8,818 research outputs found
Establishing a department of community affairs in Illinois
"This paper was filed with the Illinois Cities and Villages Municipal Problems Commission of the Illinois General Assembly on February 10, 1969."Cover title
On the complete integrability of the discrete Nahm equations
The discrete Nahm equations, a system of matrix valued difference equations,
arose in the work of Braam and Austin on half-integral mass hyperbolic
monopoles.
We show that the discrete Nahm equations are completely integrable in a
natural sense: to any solution we can associate a spectral curve and a
holomorphic line-bundle over the spectral curve, such that the discrete-time DN
evolution corresponds to walking in the Jacobian of the spectral curve in a
straight line through the line-bundle with steps of a fixed size. Some of the
implications for hyperbolic monopoles are also discussed
Circle actions, central extensions and string structures
The caloron correspondence can be understood as an equivalence of categories
between -bundles over circle bundles and -bundles where
is the group of smooth loops in . We use it, and lifting bundle gerbes,
to derive an explicit differential form based formula for the (real) string
class of an -bundle.Comment: 25 page
Hot Jupiters in binary star systems
Radial velocity surveys find Jupiter mass planets with semi-major axes a less
than 0.1 AU around ~1% of solar-type stars; counting planets with as large
as 5 AU, the fraction of stars having planets reaches ~ 10% {Marcy,Butler}. An
examination of the distribution of semi-major axes shows that there is a clear
excess of planets with orbital periods around 3 or 4 days, corresponding to
a~0.03$ AU, with a sharp cutoff at shorter periods (see Figure 1). It is
believed that Jupiter mass planets form at large distances from their parent
stars; some fraction then migrate in to produce the short period objects. We
argue that a significant fraction of the `hot Jupiters' (a<0.1 AU) may arise in
binary star systems in which the orbit of the binary is highly inclined to the
orbit of the planet. Mutual torques between the two orbits drive down the
minimum separation or periapse r_p between the planet and its host star (the
Kozai mechanism). This periapse collapse is halted when tidal friction on the
planet circularizes the orbit faster than Kozai torque can excite it. The same
friction then circularizes the planet orbit, producing hot Jupiters with the
peak of the semimajor axis distribution lying around 3 days. For the observed
distributions of binary separation, eccentricity and mass ratio, roughly 2.5%
of planets with initial semimajor axis a_p ~ 5au will migrate to within 0.1au
of their parent star. Kozai migration could account for 10% or more of the
observed hot Jupiters.Comment: accepted to ApJ main journal, added one figure and expanded
discussion
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