344 research outputs found
The Ising model universality of the electroweak theory
Lattice simulations have shown that the first order electroweak phase
transition turns into a regular cross-over at a critical Higgs mass m_{H,c}. We
have developed a method which enables us to make a detailed investigation of
the critical properties of the electroweak theory at m_{H,c}. We find that the
transition falls into the 3d Ising universality class. The continuum limit
extrapolation of the critical Higgs mass is m_{H,c} = 72(2) GeV, which implies
that there is no electroweak phase transition in the Standard Model.Comment: 3 pages, contribution to LATTICE98(electroweak
Comparison of Campylobacter coli strains isolated from pigs and humans - porcine strains a possible source of human infection?
The primary aim of this study was to detect and genotype Campylobacter strains from pigs and humans. AFLP (amplified fragment length polymorphism) analysis was used to compare different genotypes to identify the genetic diversity of Campylobacter coli (C. coli) strains. Heterogeneous patterns were detectable among the porcine and human C. coli pool. By using an optimized extraction method combined with a PCR it was possible to detect C. coli DNA in some samples of the investigated minced meat but it could not be distinguished between dead bacterial cells and viable but nonculturable cell (VBNC)-forms of C. coli strains
Endpoint of the hot electroweak phase transition
We give the nonperturbative phase diagram of the four-dimensional hot
electroweak phase transition. The Monte-Carlo analysis is done on lattices with
different lattice spacings (). A systematic extrapolation is done.
Our results show that the finite temperature SU(2)-Higgs phase transition is of
first order for Higgs-boson masses GeV. At this endpoint the
phase transition is of second order, whereas above it only a rapid cross-over
can be seen. The full four-dimensional result agrees completely with that of
the dimensional reduction approximation. This fact is of particular importance,
because it indicates that the fermionic sector of the Standard Model can be
included perturbatively. We obtain that the Higgs-boson endpoint mass in the
Standard Model is GeV. Taking into account the LEP Higgs-boson
mass lower bound excludes any electroweak phase transition in the Standard
Model.Comment: Latex, 7 pages, 4 figure
Where the electroweak phase transition ends
We give a more precise characterisation of the end of the electroweak phase
transition in the framework of the effective 3d SU(2)--Higgs lattice model than
has been given before. The model has now been simulated at gauge couplings
beta_G=12 and 16 for Higgs masses M_H^*=70, 74, 76 and 80 GeV up to lattices
96^3 and the data have been used for reweighting. The breakdown of finite
volume scaling of the Lee-Yang zeroes indicates the change from a first order
transition to a crossover at lambda_3/g_3^2=0.102(2) in rough agreement with
results of Karsch et al (hep-lat/9608087) at \beta_G=9 and smaller lattices.
The infinite volume extrapolation of the discontinuity Delta
/g_3^2 turns out to be zero at lambda_3/g_3^2=0.107(2) being an upper limit. We
comment on the limitations of the second method.Comment: RevTeX, 19 pages, 11 figures, 2 tables; additional MC-data near the
endpoint considere
The MSSM Electroweak Phase Transition on the Lattice
We study the MSSM finite temperature electroweak phase transition with
lattice Monte Carlo simulations, for a large Higgs mass (m_H ~ 95 GeV) and
light stop masses (m_tR ~ 150...160 GeV). We employ a 3d effective field theory
approach, where the degrees of freedom appearing in the action are the SU(2)
and SU(3) gauge fields, the weakly interacting Higgs doublet, and the strongly
interacting stop triplet. We determine the phase diagram, the critical
temperatures, the scalar field expectation values, the latent heat, the
interface tension and the correlation lengths at the phase transition points.
Extrapolating the results to the infinite volume and continuum limits, we find
that the transition is stronger than indicated by 2-loop perturbation theory,
guaranteeing that the MSSM phase transition is strong enough for baryogenesis
in this regime. We also study the possibility of a two-stage phase transition,
in which the stop field gets an expectation value in an intermediate phase. We
find that a two-stage transition exists non-perturbatively, as well, but for
somewhat smaller stop masses than in perturbation theory. Finally, the latter
stage of the two-stage transition is found to be extremely strong, and thus it
might not be allowed in the cosmological environment.Comment: 43 pages, 17 figure
The Electroweak Phase Transition in a Magnetic Field
We study the finite temperature electroweak phase transition in an external
hypercharge U(1) magnetic field H_Y, using lattice Monte Carlo simulations. For
sufficiently small fields, H_Y/T^2 < 0.3, the magnetic field makes the first
order transition stronger, but it still turns into a crossover for Higgs masses
m_H ~ 80 GeV. For larger fields, we observe a mixed phase analogous to a type I
superconductor, where a single macroscopic tube of the symmetric phase,
parallel to H_Y, penetrates through the broken phase. For the magnetic fields
and Higgs masses studied, we did not see indications of the expected
Ambjorn-Olesen phase, which should be similar to a type II superconductor.Comment: 20 pages, 7 figures. Discussion on lattice results extended. To
appear in Nucl.Phys.
The universality class of the electroweak theory
We study the universality class and critical properties of the electroweak
theory at finite temperature. Such critical behaviour is found near the
endpoint m_H=m_{H,c} of the line of first order electroweak phase transitions
in a wide class of theories, including the Standard Model (SM) and a part of
the parameter space of the Minimal Sypersymmetric Standard Model (MSSM). We
find that the location of the endpoint corresponds to the Higgs mass m_{H,c} =
72(2) GeV in the SM with sin^2 theta_W = 0, and m_{H,c} < 80 GeV with sin^2
theta_W = 0.23. As experimentally m_H > 88 GeV, there is no electroweak phase
transition in the SM. We compute the corresponding critical indices and provide
strong evidence that the phase transitions near the endpoint fall into the
three dimensional Ising universality class.Comment: 35 pages, 15 figure
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
Goodness-of-Fit Tests for Symmetric Stable Distributions -- Empirical Characteristic Function Approach
We consider goodness-of-fit tests of symmetric stable distributions based on
weighted integrals of the squared distance between the empirical characteristic
function of the standardized data and the characteristic function of the
standard symmetric stable distribution with the characteristic exponent
estimated from the data. We treat as an unknown parameter,
but for theoretical simplicity we also consider the case that is
fixed. For estimation of parameters and the standardization of data we use
maximum likelihood estimator (MLE) and an equivariant integrated squared error
estimator (EISE) which minimizes the weighted integral. We derive the
asymptotic covariance function of the characteristic function process with
parameters estimated by MLE and EISE. For the case of MLE, the eigenvalues of
the covariance function are numerically evaluated and asymptotic distribution
of the test statistic is obtained using complex integration. Simulation studies
show that the asymptotic distribution of the test statistics is very accurate.
We also present a formula of the asymptotic covariance function of the
characteristic function process with parameters estimated by an efficient
estimator for general distributions
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