237,408 research outputs found
Matter Effects in Active-Sterile Solar Neutrino Oscillations
The matter effects for solar neutrino oscillations are studied in a general
scheme with an arbitrary number of sterile neutrinos, without any constraint on
the mixing, assuming only a realistic hierarchy of neutrino squared-mass
differences in which the smallest squared-mass difference is effective in solar
neutrino oscillations. The validity of the analytic results are illustrated
with a numerical solution of the evolution equation in three examples of the
possible mixing matrix in the simplest case of four-neutrino mixing.Comment: 26 pages. Final version published in Phys. Rev. D80 (2009) 11300
The B\to D_s^{(*)}\eta^{(\prime)} decays in the perturbative QCD
In this paper, we calculate the branching ratios for , and decays by employing the perturbative QCD (pQCD)
factorization approach. Under the two kinds of mixing
schemes, the quark-flavor mixing scheme and the singlet-octet mixing scheme, we
find that the calculated branching ratios are consistent with the currently
available experimental upper limits. We also considered the so called
" puzzle", by using two groups of parameters about the
meson decay constants, that is MeV, MeV and
MeV, MeV, to calculate the branching ratios for
the considered decays. We find that the results change by using these
two different groups of paramters.Comment: 12 pages, 1 figure. Typos removed, minor correction
Captures of Hot and Warm Sterile Antineutrino Dark Matter on EC-decaying Ho-163 Nuclei
Capturing low-energy electron antineutrinos on radioactive Ho-163 nuclei,
which decay into Dy-163 via electron capture (EC), is a noteworthy opportunity
to detect relic sterile antineutrinos. Such hypothetical particles are more or
less implied by current experimental and cosmological data, and they might be a
part of hot dark matter or a candidate for warm dark matter in the Universe.
Using the isotope Ho-163 as a target and assuming reasonable active-sterile
antineutrino mixing angles, we calculate the capture rate of relic electron
antineutrinos against the corresponding EC-decay background in the presence of
sterile antineutrinos at the sub-eV or keV mass scale. We show that the
signature of hot or warm sterile antineutrino dark matter should in principle
be observable, provided the target is big enough and the energy resolution is
good enough.Comment: 16 pages, 6 figures, more discussions and references added. To appear
in JCA
The Coupled Cluster Method Applied to Quantum Magnets: A New LPSUB Approximation Scheme for Lattice Models
A new approximation hierarchy, called the LPSUB scheme, is described for
the coupled cluster method (CCM). It is applicable to systems defined on a
regular spatial lattice. We then apply it to two well-studied prototypical
(spin-1/2 Heisenberg antiferromagnetic) spin-lattice models, namely: the XXZ
and the XY models on the square lattice in two dimensions. Results are obtained
in each case for the ground-state energy, the ground-state sublattice
magnetization and the quantum critical point. They are all in good agreement
with those from such alternative methods as spin-wave theory, series
expansions, quantum Monte Carlo methods and the CCM using the alternative
LSUB and DSUB schemes. Each of the three CCM schemes (LSUB, DSUB
and LPSUB) for use with systems defined on a regular spatial lattice is
shown to have its own advantages in particular applications
Lattice gluodynamics at negative g^2
We consider Wilson's SU(N) lattice gauge theory (without fermions) at
negative values of beta= 2N/g^2 and for N=2 or 3. We show that in the limit
beta -> -infinity, the path integral is dominated by configurations where links
variables are set to a nontrivial element of the center on selected non
intersecting lines. For N=2, these configurations can be characterized by a
unique gauge invariant set of variables, while for N=3 a multiplicity growing
with the volume as the number of configurations of an Ising model is observed.
In general, there is a discontinuity in the average plaquette when g^2 changes
its sign which prevents us from having a convergent series in g^2 for this
quantity. For N=2, a change of variables relates the gauge invariant
observables at positive and negative values of beta. For N=3, we derive an
identity relating the observables at beta with those at beta rotated by +-
2pi/3 in the complex plane and show numerical evidence for a Ising like first
order phase transition near beta=-22. We discuss the possibility of having
lines of first order phase transitions ending at a second order phase
transition in an extended bare parameter space.Comment: 7 pages, 7 figures, uses revtex, Eqs. 15-17 corrected, minor change
- …