V. Borka Jovanović

High-energy plasmon spectroscopy of freestanding multilayer graphene

We present several applications of the layered electron gas model to electron energy loss spectroscopy of freestanding films consisting of

Constraining the range of Yukawa gravity interaction from S2 star orbits

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Constraints on

graphene layers in a scanning transmission electron microscope. Using a two-fluid model for the single-layer polarizability, we discuss the evolution of high-energy plasmon spectra with

R^n

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gravity from precession of orbits of S2-like stars: a case of a bulk distribution of mass

and find good agreement with the recent experimental data for both multilayer graphene with

Constraining the range of Yukawa gravity interaction from S2 star orbits II: bounds on graviton mass

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Constraining the range of Yukawa gravity interaction from S2 star orbits III: improvement expectations for graviton mass bounds

and thick slabs of graphite. Such applications of these analytical models help shed light on several features observed in the plasmon spectra of those structures, including the role of plasmon dispersion, dynamic interference in excitations of various plasmon eigenmodes, as well as the relevance of the bulk plasmon bands, rather than surface plasmons, in classifying the plasmon peaks.

Addressing the missing matter problem in galaxies through a new fundamental gravitational radius

We consider possible signatures for Yukawa gravity within the Galactic Central Parsec, based on our analysis of the S2 star orbital precession around the massive compact dark object at the Galactic Centre, and on the comparisons between the simulated orbits in Yukawa gravity and two independent sets of observations. Our simulations resulted in strong constraints on the range of Yukawa interaction Λ and showed that its most probable value in the case of S2 star is around 5000 - 7000 AU. At the same time, we were not able to obtain reliable constrains on the universal constant δ of Yukawa gravity, because the current observations of S2 star indicated that it may be highly correlated with parameter Λ in the range (0 2 they are not correlated. However, the same universal constant which was successfully applied to clusters of galaxies and rotation curves of spiral galaxies (δ = 1/3) also gives a satisfactory agreement with the observed orbital precession of the S2 star, and in that case the most probable value for the scale parameter is Λ ≈ 3000±1500 AU. Also, the Yukawa gravity potential induces precession of S2 star orbit in the same direction as General Relativity for δ > 0 and for δ < −1, and in the opposite direction for −1 < δ < 0. The future observations with advanced facilities, such as GRAVITY or/and European Extremely Large Telescope, are needed in order to verify these claims.

Probing hybrid modified gravity by stellar motion around Galactic Center

Abstract Here we investigate possible applications of observed stellar orbits around Galactic Center for constraining the Rn gravity at Galactic scales. For that purpose, we simulated orbits of S2-like stars around the massive black hole at Galactic Center, and study the constraints on the Rn gravity which could be obtained by the present and next generations of large telescopes. Our results show that Rn gravity affects the simulated orbits in the qualitatively similar way as a bulk distribution of matter (including a stellar cluster and dark matter distributions) in Newton’s gravity. In the cases where the density of extended mass is higher, the maximum allowed value of parameter β in Rn gravity is noticeably smaller, due to the fact that the both extended mass and R n gravity cause the retrograde orbital precession.

The Monoceros radio loop: Temperature, brightness, spectral index, and distance

Recently LIGO collaboration discovered gravitational waves \cite{Abbott_16} predicted 100 years ago by A. Einstein. Moreover, in the key paper reporting about the discovery, the joint LIGO \& VIRGO team presented an upper limit on graviton mass such as