2,408 research outputs found
Interference of Conversion and Bremsstrahlung Amplitudes in the Decay K_L -> mu^+ mu^- gamma
In the region of large mu^+ mu^- invariant mass, the decay spectrum of K_L ->
mu^+ mu^- gamma deviates from the Dalitz pair spectrum, as a result of
interference between conversion (K_L -> gamma^* gamma -> mu^+ mu^- gamma) and
bremsstrahlung amplitudes. The latter is proportional to the K_L -> mu^+ mu^-
matrix element, whose 2 gamma-absorptive part appears to dominate the observed
K_L -> mu^+ mu^- decay rate. We examine the extent to which a scrutiny of the
K_L -> mu^+ mu^- gamma spectrum in the end-point region could provide evidence
on the real part of the K_L -> mu^+ mu^- amplitude. As a by-product, we obtain
the absorptive part of the K_L -> gamma^* gamma form factor, using data on the
K_L -> pi^+ pi^- gamma spectrum.Comment: 7 pages, 4 figure
Hyperfine splitting in noncommutative spaces
We study the hyperfine splitting in the framework of the noncommutative
quantum mechanics (NCQM) developed in the literature. The results show
deviations from the usual quantum mechanics. We show that the energy difference
between two excited F = I + 1/2 and the ground F = I - 1/2 states in a
noncommutative space (NCS) is bigger than the one in the commutative case, so
the radiation wavelength in NCSs must be shorter than the radiation wavelength
in commutative spaces. We also find an upper bound for the noncommutativity
parameter.Comment: No figure
Explicitly correlated plane waves: Accelerating convergence in periodic wavefunction expansions
We present an investigation into the use of an explicitly correlated plane
wave basis for periodic wavefunction expansions at the level of second-order
M{\o}ller-Plesset perturbation theory (MP2). The convergence of the electronic
correlation energy with respect to the one-electron basis set is investigated
and compared to conventional MP2 theory in a finite homogeneous electron gas
model. In addition to the widely used Slater-type geminal correlation factor,
we also derive and investigate a novel correlation factor that we term
Yukawa-Coulomb. The Yukawa-Coulomb correlation factor is motivated by analytic
results for two electrons in a box and allows for a further improved
convergence of the correlation energies with respect to the employed basis set.
We find the combination of the infinitely delocalized plane waves and local
short-ranged geminals provides a complementary, and rapidly convergent basis
for the description of periodic wavefunctions. We hope that this approach will
expand the scope of discrete wavefunction expansions in periodic systems.Comment: 15 pages, 13 figure
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Are smooth pseudopotentials a good choice for representing short-range interactions?
Are smooth pseudopotentials a good choice for representing short-range interactions?
When seeking a numerical representation of a quantum-mechanical multiparticle
problem it is tempting to replace a singular short-range interaction by a
smooth finite-range pseudopotential. Finite basis set expansions, e.g.~in Fock
space, are then guaranteed to converge exponentially. The need to faithfully
represent the artificial length scale of the pseudopotential, however, places a
costly burden on the basis set. Here we discuss scaling relations for the
required size of the basis set and demonstrate the basis set convergence on the
example of a two-dimensional system of few fermions with short-range -wave
interactions in a harmonic trapping potential. In particular we show that the
number of harmonic-oscillator basis functions needed to reach a regime of
exponential convergence for a Gaussian pseudopotential scales with the fourth
power of the pseudopotential length scale, which can be improved to quadratic
scaling when the basis functions are re-scaled appropriately. Numerical
examples for three fermions with up to a few hundred single-particle basis
functions are presented and implications for the feasibility of accurate
numerical multi-particle simulations of interacting ultra-cold atom systems are
discussed.Comment: 11 pages, 2 figure
Heisenberg quantization for the systems of identical particles and the Pauli exclusion principle in noncommutative spaces
We study the Heisenberg quantization for the systems of identical particles
in noncommtative spaces. We get fermions and bosons as a special cases of our
argument, in the same way as commutative case and therefore we conclude that
the Pauli exclusion principle is also valid in noncommutative spaces.Comment: 8 pages, 1 figur
Accelerating the convergence of exact diagonalization with the transcorrelated method: Quantum gas in one dimension with contact interactions
Exact diagonalization expansions of Bose or Fermi gases with contact
interactions converge very slowly due to a non-analytic cusp in the wave
function. Here we develop a transcorrelated approach where the cusp is treated
exactly and folded into the many-body Hamiltonian with a similarity
transformation that removes the leading order singularity. The resulting
transcorrelated Hamiltonian is not hermitian but can be treated numerically
with a standard projection approach. The smoothness of the wave function
improves by at least one order and thus the convergence rate for the ground
state energy improves. By numerical investigation of a one-dimensional gas of
spin- fermions we find the error in the transcorrelated energy to
scale as with a single-particle basis of plane waves compared to
for the expansion of the original Hamiltonian and using
conventional lattice renormalization
The effect of heavy metal on Chlorella vulgaris, Scenedesmus obliquus and Anabaena flos-aquae
In this survey two species of chlorophyta (Chlorella vulgaris and Scenedesmus obliquus) and one species of blue-green algae (Anabaena flos- aquae) were exposed with heavy metal (zinc) under lab condition (temp. 25±2°C, light 3500±350 lux) for 96 hours. After this time, these species were counted with hemocytometer and based on probit analysis method and was determined ECIO, EC50 and EC90. Amount of EC50 for C. vulgaris, S. obliquus and A. flos-aquae were 0.134,0.047 and 0.093 mg/lit, respectively and this subject was distincted that S obliquus has more endurance than other species. Max value of zinc for these species (C. vulgaris, S. obiquus and A. flos-aquae ) were 0.0134, 0.0047 and 0.0093 mg/l respectively. Regression coefficient was 92-98 percent between concentration logarithm of zinc and decrease of these species density
Rare K decays in a model of quark and lepton masses
An extension of a model of neutrino masses to the quark sector provides an
interesting link between these two sectors. A parameter which is important to
describe neutrino oscillations and masses is found to be a crucial one
appearing in various ``penguin'' operators, in particular the so-called Z
penguin. This parameter is severely constrained by the rare decay process
. This in turn has interesting implications on the
decay rates of other rare processes such as , etc..., as well
as on the masses of the neutrinos and the masses of the vector-like quarks and
leptons which appear in our model.Comment: 34 pages, 10 figures, corrected some typos in the introductio
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