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Register a new userTest of Einsteins Equivalence Principle by Galactic Dark Matter
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Ramanath Cowsik PROF
Publication date
2018
fields
Physics
and research's language is
English
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We report here the results of operation of a torsion balance with a period of $sim 1.27 times 10^4$ s. The analysis of data collected over a period of $sim$115 days shows that the difference in the accelerations towards the Galactic Center of test bodies made of aluminum and quartz was $(0.61 pm 1.27) times 10^{-15} , mathrm{ m , s}^{-2}$. This sets a bound on the violation of the equivalence principle by forces exerted by Galactic dark matter which is expressed by the Eotvos parameter $eta_{DM} = (1.32 pm 2.68) times 10^{-5}$, a significant improvement upon earlier bounds.
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Aims: Recently, cosmological fast radio bursts (FRBs) have been used to provide the most stringent limit up to date on Einsteins Equivalence Principle (EEP). We study how to further test EEP with FRBs. Methods: Future systematic radio surveys will certainly find abundant FRBs at cosmological distances and some of them will inevitably be located behind clusters of galaxies. Here we suggest to use those FRBs to further test EEP. Results: We find that the robustness and accuracy of testing EEP can be improved further by orders of magnitude with these FRBs. The same methodology can also be applied to any other types of fast and bright transients at cosmological distances.
We used a continuously rotating torsion balance instrument to measure the acceleration difference of beryllium and titanium test bodies towards sources at a variety of distances. Our result Delta a=(0.6+/-3.1)x10^-15 m/s^2 improves limits on equivalence-principle violations with ranges from 1 m to infinity by an order of magnitude. The Eoetvoes parameter is eta=(0.3+/-1.8)x10^-13. By analyzing our data for accelerations towards the center of the Milky Way we find equal attractions of Be and Ti towards galactic dark matter, yielding eta=(-4 +/- 7)x10^-5. Space-fixed differential accelerations in any direction are limited to less than 8.8x10^-15 m/s^2 with 95% confidence.
We review matter wave and clock comparison tests of the gravitational redshift. To elucidate their relationship to tests of the universality of free fall (UFF), we define scenarios wherein redshift violations are coupled to violations of UFF (type II), or independent of UFF violations (type III), respectively. Clock comparisons and atom interferometers are sensitive to similar effects in type II and precisely the same effects in type III scenarios, although type III violations remain poorly constrained. Finally, we describe the Geodesic Explorer, a conceptual spaceborne atom interferometer that will test the gravitational redshift with an accuracy 5 orders of magnitude better than current terrestrial redshift experiments for type II scenarios and 12 orders of magnitude better for type III.
Tensor-scalar theory is a wide class of alternative theory of gravitation that can be motivated by higher dimensional theories, by models of dark matter or dark ernergy. In the general case, the scalar field will couple non-universally to matter producing a violation of the equivalence principle. In this communication, we review a microscopic model of scalar/matter coupling and its observable consequences in terms of universality of free fall, of frequencies comparison and of redshifts tests. We then focus on two models: (i) a model of ultralight scalar dark matter and (ii) a model of scalarized black hole in our Galactic Center. For both these models, we present constraints using recent measurements: atomic clocks comparisons, universality of free fall measurements, measurement of the relativistic redshift with the short period star S0-2 orbiting the supermassive black hole in our Galactic Center.
We propose an experiment to test the Weak Equivalence Principle (WEP) with a test mass consisting of two entangled atoms of different species. In the proposed experiment, a coherent measurement of the differential gravity acceleration between the two atomic species is considered, by entangling two atom interferometers operating on the two species. The entanglement between the two atoms is heralded at the initial beam splitter of the interferometers through the detection of a single photon emitted by either of the atoms, together with the impossibility of distinguishing which atom emitted the photon. In contrast to current and proposed tests of the WEP, our proposal explores the validity of the WEP in a regime where the two particles involved in the differential gravity acceleration measurement are not classically independent, but entangled. We propose an experimental implementation using $^{85}$Rb and $^{87}$Rb atoms entangled by a vacuum stimulated rapid adiabatic passage protocol implemented in a high finesse optical cavity. We show that an accuracy below $10^{-7}$ on the Eotvos parameter can be achieved.
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