16,312 research outputs found
Random Matching in the College Admissions Problem
In the college admissions problem, we consider the incentives confronting agents who face the prospect of being matched by a random stable mechanism. We provide a fairly complete characterization of ordinal equilbria. Namely, every ordinal equilib- rium yields a degenerate probability distribution. Furthermore, individual rationality is a necessary and sufficient condition for an equilibrium outcome, while stability is guaranteed in ordinal equilibrium where firms act straightforwardly. Finally, we re- late equilibrium behavior in random and in deterministic mechanisms.Matching; College Admissions Problem; Stability; Random Mechanism.
Revisiting the gauge fields of strained graphene
We show that, when graphene is only subject to strain, the spin connection
gauge field that arises plays no measurable role, but when intrinsic curvature
is present and strain is small, spin connection dictates most the physics. We
do so by showing that the Weyl field associated with strain is a pure gauge
field and no constraint on the -dimensional spacetime appears. On the
other hand, for constant intrinsic curvature that also gives a pure-gauge Weyl
field, we find a classical manifestation of a quantum Weyl anomaly, descending
from a constrained spacetime. We are in the position to do this because we find
the equations that the conformal factor in -dimensions has to satisfy,
that is a nontrivial generalization to -dimensions of the classic
Liouville equation of differential geometry of surfaces. Finally, we comment on
the peculiarities of the only gauge field that can describe strain, that is the
well known {\it pseudogauge field} and , and conclude by offering some scenarios of fundamental physics that
this peculiar field could help to realize.Comment: 24 pages, 6 figures. Comments added, text reduced and relevant
references include
Three-quark exchange operators, crossing matrices and Fierz transformations in SU(2) and SU(3)
We give explicit expressions for the three-quark exchange operators, crossing
matrices and Fierz transforms for the SU(2) and SU(3) groups. We identify the
invariant terms in these operators and express them in terms of Casimir
operators.Comment: 8 pages, RevTex, to appear in Jour. Math. Phy
Adaptive Network Dynamics and Evolution of Leadership in Collective Migration
The evolution of leadership in migratory populations depends not only on
costs and benefits of leadership investments but also on the opportunities for
individuals to rely on cues from others through social interactions. We derive
an analytically tractable adaptive dynamic network model of collective
migration with fast timescale migration dynamics and slow timescale adaptive
dynamics of individual leadership investment and social interaction. For large
populations, our analysis of bifurcations with respect to investment cost
explains the observed hysteretic effect associated with recovery of migration
in fragmented environments. Further, we show a minimum connectivity threshold
above which there is evolutionary branching into leader and follower
populations. For small populations, we show how the topology of the underlying
social interaction network influences the emergence and location of leaders in
the adaptive system. Our model and analysis can describe other adaptive network
dynamics involving collective tracking or collective learning of a noisy,
unknown signal, and likewise can inform the design of robotic networks where
agents use decentralized strategies that balance direct environmental
measurements with agent interactions.Comment: Submitted to Physica D: Nonlinear Phenomen
Dynamical Contents of Unconventional Supersymmetry
The Dirac Hamiltonian formalism is applied to a system in -dimensions
consisting of a Dirac field minimally coupled to Chern-Simons and
connections, and , respectively. This theory is connected
to a supersymmetric Chern-Simons form in which the gravitino has been projected
out (unconventional supersymmetry) and, in the case of a flat background,
corresponds to the low energy limit of graphene. The separation between
first-class and second-class constraints is performed explicitly, and both the
field equations and gauge symmetries of the Lagrangian formalism are fully
recovered. The degrees of freedom of the theory in generic sectors shows that
the propagating states correspond to fermionic modes in the background
determined by the geometry of the graphene sheet and the nondynamical
electromagnetic field. This is shown for the following canonical sectors: i) a
conformally invariant generic description where the spinor field and the
dreibein are locally rescaled; ii) a specific configuration for the Dirac
fermion consistent with its spin, where Weyl symmetry is exchanged by time
reparametrizations; iii) the vacuum sector , which is of interest for
perturbation theory. For the latter the analysis is adapted to the case of
manifolds with boundary, and the corresponding Dirac brackets together with the
centrally extended charge algebra are found. Finally, the
generalization of the gauge group is briefly treated, yielding analogous
conclusions for the degrees of freedom.Comment: 17 pages. Accepted version for publication in JHE
School Choice and Information An Experimental Study on Matching Mechanisms
We present an experimental study where we analyze three well- known matching mechanisms - the Boston, the Gale-Shapley, and the Top Trading Cycles mechanisms - in three different informational set- tings. Our experimental results are consistent with the theory, sug- gesting that the TTC mechanism outperforms both the Boston and the Gale-Shapley mechanisms in terms of efficiency and it is as suc- cessful as the Gale-Shapley mechanism regarding the proportion of truthful preference revelation, whereas manipulation is stronger un- der the Boston mechanism. In addition, even though agents are much more likely to revert to truthtelling in lack of information about the others' payooffs - ignorance may be beneficial in this context - , the TTC mechanism results less sensitive to the amount of information that participants hold. These results therefore suggest that the use of the TTC mechanism in practice is more desirable than of the others.
Comparative study of patients knowledge on osteoarthritis treatment options to ACR guidelines
Portuguese population is growing older, according to national
data in 2011 the aging index was 129. The number of elderly population
is higher than the younger; average life expectancy is 79,2 years (1).
Because knee Osteoarthritis increases with age, and according to WHO
80% of these subjects will have some degree of impairment and 25% will
not be able to do their daily living activities (2), OA has a big impact on
the sustainability of both health and social care as populations grow
older. Our goal was to compare current guidelines of managing knee OA,
to the degree of information each patient has about their treatment
options.info:eu-repo/semantics/publishedVersio
College admissions and the role of information : an experimental study
We analyze two well-known matching mechanismsâthe Gale-Shapley, and the Top
Trading Cycles (TTC) mechanismsâin the experimental lab in three different informational
settings, and study the role of information in individual decision making. Our results suggest
thatâin line with the theoryâin the college admissions model the Gale-Shapley mechanism
outperforms the TTC mechanisms in terms of efficiency and stability, and it is as successful as
the TTC mechanism regarding the proportion of truthful preference revelation. In addition, we
find that information has an important effect on truthful behavior and stability. Nevertheless,
regarding efficiency, the Gale-Shapley mechanism is less sensitive to the amount of information
participants hold
Local supersymmetry without SUSY partners
A gauge theory for a superalgebra that includes an internal gauge (G) and
local Lorentz algebras, and that could describe the low energy particle
phenomenology is constructed. These two symmetries are connected by fermionic
supercharges. The system includes an internal gauge connection 1-form , a
spin-1/2 Dirac spinor , the Lorentz connection , and the vielbein
. The connection one-form is in the adjoint representation of G, while
is in the fundamental. In contrast to standard supergravity, the metric
is not a fundamental field and is in the center of the superalgebra: it is not
only invariant under the internal gauge group and under Lorentz
transformations, but is also invariant under supersymmetry. The features of
this theory that mark the difference with standard supersymmetry are: A) The
number of fermionic and bosonic states is not necessarily the same; B) There
are no superpartners with equal mass, "bosoninos", sleptons and squarks are
absent; C) Although this supersymmetry originates in a local gauge theory and
gravity is included, there is no gravitino; D) Fermions acquire mass from their
coupling to the background or from self-couplings, while bosons remain
massless. In odd dimensions, the Chern-Simons form provides an action that is
quasi-invariant under the entire superalgebra. In even dimensions, the
Yang-Mills form is the only natural option, and the symmetry breaks
down to [G x SO(1,D-1)]. In 4D, the construction follows the Townsend - Mac
Dowell-Mansouri approach. Due to the absence of osp(4|2)-invariant traces in
four dimensions, the resulting Lagrangian is only invariant under [U(1) x
SO(3,1)], and includes a Nambu--Jona-Lasinio term. In this case, the Lagrangian
depends on a single dimensionful parameter that fixes Newton's constant, the
cosmological constant and the NJL coupling.Comment: 24 pages, no figures. Title changed in journal version to
"Unconventional supersymmetry and its breaking". Few references added and
some paragraphs rewritten from v.1. This version includes two appendices that
are not found in the journal versio
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