10,873 research outputs found
Polytropic spheres in Palatini f(R) gravity
We examine static spherically symmetric polytropic spheres in Palatini f(R)
gravity and show that no regular solutions to the field equations exist for
physically relevant cases such as a monatomic isentropic gas or a degenerate
electron gas, thus casting doubt on the validity of Palatini f(R) gravity as an
alternative to General Relativity.Comment: Talk given by EB at the 30th Spanish Relativity Meeting, 10 - 14
September 2007, Tenerife (Spain). Based on arXiv:gr-qc/0703132 and
arXiv:0712.1141 [gr-qc
Confidence Building in Emerging Stock Markets
Investor confidence is a major determinant of financial integration for emerging markets and their stock prices. We investigate whether privatization also has a significant effect on emerging stock market development through the resolution of policy risk. We argue that a sustained privatization program represents a major test of political commitment to market oriented reforms and to safer private property rights. The evidence suggests that progress in privatization gradually leads to increased confidence as measured by perceived policy risk. Moreover, increased confidence has a strong effect on local market development and excess returns. We conclude that, while liberalization is a necessary condition for market development, the resolution of policy risk resulting from successful privatization has been an important source for the rapid growth of stock markets in emerging economies.http://deepblue.lib.umich.edu/bitstream/2027.42/39750/3/wp366.pd
A no-go theorem for polytropic spheres in Palatini f(R) gravity
Non-vacuum static spherically-symmetric solutions in Palatini f(R) gravity
are examined. It is shown that for generic choices of f(R), there are
commonly-used equations of state for which no satisfactory physical solution of
the field equations can be found within this framework, apart from in the
special case of General Relativity, casting doubt on whether Palatini f(R)
gravity can be considered as giving viable alternatives to General Relativity.Comment: 7 pages, 1 figure. Version accepted for publication as a Fast Track
Communication in CQ
Unbinding of mutually avoiding random walks and two dimensional quantum gravity
We analyze the unbinding transition for a two dimensional lattice polymer in
which the constituent strands are mutually avoiding random walks. At low
temperatures the strands are bound and form a single self-avoiding walk. We
show that unbinding in this model is a strong first order transition. The
entropic exponents associated to denaturated loops and end-segments
distributions show sharp differences at the transition point and in the high
temperature phase. Their values can be deduced from some exact arguments
relying on a conformal mapping of copolymer networks into a fluctuating
geometry, i.e. in the presence of quantum gravity. An excellent agreement
between analytical and numerical estimates is observed for all cases analized.Comment: 9 pages, 11 figures, revtex
The gravity of magnetic stresses and energy
In the framework of designing laboratory tests of relativistic gravity, we
investigate the gravitational field produced by the magnetic field of a
solenoid. Observing this field might provide a mean of testing whether stresses
gravitate as predicted by Einstein's theory. A previous study of this problem
by Braginsky, Caves and Thorne predicted that the contribution to the
gravitational field resulting from the stresses of the magnetic field and of
the solenoid walls would cancel the gravitational field produced by the
mass-energy of the magnetic field, resulting in a null magnetically-generated
gravitational force outside the solenoid. They claim that this null result,
once proved experimentally, would demonstrate the stress contribution to
gravity. We show that this result is incorrect, as it arises from an incomplete
analysis of the stresses, which neglects the axial stresses in the walls. Once
the stresses are properly evaluated, we find that the gravitational field
outside a long solenoid is in fact independent of Maxwell and material
stresses, and it coincides with the newtonian field produced by the linear mass
distribution equivalent to the density of magnetic energy stored in a unit
length of the solenoid. We argue that the gravity of Maxwell stress can be
directly measured in the vacuum region inside the solenoid, where the newtonian
noise is absent in principle, and the gravity generated by Maxwell stresses is
not screened by the negative gravity of magnetic-induced stresses in the
solenoid walls.Comment: 10 pages, final version accepted for publication in PR
Outside Finance, Dominant Investors and Strategic Transparency
This paper studies optimal financial contracts and product market competition under a strategic transparency decision. When firms seeking outside finance resort to actively monitored debt in order to commit against opportunistic behaviour, the dominant lender can influence corporate transparency. More transparency about a firm's competitive position has both strategic advantages and disadvantages: in general, transparency results in higher variability of profits and output. Thus lenders prefer less information dissemination, as this protects firms when in a weak competitive position, while equityholders prefer more disclosure to maximize profitability when in a strong position. We show that bank-controlled firms will be opaque, while shareholder- run firms prefer more transparency. In fact, we can predict a clustering of characteristics associated with bank dominance: opaqueness, low variability of profits, slightly reduced average profits, uncertainty about assets in place, and relatively high financing needs all should be observed jointly for bank controlled firms.corporate governance; transparency; bank finance; product market competition; capital structure
Design and Implementation of Distributed Resource Management for Time Sensitive Applications
In this paper, we address distributed convergence to fair allocations of CPU
resources for time-sensitive applications. We propose a novel resource
management framework where a centralized objective for fair allocations is
decomposed into a pair of performance-driven recursive processes for updating:
(a) the allocation of computing bandwidth to the applications (resource
adaptation), executed by the resource manager, and (b) the service level of
each application (service-level adaptation), executed by each application
independently. We provide conditions under which the distributed recursive
scheme exhibits convergence to solutions of the centralized objective (i.e.,
fair allocations). Contrary to prior work on centralized optimization schemes,
the proposed framework exhibits adaptivity and robustness to changes both in
the number and nature of applications, while it assumes minimum information
available to both applications and the resource manager. We finally validate
our framework with simulations using the TrueTime toolbox in MATLAB/Simulink
Confidence Building in Emerging Stock Markets
Investor confidence is a major determinant of financial integration for emerging markets and their stock prices. We investigate whether privatization also has a significant effect on emerging stock market development through the resolution of policy risk. We argue that a sustained privatization program represents a major test of political commitment to market oriented reforms and to safer private property rights. The evidence suggests that progress in privatization gradually leads to increased confidence as measured by perceived policy risk. Moreover, increased confidence has a strong effect on local market development and excess returns. We conclude that, while liberalization is a necessary condition for market development, the resolution of policy risk resulting from successful privatization has been an important source for the rapid growth of stock markets in emerging economies.
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