8,726 research outputs found
Testing General Relativity with Satellite Laser Ranging: Recent Developments
In this paper the most recent developments in testing General Relativity in
the gravitational field of the Earth with the technique of Satellite Laser
Ranging are presented. In particular, we concentrate our attention on some
gravitoelectric and gravitomagnetic post--Newtonian orbital effects on the
motion of a test body in the external field of a central mass.Comment: Latex2e, 10 pages, no figures, no tables. Paper presented at
COSPAR2002 conference held in Houston, TX, from 10 October 2002 to 19 October
2002. To appear in Advance in Space Research. References added and update
A note on Seiberg-Witten central charge
The central charge for the Seiberg-Witten low-energy effective Action is
computed using Noether supercharges. A reliable method to construct
supersymmetric Noether currents is presented.Comment: 6 pages, Latex. Changed reference
Weyl-Gauge Symmetry of Graphene
The conformal invariance of the low energy limit theory governing the
electronic properties of graphene is explored. In particular, it is noted that
the massless Dirac theory in point enjoys local Weyl symmetry, a very large
symmetry. Exploiting this symmetry in the two spatial dimensions and in the
associated three dimensional spacetime, we find the geometric constraints that
correspond to specific shapes of the graphene sheet for which the electronic
density of states is the same as that for planar graphene, provided the
measurements are made in accordance to the inner reference frame of the
electronic system. These results rely on the (surprising) general
relativistic-like behavior of the graphene system arising from the combination
of its well known special relativistic-like behavior with the less explored
Weyl symmetry. Mathematical structures, such as the Virasoro algebra and the
Liouville equation, naturally arise in this three-dimensional context and can
be related to specific profiles of the graphene sheet. Speculations on possible
applications of three-dimensional gravity are also proposed.Comment: 22 pages, 3 figures - two new references and few typos fixed, matches
published version by Annals of Physic
On the possibility of measuring the solar oblateness and some relativistic effects from planetary ranging
In this paper we first calculate the post-Newtonian gravitoelectric secular
rate of the mean anomaly of a test particle freely orbiting a spherically
symmetric central mass. Then, we propose a novel approach to suitably combine
the presently available planetary ranging data to Mercury, Venus and Mars in
order to determine, simultaneously and independently of each other, the Sun's
quadrupole mass moment J_2 and the secular advances of the perihelion and the
mean anomaly. This would also allow to obtain the PPN parameters gamma and beta
independently. We propose to analyze the time series of three linear
combinations of the experimental residuals of the rates of the nodes, the
longitudes of perihelia and mean anomalies of Mercury, Venus and Mars built up
in order to absorb the secular precessions induced by the solar oblateness and
the post-Newtonian gravitoelectric forces. The values of the three investigated
parameters can be obtained by fitting the expected linear trends with straight
lines, determining their slopes in arcseconds per century and suitably
normalizing them. According to the present-day EPM2000 ephemerides accuracy,
the obtainable precision would be of the order of 10^-4-10^-5 for the PPN
parameters and, more interestingly, of 10^-9 for J_2. The future BepiColombo
mission should improve the Mercury's orbit by one order of magnitude.Comment: LaTex2e, 11 pages, no figures, 3 tables. Extensively rewritten
version. The role of the classical N-body secular precessions has been
discussed. New observable found for J2. Improved accuracy in it: 10^-9. The
role of BepiColombo discusse
First preliminary tests of the general relativistic gravitomagnetic field of the Sun and new constraints on a Yukawa-like fifth force from planetary data
The general relativistic Lense-Thirring precessions of the perihelia of the
inner planets of the Solar System are about 10^-3 arcseconds per century.
Recent improvements in planetary orbit determination may yield the first
observational evidence of such a tiny effect. Indeed, corrections to the known
perihelion rates of -0.0036 +/- 0.0050, -0.0002 +/- 0.0004 and 0.0001 +/-
0.0005 arcseconds per century were recently estimated by E.V. Pitjeva for
Mercury, the Earth and Mars, respectively, on the basis of the EPM2004
ephemerides and a set of more than 317,000 observations of various kinds. The
predicted relativistic Lense-Thirring precessions for these planets are
-0.0020, -0.0001 and -3 10^-5 arcseconds per century, respectively and are
compatible with the determined perihelia corrections. The relativistic
predictions fit better than the zero-effect hypothesis, especially if a
suitable linear combination of the perihelia of Mercury and the Earth, which a
priori cancels out any possible bias due to the solar quadrupole mass moment,
is considered. However, the experimental errors are still large. Also the
latest data for Mercury processed independently by Fienga et al. with the INPOP
ephemerides yield preliminary insights about the existence of the solar
Lense-Thirring effect. The data from the forthcoming planetary mission
BepiColombo will improve our knowledge of the orbital motion of this planet
and, consequently, the precision of the measurement of the Lense-Thirring
effect. As a by-product of the present analysis, it is also possible to
constrain the strength of a Yukawa-like fifth force to a 10^-12-10^-13 level at
scales of about one Astronomical Unit (10^11 m).Comment: LaTex, 22 pages, 1 figure, 5 tables, 62 references. To appear in
Planetary and Space Scienc
The Hawking-Unruh phenomenon on graphene
We find that, for a very specific shape of a monolayer graphene sample, a
general relativistic-like description of a back-ground spacetime for graphene's
conductivity electrons is very natural. The corresponding electronic local
density of states is of finite temperature. This is a Hawking-Unruh effect that
we propose to detect through an experiment with a Scanning Tunneling
Microscope.Comment: 7 pages, 2 figures; insignificant changes to fit the letter format;
it matches published version; Physics Letters B (2012
- …