126 research outputs found
A Free-Algebraic Solution for the Planar Approximation
An explicit solution for the generating functional of n-point functions in
the planar approximation is given in terms of two sets of free-algebraic
annihilation and creation operators.Comment: 15 pages, added referenc
Interactions of the magnetospheres of stars and close-in giant planets
Since the first discovery of an extrasolar planetary system more than a
decade ago, hundreds more have been discovered. Surprisingly, many of these
systems harbor Jupiter-class gas giants located close to the central star, at
distances of 0.1 AU or less. Observations of chromospheric 'hot spots' that
rotate in phase with the planetary orbit, and elevated stellar X-ray
luminosities,suggest that these close-in planets significantly affect the
structure of the outer atmosphere of the star through interactions between the
stellar magnetic field and the planetary magnetosphere. Here we carry out the
first detailed three-dimensional MagnetoHydroHynamics (MHD) simulation
containing the two magnetic bodies and explore the consequences of such
interactions on the steady-state coronal structure. The simulations reproduce
the observable features of 1) increase in the total X-ray luminosity, 2)
appearance of coronal hot spots, and 3) phase shift of these spots with respect
to the direction of the planet. The proximate cause of these is an increase in
the density of coronal plasma in the direction of the planet, which prevents
the corona from expanding and leaking away this plasma via a stellar wind. The
simulations produce significant low temperature heating. By including dynamical
effects, such as the planetary orbital motion, the simulation should better
reproduce the observed coronal heating
Chromosphere of K giant stars Geometrical extent and spatial structure detection
We aim to constrain the geometrical extent of the chromosphere of non-binary
K giant stars and detect any spatial structures in the chromosphere. We
performed observations with the CHARA interferometer and the VEGA beam combiner
at optical wavelengths. We observed seven non-binary K giant stars. We measured
the ratio of the radii of the photosphere to the chromosphere using the
interferometric measurements in the Halpha and the Ca II infrared triplet line
cores. For beta Ceti, spectro-interferometric observations are compared to an
non-local thermal equilibrium (NLTE) semi-empirical model atmosphere including
a chromosphere. The NLTE computations provide line intensities and contribution
functions that indicate the relative locations where the line cores are formed
and can constrain the size of the limb-darkened disk of the stars with
chromospheres. We measured the angular diameter of seven K giant stars and
deduced their fundamental parameters: effective temperatures, radii,
luminosities, and masses. We determined the geometrical extent of the
chromosphere for four giant stars. The chromosphere extents obtained range
between 16% to 47% of the stellar radius. The NLTE computations confirm that
the Ca II/849 nm line core is deeper in the chromosphere of ? Cet than either
of the Ca II/854 nm and Ca II/866 nm line cores. We present a modified version
of a semi-empirical model atmosphere derived by fitting the Ca II triplet line
cores of this star. In four of our targets, we also detect the signature of a
differential signal showing the presence of asymmetries in the chromospheres.
Conclusions. It is the first time that geometrical extents and structure in the
chromospheres of non-binary K giant stars are determined by interferometry.
These observations provide strong constrains on stellar atmosphere models.Comment: 10 pages, 12 figure
The Dynamics of Stellar Coronae Harboring Hot-jupiters II. A Space Weather Event on A Hot-jupiter
We carry out a numerical simulation depicting the effects of a Coronal Mass
Ejection (CME) event on a close-in giant planet in an extrasolar system. We
drive the CME in a similar manner as in simulations of space weather events on
Earth. The simulation includes the planetary orbital motion, which leads to the
forming of a comet-like planetary magnetotail which is oriented almost
perpendicular to the direction of propagation of the CME. The combination of
this feature and the fact that the CME does not expand much by the time it
reaches the planet leads to a unique CME-magnetosphere interaction, where the
CME itself is highly affected by the presence of the planetary magnetosphere.
We find that the planet is well-shielded from CME penetration, even for a
relatively weak internal magnetic field. The planetary angular momentum loss
associated with such an event is negligible compared to the total planetary
angular momentum. We also find that the energy which is deposited in the
magnetosphere is much higher than in the case of the Earth, and our simulation
suggests there is a large-scale change in the orientation of the
magnetosphere-ionosphere current system during the CME event.Comment: 16 pages, 10 figures, accepted to Ap
Radon--Nikodym representations of Cuntz--Krieger algebras and Lyapunov spectra for KMS states
We study relations between --KMS states on Cuntz--Krieger algebras
and the dual of the Perron--Frobenius operator .
Generalising the well--studied purely hyperbolic situation, we obtain under
mild conditions that for an expansive dynamical system there is a one--one
correspondence between --KMS states and eigenmeasures of
for the eigenvalue 1. We then consider
representations of Cuntz--Krieger algebras which are induced by Markov fibred
systems, and show that if the associated incidence matrix is irreducible then
these are --isomorphic to the given Cuntz--Krieger algebra. Finally, we
apply these general results to study multifractal decompositions of limit sets
of essentially free Kleinian groups which may have parabolic elements. We
show that for the Cuntz--Krieger algebra arising from there exists an
analytic family of KMS states induced by the Lyapunov spectrum of the analogue
of the Bowen--Series map associated with . Furthermore, we obtain a formula
for the Hausdorff dimensions of the restrictions of these KMS states to the set
of continuous functions on the limit set of . If has no parabolic
elements, then this formula can be interpreted as the singularity spectrum of
the measure of maximal entropy associated with .Comment: 30 pages, minor changes in the proofs of Theorem 3.9 and Fact
Coherent States of the q--Canonical Commutation Relations
For the -deformed canonical commutation relations for in some Hilbert
space we consider representations generated from a vector
satisfying , where .
We show that such a representation exists if and only if .
Moreover, for these representations are unitarily equivalent
to the Fock representation (obtained for ). On the other hand
representations obtained for different unit vectors are disjoint. We
show that the universal C*-algebra for the relations has a largest proper,
closed, two-sided ideal. The quotient by this ideal is a natural -analogue
of the Cuntz algebra (obtained for ). We discuss the Conjecture that, for
, this analogue should, in fact, be equal to the Cuntz algebra
itself. In the limiting cases we determine all irreducible
representations of the relations, and characterize those which can be obtained
via coherent states.Comment: 19 pages, Plain Te
The Highly Eccentric Pre-Main Sequence Spectroscopic Binary RX J0529.3+1210
The young system RX J0529.3+1210 was initially identified as a single-lined
spectroscopic binary. Using high-resolution infrared spectra, acquired with
NIRSPEC on Keck II, we measured radial velocities for the secondary. The method
of using the infrared regime to convert single-lined spectra into double-lined
spectra, and derive the mass ratio for the binary system, has been successfully
used for a number of young, low-mass binaries. For RX J0529.3+1210, a long-
period(462 days) and highly eccentric(0.88) binary system, we determine the
mass ratio to be 0.78+/-0.05 using the infrared double-lined velocity data
alone, and 0.73+/-0.23 combining visible light and infrared data in a full
orbital solution. The large uncertainty in the latter is the result of the
sparse sampling in the infrared and the high eccentricity: the stars do not
have a large velocity separation during most of their ~1.3 year orbit. A mass
ratio close to unity, consistent with the high end of the one sigma uncertainty
for this mass ratio value, is inconsistent with the lack of a visible light
detection of the secondary component. We outline several scenarios for a color
difference in the two stars, such as one heavily spotted component, higher
order multiplicity, or a unique evolutionary stage, favoring detection of only
the primary star in visible light, even in a mass ratio ~1 system. However, the
evidence points to a lower ratio. Although RX J0529.3+1210 exhibits no excess
at near-infrared wavelengths, a small 24 micron excess is detected, consistent
with circumbinary dust. The properties of this binary and its membership in
Lambda Ori versus a new nearby stellar moving group at ~90 pc are discussed. We
speculate on the origin of this unusual system and on the impact of such high
eccentricity on the potential for planet formation.Comment: 4 Figure
Models of Star-Planet Magnetic Interaction
Magnetic interactions between a planet and its environment are known to lead
to phenomena such as aurorae and shocks in the solar system. The large number
of close-in exoplanets that were discovered triggered a renewed interest in
magnetic interactions in star-planet systems. Multiple other magnetic effects
were then unveiled, such as planet inflation or heating, planet migration,
planetary material escape, and even modification of the host star properties.
We review here the recent efforts in modelling and understanding magnetic
interactions between stars and planets in the context of compact systems. We
first provide simple estimates of the effects of magnetic interactions and then
detail analytical and numerical models for different representative scenarii.
We finally lay out a series of future developments that are needed today to
better understand and constrain these fascinating interactions.Comment: 23 pages, 10 figures, accepted as a chapter in the Handbook of
Exoplanet
Kitaev's quantum double model from a local quantum physics point of view
A prominent example of a topologically ordered system is Kitaev's quantum
double model for finite groups (which in particular
includes , the toric code). We will look at these models from
the point of view of local quantum physics. In particular, we will review how
in the abelian case, one can do a Doplicher-Haag-Roberts analysis to study the
different superselection sectors of the model. In this way one finds that the
charges are in one-to-one correspondence with the representations of
, and that they are in fact anyons. Interchanging two of such
anyons gives a non-trivial phase, not just a possible sign change. The case of
non-abelian groups is more complicated. We outline how one could use
amplimorphisms, that is, morphisms to study the superselection
structure in that case. Finally, we give a brief overview of applications of
topologically ordered systems to the field of quantum computation.Comment: Chapter contributed to R. Brunetti, C. Dappiaggi, K. Fredenhagen, J.
Yngvason (eds), Advances in Algebraic Quantum Field Theory (Springer 2015).
Mainly revie
Generalized Fock Spaces, New Forms of Quantum Statistics and their Algebras
We formulate a theory of generalized Fock spaces which underlies the
different forms of quantum statistics such as ``infinite'', Bose-Einstein and
Fermi-Dirac statistics. Single-indexed systems as well as multi-indexed systems
that cannot be mapped into single-indexed systems are studied. Our theory is
based on a three-tiered structure consisting of Fock space, statistics and
algebra. This general formalism not only unifies the various forms of
statistics and algebras, but also allows us to construct many new forms of
quantum statistics as well as many algebras of creation and destruction
operators. Some of these are : new algebras for infinite statistics,
q-statistics and its many avatars, a consistent algebra for fractional
statistics, null statistics or statistics of frozen order, ``doubly-infinite''
statistics, many representations of orthostatistics, Hubbard statistics and its
variations.Comment: This is a revised version of the earlier preprint: mp_arc 94-43.
Published versio
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