Radioemission from extensive air showers and the composition of primary cosmic rays
SummaryFinal results obtained from the array at Medicina on radioemission from extensive air showers are presented. It is shown that, although not in contradiction with theory, the frequency spectrum and the radio lateral distribution cannot provide information about the primary-cosmic-ray composition, because measurements are taken at small core distances and intrinsic errors are large. If we take the electric-field strengthEν as a measure of the primary energyEp, it is shown that fluctuations of ∼100% are found in shower parameters such as the sizeN and the density ϱ100. The data suggest the presence of protons in the primary cosmic-ray flux at ∼1017 eV. Uncertainties in measurements and in radiopulse production mechanisms are discussed and it is shown that this method alone is not as reliable as was previously predicted.RiassuntoIn questo lavoro si forniscono i risultati e le considerazioni finali sulla radioemissione da sciami estesi studiata mediante l’«array» sito in Medicina (Bo). Si mostra qui come lo spettro di frequenza e la distribuzione laterale, sebbene non siano in contraddizione con la teoria, non possano fornire informazioni utili sulla composizione dei raggi cosmici primari e perchè le misure sono state effettuate a piccole distanze dal «core» e perchè vi sono, nel processo di emissione, fluttuazioni intrinseche troppo grandi. Se si considera l’intensità del campo elettricoEν come una misura dell’energia primariaEp si vede come si possono trovare fluttuazioni di ∼100% nei parametri dello sciame quali il «size”N e la densità ϱ100. I dati sperimentali suggeriscono la presenza di protoni nel flusso dei raggi cosmici primari ed energie di ∼1017 eV. Sono inoltre discusse le incertezze sui meccanismi di produzione e sulle misure ed si mostra come su questo metodo, non associato ad altri metodi di rivelazione, non sia possibile fare quell’affidamento che era stato predetto.РезюмеПриводятся окончательные результаты по радиоизлучению из протяженных атмосферных ливней, полученные на антенной решетке в Меди-чина. Показывается, что, несмотря на отсутствие противоречий с теорией, частотный спектр и поперечное распределение радиоизлучения не могут дать информацию о составе первичного космического излучения, так как измерения проводились на малых расстояниях от центра и большие внутренние ошибки при измерениях. Принимая напряженность электрического поляEν за меру первичной энергииEp, показывается, что флуктуации таких параметров ливня, как размерN и плотность ϱ100, достигают ∼100%. Полученные данные подтверж-дают наличие протонов в потоке космических лучей при ∼1017 эВ. Обсуждаются неопреденности в измерэниях и в механизме образования радиоимпульсов. Показывается, что предложенный метод сам по себе не является надежным, как ранее предсказывалось.

title: Probing the Hard X-Ray Properties of High-Redshift Radio-Quiet Quasars with ASCA
abstract: This paper reports the X-ray spectral analysis of five high-redshift (z≥2), radio-quiet quasars observed by ASCA. A simple power-law continuum plus cold Galactic absorption model well fits all the spectra (typically between ~2 and 30 keV in the sources frame). Neither the X-ray spectral hardening, which is attributed to a reflection component and observed in Seyfert galaxies, nor the excess absorption previously detected in high-redshift, radio-loud quasars have been revealed. Only marginal evidence of a neutral or mildly ionized FeKα line is found in one of the quasars. The average spectral slope in the observed 0.7-10 keV energy range, Γ=1.67 ± 0.11 (dispersion σ ~0.07), appears to be flatter than that of low-z, radio-quiet quasars (Γ 1.9-2) and slightly steeper but consistent with Γ=1.61 ± 0.04 (σ ~0.10) of high-z, radio-loud quasars.

title: First Results from a XMM-Newton Survey of a Distance-Limited (D<22 Mpc) Sample of Seyfert Galaxies: I- the Agns
abstract: We report here preliminary results from a survey of nearby Seyfert galaxies using the EPIC CCDs on board XMM-Newton. The total sample consists of 28 Seyfert galaxies, and constitute a well-defined, complete (B 0 deg.) hemisphere. The survey has been initiated in June, 2001, and we report here the results for the 6 objects analyzed so far, namely: NGC3185, NGC3486, NGC3941, NGC4138, NGC4565, and NGC5033. The main goal of this survey is to obtain a better and unbiased understanding of the ``typical'' Seyfert X-ray spectrum (e.g. the distribution of their absorption column density) in the local Universe. This is crucial to verify the predictions and, thus, to validate unified models, and is a fundamental parameter of synthesis models for the X-ray background. A companion poster (paper II: L. Foschini et al., these proceedings) illustrates how this survey will also allow a comprehensive spectral study of the brightest (highest-luminosity) off-nuclear sources in the galaxies.

title: ASCA view on high-redshift radio-quiet quasars
abstract: We briefly discuss the latest ASCA results on the X-ray spectral properties of high-redshift radio-quiet quasars.

title: The INTEGRAL mission
abstract: INTEGRAL, the International Gamma-Ray Astrophysics Laboratory, to be launched in 2001, is the second medium-size scientific mission (M2) of the ESA long term programme “Horizon 2000”. INTEGRAL addresses the fine spectroscopy and accurate positioning of celestial gamma-ray sources in the energy range 10 keV to 10 MeV. The observational requirements will be met by a payload utilising coded mask imaging in combination with detector pixel arrays (Imaging) and cooled Germanium detectors (Spectroscopy). INTEGRAL is an ESA led mission in collaboration with Russia and USA. Most of the observing time will be made available to the general scientific community.

title: MOLECULAR LINES IN BOK GLOBULES AND AROUND HERBIG AE/BE STARS
abstract: We have studied a sample of seven small dark clouds (Bok globules) and eight Herbig Ae/Be stars in the J=1->0 transition of HCO$^{+}$, H$^{13}$CO$^{+}$, HCN and H$^{13}$CN. The choice of these molecules is determined by the simple chemistry and the predicted high abundance of the reactants leading to their formation. The isotopically substituted species (isotopomers), H$^{13}$CO$^{+}$ and H$^{13}$CN, were observed in order to determine, whenever possible, the optical thickness of the main species. The most abundant isotopomers were found in almost all the sources (detection rate 70-90\%). Those sources which exhibited the strongest signals were also searched for the $^{13}$C isotopomers. H$^{13}$CO$^{+}$ was found in one dark cloud and around three Herbig Ae/Be stars, while H$^{13}$CN around only one star. The column densities for each species and the physical conditions of the objects were derived whenever the observational data allowed it.

title: A crucial hypothesis for Inflation
abstract: As is well known there are many different inflationary models that can explain the accelerated expansion occurred in the early Universe. It is possible that there exists a fundamental property of this period that could provide the corresponding field theory. Our hypothesis is that the Ricci scalar should assume a positive constant value during Inflation. Considering a single scalar field that drives the inflationary phase, we obtain uniquely the scalar potential and the coupling term between the scalar field and spacetime geometry. For this potential, that is well known in the inflationary scenario, the theoretical prediction of the spectral index ns is in perfect agreement with the experimental data. Interestingly in two dimensions, our model is equivalent to Liouville gravity.

title: Abelian Chern-Simons-Maxwell theory from a tight-binding model of spinless fermions.
abstract: Abelian Chern-Simons-Maxwell theory can emerge from the bosonization of the (2+1)-dimensional Thirring model that describes interacting Dirac fermions. Here we show how the Thirring model manifests itself in the low energy limit of a two-dimensional tight-binding model of spinless fermions. To establish that, we employ a modification of Haldane's model, where the "doubling" of fermions is rectified by adiabatic elimination. Subsequently, fermionic interactions are introduced that lead to the analytically tractable Thirring model. By local density measurements of the lattice fermions we can establish that for specific values of the couplings the model exhibits the confining (2+1)-dimensional QED phase or a topological ordered phase that corresponds to the Chern-Simons theory. The implementation of the model as well as the measurement protocol are accessible with the current technology of cold atoms in optical lattices.

title: Topological effective field theories for Dirac fermions from index theorem
abstract: Dirac fermions have a central role in high energy physics but it is well known that they emerge also as quasiparticles in several condensed matter systems supporting topological order. We present a general method for deriving the topological effective actions of (3+1) massless Dirac fermions living on general backgrounds and coupled with vector and axial-vector gauge fields. The first step of our strategy is standard (in the Hermitian case) and consists in connecting the determinants of Dirac operators with the corresponding analytical indices through the zeta-function regularization. Then, we introduce a suitable splitting of the heat kernel that naturally selects the purely topological part of the determinant (i.e. the topological effective action). This topological effective action is expressed in terms of gauge fields using the Atiyah-Singer index theorem which computes the analytical index in topological terms. The main new result of this paper is to provide a consistent extension of this method to the non Hermitian case where a well-defined determinant does not exist. Quantum systems supporting relativistic fermions can thus be topologically classified on the basis of their response to the presence of (external or emergent) gauge fields through the corresponding topological effective field theories.

title: Skyrmion Superfluidity in Two-Dimensional Interacting Fermionic Systems
abstract: In this article we describe a multi-layered honeycomb lattice model of interacting fermions which supports a new kind of parity-preserving skyrmion superfluidity. We derive the low-energy field theory describing a non-BCS fermionic superfluid phase by means of functional fermionization. Such effective theory is a new kind of non-linear sigma model, which we call double skyrmion model. In the bi-layer case, the quasiparticles of the system (skyrmions) have bosonic statistics and replace the Cooper-pairs role. Moreover, we show that the model is also equivalent to a Maxwell-BF theory, which naturally establishes an effective Meissner effect without requiring a breaking of the gauge symmetry. Finally, we map effective superfluidity effects to identities among fermionic observables for the lattice model. This provides a signature of our theoretical skyrmion superfluidy that can be detected in a possible implementation of the lattice model in a real quantum system.

title: Gravitational Behaviour of an Effective Topological Field Theory
abstract: Effective topological field theories describe the properties of Dirac fermions in the low-energy regime. In this work, we introduce a new emergent gravity model by considering Dirac fermions invariant under local de Sitter transformations in four-dimensional open manifolds. In the context of Cartan geometry, fermions couple to spacetime through a $Spin(5)$ Cartan connection that can be decomposed in spin connection and tetrads. In presence of a gravitational instanton background, we show that the corresponding effective topological field theory becomes equivalent to a dynamical gravitational theory with positive cosmological constant and Barbero-Immirzi parameter. At classical level and in absence of matter, this theory is compatible with general relativity.