ON-GOING WORKS
Towards a self-consistent orbital evolution for EMRIs
S. Aoudia (MPI Golm), S. Cordier (MAPMO Orléans), S. Jubertie (LIFO Orléans), S. Limet (LIFO Orléans), P. Ritter (LPC2E-MAPMO Orléans),
A. Spallicci (LPC2E Orléans)
We intend to develop part of the theoretical tools needed for the detection of gravitational waves coming from the capture of a compact object, 1-100 solar masses, by
a Supermassive Black Hole (SMBH), up to a billion solar masses, located at the centres of most galaxies. The analysis of the accretion activity of SBMHs unveils the
star population around the galactic nuclei, and tests the physics of black holes and motion in general relativity. In this context, we focus on the implications of
radiation reaction (self-force), complex and traditional problem of general relativity, on the eLISA-NGO project. The captured small mass is considered a probe of the
gravitational field of the massive body, allowing a precise measurement of its motion up to the final absorption by the SMBH. The knowledge of the gravitational
signal, strongly affected by radiation reaction - the orbital displacement due to gravitational radiation emission - is imperative for a successful detection by
eLISA-NGO. At Orléans (a CNRS school on Mass and the Capra conference in 2008, two doctorate thesis, master stages and scientific visits, a topical book and recent
publications), the results include an efficient computational strategy for wave equations with singular source terms for all type of orbits. We are now tackling the
evolution problem, first for radial orbit in Regge-Wheeler gauge, and later we will consider generic orbits in de Donder (harmonic) gauge for Schwarzschild-Droste
black holes. In the Extreme Mass Ratio Inspiral (EMRI) two-body problem, the determination of the orbital evolution demands that the motion of the small mass be
continuously corrected by the self-force, i.e. the self-consistent evolution. The latter has been evoked by S. Gralla and R. Wald, but yet not implemented. The
project wishes to stretch beyond the first applications, up to encompassing any non-adiabatic orbit in non-rotating SMBH geometry, though it is desirable that the
acquired expertise serves as a future path for stepping towards rotating SMBHs. The objective being the first description ever of a self-consistent evolved orbit, any
partial accomplishment along this road constitutes an achievement at this time. Subtle gauge issues may render the task difficult to handle. Numerically, a
self-consistent approach is a cumbersome task. At each of the integration steps, the self-force must be computed over an adequate number of modes; further, a complex
differential-integral system of general relativistic equations is to be solved and the outputs regularised for suppressing divergences. For provision of the
computational power needed to solve the EMRI problem, several levels of parallelisation are to consider: a parametric computation level, i.e. several simulations
running with different inputs parameters; a data parallel level i.e. splitting the domain into sub-domains; a task parallel level to solve independent modes required
to compute the self-force. Multi-scale modelling techniques are also considered, since the computation time of the integration steps is tied to the locality of the
particle, while radiation is also evaluated at infinity.
Space test on Proca's massive photon through CLUSTER data
A. Retinò (LPP Paris), A. Spallicci (LPC2E Orléans)
We intend to use CLUSTER spacecraft data in the solar wind at 1 AU to try improving the estimation of the upper limit of photon’s mass. The envisaged method will be to
look for deviations of classical Ampere’s law. CLUSTER is a constellation of four spacecraft flying in formation that has allowed for the first time the computation
of three-dimensional quantities such as J, curl B, divergence B etc. starting from in situ particle and field measurements.
Compared to earlier studies, CLUSTER data will allow to directly make independent estimations of the two quantities curl B and J without any special assumptions on the
structure of solar wind plasma flow and of the interplanetary magnetic field. The high resolution of CLUSTER’s particle distribution function and electromagnetic
field measurements will allow to perform such estimations and the associated error analysis with very good accuracy.
Complementarity of pulsar timing and space laser interferometry for the individual detection of supermassive black hole binaries
A. Spallicci (LPC2E Orléans)
The observation and the detection of gravitational waves coming from Supermassive Black Hole Binaries (SMBHBs) are targeted by both Pulsar Timing Array (PTA) and
Space Laser Interferometry (SLI). The possibility of a single SMBHB coalescence being tracked first by PTA and later by SLI has been previously suggested. We
thoroughly examine such a sequential detection. Although the bounding parameters are drawn by PTA, the future SKA (Square Kilometer Array), and by the New
Gravitational Observatory (NGO), a derived configuration of the Laser Interferometer Space Antenna (LISA), we address sequential detection also beyond specific
project constraints. We consider PTA(SKA), sensitive in the 10^{-9} to p x 10^{-7} Hz frequency band (here p = 4 - 8), and SLI, operating from s x 10^{-5} up to 1 Hz
(here s = 1 - 3). An SMBHB may indeed move from PTA(SKA) to SLI bandwidth after a lapse of time dependent on its mass and the value of p. Finally, SLI would detect the
final moments of the coalescence or solely the ring-down, if its sensitivity at low frequencies is adequate. Nine astrophysical scenarios are examined, by combining
three Supermassive Black Hole (SMBH)-host relations with three accretion prescriptions. Further, we relate the nine scenarios to three levels of performance in time
residuals (50, 5, 1 ns), generating twenty-seven cases. Our findings refer to total binary masses normalised to a (1+z) factor, z being the redshift (the resolvable
sources are situated mostly between z=0.2 and z=1.5), and they are summarised as follows: i) SMBHBs between 2 x 10^8 and 2 x 10^9 solar masses, transit from
PTA(SKA) to SLI bandwidth in a period ranging from few months to several years (we disregard transit times longer than 20 years); ii) for timing residuals of only 1
ns, the optimal (noiseless interferometer) rate of sequential detection ranges (n/20y units) from 4.38 x 10^{-4} to 1.19 x 10^{-2} (s = 1), and from 7.35 x 10^{-5}
to 3.62 x 10^{-4} (s = 3), where the lower and upper limits are given by the most pessimistic and optimistic astrophysical scenarios, respectively; iii) the rate of
sequential detection increases with the value of spin (dimensionless spin Kerr parameter a) of the remnant SMBH, and it is heavily dependent on s (for an SLI
cut-off frequency at 10^{-4} Hz, the rates vanish in our models); iv) inclusion of intereferometer noise reduces sequential detection rates even further
depending upon the space project considered. So, while transit times and SNRs may be adequate to our expectations, the likelihood of sequential
detection is strongly hindered by the current estimates on PTA(SKA) observable individual coalescences, the large separation between the pulsar timing and space
interferometry bandwidths and by the severe requirements on timing residuals. The perspectives for sequential detection would be greatly enhanced by SKA performances
of 1 ns residual, around 10^{-7} Hz, and by future SLI detectors operating well below 10^{-5} Hz.
PROJECTS
- SILEX Semi conductor Intersatellite Link Experiment
- ESA Study scientist for Time & Frequency Science Utilization and Space Station Study, Contract 11287/94/NL/VK with Un. Stuttgart, CERGA
Grasse, Lab. de Spectroscopie Herzienne ENS Paris, Un. Tübingen (Un. Dresden), Un. München, DLR,
DASA-RI. The study has conceived ACES, Atomic Clock Ensemble in Space.
- eLISA/NGO Evolved Laser Interferometer Space Antenna / New Gravitational Wave Observatory.
LISA France
- Virgo gravitational wave detector. VESF
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SOME DOCTORATE STUDENTS - POST-DOCS
- Vincenzo Pierro, Professore Associato at the Università del Sannio, Benevento
- Sofiane Aoudia, post-doc at the Max Planck Institut für Gravitationphysik A. Einstein, Golm
- Patxi Ritter, Doctorate student, Orléans
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TEACHING, RESEARCH AND POLITICS IN FRANCE
University Professors are named by the President of the Republic. Though Italian, I was honoured by the former President
Jacques Chirac. [pdf]
Foreign researchers are sometime victims of discrimination, as it occurred to one of my previous non-EU students for a visa renewal. Lately, the government had to
step back as the Washington Post reports
herein.
USEFUL LINKS
ma page 2
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link 3
link 4
MY FULL NAME
My full name
NOVELIST
Novelist
WHERE I HANG MOST
Where I hang most
SOME RELATIVES
Some relatives
PEOPLE I HAVE MET
People I have met
ALESSANDRO SPALLICCI
General Relativity and Fundamental (Astro-)Physics
Responsible of the following courses at the Université d'Orléans
1986-1996 European Space Research and Technology Centre, Noordwijk
Invitation at the E. Fermi Inst. Chicago by S. Chandrasekhar 1995