2,100 research outputs found
Welfare Tradeoffs in U.S. Rail Mergers
The renegotiation of regulatory contracts is known to prevent regulators from achieving the full commitment efficient outcome in dynamic contexts. However, assessing the cost of such renegotiation remains an open issue from an empirical viewpoint. To address this question, we fit a structural principal-agent model with renegotiation on a set of urban transport service contracts. The model captures two important features of the industry. First, only two types of contracts are used in practice (fixed-price and cost-plus). Second, subsidies increase over time. We compare a scenario with renegotiation and a hypothetical situation with full commitment. We conclude that the welfare gains from improving commitment would be significant but would accrue mostly to operators.
Upper Bounds on epsilon'/epsilon Parameters B_6^{(1/2)} and B_8^{(3/2)} from Large N QCD and other News
We demonstrate that in the large N approach developed by the authors in
collaboration with Bardeen, the parameters B_6^{(1/2)} and B_8^{(3/2)}
parametrizing the K\to\pi\pi matrix elements _0 and _2 of the
dominant QCD and electroweak operators receive both negative O(1/N) corrections
such that B_6^{(1/2)} < B_8^{(3/2)}<1 in agreement with the recent lattice
results of the RBC-UKQCD collaboration. We also point out that the pattern of
the size of the hadronic matrix elements of all QCD and electroweak penguin
operators Q_i contributing to the K\to \pi \pi amplitudes A_0 and A_2, obtained
by this lattice collaboration, provides further support to our large N
approach. In particular, a very precise lattice result for the matrix element
_0 implies for the corresponding parameter B_8^{(1/2)}=1.0\pm 0.2 to be
compared with large N value B_8^{(1/2)}=1.1\pm 0.1. We discuss briefly the
implications of these findings for the ratio epsilon'/epsilon. In fact, with
the precise value for B_8^{(3/2)} from RBC-UKQCD collaboration, our upper bound
on B_6^{(1/2)} implies epsilon'/epsilon in the SM roughly by a factor of two
below its experimental value (16.6\pm 2.3)\times 10^{-4}. We also briefly
comment on the parameter \hat B_K and the \Delta I=1/2$ rule.Comment: 19 pages, Additional section on results from other large N approaches
added. References added. Conclusions unchanged. Matches the version to appear
in JHE
Isospin-breaking in : Impact of at the Dawn of the 2020s
For direct CP-violation in decays, the usual isospin-breaking
effects at the percent level are amplified by the dynamics behind the rule and conventionally encoded in parameters. The
updated prediction of the
Chiral Perturbation Theory for the strong isospin-breaking due to
mixing confirms such a tendency but is quite sensitive to the
theoretical input value of the low-energy constant corresponding to the
flavour-singlet exchange contribution in this truncated octet scheme.
We rather exploit the phenomenological mixing as a probe for
the non-negligible flavour-singlet component of the physical pole to
find in a complete nonet scheme.
A large central value in the nonet scheme is thus substituted for a large
uncertainty in the octet one. Including the experimental mass
difference as the dominant electromagnetic isospin-breaking, we obtain for the
effective parameter entering the ratio an improved result
to be compared with
used in recent analyses of
. Accordingly, we get a reduction from
to
and thereby
an effective suppression of by isospin-breaking
corrections as large as relative to the recent RBC-UKQCD value.Comment: 18 pages, no figures, typos removed, additional clarifying comments
and one reference added, results unchanged. Version to appear in EPJ
Cosmological-parameter determination with microwave background maps
The angular power spectrum of the cosmic microwave background (CMB) contains information on virtually all cosmological parameters of interest, including the geometry of the Universe (Ω), the baryon density, the Hubble constant (h), the cosmological constant (Λ), the number of light neutrinos, the ionization history, and the amplitudes and spectral indices of the primordial scalar and tensor perturbation spectra. We review the imprint of each parameter on the CMB. Assuming only that the primordial perturbations were adiabatic, we use a covariance-matrix approach to estimate the precision with which these parameters can be determined by a CMB temperature map as a function of the fraction of sky mapped, the level of pixel noise, and the angular resolution. For example, with no prior information about any of the cosmological parameters, a full-sky CMB map with 0.5° angular resolution and a noise level of 15 μK per pixel can determine Ω, h, and Λ with standard errors of ±0.1 or better, and provide determinations of other parameters which are inaccessible with traditional observations. Smaller beam sizes or prior information on some of the other parameters from other observations improves the sensitivity. The dependence on the underlying cosmological model is discussed
Mass Issues in Fundamental Interactions
Driven by the mass problem, we raise some issues of the fundamental
interactions in terms of non trivial commutation relations implemented within
toy theories.Comment: Based on lectures given at the 2008 European School of HE
Treatment evaluation in the case of interactions within markets
We extend the standard evaluation framework to allow for interactions between individuals within segmented markets. An individualâs outcome depends not only on the assigned treatment status but also on (features of) the distribution of the assigned treatments in his market. To evaluate how the distribution of treatments within a market causally affects the average effect within the market, averaged over the full population, we develop an identification and estimation method in two steps. The first one focuses on the distribution of the treatment within markets and between individuals and the second step addresses the distribution of the treatment between markets. We apply our method to data on training programs for unemployed workers in France. We use a rich administrative register of unemployment and training spells as well as the information on local labor demand that is used by unemployment agencies to allocate training programs. The results show that the average treatment effect on the employment rate causally decreases with respect to the proportion of treated in the market. Our analysis accounts for unobserved heterogeneity between markets (using the longitudinal dimension of the data) and, in a robustness check, between individuals.Treatment evaluation; equilibrium effects; matching estimators
LiveCap: Real-time Human Performance Capture from Monocular Video
We present the first real-time human performance capture approach that
reconstructs dense, space-time coherent deforming geometry of entire humans in
general everyday clothing from just a single RGB video. We propose a novel
two-stage analysis-by-synthesis optimization whose formulation and
implementation are designed for high performance. In the first stage, a skinned
template model is jointly fitted to background subtracted input video, 2D and
3D skeleton joint positions found using a deep neural network, and a set of
sparse facial landmark detections. In the second stage, dense non-rigid 3D
deformations of skin and even loose apparel are captured based on a novel
real-time capable algorithm for non-rigid tracking using dense photometric and
silhouette constraints. Our novel energy formulation leverages automatically
identified material regions on the template to model the differing non-rigid
deformation behavior of skin and apparel. The two resulting non-linear
optimization problems per-frame are solved with specially-tailored
data-parallel Gauss-Newton solvers. In order to achieve real-time performance
of over 25Hz, we design a pipelined parallel architecture using the CPU and two
commodity GPUs. Our method is the first real-time monocular approach for
full-body performance capture. Our method yields comparable accuracy with
off-line performance capture techniques, while being orders of magnitude
faster
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