In preceding papers (L2) a model for the diffractive photon-induced processes a t high energies was developed and an analysis of the most important reactions was carried out. The description was based on a multiehannel impact-parameter formalism which provided a unified picture of the elastic, i.e. Compton process, as well as the inelastic diffraction dissociation channel (like vector-meson photoproduction) at high energies. The analysis of Compton scattering was carried throughout neglecting spin because of lack of appropriate experimental information concerning the helieity structure of the reaction (3). However, since in the case of vector-meson photoproduction there is an important amount of knowledge on the density matrix elements of the decaying vector meson (especially for the p0) and, furthermore, one possesses a lot of information from experiments with polarized photon beams, the model was enlarged in order to incorporate these facts into the actual analysis of data. A specific feature of the model is the inherent possibility of existence in the asymptotic amplitude of a helicity-fiip component which is absent in the usual descriptions of diffraction. Moreover, this Pomeranchuk flip amplitude was supposed to completely dominate the flip components coming from secondary Regge exchanges and, indeed, this assumption was subsequently tested in the analysis of ~0 photoproduction, where, as is well known, the Pomeranchuk contr ibution is the only exchange present in the production mechanism (4). In fact, a better fit to the data required a substantial amount of helicityflip present at the nucleonic vertex. Also in po photoproduction the best agreement with the differential-cross-section data was achieved imposing a flipping pomeron at the nucleon vertex, whose coupling strength turned out to be of the same order as in ~o photoproduetion. The lack of experiments with polarized targets does not allow us to directly check the actual existence of such a term since this amplitude cannot be separated with present experiments from the nonflip one. Owing to the fact that great progress has been recently made in obtaining highly polarized ((70--80)%) targets,

In a medium composed of scalar particles with non-zero mass, the range of Van-der-Waals-type scalar mediated interactions among nucleons becomes infinite when the medium makes a transition to a Bose–Einstein condensed phase. We explore this phenomenon in an astrophysical context. Namely, we study the effect of a scalar dark matter background on the equilibrium of degenerate stars. In particular we focus on white dwarfs and the changes induced in their masses and in their radii.

In a medium composed of scalar particles with non-zero mass, the range of Van-der-Waals-type scalar mediated interactions among nucleons becomes infinite when the medium makes a transition to a Bose-Einstein condensed phase. We explore this phenomenon in an astrophysical context. Namely, we study the effect of a scalar dark matter background on the equilibrium of degenerate this http URL particular we focus on white dwarfs and the changes induced in their masses and in their radii.

Neutrinos with non-zero magnetic moments can dissociate deuterium nuclei by a photon exchange, in addition to the weak neutral current process. We calculate the neutrino magnetic moment induced photo-dissociation cross section of deuterium using the equivalent photon method. This process would contribute extra events to the neutral current reaction which is observed with high precision in the salt-phase of SNO experiment. Using the SNO data and the recent laboratory measurements of the 7Be(p,γ)8B reaction which give a more precise value of the solar 8B flux we find that the neutrino effective magnetic moment is μeff2=(−2.76±1.46)×10−16μB2 which can be interpreted as an upper bound |μeff|<3.71×10−9μB (at 95% C.L.) on the neutrino magnetic moments.

Scalar mediated interactions among baryons extend well above the Compton wavelength, when they are embedded in a Bose- Einstein condensate composed of the mediating particles. Indeed, this non-trivial environment results in an infinite-ranged interaction. We show that if the dark matter of the Universe is composed of such a condensate, the imprints of an interaction between baryonic and dark matter could be manifest as anomalies in the peak structure of the cosmic microwave background.

Lepton number charges might be the source of long range forces. If one accepts that neutrinos produced in the Sun do indeed oscillate while crossing the interior of the Sun, then the shift in the phase of the neutrino wave-function caused by an hypothetical potential associated to the leptonic charge of the electrons in the Sun could affect the oscillation pattern beyond what is actually observed. We show that a “fine structure” constant αL in excess of 6.4×10−54 is incompatible with present observational data. This bound is not valid for forces whose range is shorter than the size of the Sun.

Compelling evidences in favor of neutrino masses and mixing obtained in the last years in Super-Kamiokande, SNO, KamLAND and other neutrino experiments made the physics of massive and mixed neutrinos a frontier field of research in particle physics and astrophysics. There are many open problems in this new field. In this review we consider the problem of the absolute values of neutrino masses, which apparently is the most difficult one from the experimental point of view. We discuss the present limits and the future prospects of β-decay neutrino mass measurements and neutrinoless double-β decay. We consider the important problem of the calculation of nuclear matrix elements of neutrinoless double-β decay and discuss the possibility to check the results of different model calculations of the nuclear matrix elements through their comparison with the experimental data. We discuss the upper bound of the total mass of neutrinos that was obtained recently from the data of the 2dF Galaxy Redshift Survey and other cosmological data and we discuss future prospects of the cosmological measurements of the total mass of neutrinos. We discuss also the possibility to obtain information on neutrino masses from the observation of the ultra high-energy cosmic rays (beyond the GZK cutoff). Finally, we review the main aspects of the physics of core-collapse supernovae, the limits on the absolute values of neutrino masses from the observation of SN1987A neutrinos and the future prospects of supernova neutrino detection.

We calculate the probability of the decay of external inhomogeneous electromagnetic fields to neutral pseudoscalar particles that have a coupling to two photons. We also point out that our estimate for axion emission in a previous paper was incorrect.

The existing calculations of the nuclear matrix elements of the neutrinoless double beta-decay differ by about a factor three. This uncertainty prevents quantative interpretation of the results of experiments searching for this process. We suggest here that the observation of the neutrinoless double beta-decay of several nuclei in future experiments of could allow to test different calculations of the nuclear matrix elements through the direct comparison of them with the experimental data.

We calculate the rate for pair production of light pseudoscalars by strong inhomogeneous and static electric (magnetic) fields. We show that, in the case of axions, the stability of atoms over cosmic lifetimes is jeopardised unless the Peccei-Quinn symmetry breaking scale $f_a$ is larger than ${\cal O} (10^{10} GeV)$.

The existing calculations of the nuclear matrix elements of the neutrinoless double β-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 β-decay of 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.

The existing calculations of the nuclear matrix elements of the neutrinoless double beta-decay differ by about a factor three. This uncertainty prevents quantative interpretation of the results of experiments searching for this process. We suggest here that the observation of the neutrinoless double beta-decay of several nuclei in future experiments of could allow to test different calculations of the nuclear matrix elements through the direct comparison of them with the experimental data.

We explore the consequences of Bose-Einstein condensation on two-scalar-exchange mediated forces among bodies that sit in a boson gas. We find that below the condensation temperature the range of the forces becomes infinite, while it is finite at temperatures above condensation.

We study the effect of a photon background at finite temperature $T$ on the Van der Waals interactions among neutral bodies. It turns out that the long-range Casimir-Polder force is unaffected for distances much less than $T^{-1}$ and strongly enhanced for distances much above $T^{-1}$.

Neutrinos mediate long range forces among macroscopic bodies in vacuum. When the bodies are placed in the neutrino cosmic background, these forces are modified. Indeed, at distances long compared to the scale $T^{-1}$, the relic neutrinos completely screen off the 2-neutrino exchange force, whereas for small distances the interaction remains unaffected.

We revisit and extend previous work on neutrino mediated long range forces in a backround at finite temperature. For Dirac neutrinos, we correct existing results. We also give new results concerning spin-dependent as well as spin-independent long range forces associated to Majorana neutrinos. An interesting outcome of the investigation is that, for both types of neutrinos whether massless or not, the effect of the relic neutrino heat bath is to convert those forces into attractive ones in the supra-millimeter scale while they stay repulsive within the sub-millimeter scale.

I review the constraints on the mass of gravitinos that follow from considerations on energy loss in stars and from big bang nucleosynthesis arguments.