MEETING NA12, 25 Ottobre 2010, Napoli, Dipartimento di Scienze Fisiche e Sezione INFN, aula Caianiello (-2Ma05)

Lunedi 25 Ottobre 2010:

Scaletta temporale dei Talks (la durata di 30 (risp. 25) minuti va intesa come segue: 25  (risp. 20) minuti per la presentazione, e 5 minuti per le domande)

9-9.30: Saluto dei Direttori Maddalena (DSF) e Merola (Sezione INFN), e del Coordinatore GrIV (D'Ambrosio)

9.30-10.10: L. Lusanna (Chairman: Francaviglia)

10.10-10.50: M. Francaviglia (Chairman: Tartaglia)

10.50-11.20: Pausa Caffe`

11.20-12: A. Tartaglia (Chairman: Lusanna)

12-12.30: D. Bini (Chairman: Lusanna)

12.30-14: Pausa Pranzo

14-14.30: S. Capozziello (Chairman: Scudellaro)

14.30-15: G. Esposito (Chairman: Scudellaro)

15-15.25: E. Piedipalumbo (Chairman: Scudellaro)

15.25-15.55: Pausa Caffe`

15.55-16.25: C. Stornaiolo (Chairman: Rubano)

16.25-16.55: S. Calchi Novati (Chairman: Rubano)

16.55-17.25: M. Capone (Chairman: Rubano)

17.25-17.50: G. Covone (Chairman: Rubano)

17.50-18.15: M. De Laurentis (Chairman: Esposito)

18.15-18.40: L. Mancini (Chairman: Esposito)

18.40-19.10: M.L. Ruggiero (Chairman: Esposito)

19.10-19.35: R. Roychowdhury (Chairman: Esposito)

19.35-20: V.F. Cardone (Chairman: Esposito)

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Elenco delle relazioni, con titolo e riassunto, secondo l'ordine alfabetico.

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D. Bini: Poynting-Robertson effect around black holes

The effect of absorbing and re-emitting radiation  by a particle moving around black
holes is taken into account by postulating a drag force (Poynting-Robertson effect)
wich  causes the spiral motion  of the particle itself.
Certaing interesting consequences for special radiation field or even structured
particles are discussed in view of possible observations.

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S. Calchi Novati: M31 pixel lensing event OAB-N2: a study of the lens proper motion

I discuss the microlensing event OAB-N2 detected during the long-term monitoring pixel lensing campaign
of M31 carried out by the PLAN collaboration  at the Loiano telescope. Through an analysis of the lens proper motion
I address the issue of MACHO lensing versus self-lensing hypothesis for this event.

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M. Capone: Jumping from metric f(R) to scalar-tensor theories and the relations
between PPN parameters

We review the dynamical equivalence between $f(R)$ metric gravity and
scalar-tensor gravity, and use this equivalence to deduce the post-Newtonian
parameters gamma and beta for a f(R) theory, obtaining a result that is
different with respect to that known in the literature. Then, we obtain explicit
expressions of these parameters in terms of the mass of the scalar field, or,
differently speaking, the mass of the additional scalar degree of freedom
associated to a f(R) theory, which can be used to constrain f(R) gravity by
means of current observations.

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S. Capozziello: Massive, massless and ghost modes of gravitational waves from
higher-order gravity

We linearize the field equations for higher order theories that contain
scalar invariants other than the Ricci scalar. We find that besides a
massless spin-2 field (the standard graviton), the theory contains also
spin-0 and spin-2 massive modes. Then, we investigate the possible
detectability of such additional polarization modes of a stochastic
gravitational wave by ground-based and space interferometric detectors.
Finally, we extend the formalism of the cross-correlation analysis,
including the additional polarization modes, and calculate the detectable
energy density of the spectrum for a stochastic background of the relic
gravity waves that corresponds to our model. For the situation considered
here, we find that these massive modes are certainly of interest for
direct detection by the LISA experiment.

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V.F. Cardone: Systematic biases on halo model parameters from modified gravity theories

Rotation curves of spiral galaxies are usually fitted assuming a parametric
dark halo model and the validity of General Relativity, and hence the
Newtonian gravitational potential. On cosmological scales, modified gravity
theories seem to be a viable alternative to dark energy for explaining the
cosmic speed up. Should the correct theory of gravity be actually a modified
one, the gravitational potential on galactic scales could also differ
significantly from the Newtonian one. We investigate the bias on halo model
parameters and dark matter mass profile due to an incorrect assumption of a
Newtonian potential, whereas the underlying one is Yukawa-like. We show
that some empirical results commonly interpreted as failure of the standard
LCDM paradigm can actually be evidences for a modified theory of gravity.

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G. Covone: The end of the dark ages: searching for a population of low-luminosity 
galaxies

L'epoca di Reionizzazione copre l'intervallo fra redshift z=12 e z=6.
Descriverò i primi risultati di un progetto osservativo mirato alla ricerca e alla caratterizzazione
delle sorgenti della radiazione UV che ha ionizzato l'idrogeno neutro intergalattico a z>7.
In particolare, l'obiettivo è verificare l'esistenza di una popolazione di galassie di bassa luminosità
prevista nei modelli di formazione gerarchica delle galassie, ma ancora non identificata.
La ricerca si basa sull'uso dei telescopi gravitazionali (ammassi di galassie agenti come lenti gravitazionali)
e richiede come primo passo una determinazione accurata della loro distribuzione di massa.

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M. De Laurentis: Axially symmetric solutions in f(R)-gravity

Axially symmetric solutions for f(R)-gravity can be derived starting from exact
spherically symmetric solutions achieved by Noether symmetries. The method takes
advantage of a complex coordinate transformation previously developed by Newman and
Janis in general relativity. An example is worked out to show the general validity
of the approach. The physical properties of the solution are also considered.

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G. Esposito: The NA12 history from 1995 to 2009, and our plans from 2010 to 2013

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M. Francaviglia: Dark energy from curvature and ordinary matter: fitting Ehlers-Pirani-Schild foundational hypotheses

It is known that – both in purely metric formalism (higher order gravity) and in the Palatini approach (first order gravity) – coupling with matter generates relativistic effects that are not present in vacuum.

This is particularly evident when one relies on non-linear Lagrangians of the type f(R), where R can be either the scalar curvature of a metric g (metric formalism) or the scalar curvature of a connection G with respect to an “a priori independent” metric g (Palatini approach).

The analysis of Ehlers-Pirani-Schild – concerning the mathematical and physical foundations of relativistic theories of gravitation and the compatibility between (conformal classes of) metrics and (projective classes of) connections - is revisited and it is shown that EPS axioms select a class of Lagrangian theories of gravitation much larger than GR, a class that includes all theories of the (Palatini) type f(R) as well as many more.

In these theories the coupling of a nonlinear gravitational Lagrangian f(R) with matter Lagrangians depending on the metric g in an arbitrary way or even on the connection G in a peculiar way (dictated by EPS compatibility) generate a set of modified Einstein equations in which the following effects are easily recognizable:

1)    (1) A new metric h – conformally related to the original metric g – arises. The conformal factor is a computable function of curvature and, through functional inversion, of the trace of the stress tensor that corresponds to the “ordinary” matter distribution (including possible dark matter contributions). In the Palatini approach this new metric generates the connection G as its Levi-Civita connection, so that this new metric describes the free fall of ordinary matter.

2)    (2) This new metric induces in fact a change of rulers and clocks that affectes measurements and conservation laws, while the original metric g is directly related with light propagation.

3)    (3) By virtue of conformal equivalence, light propagates on the same null geodesics of both g and h, although clock rates are different in presence of matter.

4)    (4) The net effect of non-linearity and of  (non-trivial) interaction with matter resides in a change of the stress tensor that couples to the Einstein tensor of h; a change that induces additions to the previously existing one (directly generated from the matter Lagrangian).

5)    (5) This new stress tensor defines conservation laws that are fully covariant with respect to the Einstein frame of h.

2)    (7) All these effects disappear in the limit of vacuum linear theory (no changes wrt GR) or in the limit of linear theory with ordinary matter (GR with a true constant L).

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L. Lusanna: The gauge problem in GR and dark matter as a relativistic inertial effect in Einstein canonical gravity

I review the Post-Minkowskian approximation to ADM tetrad gravity in
asymptotically Minkowskian spacetimes admitting the asymptotic ADM Poincare' group. This is done in
a family of non-harmonic 3-orthogonal Schwinger time gauges labeled by the value of the York
time, namely the trace of the extrinsic curvature
of the 3-spaces (the general relativistic remnant of the gauge freedom
in clock synchronization). The study
of the Post-Newtonian limit of the equations of motion for two particles
shows the presence of an inertial effect at the 0.5PN order
depending on the York time: it shows that there is the possibility that
the dark matter (at least the one used to
explain the rotation curves of galaxies) may be explained as a
relativistic inertial effect not existing in Newton gravity.
See arXiv  0907.4087, 1003.5143, 1009.1794 and the review arXiv  1006.4973

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L. Mancini: Accurate properties of extrasolar planets via telescope defocussing

Our project, which has just entered its third season, concerns the
observations of planetary transits, carried out from both hemispheres,
in order to obtain accurate measurements of the physical properties of
the corresponding planetary systems. It has already run for three
seasons (2008, 2009, and 2010) into the southern hemisphere using the
Danish 1.5m telescope at the ESO Observatory in La Silla (Chile), and
for two seasons into the northern hemisphere using the Loiano 1.5m,
the Calar Alto 2.2m, and the INT 2.5m telescopes. Our strategy is to
obtain ultra-high-precision differential photometry of complete
transit events of extrasolar planetary systems, which will be analysed
to measure the physical properties of the planet and its parent star.

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E. Piedipalumbo: The GRBs Hubble diagram in quintessential cosmological models

It has been recently empirically established that some of the directly
observed parameters of GRBs are correlated with their important intrinsic
parameters, like the luminosity or the total radiated energy. These
correlations were derived, calibrated and tested assuming that radiation
propagates in the standard LambdaCDM cosmological model. We extend this
analysis by considering the correlation between the Ep,i and Eiso, in more
general models of dark energy, and we use  the updated data set of high
redshift GRBs. Moreover, we compare our fiducial HD with a model
indipendent calibrated HD, carried out using SNIa as distance indicator.
It turns out that the correlation parameters depend weakly on the
cosmological model. This means that the high redshift GRBs can be used to
test different models of dark energy. Finally, we use our fiducial
cosmological model to derive the likelihood values of Omega_m  and w_0.

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R. Roychowdhury: Black Holes, attractors and special Kahler geometry

Black Holes are truely unique objects:for theoretical physicists as they
pose various fascinating problems,which may offer a clue for solving the
riddles of Quantum Gravity.One of the recent developments in Black Hole
Physics is the Attractor Mechanism in Extremal Black Holes.In Such a
framework Supersymmetry seems to be related to dynamical systems with
fixed points, describing the equilibrium state and the stability features
of the thermodynamics of Black Holes.The Attractor Mechanism determines
the long range behaviour of the flows in such (dissipative) systems,
characterized by the following phenomenon:when approaching the fixed
points,properly named ''attractors'',the orbits of the dynamical evolution
lose all memory of their initial conditions, although the overall dynamics
remain deterministic.After a qualitative overview,explicit examples
realizing attractor mechanism will be treated at some length in the
talk.Finally I'll mention a number of recent advances along various
directions of research on the attractor mechanism.As an example,We will
compute the effective black hole potential V_BH of the most general
N=2,d=4 local special Kahler geometry with quantum perturbative
corrections, consistent with axion-shift Peccei-Quinn symmetry and with
cubic leading order behaviour and will determine the charge configurations
supporting axion-free attractors,explaining the differences among various
configurations in relations to the presence of ``flat'' directions of V_BH
at its critical points.Furthermore, we will try to elucidate the role of
the sectional curvature at the non-supersymmetric critical points of V_BH,
and compute the Riemann tensor(and related quantities), as well as the
so-called E-tensor. The latter expresses the non-symmetricity of the
considered quantum perturbative special Kahler geometry.
 

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M.L. Ruggiero: Pulsars as celestial beacons to detect the motion of the Earth

Abstract: We apply a previously proposed relativistic positioning
method based on the use of pulsed signals from sources at infinity, to
the reconstruction of the world-line of the Earth in the reference
frame of distant pulsars. The method, which considers the null
four-vectors built from the period of the pulses and the direction
cosines of the propagation from each source, has  been applied to the
case of the Earth, simulating the arrival times of the signals from
four pulsars at the location of the Parkes radiotelescope in Australia.

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C. Stornaiolo: Classical and quantum cosmological tomograms

I discuss the use of tomograms in cosmology and give a definition of cosmological
tomogram using cosmography. This definition is useful to analyze the state of the
universe and reconstruct the state of the universe at its initial stages.

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A. Tartaglia: Test of the cosmic defect theory on baryogenesis and structure formation
 

The Cosmic Defect theory has been confronted with
three constraints: primordial nuclear species abundances
emerging from the Big Bang Nucleosynthesis; Large
Scale Structure formation in the universe; luminosity
distances of type Ia supernovae. The test has
been based on a statistical analysis of the a posteriori probabilities
for three parameters of the theory. The result
has been quite satisfactory and such that the performance of the
theory is not distinguishable from the one of the
ËCDM theory. The use of the optimal values of the parameters
for the calculation of the Hubble constant and
the age of the universe confirms the compatibility of the Cosmic
Defect approach with observations.