3,368 research outputs found
Integral representations combining ladders and crossed-ladders
We use the worldline formalism to derive integral representations for three
classes of amplitudes in scalar field theory: (i) the scalar propagator
exchanging N momenta with a scalar background field (ii) the "half-ladder" with
N rungs in x - space (iii) the four-point ladder with N rungs in x - space as
well as in (off-shell) momentum space. In each case we give a compact
expression combining the N! Feynman diagrams contributing to the amplitude. As
our main application, we reconsider the well-known case of two massive scalars
interacting through the exchange of a massless scalar. Applying asymptotic
estimates and a saddle-point approximation to the N-rung ladder plus crossed
ladder diagrams, we derive a semi-analytic approximation formula for the lowest
bound state mass in this model.Comment: 39 pages, 10 pdf figure
Electroweak Baryogenesis in the Presence of an Isosinglet Quark
We consider the possibility of electroweak baryogenesis in a simple extension
of the standard model with an extra singlet complex scalar and a vector-like
down quark. We show that in the present model the first-order electroweak phase
transition can be strong enough to avoid the baryon asymmetry washout by
sphalerons and that the CP-violating effects can be sufficient to explain the
observed baryon-to-entropy ratio nB/s ~ 10^(-10). Other appealing features of
the model include the generation of a CKM phase from spontaneous CP breaking at
a high energy scale and a possible solution of the strong CP problem through
the natural suppression of the parameter theta.Comment: LaTeX, 19 pages, 2 EPS figures, uses epsf, amsmath, amsfonts, amssym
Generating TV summaries for CE-devices
Automatically generated summaries of TV content are indispensable for content selection and navigation in CE-devices. We show two types of summaries: Short video trailers and visual overviews consisting of representative frames. The demo does not only show the feasibility of the proposed algorithms, but also shows how different types of generated summaries can be used in future CE-devices
On the decay law for unstable open systems
We use (nonconservative) dynamical semigroups to investigate the decay law of
a quantum unstable system weakly coupled with a large environment. We find that
the deviations from the classical exponential law are small and can be safely
ignored in any actual experiment.Comment: 12 pages, plain-TeX, to appear in Phys. Lett.
Complete positivity and correlated neutral kaons
In relation with experiments on correlated kaons at phi-factories, it is
shown that the request of complete positivity is necessary in any physically
consistent description of neutral kaons as open quantum systems.Comment: LaTeX, 9 page
Transformation zone location and intraepithelial neoplasia of the cervix uteri.
We examined the relationship between the frequency of premalignant lesions of the cervix and location of the transformation zone on the cervix among 8758 women as assessed using cervicography. An endo- and exocervical smear test was performed at the same time. Women with smear test classified CIN I or more were recalled and any abnormal area was biopsied under colposcopy. The transformation zone was located on the exocervix in 94% of women younger than 25 years old; as age increased, the proportion of women with a transformation zone located on the exocervix steadily decreased to reach less than 2% after 64 years old. As compared with women having a transformation zone in the endocervical canal, the age-adjusted likelihood of discovering a histologically proven dysplastic lesion was 1.8 times more frequent among women with a transformation zone located on the exocervix (95% confidence interval 1.1-2.9). This higher frequency seemed not attributable to a lower sensitivity of the smear test when the transformation zone was hidden. The results also showed that deliveries tended significantly to maintain the transformation zone on the exocervix. Parity is a known risk factor for cervix cancer, but the mechanism by which it favours malignant lesions remain unknown. Our results suggest that with increasing numbers of livebirths, the transformation zone is directly exposed for longer periods to external agents involved in dysplastic lesions
Moments of unconditional logarithmically concave vectors
We derive two-sided bounds for moments of linear combinations of coordinates
od unconditional log-concave vectors. We also investigate how well moments of
such combinations may be approximated by moments of Gaussian random variables.Comment: 14 page
Dissipative effects in semileptonic B decays
We study the time evolution and decay of the neutral B-meson system using
quantum dynamical semigroups. New, nonstandard terms appear in the expression
of relevant observables; they can be parametrized in terms of six
phenomenological constants. Although very small, these parameters may be
detected in the new generation of dedicated B-meson experiments.Comment: 14 pages, plain-Te
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