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SUMMARY:Contributory: f(R) gravity scalarons near black hole horizon
DTSTART;VALUE=DATE-TIME:20261119T070000Z
DTEND;VALUE=DATE-TIME:20261119T071500Z
DTSTAMP;VALUE=DATE-TIME:20261026T185259Z
UID:indico-contribution-988@indico.narit.or.th
DESCRIPTION:Speakers: Pranjali Bhattacharjee (Gauhati University)\nThe Gal
 actic Center (GC) black hole Sgr A* gives us an opportunity to perform hor
 izon scale tests of black hole physics and deviations from General Relativ
 ity\, thanks to observations carried out by the Event Horizon Telescope (E
 HT). In this work we study the impact of the scalar degree of freedom (sca
 laron) of f(R) gravity theory on the size and shape of GC black hole by us
 ing a recently developed stationary\, axisymmetric and vacuum metric of f(
 R) theory. We encounter a minimum bound of $10^{-17}$ eV for the scalaron 
 mass using 1σ upper bound on the deviation parameter produced by EHT-Keck
  and EHT-VLT measurements. Lighter scalarons increase the shadow size beyo
 nd that measured by the EHT. The displacement and asymmetry in the shape o
 f the black hole shadow are employed to test the no-hair theorem and it is
  observed that $10^{-16}$ eV scalarons yield the exact Kerr like shadow an
 d a $6\\%$ departure from the Kerr quadrupole. We infer preservation of th
 e no-hair theorem for such scalaron mass and further examine the possibili
 ty of violation of the theorem. The same mass scale reproduces the PPN par
 ameter $\\gamma$ constrained in the weak field limit of the solar system. 
 This is for the first time we report a convergence of horizon scale test a
 nd solar system test of f(R) gravity by using the scalaron mass. The prosp
 ect of constraining the scalaron mass using gravitational waves is an exci
 ting avenue to be highlighted.\n\nhttps://indico.narit.or.th/event/234/con
 tributions/988/
LOCATION:Pattaya\, Thailand D Varee Jomtien Beach Pattaya Hotel
URL:https://indico.narit.or.th/event/234/contributions/988/
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