Generalised Ellis–Bronnikov wormholes embedded in warped braneworld background and energy conditions

Ellis–Bronnikov (EB) wormholes require violation of null energy conditions at the ‘throat’. This problem was cured by a simple modification of the ‘shape function’, which introduces a new parameter $$m\ge 2$$ m ≥ 2 ($$m=2$$ m = 2 corresponds to the EB model). This leads to a generalised (GEB) version. In this work, we consider a model where the GEB wormhole geometry is embedded in a five dimensional warped background. We studied the status of all the energy conditions in detail for both EB and GEB embedding. We present our results analytically (wherever possible) and graphically. Remarkably, the presence of decaying warp factor leads to satisfaction of weak energy conditions even for the EB geometry, while the status of all the other energy conditions are improved compared to the four dimensional scenario. Besides inventing a new way to avoid the presence of exotic matter, in order to form a wormhole passage, our work reveals yet another advantage of having a warped extra dimension.

Internal structure of cuscuton Bloch brane

This work deals with thick branes in bulk with a single extra dimension modeled by a two-field configuration. We first consider the inclusion of the cuscuton to also control the dynamics of one of the fields and investigate how it contributes to change the internal structure of the configuration in two distinct situations, with the standard and the asymmetric Bloch brane. The results show that the branes get a rich internal structure, with the geometry presenting a novel behavior which is also governed by the parameter that controls the strength of the cuscuton term. We also study the case where the dynamics of one of the two fields is only described by the cuscuton. All the models support analytical solutions which are stable against fluctuations in the metric, and the main results unveil significant modifications in the warp factor and energy density of the branes.

Gravitational resonances on f(T)-branes

In this work, we investigate the gravitational resonances in various f(T)-brane models with the warp factor $$\text {e}^{A(y)}=\tanh \big (k(y+b)\big )-\tanh \big (k(y-b)\big )$$ e A ( y ) = tanh ( k ( y + b ) ) - tanh ( k ( y - b ) ) , where f(T) is an arbitrary function of the torsion scalar T. For three kinds of f(T), we give the solutions to the system. Besides, we consider the tensor perturbation of the vielbein and obtain the effective potentials by the Kaluza–Klein (KK) decomposition. Then we analyze what kind of effective potential can produce the gravitational resonances. The effects of different parameters on the gravitational resonances are analyzed. The lifetimes of the resonances could be long enough as regards the age of our universe in some ranges of the parameters. This indicates that the gravitational resonances might be considered as one of the candidates for dark matter. Combining the current experimental observations, we constrain the parameters for these brane models.

Warping Effects in Strongly Perturbed Metrics

A technique devised some years ago permits us to develop a theory regarding a regime of strong perturbations. This translates into a gradient expansion that, at the leading order, can recover the Belinsky-Kalathnikov-Lifshitz solution for general relativity. We solve exactly the leading order Einstein equations in a spherical symmetric case, assuming a Schwarzschild metric under the effect of a time-dependent perturbation, and we show that the 4-velocity in such a case is multiplied by an exponential warp factor when the perturbation is properly applied. This factor is always greater than one. We will give a closed form solution of this factor for a simple case. Some numerical examples are also given.

On α′-effects from D-branes in 4d $$ \mathcal{N} $$ = 1

In this work we study type IIB Calabi-Yau orientifold compactifications in the presence of space-time filling D7-branes and O7-planes. In particular, we conclude that α′2gs-corrections to their DBI actions lead to a modification of the four-dimensional $$ \mathcal{N} $$ N = 1 Kähler potential and coordinates. We focus on the one-modulus case of the geometric background i.e. h1,1 = 1 where we find that the α′2gs-correction is of topological nature. It depends on the first Chern form of the four-cycle of the Calabi-Yau orientifold which is wrapped by the D7-branes and O7-plane. This is in agreement with our previous F-theory analysis and provides further evidence for a potential breaking of the no-scale structure at order α′2gs. Corrected background solutions for the dilaton, the warp-factor as well as the internal space metric are derived. Additionally, we briefly discuss α′-corrections from other Dp-branes.

Warping Effects in Strongly Perturbed Metrics

A technique devised some years ago permits to study a theory in a regime of strong perturbations. This translate into a gradient expansion that, at the leading order, can recover the BKL solution. We solve exactly the leading order equations in a spherical symmetric case and we show that the 4-velocity in such a case is multiplied by an exponential warp factor when the perturbation is properly applied. This factor is always greater than one. We will give a closed form solution of this factor for a simple case. Some numerical examples are also given.

The Hamilton-Jacobi equation and holographic renormalization group flows on sphere

We study the Hamilton-Jacobi formulation of effective mechanical actions associated with holographic renormalization group flows when the field theory is put on the sphere and mass terms are turned on. Although the system is supersymmetric and it is described by a superpotential, Hamilton’s characteristic function is not readily given by the superpotential when the boundary of AdS is curved. We propose a method to construct the solution as a series expansion in scalar field degrees of freedom. The coefficients are functions of the warp factor to be determined by a differential equation one obtains when the ansatz is substituted into the Hamilton-Jacobi equation. We also show how the solution can be derived from the BPS equations without having to solve differential equations. The characteristic function readily provides information on holographic counterterms which cancel divergences of the on-shell action near the boundary of AdS.

Non-Kähler deformed conifold, ultraviolet completion and supersymmetric constraints in the baryonic branch

Gravity duals for a class of UV complete minimally supersymmetric nonconformal gauge theories require deformed conifolds with fluxes. However these manifolds do not allow for the standard Kähler or conformally Kähler metrics on them, instead the metrics are fully non-Kähler. We take a generic such configuration of a non-Kähler deformed conifold with fluxes and ask what constraints do supersymmetry impose in the baryonic branch. We study the supersymmetry conditions and show that for the correct choices of the vielbeins and the complex structure all the equations may be consistently solved. The constraints now lead not only to the known cases in the literature but also to some new backgrounds. We also show how geometric features of these backgrounds, including the overall warp-factor and the resolution parameters, can be seen on the field theory side from perturbative “probe-brane” type calculations by Higgsing the theory and studying one-loop 4-point functions of vector and chiral multiplets. Finally we discuss how UV completions of these gauge theories may be seen from our setup, both from type IIB as well as from the T-dual type IIA brane constructions.

A solution to the possible increment in velocity than that of light

Imagine taking grasp the larger distances in the scale of Mega-Parsec or Giga-Parsec and navigating through tunnels of time. The passageways that I would be shortly describing below are not to be misinterpreted as a wormhole although there are few similarities between the two. Theoretical physics often describes things which are beyond the scope of demonstrating experimentally. Argumently, on a theoretical standard our main weapon is to use mathematics to describe the unseenable beauties of nature. This can be easily demonstrated that a spatial cylinder of a non-trivial topology can be made or constructed across the universe passing from one corner of the observable universe to the other corner. The scale of distance if taken into account would be unimaginable and therefore, if any normal, like today’s jet engines or rocket engines are used to circumnavigate through the tunnels then the time scale that’s needed would be at least a billion years or so, million in some cases where the distances are quite small, but although being small, in theoretical cosmology small is accounted for a very arbitrarily large distances by rounding distances thereby giving them a name like ‘light years’, ‘parsecs’, etcetera. The key ingredient or the pickle used to taste up the journey by reducing the distances is by implementation of the warping of space within that tunnel, so that space gets so much twisted inside it, that the present would get unfolded into past and future and also the warping induces such a spatial shortcut, such that CTC’s or closed timelike curves tends to appear in between the cylinder shrinking the limit of ‘mega-parsecs’ to almost nothing at all. Therefore, the play with the distances, we have to manipulate the geometry of space-time, making the notion of time and space smaller and smaller until the point of departing stands a little next to post of arriving. And we have to remember that our weapon for curvature is theoretical physics and abstract mathematics. Gravity is not so important here as because it’s not like a ‘black hole’ without an event horizon or ‘Einstein-Rosen bridges’ but rather this is a simple 3-dimensional topological construction needed to make a ‘mega-parsec’ across cylinder in space and time and alter the geometry of this tunnel in such a way that there exists a ‘warp factor’ and that ‘warp factor’ would tell us precisely how much less time we can take through the tunnel to go from one point of universe to other keeping speed of light in vacuum ‘c’ as the limit paving the way for a real life time machines. Who hasn’t wondered to explore the vast cosmic distances physically rather than visually with the help of space telescopes? But, to do this, we have to construct a warped passageway that is not of higher dimensions but within the limits of our observable dimensions and thereby warping the space inside it in such a clever way so that large distances appears tiny or none at all. The main objective lies in the transformation of a linear velocity to an angular velocity provided that transformation would occur only when the linear velocity crosses the speed of the light thereby the extra or additional velocity that contributes to the existing velocity would no longer contribute in a linear way rather in an angular way creating a cylindrical domain in space-time and the warp factor related in the angular motion of the additional increment in linear velocity warps the space-time inside the cylinder with the aforesaid radius permitting the creation of CTC’s or closed timelike curves which would ultimately help in the shrinking of distances between the place of journey and destination paving the way for faster than time travel without the need for exotic matters or negative energies.