Search Publications
Testing general relativity with x-ray reflection spectroscopy: The Konoplya-Rezzolla-Zhidenko parametrization
Tripathi, Ashutosh; Abdikamalov, Askar B.; Ayzenberg, Dimitry +6 more
X-ray reflection spectroscopy is a promising technique for testing general relativity in the strong-field regime as it can be used to test the Kerr black hole hypothesis. In this context, the parametrically deformed black hole metrics proposed by Konoplya, Rezzolla, and Zhidenko [Phys. Rev. D 93, 064015 (2016), 10.1103/PhysRevD.93.064015] form an …
Testing the Keplerian disk hypothesis using x-ray reflection spectroscopy
Tripathi, Ashutosh; Zhou, Biao; Abdikamalov, Askar B. +3 more
The Novikov-Thorne model is the standard framework for the description of geometrically thin and optically thick accretion disks around black holes and is widely used to study the electromagnetic spectra of accreting black holes. One of the assumptions of the model is that the particles of the gas move on nearly geodesic circular orbits on the equ…
Constraining the Johannsen deformation parameter ɛ3 with black hole x-ray data
Tripathi, Ashutosh; Abdikamalov, Askar B.; Ayzenberg, Dimitry +2 more
We extend our previous work on tests of the Kerr black hole hypothesis using x-ray reflection spectroscopy and we infer observational constraints on the Johannsen deformation parameter ɛ3 . We analyze a NuSTAR observation of the stellar-mass black hole in GS 1354-645, Suzaku data of the supermassive black holes in Ark 564, 1H0419-577, a…
Search for astrophysical rotating Ellis wormholes with x-ray reflection spectroscopy
Bambi, Cosimo; Zhou, Menglei; Cardenas-Avendano, Alejandro +2 more
Recently, two of us have found numerically rotating Ellis wormholes as solutions of four-dimensional Einstein gravity coupled to a phantom field. In this paper, we investigate possible observational signatures to identify similar objects in the Universe. These symmetric wormholes have a mass and are compact, so they may look like black holes. We s…
Moduli dark matter and the search for its decay line using Suzaku x-ray telescope
Loewenstein, Michael; Kusenko, Alexander; Yanagida, Tsutomu T.
Light scalar fields called moduli arise from a variety of different models involving supersymmetry and/or string theory; thus their existence is a generic prediction of leading theories for physics beyond the standard model. They also present a formidable, long-standing problem for cosmology. We argue that an anthropic solution to the moduli probl…
Gas Density Profile in Dark Matter Halo in Chameleon Cosmology
Terukina, Ayumu; Yamamoto, Kazuhiro
We investigate the gas density, temperature, and pressure profiles in a dark matter halo under the influence of the chameleon force. We solve the hydrostatic equilibrium equation for the gas coupled with the chameleon field in an analytic manner, using an approximate solution for the chameleon field equation with the source term, with a generalize…