Abstract:
Basic aspects of phononless resonant capture of monoenergetic electron antineutrinos (Moessbauer antineutrinos) emitted in boundstate beta-decay in the 3H - 3He system are considered. It is shown that stochastic magnetic relaxation phenomena as well as the direct influence of solid-state effects on the energy of the electron antineutrino will cause line broadening by a factor of more than 10^(13). Lattice expansion and contraction after the transformation of the nucleus will drastically reduce the probability for phononless transitions. Thus, the observation of Moessbauer electron antineutrinos of the 3H - 3He system will most probably be unsuccessful. As a possible alternative, the Rare-Earth system 163Ho - 163Dy is briefly discussed.

Abstract:
Recoilless resonant capture of monoenergetic electron antineutrinos (Moessbauer antineutrinos) emitted in bound-state beta-decay in the system 3H - 3He is discussed. The recoilfree fraction including a possible phonon excitation due to local lattice expansion and contraction at the time of the nuclear transition, homogeneous and inhomogeneous line broadening, and the relativistic second-order Doppler effect are considered. It is demonstrated that homogeneous line broadening is essential due to stochastic magnetic relaxation processes in a metallic lattice. Inhomogeneous line broadening plays an equally important role. An essential issue which has been overlooked up to now, is an energy shift of the resonance line due to the direct influence of the binding energies of the 3H and 3He atoms in the lattice on the energy of the electron antineutrinos. This energy shift as well as the second-order Doppler shift exhibit variations in a non-perfect (inhomogeneous) lattice and may seriously jeopardize the observation of Moessbauer antineutrinos. If successful in spite of these enormous difficulties, Moessbauer antineutrino experiments could be used to gain new and deep insights into the nature of neutrino oscillations, determine the neutrino mass hierarchy as well as up to now unknown oscillation parameters, search for sterile neutrinos, and measure the gravitational redshift of electron antineutrinos in the field of the Earth.

Abstract:
Results obtained several years ago using the high-resolution 93.3 keV M\"ossbauer resonance in $^{67}$ZnO and $\beta'$-brass have been reanalyzed with the notion that the clock hypothesis of Special Relativity Theory is not sufficient, but that a maximal acceleration $a_m$ exists and that an acceleration $a$ contributes to the temperature dependence of the center shift by a term $\pm(1/2)(a/a_m)^2$. The significance of the sign of this term is discussed in detail. For both substances a lower limit of $a_m>1.5\cdot10^{21}m/s^2$ is inferred which is more than two orders of magnitude larger than the value $a_m=1\cdot10^{19}m/s^2$ suggested by $^{57}$Fe rotor experiments.

Abstract:
The large-volume liquid-scintillator detector LENA (Low Energy Neutrino Astronomy) has been proposed as a next-generation experiment for low-energy neutrinos. High-precision spectroscopy of solar, Supernova and geo-neutrinos provides a new access to the otherwise unobservable interiors of Earth, Sun and heavy stars. Due to the potent background discrimination, the detection of the Diffuse Supernova Neutrino Background is expected for the first time in LENA. The sensitivity of the proton lifetime for the decay into Kaon and antineutrino will be increased by an order of magnitude over existing experimental limits. Recent studies indicate that liquid-scintillator detectors are capable to reconstruct neutrino events even at GeV energies, providing the opportunity to use LENA as far detector in a long-baseline neutrino beam experiment.

Abstract:
For liquid-scintillator neutrino detectors of kiloton scale, the transparency of the organic solvent is of central importance. The present paper reports on laboratory measurements of the optical scattering lengths of the organic solvents PXE, LAB, and Dodecane which are under discussion for next-generation experiments like SNO+, Hanohano, or LENA. Results comprise the wavelength range from 415 to 440nm. The contributions from Rayleigh and Mie scattering as well as from absorption/re-emission processes are discussed. Based on the present results, LAB seems to be the preferred solvent for a large-volume detector.

In relativistic quantum mechanics, elementary particles are
described by irreducible unitary representations of the Poincaré group. The
same applies to the center-of-mass kinematics of a multi-particle system that
is not subject to external forces. As shown in a previous article, for spin-1/2
particles, irreducibility leads to a correlation between the particles that has
the structure of the electromagnetic interaction, as described by the
perturbation algorithm of quantum electrodynamics. The present article examines
the consequences of irreducibility for a multi-particle system of spinless
particles. In this case, irreducibility causes a gravitational force, which in
the classical limit is described by the field equations of conformal gravity.
The strength of this force has the same order of magnitude as the strength of
the empirical gravitational force.

General relativity predicts a
singularity in the beginning of the universe being called big bang. Recent
developments in loop quantum cosmology avoid the singularity and the big bang
is replaced by a big bounce. A classical theory of gravitation in flat
space-time also avoids the singularity under natural conditions on the density
parameters. The universe contracts to a positive minimum and then it expands
during all times. It is not symmetric with regard to its minimum implying a
finite age measured with proper time of the universe. The space of the universe
is flat and the total energy is conserved. Under the assumption that the sum of
the density parameters is a little bit bigger than one the universe is very hot
in early times. Later on, the cosmological model agrees with the one of general
relativity. A new interpretation of a non-expanding universe may be given by
virtue of flat space-time theory of gravitation.

The S matrix of e-e scattering has the structure of a projection operator that projects incoming separable product states onto entangled two-electron states. In this projection operator the empirical value of the fine-structure constantαacts as a normalization factor. When the structure of the two-particle state space is known, a theoretical value of the normalization factor can be calculated. For an irreducible two-particle representation of the Poincaré group, the calculated normalization factor matches Wyler’s semi-empirical formula for the fine-structure constantα. The empirical value ofα, therefore, provides experimental evidence that the state space of two interacting electrons belongs to an irreducible two-particle representation of the Poincaré group.

Abstract:
A covariant theory of gravitation in flat space-time is stated and compared with general relativity. The results of the theory of gravitation in flat space-time and of general relativity agree for weak gravitational fields to low approximations. For strong fields the results of the two theories deviate from one another. Flat space-time theory of gravitation gives under some natural assumptions non-singular cosmological models with a flat space. The universe contracts to a positive minimum and then it expands for all times. Shortly, after the minimum is reached, the cosmological models of two theories approximately agree with one another if models in general relativity with zero curvature are considered. A flat space is proved by experiments.

Abstract:
Static, spherically symmetric bodies are
studied by the use of flat space-time theory of gravitation. In empty space a
singularity at a Euclidean distance from the centre can exist. But the radius
of this singular sphere is smaller than the radius of the body. Hence, there is
no event horizon, i.e. black holes do
not exist. Escape of energy and information is possible. Flat space-time theory
of gravitation and quantum mechanics do not contradict to one another.