arXiv subjects

Ilham Prasetyo

Publications and source records attributed to Ilham Prasetyo.

7 recordsLinked to original sources

arXiv2026

Preliminary study on the impact of stress-energy tensor compared to scalar field in Nonminimal Derivative model

In this article, we report the results of comparing the effect of using trace of stress-energy tensor versus real-valued scalar field in Nonminimal Derivative Coupling gravitation model, respectively denoted as NMDC-T and NMDC-phi. We employ the model into an incompressible star and see the effect of both models NMDC-T and NMDC-phi on the compactness and mass-radius relation. We find that coupling parameters of NMDC-T is less sensitive than NMDC-phi.

gr-qc↗

arXiv2025

Bogomol'nyi equations for Dirac-Born-Infeld cosmic string

We revisit the question of whether Dirac-Born-Infeld (DBI) cosmic strings can admit Bogomol'nyi-Prasad-Sommerfield (BPS) configurations. Earlier work by Babichev et al. arXiv:0809.2013 concluded that DBI strings with the standard Mexican-hat potential possess no BPS limit, implying an unavoidable nonzero binding energy. In contrast, using the BPS Lagrangian method, we show that DBI strings do admit BPS solutions, provided the potential is chosen self-consistently. Imposing the existence of Bogomol'nyi equations uniquely determines the admissible potential and yields exact first-order BPS equations for DBI vortices. We independently verify the consistency of these equations using the stressless (vanishing-pressure) condition on the energy-momentum tensor. The resulting solutions saturate the Bogomol'nyi bound, exhibit zero binding energy, and smoothly recover the Nielsen-Olesen string in the limit $α\to 0$. Regularity of the gauge-field equation requires $α< π^2$. A notable outcome of the construction is that the BPS-compatible potential takes a trigonometric form closely related to the sine-Gordon potential, revealing a natural correspondence between the sine-Gordon string and the BPS DBI string. The BPS tension scales linearly with the winding number $n$ but acquires an $α$-dependent deformation.

hep-th↗

arXiv2020

BPS Submodels of The Generalized Skyrme Model and How to Find Them

Using the BPS Lagrangian method we show that all known BPS submodels of the generalized Skyrme model, with a particular ansatz for the fields content, can be devided into three groups based on the (effective) number of derivative-terms in the BPS submodels. We are able to derive rigorously the Bogomolny's equations of those BPS submodels. The resulting Bogomolny's equations, along with possible constraint equations, are in general forms in which some of the known BPS submodels may contain other possible non-trivial (non-vacuum) solutions then the ones found in the literature. Furthermore, we derive some other new BPS submodels of the generalized Skyrme model for each of the groups and some of them yield new solutions.

hep-th↗

arXiv2018

BPS Equations of Monopole and Dyon in $SU(2)$ Yang-Mills-Higgs Model, Nakamula-Shiraishi Models, and Their Generalized Versions from The BPS Lagrangian Method

We apply the BPS Lagrangian method~\cite{Atmaja:2015umo} to derive BPS equations of monopole and dyon in the $SU(2)$ Yang-Mills-Higgs model, Nakamula-Shiraishi models, and their Generalized versions. We argue that by identifying the effective fields of scalar field, $f$, and of time-component gauge field, $j$, explicitly by $j=βf$ with $β$ is a real constant, the usual BPS equations for dyon can be obtained naturally. We validate this identification by showing that both Euler-Lagrange equations for $f$ and $j$ are identical in the BPS limit. The value of $β$ is bounded to $|β|<1$ due to reality condition on the resulting BPS equations. In the Born-Infeld type of actions, namely Nakamula-Shiraishi models and their Generalized versions, we find a new feature that adding the energy density by a constant $4b^2$, with $b$ is the Born-Infeld parameter, will turn monopole(dyon) to anti-monopole(anti-dyon) and vice versa. In all Generalized versions there are additional constraint equations that relate the scalar-dependent couplings of scalar and of gauge kinectic terms; or $G$ and $w$ respectively. For monopole the constraint equation is $G=w^{-1}$, while for dyon is $w(G-β^2 w)=1-β^2$ which further gives lower bound to $G$ as such $G\geq|2β\sqrt{1-β^2}|$. We also write down the complete square-forms of all effective Lagrangians.

hep-th↗

arXiv2018

Higher-dimensional black holes with Dirac-Born-Infeld (DBI) global defects

It is well-known that the exact solution of non-linear $σ$ model coupled to gravity can be perceived as an exterior gravitational field of a global monopole. Here we study Einstein's equations coupled to a non-linear $σ$ model with Dirac-Born-Infeld (DBI) kinetic term in $D$ dimensions. The solution describes a metric around a DBI global defects. When the core is smaller than its Schwarzschild radius it can be interpreted as a black hole having DBI scalar hair with deficit conical angle. The solutions exist for all $D$, but they can be expressed as polynomial functions in $r$ only when $D$ is even. We give conditions for the mass $M$ and the scalar charge $η$ in the extremal case. We also investigate the thermodynamic properties of the black holes in canonical ensemble. The monopole alter the stability differently in each dimensions. As the charge increases the black hole radiates more, in contrast to its counterpart with ordinary global defects where the Hawking temperature is minimum for critical $η$. This behavior can also be observed for variation of DBI coupling, $β$. As it gets stronger ($β\ll1$) the temperature increases. By studying the heat capacity we can infer that there is no phase transition in asymptotically-flat spacetime. The AdS black holes, on the other hand, undergo a first-ordered phase transition in the Hawking-Page type. The increase of the DBI coupling renders the phase transition happen for larger radius.

gr-qc↗

arXiv2017

Classical defects in higher-dimensional Einstein gravity coupled to nonlinear $σ$-models

We construct solutions of higher-dimensional Einstein gravity coupled to nonlinear $σ$-model with cosmological constant. The $σ$-model can be perceived as exterior configuration of a spontaneously-broken $SO(D-1)$ global higher-codimensional "monopole". Here we allow the kinetic term of the $σ$-model to be noncanonical; in particular we specifically study a quadratic-power-law type. This is some possible higher-dimensional generalization of the Bariola-Vilenkin (BV) solutions with $k$-global monopole studied recently. The solutions can be perceived as the exterior solution of a black hole swallowing up noncanonical global defects. Even in the absence of comological constant its surrounding spacetime is asymptotically non-flat; it suffers from deficit solid angle. We discuss the corresponding horizons. For $Λ>0$ in $4d$ there can exist three extremal conditions (the cold, ultracold, and Nariai black holes), while in higher-than-four dimensions the extremal black hole is only Nariai. For $Λ<0$ we only have black hole solutions with one horizon, save for the $4d$ case where there can exist two horizons. We give constraints on the mass and the symmetry-breaking scale for the existence of all the extremal cases. In addition, we also obtain factorized solutions, whose topology is the direct product of two-dimensional spaces of constant curvature ($M_2$, $dS_2$, or $AdS_2$) with (D-2)-sphere. We study all possible factorized channels.

gr-qc↗

arXiv2016

Gravity of a noncanonical global monopole: conical topology and compactification

We obtain solutions of Einstein's equations describing gravitational field outside a noncanonical global monopole with cosmological constant. In particular, we consider two models of k-monopoles: the Dirac-Born-Infeld (DBI) and the power-law types, and study their corresponding exterior gravitational fields. For each model we found two types of solutions. The first of which are global k-monopole black hole with conical global topology. These are generalizations of the Barriola-Vilenkin solution of global monopole. The appearance of noncanonical kinetic terms does not modify the critical symmetry-breaking scale, $η_{crit}$, but it does affect the corresponding horizon(s). The second type of solution is compactification, whose topology is a product of two $2$-dimensional spaces with constant curvatures; ${\mathcal Y}_4\rightarrow {\mathcal Z}_2\times S^2$, with ${\mathcal Y}, {\mathcal Z}$ can be de Sitter, Minkowski, or Anti-de Sitter, and $S^2$ is the $2$-sphere. We investigate all possible compactifications and show that the nonlinearity of kinetic terms opens up new channels which are otherwise non-existent. For $Λ=0$ four-dimensional geometry, we conjecture that these compactification channels are their (possible) non-static super-critical states, right before they undergo topological inflation.

gr-qc↗