a brief and gentle introduction, aimed at graduate students, to the
subject of model subspaces of the Hardy space.Comment: 55 page
Partial orders on partial isometries
This paper studies three natural pre-orders of increasing generality on the
set of all completely non-unitary partial isometries with equal defect indices.
We show that the problem of determining when one partial isometry is less than
another with respect to these pre-orders is equivalent to the existence of a
bounded (or isometric) multiplier between two natural reproducing kernel
Hilbert spaces of analytic functions. For large classes of partial isometries
these spaces can be realized as the well-known model subspaces and
deBranges-Rovnyak spaces. This characterization is applied to investigate
properties of these pre-orders and the equivalence classes they generate.Comment: 30 pages. To appear in Journal of Operator Theor
Failed delivery and daily Treasury bill returns
If the seller of a Treasury bill does not provide timely and correct delivery instructions to the clearing bank, the bank does not deliver the security. Further, the seller is not paid until this "failed delivery" is rectified. Since the purchase price is not changed, these "fails" generate interest-free loans from the seller to the buyer. ; This paper studies the effect of failed delivery on Treasury-bill prices. We find that investors bid prices to a premium to reflect the possibility of obtaining the interest-free loans that fails represent. This premium is a function of the opportunity cost of the fail. We also find that the bid-ask spread varies directly with the length of the fail. We rule out the possibility that our results are due to liquidity premiums, or to a general weekly pattern in short-term interest rates or the bid-ask spread.Treasury bills
Real complex functions
We survey a few classes of analytic functions on the disk that have real
boundary values almost everywhere on the unit circle. We explore some of their
properties, various decompositions, and some connections these functions make
to operator theory.Comment: 44 page
Transient gamma-ray emission from Cygnus X-3
The high-mass microquasar Cygnus X-3 has been recently detected in a flaring
state by the gamma-ray satellites Fermi and Agile. In the present contribution,
we study the high-energy emission from Cygnus X-3 through a model based on the
interaction of clumps from the Wolf-Rayet wind with the jet. The clumps inside
the jet act as obstacles in which shocks are formed leading to particle
acceleration and non-thermal emission. We model the high energy emission
produced by the interaction of one clump with the jet and briefly discus the
possibility of many clumps interacting with the jet. From the characteristics
of the considered scenario, the produced emission could be flare-like due to
discontinuous clump penetration, with the GeV long-term activity explained by
changes in the wind properties.Comment: Contribution to the proceedings of the 25th Texas Symposium on
Relativistic Astrophysics - TEXAS 2010, December 06-10, Heidelberg, German
-algebras generated by truncated Toeplitz operators
We obtain an analogue of Coburn's description of the Toeplitz algebra in the
setting of truncated Toeplitz operators. As a byproduct, we provide several
examples of complex symmetric operators which are not unitarily equivalent to
truncated Toeplitz operators having continuous symbols.Comment: 12 page
High-energy flares from jet-clump interactions
High-mass microquasars are binary systems composed by a massive star and a
compact object from which relativistic jets are launched. Regarding the
companion star, observational evidence supports the idea that winds of hot
stars are formed by clumps. Then, these inhomogeneities may interact with the
jets producing a flaring activity. In the present contribution we study the
interaction between a jet and a clump of the stellar wind in a high-mass
microquasar. This interaction produces a shock in the jet, where particles may
be accelerated up to relativistic energies. We calculate the spectral energy
distributions of the dominant non-thermal processes: synchrotron radiation,
inverse Compton scattering, and proton-proton collisions. Significant levels of
X- and gamma-ray emission are predicted, with luminosities in the different
domains up to ~ 10^{34} - 10^{35} erg/s on a timescale of about ~ 1 h. Finally,
jet-clump interactions in high-mass microquasars could be detectable at high
energies. These phenomena may be behind the fast TeV variability found in some
high-mass X-ray binary systems, such as Cygnus X-1, LS 5039 and LS I+61 303. In
addition, our model can help to derive information on the properties of jets
and clumpy winds.Comment: Proceeding of the conference "High Energy Phenomena in Massive
Stars". Jaen (Spain), 2-5 February 200
Jet-Cloud Interactions in AGNs
Active galactic nuclei present continuum and line emission. The former is
produced by the accretion disk and the jets, whereas the latter is originated
by gas located close to the super-massive black hole. The small region where
the broad lines are emitted is called the broad-line region. The structure of
this region is not well known, although it has been proposed that it may be
formed by small and dense ionized clouds surrounding the supermassive
black-hole. In this work, we study the interaction of one cloud from the broad
line region with the jet of the active galactic nuclei. We explore the
high-energy emission produced by this interaction close to the base of the jet.
The resulting radiation may be detectable for nearby non-blazar sources as well
as for powerful quasars, and its detection could give important information on
the broad line region and the jet itself.Comment: Proceeding of the conference "High-Energy Gamma-rays and Neutrinos
from Extra-Galactic Sources". Heidelberg, 13-16 January 200
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