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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]

Recently, inspired by Eddington's theory, an alternative gravity called Eddington-inspired Born-Infeld gravity was proposed by Bañados and Ferreira. It is equivalent to Einstein's general relativity in vacuum, but deviates from it when matter is included. Interestingly, it seems that the cosmological singularities are prevented in this theory. Based on the new theory, we investigate a thick brane model with a scalar field presenting in the five-dimensional background. A domain wall solution is obtained, and further, we find that at low energy the four-dimensional Einstein gravity is recovered on the brane. Moreover, the stability of gravitational perturbations is ensured in this model. [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 this paper, we obtain a new solution of a brane made up of a scalar field coupled to a dilaton. There is a unique parameter b in the solution, which decides the distribution of the energy density and will affect the localization of bulk matter fields. For free vector fields, we find that the zero mode can be localized on the brane. And for vector fields coupled with the dilaton via eτπFMNFMN, the condition for localizing the zero mode is τ ≥ -√b/3 with 0 < b ≤ 1, or τ > - 1/ √3b with b > 1, which includes the case τ = 0. While the zero mode for free Kalb-Ramond fields cannot be localized on the brane, if only we introduce a coupling between the Kalb-Ramond fields and the dilaton via eζπHMNLHMNL. When the coupling constant satisfies ζ > 1/√3b with b ≥ 1 or ζ > 2-b / √3b, with 0 < b < 1, the zero mode for the KR fields can be localized on the brane. For spin half fermion fields, we consider the coupling ηΨ;̄eλππΨ between the fermions and the background scalars with positive Yukawa coupling η. The effective potentials for both chiral fermions have three types of shapes decided by the relation between the dilaton-fermion coupling constant λ and the parameter b. For λ ≥ - 1 √3b, the zero mode of left-chiral fermion can be localized on the brane. While for λ > - 1 √3b with b > 1 or 1 / √3b < λ <- √b/3 with 0 < b ≤ 1, the zero mode for left-chiral fermion also can be localized. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the localization and the mass spectra of gravity and various bulk matter fields on a thick anti--de Sitter (ADS) brane, by presenting the mass-independent potentials of the Kaluza-Klein (KK) modes in the corresponding Schrödinger equations. For gravity, the potential of the KK modes tends to infinity at the boundaries of the extra dimension, which leads to an infinite number of the bound KK modes. Although the gravity zero mode cannot be localized on the AdS brane, the massive modes are trapped on the brane. The scalar perturbations of the thick AdS brane have been analyzed, and the brane is stable under the scalar perturbations. For spin-0 scalar fields and spin- 1 vector fields, the potentials of the KK modes also tend to infinity at the boundaries of the extra dimension, and the characteristic of the localization is the same as the case of gravity. For spin-1/2 fermions, by introducing the usual Yukawa coupling ηΨ̄φΨ with the positive coupling constant η, the four-dimensional massless left-chiral fermion and massive Dirac fermions are obtained on the AdS thick brane. [ABSTRACT FROM AUTHOR]

In this paper, we mainly investigate the problems of resonances of massive Kaluza-Klein (KK) fermions on a single scalar constructed thick brane with a piecewise warp factor matching smoothly. The distance between two boundaries and the other parameters are determined by one free parameter through three junction conditions. For the generalized Yukawa coupling ηΨ¯φkΨ with odd k = 1, 3, 5,…, the mass eigenvalue m, width Γ, lifetime π, and maximal probability Pmax of fermion resonances are obtained. Our numerical calculations show that the brane without internal structure also favors the appearance of resonant states for both left- and right-handed fermions. The scalar-fermion coupling and the thickness of the brane influence the resonant behaviors of the massive KK fermions. [ABSTRACT FROM AUTHOR]

The recent detections of the gravitational wave (GW) event GW170817 and its electromagnetic counterpart GRB 170817A produced by a binary neutron star (NS) merger is a new milestone of multimessenger astronomy. The time interval between these two signals has attracted widespread attention from physicists. In the braneworld scenario, GWs could propagate through the bulk while electromagnetic waves (EMWs) are bounded on the brane, i.e., our Universe. Therefore, the trajectories of GWs and EMWs may follow different pathes. If GWs and EMWs are originated simultaneously from the same source on the brane, they are expected to arrive at the observer successively. Consequently, the time delay between GW170817 and GRB 170817A may carry the information of the extra dimension. In this paper, we try to investigate the phenomenon in the context of a five-dimensional dS (dS5) spacetime. We first study two special Universe models, i.e., de Sitter and Einstein-de Sitter models, and calculate the gravitation horizon radius in each case. For the real Universe, we then consider the ΛCDM model. Our results show that for the de Sitter model of the Universe, the dS5 radius could not contribute to the time delay. With the data of the observation, we constrain the dS5 radius to ℓ≳7.5×10² Tpc for the Einstein-de Sitter model and ℓ≳2.4×10³ Tpc for the ΛCDM model. After considering the uncertainty in the source redshift and the time-lags given by different astrophysical processes of the binary NS merger, we find that our constraints are not sensitive to the redshift in the range of (0.005, 0.01) and the time-lag in the range of (-100 s, 1.734 s). [ABSTRACT FROM AUTHOR]

We investigate the thick brane model in Palatini fill) gravity. The brane is generated by a real scalar field with a scalar potential. We solve the system analytically and obtain a series of thick brane solutions for the f(R) = R + aR²-brane model. It is shown that tensor perturbations of the metric are stable for df(R)/dR > 0. For nonconstant curvature solutions, the graviton zero mode can be localized on the brane, which indicates that the four-dimensional gravity can be recovered on the brane. The mass spectrum of graviton Kaluza-Klein modes and their corrections to the Newtonian potential are also discussed. [ABSTRACT FROM AUTHOR]

The stability and localization of the gravitational perturbations for a special brane system in Eddingtoninspired Born-Infeld gravity were studied in Liu et al. [Phys. Rev. D 85, 124053 (2012)]. In this paper, we show that the gravitational perturbations for a general brane system are stable, the four-dimensional graviton (massless KK gravitan) can be localized on the brane, and the mass spectra of massive KK gravitons are gapless and continuous. Two models are constructed as examples. In the first model, which is a generalization of Liu et al. [Phys. Rev. D 85, 124053 (2012)], the brane has no inner structure and there is no gravitational resonance (quasilocalized KK gravitons). In the second one, the background scalar field is a double kink when the parameter in the model approaches its critical value. Correspondingly, the brane has inner structure and some gravitational resonances appear. [ABSTRACT FROM AUTHOR]

It is known that a five-dimensional free vector field AM cannot be localized on Randall-Sundrum (RS)-like thick branes--namely, the thick branes embedded in asymptotic anti-de Sitter spacetime. To localize a vector field on the RS-like thick brane, an extra coupling term should be introduced. We generalize the geometrical coupling mechanism by adding two mass terms (αRgMNAMAN+βRMNAMAN) to the action. We decompose the fundamental vector field AM into three parts: transverse vector part Aμ and scalar parts ϕ and A5. Then we find that the transverse vector part Aμ decouples from the scalar parts. To eliminate the tachyonic modes of Aμ, the two coupling parameters α and β should satisfy a relation. Combining the restricted condition, we can get a combination parameter as γ=3/2±1+12α. Only if γ>1/2 can the zero mode of Aμ be localized on the RS-like thick brane. We also investigate the resonant character of the vector part Aμ for a general RS-like thick brane with a warp factor A(z)=-ln(1+k²z²)/2 by choosing the relative probability method. The results show that the massive resonant Kaluza-Klein modes can exist only for γ>3. The number of resonant Kaluza-Klein states increases with the combination parameter γ, and the lifetime of the first resonant state can be as long as our Universe's. This indicates that the vector resonances might be considered one of the candidates of dark matter. Combining the conditions of experimental observations, the constraint shows that the parameter k has a lower limit with k≳10-17 eV, the combination parameter γ should be greater than 57, and, accordingly, the mass of the first resonant state should satisfy m1≳10-15 eV. [ABSTRACT FROM AUTHOR]

Horndeski theory is the most general scalar-tensor theory retaining second-order field equations, although the action includes higher-order terms. This is achieved by a special choice of coupling constants. In this paper, we investigate the thick brane system in reduced Horndeski theory, especially the effects of the nonminimal derivative coupling and the cubic Galileon term on thick brane. First, the equations of motion are presented and a set of analytic background solutions are obtained. Then, the effects of these two terms on the thick brane are analyzed. It is found that the background solutions become asymmetric with the presence of the cubic Galileon term. However, the energy density of the thick brane is still symmetric with or without this term and splits with the presence of the nonminimal derivative coupling. The stability of the thick brane under tensor perturbation is also considered. It is shown that the tachyon is absent and the graviton zero mode can be localized on the brane. The localized graviton zero mode recovers the four-dimensional Newtonian potential and the presence of the nonminimal derivative coupling results in a splitting of its wave function. Besides, the presence of the cubic Galileon term results in the asymmetry of the effective potential and zero mode of the graviton. The correction of the massive graviton Kaluza-Klein modes to the Newtonian potential is also analyzed briefly. [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]

In this paper, we investigate the braneworld scenario in f(T) gravity with a K-field as the background field. We consider various different specific forms of f(T) gravity and K-field and find a general way to construct the braneworld model. Based on our solutions, the split of branes is investigated. In addition, the stability of the braneworld is studied by investigating the tensor perturbation of the vielbein. [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]