21 research outputs found
Many-body interactions and high-pressure equations of state in rare-gas solids
The T 0K equations of state (EOS) of rare-gas solids (RGS) (He, Ne, Ar, Kr, and Xe) are calculated in
the experimentally studied ranges of pressures accounting for two- and three-body interatomic forces.
Solid-state corrections to the pure two-body Aziz et al. potentials included the long-range Axilrod–Teller
three-body interaction and short-range three-body exchange interaction. The energy-scale and length-scale
parameters of the latter were taken as adjustable parameters of theory. The calculated T 0K EOS for all
RGS are in excellent agreement with experiment in the whole range of pressures. The calculated EOS for Ar,
Kr, and Xe exhibit inflection points where the isothermal bulk moduli have non-physical maxima indicating
that account of only three-body forces becomes insufficient. These points lie at pressures 250, 200, and 175
GPa (volume compressions of approximately 4.8, 4.1, and 3.6) for Ar, Kr, and Xe, respectively. No such
points were found in the calculated EOS of He and Ne. The relative magnitude of the three-body contribution
to the ground-state energy with respect to the two-body one as a function of the volume compression
was found to be non-monotonic in the sequence Ne–Ar–Kr–Xe. In a large range of compressions, Kr has the
highest value of this ratio. This anomally high three-body exchange forces contributes to the EOS so large
negative pressure that the EOS for Kr and Ar as a function of compression nearly coincide. At compressions
higher approximately 3.5, the curves intersect and further on the EOS of Kr lies lower than that of Ar
Lattice distortion of quantum cryocrystals under pressure
The hcp lattice distortion parameter δ, the deviation of c/a ratio from the ideal hcp value √ 8/3 , have been calculated for solid He under pressure taking into account two- and three-body interatomic forces. The resulting lattice distortion parameter is small and negative, that is the lattice is slightly flattened compared with the ideal hcp lattice. It monotonically increases in absolute value with pressure and reaches 10⁻³ for molar volume of ~ 2.5 cm³/mol. Such small distrotions are most likely outside of possibilities of x-ray or neutron experiments but can be detected by optical methods based on measurements of the birefringence. The data on δ can be used as a probe of the many-body forces
Lattice distortion in hcp rare gas solids
The lattice distortion parameter δ≡c/a – √8/3 has been calculated as a function of molar volume for the hcp phases of He, Ar, Kr, and Xe. Results from both semi-empirical potentials and density functional theory are presented. Our study shows that δ is negative for helium in the entire pressure range. For Ar, Kr, and Xe, however, δ changes sign from negative to positive as the pressure increases, growing rapidly in magnitude at higher pressures
CP Violation in B and K Decays: 2003
These lectures give a brief description of CP violation in B and K meson
decays with particular emphasize put on the determination of the CKM matrix.
The following topics will be discussed: i) The CKM matrix, the unitarity
triangle and general aspects of the theoretical framework, ii)
Particle-antiparticle mixing and various types of CP violation, iii) Standard
analysis of the unitarity triangle, iv) The ratio epsilon^prime/epsilon, v) The
most important strategies for the determination of the angles ,
and from B decays, vi) Rare decays and
vii) Models with minimal flavour violation.Comment: Schladming lectures 2003, Main latex-file, 8 figures, 51 page
Molecular rotation in p-H₂ and o-D₂ in phase I under pressure
The orientational order parameter, rotational ground-state energy, and lattice distortion parameter (the deviation of the c/a ratio from the ideal hcp value 1.633) in hcp lattice of phase I of p-H₂ and o-D₂ are calculated using a semi-empirical approach. It is shown that the lattice distortion in these J-even species is small compared with that found in n-H₂, and n-D₂. The difference presumably is caused by the J-odd species
Poisson’s ratio in cryocrystals under pressure
We present results of lattice dynamics calculations of Poisson’s ratio (PR) for solid hydrogen and rare gas
solids (He, Ne, Ar, Kr and Xe) under pressure. Using two complementary approaches — the semi-empirical
many-body calculations and the first-principle density-functional theory calculations we found three different
types of pressure dependencies of PR. While for solid helium PR monotonically decreases with rising pressure,
for Ar, Kr, and Xe it monotonically increases with pressure. For solid hydrogen and Ne the pressure dependencies
of PR are nonmonotonic displaying rather deep minimums. The role of the intermolecular potentials in this
diversity of patterns is discussed
Sound velocities in solid hydrogen under pressure
We present results of semi-empirical lattice dynamics calculations of the sound velocities in solid hydrogen under
pressure based on the many-body intermolecular potential and first-principle density-functional theory (DFT).
Both the sound velocities and elastic moduli are in excellent agreement with data from Brillouin scattering measurements
while Silvera–Goldman and Hemley–Silvera–Goldman potentials tend to overestimate the sound velocity.
It is shown that the stiffer is the potential the greater is overestimated the sound velocity. As was the case for equation
of state and Raman-active lattice phonon calculations, the employed many-body potential works well for
phases I and II (up to ~ 140 GPa while for higher pressures the use of the DFT is preferable
What can we learn from neutrinoless double beta decay experiments?
We assess how well next generation neutrinoless double beta decay and normal
neutrino beta decay experiments can answer four fundamental questions. 1) If
neutrinoless double beta decay searches do not detect a signal, and if the
spectrum is known to be inverted hierarchy, can we conclude that neutrinos are
Dirac particles? 2) If neutrinoless double beta decay searches are negative and
a next generation ordinary beta decay experiment detects the neutrino mass
scale, can we conclude that neutrinos are Dirac particles? 3) If neutrinoless
double beta decay is observed with a large neutrino mass element, what is the
total mass in neutrinos? 4) If neutrinoless double beta decay is observed but
next generation beta decay searches for a neutrino mass only set a mass upper
limit, can we establish whether the mass hierarchy is normal or inverted? We
base our answers on the expected performance of next generation neutrinoless
double beta decay experiments and on simulations of the accuracy of
calculations of nuclear matrix elements.Comment: Added reference
The possible test of the calculations of nuclear matrix elements of the -decay
The existing calculations of the nuclear matrix elements of the neutrinoless
double -decay differ by about a factor three. This uncertainty prevents
quantitative interpretation of the results of experiments searching for this
process. We suggest here that the observation of the neutrinoless double
-decay of {\em several} nuclei could allow to test calculations of the
nuclear matrix elements through the comparison of the ratios of the calculated
lifetimes with experimental data. It is shown that the ratio of the lifetimes
is very sensitive to different models
Recent advances in neutrinoless double beta decay search
Even after the discovery of neutrino flavour oscillations, based on data from
atmospheric, solar, reactor, and accelerator experiments, many characteristics
of the neutrino remain unknown. Only the neutrino square-mass differences and
the mixing angle values have been estimated, while the value of each mass
eigenstate still hasn't. Its nature (massive Majorana or Dirac particle) is
still escaping. Neutrinoless double beta decay (-DBD) experimental
discovery could be the ultimate answer to some delicate questions of elementary
particle and nuclear physics. The Majorana description of neutrinos allows the
-DBD process, and consequently either a mass value could be measured or
the existence of physics beyond the standard should be confirmed without any
doubt. As expected, the -DBD measurement is a very difficult field of
application for experimentalists. In this paper, after a short summary of the
latest results in neutrino physics, the experimental status, the R&D projects,
and perspectives in -DBD sector are reviewed.Comment: 36 pages, 7 figures, To be publish in Czech Journal of Physic