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We propose a novel first-order formalism for a type of K-brane system. An example solution is presented and studied. We illustrate how the deviation parameter affects the properties of the model, such as the stability of the solutions and the localization of fermions and gravitons. We argue that our solution is stable against linear perturbations. The tensor zero mode of a graviton can be localized on the brane while the scalar zero mode cannot. The localization condition for fermion is also discussed. [ABSTRACT FROM AUTHOR]

It is known that by introducing the Yukawa coupling between the fermion and the background scalar field, a bulk spin-half fermion can be localized on general Randall-Sundrum braneworlds generated by a kinklike background scalar. However, this localization mechanism does not work anymore for Randall-Sundrum braneworlds generated by a scalar whose configuration is an even function of the extra dimension. In this paper, we present a new localization mechanism for spin-half fermions for such a class of braneworld models, in which extra dimension has the topology Sl/Z2. By two examples, it is shown that the new localization mechanism produces interesting results. In the first model with the brane generated by two scalars, the zero mode of the left-handed fermion is localized on the brane and there is a mass gap between the fermion zero mode and excited KK modes. In the second model with the brane generated by a dilaton scalar, the zero mode of the left- or right-chiral fermion can be localized on the brane and there is no mass gap. [ABSTRACT FROM AUTHOR]

Recently, Lü and Pope proposed critical gravities in [Phys. Rev. Lett. 106, 181302 (2011)]. In this paper we construct analytic brane solutions in critical gravity with matter. The Gibbons-Hawking surface term and junction condition are investigated, and the thin and thick brane solutions are obtained. All these branes are embedded in five-dimensional anti-de Sitter spacetimes. Our solutions are stable against scalar perturbations, and the zero modes of scalar perturbations cannot be localized on the branes. [ABSTRACT FROM AUTHOR]

We study the linearization of a class of thick K-branes, namely, four-dimensional domain walls generated by a scalar field with particular nonstandard kinetic terms. The master equations for linear perturbations are derived from the point of view of both dynamical equations and quadratic action. The spectra of the canonical normal modes are studied using supersymmetric quantum mechanics. Our results indicate that the scalar perturbation is nonlocalizable in general. Conditions for stable K-branes are also found. [ABSTRACT FROM AUTHOR]

Recently, a new spin-1/2 fermionic quantum field with mass dimension one in four dimensions-Elko field λ was introduced as a candidate of dark matter. In this paper, we investigate the localization of 5D Elko spinors on Minkowski branes by presenting the equation of the Elko KK modes. For the 5D free massless Elko field, the zero mode can be localized on Randall-Sundrum thin branes but cannot be localized on the majority of thick branes. There do not exist bound massive KK modes on all these branes. If the 5D mass term is introduced, there will exist a bound Elko_zero mode in the Randall-Sundrum brane model. And when we introduce the Yukawa type coupling ηφ²λλ with φ the background scalar field, the Elko zero mode can be localized on some special thick branes with a particular coupling constant η. Nevertheless, the massive KK modes still cannot be localized on these branes. These results are very different from that of the conventional Dirac spinor field and the scalar field. [ABSTRACT FROM AUTHOR]

In this paper, we investigate thick branes with a nonminimally coupled background scalar field, whose solution is a single-kink or a double-kink. The effects of the nonminimal coupling constant &xgr; on the structure of the thick branes and the localization of gravity, fermions, scalars, and vectors are discussed. It is shown that each brane will split into two sub-branes as increasing the nonminimal coupling constant &xgr;. By investigating the tensor perturbation equations of gravity and the general covariant Dirac equation of fermions, we find that both the gravity zero mode and left-chiral fermion zero mode are localized at the center of the single-kink branes and localized between the two sub-branes generated by the double kink, which indicates that the constant &xgr; does not effect the localization of these zero modes. However, the zero mode of scalars is localized on each sub-brane (for both single-kink and double-kink branes) when £ is larger than its critical value &xgr;0. The effects of the nonminimal coupling constant £ on the resonances of gravity and fermions with finite lifetime on the branes are also discussed. [ABSTRACT FROM AUTHOR]

We construct a deformed brane solution generated by a double-kink scalar field and a dilaton scalar field. In this brane scenario the extra dimension is finite, which is due to the introduction of the dilaton field with a special form. The finity of the extra dimension will result in the localization of the zero mode for the vector fields, while the localization of the Kalb-Ramond fields depends on the coupling to the dilaton. For the fermion fields, with different values of the dilaton-fermion coupling constant, there are three types of the effective potential for the fermion Kaluza-Klein modes. Moreover, we investigate the effect of the deformation of the brane on the localization, and find that the number of the resonances will increase with the distances of the two sub-branes. [ABSTRACT FROM AUTHOR]

In the context of a complex scalar field coupled to Einstein gravity theory, we present a novel family of solutions of Kerr black holes with excited state scalar hair inspired by the work of Herdeiro and Radu in [Phys. Rev. Lett. 112, 221101 (2014)], which can be regarded as numerical solutions of rotating compact objects with excited scalar hair, including boson stars and black holes. In contrast to Kerr black holes with ground state scalar hair, we find that the first excited Kerr black holes with scalar hair have two types of nodes, including radial nr=1 and angular nθ=1 nodes. Moreover, in the case of both nodes the curves of the mass versus the frequency form nontrivial loops. Furthermore, we also show the numerical results of the second excited states with even parity, and find that the curves can be divided into two kinds: closed and open loops. We also study the dependence of the horizon area on angular momentum and Hawking temperature in these excited states. [ABSTRACT FROM AUTHOR]

We consider the scalar perturbations of Eddington-inspired Born-Infeld braneworld models in this paper. The dynamical equation for the physical propagating degree of freedom ξ(xμ,y) is achieved by using the Arnowitt-Deser-Misner decomposition method: F1(y)∂²yξ+F2(y)∂yξ+∂μ∂μξ=0. We conclude that the solution is tachyonic-free and stable under scalar perturbations for F1(y)>0 but unstable for F1(y)<0. The stability of a known analytic domain wall solution with the warp factor given by a(y)=sech¾p(ky) is analyzed and it is shown that only the solution for 0

We study the large scale structure formation in Eddington-inspired Born-Infeld (EiBI) gravity. It is found that the linear growth of scalar perturbations in EiBI gravity deviates from that in general relativity for modes with large wave numbers (k), but the deviation is largely suppressed with the expansion of the Universe. We investigate the integrated Sachs-Wolfe effect in EiBI gravity, and find that its effect on the angular power spectrum of the anisotropy of the cosmic microwave background is almost the same as that in the Lambda-cold dark matter (ΛCDM) model. We further calculate the linear matter power spectrum in EiBI gravity and compare it with that in the ΛCDM model. Deviation is found on small scales (k > 0.1 h Mpc-1), which can be tested in the future by observations from galaxy surveys. [ABSTRACT FROM AUTHOR]

Motivated by the recent research of black holes with NUT charge, we investigate the validity of the weak cosmic censorship conjecture for the Kerr-Taub-NUT black hole with a test massive scalar field and a test particle, respectively. For the scalar field scattering gedanken experiment, we consider an infinitesimal time interval process. The result shows that both extremal and near-extremal Kerr-Taub-NUT black holes cannot be overspun. For the test particle thought experiment, the study suggests that the extremal Kerr-Taub-NUT black hole cannot be overspun; while the near-extremal Kerr-Taub-NUT black hole can be overspun. By comparing the two methods, the results indicate the time interval for particles crossing the black hole horizon might be important for consideration of the weak cosmic censorship conjecture. [ABSTRACT FROM AUTHOR]

The Palatini f(|Ω̂|) gravity is a generalized theory of the Eddington-inspired Born-Infeld gravity, where ΩKN≡δKN+bgKLRLN(Γ) is an auxiliary tensor constructed with the spacetime metric g and independent connection Γ. In this paper, we study f(|Ω̂|) theory with f(|Ω̂|)=|Ω̂|1/2+n in the thick brane scenario and give some constraints on the brane model. We finally found an analytic solution of the thick brane generated by a single scalar field. The behavior of the negative energy density denotes the localization of the thick brane at the origin of the extra dimension. In our braneworld, the warp factor is divergent at the boundary of the extra dimension while the brane system is asymptotically anti-de Sitter. It is shown that the tensor perturbation of the brane is stable and the massless graviton is localized on the thick brane. Therefore, the effective Einstein-Hilbert action on the brane can be rebuilt in the low-energy approximation. According to the recent test of the gravitational inverse-square law, we give some constraints on the f(|Ω̂|) brane. [ABSTRACT FROM AUTHOR]

The scalar particle production through a scalar field nonminimally coupled with geometry is investigated in the context of a spatially homogeneous and isotropic Universe. In this paper, to study the evolution of particle production over time in the case of analytical solutions, we focus on a simple Horndeski theory. We first suppose that the Universe is dominated by a scalar field and derive the energy conservation condition. Then, from the thermodynamic point of view, the macroscopic nonconservation of the scalar field energy-momentum tensor can be explained as an irreversible production of the scalar particles. Based on the explanation, we obtain a scalar particle-production rate and the corresponding entropy. Finally, since the Universe, in general, could be regarded as a closed system satisfying the laws of thermodynamics, we naturally impose some thermodynamic constraints on it. The thermodynamic properties of the Universe can provide additional constraints on the simple Horndeski theory. [ABSTRACT FROM AUTHOR]

In order to localize fermions on branes with codimension 1, one usually introduces the Yukawa coupling between fermions and background scalar fields or the recently proposed derivative fermion-scalar coupling [Phys. Rev. D 89, 086001 (2014)]. In this paper, we explore the coupling between a spinor field Ψ and the scalar curvature of spacetime R, η Ψ ΓM ∂M F (R) γ5 ¯ Ψ with F (R) a function of R, to investigate the localization of the fermion. Because of the Z2 symmetry of the extra dimension, the new coupling mechanism proposed here can easily deal with the problem encountered in the Yukawa coupling with even background scalar fields. More importantly, the new mechanism will also work for branes without background scalar fields. By investigating three examples, we find that fermions can be localized on branes with the new mechanism. We also study the case of both couplings of fermions, those with the scalar field and those with the curvature. [ABSTRACT FROM AUTHOR]