4,411 research outputs found
Baryon Number Violation Involving Higher Generations
Proton stability seems to constrain rather strongly any baryon number
violating process. We investigate the possibility of baryon number violating
processes involving right-handed dynamics or higher generation quarks. Our
results strongly suggest that there will be no possibility to observe baryon
number violation in tau or higher generation quark decays, at any future
machine.Comment: Improved figures, small changes in the text, added reference. To
appear in Phys. Rev.
CP Violation in Fourth Generation Quark Decays
We show that, if a fourth generation is discovered at the Tevatron or LHC,
one could study CP violation in b' \to s decays. Asymmetries could reach 30%
for b'\to sZ for m_{b'} \lesssim 350 GeV, while it could be greater than 50%
for b'\to s\gamma and extend to higher m_{b'}. Branching ratios are
10^{-3}--10^{-5}, and CPV measurement requires tagging. Once measured, however,
the CPV phase can be extracted with little theoretical uncertainty.Comment: 4 pages, 7 eps figure
Plaquette Ordered Phase and Quantum Phase Diagram in the Spin-1/2 J1-J2 Square Heisenberg Model
We study the spin-1/2 Heisenberg model on the square lattice with first- and
second-neighbor antiferromagnetic interactions J1 and J2, which possesses a
nonmagnetic region that has been debated for many years and might realize the
interesting Z2 spin liquid. We use the density matrix renormalization group
approach with explicit implementation of SU(2) spin rotation symmetry and study
the model accurately on open cylinders with different boundary conditions. With
increasing J2, we find a Neel phase, a plaquette valence-bond (PVB) phase with
a finite spin gap, and a possible spin liquid in a small region of J2 between
these two phases. From the finite-size scaling of the magnetic order parameter,
we estimate that the Neel order vanishes at J2/J1~0.44. For 0.5<J2/J1<0.61, we
find dimer correlations and PVB textures whose decay lengths grow strongly with
increasing system width, consistent with a long-range PVB order in the
two-dimensional limit. The dimer-dimer correlations reveal the s-wave character
of the PVB order. For 0.44<J2/J1<0.5, spin order, dimer order, and spin gap are
small on finite-size systems and appear to scale to zero with increasing system
width, which is consistent with a possible gapless SL or a near-critical
behavior. We compare and contrast our results with earlier numerical studies.Comment: 11 pages, 17 figures, and 1 tabl
Study on the control of end quality by one closed cross wedge rolling based wedge block
The paper presents a new method of one closed cross wedge rolling (CWR) based wedge block to achieve near net forming of CWR shafts. The modeling is performed by using the Finite Element Method (FEM) software DEFORM-3D. The metal flow rule of the shaft is clarified by analyzing the strain and displacement field of the shaft. The results demonstrate that the concave heart value of rolled part end will be reduced by about 70 % by one closed CWR based wedge block, comparing it with the case without wedge block. And also the rolling experiments are performed the result of which provides reliable theoretical basis for achieving near net forming of CWR
A General, Practical Palladium-Catalyzed Cyanation of (Hetero)Aryl Chlorides and Bromides
Playing it safe: The nontoxic cyanide source K[subscript 4][Fe(CN)[subscript 6]⋅3 H[subscript 2]O can be used for the cyanation of (hetero)aryl halides. The application of palladacycle catalysts prevents poisoning during catalyst formation, thereby allowing for low catalyst loadings, fast reaction times, and wide heterocyclic substrate scope.National Institutes of Health (U.S.) (Award GM46059
- …