4,638 research outputs found
Universal Unitarity Triangle and Physics Beyond the Standard Model
We make the simple observation that there exists a universal unitarity
triangle for all models, like the SM, the Two Higgs Doublet Models I and II and
the MSSM with minimal flavour violation, that do not have any new operators
beyond those present in the SM and in which all flavour changing transitions
are governed by the CKM matrix with no new phases beyond the CKM phase. This
universal triangle can be determined in the near future from the ratio (Delta
M)_d/(Delta M)_s and sin(2 beta) measured first through the CP asymmetry in
B_d^0 to psi K_S and later in K to pi nu nubar decays. Also suitable ratios of
the branching ratios for B to X_{d,s} nu nubar and B_{d,s} to mu^+ mu^- and the
angle gamma measured by means of CP asymmetries in B decays can be used for
this determination. Comparison of this universal triangle with the
non-universal triangles extracted in each model using epsilon, (Delta M)_d and
various branching ratios for rare decays will allow to find out in a
transparent manner which of these models, if any, is singled out by experiment.
A virtue of the universal triangle is that it allows to separate the
determination of the CKM parameters from the determination of new parameters
present in the extensions of the SM considered here.Comment: 12 pages, 1 figur
Six Years of ScoX-1 Monitoring with BeppoSAX Wide Field Cameras
We performed a systematic analysis of 54 Wide Field Camera (WFC) observations
of ScoX-1 available in the BeppoSAX public archive. Observations span over the
six years of BeppoSAX mission lifetime and include 690 hr of data. We searched
for shifts and shape changes of the Z pattern in the color-color diagrams. We
find that the Z pattern occupies most of the time the same locus in the
color-color diagram. There are however a few exceptions, which are discussed in
detail.Comment: 4 Pages, 4 figures. To appear in Proc. of the BeppoSAX Symposium:
"The Restless High-Energy Universe", E.P.J. van den Heuvel, J.J.M. in 't
Zand, and R.A.M.J. Wijers (Eds
2-Dust : a Dust Radiative Transfer Code for an Axisymmetric System
We have developed a general purpose dust radiative transfer code for an
axisymmetric system, 2-Dust, motivated by the recent increasing availability of
high-resolution images of circumstellar dust shells at various wavelengths.
This code solves the equation of radiative transfer following the principle of
long characteristic in a 2-D polar grid while considering a 3-D radiation field
at each grid point. A solution is sought through an iterative scheme in which
self-consistency of the solution is achieved by requiring a global luminosity
constancy throughout the shell. The dust opacities are calculated through Mie
theory from the given size distribution and optical properties of the dust
grains. The main focus of the code is to obtain insights on (1) the global
energetics of dust grains in the shell (2) the 2-D projected morphologies that
are strongly dependent on the mixed effects of the axisymmetric dust
distribution and inclination angle of the shell. Here, test models are
presented with discussion of the results. The code can be supplied with a
user-defined density distribution function, and thus, is applicable to a
variety of dusty astronomical objects possessing the axisymmetric geometry.Comment: To be published in ApJ, April 2003 issue; 13 pages, 4 tables, 17
figures, 5-page appendix (no figures for the main text included in this
preprint). For the complete preprint and code distribution, contact the
author
The complete catalogue of gamma-ray bursts observed by the Wide Field Cameras on board BeppoSAX
We present the complete on-line catalogue of gamma-ray bursts observed by the
two Wide Field Cameras on board \sax in the period 1996-2002. Our aim is to
provide the community with the largest published data set of GRB's prompt
emission X-ray light curves and other useful data. This catalogue
(BS-GRBWFCcat) contains data on 77 bursts and a collection of the X-ray light
curves of 56 GRB discovered or noticed shortly after the event and of other
additional bursts detected in subsequent searches. Light curves are given in
the three X-ray energy bands (2-5, 5-10, 10-26 keV). The catalogue can be
accessed from the home web page of the ASI Science Data Center-ASDC
(http://www.asdc.asi.it)Comment: 4 pages, 3 figure
Collisionless Damping of Fast MHD Waves in Magneto-rotational Winds
We propose collisionless damping of fast MHD waves as an important mechanism
for the heating and acceleration of winds from rotating stars. Stellar rotation
causes magnetic field lines anchored at the surface to form a spiral pattern
and magneto-rotational winds can be driven. If the structure is a magnetically
dominated, fast MHD waves generated at the surface can propagate almost
radially outward and cross the field lines. The propagating waves undergo
collisionless damping owing to interactions with particles surfing on magnetic
mirrors that are formed by the waves themselves. The damping is especially
effective where the angle between the wave propagation and the field lines
becomes moderately large ( to ). The angle tends naturally
to increase into this range because the field in magneto-rotational winds
develops an increasingly large azimuthal component. The dissipation of the wave
energy produces heating and acceleration of the outflow. We show using
specified wind structures that this damping process can be important in both
solar-type stars and massive stars that have moderately large rotation rates.
This mechanism can play a role in coronae of young solar-type stars which are
rapidly rotating and show X-ray luminosities much larger than the sun. The
mechanism could also be important for producing the extended X-ray emitting
regions inferred to exist in massive stars of spectral type middle B and later.Comment: 12 pages, including 7 figures, accepted for publication in Ap
Depth concentrations of deuterium ions implanted into some pure metals and alloys
Pure metals (Cu, Ti, Zr, V, Pd) and diluted Pd-alloys (Pd-Ag, Pd-Pt, Pd-Ru,
Pd-Rh) were implanted by 25 keV deuterium ions at fluences in the range
(1.2{\div}2.3)x1022 D+/m2. The post-treatment depth distributions of deuterium
ions were measured 10 days and three months after the implantation using
Elastic Recoil Detection Analysis (ERDA) and Rutherford Backscattering (RBS).
Comparison of the obtained results allowed to make conclusions about relative
stability of deuterium and hydrogen gases in pure metals and diluted Pd alloys.
Very high diffusion rates of implanted deuterium ions from V and Pd pure metals
and Pd alloys were observed. Small-angle X-ray scattering revealed formation of
nanosized defects in implanted corundum and titanium.Comment: 12 pages, 9 figure
FU Orionis - The MIDI/VLTI Perspective
We present the first mid-infrared interferometric measurements of FU Orionis.
We clearly resolve structures that are best explained with an optically thick
accretion disk. A simple accretion disk model fits the observed SED and
visibilities reasonably well and does not require the presence of any
additional structure such as a dusty envelope. The inclination and also the
position angle of the disk can be constrained from the multibaseline
interferometric observations. Our disk model is in general agreement with most
published near-infrared interferometric measurements. From the shape and
strength of the 8-13 micrometer spectrum the dust composition of the accretion
disk is derived for the first time. We conclude that most dust particles are
amorphous and already much larger than those typically observed in the ISM.
Although the high accretion rate of the system provides both, high temperatures
out to large radii and an effective transport mechanism to distribute
crystalline grains, we do not see any evidence for crystalline silicates
neither in the total spectrum nor in the correlated flux spectra from the inner
disk regions. Possible reasons for this non-detection are mentioned. All
results are discussed in context with other high-spatial resolution
observations of FU Ori and other FU Ori objects. We also address the question
whether FU Ori is in a younger evolutionary stage than a classical TTauri star.Comment: 41 pages (aastex style), 11 figures, 8 tables, accepted by Ap
Geometric Parameterization of Absorption in Heavy Ion Collisions
We calculate the survival probability of particles in various
colliding systems using a Glauber model. An analysis of recent data has
reported a -nucleon breakup cross section of 6.20.7 mb derived
from an exponential fit to the ratio of to Drell-Yan yields as a
function of a simple, linearly-averaged mean path length through the nuclear
medium. Our calculations indicate that, due to the nature of the calculation,
this approach yields an apparent breakup cross section which is systematically
lower than the actual value.Comment: LaTex, 7 pages, 2 figure
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