165 research outputs found
Scalar-gauge dynamics in (2+1) dimensions at small and large scalar couplings
We present the results of a detailed calculation of the excitation spectrum
of states with quantum numbers J^{PC}=0++, 1-- and 2++ in the three-dimensional
SU(2) Higgs model at two values of the scalar self-coupling and for fixed gauge
coupling. In the context of studies of the electroweak phase transition at
finite temperature these couplings correpond to tree-level, zero temperature
Higgs masses of 35 GeV and 120 GeV, respectively. We also study the properties
of Polyakov loop operators, which serve to test the confining properties of the
model in the symmetric phase. At both values of the scalar coupling we obtain
masses of bound states consisting entirely of gauge degrees of freedom
("W-balls"), which are very close to those obtained in the pure gauge theory.
We conclude that the previously observed, approximate decoupling of the scalar
and gauge sectors of the theory persists at large scalar couplings. We study
the crossover region at large scalar coupling and present a scenario how the
confining properties of the model in the symmetric phase are lost inside the
crossover by means of flux tube decay. We conclude that the underlying dynamics
responsible for the observed dense spectrum of states in the Higgs region at
large couplings must be different from that in the symmetric phase.Comment: 36 pages, LaTeX, 13 postscript files, to be included with epsf;
improved presentation, updated references, conclusions unchanged; version to
appear in Nucl. Phys.
Sabotage in Contests: A Survey
A contest is a situation in which individuals expend irretrievable resources to win valuable prize(s). ‘Sabotage’ is a deliberate and costly act of damaging a rival’s' likelihood of winning the contest. Sabotage can be observed in, e.g., sports, war, promotion tournaments, political or marketing campaigns. In this article, we provide a model and various perspectives on such sabotage activities and review the economics literature analyzing the act of sabotage in contests. We discuss the theories and evidence highlighting the means of sabotage, why sabotage occurs, and the effects of sabotage on individual players and on overall welfare, along with possible mechanisms to reduce sabotage. We note that most sabotage activities are aimed at the ablest player, the possibility of sabotage reduces productive effort exerted by the players, and sabotage may lessen the effectiveness of public policies, such as affirmative action, or information revelation in contests. We discuss various policies that a designer may employ to counteract sabotage activities. We conclude by pointing out some areas of future research
String Breaking in Non-Abelian Gauge Theories with Fundamental Matter Fields
We present clear numerical evidence for string breaking in three-dimensional
SU(2) gauge theory with fundamental bosonic matter through a mixing analysis
between Wilson loops and meson operators representing bound states of a static
source and a dynamical scalar. The breaking scale is calculated in the
continuum limit. In units of the lightest glueball we find . The implications of our results for QCD are discussed.Comment: 4 pages, 2 figures; equations (4)-(6) corrected, numerical results
and conclusions unchange
Gauge-invariant scalar and field strength correlators in 3d
Gauge-invariant non-local scalar and field strength operators have been
argued to have significance, e.g., as a way to determine the behaviour of the
screened static potential at large distances, as order parameters for
confinement, as input parameters in models of confinement, and as
gauge-invariant definitions of light constituent masses in bound state systems.
We measure such "correlators" in the 3d pure SU(2) and SU(2)+Higgs models on
the lattice. We extract the corresponding mass parameters and discuss their
scaling and physical interpretation. We find that the finite part of the MS-bar
scheme mass measured from the field strength correlator is large, more than
half the glueball mass. We also determine the non-perturbative contribution to
the Debye mass in the 4d finite T SU(2) gauge theory with a method due to
Arnold and Yaffe, finding .Comment: 26 pages LaTeX, 8 Figure
Magnetic Screening in the High Temperature Phase of the Standard Model
Non-perturbative effects in the high-temperature phase of the electroweak
theory are characterized by a magnetic screening length. Its size influences
the range of validity of perturbation theory, and it also determines the
critical Higgs boson mass where the first-order phase transition changes to a
crossover. We propose a gauge-invariant definition of the magnetic screening
length and discuss its role in several gauge-dependent and gauge-invariant
correlation functions.Comment: 11 pages Latex, 3 figures, uses epsf.st
The spectrum of the three-dimensional adjoint Higgs model and hot SU(2) gauge theory
We compute the mass spectrum of the SU(2) adjoint Higgs model in 2+1
dimensions at several points located in the (metastable) confinement region of
its phase diagram. We find a dense spectrum consisting of an almost unaltered
repetition of the glueball spectrum of the pure gauge theory, and additional
bound states of adjoint scalars. For the parameters chosen, the model
represents the effective finite temperature theory for pure SU(2) gauge theory
in four dimensions, obtained after perturbative dimensional reduction.
Comparing with the spectrum of screening masses obtained in recent simulations
of four-dimensional pure gauge theory at finite temperature, for the low lying
states we find quantitative agreement between the full and the effective theory
for temperatures as low as T = 2 Tc. This establishes the model under study as
the correct effective theory, and dimensional reduction as a viable tool for
the description of thermodynamic properties. We furthermore compare the
perturbative contribution O(g.T) with the non-perturbative contributions
O(g^2.T) and O(g^3.T) to the Debye mass. The latter turns out to be dominated
by the scale g^2.T, whereas higher order contributions are small corrections.Comment: LaTeX. Typos corrected and references adde
Static correlation lengths in QCD at high temperatures and finite densities
We use a perturbatively derived effective field theory and three-dimensional
lattice simulations to determine the longest static correlation lengths in the
deconfined QCD plasma phase at high temperatures (T\gsim 2 Tc) and finite
densities (\mu\lsim 4 T). For vanishing chemical potential, we refine a
previous determination of the Debye screening length, and determine the
dependence of different correlation lengths on the number of massless flavours
as well as on the number of colours. For non-vanishing but small chemical
potential, the existence of Debye screening allows us to carry out simulations
corresponding to the full QCD with two (or three) massless dynamical flavours,
in spite of a complex action. We investigate how the correlation lengths in the
different quantum number channels change as the chemical potential is switched
on.Comment: 34 pages; references, clarifications and a note on recent literature
added; to appear in Nucl.Phys.
Strong Host-Feeding Preferences of the Vector Triatoma infestans Modified by Vector Density: Implications for the Epidemiology of Chagas Disease
Chagas disease is a complex zoonosis with more than 150 mammalian host species, nearly a dozen blood-sucking triatomine species as main vectors, and 9–11 million people infected with Trypanosoma cruzi (its causal agent) in the Americas. Triatoma infestans, a highly domesticated species and one of the main vectors, feeds more often on domestic animals than on humans in northern Argentina. The question of whether there are host-feeding preferences among dogs, cats, and chickens is crucial to estimating transmission risks and predicting the effects of control tactics targeting them. This article reports the first host choice experiments of triatomine bugs conducted in small huts under natural conditions. The results demonstrate that T. infestans consistently preferred dogs to chickens or cats, with host shifts occurring more frequently at higher vector densities. Combined with earlier findings showing that dogs have high infection rates, are highly infectious, and have high contact rates with humans and domestic bugs, our results reinforce the role of dogs as the key reservoirs of T. cruzi. The strong bug preference for dogs can be exploited to target dogs with topical lotions or insecticide-impregnated collars to turn them into baited lethal traps or use them as transmission or infestation sentinels
Astrometric confirmation of young low-mass binaries and multiple systems in the Chamaeleon star-forming regions
The star-forming regions in Chamaeleon are one of the nearest (distance ~165
pc) and youngest (age ~2 Myrs) conglomerates of recently formed stars and the
ideal target for population studies of star formation. We investigate a total
of 16 Cha targets, which have been suggested, but not confirmed as binaries or
multiple systems in previous literature. We used the adaptive optics instrument
Naos-Conica (NACO) at the Very Large Telescope Unit Telescope 4 of the Paranal
Observatory, at 2-5 different epochs, in order to obtain relative and absolute
astrometric measurements, as well as differential photometry in the J, H, and K
band. On the basis of known proper motions and these observations, we analyse
the astrometric results in our "Proper Motion Diagram" (PMD: angular separation
/ position angle versus time), to eliminate possible (non-moving) background
stars, establish co-moving binaries and multiples, and search for curvature as
indications for orbital motion. All previously suggested close components are
co-moving and no background stars are found. The angular separations range
between 0.07 and 9 arcseconds, corresponding to projected distances between the
components of 6-845 AU. Thirteen stars are at least binaries and the remaining
three (RX J0919.4-7738, RX J0952.7-7933, VW Cha) are confirmed high-order
multiple systems with up to four components. In 13 cases, we found significant
slopes in the PMDs, which are compatible with orbital motion whose periods
range from 60 to 550 years. However, in only four cases there are indications
of a curved orbit, the ultimate proof of a gravitational bond. Massive primary
components appear to avoid the simultaneous formation of equal-mass secondary
components. (abridged)Comment: 33 pages, 22 figures, accepted for publication in A&A, 2nd version:
typos and measurement unit added in Table
Hidden Sylvatic Foci of the Main Vector of Chagas Disease Triatoma infestans: Threats to the Vector Elimination Campaign?
Triatoma infestans, a highly domesticated species and historically the main vector of Trypanosoma cruzi, is the target of an insecticide-based elimination program in the southern cone countries of South America since 1991. Only limited success has been achieved in the Gran Chaco region due to repeated reinfestations. We conducted full-coverage spraying of pyrethroid insecticides of all houses in a well-defined rural area in northwestern Argentina, followed by intense monitoring of house reinfestation and searches for triatomine bugs in sylvatic habitats during the next two years, to establish the putative sources of new bug colonies. We found low-density sylvatic foci of T. infestans in trees located within the species' flight range from the nearest infested house detected before control interventions. Using multiple methods (fine-resolution satellite imagery, geographic information systems, spatial statistics, genetic markers and wing geometric morphometry), we corroborated the species identity of the sylvatic bugs as T. infestans and found they were indistinguishable from or closely related to local domestic or peridomestic bug populations. Two sylvatic foci were spatially associated to the nearest peridomestic bug populations found before interventions. Sylvatic habitats harbor hidden foci of T. infestans that may represent a threat to vector suppression attempts
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