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All Journal Jurnal Matematika & Sains INDONESIAN JOURNAL OF APPLIED PHYSICS Indonesian Journal of Physics (IJP)

Bobby Eka Gunara

Theoretical High Energy Physics Laboratory, Department of Physics, ITB

Author-ID : 242864

Astronomy Computer Science & IT Earth & Planetary Sciences Electrical & Electronics Engineering Energy Engineering Materials Science & Nanotechnology Mathematics Physics

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Articles

â¤6-II Orbifold Model of the Heterotic String Freddy Permana Zen; Bobby Eka Gunara; Asep Yoyo Wardaya
Jurnal Matematika & Sains Vol 10, No 3 (2005)
Publisher : Institut Teknologi Bandung

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We study a â¤6-II orbifold model which is derived from the ten-dimensional SO(16) × SO(16) heterotic string theory whose the extra six dimensional space is devided by the â¤6-II rotations. All independent embeddings are classified using both shifting and rotation procedures of an SO(16) × SO(16) root lattice. SO(10) × SU(3) × U(1) × SO(16) models are elucidated as examples among the models.

S-Brane Solutions with Accelerating Cosmology in M-theory Freddy Permana Zen; Arianto Arianto; Bobby Eka Gunara; Selly Feranie
Jurnal Matematika & Sains Vol 11, No 1 (2006)
Publisher : Institut Teknologi Bandung

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We study the expansion and accelerated expansion of universe from S-branes of the M-theory. The dynamics of expansion is described by the scale factor of S-brane solutions and equation of state from the S-bran dark energy models. We provide analytic expressions to calculate the equation of state of these models as a function of time. Moreover, we also study cosmological expansion with the intersection solutions, which may have an interesting characteristic, namely, they never obtain the accelerated expansion. The critical expansion is given by the limit Î²â0.

Spontaneous Breaking of N = 2 to N = 1 in Supergravity Bobby Eka Gunara
Indonesian Journal of Physics Vol 14 No 4 (2003): IJP Vol. 14 No. 4, October 2003
Publisher : Institut Teknologi Bandung

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We address some issues related to spontaneous N = 2 ! N = 1 supersymmetry breaking in supergravity. In particular, we discuss the super-Higgs eect in N = 2 supergravity and give the general conditions for the scalar potential which preserves N = 1 supersymmetry with various ground states of the scalar potential such as the Minkowski ground states and the spaces of constant curvature (anti-de Sitter). Furthermore, we also derive the low energy eective N = 1 theory by integrating out the massive gravitino multiplet and show that it saties non-trivial consistency conditions which can also be viewed as conditions on the geometry of the scalar manifold. As an example we brie y discuss the scalar manifold SU(1;1)/U(1) x SO(4;1)/SO(4)

Einstein-Klein-Gordon System in Higher Dimensional Mirda Prisma Wijayanto; Fiki Taufik Akbar Sobar; Bobby Eka Gunara
Indonesian Journal of Physics Vol 32 No 2 (2021): Vol 32 No 2 (2021)
Publisher : Institut Teknologi Bandung

In this present work, we study the Einstein equation coupled with the nonlinear Klein-Gordon equation. We obtain Ricci tensor, scalar curvature, and Einstein equation of the Einstein-Klein-Gordon system in higher dimensional. If we put D=4, our formulations reduce to the four dimensional Einstein-Klein-Gordon system.

Scalar-Torsion Theories in Four Dimensional Static Spacetimes Mulyanto .; Fiki Taufik Akbar; Bobby Eka Gunara
Indonesian Journal of Physics Vol 32 No 2 (2021): Vol 32 No 2 (2021)
Publisher : Institut Teknologi Bandung

In this paper, we consider a class of static spacetimes scalar-torsion theories in four dimensioanal static spacetimes with the scalar potential turned on. We discover that the 2-dimensional submanifold must admit constant triplet structures, one of which is the torsion scalar. This indicates that these equations of motion can be reduced to a single highly non-linear ordinary differential equation known as the master equation. Then, we show that there are no exact solution of the scalar-torsion theory in four dimensions considering the Sinh-Gordon potential.

Blow-up Dynamics of Higher Dimensional Klein-Gordon Equation with Nonminimal Coupling in Subcritical Case Mirda Prisma Wijayanto; Fiki Taufik Akbar; Bobby Eka Gunara
Indonesian Journal of Physics Vol 33 No 1 (2022): Vol 33 No 1 (2022)
Publisher : Institut Teknologi Bandung

The aim of this present work is to study the blow-up dynamics and lifespanestimate for solution to higher dimensional Klein-Gordon Equation in subcritical case, in which1 < p < psc. We construct the equation of motion from the Lagrangian of Klein-Gordon withnon-minimal coupling, where the coupling interaction of the scalar field is proportional to thescalar curvature of the spacetime. The equation of motion has the form like nonlinear dampedwave equation with mass. The novelty of this work is the time dependent of nonlinear term. Weuse test function method to proof the lifespan estimate.

Thermoelectrics of type-I and type-II nodal line semimetals within the two-band model Jyesta Mahayu Adhidewata; Ahmad R. T. Nugraha; Eddwi Hesky Hasdeo; Bobby Eka Gunara
Indonesian Journal of Physics Vol 33 No 1 (2022): Vol 33 No 1 (2022)
Publisher : Institut Teknologi Bandung

Metals and semimetals are often considered poor thermoelectric (TE) materials due to their lowSeebeck coefficients. However, we will show that topological semimetals in the class of nodal-linesemimetals (NLSs) may potentially exhibit better performance as TE materials. The NLSs are semimetalswith an intersection between the conduction band and valence band in the forms of a line (thus called thenodal line). We construct a two-band model using an almost-linear conduction and parabolic (or Mexicanhat) valence bands that overlap each other near the band edge to represent a type-I (or type-II) NLS. Wecalculate TE properties of the NLSs using the semiclassical Boltzmann transport theory and the relaxationtime approximation. By varying the band parameters in our model, we find that the type-II NLS generallyhas better TE performance than the type-I NLS. The type-II NLS, in particular, possesses a Seebeckcoefficient with a value possibly larger than twice that of normal metals. The origin of this feature mightbe the presence of a discontinuity in the density of states due to the intersection of the valence andconduction bands.

Curved Dyonic Domain Walls in Four Dimensions Bobby Eka Gunara
INDONESIAN JOURNAL OF APPLIED PHYSICS Vol 4, No 01 (2014): April
Publisher : Department of Physics, Sebelas Maret University

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.13057/ijap.v4i01.1164

In this short paper we show the existence of solitonic solutions of four dimensional ungauged N=1 supergravity coupled to arbitrary vector and chiral multiplets whose Ricci scalar curvature is constant. The Ricci scalar of spacetimes indeed depends on the σ-model, namely the complex scalars and their first derivative. Then, we give two explicit models, namely static domain walls and static spherical symmetric black holes which are related to our previous works.

Co-Authors Ahmad R. T. Nugraha Arianto Arianto Asep Yoyo Wardaya Eddwi Hesky Hasdeo Fiki Taufik Akbar Fiki Taufik Akbar Fiki Taufik Akbar Sobar Freddy Permana Zen Jyesta Mahayu Adhidewata Mirda Prisma Wijayanto Mulyanto . Selly Feranie

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