1,918 research outputs found
Oscillation of the tunnel splitting in nanospin systems within the particle mapping formalism
The oscillation of tunnel splitting in the biaxial spin system within
magnetic field along the anisotropy axis is analyzed within the particle
mapping approach, rather than in the (\theta-\phi) spin coherent-state
representation. In our mapping procedure, the spin system is transformed into a
particle moving in the restricted geometry whose wave function subjects
to the boundary condition involving additional phase shift. We obtain the new
topological phase that plays the same role as the Wess-Zumino action in spin
coherent-state representation. Considering the interference of two possible
trajectories, instanton and anti-instanton, we get the identical condition for
the field at which tunneling is quenched, with the previous result within spin
coherent-state representation.Comment: 11 pages, 1 figure; Some typographical errors have been correcte
Higgs Signal for h to aa at Hadron Colliders
We assess the prospect of observing a neutral Higgs boson at hadron colliders
in its decay to two spin-zero states, a, for a Higgs mass of 90-130 GeV, when
produced in association with a W or Z boson. Such a decay is allowed in
extensions of the MSSM with CP-violating interactions and in the NMSSM, and can
dominate Higgs boson final states, thereby evading the LEP constraints on
standard Higgs boson production. The light spin-zero state decays primarily via
a to bb and tau+tau-, so this signal channel retains features distinct from the
main backgrounds. Our study shows that at the Tevatron, there may be potential
to observe a few events in the bb tau+tau- or bbbb channels with relatively
small background, although this observation would be statistically limited. At
the LHC, the background problem is more severe, but with cross sections and
integrated luminosities orders of magnitude larger than at the Tevatron, the
observation of a Higgs boson in this decay mode would be possible. The channel
h to aa to bbbb would provide a large statistical significance, with a
signal-to-background ratio on the order of 1:2. In these searches, the main
challenge would be to retain the adequate tagging efficiency of b's and tau's
in the low p_T region.Comment: Version to be published in JHEP. 20 pages, 5 figure
Quantum nucleation in ferromagnets with tetragonal and hexagonal symmetries
The phenomenon of quantum nucleation is studied in a ferromagnet in the
presence of a magnetic field at an arbitrary angle. We consider the
magnetocrystalline anisotropy with tetragonal symmetry and that with hexagonal
symmetry, respectively. By applying the instanton method in the
spin-coherent-state path-integral representation, we calculate the dependence
of the rate of quantum nucleation and the crossover temperature on the
orientation and strength of the field for a thin film and for a bulk solid. Our
results show that the rate of quantum nucleation and the crossover temperature
depend on the orientation of the external magnetic field distinctly, which
provides a possible experimental test for quantum nucleation in nanometer-scale
ferromagnets.Comment: 19 pages and 3 figures, Final version and accepted by Phys. Rev. B
(Feb. B1 2001
The leading particle effect from light quark fragmentation in charm hadroproduction
The asymmetry of and meson production in scattering
observed by the E791 experiment is a typical phenomenon known as the leading
particle effect in charm hadroproducton. We show that the phenomenon can be
explained by the effect of light quark fragmentation into charmed hadrons
(LQF). Meanwhile, the size of the LQF effect is estimated from data of the E791
experiment.
A comparison is made with the estimate of the LQF effect from prompt
like-sign dimuon rate in neutrino experiments. The influence of the LQF effect
on the measurement of nucleon strange distribution asymmetry from charged
current charm production processes is briefly discussed.Comment: 6 latex pages, 1 figure, to appear in EPJ
Spin Dependent Fragmentation Functions for Heavy Flavor Baryons and Single Heavy Hyperon Polarization
Spin dependent fragmentation functions for heavy flavor quarks to fragment
into heavy baryons are calculated in a quark-diquark model. The production of
intermediate spin 1/2 and 3/2 excited states is explicity included.
, and production rate and polarization at LEP energies are
calculated and, where possible, compared with experiment. A different approach,
also relying on a heavy quark-diquark model, is proposed for the small momentum
transfer inclusive production of polarized heavy flavor hyperons. The predicted
polarization is roughly in agreement with experiment.Comment: LaTeX2e 11 pages with 4 PostScript figures. To be published in
Proceedings of the International Workshop ``Symmetries and spin'',
Praha-SPIN-200
Experimental pulse technique for the study of microbial kinetics in continuous culture
A novel technique was developed for studying the growth kinetics of microorganisms in continuous culture. The method is based on following small perturbations of a chemostat culture by on-line measurement of the dynamic response in oxygen consumption rates. A mathematical model, incorporating microbial kinetics and mass transfer between gas and liquid phases, was applied to interpret the data. Facilitating the use of very small disturbances, the technique is non-disruptive as well as fast and accurate. The technique was used to study the growth kinetics of two cultures, Methylosinus trichosporium OB3b growing on methane, both in the presence and in the absence of copper, and Burkholderia (Pseudomonas) cepacia G4 growing on phenol. Using headspace flushes, gas blocks and liquid substrate pulse experiments, estimates for limiting substrate concentrations, maximum conversion rates Vmax and half saturation constants Ks could rapidly be obtained. For M. trichosporium OB3b it was found that it had a far higher affinity for methane when particulate methane monooxygenase (pMMO) was expressed than when the soluble form (sMMO) was expressed under copper limitation. While for B. cepacia G4 the oxygen consumption pattern during a phenol pulse in the chemostat indicated that phenol was transiently converted to an intermediate (4-hydroxy-2-oxovalerate), so that initially less oxygen was used per mole of phenol.
Transitions in Family-dependent Models
We analyze flavor-changing-neutral-current (FCNC) effects in the
transitions that are induced by family non-universal gauge symmetries.
After systematically developing the necessary formalism, we present a
correlated analysis for the processes. We adopt a
model-independent approach in which we only require family-universal charges
for the first and second generations and small fermion mixing angles. We
analyze the constraints on the resulting parameter space from
mixing and the time-dependent CP asymmetries of the penguin-dominated decays. Our results indicate that the
currently observed discrepancies in some of these modes with respect to the
Standard Model predictions can be consistently accommodated within this general
class of models.Comment: 36 pages, 11 figure
Smearing of Observables and Spectral Measures on Quantum Structures
An observable on a quantum structure is any -homomorphism of quantum
structures from the Borel -algebra of the real line into the quantum
structure which is in our case a monotone -complete effect algebras
with the Riesz Decomposition Property. We show that every observable is a
smearing of a sharp observable which takes values from a Boolean
-subalgebra of the effect algebra, and we prove that for every element
of the effect algebra there is its spectral measure
The mixed problem in L^p for some two-dimensional Lipschitz domains
We consider the mixed problem for the Laplace operator in a class of
Lipschitz graph domains in two dimensions with Lipschitz constant at most 1.
The boundary of the domain is decomposed into two disjoint sets D and N. We
suppose the Dirichlet data, f_D has one derivative in L^p(D) of the boundary
and the Neumann data is in L^p(N). We find conditions on the domain and the
sets D and N so that there is a p_0>1 so that for p in the interval (1,p_0), we
may find a unique solution to the mixed problem and the gradient of the
solution lies in L^p
Sharp Trace Hardy-Sobolev-Maz'ya Inequalities and the Fractional Laplacian
In this work we establish trace Hardy and trace Hardy-Sobolev-Maz'ya
inequalities with best Hardy constants, for domains satisfying suitable
geometric assumptions such as mean convexity or convexity. We then use them to
produce fractional Hardy-Sobolev-Maz'ya inequalities with best Hardy constants
for various fractional Laplacians. In the case where the domain is the half
space our results cover the full range of the exponent of the
fractional Laplacians. We answer in particular an open problem raised by Frank
and Seiringer \cite{FS}.Comment: 42 page
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