14,103 research outputs found
A nonparametric test of exogeneity
This paper is concerned with inference about a function g that is identified by a conditional moment restriction involving instrumental variables. The function is nonparametric.
It satisfies mild regularity conditions but is otherwise unknown. The paper presents test of the hypothesis that g is the mean of a random variable Y conditional on a covariate X. The need to test this hypothesis arises frequently in economics. The test does not require nonparametric instrumental-variables (IV) estimation of g and is not subject to the ill-posed inverse problem
that nonparametric IV estimation entails. The test is consistent whenever g differs from the conditional mean function of Y on a set of non-zero probability. Moreover, the power of the test is arbitrarily close to 1 uniformly over a set of functions g whose distance from the conditional mean function is O(n^{-1/2}) where n is the sample size
Strong-coupling Jet Energy Loss from AdS/CFT
We propose a novel definition of a holographic light hadron jet and consider
the phenomenological consequences, including the very first fully
self-consistent, completely strong-coupling calculation of the jet nuclear
modification factor , which we find compares surprisingly well with
recent preliminary data from LHC. We show that the thermalization distance for
light parton jets is an extremely sensitive function of the \emph{a priori}
unspecified string initial conditions and that worldsheets corresponding to
non-asymptotic energy jets are not well approximated by a collection of null
geodesics. Our new string jet prescription, which is defined by a separation of
scales from plasma to jet, leads to the re-emergence of the late-time Bragg
peak in the instantaneous jet energy loss rate; unlike heavy quarks, the energy
loss rate is unusually sensitive to the very definition of the string theory
object itself. A straightforward application of the new jet definition leads to
significant jet quenching, even in the absence of plasma. By renormalizing the
in-medium suppression by that in the vacuum we find qualitative agreement with
preliminary CMS data in our simple plasma brick model. We
close with comments on our results and an outlook on future work.Comment: 28 pages, 9 figure
Self-Gravitating Strings and String/Black Hole Correspondence
In a recent essay, we discussed the possibility of using polymer sizing to
model the collapse of a single, long excited string to a black hole. In this
letter, we apply this idea to bring further support to string/black hole
correspondence. In particular, we reproduce Horowitz and Polchinki's results
for self-gravitating fundamental strings and speculate on the nature of the
quantum degrees of freedom of black holes in string theory.Comment: 8 pages, harvma
Supplement to the 1975 report on active and planned spacecraft and experiments
A listing and brief description of spacecraft and experiments designed to update the January 1975 report on active and planned spacecraft and experiments to March 31, 1975 was presented. The information is given in two sections. In the first, spacecraft and experiments that have become known to NSSDC since the original report or that have changed significantly are described. In the second, an alphabetical listing is given for all spacecraft and experiments described in the first section and in the original report. It also updates status of operation and launch dates to March 31, 1975
Supplement no. 1 to the January 1974 report on active and planned spacecraft and experiments
Updated information and descriptions on spacecraft and experiments are listed according to spacecraft name and principle experimental investigator. A cumulative index of active and planned spacecraft and experiments is provided; bar graph indexes for electromagnetic radiation experiments are included in table form
Atmospheric densities from Explorer 17 density gauges and a comparison with satellite drag data
Atmospheric density data from Explorer XVII GAUGES and satellite drag dat
Fundamental Bounds on First Passage Time Fluctuations for Currents
Current is a characteristic feature of nonequilibrium systems. In stochastic
systems, these currents exhibit fluctuations constrained by the rate of
dissipation in accordance with the recently discovered thermodynamic
uncertainty relation. Here, we derive a conjugate uncertainty relationship for
the first passage time to accumulate a fixed net current. More generally, we
use the tools of large-deviation theory to simply connect current fluctuations
and first passage time fluctuations in the limit of long times and large
currents. With this connection, previously discovered symmetries and bounds on
the large-deviation function for currents are readily transferred to first
passage times.Comment: 7 pages including S
Proof of the Finite-Time Thermodynamic Uncertainty Relation for Steady-State Currents
The thermodynamic uncertainty relation offers a universal energetic
constraint on the relative magnitude of current fluctuations in nonequilibrium
steady states. However, it has only been derived for long observation times.
Here, we prove a recently conjectured finite-time thermodynamic uncertainty
relation for steady-state current fluctuations. Our proof is based on a
quadratic bound to the large deviation rate function for currents in the limit
of a large ensemble of many copies.Comment: 3 page
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