311 research outputs found
Gravitational shock waves and vacuum fluctuations
We show that the vacuum expectation value of the stress-energy tensor of a
scalar particle on the background of a spherical gravitational shock wave does
not give a finite expression in second order perturbation theory, contrary to
the case seen for the impulsive wave. No infrared divergences appear at this
order. This result shows that there is a qualitative difference between the
shock and impulsive wave solutions which is not exhibited in first order.Comment: Submitted to Class. and Quant. Grav.,7 pages, no figure
Heun-type solutions for Schwarzschild metric with electromagnetic fields
We find confluent Heun solutions to the radial equations of two
Halilsoy-Badawi metrics. For the first metric, we studied the radial part of
the massless Dirac equation and for the second case, we studied the radial part
of the massless Klein-Gordon equation.Comment: 8 pages, 2 figures. Matches the published versio
Heun and Mathieu functions as solutions of the Dirac equation
We give examples of where the Heun function exists as solutions of wave
equations encountered in general relativity. While the Dirac equation written
in the background of Nutku helicoid metric yields Mathieu functions as its
solutions in four spacetime dimensions, the trivial generalization to five
dimensions results in the double confluent Heun function. We reduce this
solution to the Mathieu function with some transformations. We must apply
Atiyah-Patodi-Singer spectral boundary conditions to this system since the
metric has a singularity at the origin.Comment: 5 pages, Prepared for the Spanish Relativity Meeting (ERE 2007),
Tenerife, Spain, 10-14 Sep 200
Analyzing Default Risk and Liquidity Demand during a Financial Crisis: The Case of Canada
This paper explores the reliability of using prices of credit default swap contracts (CDS) as indicators of default probabilities during the 2007/2008 financial crisis. We use data from the Canadian financial system to show that these publicly available risk measures, while indicative of initial problems of the financial system as a whole, do not seem to correspond to risks implied by the cross-sectional heterogeneity in bank behavior in short-term lending markets. Strategies in, and reliance on the payments system as well as special liquidity-supplying tools provided by the central bank seem to be more important additional indicators of distress of individual banks, or lack thereof than the CDSs. It therefore seems that central banks should utilize high-frequency data on liquidity demand to obtain a better picture of financial health of individual participants of the financial system.Financial Institutions; Financial markets; Payment, clearing, and settlement systems
Gürsey Modeli Ve Bazı Uygulamaları
Konferans Bildirisi -- Teorik ve Uygulamalı Mekanik Türk Milli Komitesi, 2008Conference Paper -- Theoretical and Applied Mechanical Turkish National Committee, 2008Feza Gürsey’in 1956 yılında ortaya attığı ve Fikret Kortel’in aynı yıl klasik çözümlerini bulduğu temel parçacık fiziği modeli tanıtılmış ve modeli kuantalaştırmak için gösterilen bazı çabalar anlatılmıştır.We review the model proposed by Feza Gürsey in 1956 for elementary particle physics, whose classical solutions were found by Fikret Kortel during the same year. We also summarize some attempts to quantize this classical model
Comparison of Exact and perturbative Results for Two Metrics
We compare the exact and perturbative results in two metrics and show that
the spurious effects due to the perturbation method do not survive for
physically relevant quantities such as the vacuum expectation value of the
stress-energy tensor.Comment: 12 page
The collision and snapping of cosmic strings generating spherical impulsive gravitational waves
The Penrose method for constructing spherical impulsive gravitational waves
is investigated in detail, including alternative spatial sections and an
arbitrary cosmological constant. The resulting waves include those that are
generated by a snapping cosmic string. The method is used to construct an
explicit exact solution of Einstein's equations describing the collision of two
nonaligned cosmic strings in a Minkowski background which snap at their point
of collision.Comment: 10 pages, 6 figures, To appear in Class. Quantum Gra
Gauged System Mimicking the G\"{u}rsey Model
We comment on the changes in the constrained model studied earlier when
constituent massless vector fields are introduced. The new model acts like a
gauge-Higgs-Yukawa system, although its origin is different.Comment: 8 pages, RevTex4; published versio
Dynamic Price Competition: Theory and Evidence from Airline Markets
We introduce a model of oligopoly dynamic pricing where firms with limited capacity face a sales deadline. We establish conditions under which the equilibrium is unique and converges to a system of differential equations. Using unique and comprehensive pricing and bookings data for competing U.S. airlines, we estimate our model and find that dynamic pricing results in higher output but lower welfare than under uniform pricing. Our theoretical and empirical findings run counter to standard results in single-firm settings due to the strategic role of competitor scarcity. Pricing heuristics commonly used by airlines increase welfare relative to estimated equilibrium predictions
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