Negative Tension Brane Research Articles

Big Rip in Swiss-cheese brane-worlds with cosmic transit

We study the Big Rip scenario in Swiss-cheese brane-worlds. The results obtained have been found to be independent of the value of the cosmological constant Λ whether it is positive, negative, or zero. Negative tension branes are not allowed in the current model. There is a sign flipping in cosmic pressure corresponding to the sign flipping in the deceleration parameter from positive to negative. The evolution of the equation of state parameter shows the presence of three phases: the matter-dominant decelerating era, the accelerated-Quitessence phase, and the phantom phase. The evolution of the potential and kinetic term also shows a change of sign. The energy conditions and cosmographic parameters have also been investigated.

AdS/BCFT from conformal bootstrap: construction of gravity with branes and particles

We initiate a conformal bootstrap program to study AdS3/BCFT2 with heavy excitations. We start by solving the bootstrap equations associated with two-point functions of scalar/non-scalar primaries under the assumption that one-point functions vanish. These correspond to gravity with a brane and a non-spinning/spinning particle where the brane and the particle do not intersect with each other. From the bootstrap equations, we obtain the energy spectrum and the modified black hole threshold. We then carefully analyze the gravity duals and find the results perfectly match the BCFT analysis. In particular, brane self-intersections, which are usually considered to be problematic, are nicely avoided by the black hole formation. Despite the assumption to solve the bootstrap equations, one-point functions of scalar primaries can be non-zero in general. We construct the holographic dual for a non-vanishing one-point function, in which the heavy particle can end on the brane, by holographically computing the Rényi entropy in AdS/BCFT. As a bonus, we find a refined formula for the holographic Rényi entropy, which appears to be crucial to correctly reproduce the boundary entropy term. On the other hand, we explain why one-point functions of non-scalar primaries always vanish from the gravity dual. The non-sensitivity of the solution for the bootstrap equation to the boundary entropy helps us to construct gravity duals with negative tension branes. We also find a holographic dual of boundary primaries.

Thin-Shell Wormholes in Einstein and Einstein–Gauss–Bonnet Theories of Gravity

We review recent works on the possibility for eternal existence of thin-shell wormholes on Einstein and Einstein–Gauss–Bonnet gravity. We introduce thin-shell wormholes that are categorized into a class of traversable wormhole solutions. After that, we discuss stable thin-shell wormholes with negative-tension branes in Reissner–Nordström–(anti) de Sitter spacetimes in d-dimensional Einstein gravity. Imposing Z2 symmetry, we construct and classify traversable static thin-shell wormholes in spherical, planar and hyperbolic symmetries. It is found that the spherical wormholes are stable against spherically symmetric perturbations. It is also found that some classes of wormholes in planar and hyperbolic symmetries with a negative cosmological constant are stable against perturbations preserving symmetries. In most cases, stable wormholes are found with the appropriate combination of an electric charge and a negative cosmological constant. However, as special cases, there are stable wormholes even with a vanishing cosmological constant in spherical symmetry and with a vanishing electric charge in hyperbolic symmetry. Subsequently, the existence and dynamical stability of traversable thin-shell wormholes with electrically neutral negative-tension branes is discussed in Einstein–Gauss–Bonnet theory of gravitation. We consider radial perturbations against the shell for the solutions, which have the Z2 symmetry. The effect of the Gauss–Bonnet term on the stability depends on the spacetime symmetry.

The possibility of a stable flat dark energy-dominated Swiss-cheese brane-world universe

In this paper, we study the possibility of obtaining a stable flat dark energy-dominated universe in a good agreement with observations in the framework of Swiss-cheese brane-world cosmology. Two different brane-world cosmologies with black strings have been introduced for any cosmological constant [Formula: see text] using two empirical forms of the scale factor. In both models, we have performed a fine-tuning between the brane tension and the cosmological constant so that the Equation of state (EoS) parameter [Formula: see text] for the current epoch, where the redshift [Formula: see text]. We then used these fine–tuned values to calculate and plot all parameters and energy conditions. The deceleration–acceleration cosmic transition is allowed in both models, and the jerk parameter [Formula: see text] at late-times. Both solutions predict a future dark energy-dominated universe in which [Formula: see text] with no crossing to the phantom divide line. While the pressure in the first solution is always negative, the second solution predicts a better behavior of cosmic pressure where the pressure is negative only in the late-time accelerating era but positive in the early-time decelerating era. Such a positive-to-negative transition in the evolution of pressure helps to explain the cosmic deceleration–acceleration transition. Since black strings have been proved to be unstable by some authors, this instability can actually reflect doubts on the stability of cosmological models with black strings (Swiss-cheese type brane-worlds cosmological models). For this reason, we have carefully investigated the stability through energy conditions and sound speed. Because of the presence of quadratic energy terms in Swiss-cheese type brane-world cosmology, we have tested the new nonlinear energy conditions in addition to the classical energy conditions. We have also found that a negative tension brane is not allowed in both models of the current work as the energy density will no longer be well defined.

Localization and mass spectra of various matter fields on Weyl thin brane

It has been shown that the thin brane model in a five-dimensional Weyl gravity can deal with the wrong-signed Friedmann-like equation in the Randall–Sundrum-1 (RS1) model. In the Weyl brane model, there are also two branes with opposite brane tensions, but the four-dimensional graviton (the gravity zero mode) is localized near the negative tension brane, while our four-dimensional universe is localized on the positive tension brane. In this paper, we consider the mass spectra of various bulk matter fields (i.e., scalar, vector, and fermion fields) on the Weyl brane. It is shown that the zero modes of those matter fields can be localized on the positive tension brane under some conditions. The mass spectra of the bulk matter fields are equidistant for the higher excited states, and relatively sparse for the lower excited states. The size of the extra dimension determines the gap of the mass spectra. We also consider the correction to the Newtonian potential in this model and it is proportional to 1/r^{3}.

Does the Gauss–Bonnet term stabilize wormholes?

The effect of the Gauss–Bonnet term on the existence and dynamical stability of thin-shell wormholes as negative tension branes is studied in the arbitrary-dimensional spherically, planar and hyperbolically symmetric spacetimes. We consider radial perturbations against the shell for the solutions that have the Z2 symmetry and admit the general relativistic limit. It is shown that the Gauss–Bonnet term shrinks the parameter region that admits static wormholes. The effect of the Gauss–Bonnet term on the stability depends on the spacetime symmetry. For planar symmetric wormholes, the Gauss–Bonnet term does not affect their stability. If the coupling constant is positive but small, the Gauss–Bonnet term tends to destabilize spherically symmetric wormholes, while it stabilizes hyperbolically symmetric wormholes. The Gauss–Bonnet term can destabilize hyperbolically symmetric wormholes as a non-perturbative effect, but spherically symmetric wormholes cannot be stable.

Negative tension branes as stable thin shell wormholes

We investigate negative tension branes as stable thin shell wormholes (TSWs) in Reissner–Nordström-(anti) de Sitter spacetimes in d dimensional Einstein gravity. Imposing Z2 symmetry, we construct and classify traversable static TSWs in spherical, planar (or cylindrical) and hyperbolic symmetries. In spherical geometry, we find the higher dimensional counterpart of Barceló and Visser’s wormholes, which are stable against spherically symmetric perturbations. We also find the classes of TSWs in planar and hyperbolic symmetries with a negative cosmological constant, which are stable against perturbations preserving symmetries. In most cases, stable wormholes are found with the combination of an electric charge and a negative cosmological constant. However, as special cases, we find stable wormholes even with vanishing cosmological constant in spherical symmetry and with vanishing electric charge in hyperbolic symmetry.

Localization and mass spectra of various matter fields on scalar-tensor brane

Recently, a new scalar-tensor braneworld model was presented in [Phys. Rev. D 86 (2012) 127502]. It not only solves the gauge hierarchy problem but also reproduces a correct Friedmann-like equation on the brane. In this new model, there are two different brane solutions, for which the mass spectra of gravity on the brane are the same. In this paper, we investigate localization and mass spectra of various bulk matter fields (i.e., scalar, vector, Kalb-Ramond, and fermion fields) on the brane. It is shown that the zero modes of all the matter fields can be localized on the positive tension brane under some conditions, and the mass spectra of each kind of bulk matter field for the two brane solutions are different except for some special cases, which implies that the two brane solutions are not physically equivalent. When the coupling constants between the dilaton and bulk matter fields take special values, the mass spectra for both solutions are the same, and the scalar and vector zero modes are localized on the negative tension brane, while the KR zero mode is still localized on the positive tension brane.

Localization of q-form fields on [formula omitted] branes

In this paper, we investigate localization of a free massless q-form bulk field on thin and thick AdSp+1 branes with codimension one. It is found that the zero mode of the q-form field with q>(p+2)/2 can be localized on the thin negative tension brane, which is different from the flat brane case given in Fu et al. (2012) [57]. For the thick AdSp+1 branes, the q-form field with q>(p+2)/2 also has a localized zero mode under some conditions. Furthermore, we find that there are massive bound KK modes of the q-form field, which are localized on this type p-branes.

Dynamics of interacting generalized cosmic Chaplygin gas in brane-world scenario

In this work we explore the background dynamics when dark energy is coupled to dark matter with a suitable interaction in the universe described by brane cosmology. Here DGP and the RSII brane models have been considered separately. Dark energy in the form of Generalized Cosmic Chaplygin gas is considered. A suitable interaction between dark energy and dark matter is considered in order to at least alleviate (if not solve) the cosmic coincidence problem. The dynamical system of equations is solved numerically and a stable scaling solution is obtained. A significant attempt towards the solution of the cosmic coincidence problem is taken. The statefinder parameters are also calculated to classify the dark energy models. Graphs and phase diagrams are drawn to study the variations of these parameters. It is also seen that the background dynamics of Generalized Cosmic Chaplygin gas is consistent with the late cosmic acceleration, but not without satisfying certain conditions. It has been shown that the universe in both the models follows the power law form of expansion around the critical point, which is consistent with the known results. Future singularities were studied and our models were declared totally free from any types of such singularities. Finally, some cosmographic parameters were also briefly studied. Our investigation led to the fact that although Generalized cosmic Chaplygin gas with a far lesser negative pressure compared to other dark energy models, can overcome the relatively weaker gravity of RS II brane, with the help of the negative brane tension, yet for the DGP brane model with much higher gravitation, the incompetency of Generalized cosmic Chaplygin gas is exposed, and it cannot produce the accelerating scenario until it reaches the phantom era.

Five-dimensionalf(R)braneworld models

After incorporating the f(R) gravity into the general braneworld sum rules scope, it is shown that some particular class of warped five dimensional nonlinear braneworld models, which may be interesting for the hierarchy problem solution, still require a negative tension brane. For other classes of warp factors (suitable and not suitable for approaching the hierarchy problem) it is not necessary any negative brane tension in the compactification scheme. In this vein, it is argued that in the bulk f(R) gravity context, some types of warp factors may be useful for approaching the hierarchy problem and for evading the necessity of a negative brane tension in the compactification scheme.

Non-Linear Equation of State and Effective Phantom Divide in Brane Models

Here, DGP model of brane-gravity is analyzed and compared with the standard general relativity and Randall-Sundrum cases using non-linear equation of state. Phantom fluid is known to violate the weak energy condition. In this paper, it is found that this characteristic of phantom energy is affected drastically by the negative brane-tension $\lambda$ of the RS-II model. It is found that in DGP model strong energy condition(SEC) is always violated and the universe accelerates only where as in RS-II model even SEC is not violated for $1 < \rho/\lambda < 2$ and the universe decelerates.

Bare and effective fluid description in brane world cosmology

An effective fluid description, for a brane world model in five dimensions, is discussed for both signs of the brane tension. We found several cosmological scenarios where the effective equation differs widely from the bare equation of state. For universes with negative brane tension, with a bare fluid satisfying the strong energy condition, the effective fluid can cross the barrier ω eff=−1.

Smoothing out negative tension brane

We propose an extension of the five-dimensional gravitational action with an external source in order to allow arbitrary smoothing of the negative tension brane in the Randall–Sundrum model. This extended action can be derived from a model with an auxiliary four form field coupled to the gravity. We point out a further generalization of our model in relation to tachyon condensation. A possible mechanism for radion stabilization in our model is also discussed.

General perturbations for braneworld compactifications and the six dimensional case

Our main objective is to study how braneworld models of higher codimension differ from the 5D case and traditional Kaluza-Klein compactifications. We first derive the classical dynamics describing the physical fluctuations in a wide class of models incorporating gravity, non-Abelian gauge fields, the dilaton and two-form potential, as well as 3-brane sources. Next, we use these results to study braneworld compactifications in 6D supergravity, focusing on the bosonic fields in the minimal model; composed of the supergravity-tensor multiplet and the U(1) gauge multiplet whose flux supports the compactification. For unwarped models sourced by positive tension branes, a harmonic analysis allows us to solve the large, coupled, differential system completely and obtain the full 4D spin-2,1 and 0 particle spectra, establishing (marginal) stability and a qualitative behaviour similar to the smooth sphere compactification. We also find interesting results for models with negative tension branes; extra massless Kaluza-Klein vector fields can appear in the spectra, beyond those expected from the isometries in the internal space. These fields imply an enhanced gauge symmetry in the low energy 4D effective theory obtained by truncating to the massless sector, which is explicitly broken as higher modes are excited, until the full 6D symmetries are restored far above the Kaluza-Klein scale. Remarkably, the low energy effective theory does not seem to distinguish between a compactification on a smooth sphere and these singular, deformed spheres.

NONLINEAR EQUATION OF STATE, COSMIC ACCELERATION AND DECELERATION DURING PHANTOM DOMINANCE

In this paper, the RS-II model of brane gravity is considered for the phantom universe using a nonlinear equation of state. Phantom fluid is known to violate the weak energy condition. It is found that this characteristic of phantom energy is affected drastically by the negative brane tension λ of the RS-II model. It is interesting to see that up to a certain value of energy density ρ satisfying ρ/λ &lt; 1, the weak energy condition is violated and the universe superaccelerates. But, as ρ increases more, only the strong energy condition is violated and the universe accelerates. When 1 &lt; ρ/λ &lt; 2, even the strong energy condition is not violated and the universe decelerates. Expansion of the universe stops when ρ = 2 λ. This is contrary to earlier results of the phantom universe exhibiting acceleration only.

Negative-tension branes and tensionless12brane in boundary conformal field theory

In the framework of boundary conformal field theory we consider a flat unstable $\mathrm{D}p$-brane in the presence of a large constant electromagnetic field. Specifically, we study the case that the electromagnetic field satisfy the following three conditions: (i) a constant electric field is turned on along the ${x}^{1}$ direction (${E}_{1}\ensuremath{\ne}0$); (ii) the determinant of the matrix ($\ensuremath{\eta}+F$) is negative so that it lies in the physical region ($\ensuremath{-}\mathrm{det}(\ensuremath{\eta}+F)&gt;0$); (iii) the 11-component of its cofactor is positive to the large electromagnetic field. In this case, we identify exactly marginal deformations depending on the spatial coordinate ${x}^{1}$. They correspond to tachyon profiles of hyperbolic sine, exponential, and hyperbolic cosine types. Boundary states are constructed for these deformations by utilizing $T$-duality approach and also by directly solving the overlap conditions in BCFT. The exponential type deformation gives a tensionless half brane connecting the perturbative string vacuum and one of the true tachyon vacua, while the others have negative tensions. This is in agreement with the results obtained in other approaches.

GHOSTS AND TACHYONS IN THE FIFTH DIMENSION

We present several solutions for the five-dimensional gravity models in the presence of bulk ghosts and tachyons to argue that these "troublesome" fields can be a useful model-building tool. The ghost-like signature of the kinetic term for a bulk scalar creates a minimum in the scale factor, removing the necessity for a negative tension brane in models with the compactified fifth dimension. It is shown that the model with the positive tension branes and a ghost field in the bulk leads to the radion stabilization. The bulk scalar with the variable sign kinetic term can be used to model both positive and negative tension branes of a finite width in the compact dimension. Finally, we present several ghost and tachyon field configurations in the bulk that lead to the localization of gravity in four dimensions, including one solution with the Gaussian profile for the metric, gμν(y) = ημν exp {-αy2}, which leads to a stronger localization of gravity than the Randall–Sundrum model.

Stability and negative tensions in 6D brane worlds

We investigate the dynamical stability of warped, axially symmetric compactifications in anomaly free 6D gauged supergravity. The solutions have conical defects, which we source by 3-branes placed on orbifold fixed points, and a smooth limit to the classic sphere-monopole compactification. Like for the sphere, the extra fields that are generically required by anomaly freedom are especially relevant for stability. With positive tension branes only, there is a strict stability criterion (identical to the sphere case) on the charges present under the monopole background. Thus brane world models with positive tensions can be embedded into anomaly free theories in only a few ways. Meanwhile, surprisingly, in the presence of a negative tension brane the stability criteria can be relaxed. We also describe in detail the geometries induced by negative tension codimension two branes.

Bouncing negative-tension branes

Braneworlds, understood here as double domain wall spacetimes, can be described in terms of a linear harmonic function, with kinks at the locations of the boundary branes. In a dynamical setting, there is therefore the risk that the boundary brane of negative tension, at whose location the value of the harmonic function is always lowest, can encounter a zero of this harmonic function, corresponding to the formation of a singularity. We show that for certain types of brane-bound matter this singularity can be avoided, and the negative-tension brane can shield the bulk spacetime from the singularity by bouncing back smoothly before reaching the singularity. In our analysis we compare the 5- and 4-dimensional descriptions of this phenomenon in order to determine the validity of the moduli space approximation.