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Peer-reviewedCC BY 4.0The European Physical Journal C

Spherically symmetric vacuum solution in Freund–Nambu scalar–tensor gravity

  • Akbar Davlataliev1,2,3
  • Bobur Turimov4,5,6
  • Bobomurat Ahmedov1,7,2
  • Yuri Vyblyi8
  • Chengxun Yuan1
  • Chen Zhou1
8 affiliations
  1. 1Harbin Institute of Technology
  2. 2New Uzbekistan University
  3. 3University of Tashkent for Applied Sciences
  4. 4Central Asian University
  5. 5Khazar University
  6. 6Ulugh Beg Astronomical Institute
  7. 7National University of Uzbekistan
  8. 8Center for Fundamental Interactions and Astrophysics
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Abstract

We present an exact solution in Freund–Nambu scalar–tensor gravity that extends the Janis–Newman–Winnicour (JNW) naked-singularity spacetime. The metric retains the JNW form governed by parameter n , while a new parameter q deforms the profile of the massive scalar field φ . φ . Test-particle dynamics incorporate a direct linear coupling gs g s to φ . φ . We compute the specific angular momentum, innermost stable circular orbit, and radiative efficiency, and derive epicyclic frequencies for quasi-periodic oscillations (QPOs). Within the epicyclic resonance model, the twin-peak QPO frequencies depend on n , q , and gs. g s . A Markov Chain Monte Carlo analysis of microquasars XTE J1550-564 and GRS 1915+105 yields black-hole masses M = 8.99 ± 0.55 M⊙ M = 8.99 ± 0.55 M ⊙ and 13.3 ± 1.0 M⊙ , 13.3 ± 1.0 M ⊙ , consistent with previous estimates, and gives the first observational constraints q ≈ 3, q ≈ 3 , gs ≈ 0.45. g s ≈ 0.45 . These distinctive imprints demonstrate that this modified gravity framework provides a viable, testable arena for strong-field physics beyond general relativity.

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Cite

BibTeXRIS
BibTeX
@article{davlataliev2026spherically,
  title = {{Spherically symmetric vacuum solution in Freund–Nambu scalar–tensor gravity}},
  author = {Akbar Davlataliev and Bobur Turimov and Bobomurat Ahmedov and Yuri Vyblyi and Chengxun Yuan and Chen Zhou},
  journal = {The European Physical Journal C},
  year = {2026},
  month = oct,
  doi = {10.1140/epjc/s10052-026-16324-5},
  url = {https://link.springer.com/article/10.1140/epjc/s10052-026-16324-5},
  note = {CC BY 4.0},
}
RIS
TY  - JOUR
TI  - Spherically symmetric vacuum solution in Freund–Nambu scalar–tensor gravity
AU  - Akbar Davlataliev
AU  - Bobur Turimov
AU  - Bobomurat Ahmedov
AU  - Yuri Vyblyi
AU  - Chengxun Yuan
AU  - Chen Zhou
PY  - 2026
DA  - 2026/10/19
JO  - The European Physical Journal C
DO  - 10.1140/epjc/s10052-026-16324-5
UR  - https://link.springer.com/article/10.1140/epjc/s10052-026-16324-5
AB  - We present an exact solution in Freund–Nambu scalar–tensor gravity that extends the Janis–Newman–Winnicour (JNW) naked-singularity spacetime. The metric retains the JNW form governed by parameter n , while a new parameter q deforms the profile of the massive scalar field φ . φ . Test-particle dynamics incorporate a direct linear coupling g_s g s to φ . φ . We compute the specific angular momentum, innermost stable circular orbit, and radiative efficiency, and derive epicyclic frequencies for quasi-periodic oscillations (QPOs). Within the epicyclic resonance model, the twin-peak QPO frequencies depend on n , q , and g_s. g s . A Markov Chain Monte Carlo analysis of microquasars XTE J1550-564 and GRS 1915+105 yields black-hole masses M = 8.99 ± 0.55 M_⊙ M = 8.99 ± 0.55 M ⊙ and 13.3 ± 1.0 M_⊙ , 13.3 ± 1.0 M ⊙ , consistent with previous estimates, and gives the first observational constraints q ≈ 3, q ≈ 3 , g_s ≈ 0.45. g s ≈ 0.45 . These distinctive imprints demonstrate that this modified gravity framework provides a viable, testable arena for strong-field physics beyond general relativity.
SN  - 1434-6044
SN  - 1434-6052
ER  -