18,837 research outputs found
Partial Strategyproofness: Relaxing Strategyproofness for the Random Assignment Problem
We present partial strategyproofness, a new, relaxed notion of
strategyproofness for studying the incentive properties of non-strategyproof
assignment mechanisms. Informally, a mechanism is partially strategyproof if it
makes truthful reporting a dominant strategy for those agents whose preference
intensities differ sufficiently between any two objects. We demonstrate that
partial strategyproofness is axiomatically motivated and yields a parametric
measure for "how strategyproof" an assignment mechanism is. We apply this new
concept to derive novel insights about the incentive properties of the
probabilistic serial mechanism and different variants of the Boston mechanism.Comment: Working Pape
Cosmological Perturbations in a Universe with a Domain Wall Era
Topologically protected sheet-like surfaces, called domain walls, form when
the potential of a field has a discrete symmetry that is spontaneously broken.
Since this condition is commonplace in field theory, it is plausible that many
of these walls were produced at some point in the early universe. Moreover, for
potentials with a rich enough structure, the walls can join and form a (at
large scales) homogeneous and isotropic network that dominates the energy
density of the universe for some time before decaying. In this thesis, we study
the faith of large scale perturbations in a cosmology with a short period of
domain wall dominance. Treating the domain wall network as a relativistic
elastic solid at large scales, we show that the perturbations that exited the
horizon during inflation get suppressed during the domain wall era, before
re-entering the horizon. This power suppression occurs because, unlike a
fluid-like universe, a solid-like universe can support sizable anisotropic
stress gradients across large scales which effectively act as mass for the
scalar and tensor modes. Interestingly, the amplitude of the primordial scalar
power spectrum can be closer to one in this cosmology and still give the
observed value of today. As a result, the usual bounds on the energy
scale of inflation get relaxed to values closer to the (more natural) Planck
scale. In the last part of this thesis, as an existence proof, we present a
hybrid inflation model with `waterfall' fields that can realize the
proposed cosmology. In this model, a domain wall network forms when an
approximate symmetry gets spontaneously broken at the end of inflation,
and for , we show that there is a region in parameter space where the
network dominates the energy density for a few e-folds before decaying and
reheating the universe.Comment: Ph.D. Thesis, Dec 201
On Iterated Dominance, Matrix Elimination, and Matched Paths
We study computational problems arising from the iterated removal of weakly
dominated actions in anonymous games. Our main result shows that it is
NP-complete to decide whether an anonymous game with three actions can be
solved via iterated weak dominance. The two-action case can be reformulated as
a natural elimination problem on a matrix, the complexity of which turns out to
be surprisingly difficult to characterize and ultimately remains open. We
however establish connections to a matching problem along paths in a directed
graph, which is computationally hard in general but can also be used to
identify tractable cases of matrix elimination. We finally identify different
classes of anonymous games where iterated dominance is in P and NP-complete,
respectively.Comment: 12 pages, 3 figures, 27th International Symposium on Theoretical
Aspects of Computer Science (STACS
A note on blockers in posets
The blocker of an antichain in a finite poset is the set of
elements minimal with the property of having with each member of a common
predecessor. The following is done:
1. The posets for which for all antichains are characterized.
2. The blocker of a symmetric antichain in the partition lattice is
characterized.
3. Connections with the question of finding minimal size blocking sets for
certain set families are discussed
Melnikov's approximation dominance. Some examples
We continue a previous paper to show that Mel'nikov's first order formula for
part of the separatrix splitting of a pendulum under fast quasi periodic
forcing holds, in special examples, as an asymptotic formula in the forcing
rapidity.Comment: 46 Kb; 9 pages, plain Te
A consistency check for Renormalons in Lattice Gauge Theory: beta^(-10) contributions to the SU(3) plaquette
We compute the perturbative expansion of the Lattice SU(3) plaquette to
beta^(-10) order. The result is found to be consistent both with the expected
renormalon behaviour and with finite size effects on top of that.Comment: 15 pages, 5 colour eps figures. Axes labels added in the figures. A
comment added in the appendi
Map Matching with Simplicity Constraints
We study a map matching problem, the task of finding in an embedded graph a
path that has low distance to a given curve in R^2. The Fr\'echet distance is a
common measure for this problem. Efficient methods exist to compute the best
path according to this measure. However, these methods cannot guarantee that
the result is simple (i.e. it does not intersect itself) even if the given
curve is simple. In this paper, we prove that it is in fact NP-complete to
determine the existence a simple cycle in a planar straight-line embedding of a
graph that has at most a given Fr\'echet distance to a given simple closed
curve. We also consider the implications of our proof on some variants of the
problem
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