Randall-Sundrum Research Articles

Shaft inflation in Randall-Sundrum model

Shaft inflation is a model in which the inflaton potential approaches a plateau far from the origin, while it mimics chaotic inflation near the origin. Meanwhile, the Randall-Sundrum type II model (RSII) is an interesting extra-dimensional model to study cosmological phenomenology. In this paper, we study shaft inflation in the RSII model. We find that the predictions are in excellent agreement with observation. The fundamental five-dimensional Planck scale is found to be M 5 ≃ 1016 GeV, which is consistent with the lower bound M 5 ≳ 109 GeV obtained from experimental Newtonian gravitational bound. This is an important result that can be used to explore further the implications of extra dimension in other contexts.

Flavor-violating charged lepton decays in the little Randall-Sundrum model

The little Randall-Sundrum (little RS) model receives significantly stronger constraints from the flavor observables in comparison to the Randall-Sundrum (RS) model. In this paper, we analyze the effect of the electroweak sector in little RS on flavor-changing decays of charged leptons. We compare the predictions of the model with the current limits on the flavor-violating branching ratios of $\ensuremath{\mu}\ensuremath{\rightarrow}eee$, $\ensuremath{\tau}\ensuremath{\rightarrow}eee$, $\ensuremath{\tau}\ensuremath{\rightarrow}\ensuremath{\mu}\ensuremath{\mu}\ensuremath{\mu}$, $\ensuremath{\tau}\ensuremath{\rightarrow}\ensuremath{\mu}ee$, $\ensuremath{\tau}\ensuremath{\rightarrow}e\ensuremath{\mu}\ensuremath{\mu}$, $\ensuremath{\mu}\ensuremath{\rightarrow}e\ensuremath{\gamma}$, and $\ensuremath{\mu}Ti\ensuremath{\rightarrow}eTi$, and we show that the dominant constraint arises from the $\ensuremath{\mu}Ti\ensuremath{\rightarrow}eTi$ process which strongly limits the KK-1 gauge boson mass (${M}_{KK}$) to be $\ensuremath{\gtrsim}30.7\text{ }\text{ }\mathrm{TeV}$. We then derive and show that generalizing the electroweak gauge sector to include the brane localized kinetic term relaxes this constraint to $\ensuremath{\gtrsim}12\text{ }\text{ }\mathrm{TeV}$. Toward the conclusion, we comment on the possibility that the large flavor-violating currents can be mitigated by relaxing the assumption regarding the unnatural thinness and rigidity of the UV brane and discuss the possibility of suppression of these currents in the presence of fat fluctuating branes.

ClonoCluster: A method for using clonal origin to inform transcriptome clustering

Clustering cells based on their high-dimensional profiles is an important data reduction process by which researchers infer distinct cellular states. The advent of cellular barcoding, however, provides an alternative means by which to group cells: by their clonal origin. We developed ClonoCluster, a computational method that combines both clone and transcriptome information to create hybrid clusters that weight both kinds of data with a tunable parameter. We generated hybrid clusters across six independent datasets and found that ClonoCluster generated qualitatively different clusters in all cases. The markers of these hybrid clusters were different but had equivalent fidelity to transcriptome-only clusters. The genes most strongly associated with the rearrangements in hybrid clusters were ribosomal function and extracellular matrix genes. We also developed the complementary tool Warp Factor that incorporates clone information in popular 2D visualization techniques like UMAP. Integrating ClonoCluster and Warp Factor revealed biologically relevant markers of cell identity.

Holographic Complexity of Braneworld in Horndeski Gravity

AbstractThis work investigates the influence of a probe string on a complexity of braneworld according to the CA (Complexity equals action) conjecture within the Horndeski gravity. In the current study, it is considered that scalar fields that source Horndeski gravity have a spatial dependence. In addition, our system contains a particle moving on the boundary, which corresponds to the insertion of a fundamental string in the higher dimensional bulk. Such an effect is given by the Nambu‐Goto term, that also incorporates the time‐dependence and evolution in our system. Both warp factor, scalar field and superpotential values are derived numerically assuming appropriate initial conditions and the growth rate of holographic complexity is analysed within the so‐called Wheeler‐De Witt (WDW) patch with null‐like hypersurfaces present.

Shadows around Sgr A* and M87* as a tool to test gravity theories

In the framework of Randall–Sundrum theory with extra dimension Reissner–Nordstrom black hole solutions with a tidal charge have been found. The shadow around the supermassive black hole in M87 was reconstructed in 2019 based on observations with the Event Horizon Telescope (EHT) in April 2017. In May 2022 the EHT Collaboration presented results of a shadow reconstruction for our Galactic Center. Earlier, for Reissner–Nordstrom metric we derived analytical expressions for shadow size as a function of charge and later generalized these results for a tidal charge case. We discuss opportunities to evaluate parameters of alternative theories of gravity with shadow size estimates done by the EHT Collaboration, in particular, a tidal charge could be estimated from these observations.

A natural model of spontaneous CP violation

We examine the possibility of building a natural non-supersymmetric model of spontaneous CP violation equipped with the Nelson-Barr (NB) mechanism to address the strong CP problem. Our approach is to utilize a doubly composite dynamics where the first confinement of the CFT occurs at the scale of spontaneous CP violation (SCPV) and the second confinement at the TeV scale. A holographic dual description of this 4D set-up via a warped extra dimension with three 3-branes provides an explicit realization of this idea. In this model, radiative corrections to the strong CP phase are well under control, and the coincidence of mass scales, which we generally encounter in NB models, is addressed. Our model also provides an explanation to the quark Yukawa hierarchies, and a solution to the gauge hierarchy problem just as in the usual Randall-Sundrum model with the Higgs being localized on the TeV brane.

Moduli stabilization with bulk scalar in nested doubly warped braneworld model

We examine the modulus stabilization mechanism of a warped geometry model with nested warping. Such a model with multiple moduli is known to offer a possible resolution of the fermion mass hierarchy problem in the Standard Model. A six dimensional doubly warped braneworld model under consideration admits two distinct moduli, with the associated warp factors dynamically generating different physical mass scales on four 3-branes. In order to address the hierarchy problem related to the Higgs mass, both moduli need to be stabilized around their desired values without any extreme fine tuning of parameters. We show that it is possible to stabilize them simultaneously due to the appearence of an effective 4D moduli potential, which is generated by a single massive bulk scalar field having non-zero VEVs frozen on the 3-branes. This gives rise to two scalar radions, one of which has mass slightly below {mathcal {O}}(TeV) and couplings to SM fields proportional to the inverse of its {mathcal {O}}(TeV) VEV, and the other has nearly {mathcal {O}}(M_{Pl}) mass and interactions with SM fields suppressed by the Planck scale. We also discuss how the entire mechanism can possibly be understood from a purely gravitational point of view, with higher curvature f(R) contributions in the bulk automatically providing a scalar degree of freedom that can serve as the stabilizing field in the Einstein frame.

NS three-form flux deformation for the critical non-Abelian vortex string

It has been shown that the non-Abelian solitonic vortex string supported in four-dimensional (4D) $\mathcal{N}=2$ supersymmetric QCD (SQCD) with the U(2) gauge group and ${N}_{f}=4$ quark flavors becomes a critical superstring. This string propagates in the ten-dimensional space formed by a product of the flat 4D space and an internal space given by a Calabi-Yau noncompact threefold, namely, the conifold. The spectrum of low-lying closed string states in the associated type-IIA string theory was found and interpreted as a spectrum of hadrons in 4D $\mathcal{N}=2$ SQCD. In particular, the lowest string state appears to be a massless BPS baryon associated with the deformation of the complex structure modulus $b$ of the conifold. In the previous work the deformation of the ten-dimensional background with nonzero Neveu-Schwarz 3-form flux was considered and interpreted as a switching on a particular choice of quark masses in 4D SQCD. This deformation was studied to leading order at small 3-form flux. In this paper we study the back reaction of the nonzero 3-form flux on the metric and the dilaton introducing the ansatz with several warp factors and solving the gravity equations of motion. We show that 3-form flux produces a potential for the conifold complex structure modulus $b$, which leads to the runaway vacuum. At the runaway vacuum warp factors disappear, while the conifold degenerates. In 4D SQCD we relate this to the flow to the U(1) gauge theory upon switching on quark masses and decoupling of two flavors.

Alternative for black hole paradoxes

In this paper, we investigate the exact time-dependent black hole solution on a warped five-dimensional Randall–Sundrum space–time in conformal dilaton gravity. The zeroes of the model are described by a meromorphic quintic polynomial, which has no essential singularities. The quintic equation can be reduced to the Brioschi form by means of the Weierstrass elliptic curve over [Formula: see text]. The model fits the antipodal boundary condition, i.e. antipodal points in the projected space are identified using the embedding of a Klein surface in [Formula: see text], using the [Formula: see text] symmetry on the two sides of the brane. If one writes [Formula: see text], [Formula: see text], with [Formula: see text] the normal to the brane and [Formula: see text] the dilaton field, then [Formula: see text] is conformally flat. It is the contribution from the bulk which determines the real pole on the effective four-dimensional space–time. There is no objection applying ’t Hooft’s back reaction method in constructing the unitary S-matrix for the Hawking radiation. Again, there is no “inside” of the black hole. The zeroes can also be analyzed by the icosahedron equation and by the Hopf-fibration of the Klein surface.

Safe gauge-string correspondence

Safe theories are quantum field theories whose continuum limit is defined by a non-Gaussian ultraviolet fixed point when the ultraviolet cutoff is removed. They constitute an important set in the space of quantum field theories. Here we develop the ‘safe’ gauge-string correspondence program according to which d-dimensional safe gauge theories, admitting the 't Hooft-Veneziano limit, are holographically dual to (d+1)-dimensional safe noncritical string theories on asymptotically anti-de Sitter space. We provide evidences for this correspondence on a class of safe templates that engage fermion and scalar matter fields into gauge, Yukawa and Higgs self-interactions. Safe theories can feature in the infrared both a weak coupling phase and a strong coupling phase on either side of the ultraviolet fixed point. They correspond respectively to dilaton and warp factors taking domain-wall or Liouville-wall profiles on asymptotically anti-de Sitter space. We argue that four-dimensional N=4 super Yang-Mills theories and all known interacting (super)conformal field theories are nonperturbative limit situations of safe gauge theories. The weak coupling phase provides a solvable holographic renormalization group flow while the strong coupling infrared phase provides a runaway-free alternative to holographic QCD.

Cosmology in 5D and 4D Einstein–Gauss–Bonnet gravity

We consider the five-dimensional Einstein–Gauss–Bonnet gravity, which can be obtained by means of an appropriate choice of coefficients in the five-dimensional Lanczos–Lovelock gravity theory. The Einstein–Gauss–Bonnet field equations for the Friedmann–Lemaître–Robertson–Walker metric are found as well as some of their solutions. The hyperbolicity of the corresponding equations of motion is discussed. A four-dimensional gravity action is obtained from the Gauss–Bonnet gravity using the Randall–Sundrum compactification procedure and then it is studied the implications of the compactification procedure in the cosmological solutions. The same procedure is used to obtain gravity in four dimensions from the five-dimensional AdS–Chern–Simons gravity to then study some cosmological solutions. Some aspects of the construction of the four-dimensional action gravity, as well as a brief review of Lovelock gravity in 5D are considered in an Appendix.

Self-tuning of the cosmological constant in brane-worlds with P(X,ϕ)

We revisit the idea of self-tuning the observed cosmological constant to a vanishing value and promote it to a selection criterion of brane-world models, in which our Universe is described by a 3-brane embedded in a 5d bulk. As a concrete setup, we consider a bulk scalar field ϕ described by a general Lagrangian P(X,ϕ) with X = -(∂ϕ)2/2. By requiring that the model enforces the 4d curvature of the maximally symmetric 3-brane world-volume to vanish independently of the 4d effective vacuum energy, only two possibilities remain: one with a canonical bulk kinetic term and the other with an unconventional bulk kinetic term similar to a Cuscuton field. Further demanding the absence of bulk singularity, the latter is selected as a unique possibility within the class of models. At the background level, the solution can accommodate any warp factor profile free from bulk singularity and with a finite effective 4d Planck mass. In a cosmological context, our solution would describe our (almost) flat Universe at late times, with a bulk warp factor profile expected to be determined by the evolution of the Universe before dilution of the matter fields by cosmic expansion. Eventually, a simple analysis is performed in the bulk showing no obvious instability around the background solution. A full stability analysis taking into account brane bending modes is nevertheless necessary and left for future work.

Effective Lagrangian and stability analysis in warped space

In the warped space model, the inter-brane distance can be stabilized by the Goldberger-Wise mechanism. Of particular importance, the stabilization potential calls for a proper identification of the dynamical degree of freedom. In this paper, we provided a complete calculation of the effective Lagrangian till the quadratic order that is generic for the Randall-Sundrum model and its N-brane (N ≥ 4) extensions. By applying the variation principle to a specific perturbation field, we derived the equations of motion and orthogonal conditions for decoupling the graviton. This approach is demonstrated to be equivalent to the analysis using the linearized Einstein equation. Our derivation clarifies that in the N-brane set up, just one degree of freedom for the radion field is dynamical, with the other modes eliminated by the gauge fixings. Thus we can directly generalize the GW stabilization to the N-brane model in a way similar to the RS1 scenario.

Gravastar under the framework of braneworld gravity II: Effect of the Kuchowicz metric function

In recent years, a class of compact objects called gravastars have drawn immense interest as regular solutions to end state stellar collapse. Since the energy density involved in collapse process is expected to be high, it is a natural choice to study such compact objects in context of modified gravity theories which reduce to General Relativity (GR) in the low energy regime. We have already framed a model of gravastar in such a modified gravity framework involving extra dimensional Randall–Sundrum (RS) single brane gravity [R. Sengupta, S. Ghosh, S. Ray, B. Mishra and S. K. Tripathy, Phys. Rev. D 102, 024037 (2020)]. As a sequel in this paper, we substantially improve our previous model by choosing the Kuchowicz function as one of the metric potentials, which leads to many new interesting results and physical features from our analysis as discussed in this paper. Also, we provide essential additional stability checks on our gravastar model to investigate the possibility of any instability creeping in due to the higher-dimensional framework. Our present improved gravastar model is found to clear all the stability checks successfully. Very interestingly, the static spherically symmetric matter distributions are found to accommodate both classes of solutions obeying and violating the modified energy conditions on the RS brane as we find in this work. We can conclude from our analysis that the Kuchowicz metric potential is very effective for describing regular solutions to compact objects at substantially high energies on the three-brane.

A -anomalous interactions of the holographic dilaton

We explore higher-derivative terms in the low-energy effective action for the dilaton, the Goldstone boson of spontaneously broken scale invariance. Focusing on the simplest holographic realization of spontaneously broken scale invariance, the Randall-Sundrum (RS) scenario, we identify the nonlinear action for the RS dilaton by integrating out Kaluza-Klein graviton modes. The coefficient of a particular fourth-derivative dilaton self-interaction can be identified with the Weyl $a$-anomaly of the dual conformal field theory, which we use to verify anomaly matching arguments. We also find novel, $a$-dependent couplings of the dilaton to light matter fields. These anomalous interactions can have a significant effect on the collider phenomenology and the cosmology, potentially allowing us to probe the structure of the underlying conformal sector via low-energy physics. The dilaton effective theory also serves as an interesting scalar analog of gravity, and we study solutions to the equation of motion that parallel black holes and cosmologies.

Sphaleron bound in some nonstandard cosmology scenarios

In the first scenario, we revise the upper bound of the cutoff scale of the dimension-six potential Higgs operator required for a successful electroweak baryogenesis in the case of a modified expansion history caused by the existence of a noninteracting scalar field at the time phase transition happens. The upper bound 860[Formula: see text]GeV of the cutoff scale in the conventional case can be improved to 1[Formula: see text]TeV in the modified expansion case under certain conditions. In the second scenario, we consider the Randall–Sundrum type II model. We show that the lower bound of the five-dimensional Planck scale in this model, which is determined from the validity of Newtonian gravitational potential at small distance, turns out to be crucial in eliminating this model as a viable candidate to satisfy the sphaleron bound; however, again modifying the expansion history by including a noninteracting scalar field at the electroweak scale can then make this model satisfy the sphaleron bound with a certain parameter space.

Supersymmetry and sum rules in the Goldberger-Wise model

In this work we demonstrate that the mixed gravitational and scalar sectors of the five-dimensional Goldberger-Wise (GW) model, in which the size of a warped extra dimension is dynamically determined, has a ``hidden'' dual $N=2$ supersymmetric structure. This symmetry structure, a generalization of one found in the unstabilized Randall-Sundrum model, is a result of the spontaneously broken five-dimensional diffeomorphism invariance of the underlying gravitational theory. The supersymmetries relate the properties of the spin-1 and spin-0 modes ``eaten'' by the massive spin-2 Kaluza-Klein states of the theory to the mode functions of the spin-2 modes. Because the symmetries relate the couplings and masses of the massive spin-2 states to those of the tower of physical spin-0 states of the GW model, they enable us to analytically prove the sum rule relations which ensure the tree-level scattering amplitudes of the massive spin-2 states will grow no faster than $\mathcal{O}(s)$. The analysis given here also explains the unconventional forms of the spin-0 mode equation, boundary condition(s), and normalization found in the GW model.

New results for cuscuton multi-field brane

We investigate braneworld models in the presence of the several scalar fields with generalized dynamics. A new mechanism to control the internal structure of brane in modified gravity is used to induce changes in the models in the presence of cuscuton dynamics. Examples with two- and three-field are considered, and we have found that the inclusion of the cuscuton can significantly alter the profile of the brane, causing unique changes in the warp factor, energy density, stability potential and the corresponding zero mode.

Dynamics of constant sound speed inspires warm inflation

In this work, we consider a modern form of single-field inflationary models (known as power-law plateau inflation and preheating phase for a class of plateau inflationary model) and ASPIC models by considering the Dirac–Born–Infeld (DBI) non-canonical scalar field in the light of warm inflationary scenario. For these models, we assume constant sound speed [Formula: see text] and compute different slow-roll [Formula: see text], [Formula: see text] and [Formula: see text] as well as inflationary parameters (number of [Formula: see text]-folds [Formula: see text], spectral index [Formula: see text], scalar spectral index [Formula: see text] and tensor-to-scalar ratio [Formula: see text]) for specific anti-de Sitter warp factor of the DBI inflation. Next, we plot the trajectories of [Formula: see text], [Formula: see text] and [Formula: see text] with different choices of [Formula: see text] and found the ranges [Formula: see text], [Formula: see text], [Formula: see text] (for minimal inflation model), [Formula: see text], [Formula: see text], [Formula: see text] (for modified minimal inflation model) and [Formula: see text], [Formula: see text], [Formula: see text] (mixed large field inflation), respectively. Moreover, the ranges of these parametric plots for power-law plateau inflationary model are [Formula: see text], [Formula: see text], [Formula: see text]. Finally, we find that the results of all these parametric plots are consistent with 68% and 95% with current observational data except scalar-to-tensor ratio [Formula: see text] for modified minimal and power-law Plateau inflation models.

Generalized Jackiw-Teitelboim gravity in presence of Block brane-like models* *DB and RM would like to thank CNPq (Brazil), grants No. 303469/2019-6 (DB) and No. 310994/2021-7 (RM). They also thank Paraiba State Research Foundation, FAPESQ-PB, grants No. 0003/2019 (RM) and No. 0015/2019 (DB), for partial financial support

We investigate generalized Jackiw-Teitelboim gravity, coupling the dilaton field with two scalar matter fields. We obtain the equations of motion for the fields and investigate a linear perturbation of the solutions in general. We study two specific situations that allow for analytic solutions with topological behavior and check how the dilaton field, the warp factor and the Ricci scalar behave. In particular, we show how the parameters can be used to modify the structure of the solutions. Moreover, the perturbations are, in general, described by intricate coupled differential equations, but in some specific cases, we can construct the corresponding zero modes analytically.