arXiv subjects

Getbogi Hikmawan

Publications and source records attributed to Getbogi Hikmawan.

4 recordsLinked to original sources

arXiv2024

Rotating neutron stars with chaotic magnetic fields in general relativity and Rastall gravity

Observations indicate that the magnetic fields on neutron stars (NSs) lie in the range of $10^{8}$-$10^{15}$ G. We investigate rotating NSs with chaotic magnetic fields in both general relativity (GR) and Rastall gravity (RG). The equation of state (EOS) of NS matter is formulated within the framework of quantum hadrodynamics (QHD). The Hartle-Thorne formalism, extended to RG, is employed as an approximation for describing rotating NSs, while the magnetic field is modeled through an ansatz in which it is coupled to the energy density. We find that at high masses, neither rotation nor the Rastall parameter significantly affects the total mass, whereas the magnetic field strength can increase the maximum allowed mass. At lower masses, both the magnetic field and an increasing Rastall parameter reduce the stellar radius in the static configuration. Although higher angular velocities enhance stellar deformation, both magnetic field and larger Rastall parameter tend to suppress it. Regarding the moment of inertia, the Rastall parameter has little impact, whereas the magnetic field strength can increase it within the mass range $1.50$-$1.99 M_\odot$. All parameters considered in this study are consistent with observational constraints on the moment of inertia obtained from radio observations of massive pulsars.

astro-ph.HE↗

arXiv2024

Decoherence Induced by the Noise of Primordial Graviton with Minimum Uncertainty Initial States

We have investigated the decoherence induced by the primordial graviton, using the influence functional method, to show whether this method is still effective in detecting graviton if the initial state is not a Bunch-Davies vacuum but rather a minimum uncertainty state. This minimum uncertainty condition allows the initial state of the primordial graviton to be an entanglement state between the polarization or, more generally, a superposition state between a vacuum and that entanglement. Both of those states have a non-classical correlation between the two polarization modes. We found that this method is still effective for detecting gravitons if the density matrix of the initial state does not have non-diagonal elements, where the maximum decoherence time is about 20 seconds, and the dimensions of the interferometer could be reduced if the total graviton increases.

hep-th↗

arXiv2019

Dynamics of Charged and Rotating NUT Black Holes in Rastall Gravity

In this work, we generalized the Kerr-Newman-NUT black hole solution in Rastall gravity from Ref. 1. Here we are more focused on the black hole dynamics such as the event horizons, ergosurface, ZAMO, thermodynamic properties, and the equatorial circular orbit around the black hole such as static radius limit, null equatorial circular orbit, and innermost stable circular orbit. We present how the NUT and Rastall parameter affects the dynamic of the black hole.

gr-qc↗

arXiv2015

No-Go Theorem for Gauss-Bonnet Inflation without Inflaton Potential

Recently, an interesting inflationary scenario, named Gauss-Bonnet inflation, is proposed by Kanti et al.~\cite{Kanti:2015pda,Kanti:2015dra}. In the model, there is no inflaton potential but the inflaton couples to the Guass-Bonnet term. In the case of quadratic coupling, they find inflation occurs with graceful exit. The scenario is attractive because of the natural set-up. However, we show there exists the gradient instability in the tensor perturbations in this inflationary model. We further prove the no-go theorem for the Gauss-Bonnet inflation without an inflaton potential.

hep-th↗