Antimatter research in Space

Two of the most compelling issues facing astrophysics and cosmology today are to understand the nature of the dark matter that pervades the universe and to understand the apparent absence of cosmological antimatter. For both issues, sensitive measurements of cosmic-ray antiprotons and positrons, in a wide energy range, are crucial. Many different mechanisms can contribute to antiprotons and positrons production, ranging from conventional reactions up to exotic processes like neutralino annihilation. The open problems are so fundamental (i.e.: is the universe symmetric in matter and antimatter ?) that experiments in this field will probably be of the greatest interest in the next years. Here we will summarize the present situation, showing the different hypothesis and models and the experimental measurements needed to lead to a more established scenario.Comment: 10 pages, 7 figures, Invited talk at the 18th European Cosmic Ray Symposium, Moscow, July 2002, submitted to Journal of Physics

Ultrafast amplification and non-linear magneto-elastic coupling of coherent magnon modes in an antiferromagnet

We study the magnon dynamics of an antiferromagnetic NiO single crystal in a pump-probe experiment with variable pump photon energy. Analysing the amplitude of the energy-dependent photo-induced ultrafast spin dynamics, we detect a yet unreported coupling between the material's characteristic THz- and a GHz-magnon modes. We explain this unexpected coupling between two orthogonal eigenstates of the corresponding Hamiltonian by modelling the magneto-elastic interaction between spins in different domains. We find that such interaction, in the non-linear regime, couples the two different magnon modes via the domain walls and it can be optically exploited via the exciton-magnon resonance.Comment: 6 pages, 4 figure

Deriving the mass of particles from Extended Theories of Gravity in LHC era

We derive a geometrical approach to produce the mass of particles that could be suitably tested at LHC. Starting from a 5D unification scheme, we show that all the known interactions could be suitably deduced as an induced symmetry breaking of the non-unitary GL(4)-group of diffeomorphisms. The deformations inducing such a breaking act as vector bosons that, depending on the gravitational mass states, can assume the role of interaction bosons like gluons, electroweak bosons or photon. The further gravitational degrees of freedom, emerging from the reduction mechanism in 4D, eliminate the hierarchy problem since generate a cut-off comparable with electroweak one at TeV scales. In this "economic" scheme, gravity should induce the other interactions in a non-perturbative way.Comment: 30 pages, 1 figur

Diffractive Interaction and Scaling Violation in pp->pi^0 Interaction and GeV Excess in Galactic Diffuse Gamma-Ray Spectrum of EGRET

We present here a new calculation of the gamma-ray spectrum from pp->pi^0 in the Galactic ridge environment. The calculation includes the diffractive pp interaction and incorporates the Feynman scaling violation for the first time. Galactic diffuse gamma-rays come, predominantly, from pi^0->gamma gamma in the sub-GeV to multi-GeV range. Hunter et al. found, however, an excess in the GeV range ("GeV Excess") in the EGRET Galactic diffuse spectrum above the prediction based on experimental pp->pi^0 cross-sections and the Feynman scaling hypothesis. We show, in this work, that the diffractive process makes the gamma-ray spectrum harder than the incident proton spectrum by ~0.05 in power-law index, and, that the scaling violation produces 30-80% more pi^0 than the scaling model for incident proton energies above 100GeV. Combination of the two can explain about a half of the "GeV Excess" with the local cosmic proton (power-law index ~2.7). The excess can be fully explained if the proton spectral index in the Galactic ridge is a little harder (~0.2 in power-law index) than the local spectrum. Given also in the paper is that the diffractive process enhances e^+ over e^- and the scaling violation gives 50-100% higher p-bar yield than without the violation, both in the multi-GeV range.Comment: 35 pages, 11 figures, to appear in Astrophysical Journa

Nanoplastics impair in vitro swine granulosa cell functions

Soil, water and air pollution by plastic represents an issue of great concern since the particles produced by degradation of plastic materials can be ingested by animals and humans, with still uncertain health consequences. As a contribution on this crucial subject, the present work reports an investigation on the in vitro effects of different concentrations of polystyrene nanoplastics (5, 25 and 75 μg/mL) on swine granulosa cells, a model of endocrine reproductive cells. In particular, cell growth (BrDU incorporation and ATP production), steroidogenesis (17-β estradiol and progesterone secretion) and redox status (superoxide and nitric oxide production, enzymatic and non-enzymatic scavenging activity) were studied. Nanoplastics, at the highest concentration, stimulated cell proliferation (P < 0.05), while cell viability resulted unaffected. Steroidogenesis were disrupted (P < 0.05). Both enzymatic and non-enzymatic scavenging activity were increased after exposure at the highest nanoplastic dose (P < 0.05, P < 0.001). Nitric oxide secretion was increased by 25 and 75 μg/mL (P < 0.05) while superoxide generation was stimulated (P < 0.001) only by the highest concentration tested. Taken together, main features of cultured swine granulosa cells resulted affected by exposure to nanoplastics. These results raise concerns since environment nanoplastic contamination can represents a serious threat to animal and human health

Low-temperature anomalies in muon spin relaxation of solid and hollow nanoparticles: a pathway to detect unusual local spin dynamics

By means of muon spin relaxation measurements we unraveled the temperature spin dynamics in monodisperse maghemite spherical nanoparticles with different surface to volume ratio, in two samples with a full core (diameter D∼4 and D∼5nm) and one with a hollow core (external diameter D∼7.4nm). The behavior of the muon longitudinal relaxation rates as a function of temperature allowed us to identify two distinct spin dynamics. The first is well witnessed by the presence of a characteristic peak for all the samples around the so-called muon blocking temperature T$_{B}^{μ+}$. A Bloembergen-Purcell-Pound (BPP)-like model reproduces the experimental data around the peak and at higher temperatures (20<T<100K) by assuming the Néel reversal time of the magnetization as the dominating correlation time. An additional dynamic emerges in the samples with higher surface to volume ratio, namely, full 4 nm and hollow samples. This is witnessed by a shoulder of the main peak for T<20K at low longitudinal field (μ$_{0}$H≈15mT), followed by an abrupt increase of the relaxation rate at T<10K, which is more evident for the hollow sample. These unusual anomalies of the longitudinal relaxation rate for T<T$_{B}^{μ+}$ are suggested to be due to the surface spins’ dynamical behavior. Furthermore, for weak applied longitudinal magnetic field (μ$_{0}$H≈15mT) and T<T$_{B}^{μ+}$ we observed damped coherent oscillations of the muon asymmetry, which are a signature of a quasistatic local field at the muon site as probed by muons implanted in the inner magnetic core of the nanoparticles. The muon spin relaxation technique turns out to be very successful to study the magnetic behavior of maghemite nanoparticles and to detect their unusual local spin dynamics in low magnetic field conditions

Cosmic-Ray Positrons: Are There Primary Sources?

Cosmic rays at the Earth include a secondary component originating in collisions of primary particles with the diffuse interstellar gas. The secondary cosmic rays are relatively rare but carry important information on the Galactic propagation of the primary particles. The secondary component includes a small fraction of antimatter particles, positrons and antiprotons. In addition, positrons and antiprotons may also come from unusual sources and possibly provide insight into new physics. For instance, the annihilation of heavy supersymmetric dark matter particles within the Galactic halo could lead to positrons or antiprotons with distinctive energy signatures. With the High-Energy Antimatter Telescope (HEAT) balloon-borne instrument, we have measured the abundances of positrons and electrons at energies between 1 and 50 GeV. The data suggest that indeed a small additional antimatter component may be present that cannot be explained by a purely secondary production mechanism. Here we describe the signature of the effect and discuss its possible origin.Comment: 15 pages, Latex, epsfig and aasms4 macros required, to appear in Astroparticle Physics (1999

Gravitation and inertia; a rearrangement of vacuum in gravity

We address the gravitation and inertia in the framework of 'general gauge principle', which accounts for 'gravitation gauge group' generated by hidden local internal symmetry implemented on the flat space. We connect this group to nonlinear realization of the Lie group of 'distortion' of local internal properties of six-dimensional flat space, which is assumed as a toy model underlying four-dimensional Minkowski space. The agreement between proposed gravitational theory and available observational verifications is satisfactory. We construct relativistic field theory of inertia and derive the relativistic law of inertia. This theory furnishes justification for introduction of the Principle of Equivalence. We address the rearrangement of vacuum state in gravity resulting from these ideas.Comment: 17 pages, no figures, revtex4, Accepted for publication in Astrophys. Space Sc

On inconsistency of experimental data on primary nuclei spectra with sea level muon intensity measurements

For the first time a complete set of the most recent direct data on primary cosmic ray spectra is used as input into calculations of muon flux at sea level in wide energy range $E_\mu=1-3\cdot10^5$ GeV. Computations have been performed with the CORSIKA/QGSJET and CORSIKA/VENUS codes. The comparison of the obtained muon intensity with the data of muon experiments shows, that measurements of primary nuclei spectra conform to sea level muon data only up to several tens of GeV and result in essential deficit of muons at higher energies. As it follows from our examination, uncertainties in muon flux measurements and in the description of nuclear cascades development are not suitable to explain this contradiction, and the only remaining factor, leading to this situation, is underestimation of primary light nuclei fluxes. We have considered systematic effects, that may distort the results of the primary cosmic ray measurements with the application of the emulsion chambers. We suggest, that re-examination of these measurements is required with the employment of different hadronic interaction models. Also, in our point of view, it is necessary to perform estimates of possible influence of the fact, that sizable fraction of events, identified as protons, actually are antiprotons. Study of these cosmic ray component begins to attract much attention, but today nothing definite is known for the energies $>40$ GeV. In any case, to realize whether the mentioned, or some other reasons are the sources of disagreement of the data on primaries with the data on muons, the indicated effects should be thoroughly analyzed

Balloon Measurements of Cosmic Ray Muon Spectra in the Atmosphere along with those of Primary Protons and Helium Nuclei over Mid-Latitude

We report here the measurements of the energy spectra of atmospheric muons and of the cosmic ray primary proton and helium nuclei in a single experiment. These were carried out using the MASS superconducting spectrometer in a balloon flight experiment in 1991. The relevance of these results to the atmospheric neutrino anomaly is emphasized. In particular, this approach allows uncertainties caused by the level of solar modulation, the geomagnetic cut-off of the primaries and possible experimental systematics to be decoupled in the comparison of calculated fluxes of muons to measured muon fluxes. The muon observations cover the momentum and depth ranges of 0.3-40 GeV/c and 5-886 g/cmsquared, respectively. The proton and helium primary measurements cover the rigidity range from 3 to 100 GV, in which both the solar modulation and the geomagnetic cut-off affect the energy spectra at low energies.Comment: 31 pages, including 17 figures, simplified apparatus figure, to appear in Phys. Rev.