Thinking, Observing and Mining the Universe

The following sections are included:

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I briefly review some scenarios for the role of the Planck length in quantum gravity. In particular, I examine the differences between the schemes in which quantum gravity is expected to introduce a maximum acceleration and the schemes in which the Planck length sets the minimum value of wavelengths (maximum value of momentum). I also comment on some pictures for the structure of spacetime at the Planck scale, such as spacetime discretization and spacetime noncommutativity. I stress that some of these proposals can have significant implications in astrophysics and cosmology.

We propose a possible approach for the determination of very high energy cosmic ray primary mass A based on the information provided by the reconstruction of shower longitudinal development in the Earth atmosphere. We refer to an apparatus such as the Pierre Auger Observatory, which is a unique "hybrid" UHECR detector. The surface detector (SD) and air fluorescence detector (FD) of the observatory are designed for observation of cosmic ray showers in coincidence, with a 10% duty cycle, with resulting data expected to be superior in quality especially for the primary energy E₀ which is determined with a 5% accuracy. We present results obtained using an approach for the determination of A in the individual event based on only FD information (MMM - 'Minimum Momentum Method'). This approach shows that, if the entire information contained in the longitudinal profile is exploited, reliable results may be obtained.

The main aim of the ≃ 100 kg highly radiopure NaI(Tl) set-up of the DAMA project (DAMA/NaI) has been the exploitation of the model independent WIMP annual modulation signature. The total exposure (107731 kg × day), collected during seven annual cycles, has given a model independent evidence for the presence of a Dark Matter particle component in the galactic halo at 6.3 σ C.L.; this main result is summarised here. Some of the many possible corollary model dependent quests for the candidate particle are mentioned. At present, after about five years of new developments, a second generation low background set-up (DAMA/LIBRA with a mass of ≃ 250 kg NaI(Tl)) was built and is taking data since March 2003. New R&D efforts toward a possible NaI(Tl) ton set-up, we proposed in 1996, have been funded and started in 2003.

The detection of cosmic rays with energy around and in excess of 10²⁰ eV raises many questions that future experiments will help answering to. I address here my view of some of these open issues, as they are now and as they might be affected by future observations.

Models of gravity with variable G and Λ have acquired greater relevance after the recent evidence in favour of the Einstein theory being non-perturbatively renormalizable. The present paper applies the Arnowitt–Deser–Misner formalism and the Dirac–Bergmann theory of constrained Hamiltonian systems to such a class of gravitational models. A modified action functional is then built that reduces to the Einstein–Hilbert action when G is constant, and leads to a linear growth of the scale factor when gravity is coupled to a massless self-interacting ϕ⁴ theory in a Universe with Friedmann–Lemaitre–Robertson–Walker symmetry, in agreement with the recently developed fixed-point cosmology. Interestingly, our modified action functional makes it necessary to consider an external field that decays as the inverse of the sixth power of cosmological time in the early universe, although the relevant solutions are actually independent of the strength of this new field.

In curvaton models the convertion of isocurvature perturbations into adiabatic ones takes place through the decay of an auxiliary massive scalar field. In the Pre-Big Bang scenario, the role of the curvaton can be naturally played by the Kalb-Ramond axion present in the low energy effective action of superstring theory. A complete analysis of the coupled equations of axion and metric perturbations shows that a scale-invariant adiabatic spectrum for scalar perturbations can be obtained in this context. Recent observations of CMB anisotropies are used to constrain the parameter space of the model. A recent analytic model for the Big-Bang transition is also briefly discussed.

The internal structure of galaxies carries information on their formation and evolutionary history. Here we focus on a particular aspect of the problem: the internal colour gradients of cluster galaxies. We derive optical and optical-near infrared colour gradients for a large sample of galaxies belonging to clusters at different redshifts, from z~0.2 to z~0.6, spanning a range of cosmic time of about 6 Gyr. The observed evolution of colour gradients turns out to be consistent with a hierarchical merging picture for the evolution of cluster galaxies, while it is not consistent with a simple monolithic collapse scenario.

Recent results of the SLOTT-AGAPB and POINT-AGAPE collaborations on a search for microlensing events in direction of the Andromeda galaxy, by using the pixel method, are reported. The detection of 4 microlensing events, some likely to be due to self-lensing, is discussed. One microlensing light curve is shown to be compatible with a binary lens. The present analysis still does not allow us to draw conclusions on the MACHO content of the M31 galaxy.

We consider the evolution of scalar perturbations in a class of non-singular bouncing universes obtained with higher-order corrections to the low-energy bosonic string action. We show that previous studies have relied on a singular evolution equation for the perturbations, and we propose a new system of coupled differential equations. Given a background evolution, we obtain numerically that both Bardeen's potential, Φ(η, k), and the curvature perturbation in the uniform curvature gauge, , lead to a blue spectral distribution long after the transition.

Depending on their mass, dark compact objects uniformly distributed in space induce different observable lensing effects on background sources such as QSOs or Gamma Ray Bursts. Observational upper limits on the cosmic density of those putative (baryonic or nonbaryonic) compact objects may be derived in the mass range 10^-3 - 10¹³ M_⊙.

The interest surrounding gravitational waves has grown. The current search for gravitational wave entails studying and solving statistical issues, related to the potential sources that ground-based antennas are sensitive to. The case we will address is the status of the data analysis for LIGO I. The techniques for identifying gravitational wave signals depend on both the kind of source that is being searched and also on the characteristics of the detector. This is due to the fact that events which might be analysed as possible candidates, can be artifacts the detector responds to, in a similar way it would do if excited by an astrophysical signal. For example the detector response itself is monitored by calibration lines, that are injected in order to analyse the data according to the characteristic behaviour of the detector. After reviewing the status of the LIGO I interferometers, we will describe the different analyses applied to the data collected during the first scientific data run, aimed to search for a variety of astrophysical events.

We investigate the evolution of matter density perturbations and some properties of the peculiar velocity field for two classes of exponential potentials in a minimally coupled scalar field model for quintessence. The updated data from the 2-degree Field Galaxy Redshift Survey (2dFGRS) suggest a value of the today pressureless matter density Ω_M0 = 0.25±0.09, and Ω_M0 = 0.28±0.07 respectively. Both these results are comparable with the value Ω_M0 = 0.25±0.09, which we obtain in a standard model with a pure cosmological constant Λ.

We discuss the possible impact of astrophysical foregrounds on three recent exciting results of Cosmic Microwave Background (CMB) experiments: the WMAP measurements of the temperature-polarization (TE) correlation power spectrum, the detection of CMB polarization fluctuations on degree scales by the DASI experiment, and the excess power on arcminute scales reported by the CBI and BIMA groups. A big contribution from the Galactic synchrotron emission to the TE power spectrum on large angular scales is indeed expected, in the lower frequency WMAP channels, based on current, albeit very uncertain, models; at higher frequencies the rapid decrease of the synchrotron signal may be, to some extent, compensated by polarized dust emission. Recent measurements of polarization properties of extragalactic radio sources at high radio frequency indicate that their contamination of the CMB polarization on degree scales at 30 GHz is substantially below the expected CMB E-mode amplitude. Adding the synchrotron contribution, we estimate that the overall foreground contamination of the signal detected by DASI may be significant but not dominant. The excess power on arc-min scales detected by the BIMA experiment may be due to galactic-scale Sunyaev-Zeldovich effects, if the proto-galactic gas is heated to its virial temperature and its cooling time is comparable to the Hubble time at the epoch of galaxy formation. A substantial contamination by radio sources of the signal reported by the CBI group on scales somewhat larger than BIMA's cannot be easily ruled out.

We calculate the effect of photopion and pair production in the propagation of ultrahigh energy protons produced in sources distributed uniformly throughout the Universe. We study the implications for the secondary neutrino flux and obtain an analytical approximation which allows us to establish the effect of different unknown parameters in proton acceleration models on these fluxes. The implications of ultra high energy cosmic rays, gamma rays in the MeV to GeV range and very high energy neutrinos is discussed in some detail.

The cosmic reionization era, which includes formation of the first stars, galaxies, and AGN, is now one of the most active frontiers of cosmological research. We review briefly our current understanding of the early structure formation, and use the ideas about a joint formation of massive black holes (which power the early QSOs) and their host galaxies to employ high-redshift QSOs as probes of the early galaxy formation and primordial large-scale structure. There is a growing evidence for a strong biasing in the formation of the first luminous sources, which would lead to a clumpy reionization. Absorption spectroscopy of QSOs at z ≥ 6 indicates the end of the reionization era at z ~ 6; yet measurements from the WMAP satellite suggest and early reionization at z ~ 10 – 20. The first generation of massive stars, perhaps aided by the early mini-quasars, may have reionized the universe at such high redshifts, but their feedback may have disrupted the subsequent star and galaxy formation, leading to an extended and perhaps multimodal reionization history ending by z ~ 6. Observations of γ-ray bursts from the death events of these putative Population III stars may provide essential insight into the primordial structure formation, reionization, early chemical enrichment, and formation of seed black holes which may grow to become central engines of luminous quasars.

The study of the renormalized energy-momentum tensor (EMT) of quantum fluctuations in an inflationary universe driven by a massive scalar field is presented and compared with the known results in de Sitter space-time. When metric fluctuations are included, the renormalized EMT is characterized by a negative energy density which grows in time during the inflationary regime. We also approach the back-reaction problem as a second-order calculation in perturbation theory, and find that the average expansion rate is decreased, in agreement with the result on the EMT. Finally, we discuss common concerns and the implications of our results.

We review the status of the neutrino oscillations physics, with a particular emphasis on the present knowledge of the neutrino mass-mixing parameters. We consider first the ν_μ → ν_τ flavor transitions of atmospheric neutrinos. It is found that standard oscillations provide the best description of the SK+K2K data, and that the associated mass-mixing parameters are determined at ±1σ (and N_DF = 1) as: Δm² = (2.6 ± 0.4) × 10^-3 eV² and . Such indications, presently dominated by SK, could be strengthened by further K2K data. Then we point out that the recent data from the Sudbury Neutrino Observatory, together with other relevant measurements from solar and reactor neutrino experiments, in particular the KamLAND data, convincingly show that the flavor transitions of solar neutrinos are affected by Mikheyev-Smirnov-Wolfenstein (MSW) effects. Finally, we perform an updated analysis of two-family active oscillations of solar and reactor neutrinos in the standard MSW case.

We present a model of dark energy based on the string effective action, and on the assumption that the dilaton is strongly coupled to dark matter. We discuss the main differences between this class of models and more conventional models of quintessence, uncoupled to dark matter.

Measurements of the highest energy cosmic rays provide compelling evidence for EeV neutrino sources. Characterization of these sources will have strong diagnostic value if we can achieve the Teraton target volumes needed to get sufficient event rates. At 10 TeV energies and above neutrino astronomy is in fact the only astronomy with a clear view of the whole universe. Radio detection of neutrino cascade interactions in ice and other solid dielectric media, via the Askaryan effect, provide a realistic path toward this goal.

Kilometer-scale neutrino detectors such as IceCube are discovery instruments covering nuclear and particle physics, cosmology and astronomy. Examples of their multidisciplinary missions include the search for the particle nature of dark matter and for additional small dimensions of space. In the end, their conceptual design is very much anchored to the observational fact that Nature accelerates protons and photons to energies in excess of 10²⁰ and 10¹³ eV, respectively. The cosmic ray connection sets the scale of cosmic neutrino fluxes. In this context, we discuss the first results of the completed AMANDA detector and the reach of its extension, IceCube. Similar experiments are under construction in the Mediterranean. Neutrino astronomy is also expanding in new directions with efforts to detect air showers, acoustic and radio signals initiated by super-EeV neutrinos.

Present cosmological observations yield an upper bound on the neutrino mass which is significantly stronger than laboratory bounds. However, the exact value of the cosmological bound is model dependent and therefore less robust. Here, I review the current status of cosmological neutrino mass bounds and also discuss implications for sterile neutrinos and LSND in particular.

The nature and the location of the lenses discovered in the microlensing surveys done so far towards the LMC remain unclear. Motivated by these questions we computed the optical depth for the different intervening populations and the number of expected events for self-lensing, using a recently drawn coherent picture of the geometrical structure and dynamics of the LMC. By comparing the theoretical quantities with the values of the observed events it is possible to put some constraints on the location and the nature of the MACHOs. Clearly, given the large uncertainties and the few events at disposal it is not yet possible to draw sharp conclusions, nevertheless we find that up to 3-4 MACHO events might be due to lenses in LMC, which are most probably low mass stars, but that hardly all events can be due to self-lensing. The most plausible solution is that the events observed so far are due to lenses belonging to different intervening populations: low mass stars in the LMC, in the thick disk, in the spheroid and some true MACHOs in the halo of the Milky Way and the LMC itself.

Neutrino oscillations have been studied using various neutrino sources including solar, atmospheric, reactor and accelerator neutrinos. Our understanding on neutrino masses and mixing angles has been improved significantly by recent experiments. This report summarizes the present status and the future prospect of our understanding of neutrino masses and mixing angles.

Recent results from the KASCADE experiment on measurements of cosmic rays in the energy range of the knee are presented. Emphasis is placed on energy spectra of individual mass groups as obtained from sophisticated unfolding procedures applied to the reconstructed electron and truncated muon numbers of EAS. The data clearly show a knee in the energy spectra of the light primaries (p, He, C) and an increasing dominance of heavy ones (A > 20) toward higher energies. This basic result is robust against uncertainties of the applied interaction models QGSJET and SIBYLL. Slight differences observed between experimental data and EAS simulations provide important clues for improvements of the interaction models. Astrophysical implications for discriminating models of maximum acceleration energy vs galactic diffusion/drift models of the knee will be discussed. To improve the reconstruction quality and statistics around 10¹⁷ eV, KASCADE has recently been extended by a factor 10 in area. The status and expected performance of the new experiment KASCADE-Grande is discussed.

I discuss whether the standard cosmological models fit the WMAP data well enough to justify parameter estimation with standard assumptions. The observed quadrupole is low (but has significant foreground uncertainty) and drives weak evidence for theoretical models predicting low values, such as models with a running spectral index. Other more seriously outlying points of the WMAP power spectrum appear not to fit the expectations of simple Gaussian models very well. The effective temperature chi-squared is however acceptable on large scales. There also appears to be evidence for an anisotropic distribution of power, which taken together with the other points may indicate that either there is a problem with the WMAP data or that standard cosmological models are incorrect. These issues should be clarified before cosmological parameter extraction for the usual standard models can be trusted, and hint that maybe the CMB is more interesting than we imagined. I also discuss various systematic and analysis issues, and comment on various oddities in the publicly available first year WMAP data and code.

A review of axions physics, with particular atention to the potential role of axions as dark matter, is presented.

By making use of the wavefront method the time delay Δt in a lens system with axially symmetric lens and 2 images is derived with simple geometric arguments. This is probably the simplest way to show that the derived value of H₀ is proportional to (2– β) , where β depends on the radial density profile (deflection angle α ∝ ξ^{β – 1}). Lensing therfore offers unique possibilities for obtaining good constraints on the radial mass distribution in the lens. This is of great relevance for the dark matter problem, particularly in galactic halos.

A large hybrid detector will be operated at the Pierre Auger observatory. It will use both the surface detection method and the fluorescence detection method in detecting the highest energy cosmic rays. One of the main goals of the project is to cross-calibrate the two techniques. To achieve this, great attention is paid to the control of systematic errors. This talk concentrates on a description of individual methods used to control the precision of fluorescence measurements.

In 2003, five ground-based laser-interferometric gravitational wave detectors are being commissioned for scientific use. With armlengths of km scales, they cover the audio frequency range: 10 Hz up to a few kHz. Although one of the smallest in size, the British-German detector GEO 600 incorporates some advanced features that will later find their way also into upgraded versions of the larger detectors. The space project LISA is composed of three spacecraft in a triangular formation, of 5 million km sides. LISA will thus search in a much lower frequency band, below 1 Hz and down to 10^-4 Hz. A technology demonstrator (LTP on SMART-2) will be launched in 2006,and launch of LISA proper is planned for 2011/12.

The presence of large amounts of unseen material in the universe has been puzzling astronomers – and resisted them – for decades. The very nature of the so–called astronomical dark matter is still disputed. The neutralinos – a neutral and weakly interacting species predicted by the supersymmetric or extra–dimension extensions of the standard subnuclear model – arise as natural candidates. Would neutralinos pervade the Milky Way as well as extra–galactic systems, they should still annihilate today and produce gamma–rays, antiprotons and positrons which may be detected through the distortions generated in the corresponding energy spectra of the cosmic radiation. I shortly review the status of the various ongoing efforts to reveal these indirect astrophysical signatures, paying particular attention to the propagation and diffusion of cosmic–rays throughout our galaxy as well as to the clumpiness of neutralino dark matter.

CSL1 is a peculiar object discovered in the OAC-Deep Field. Detailed photometric and spectroscopic investigations reveal peculiar properties which are best explained as the result of gravitational lensing by a cosmic string. This explanation finds additional support in the existence of a strong excess of gravitational lens candidates in the area immediately surrounding CSL1.

The properties of the neutralino in R–parity conserving supersymmetric models as a candidate to form the Dark Matter in the Universe are briefly presented. By making use of the latest WMAP data on the Cosmic Microwave Background Radiation, combined with other observations, a cosmological lower bound on the neutralino mass of 6 GeV is derived in scenarios without GUT–inspired relations among gaugino masses. Prospects for direct and indirect searches of these neutralinos are also discussed.

The present situation with regard to experimental data on ultra high-energy cosmic rays is briefly reviewed. Whilst detailed knowledge of the shape of the energy spectrum is still lacking, it is clear that events above 10²⁰ eV do exist. Evidence for clustering of the directions of some of the highest energy events remains controversial. Clearly, more data are needed and these will come from the southern branch of the Pierre Auger Observatory in the next few years. What is evident is that our knowledge of the mass composition of cosmic rays is deficient at all energies above 10¹⁸ eV. It must be improved if we are to discover the origin of the highest energy cosmic rays. The major part of the paper is concerned with this problem: it is argued that there is no compelling evidence to support the common assumption that cosmic rays of the highest energies are protons.

This contribution discusses the importance of mass model degeneracies in gravitational lensing for cosmological applications, especially the still important determination of H₀. The lens effect avoids most systematic uncertainties inherent in other methods and is in principle able to determine cosmological parameters relatively independent of knowledge or prejudice from other astrophysical fields. In order to utilize this advantage, it is necessary to have the possible systematic errors of the lens method itself well under control. The most important model degeneracies as well as possible ways to overcome the difficulties are reviewed.

The Pierre Auger Observatory has been designed to compound the puzzle on the ultra-high energy cosmic rays, combining the advantages of two different techniques: the Ground Array and the Fluorescence Detector (FD), both detecting the Extensive Air Showers (EAS) generated by the primaries. The Fluorescence Detector uses the atmosphere as an electromagnetic calorimeter: it is then crucial an accurate calibration of this calorimeter. Many atmospheric monitoring techniques and devices are under study and implementation on the South Auger Site, in Malargüe, Argentina, to get the most through understanding of atmospheric composition and properties. A LIDAR station for each of the four Fluorescence eyes will be located on the site. Presently the first one is fully operational and a second one is very near to be completed.

The VLT Survey Telescope (VST) is a 2.6 m aperture, wide-field (1°1°), UV to I facility, to be installed at the European Southern Observatory (ESO) on the Cerro Paranal Chile. VST was primarily intended to complement the observing capabilities of VLT with wide-angle imaging for detecting and pre-characterising sources for further observations with the VLT.

A quintessential cosmological model can be achieved by taking into account higher order curvature terms into the gravity lagrangian. This approach is related to fundamental schemes of quantum gravity which predict the existence of higher order curvature term to renormalize quantum field theory on curved space-times. In this framework, we obtain a class of cosmological solutions which are fitted against cosmological data.

We discuss an alternative approach to quintessence modifying the usual equation of state of cosmological fluid in order to see whether going further than the approximation of perfect fluid allows to better reproduce the available data. We consider a standard cosmology with a Van der Waals equation of state for matter and without any other kind of energy source. The corresponding cosmological model has two vacuum states driven by a two phase fluid that gives account of an asymptotic quintessential behaviour. We fit the model with the Hubble diagram of type Ia Supernovae and, as a further test, we evaluate a lower limit of the age of the universe and compare it with the available estimates.

In the framework of extended theories of gravity, torsion can be considered a way to implement spin in General Relativity. It seems reasonable that torsion could have had relevant cosmological effects at the huge densities typical of early universe. In fact, primordial local magnetic fields could have aligned spin of particles influencing the evolution of mass-density perturbations. On the other hand torsion could also affect dramatically the current universe dynamics. Our aim is to investigate the possibility that this contribute to the energy-momentum tensor could act like a source of dark energy and drive the observed accelerated expansion. Clearly a fundamental role for such a scheme is played by the origin of the torsion.

In this work we present the first results of a multiscale image analysis performed on Monte Carlo events by taking into account all the processes of shower development in the atmosphere and a full simulation of the ARGO-YBJ detector response in order to discriminate γ showers from hadron initiated ones.

I want to give a brief summary of the results reported in ¹, in collaboration with A. Funel, G. Esposito, G. Mangano, G. Miele.

We investigate the environmental effects on the global photometric properties of galaxies for the rich cluster A209 at z = 0.21 using wide-field optical data. We find trends between the galaxy luminosity function and local galaxy surface density, with the faint-end slopes becoming shallower and the characteristic luminosities increasing with density, due to the morphology-density relation and to dwarf galaxies being cannibalised and/or disrupted in the cluster core. We find the environment affects also the cluster red sequence, it appearing 0.022±0.014 mag redder in B – R for galaxies in the cluster core than for the periphery, indicative of the stellar populations of these galaxies being marginally (< 5%) older or (< 20%) more metal-rich.

The presence (or absence) of CNO elements in the primordial gas determines different behaviours in population III stars formation and evolution: we therefore present an analysis of the main channels for the synthesis of these elements in BBN in order to understand, within a reliable interval, their abundance in the primordial material.

It was shown by the author (gr-qc/0207006) that screening the background of super-strong interacting gravitons creates Newtonian attraction if single gravitons are pairing and graviton pairs are destructed by collisions with a body. In such the model, Newton's constant is connected with Hubble's constant, for which the estimate is obtained: 94.576 km · s^-1 · Mpc^-1. It is necessary to assume an atomic structure of any body to have the working model. Because of it, an existence of black holes contradicts to the equivalence principle in a frame of the model. For usual matter, the equivalence principle should be broken at distances ~ 10^-11 m, if the model is true.

We analyze new optical/NIR structural parameters (half-light radius r_e, mean surface brightness < μ >_e and Sersic shape parameter n) for N ~ 60 spheroidal galaxies in the cluster A2163B at redshift z ~ 0.2. The structural parameters are used (I) to estimate the internal color gradients (CGRs) of galaxies and (II) to derive the optical/NIR Kormendy relations (KRs). We find that the differences in the stellar population properties from the galaxy center to the periphery do not change or become less marked for brighter galaxies. This result is in sharp contrast with the predictions of the monolithic formation scenario, while it can be well accommodated within a hierarchical merging picture.

GEO 600 is a laser-interferometric gravitational wave detector with relatively short armlength, 600 m. Despite this size, it is expected to provide rather competitive sensitivities, due to a number of innovative schemes. Foremost among these is the utilisation of "signal recycling", which will effectively make up for the short armlength. The commissioning of GEO 600 is nearing completion. Several successful data runs have been performed, in conjunction with the US detectors of LIGO, and the in-lock duty cycle was repeatedly above 98%.

LISA (Laser Interferometer Space Antenna) is a joint ESA-NASA space project to detect and measure gravitational waves in space. LISA consists of three identical spacecraft in an equilateral triangle of 5 million km sides. Frequencies of gravitational waves covered by LISA range from 10^-4 Hz to 1 Hz. The sensitivity targeted will allow measurements of cosmic events with high signal-to-noise ratio. Crucial aspects will be tested and verified in a technology demonstrator, 'LISA Pathfinder', to be launched in 2006. Launch of LISA proper is expected for 2011.

The key Standard-Physics inputs of the Big Bang Nucleosynthesis (BBN) are the light nuclei reaction rates. Both the network and the nuclear rates have been recently reanalyzed and updated, and cosmological and New-Physics constraints (taking into account the WMAP Cosmic Microwave Background anisotropies measurement) obtained with a new code are presented.

We explore the close environment of active star-forming (ASF) galaxies in the 2dF. We find ASF galaxies to be the most likely population to inhabit extremely close pairs located in low density regions. In addition, we find that ASF galaxies in these pairs are almost entirely concentrated in the [–20≤M_B≤–19] magnitude range.

We use the latest solar neutrino data, combined with the results of the reactor experiment KamLAND, to derive stringent bounds on Majorana neutrino transition moments (TMs). Furthermore, we show how the inclusion of data from the reactor experiments Rovno, MUNU and TEXONO in our analysis improves significantly the current constraints on TMs. Finally, we perform a simulation of the future Borexino experiment and show that it will improve the bounds from today's data by one order of magnitude.

We present a set of numerical codes to estimate the lensing parameters and the Hubble constant H₀ from quadruply imaged gravitational lens systems. The lens galaxy is modelled using both separable deflection potentials and constant massto - light ratio profiles, while possible perturbations have been taken into account introducing an external shear. The model parameters are recovered inverting the lens and the time delay ratio equations and imposing a set of physically motivated selection criteria. Having successfully tested our codes on simulated cases, we investigate correlations among the model parameters and the Hubble constant. Finally, we apply the codes to the real lensed quasars PG 1115+080 and RX J0911+0551 and combine the results from these two systems to get H₀ = 56 ± 23 km s^-1 Mpc^-1.

Can the signal amplification provided by gravitational lensing (GL) ease the detection of gravitational waves (GW)? To answer this question, two lens models are considered: the results are model-dependent, but in both cases the increase in the number of visible GW signals is negligible.

The use of a magnetic levitation system as a part of a multi-stage seismic attenuator for gravitational wave interferometric detectors is described. The proposed configuration, analyzed in simulation, uses permanent magnets in attraction to balance the suspended weight, plus a closed loop position control to obtain a stable levitation. The validity of this model has been tested by comparing simulations with experimental data taken from a levitated suspension prototype.

The following sections are included:

• List of Participants