1,721,001 research outputs found
Constraining some r-n extra-potentials in modified gravity models with LAGEOS-type laser-ranged geodetic satellites
Full text linkWe focus on several models of modified gravity which share the characteristic of leading to perturbations of the Newtonian potential K2 r-2 and K3 r-3. In particular, by using existing long data records of the LAGEOS satellites, tracked on an almost continuous basis with the Satellite Laser Ranging (SLR) technique, we set preliminary constraints on the free parameters K2, K3 in a model-independent, phenomenological way. We obtain |K2|< 2.1× 106 m4 s-2, -2.5× 1012 m5 s-2< K3 < 4.1× 1012 m5 s-2. They are several orders of magnitude tighter than corresponding bounds existing in the literature inferred with different techniques and in other astronomical and astrophysical scenarios. Then, we specialize them to the different parameters characterizing the various models considered. The availability of SLR data records of increasing length and accuracy will allow to further refine and strengthen the present results
Probing a r-nmodification of the Newtonian potential with exoplanets
Full text linkThe growing availability of increasingly accurate data on transiting exoplanets suggests the possibility of using these systems as possible testbeds for modified models of gravity. In particular, we suggest that the post-Keplerian (pK) dynamical effects from the perturbations of the Newtonian potential falling off as the square or the cube of the distance from the mass of the host star break the degeneracy of the anomalistic, draconitic and sidereal periods. The latter are characteristic temporal intervals in the motion of a binary system, and all coincide in the purely Keplerian case. We work out their analytical expressions in presence of the aforementioned perturbations to yield preliminary insights on the potential of the method proposed for constraining the modified models of gravity considered. A comparison with other results existing in the literature is made
Gravitomagnetic resonance in the field of a gravitational wave
Full text linkUsing the construction of the Fermi frame, the field of a gravitational wave can be described in terms of gravitoelectromagnetic fields that are transverse to the propagation direction and orthogonal to each other. In particular, the gravitomagnetic field acts on spinning particles and we show that, due to the action of the gravitational-wave field, a new phenomenon - which we call gravitomagnetic resonance - may appear. We give both a classical and a quantum description of this phenomenon and suggest that it can be used as the basis for a new type of gravitational-wave detectors. Our results highlight the effectiveness of collective spin excitations, e.g., spin waves in magnetized materials, in detecting high-frequency gravitational waves. Here we suggest that, when gravitational waves induce a precession of the electron spin, power is released in the ferromagnetic resonant mode endowed with quadrupole symmetry of a magnetized sphere. This offers a possible path to the detection of the gravitomagnetic effects of a gravitational wave
Perturbations of the orbital elements due to the magnetic-like part of the field of a plane gravitational wave
Full text linkIn this paper, we focus on the secular changes of the orbital elements of a planet in the solar system, determined by the magnetic-like part of a gravitational wave field. Using Fermi coordinates, we show that the total force acting on a test particle is made of two contributions: A gravito-electric one and a gravito-magnetic one. While the electric-like force has been thoroughly discussed in the past, the effect of the gravito-magnetic force, which depends on the velocity of the test particle, has not been considered yet. We obtain approximated results to some orders in the orbital eccentricity and show that these effects are much smaller than the corresponding gravito-electric ones
Angular momentum effects in Michelson - Morley type experiments
Full text linkThe effect of the angular momentum density of a gravitational source on the times of flight of light rays in an interferometer is analyzed. The calculation is made imagining that the interferometer is at the equator of an axisymmetric steadily rotating gravity source. In order to evaluate the size of the effect in the case of the Earth a weak field approximation for the metric elements is introduced. For laboratory scales and non-geodesic paths the correction due to the angular momentum turns out to be comparable with the sensitivity expected in gravitational waves interferometric detectors, whereas it drops under the threshold of detectability when using free (geodesic) light rays
Physics for the masses: Teaching Einsteinian gravity in primary school
Full text linkWhy is modern physics still today, more than 100 years after its birth, the privilege of an elite of scientists and unknown for the great majority of citizens? The answer is simple, since modern physics is in general not present in the standard physics curricula, except for some general outlines, in the final years of some secondary schools. But, is it possible to teach modern physics in primary school? Is it effective? and, also, Is it engaging for students? These are the simple questions which stimulated our research, based on an intervention performed in the last year of Italian primary school, focused on teaching gravity, according to the Einsteinian approach in the spirit of the Einstein First project, an international collaboration which aims to teach school age children the concepts of modern physics. The outcomes of our research study are in agreement with previous findings obtained in Australian schools, thus they contribute to validate them and show that there is no cultural effect, since the approach works in different education systems. Finally, our results are relevant also in terms of retention and prove that the students involved really understand the key ideas
Gravitational waves physics using Fermi coordinates: A new teaching perspective
Full text linkThe detection of gravitational waves is possible thanks to a multidisciplinary approach involving different disciplines such as astrophysics, physics, engineering, and quantum optics. Consequently, it is important today for teachers to introduce the basic features of gravitational waves science in the undergraduate curriculum. The usual approach to gravitational wave physics is based on the use of traceless and transverse coordinates, which do not have a direct physical meaning and, in a teaching perspective, may cause misconceptions. In this paper, using Fermi coordinates, which are simply related to observable quantities, we show that it is possible to introduce a gravitoelectromagnetic analogy that describes the action of gravitational waves on test masses in terms of electric-like and magnetic-like forces. We suggest that this approach could be more suitable when introducing the basic principles of gravitational waves physics to students
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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