4,441 research outputs found
LAGEOS-type Satellites in Critical Supplementary Orbit Configuration and the Lense-Thirring Effect Detection
In this paper we analyze quantitatively the concept of LAGEOS--type
satellites in critical supplementary orbit configuration (CSOC) which has
proven capable of yielding various observables for many tests of General
Relativity in the terrestrial gravitational field, with particular emphasis on
the measurement of the Lense--Thirring effect.Comment: LaTex2e, 20 pages, 7 Tables, 6 Figures. Changes in Introduction,
Conclusions, reference added, accepted for publication in Classical and
Quantum Gravit
Can noncommutativity resolve the Big-Bang singularity?
A possible way to resolve the singularities of general relativity is proposed
based on the assumption that the description of space-time using commuting
coordinates is not valid above a certain fundamental scale. Beyond that scale
it is assumed that the space-time has noncommutative structure leading in turn
to a resolution of the singularity. As a first attempt towards realizing the
above programme a modification of the Kasner metric is constructed which is
commutative only at large time scales. At small time scales, near the
singularity, the commutation relations among the space coordinates diverge. We
interpret this result as meaning that the singularity has been completely
delocalized.Comment: Latex, 13 pages, 2 figures, accepted for publication in EPJ
Conservative evaluation of the uncertainty in the LAGEOS-LAGEOS II Lense-Thirring test
We deal with the test of the general relativistic gravitomagnetic
Lense-Thirring effect currently ongoing in the Earth's gravitational field with
the combined nodes \Omega of the laser-ranged geodetic satellites LAGEOS and
LAGEOS II.
One of the most important source of systematic uncertainty on the orbits of
the LAGEOS satellites, with respect to the Lense-Thirring signature, is the
bias due to the even zonal harmonic coefficients J_L of the multipolar
expansion of the Earth's geopotential which account for the departures from
sphericity of the terrestrial gravitational potential induced by the
centrifugal effects of its diurnal rotation. The issue addressed here is: are
the so far published evaluations of such a systematic error reliable and
realistic? The answer is negative. Indeed, if the difference \Delta J_L among
the even zonals estimated in different global solutions (EIGEN-GRACE02S,
EIGEN-CG03C, GGM02S, GGM03S, ITG-Grace02, ITG-Grace03s, JEM01-RL03B, EGM2008,
AIUB-GRACE01S) is assumed for the uncertainties \delta J_L instead of using
their more or less calibrated covariance sigmas \sigma_{J_L}, it turns out that
the systematic error \delta\mu in the Lense-Thirring measurement is about 3 to
4 times larger than in the evaluations so far published based on the use of the
sigmas of one model at a time separately, amounting up to 37% for the pair
EIGEN-GRACE02S/ITG-Grace03s. The comparison among the other recent GRACE-based
models yields bias as large as about 25-30%. The major discrepancies still
occur for J_4, J_6 and J_8, which are just the zonals the combined
LAGEOS/LAGOES II nodes are most sensitive to.Comment: LaTex, 12 pages, 12 tables, no figures, 64 references. To appear in
Central European Journal of Physics (CEJP
Will the recently approved LARES mission be able to measure the Lense-Thirring effect at 1%?
After the approval by the Italian Space Agency of the LARES satellite, which
should be launched at the end of 2009 with a VEGA rocket and whose claimed goal
is a about 1% measurement of the general relativistic gravitomagnetic
Lense-Thirring effect in the gravitational field of the spinning Earth, it is
of the utmost importance to reliably assess the total realistic accuracy that
can be reached by such a mission. The observable is a linear combination of the
nodes of the existing LAGEOS and LAGEOS II satellites and of LARES able to
cancel out the impact of the first two even zonal harmonic coefficients of the
multipolar expansion of the classical part of the terrestrial gravitational
potential representing a major source of systematic error. While LAGEOS and
LAGEOS II fly at altitudes of about 6000 km, LARES will be placed at an
altitude of 1450 km. Thus, it will be sensitive to much more even zonals than
LAGEOS and LAGEOS II. Their corrupting impact \delta\mu has been evaluated by
using the standard Kaula's approach up to degree L=70 along with the sigmas of
the covariance matrices of eight different global gravity solutions
(EIGEN-GRACE02S, EIGEN-CG03C, GGM02S, GGM03S, JEM01-RL03B, ITG-Grace02s,
ITG-Grace03, EGM2008) obtained by five institutions (GFZ, CSR, JPL, IGG, NGA)
with different techniques from long data sets of the dedicated GRACE mission.
It turns out \delta\mu about 100-1000% of the Lense-Thirring effect. An
improvement of 2-3 orders of magnitude in the determination of the high degree
even zonals would be required to constrain the bias to about 1-10%.Comment: Latex, 15 pages, 1 table, no figures. Final version matching the
published one in General Relativity and Gravitation (GRG
Finite SU(N)^k Unification
We consider N=1 supersymmetric gauge theories based on the group SU(N)_1 x
SU(N)_2 x ... x SU(N)_k with matter content (N,N*,1,...,1) + (1,N,N*,...,1) +
>... + (N*,1,1,...,N) as candidates for the unification symmetry of all
particles. In particular we examine to which extent such theories can become
finite and we find that a necessary condition is that there should be exactly
three families. We discuss further some phenomenological issues related to the
cases (N,k) = (3,3), (3,4), and (4,3), in an attempt to choose those theories
that can become also realistic. Thus we are naturally led to consider the
SU(3)^3 model which we first promote to an all-loop finite theory and then we
study its additional predictions concerning the top quark mass, Higgs mass and
supersymmetric spectrum.Comment: 15 page
Hard Thermal Loops, Static Response and the Composite Effective Action
First, we investigate the static non-Abelian Kubo equation. We prove that it
does not possess finite energy solutions; thereby we establish that gauge
theories do not support hard thermal solitons. A similar argument shows that
"static" instantons are absent. In addition, we note that the static equations
reproduce the expected screening of the non-Abelian electric field by a gauge
invariant Debye mass m=gT sqrt((N+N_F/2)/3). Second, we derive the non-Abelian
Kubo equation from the composite effective action. This is achieved by showing
that the requirement of stationarity of the composite effective action is
equivalent, within a kinematical approximation scheme, to the condition of
gauge invariance for the generating functional of hard thermal loops.Comment: 17 pages, MIT preprint CTP#2261. An Appendix [including one
(appended) PS figure] presenting a numerical analysis of the static solutions
has been included. A note relating our approach to alternative ones has been
added. We have also added references and comments in Section II
Algebraic characterization of the Wess-Zumino consistency conditions in gauge theories
A new way of solving the descent equations corresponding to the Wess-Zumino
consistency conditions is presented. The method relies on the introduction of
an operator which allows to decompose the exterior space-time
derivative as a commutator. The case of the Yang-Mills theories is
treated in detail.Comment: 16 pages, UGVA-DPT 1992/08-781 to appear in Comm. Math. Phy
On the Lense-Thirring test with the Mars Global Surveyor in the gravitational field of Mars
I discuss some aspects of the recent test of frame-dragging performed by me
by exploiting the Root-Mean-Square (RMS) orbit overlap differences of the
out-of-plane component N of the orbit of the Mars Global Surveyor (MGS)
spacecraft in the gravitational field of Mars. A linear fit of the full time
series of the entire MGS data (4 February 1999-14 January 2005) yields a
normalized slope 1.03 +/- 0.41 (with 95% confidence bounds). Other linear fits
to different data sets confirm the agreement with general relativity. The huge
systematic effects induced by the mismodeling in the martian gravitational
field claimed by some authors are absent in the MGS out-of-plane record. The
non-gravitational forces affect at the same level of the gravitomagnetic one
the in-plane orbital components of MGS, not the out-of-plane one. Moreover,
they experience high-frequency variations which does not matter in the present
case in which secular effects are relevant.Comment: LaTex2e, 8 pages, no figures, no tables, 17 references. It refers to
K. Krogh, Class. Quantum Grav., 24, 5709-5715, 2007 based on
astro-ph/0701653. Final version to appear in CEJP (Central European Journal
of Physics
Reduction of Couplings in Quantum Field Theories with applications in Finite Theories and the MSSM
We apply the method of reduction of couplings in a Finite Unified Theory and
in the MSSM. The method consists on searching for renormalization group
invariant relations among couplings of a renormalizable theory holding to all
orders in perturbation theory. It has a remarkable predictive power since, at
the unification scale, it leads to relations between gauge and Yukawa couplings
in the dimensionless sectors and relations involving the trilinear terms and
the Yukawa couplings, as well as a sum rule among the scalar masses and the
unified gaugino mass in the soft breaking sector. In both the MSSM and the FUT
model we predict the masses of the top and bottom quarks and the light Higgs in
remarkable agreement with the experiment. Furthermore we also predict the
masses of the other Higgses, as well as the supersymmetric spectrum, both being
in very confortable agreement with the LHC bounds on Higgs and supersymmetric
particles.Comment: 18 pages, 4 figures. To appear in the proceedings of LT-10, Varna.
Based on invited talks given at: LT-10, Varna; PACT-2013, Madrid; SQS'2013,
Dubna; CORFU 2013, Corfu, and in several invited seminar
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