9,948 research outputs found
SU(2) gauge theory of gravity with topological invariants
The most general gravity Lagrangian in four dimensions contains three
topological densities, namely Nieh-Yan, Pontryagin and Euler, in addition to
the Hilbert-Palatini term. We set up a Hamiltonian formulation based on this
Lagrangian. The resulting canonical theory depends on three parameters which
are coefficients of these terms and is shown to admit a real SU(2) gauge
theoretic interpretation with a set of seven first-class constraints. Thus, in
addition to the Newton's constant, the theory of gravity contains three
(topological) coupling constants, which might have non-trivial imports in the
quantum theory.Comment: Based on a talk at Loops-11, Madrid, Spain; To appear in Journal of
Physics: Conference Serie
Inmarsat aeronautical mobile satellite system: Internetworking issues
The Inmarsat Aeronautical Mobile Satellite System (AMSS) provides air-ground and air-air communications services to aero-mobile users on a global basis. Communicating parties may be connected either directly, or more commonly, via interconnecting networks to the Inmarsat AMSS, in order to construct end-to-end communications circuits. The aircraft earth station (AES) and the aeronautical ground earth station (GES) are the points of interconnection of the Inmarsat AMSS to users, as well as to interconnecting networks. This paper reviews the internetworking aspects of the Inmarsat AMSS, by introducing the Inmarsat AMSS network architecture and services concepts and then discussing the internetwork address/numbering and routing techniques
On the Kolmogorov--Wiener--Masani spectrum of a multi-mode weakly stationary quantum process
We introduce the notion of a -mode weakly stationary quantum process
based on the canonical Schr\"odinger pairs of position and momentum
observables in copies of , indexed by an additive abelian
group of countable cardinality. Such observables admit an autocovariance
map from into the space of real matrices.
The map on the discrete group admits a spectral
representation as the Fourier transform of a complex Hermitain
matrix-valued totally finite measure on the compact character group
, called the Kolmogorov-Wiener-Masani (KWM) spectrum of the
process . Necessary and sufficient conditions on a
complex Hermitian matrix-valued measure on to be the KWM
spectrum of a process are obtained. This enables the construction of
examples. Our theorem reveals the dramatic influence of the uncertainty
relations among the position and momentum observables on the KWM spectrum of
the process . In particular, KWM spectrum cannot admit a gap of
positive Haar measure in .
The relationship between the number of photons in a particular mode at any
site of the process and its KWM spectrum needs further investigation.Comment: 17 pages, added Theorem 4.2 and some remarks. Comments welcome.
Keywords: Weakly stationary quantum process, Kolmogorov-Wiener-Masani
spectrum, autocovariance map, spectral representation, uncertainty relation
Did Prepayments Sustain the Subprime Market?
This paper demonstrates that the reason for widespread default of mortgages in the subprime market was a sudden reversal in the house price appreciation of the early 2000's. Using loan-level data on subprime mortgages, we observe that the majority of subprime loans were hybrid adjustable rate mortgages, designed to impose substantial financial burden on reset to the fully indexed rate. In a regime of rising house prices, a financially distressed borrower could avoid default by prepaying the loan and our results indicate that subprime mortgages originated between 1998 and 2005 had extremely high prepayment rates. Most important, prepayment rates on subprime mortgages were extremely high (i) not just for ARMs but FRMs as well, (ii) even before the reset dates on hybrid-ARMs and (iii) despite prepayment penalties on the contract. However, a sudden reversal in house price appreciation increased default in this market because it made this prepayment exit option cost-prohibitive. In short, prepayments sustained the subprime boom and the extremely high default rates on 2006-2007 vintages were largely due to the inability of these mortgages to prepay (an option that was available for mortgages of earlier vintages).mortgages;subprime;refinance;prepayment;crisis
Fock spaces corresponding to positive definite linear transformations
Suppose is a positive real linear transformation on a finite dimensional
complex inner product space . The reproducing kernel for the Fock space of
square integrable holomorphic functions on relative to the Gaussian measure
is described
in terms of the holomorphic--antiholomorphic decomposition of the linear
operator . Moreover, if commutes with a conjugation on , then a
restriction mapping to the real vectors in is polarized to obtain a
Segal--Bargmann transform, which we also study in the Gaussian-measure setting
- …