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Getbogi Hikmawan
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Astronomy Computer Science & IT Earth & Planetary Sciences Electrical & Electronics Engineering Energy Engineering

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Thin-shell Solution of Chameleon Mechanism in Brans-Dicke Scalar-Tensor Model Azwar Sutiono; Agustina Widiyani; Marliana Marliana; Getbogi Hikmawan; Agus Suroso; Freddy Permana Zen
Indonesian Journal of Physics Vol 33 No 1 (2022): Vol 33 No 1 (2022)
Publisher : Institut Teknologi Bandung

Show Abstract | Download Original | Original Source | Check in Google Scholar | Full PDF (277.95 KB) | DOI: 10.5614/itb.ijp.2022.33.1.1

Abstract

We investigated the chameleon screening mechanism in Brans-Dicke scalar-tensor theory. We preserved the fundamental premise of the typical chameleon mechanism, which is that the field is huge in high-density environments but essentially free in low-density environments like the solar system. We discovered thin-shell solutions for a static and spherical symmetric body and demonstrated the model’s applicability to local data.
Compatibility of Einstein-Gauss-Bonnet inflation theory with non-minimal derivative coupling in the constant-roll Naufal Aulia Adam; Getbogi Hikmawan; Freddy Permana Zen
Indonesian Journal of Physics Vol 33 No 1 (2022): Vol 33 No 1 (2022)
Publisher : Institut Teknologi Bandung

Show Abstract | Download Original | Original Source | Check in Google Scholar | Full PDF (826.512 KB) | DOI: 10.5614/itb.ijp.2022.33.1.2

Abstract

Inflation is a theory in cosmology that explains that the early universe experienceda very fast expansion in a very short time and is able to explain some cosmological problemsand the presence of gravitational waves generated during the inflation period. Based on theevent GW170817, it was found that c2t = 1, which indicates that the speed of gravitationalwaves is nearly equal to the speed of light. This contradicts several modified theories of gravity,one of which is the Einstein-Gauss-Bonnet theory. This paper examines the compatibility ofEinstein-Gauss-Bonnet inflation theory with the GW170817 phenomenon, with the addition ofthe Non-minimal derivative coupling term and the constant-roll approach and its characteristics.The formulation of observational quantities is carried out using Horndeski theory and EffectiveField Theory with ADM formalism and the calculations are done numerically. The constantvalues are selected in such a way that the spectral index values and tensor-scalar ratios are closeto the 2018 Planck data. The results found that this theory is compatible with GW170817 withthe influence of Gauss-Bonnet term and constant-roll parameter β most dominant.
GW170817 Implementation on Einstein-Gauss-Bonnet Theory with Non Minimal and Non Minimal Derivative Coupling Fitria Khairunnisa; Getbogi Hikmawan; Freddy Permana Zen
Indonesian Journal of Physics Vol 33 No 1 (2022): Vol 33 No 1 (2022)
Publisher : Institut Teknologi Bandung

Show Abstract | Download Original | Original Source | Check in Google Scholar | Full PDF (612.572 KB) | DOI: 10.5614/itb.ijp.2022.33.1.3

Abstract

The GW170817 event manifests that gravitational wave velocity is close to thespeed of light. As a result, several theories of gravity are no longer applicable, including EinsteinGauss-Bonnet (EGB) inflation. However, a constraint equation could be applied so that thetheory could produce a viable result. In this study, the EGB inflation is being extended byadding a non-minimal coupling (NMC) and a non-minimal derivative coupling (NMDC). Freeparameters values were evaluated to obtained viability with observational indices. We use powerlaw and exponential Gauss-Bonnet coupling functions. Each model provides observational valuesof ns and r that are compatible with the observations and has its characteristic. It specifiesthe free parameter that controls the alteration of ns and r values. The power-law model iscontrolled by the power m of the Gauss-Bonnet coupling function and the potential integrationconstant, V2. While the exponential model is controlled by the potential integration constant cand the power m of the exponential function. Some approximations do not hold true so that themodels need to be rectified. Apparently, the rectified power-law model is violating null energycondition (NEC), so we also provide the non-violating NEC power-law model.
Gravitational Wave Propagation for The Generalized Proca Theories marliana lutan; Agustina Widiyani; Azwar Sutiono; Getbogi Hikmawan; Agus Suroso; Freddy Permana Zen
Indonesian Journal of Physics Vol 33 No 1 (2022): Vol 33 No 1 (2022)
Publisher : Institut Teknologi Bandung

Show Abstract | Download Original | Original Source | Check in Google Scholar | Full PDF (177.093 KB) | DOI: 10.5614/itb.ijp.2022.33.1.7

Abstract

In general relativity, a gravitational wave propagates with the speed of light, but inthe alternative theories of gravity, propagation speed could deviate from the speed of lightdue to the modification of gravity. Gravitational waves are influenced by modified gravityduring propagation at the cosmological distance. In this paper, we investigate thepropagation of a gravitational wave of the generalized Proca theories by consideringgravitational wave as the gravitational field propagates in spacetime as a wave perturbing flatspacetime. We show that the arbitrary functions G3, G4, and G5 can be the sources ofdeviation of the speed of the gravitational wave.
Co-Authors Agus Suroso Fitria Khairunnisa Freddy Permana Zen marliana lutan Marliana Marliana Naufal Aulia Adam Sutiono, Azwar Widiyani, Agustina