299 research outputs found
A simple inert model solves the little hierarchy problem and provides a dark matter candidate
We discuss a minimal extension to the standard model in which two singlet
scalar states that only interacts with the Higgs boson is added. Their masses
and interaction strengths are fixed by the two requirements of canceling the
one-loop quadratic corrections to the Higgs boson mass and providing a viable
dark matter candidate. Direct detection of the lightest of these new states in
nuclear scattering experiments is possible with a cross section within reach of
future experiments.Comment: Finite corrections included. Model modified. Conclusion unchange
Bounds on Dirac Neutrino Masses from Nucleosynthesis
We derive new bounds on the Dirac mass of the tau and muonic neutrinos. By
solving the kinetic equation for the rate of energy deposition due to helicity
flipping processes and imposing the constraint that the number of effective
species contributing to the energy density at the time of nucleosynthesis be
, we find the bounds KeV and
KeV for MeV. The constraint leads to the much stronger bound KeV for both species
of neutrinos.Comment: 10 pages, UM-TH-94-21, UMN-TH-1303-94, FERMILAB-Pub-94/199-
Azimuthal Correlations in the Target Fragmentation Region of High Energy Nuclear Collisions
Results on the target mass dependence of proton and pion pseudorapidity
distributions and of their azimuthal correlations in the target rapidity range
are presented. The data have been taken with the
Plastic-Ball detector set-up for 4.9 GeV p + Au collisions at the Berkeley
BEVALAC and for 200 GeV/ p-, O-, and S-induced reactions on
different nuclei at the CERN-SPS. The yield of protons at backward rapidities
is found to be proportional to the target mass. Although protons show a typical
``back-to-back'' correlations, a ``side-by-side'' correlation is observed for
positive pions, which increases both with target mass and with impact parameter
of a collision. The data can consistently be described by assuming strong
rescattering phenomena including pion absorption effects in the entire excited
target nucleus.Comment: 7 pages, figures included, complete postscript available at
ftp://qgp.uni-muenster.de/pub/paper/azi-correlations.ps submitted to Phys.
Lett.
Cosmic Microwave Background constraint on residual annihilations of relic particles
Energy injected into the Cosmic Microwave Background at redshifts z<10^6 will
distort its spectrum permanently. In this paper we discuss the distortion
caused by annihilations of relic particles. We use the observational bounds on
deviations from a Planck spectrum to constrain a combination of annihilation
cross section, mass, and abundance. For particles with (s-wave) annihilation
cross section, =\sigma_0, the bound is
f[(\sigma_0/6e-27cm^3/s)(\Omega_{X\bar{X}}h^2)^2]/(m_X/MeV)<0.2, where m_X is
the particle mass, \Omega_{X\bar{X}} is the fraction of the critical density
the particle and its antiparticle contribute if they survive to the present
time, h=H_0/(100km/s/Mpc), H_0 is the Hubble constant, and f is the fraction of
the annihilation energy that interacts electromagnetically. We also compute the
less stringent limits for p-wave annihilation. We update other bounds on
residual annihilations and compare them to our CMB bound.Comment: submitted to Phys. Rev.
Lepton Flavor Violating Process in Bi-maximal texture of Neutrino Mixings
We investigate the lepton flavor violation in the framework of the MSSM with
right-handed neutrinos taking the large mixing angle MSW solution in the
quasi-degenerate and the inverse-hierarchical neutrino masses. We predict the
branching ratio of and processes
assuming the degenerate right-handed Majorana neutrino masses. We find that the
branching ratio in the quasi-degenerate neutrino mass spectrum is 100 times
smaller than the ones in the inverse-hierarchical and the hierarchical neutrino
spectra. We emphasize that the magnitude of is one of important
ingredients to predict BR(). The effect of the deviation
from the complete-degenerate right-handed Majorana neutrino masses are also
estimated. Furtheremore, we examine the S_{3\sL}\times S_{3\sR} model, which
gives the quasi-degenerate neutrino masses, and the Shafi-Tavartkiladze model,
which gives the inverse-hierarchical neutrino masses. Both predicted branching
ratios of are smaller than the experimantal bound.Comment: Latex file, 38 pages, 10 figures, revised versio
Partial Wave Analysis of the Reaction to Search for the "" Bound State
Employing the Bonn-Gatchina partial wave analysis framework (PWA), we have
analyzed HADES data of the reaction . This
reaction might contain information about the kaonic cluster "" via its
decay into . Due to interference effects in our coherent description
of the data, a hypothetical (or, specifically "")
cluster signal must not necessarily show up as a pronounced feature (e.g. a
peak) in an invariant mass spectra like . Our PWA analysis includes a
variety of resonant and non-resonant intermediate states and delivers a good
description of our data (various angular distributions and two-hadron invariant
mass spectra) without a contribution of a cluster. At a
confidence level of CL=95\% such a cluster can not contribute more than
2-12\% to the total cross section with a final state, which
translates into a production cross-section between 0.7 and 4.2 ,
respectively. The range of the upper limit depends on the assumed cluster mass,
width and production process.Comment: 7 Pages, 5 Figure
Production of Sigma{\pm}pi?pK+ in p+p reactions at 3.5 GeV beam energy
We study the production of Sigma^+-pi^+-pK^+ particle quartets in p+p
reactions at 3.5 GeV kinetic beam energy. The data were taken with the HADES
experiment at GSI. This report evaluates the contribution of resonances like
Lambda(1405$, Sigma(1385)^0, Lambda(1520), Delta(1232), N^* and K^*0 to the
Sigma^+- pi^-+ p K+ final state. The resulting simulation model is compared to
the experimental data in several angular distributions and it shows itself as
suitable to evaluate the acceptance corrections properly.Comment: 15 pages, 5 figure
Microwave assisted synthesis of novel bis-flavone dimers as new anticancer agents
In this study we describe a microwave based click chemistry method used to prepare a family of novel bis-flavone dimers. The substituted 7-hydroxy and 4’-hydroxy flavonoids were linked through a triazole ring. The compounds were easily synthesized and purified in high yields. The bis-flavonoids were tested on different cell lines including HCT116, HepG2, MCF7 and MOLT-4. Several analogues showed to have anticancer activity with IC50 values in the range of 20-60 µM. Flavonoids are known for their anticancer properties and this method provides the basis for new medicinal structures
Origin of the low-mass electron pair excess in light nucleus-nucleus collisions
We report measurements of electron pair production in elementary p+p and d+p
reactions at 1.25 GeV/u with the HADES spectrometer. For the first time, the
electron pairs were reconstructed for n+p reactions by detecting the proton
spectator from the deuteron breakup. We find that the yield of electron pairs
with invariant mass Me+e- > 0.15 GeV/c2 is about an order of magnitude larger
in n+p reactions as compared to p+p. A comparison to model calculations
demonstrates that the production mechanism is not sufficiently described yet.
The electron pair spectra measured in C+C reactions are compatible with a
superposition of elementary n+p and p+p collisions, leaving little room for
additional electron pair sources in such light collision systems.Comment: 11 pages, 2 figures, \usepackage{epsfig
Particle density fluctuations
Event-by-event fluctuations in the multiplicities of charged particles and
photons at SPS energies are discussed. Fluctuations are studied by controlling
the centrality of the reaction and rapidity acceptance of the detectors.
Results are also presented on the event-by-event study of correlations between
the multiplicity of charged particles and photons to search for DCC-like
signals.Comment: Talk presented at Quark Matter 2002, Nantes, Franc
- …