8,062 research outputs found
Solar System planetary orbital motions and dark matter
In this paper we explicitly work out the effects that a spherically symmetric
distribution of dark matter with constant density would induce on the Keplerian
orbital elements of the Solar System planets and compare them with the latest
results in planetary orbit determination from the EPM2004 ephemerides. It turns
out that the longitudes of perihelia and the mean longitudes are affected by
secular precessions. The resulting upper bounds on dark matter density,
obtained from the EPM2004 formal errors in the determined mean longitude shifts
over 90 years, lie in the range 10^-19-10^-20 g cm^-3 with a peak of 10^-22 g
cm^-3 for Mars. Suitable combinations of the planetary mean longitudes and
perihelia, which cancel out the aliasing impact of some of the unmodelled or
mismodelled forces of the dynamical models of EPM2004, yield a global upper
bound of 7 10^-20 g cm^-3 and 4 10^-19 g cm^-3, respectively.Comment: Latex, 8 pages, 2 tables, no figures, 8 references. Revised version
with improved analysi
Healing Bodies: the ancient origins of massages and Roman practices
The practice of body manipulation with therapeutic aims has been used in the Western world since
the origins of Hippocratic medicine. By retracing the therapeutic use of massage as a therapeutic, preventive
and educational practice, the authors attempt to highlight the concepts, techniques and methods of massage
and the manipulation of the body in order to offer a valuable and useful historical reconstruction concerning
ancient medicine. The study on the relationship between culture, diseases and medicine constitute a significant
part of the historical medical research carried out within the Research Project of National Interest PRIN
entitled ‘Disease, health and lifestyles in Rome: from the Empire to the early Middle Ages’ funded by the
Ministry of Education, MIUR University Research in 201
Plasmons in topological insulator cylindrical nanowires
We present a theoretical analysis of Dirac magneto-plasmons in topological
insulator nanowires. We discuss a cylindrical geometry where Berry phase
effects induce the opening of a gap at the neutrality point. By taking into
account surface electron wave functions introduced in previous papers and
within the random phase approximation, we provide an analytical form of the
dynamic structure factor. Dispersions and spectral weights of Dirac plasmons
are studied with varying the radius of the cylinder, the surface doping, and
the strength of an external magnetic field. We show that, at zero surface
doping, inter-band damped plasmon-like excitations form at the surface and
survive at low electron surface dopings (). Then, we
point out that the plasmon excitations are sensitive to the Berry phase gap
closure when an external magnetic field close to half quantum flux is
introduced. Indeed, a well-defined magneto-plasmon peak is observed at lower
energies upon the application of the magnetic field. Finally, the increase of
the surface doping induces a crossover from damped inter-band to sharp
intra-band magneto-plasmons which, as expected for large radii and dopings
(), approach the proper limit of a two-dimensional
surface.Comment: 18 pages, 11 figures, 2 Appendice
Super-ASTROD: Probing primordial gravitational waves and mapping the outer solar system
Super-ASTROD (Super Astrodynamical Space Test of Relativity using Optical
Devices or ASTROD III) is a mission concept with 3-5 spacecraft in 5 AU orbits
together with an Earth-Sun L1/L2 spacecraft ranging optically with one another
to probe primordial gravitational-waves with frequencies 0.1 microHz - 1 mHz,
to test fundamental laws of spacetime and to map the outer solar system. In
this paper we address to its scientific goals, orbit and payload selection, and
sensitivity to gravitational waves.Comment: 7 pages, 1 figure, presented to 7th International LISA Symposium,
16-20 June 2008, Barcelona; submitted to Classical and Quantum Gravity;
presentation improve
Mars and frame-dragging: study for a dedicated mission
In this paper we preliminarily explore the possibility of designing a
dedicated satellite-based mission to measure the general relativistic
gravitomagnetic Lense-Thirring effect in the gravitational field of Mars. The
focus is on the systematic error induced by the multipolar expansion of the
areopotential and on possible strategies to reduce it. It turns out that the
major sources of bias are the Mars'equatorial radius R and the even zonal
harmonics J_L, L = 2,4,6... of the areopotential. An optimal solution, in
principle, consists of using two probes at high-altitudes (a\approx 9500-9600
km) and different inclinations, and suitably combining their nodes in order to
entirely cancel out the bias due to \delta R. The remaining uncancelled
mismodelled terms due to \delta J_L, L = 2,4,6,... would induce a bias \lesssim
1%, according to the present-day MGS95J gravity model, over a wide range of
admissible values of the inclinations. The Lense-Thirring out-of-plane shifts
of the two probes would amount to about 10 cm yr^-1.Comment: LaTex2e, 16 pages, 5 figures, no tables. To appear in General
Relativity and Gravitatio
On the perspectives of testing the Dvali-Gabadadze-Porrati gravity model with the outer planets of the Solar System
The multidimensional braneworld gravity model by Dvali, Gabadadze and Porrati
was primarily put forth to explain the observed acceleration of the expansion
of the Universe without resorting to dark energy. One of the most intriguing
features of such a model is that it also predicts small effects on the orbital
motion of test particles which could be tested in such a way that local
measurements at Solar System scales would allow to get information on the
global properties of the Universe. Lue and Starkman derived a secular
extra-perihelion \omega precession of 5\times 10^-4 arcseconds per century,
while Iorio showed that the mean longitude \lambda is affected by a secular
precession of about 10^-3 arcseconds per century. Such effects depend only on
the eccentricities e of the orbits via second-order terms: they are, instead,
independent of their semimajor axes a. Up to now, the observational efforts
focused on the dynamics of the inner planets of the Solar System whose orbits
are the best known via radar ranging. Since the competing Newtonian and
Einsteinian effects like the precessions due to the solar quadrupole mass
moment J2, the gravitoelectric and gravitomagnetic part of the equations of
motion reduce with increasing distances, it would be possible to argue that an
analysis of the orbital dynamics of the outer planets of the Solar System, with
particular emphasis on Saturn because of the ongoing Cassini mission with its
precision ranging instrumentation, could be helpful in evidencing the predicted
new features of motion. In this note we investigate this possibility in view of
the latest results in the planetary ephemeris field. Unfortunately, the current
level of accuracy rules out this appealing possibility and it appears unlikely
that Cassini and GAIA will ameliorate the situation.Comment: LaTex, 22 pages, 2 tables, 10 figures, 27 references. Reference [17]
added, reference [26] updated, caption of figures changed, small change in
section 1.
Orbital effects of the time-dependent component of the Pioneer anomaly
We work out the impact that the recently determined time-dependent component
of the Pioneer Anomaly (PA), interpreted as an additional exotic acceleration
of gravitational origin with respect to the well known PA-like constant one,
may have on the orbital motions of some planets of the solar system. By
assuming that it points towards the Sun, it turns out that both the semi-major
axis a and the eccentricity e of the orbit of a test particle experience
secular variations. For Saturn and Uranus, for which modern data records cover
at least one full orbital revolution, such predicted anomalies are up to 2-3
orders of magnitude larger than the present-day accuracies in empirical
determinations their orbital parameters from the usual orbit determination
procedures in which the PA was not modeled. Given the predicted huge sizes of
such hypothetical signatures, it is unlikely that their absence from the
presently available processed data can be attributable to an "absorption" for
them in the estimated parameters caused by the fact that they were not
explicitly modeled. The magnitude of a constant PA-type acceleration at 9.5 au
cannot be larger than 9 10^-15 m s^-2 according to the latest observational
results for the perihelion precession of Saturn.Comment: LaTex2e, 7 pages, no figures, 1 table, 23 references. Version
matching the one at press in Modern Physics Letters A (MPLA
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