We investigate extremal charged black hole solutions in the four-dimensional string frame Gauss-Bonnet gravity with the Maxwell field and the dilaton. Without curvature corrections, the extremal electrically charged dilatonic black holes have singular horizon and zero Bekenstein entropy. When the Gauss-Bonnet term is switched on, the horizon radius expands to a finite value provided curvature corrections are strong enough. Below a certain threshold value of the Gauss-Bonnet coupling the extremal black hole solutions cease to exist. Since decreasing Gauss-Bonnet coupling corresponds to decreasing string coupling $g_s$, the situation can tentatively be interpreted as classical indication on the black hole -- string transition. Previously the extremal dilaton black holes were studied in the Einstein-frame version of the Gauss-Bonnet gravity. Here we work in the string frame version of this theory with the S-duality symmetric dilaton function as required by the heterotic string theory.
We investigate various types of Fubini instantons in Dilatonic Einstein-Gauss-Bonnet theory of gravitation, which describe the decay of the vacuum state at a hilltop potential through the tunneling without a barrier. It is shown that the vacuum states are modified by the non-minimally coupled higher-curvature term. Accordingly, we present the new type of solutions describing the tunneling from new vacuum states in anti-de Sitter and de Sitter backgrounds. The decay probabilities of vacuum states are also influenced. Consequently, we show that the semiclassical exponents can be decreased for sp…
Exact Solutions and the Cosmological Constant Problem in Dilatonic-Domain-Wall Higher-Curvature String Gravity
在这篇文章中，我们扩展了作者以前的工作，并进一步阐述了在O（λ '）$ higher-curvature corrections, compatible with bulk string-amplitude calculations. We consider (multi)brane scenaria, dividing the bulk space into regions, in which one matches two classes of general solutions, a linear Randall-Sundrum solution and a (logarithmic) dilatonic domain wall (bulk naked singularity).We pay particular attention to examining the possibility of resolving the mass hierarchy problem together with the vanishing of the vacuum energy on the observable world, which is taken to be a positive tension brane. The appearance of naked dilatonic d…
Taking a thermodynamic perspective, we study the weak gravity conjecture in the context of 4D Einstein-Maxwell-dilaton theory. We find closed-form expressions for the corrected thermodynamic quantities in the presence of four-derivative terms in the action, and in particular the charge-to-mass ratio and entropy, for several families of solutions of special magnetic-to-electric charge ratio or dilaton coupling constant. Assuming that dyonic black holes themselves are the conjectured charged states, this places constraints on the Wilson coefficients of the theory which we show are satisfied unde…
We present a method to generate static solutions in the Einstein-Maxwell system with a (phantom) dilaton field in $n(\ge 4)$-dimensions, based upon the symmetry of the target space for the nonlinear sigma model. Unlike the conventional Einstein-Maxwell-dilaton system, there appears a critical value of the coupling constant for a phantom dilaton field. In the noncritical case, the target space is $\mathbb R\times {\rm SL}(2,\mathbb R)/H$ with the maximal subgroup $H=\{{\rm SO}(2), {\rm SO}(1,1)\}$, whereas in the critical case the target space becomes a symmetric pp-wave and the corresponding K…
We study the thermodynamic properties of a black hole and the Hawking-Page phase transition in the asymptotically anti--de Sitter spacetime in the dilatonic Einstein-Gauss-Bonnet theory of gravitation. We show how the higher-order curvature terms can influence both the thermodynamic properties and the phase transition. We evaluate both heat capacity and free energy difference to determine the local and global thermodynamic stabilities, respectively. We find that the phase transition occurs from the thermal anti--de Sitter to a small spherical black hole geometry and occurs to a hyperbolic blac…
For the bosonic gravi-dilaton system, we provide systematical approaches to construct non-perturbative string cosmological solutions without curvature singularities, which can match the perturbative solution to any order in $α^{\prime}$ expansion. When higher order $α^{\prime}$ corrections are calculated, they can be straightforwardly plugged in to generate compatible non-perturbative evolutions without curvature singularities. We also give a (phenomenological) map between $α^{\prime}$ corrected EOM and loop corrected EOM. This map enables us to easily generate a loop corrected solution from a…
In this paper we consider a static and regular fluid generating a locally spherically symmetric and time-independent space-time and calculate the leading quantum corrections to the metric to first order in curvature. Starting from a singularity free classical solution of general relativity, we show that singularities can be introduced in the curvature invariants by quantum gravitational corrections calculated using an effective field theory approach to quantum gravity. We identify non-trivial conditions that ensure that curvature invariants remain singularity free to leading order in the curva…
Charged particle dynamics in singular spacetimes: hydrogenic mapping and curvature-corrected thermodynamics
Erzurum Technical University（埃尔祖鲁姆理工大学）；Hakkari University（哈卡里大学）；Eastern Mediterranean University（东地中海大学）；University of Hradec Králové（赫拉德茨-克拉洛韦大学）；Khazar University（哈萨尔大学）
The presented thesis is devoted to the study of instabilities of compact objects within the Einstein-Gauss-Bonnet theory. This theory includes higher-order corrections in curvature, which are inspired by the low energy limit of string theory. We study linear instability of higher-dimensional black holes in the de Sitter universe. The time-domain picture allows us to obtain the parametric region of stability for the gravitational perturbations in all three channels, i.e., for scalar-type, vector-type, and tensor-type perturbations. We observed that while the scalar and tensor channels show inst…
Quantum gravitational corrections at third-order curvature, acoustic analog black holes and their quasinormal modes
Dipartimento di Fisica e Astronomia, Università di Bologna（博洛尼亚大学物理与天文学系）；I.N.F.N., Sezione di Bologna, I.S. FLAG（意大利国家核物理研究所博洛尼亚分部 FLAG 研究所）；Center for Natural and Human Sciences, Federal University of ABC（ABC 联邦大学自然与人类科学中心）；Center of Mathematics, Federal University of ABC（ABC 联邦大学数学中心）
String theory enjoys an elevated role among quantum gravity theories, since it seems to be the most consistent UV completion of general relativity and the Standard Model. However, it is hard to verify the existence of this underlying theory on terrestrial accelerators. One way to probe string theory is to study its imprints on the low-energy effective inflationary Lagrangian, which are quantified in terms of high energy correction terms. It is highly likely, thus, to find higher order curvature terms combined with string moduli, that is scalar fields, since both these types of interactions and…
Primordial blackholes formed in the early Universe via gravitational collapse of over-dense regions may contribute a significant amount to the present dark matter relic density. Inflation provides a natural framework for the production mechanism of primordial blackholes. For example, single field inflation models with a fine-tuned scalar potential may exhibit a period of ultra-slow roll, during which the curvature perturbation may be enhanced to become seeds of the primordial blackholes formed as the corresponding scales reenter the horizon. In this work, we propose an alternative mechanism fo…
