1,076,248 research outputs found

### Gravity Models of the Intra-EU Trade: Application of the Hausman-Taylor Estimation in Heterogeneous Panels with Common Time-specific Factors

In this paper we follow recent developments of panel data studies and explicitly allow for the existence of unobserved common time-specific factors where their individual responses are also allowed to be heterogeneous across cross section units. In the context of this extended panel data framework we generalize the Hausman-Taylor estimation methodology and develop the associated econometric theory. We apply our proposed estimation technique along with the conventional panel data approaches to a comprehensive analysis of the gravity equation of bilateral trade flows amongst the 15 European countries over 1960-2001. Empirical results clearly demonstrate that our proposed approach fits the data reasonably well and provides much more sensible results than the conventional approach based on the fixed time dummies. These findings may highlight the importance of allowing for a certain degree of cross section dependence through unobserved heterogeneous time specific common effects, otherwise the resulting estimates would be severely biased.Gravity Models of Trade, Heterogeneous Panel Data, Hausman-Taylor Estimation, Time-specific Common Factors, Intra-EU Trade.

### Lineal gravity from planar gravity

We show how to obtain the two-dimensional black hole action by dimensional
reduction of the three-dimensional Einstein action with a non-zero cosmological
constant. Starting from the Chern-Simons formulation of 2+1 gravity, we obtain
the 1+1 dimensional gauge formulation given by Verlinde. Remarkably, the
proposed reduction shares the relevant features of the formulation of Cangemi
and Jackiw, without the need for a central charge in the algebra. We show how
the Lagrange multipliersin these formulations appear naturally as the remnants
of the three dimensional connection associated to symmetries that have been
lostin the dimensional reduction. The proposed dimensional reduction involves a
shift in the three dimensional connection whose effect is to make the length of
the extra dimension infinite.Comment: 13 pages, plain Te

### Stochastic Gravity: Beyond Semiclassical Gravity

The back-reaction of a classical gravitational field interacting with quantum
matter fields is described by the semiclassical Einstein equation, which has
the expectation value of the quantum matter fields stress tensor as a source.
The semiclassical theory may be obtained from the quantum field theory of
gravity interacting with N matter fields in the large N limit. This theory
breaks down when the fields quantum fluctuations are important. Stochastic
gravity goes beyond the semiclassical limit and allows for a systematic and
self-consistent description of the metric fluctuations induced by these quantum
fluctuations. The correlation functions of the metric fluctuations obtained in
stochastic gravity reproduce the correlation functions in the quantum theory to
leading order in an 1/N expansion. Two main applications of stochastic gravity
are discussed. The first, in cosmology, to obtain the spectrum of primordial
metric perturbations induced by the inflaton fluctuations, even beyond the
linear approximation. The second, in black hole physics, to study the
fluctuations of the horizon of an evaporating black hole.Comment: 12 pages, no figures, proceedings of the XXIX Spanish Relativity
Meetin

### Dilaton Gravity with a Non-minmally Coupled Scalar Field

We discuss the two-dimensional dilaton gravity with a scalar field as the
source matter. The coupling between the gravity and the scalar, massless, field
is presented in an unusual form. We work out two examples of these couplings
and solutions with black-hole behaviour are discussed and compared with those
found in the literature

### On Classical Equivalence Between Noncritical and Einstein Gravity : The AdS/CFT Perspectives

We find that noncritical gravity, a special class of higher derivative
gravity, is classically equivalent to Einstein gravity at the full nonlinear
level. We obtain the viscosity-to-entropy ratio and the second order transport
coefficients of the dual fluid of noncritical gravity to all orders in the
coupling of higher derivative terms. We also compute the holographic
entanglement entropy in the dual CFT of noncritical gravity. All these results
confirm the nonlinear equivalence between noncritical gravity and Einstein
gravity at the classical level.Comment: 19 pages, no figure

### Is nonrelativistic gravity possible?

We study nonrelativistic gravity using the Hamiltonian formalism. For the
dynamics of general relativity (relativistic gravity) the formalism is well
known and called the Arnowitt-Deser-Misner (ADM) formalism. We show that if the
lapse function is constrained correctly, then nonrelativistic gravity is
described by a consistent Hamiltonian system. Surprisingly, nonrelativistic
gravity can have solutions identical to relativistic gravity ones. In
particular, (anti-)de Sitter black holes of Einstein gravity and IR limit of
Horava gravity are locally identical.Comment: 4 pages, v2, typos corrected, published in Physical Review

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