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.