23,734 research outputs found
Worries and Hopes for SUSY in CKM Physics: The b to s Example
We discuss the twofold role of flavor and CP violation as a constraint in
model building and as a signal of SUSY. Considering as an example b to s
transitions, we analyze present bounds on SUSY parameters, discuss possible
deviations from SM predictions in Bd and Bs physics and present strategies to
reveal SUSY signals in present and future experiments in the CKM domain.Comment: Invited talks given by A. Masiero and L. Silvestrini at the Workshop
on the CKM Unitarity Triangle, IPPP Durham, April 2003 (eConf C0304052). 9
pages, 5 figure
b -> s Transitions: A New Frontier for Indirect SUSY Searches
The present unitarity triangle fit, whose essential input is represented by
the s to d and b to d transition processes, fully agrees with the SM. However,
most of the phenomena involving b to s transitions are still largely unexplored
and hence b to s phenomenology still constitutes a place for new physics
manifestations, in spite of the tremendous experimental and theoretical
progress on B to X_s gamma. We perform a systematic study of the CP conserving
and violating SUSY contributions to b to s processes in a generic MSSM. We
consider gluino exchange contributions including NLO QCD corrections and
lattice hadronic matrix elements for Delta B = 2 and Delta B = 1 processes. We
take into account all available experimental information on processes involving
b to s transitions (B to X_s gamma, B to X_s l^+ l^- and the lower bound on the
B_s - bar B_s mass difference Delta M_s). We study the correlations among the
relevant observables under scrutiny at present or in a not too far future:
Delta M_s and the amount of CP violation in B to phi K_s, B_s to J/psi phi, B
to X_s gamma. In particular we discuss the recent data by BaBar and BELLE on
the time-dependent CP asymmetry in the decay B to phi K_s which suggest a
deviation from the SM expectation. Our results show that the processes
involving b to s transitions represent a splendid opportunity to constrain
different MSSM realizations, and, even more important, that they offer concrete
prospects to exhibit SUSY signals at B factories and hadron colliders in spite
of all the past frustration in FCNC searches of new physics hints.Comment: 20 pages, 8 figures. Bug in the code corrected, figures for RL and
RL=RR cases and some conclusions change
Two-body nonleptonic B decays in the Standard Model and beyond
We briefly discuss the phenomenology of B to pi pi, B to K pi and B to phi K
decays in the Standard Model and in Supersymmetry.Comment: 7 pages, 2 figures, uses moriond.sty. Talk given by L. Silvestrini at
the XXXIXth Rencontres de Moriond on ElectroWeak Interactions and Unified
Theories, La Thuile, Aosta Valley, Italy, March 21st-28th 200
On the heating of source of the Orion KL hot core
We present images of the J=10-9 rotational lines of HC3N in the vibrationally
excited levels 1v7, 1v6 and 1v5 of the hot core (HC) in Orion KL. The images
show that the spatial distribution and the size emission from the 1v7 and 1v5
levels are different. While the J=10-9 1v7 line has a size of 4''x 6'' and
peaks 1.1'' NE of the 3 mm continuum peak, the J=10--9 1v5 line emission is
unresolved (<3'') and peaks 1.3'' south of the 3 mm peak. This is a clear
indication that the HC is composed of condensations with very different
temperatures (170 K for the 1v7 peak and K for the 1v5 peak). The
temperature derived from the 1v7 and 1v5 lines increases with the projected
distance to the suspected main heating source I. Projection effects along the
line of sight could explain the temperature gradient as produced by source I.
However, the large luminosity required for source I, >5 10^5 Lsolar, to explain
the 1v5 line suggests that external heating by this source may not dominate the
heating of the HC. Simple model calculations of the vibrationally excited
emission indicate that the HC can be internally heated by a source with a
luminosity of 10^5 Lsolar, located 1.2'' SW of the 1v5 line peak (1.8'' south
of source I). We also report the first detection of high-velocity gas from
vibrationally excited HC3N emission. Based on excitation arguments we conclude
that the main heating source is also driving the molecular outflow. We
speculate that all the data presented in this letter and the IR images are
consistent with a young massive protostar embedded in an edge-on disk.Comment: 13 pages, 3 figures, To be published in Ap.J. Letter
Instabilities of the AA-stacked graphene bilayer
Tight-binding calculations predict that the AA-stacked graphene bilayer has
one electron and one hole conducting bands, and that the Fermi surfaces of
these bands coincide. We demonstrate that as a result of this degeneracy, the
bilayer becomes unstable with respect to a set of spontaneous symmetry
violations. Which of the symmetries is broken depends on the microscopic
details of the system. We find that antiferromagnetism is the more stable order
parameter. This order is stabilized by the strong on-site Coulomb repulsion.
For an on-site repulsion energy typical for graphene systems, the
antiferromagnetic gap can exist up to room temperatures.Comment: 4 pages, 2 eps figure, submitted to Phys. Rev. Let
Dynamics of a magnetic dimer with exchange, dipolar and Dzyalozhinski-Moriya interaction
We investigate the dynamics of a magnetic system consisting of two magnetic
moments coupled by either exchange, dipole-dipole, or Dzyalozhinski-Moriya
interaction. We compare the switching mechanisms and switching rates as induced
by the three couplings. For each coupling and each configuration of the two
anisotropy axes, we describe the switching modes and, using the kinetic theory
of Langer, we provide (semi-)analytical expressions for the switching rate. We
then compare the three interactions with regard to their efficiency in the
reversal of the net magnetic moment of the dimer. We also investigate how the
energy barriers vary with the coupling. For the dipole-dipole interaction we
find that the energy barrier may either increase or decrease with the coupling
depending on whether the latter is weak or strong. Finally, upon comparing the
various switching rates, we find that the dipole-dipole coupling leads to the
slowest magnetic dimer, as far as the switching of its net magnetic moment is
concerned.Comment: 20 pages, 18 Figures, 2 table
Modelling chemical reactions using semiconductor quantum dots
We propose using semiconductor quantum dots for a simulation of chemical
reactions as electrons are redistributed among such artificial atoms. We show
that it is possible to achieve various reaction regimes and obtain different
reaction products by varying the speed of voltage changes applied to the gates
forming quantum dots. Considering the simplest possible reaction, , we show how the necessary initial state can be obtained and what
voltage pulses should be applied to achieve a desirable final product. Our
calculations have been performed using the Pechukas gas approach, which can be
extended for more complicated reactions
Majorana fermions in pinned vortices
Exploiting the peculiar properties of proximity-induced superconductivity on
the surface of a topological insulator, we propose a device which allows the
creation of a Majorana fermion inside the core of a pinned Abrikosov vortex.
The relevant Bogolyubov-de Gennes equations are studied analytically. We
demonstrate that in this system the zero-energy Majorana fermion state is
separated by a large energy gap, of the order of the zero-temperature
superconducting gap , from a band of single-particle non-topological
excitations. In other words, the Majorana fermion remains robust against
thermal fluctuations, as long as the temperature remains substantially lower
than the critical superconducting temperature. Experimentally, the Majorana
state may be detected by measuring the tunneling differential conductance at
the center of the Abrikosov vortex. In such an experiment, the Majorana state
manifests itself as a zero-bias anomaly separated by a gap, of the order of
, from the contributions of the nontopological excitations.Comment: 9 pages, 2 eps figures, new references are added, several typos are
correcte
Unitarity Triangle Analysis in the Standard Model and Sensitivity to New Physics
By using the most recent determinations of the several theoretical and
experimental input parameters, we update the Unitarity Triangle analysis in the
Standard Model and discuss the sensitivity to New Physics effects. We
investigate the interest of measuring with a better precision the various
physical quantities entering the Unitarity Triangle analysis and study in a
model independent way whether, despite the undoubted success of the CKM
mechanism in the Standard Model, the Unitarity Triangle analysis still allows
the presence of New Physics.Comment: Invited talk at the Workshop on the CKM Unitarity Triangle, IPPP
Durham, April 2003 (eConf C0304052). 9 pages LaTeX, 15 eps figures. Misprint
corrected and references adde
Can the effects of anthropogenic pressures and environmental variability on nekton fauna be detected in fishery data? Insights from the monitoring of the artisanal fishery within the Venice lagoon
Nekton communities in transitional ecosystems are naturally adapted to stressful conditions associated with high environmental variability. Human activities in these systems are likely to determine additional stress with a possible effect on fish fauna, hence on fisheries. In order to test the relative importance of natural and anthropogenic factors in determining changes in nekton community, catches (incl. bycatch) from artisanal fisheries (fyke nets) were monitored seasonally in different areas of the Venice lagoon (Italy) between 2001 and 2013. Changes in nekton community composition and in the biomass of target and non-target species/groups were analysed, and the results were related to temporal factors, environmental characteristics and to the variability in anthropogenic pressures. Statistical tests were carried out using a model-based analysis of both univariate and multivariate data. Results highlighted that temporal factors and environmental conditions (i.e. the main chemico-physical descriptors) are more relevant than anthropogenic pressures in explaining spatial and temporal changes in the lagoon nekton assemblage, but that several characteristics of the assemblage, in particular the biomass of some particular categories and of the whole assemblage, are sensitive to human impacts. A particularly negligible effect seemed to be associated with fishing effort, thus suggesting that the monitoring of the local artisanal fishery is suitable also to provide useful information on the evaluation of the status of nekton assemblage
- …