385 research outputs found
A 0.821-ratio purely combinatorial algorithm for maximum k-vertex cover in bipartite graphs
We study the polynomial time approximation of the max k-vertex cover problem in bipartite graphs and propose a purely combinatorial algorithm that beats the only such known algorithm, namely the greedy approach. We present a computer-assisted analysis of our algorithm, establishing that the worst case approximation guarantee is bounded below by 0.821. © Springer-Verlag Berlin Heidelberg 2016
Effects of quantum space time foam in the neutrino sector
We discuss violations of CPT and quantum mechanics due to interactions of
neutrinos with space-time quantum foam. Neutrinoless double beta decay and
oscillations of neutrinos from astrophysical sources (supernovae, active
galactic nuclei) are analysed. It is found that the propagation distance is the
crucial quantity entering any bounds on EHNS parameters. Thus, while the bounds
from neutrinoless double beta decay are not significant, the data of the
supernova 1987a imply a bound being several orders of magnitude more stringent
than the ones known from the literature. Even more stringent limits may be
obtained from the investigation of neutrino oscillations from active galactic
nuclei sources, which have an impressive potential for the search of quantum
foam interactions in the neutrino sector.Comment: 5 page
Escape from washing out of baryon number in a two-zero-texture general Zee model compatible with the large mixing angle MSW solution
We propose a two-zero-texture general Zee model, compatible with the large
mixing angle Mikheyev-Smirnov-Wolfenstein solution. The washing out of the
baryon number does not occur in this model for an adequate parameter range. We
check the consistency of a model with the constraints coming from flavor
changing neutral current processes, the recent cosmic microwave background
observation, and the Z-burst scenario.Comment: 22 pages, 2 eps figures, Type set revtex
Lepton Flavor Violation in Z and Lepton Decays in Supersymmetric Models
The observation of charged lepton flavor non-conservation would be a clear
signature of physics beyond the Standard Model. In particular, supersymmetric
(SUSY) models introduce mixings in the sneutrino and the charged slepton
sectors which could imply flavor-changing processes at rates accessible to
upcoming experiments. In this paper we analyze the possibility to observe Z -->
lep_I lep_J in the GigaZ option of TESLA at DESY. We show that although models
with SUSY masses above the current limits could predict a branching ratio BR(Z
--> mu e) accessible to the experiment, they would imply an unobserved rate of
mu --> e gamma and thus are excluded. In models with a small mixing angle
between the first and the third (or the second and the third) slepton families
GigaZ could observe Z --> tau mu (or Z --> tau e) consistently with present
bounds on lep_J --> lep_I gamma. In contrast, if the mixing angles between the
three slepton families are large the bounds from mu --> e gamma push these
processes below the reach of GigaZ. We show that in this case the masses of the
three slepton families must be strongly degenerated (with mass differences of
order 10^{-3}). We update the limits on the slepton mass insertions
delta_{LL,RR,LR} and discuss the correlation between flavor changing and g_mu-2
in SUSY models.Comment: 23 pages, 6 figures. Version to appear in Phys. Rev.
Comparison of large-angle production of charged pions with incident protons on cylindrical long and short targets
The HARP collaboration has presented measurements of the double-differential
pi+/pi- production cross-section in the range of momentum 100 MeV/c <= p 800
MeV/c and angle 0.35 rad <= theta <= 2.15 rad with proton beams hitting thin
nuclear targets. In many applications the extrapolation to long targets is
necessary. In this paper the analysis of data taken with long (one interaction
length) solid cylindrical targets made of carbon, tantalum and lead is
presented. The data were taken with the large acceptance HARP detector in the
T9 beam line of the CERN PS. The secondary pions were produced by beams of
protons with momenta 5 GeV/c, 8 GeV/c and 12 GeV/c. The tracking and
identification of the produced particles were performed using a small-radius
cylindrical time projection chamber (TPC) placed inside a solenoidal magnet.
Incident protons were identified by an elaborate system of beam detectors.
Results are obtained for the double-differential yields per target nucleon d2
sigma / dp dtheta. The measurements are compared with predictions of the MARS
and GEANT4 Monte Carlo simulations.Comment: 43 pages, 20 figure
Forward production of charged pions with incident on nuclear targets measured at the CERN PS
Measurements of the double-differential production cross-section
in the range of momentum 0.5 \GeVc \leq p \le 8.0 \GeVc and angle 0.025 \rad
\leq \theta \le 0.25 \rad in interactions of charged pions on beryllium,
carbon, aluminium, copper, tin, tantalum and lead are presented. These data
represent the first experimental campaign to systematically measure forward
pion hadroproduction. The data were taken with the large acceptance HARP
detector in the T9 beam line of the CERN PS. Incident particles, impinging on a
5% nuclear interaction length target, were identified by an elaborate system of
beam detectors. The tracking and identification of the produced particles was
performed using the forward spectrometer of the HARP detector. Results are
obtained for the double-differential cross-sections mainly at four incident pion beam
momenta (3 \GeVc, 5 \GeVc, 8 \GeVc and 12 \GeVc). The measurements are compared
with the GEANT4 and MARS Monte Carlo simulationComment: to be published on Nuclear Physics
Quark and Lepton Mass Matrices in the SO(10) Grand Unified Theory with Generation Flipping
We investigate the SO(10) grand unified model with generation flipping. The
model contains one extra matter multiplet and it mixes with the
usual matter multiplets when the SO(10) is broken down to SU(5).
We find the parameter region of the model in which the observed quark masses
and mixings are well reproduced. The resulting parameter region is consistent
with the observation that only have a source of hierarchies and
indicates that the mixing between second and third generations tends to be
large in the lepton sector, which is consistent with the observed maximal
mixing of the atmospheric neutrino oscillation. We also show that the model can
accommodate MSW and vacuum oscillation solutions to the solar neutrino deficit
depending on the form of the Majorana mass matrix for the right-handed
neutrinos.Comment: 28 pages, Late
MICE: the Muon Ionization Cooling Experiment. Step I: First Measurement of Emittance with Particle Physics Detectors
The Muon Ionization Cooling Experiment (MICE) is a strategic R&D project intended to demonstrate the only practical solution to providing high brilliance beams necessary for a neutrino factory or muon collider. MICE is under development at the Rutherford Appleton Laboratory (RAL) in the United Kingdom. It comprises a dedicated beamline to generate a range of input muon emittances and momenta, with time-of-flight and Cherenkov detectors to ensure a pure muon beam. The emittance of the incoming beam will be measured in the upstream magnetic spectrometer with a scintillating fiber tracker. A cooling cell will then follow, alternating energy loss in Liquid Hydrogen (LH2) absorbers to RF cavity acceleration. A second spectrometer, identical to the first, and a second muon identification system will measure the outgoing emittance. In the 2010 run at RAL the muon beamline and most detectors were fully commissioned and a first measurement of the emittance of the muon beam with particle physics (time-of-flight) detectors was performed. The analysis of these data was recently completed and is discussed in this paper. Future steps for MICE, where beam emittance and emittance reduction (cooling) are to be measured with greater accuracy, are also presented
Absolute Momentum Calibration of the HARP TPC
In the HARP experiment the large-angle spectrometer is using a cylindrical
TPC as main tracking and particle identification detector. The momentum scale
of reconstructed tracks in the TPC is the most important systematic error for
the majority of kinematic bins used for the HARP measurements of the
double-differential production cross-section of charged pions in proton
interactions on nuclear targets at large angle. The HARP TPC operated with a
number of hardware shortfalls and operational mistakes. Thus it was important
to control and characterize its momentum calibration. While it was not possible
to enter a direct particle beam into the sensitive volume of the TPC to
calibrate the detector, a set of physical processes and detector properties
were exploited to achieve a precise calibration of the apparatus. In the
following we recall the main issues concerning the momentum measurement in the
HARP TPC, and describe the cross-checks made to validate the momentum scale. As
a conclusion, this analysis demonstrates that the measurement of momentum is
correct within the published precision of 3%.Comment: To be published by JINS
Constraints from muon g-2 and LFV processes in the Higgs Triplet Model
Constraints from the muon anomalous magnetic dipole moment and lepton flavor
violating processes are translated into lower bounds on v_Delta*m_H++ in the
Higgs Triplet Model by considering correlations through the neutrino mass
matrix. The discrepancy of the sign of the contribution to the muon anomalous
magnetic dipole moment between the measurement and the prediction in the model
is clarified. It is shown that mu to e gamma, tau decays (especially, tau to mu
e e), and the muonium conversion can give a more stringent bound on
v_Delta*m_H++ than the bound from mu to eee which is expected naively to give
the most stringent one.Comment: 18 pages, 16 figure
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